Laser communication system and laser communication method

The present invention relates to a laser communication system and a laser communication method.

Background Art

The studies and development of a free-space optical communication are accomplished in which a laser beam is transmitted in a space for communication. The free-space optical communication is applicable to a communication between a base station on the ground and an artificial satellite and a communication between buildings as an example.

A spatial laser communication has excellent advantages in communication speed and confidentiality of communicating data. On the other hand, since a laser beam is transmitted in the space in principle, the spatial laser communication cannot be carried out when an obstacle exists in the transmission path.

The obstacle is not always necessary to block the laser beam and makes it difficult to secure a S/N (signal/noise) ratio requested for the communication.

As a candidacy of such an obstacle, water droplets or minute particles to scatter, refract and attenuate a laser beam are thought of in addition to a solid material. The water droplets exist in air in the form of fog and cloud. The minute particles exist in the floating form in the atmosphere.

In relation to the above, Patent Literature 1 (Japanese Patent No. 3, 626,807) discloses a system that vaporizes and removes the water droplets in the transmission path by a pulse laser beam to start the spatial laser communication.

The system of Patent Literature 1 does not consider the removal of a solid obstacle. Also, the use of a pulse laser beam is assumed for removal of an obstacle of water droplets. The pulse laser beam is difficult to improve an average output, and is not suitable for removal of the solid obstacle.

On the other hand, recently, the research of a high-power laser system is accomplished that fuses and destroys an object situated on a long distance of about several kilometers to 100 kilometers. However, a high-speed modulation of the high-power laser beam is difficult, and therefore, it is difficult to use for communication just as it is.

Patent Literature

[Patent Literature 1] Japanese Patent No. 3,626,807

The laser beam communication is carried out by removing a solid obstacle which blocks off a space as a transmission path of a laser beam. Another problem and new features will become clear from the description of this Specification and the attached drawings.

According to an embodiment, a laser communication system includes a high-power laser oscillator configured to generate a high-power laser beam to remove a solid obstacle.

According to an embodiment, a laser beam communication method includes removing a solid obstacle with a high-power laser beam; and carrying out a laser beam communication through a space which had been blocked off by the removed solid obstacle.

According to the embodiment, the obstacle is removed by the high-power laser beam and it is possible to communicate in the laser beam.

FIG. 1A is a diagram showing a configuration example of a laser communication system according to an embodiment.

FIG. 1B is a diagram showing an example of state that the laser communication according to the embodiment is blocked by an obstacle.

FIG. 1C is a diagram showing an example of state that the laser communication according to the embodiment is blocked by an obstacle of water droplets.

FIG. 2 is a diagram showing the principle in which a target is removed with a high-power laser.

FIG. 3 is a block circuit diagram showing a configuration example of a laser communication system according to a first embodiment.

FIG. 4 is a flow chart showing a configuration example of a laser communication method according to the first embodiment.

FIG. 5A is a diagram showing an example of state that the laser communication system according to the first embodiment removes the obstacle with the high-power laser beam.

FIG. 5B is a diagram showing an example of state that a second communication station of the laser communication system according to the first embodiment detects the high-power laser beam to transmit a detection signal.

FIG. 5C is a diagram showing an example of state that a first communication station of the laser communication system according to the first embodiment changes the output level of the laser beam to be outputted to a communication level.

FIG. 5D is a diagram showing an example of state that the second communication station of the laser communication system according to the first embodiment detects the laser beam of the communication level and starts high-speed communication.

FIG. 6 is a block circuit diagram showing a configuration example of the laser communication system according to a second embodiment.

FIG. 7 is a block circuit diagram showing a configuration example of the laser communication system according to a third embodiment.

FIG. 8 is a block circuit diagram showing a configuration example of the laser communication system according to a fourth embodiment.

FIG. 9 is a block circuit diagram showing a configuration example of the laser communication system according to a fifth embodiment.

FIG. 10 is a block circuit diagram showing a configuration example of the laser communication system according to a sixth embodiment.

FIG. 11 is a block circuit diagram showing a configuration example of the laser communication system according to a seventh embodiment.

FIG. 12 is a block circuit diagram showing a configuration example of the laser communication system according to an eighth embodiment.

FIG. 13 is a block circuit diagram showing a configuration example of the laser communication system according to a ninth embodiment.

FIG. 14 is a block circuit diagram showing a configuration example of the laser communication system according to a tenth embodiment.

FIG. 15 is a block circuit diagram showing a configuration example of the laser communication system according to an eleventh embodiment.

FIG. 16 is a flow chart showing a configuration example of the laser communication method according to a twelfth embodiment.

FIG. 17A is a diagram showing an example of state that the laser communication system according to the twelfth embodiment removes an obstacle with the high-power laser beam.

FIG. 17B is a diagram showing an example of state that the second communication station of the laser communication system according to the twelfth embodiment detects the high-power laser beam and transmits the detection signal.

FIG. 17C is a diagram showing an example of state that the first communication station of the laser communication system according to the twelfth embodiment lowers the output level of the high-power laser beam step-by-step, and the second communication station raises the transmittance of a light-attenuating filter step-by-step.

FIG. 17D is a diagram showing an example of state that the second communication station of the laser communication system according to the twelfth embodiment detects the laser beam of the communication level and starts high-speed communication.

FIG. 18A is a first half of a flow chart showing a configuration example of the laser communication method according to a thirteenth embodiment.

FIG. 18B is a second half part of the flow chart showing the configuration example of the laser communication method according to the thirteenth embodiment.

FIG. 19A is a diagram showing an example of state that the laser communication system according to the thirteenth embodiment removes an obstacle with the high-power laser beam.

FIG. 19B is a diagram showing an example of state that the second communication station of the laser communication system according to the thirteenth embodiment detects the high-power laser beam and transmits the detection signal.

FIG. 19C is a diagram showing an example of state that the first communication station of the laser communication system according to the thirteenth embodiment lowers the output level of the high-power laser beam step-by-step.

FIG. 19D is a diagram showing an example of state that the second communication station of the laser communication system according to the thirteenth embodiment raises the transmittance of the light-attenuating filter step-by-step, and detects the laser beam of the communication level to start the high-speed communication.

Referring to the attached drawings, embodiments of a laser communication system and a laser beam method according to the present invention will be described below.

First Embodiment

A basic principle of a laser communication system and a laser communication method according to a first embodiment will be described. FIG. 1A is a diagram showing a configuration example of the laser communication system according to an embodiment. In an example of FIG. 1A , a spatial laser communication is carried out by sending and receiving a communication laser beam 300 between a first communication station (1 st COM-STA) 100 and a second communication station (2 nd COM-STA) 200 .

FIG. 1B is a diagram showing an example of state that the laser communication according to an embodiment is blocked off by solid obstacle 2 . When the solid obstacle 2 exists in a space where the communication laser beam (COM-LB) 300 is transmitted, the obstacle 2 must be removed because the communication laser beam 300 cannot be transmitted between the first communication station 100 and the second communication station 200 .

FIG. 1C is a diagram showing an example of state that a channel of the laser communication system according to an embodiment is blocked off by an obstacle 3 of water droplets. When the obstacle 3 of water droplets exists in a space where the communication laser beam 300 is transmitted, the obstacle 2 must be removed, because the communication laser beam 300 is not transmitted between the first communication station 100 and the second communication station 200 .

In the laser communication system and the laser communication method according to an embodiment, a high-power laser beam is used to establish a transmission path through the obstacle 2 . FIG. 2 is a diagram showing the principle in which a target 500 is removed with a high-power laser beam 430 . In an example of FIG. 2 , regarding the target 500 as the obstacle 2 , the high-power laser beam (HP-LB) 430 is irradiated from a high-power laser irradiation (HP-L IR) apparatus 400 to the target 500 . The high-power laser irradiation apparatus 400 uses a high-power laser oscillator (HP-L OSC) 410 to generate the high-power laser beam 430 , and sets the irradiation direction of the high-power laser beam 430 to the target 500 by using an irradiation optical system (IR OP-SYS) 420 . A part of the target 500 where the high-power laser beam 430 is irradiated is called an irradiation (IR) part 510 . When the high-power laser beam 430 is irradiated, part or whole of the target 500 is removed. At this time, the part or whole of the target 500 may be fused or destroyed. It is necessary that the target 500 is removed from a space where a communication laser beam is transmitted or that the signal-to-noise ratio necessary to communicate is secured. For example, in case of the obstacle through which the communication laser beam can be transmitted in a predetermined output level, it is necessary that the obstacle can be made thin to an extent that the necessary signal-to-noise ratio is secured. Note that the high-power laser beam 430 can remove the obstacle 3 of water droplets.

As the high-power laser beam 430 which penetrates through the obstacle 2 , a continuous-wave laser beam outputted continuously is more suitable than a pulse laser beam in a pulse. For example, such a continuous-wave laser beam is realized by a solid-state laser.

FIG. 3 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a first embodiment. The components of the laser communication system 1 shown in FIG. 3 will be described.

The laser communication system 1 shown in FIG. 3 includes a first communication station (1 st COM-STA) 10 and a second communication station (2 nd COM-STA) 20 . The first communication station 10 includes a reception optical system (Rx OP-SYS) 11 A, a reception (Rx) sensor 13 , a control (CTRL) device 14 , a high-power laser oscillator (HP-L OSC) 15 A, a communication laser oscillator (COM-L OSC) 15 B, a modulator (MOD) 16 A, a high-power laser irradiation optical system (HP-L IR OP-SYS) 19 A, and a communication laser irradiation optical system (COM-L IR OP-SYS) 19 B. The second communication station 20 includes a reception optical system (Rx OP-SYS) 21 A, a light-attenuating (LA) filter 23 , a reception (Rx) sensor 24 , a control (CTRL) device 25 , a communication laser oscillator (COM-L OSC) 26 , a modulator (MOD) 27 , a communication laser irradiation optical system (COM-L IR OP-SYS) 28 .

An optical connection relation of components of the laser communication system 1 of FIG. 3 will be described. The optical connection relation which will be described here includes connections through various optical parts such as a mirror, a lens and a beam splitter (not shown). The high-power laser irradiation optical system 19 A is arranged in the subsequent stage of the high-power laser oscillator 15 A. In other words, a high-power laser beam (HP-LB) 15 A 1 generated by the high-power laser oscillator 15 A is outputted to the high-power laser irradiation optical system 19 A.

The reception optical system 21 A is arranged in the subsequent stage of the high-power laser irradiation optical system 19 A. In other words, the high-power laser beam 15 A 1 irradiated from the high-power laser irradiation optical system 19 A is outputted to the reception optical system 21 A.

The communication laser irradiation optical system 19 B is arranged in the subsequent stage of the communication laser oscillator 15 B through the modulator (MOD) 16 A. In other words, a communication laser beam (COM-LB) 15 B 1 generated by the communication laser oscillator 15 B is modulated by the modulator 16 A, and then is supplied to the communication laser irradiation optical system 19 B.

The reception optical system 21 A is arranged in the subsequent stage of the communication laser irradiation optical system 19 B. In other words, the communication laser beam 15 B 1 irradiated from the communication laser irradiation optical system 19 B is supplied to the reception optical system 21 A.

The reception sensor 24 is arranged in the subsequent stage with the reception optical system 21 A through the light-attenuating filter 23 . In other words, the high-power laser beam (HP-LB) 15 A 1 and the communication laser beam (COM-LB) 15 B 1 emitted from the reception optical system 21 A are attenuated by the light-attenuating filter 23 , and are supplied to the reception (Rx) sensor 24 . As described later, the transmittance of the light-attenuating filter 23 is variable, and it is desirable that the control is carried out such that the transmittance becomes farther lower when the high-power laser beam 15 A 1 passes through the light-attenuating filter 23 and becomes higher when the communication laser beam 15 B 1 passes through the light-attenuating filter 23 . Or, the light-attenuating filter 23 is configured by stacking a plurality of light-attenuating sub filters, and the transmittance of the light-attenuating filter 23 may be adjusted based on the number and the combination of the light-attenuating sub filters to be stacked. In this case, a drive system may be provided to change the number and the combination of the light-attenuating sub filters to be stacked. Moreover, as another configuration, for example, the light-attenuating filter 23 may be configured to have a different transmittance depending on a place through which the laser beam passes. In this case, a drive system may be provided to move the light-attenuating filter 23 to adjust the place through which the laser beam passes.

The communication laser irradiation optical system (COM-L IR OP-SYS) 28 is arranged in the subsequent stage of the communication laser oscillator (COM-L OSC) 26 through the modulator (MOD) 27 . In other words, the communication laser beam (COM-LB) 26 A emitted from communication laser oscillator 26 is modulated by the modulator 27 and then outputted to the communication laser irradiation optical system 28 .

The reception optical system (Rx OP-SYS) 11 A is arranged in the subsequent stage of the communication laser irradiation optical system 28 . In other words, the communication laser beam (COM-LB) 26 A irradiated from the communication laser irradiation optical system 28 is outputted to the reception optical system 11 A.

The reception (Rx) sensor 13 is arranged in the subsequent stage of the reception optical system 11 A. In other words, the communication laser beam 26 A emitted from the reception optical system 11 A is supplied to the reception sensor 13 .

An electrical connection relation of components of the laser communication system 1 of FIG. 3 will be described. In the first communication station 10 , the control (CTRL) device 14 is electrically connected with the reception optical system 11 A, the reception sensor 13 , the high-power laser oscillator (HP-L OSC) 15 A, the high-power laser irradiation optical system (HP-L IR OP-SYS) 19 A, the communication laser oscillator 15 B, the modulator 16 A and the communication laser irradiation optical system (COM-L IR OP-SYS) 19 B. In the second communication station 20 , the control device 25 is connected with the reception optical system 21 A, the light-attenuating filter 23 , the reception sensor 24 , the communication laser oscillator 26 , the modulator 27 , and the communication laser irradiation optical system 28 .

The operation of the laser communication system 1 of FIG. 3 will be described.

(Control when First Communication Station 10 Receives Communication Laser Beam)

In the first communication station 10 , the control device 14 generates a reception direction control signal 141 A to control the reception direction. The control device 14 transmits the reception direction control signal 141 A to the reception optical system 11 A. The reception optical system 11 A receives the reception direction control signal 141 A. Therefore, the reception optical system 11 A adjusts the reception direction according to the reception direction control (Rx-DIR CTRL) signal 141 A. In this case, the reception direction of the reception optical system 11 A is desirable to be adjusted to a direction in which the incident precision of the communication laser beam 26 A irradiated from the communication laser irradiation optical system 28 has a maximum value.

The reception optical system 11 A receives the communication laser beam 26 A from the communication laser irradiation optical system 28 and transmits to the reception sensor 13 . The reception sensor 13 receives the communication laser beam 26 A from the reception optical system 11 A and generates a reception (Rx) signal 131 by converting the communication laser beam 26 A. The reception sensor 13 transmits the reception signal 131 to the control device 14 . In this case, the reception sensor 13 may transmit to the control device 14 , a signal which contains data for feedback control according to the incident precision of the communication laser beam 26 A.

(Control when First Communication Station 10 Emits Communication Laser Beam)

The control device 14 generates an oscillation control (OSC CTRL) signal 143 B to generate the communication laser beam 15 B 1 . The control device 14 transmits the oscillation control signal 143 B to the communication laser oscillator 15 B. The communication laser oscillator 15 B receives the oscillation control signal 143 B. The communication laser oscillator 15 B generates the communication laser beam 15 B 1 according to the oscillation control signal 143 B. The communication laser oscillator 15 B emits the communication laser beam 15 B 1 to the modulator 16 A. The modulator 16 A receives the communication laser beam 15 B 1 .

The control device 14 generates a modulation control (MOD CTRL) signal 144 A to control the modulation of the communication laser beam 15 B 1 . In this case, transmission data to be transmitted to the second communication station 20 by the communication laser beam 15 B 1 is contained in the modulation control signal 144 A in a predetermined data format. The control device 14 transmits the modulation control signal 144 A to the modulator 16 A. The modulator 16 A receives the modulation control signal 144 A. Therefore, the modulator 16 A modulates the communication laser beam 15 B 1 according to the modulation control signal 144 A. The modulator 16 A emits the modulated communication laser beam 15 B 1 to the communication laser irradiation optical system 19 B. The communication laser irradiation optical system 19 B receives the communication laser beam 15 B 1 .

The control device 14 generates an irradiation direction control (IR-DIR CTRL) signal 146 B to control the irradiation direction of the communication laser beam 15 B 1 . The control device 14 transmits the irradiation direction control signal 146 B to the communication laser irradiation optical system 19 B. The communication laser irradiation optical system 19 B receives the irradiation direction control signal 146 B. The communication laser irradiation optical system 19 B adjusts the irradiation direction of the communication laser beam 15 B 1 according to the irradiation direction control signal 146 B. Here, it is desirable that the irradiation direction of the communication laser irradiation optical system 19 B is adjusted to the direction of the reception optical system 21 A of the second communication station 20 basically. The communication laser irradiation optical system 19 B irradiates the communication laser beam 15 B 1 to the adjusted irradiation direction.

(Control when First Communication Station 10 Emits High-Power Laser Beam)

The control device 14 generates an oscillation control (OSC CTRL) signal 143 A to generate the high-power laser beam 15 A 1 . The control device 14 transmits the oscillation control signal 143 A to the high-power laser oscillator 15 A. The high-power laser oscillator 15 A receives the oscillation control signal 143 A. Therefore, the high-power laser oscillator 15 A generates the high-power laser beam 15 A 1 in response to the oscillation control signal 143 A. The high-power laser oscillator 15 A emits the high-power laser beam 15 A 1 to the high-power laser irradiation optical system 19 A. The high-power laser irradiation optical system 19 A receives the high-power laser beam 15 A 1 .

The control device 14 generates an irradiation direction control (IR-DIR CTRL) signal 146 A to control the irradiation direction of the high-power laser beam 15 A 1 . The control device 14 transmits the irradiation direction control signal 146 A to the high-power laser irradiation optical system 19 A. The high-power laser irradiation optical system 19 A receives the irradiation direction control signal 146 A. Therefore, the high-power laser irradiation optical system 19 A adjusts the irradiation direction of the high-power laser beam 15 A 1 according to the irradiation direction control signal 146 A. In this case, it is desirable that the irradiation direction of the high-power laser irradiation optical system 19 A is adjusted such that the high-power laser beam 15 A 1 is irradiated to a part of the obstacle 2 which blocks off a transmission path of the communication laser beam 15 B 1 to be transmitted from the communication laser irradiation optical system 19 B to the reception optical system 21 A. Basically, the irradiation direction of the high-power laser irradiation optical system 19 A is adjusted to a direction in which the high-power laser beam 15 A 1 heads for the reception optical system 21 A. For this purpose, it is desirable that the optical axis of the high-power laser beam 15 A 1 irradiated from the high-power laser irradiation optical system 19 A is arranged to be sufficiently near to the optical axis of the communication laser beam 15 B 1 irradiated from the communication laser irradiation optical system 19 B. The high-power laser irradiation optical system 19 A irradiates the high-power laser beam 15 A 1 to the adjusted irradiation direction.

(Control when Second Communication Station 20 Receives Communication Laser Beam)

In the second communication station 20 , the control device 25 generates a reception direction control (Rx-DIR CTRL) signal 251 A to control the reception direction. The control device 25 transmits the reception direction control signal 251 A to the reception optical system 21 A. The reception optical system 21 A receives the reception direction control signal 251 A. Therefore, the reception optical system 21 A adjusts the reception direction according to the reception direction control signal 251 A. In this case, it is desirable that the reception direction of the reception optical system 21 A is adjusted to the direction in which the incident precision of the communication laser beam 15 B 1 irradiated from the communication laser irradiation optical system 19 B has a maximum value. The reception optical system 21 A receives the high-power laser beam 15 A 1 or the communication laser beam 15 B 1 from the adjusted reception direction. The reception optical system 21 A emits the high-power laser beam 15 A 1 or the communication laser beam 15 B 1 to the reception sensor 24 through the light-attenuating filter 23 .

The control device 25 generates a transmittance control (TM CTRL) signal 253 to control the variable transmittance of the light-attenuating filter 23 . The control device 25 transmits the transmittance control signal 253 to the light-attenuating filter 23 . The light-attenuating filter 23 receives the transmittance control signal 253 . Therefore, the light-attenuating filter 23 adjusts its own transmittance according to the transmittance control signal 253 . In this case, when the high-power laser beam 15 A 1 is irradiated from the first communication station 10 , it is desirable that the transmittance of the light-attenuating filter 23 is adjusted to be low or dropped to protect the reception sensor 24 from the high-power laser beam 15 A 1 . Oppositely, when the high-power laser beam 15 A 1 is not irradiated from the first communication station 10 , it is desirable that the transmittance of the light-attenuating filter 23 is adjusted to be high such that the reception sensor 24 can receive the communication laser beam 15 B 1 precisely. More specifically, the light-attenuating filter 23 may be exchanged, the number of light-attenuating sub filters to be stacked may be decreased, the combination of the light-attenuating sub filters to be stacked may be changed, or the place of the light-attenuating filter 23 through which the laser beam passes may be changed.

The reception sensor 24 receives the high-power laser beam 15 A 1 or the communication laser beam 15 B 1 emitted from the reception optical system 21 A and then attenuated by the light-attenuating filter 23 . The reception sensor 24 converts the received laser beam to generate a reception (Rx) signal 241 . The reception sensor 24 transmits the reception signal 241 to the control device 25 . Here, when the communication laser beam 15 B 1 is received, the reception sensor 24 may transmit to the control device 25 , a signal which contains data for the feedback control according to the incident precision of the communication laser beam 26 A, together with the laser beam 15 B 1 . Also, when the high-power laser beam 15 A 1 is received, the reception sensor 24 may transmit a signal which contains the reception intensity data of the laser beam 15 A 1 to the control device 25 as the reception signal 241 .

(Control when Second Communication Station 20 Emits Communication Laser Beam)

The control device 25 generates an oscillation control (OSC CTRL) signal 254 to generate the communication laser beam 26 A. The control device 25 transmits the oscillation control signal 254 to the communication laser oscillator 26 . The communication laser oscillator 26 receives the oscillation control signal 254 . Therefore, the communication laser oscillator 26 generates the communication laser beam 26 A in response to the oscillation control signal 254 . The communication laser oscillator 26 emits the communication laser beam 26 A to the modulator 27 . The modulator 27 receives a communication laser beam 26 A.

The control device 25 generates a modulation control (MOD CTRL) signal 255 to modulate the communication laser beam 26 A. Here, the transmission data to be transmitted on the communication laser beam 26 A to the first communication station 10 is contained in the modulation control signal 255 in a predetermined data format. The control device 25 transmits the modulation control signal 255 to the modulator 27 . The modulator 27 receives the modulation control signal 255 . Therefore, the modulator 27 modulates the communication laser beam 26 A according to the modulation control signal 255 . A modulator 27 A emits the modulated communication laser beam 26 A to the communication laser irradiation optical system 28 . The communication laser irradiation optical system 28 receives the modulated communication laser beam 26 A.

The control device 25 generates an irradiation direction control (IR-DIR CTRL) signal 256 to control the irradiation direction of the communication laser beam 26 A. The control device 25 transmits the irradiation direction control signal 256 to the communication laser irradiation optical system 28 . The communication laser irradiation optical system 28 receives the irradiation direction control signal 256 . Therefore, the communication laser irradiation optical system 28 adjusts the irradiation direction of the communication laser beam 26 A according to the irradiation direction control signal 256 . Here, it is desirable that the irradiation direction of the communication laser irradiation optical system 28 is basically adjusted to the direction of the reception optical system 11 A of the first communication station 10 . The communication laser irradiation optical system 28 irradiates the communication laser beam 26 A to the adjusted irradiation direction.

(Laser Beam Communication Method)

Referring to FIG. 4 , and FIG. 5A to FIG. 5D , the overall operation of the laser communication system 1 according to the first embodiment, i.e. a laser beam communication method will be described. FIG. 4 is a flow chart showing a configuration example of the laser beam communication method according to an embodiment. The flow chart of FIG. 4 contains 11 steps of a 0 th step S 100 to a tenth step S 110 . The flow chart of FIG. 4 begins from the 0 th step S 100 . After the 0 th step S 100 , a first step S 101 is executed.

FIG. 5A is a diagram showing an example of state that the laser communication system 1 according to the first embodiment removes the obstacle 2 with the high-power laser beam 15 A 1 . In the example of FIG. 5A , the channel of the spatial laser communication between the first communication station 10 and the second communication station 20 is blocked by the obstacle 2 between the first communication station 10 and the second communication station 20 . The first communication station 10 can detect the existence of the obstacle 2 , when a period during which the communication laser beam 26 A from the second communication station 20 does not reach or cannot be received exceeds a predetermined length. In the same way, the second communication station 20 , too, can be detect the existence of the obstacle 2 when a period during which the communication laser beam 15 B 1 does not reach from the first communication station 10 exceeds a predetermined length. In this case, at the first step S 101 , the second communication station 20 protects the reception sensor 24 by the light-attenuating filter 23 , before the first communication station 10 irradiates the high-power laser beam 15 A 1 to remove the obstacle 2 . In other words, in order to prevent that the reception sensor 24 provided to receive the communication laser beam 15 B 1 of a relatively low output receives the irradiation of the high-power laser beam 15 A 1 to be destroyed, a control is carried out to drop the variable transmittance of the light-attenuating filter 23 . After the first step S 101 , a second step S 102 is executed.

At second step S 102 , the first communication station 10 irradiates the high-power laser beam 15 A 1 to remove the obstacle 2 . At this time, a part of the obstacle 2 where the high-power laser beam 15 A 1 is irradiated is called an irradiated part 2 A for convenience. It is desirable that the irradiated part 2 A contains a space where the communication laser beams 15 B 1 and 26 A are transmitted between the first communication station 10 and the second communication station 20 . Here, a case where the irradiated part 2 A in which the high-power laser beam 15 A 1 is irradiated fuses so that a hole 2 B is formed is considered. After the second step S 102 , a third step S 103 is executed.

At the third step S 103 , the second communication station 20 detects the high-power laser beam 15 A 1 . Here, the high-power laser beam 15 A 1 passes through the hole 2 B to reach the second communication station 20 . The high-power laser beam 15 A 1 having reached the second communication station 20 is received by the reception sensor 24 of the second communication station 20 in the condition that the power of the high-power laser beam 15 A 1 drops sufficiently by passing through the light-attenuating filter 23 . When detecting the incidence of the high-power laser beam 15 A 1 , the reception sensor 24 generates and transmits the reception signal 241 , which contains data showing the detection, to the control device 25 . After the third step S 103 , a fourth step S 104 is executed.

At the fourth step S 104 , the second communication station 20 transmits the detection signal to the first communication station 10 . The detection signal is a signal to inform to the first communication station 10 that the second communication station 20 detected the high-power laser beam 15 A 1 . In other words, the detection signal is a signal to inform to the first communication station 10 that the obstacle 2 has been removed to an extent that the spatial laser beam communication becomes possible between the first communication station 10 and the second communication station 20 at least. This detection signal is generated by the control device 25 of the second communication station 20 having received the reception signal 241 . After that, the detection signal is transmitted to the first communication station 10 by the communication laser beam 26 A generated by the communication laser oscillator 26 , the modulator 27 and the communication laser irradiation optical system 28 . FIG. 5B is a diagram showing an example of state that the second communication station of the laser communication system 1 according to the first embodiment detects the high-power laser beam to transmit the detection signal. After the fourth step S 104 , a fifth step S 105 is executed.

At the fifth step S 105 , the first communication station 10 receives the detection signal. More specifically, at the fourth step S 104 , the first communication station 10 receives the detection signal by the communication laser beam 26 A irradiated from the second communication station 20 . In other words, this detection signal is received by the reception optical system 11 A of the first communication station 10 as the communication laser beam 26 A, and is converted into the reception signal 131 by the reception sensor 13 to be transmitted to the control device 14 . After the fifth step S 105 , a sixth step S 106 is executed.

At the sixth step S 106 , the first communication station 10 changes the output level of the laser beam from the high-power level for removal of the obstacle 2 to the low output level for the communication. In the present embodiment, the irradiation of the high-power laser beam 15 A 1 is stopped and the irradiation of the communication laser beam 15 B 1 is started instead. The changing of the output level may be carried out by reducing the output level of the high-power laser beam 15 A 1 continuously or step-by-step. FIG. 5C is a diagram showing an example of state that the output level of the laser beam outputted from the first communication station 10 of the laser communication system 1 according to the first embodiment is changed to the power level for the communication. After the sixth step S 106 , a seventh step S 107 is executed.

At the seventh step S 107 , the second communication station 20 detects the laser beam of an output level for the communication. The intensity of the laser beam irradiated to the second communication station 20 from the first communication station 10 may not always be equal to the output level for the communication. What is important is to confirm that the intensity of the laser beam is low to an extent not to destroy the reception sensor 24 of the second communication station 20 irradiated to the second communication station 20 even if the light-attenuating filter 23 is removed. This confirmation may be carried out by the control device 25 using the intensity of the laser beam received by the reception sensor 24 and the transmittance of the light-attenuating filter 23 . After the seventh step S 107 , an eighth step S 108 is executed.

At the eighth step S 108 , the second communication station 20 removes the light-attenuating filter 23 . The light-attenuating filter 23 may be physically moved from the position between the reception optical system 21 A and the reception sensor 24 to a different position. Or, the transmittance of the light-attenuating filter 23 may be raised to an extent that the reception sensitivity of the communication laser beam 15 B 1 of a comparatively low output level is sufficiently acquired, without moving the light-attenuating filter 23 from the position between the reception optical system 21 A and the reception sensor 24 . After the eighth step S 108 , a ninth step S 109 is executed.

At the ninth step S 109 , the first communication station 10 and the second communication station 20 start the high-speed communication by using the communication laser beams 15 B 1 and 26 A. FIG. 5D is a diagram showing an example of state that the second communication station of the laser communication system 1 according to the first embodiment detects the communication laser beam of the low output level to start the high-speed communication. After the ninth step S 109 , a tenth step S 110 is executed, and the flow chart of FIG. 4 ends. When the obstruction of the communication due to the obstacle recurs during the high-speed communication, the flow chart of FIG. 4 may be started once again from the 0 th step S 100 .

As described above, in the laser communication system 1 and the laser communication method according to the present embodiment, the confirmation of securement of the transmission path between the communication stations is carried out by the following method:

(1) Until the transmission path is established, the reception sensor 24 is protected by the light-attenuating filter 23 (the first step S 101 ).

(2) After the hole is formed to pass through the obstacle 2 (the second step S 102 ), when the second communication station 20 receives the high-power laser beam 15 A 1 (the third step S 103 ), the second communication station 20 transmits the detection signal to the first communication station 10 (the fourth step S 104 ).

(3) When receiving the detection signal from the second communication station 20 (the fifth step S 105 ), the first communication station 10 reduces the power of the laser beam to be outputted (the sixth step S 106 ).

(4) When the intensity of the laser beam irradiated from the first communication station 10 is reduced to the output level for communication (the seventh step S 107 ), the light-attenuating filter 23 of the second communication station 20 is removed (the eighth step S 108 ) and the high-speed communication is started (the ninth step S 109 ).

In this way, according to the laser communication system 1 and the laser communication method of the present embodiment, it is possible to exclude the obstacle 2 from the transmission path, which makes a spatial laser communication possible. This means that the communication having high confidentiality can be established in a short time without removing rubble physically in heavy equipment, underlying a communication cable among communication stations and carrying out the large-scale work, even if the rubble is produced under the disaster, so that the transmission path is covered by the rubble. Also, for example, in the communication between an artificial satellite and a ground station, even if a transmission path is covered by so-called space debris so that the physical removal is impossible, or the construction of a communication cable is impossible, the communication can be made possible by removing an obstacle.

Second Embodiment

FIG. 6 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a second embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 6 has the following difference points, compared with the laser communication system 1 according to the first embodiment shown in FIG. 3 . That is, in the present embodiment, the optical axes of the laser beams which are transmitted and received are coaxialized in the second communication station 20 .

Specifically, the reception optical system 21 A and the communication laser irradiation optical system 28 in the first embodiment are unified. The reception optical system 21 A and the communication laser irradiation optical system 28 which have been unified corresponds to an irradiation/reception coaxial optical system (IR/Rx COAX OP-SYS) 21 B in the present embodiment. In other words, in the second communication station 20 , the communication laser beam 15 B 1 irradiated from the first communication station 10 and the communication laser beam 26 A irradiated to the first communication station 10 are received and emitted by the irradiation/reception coaxial optical system 21 B. As a result, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 is smaller than that of the first embodiment. This leads to the saving of energy which is necessary to remove the obstacle 2 , and the reduction of time to secure a transmission path.

In the laser communication system 1 according to the present embodiment, a transmission and reception separating (Tx & Rx SEP) unit 22 is added, compared with the first embodiment. The transmission and reception separating unit 22 separates a laser beam irradiated from and a laser beam received by the irradiation/reception coaxial optical system 21 B. For example, this separation can be realized by rotating a reflector having a hole. That is, when receiving a laser beam by the irradiation/reception coaxial optical system 21 B, the laser beam is reflected to the light-attenuating filter 23 by the reflector. Oppositely, when irradiating the laser beam, the laser beam supplied from the modulator 27 is led to the irradiation/reception coaxial optical system 21 B through the hole of the reflector.

The connection relation of the transmission and reception separating unit 22 will be described.

When paying attention to the optical connection relation, the transmission and reception separating unit 22 is connected with the irradiation/reception coaxial optical system 21 B, the light-attenuating filter 23 and the modulator 27 . In case of the laser beam irradiated to the second communication station 20 from the first communication station 10 , the transmission and reception separating unit 22 is arranged in the subsequent stage of the irradiation/reception coaxial optical system 21 B, and arranged in the front stage of the light-attenuating filter 23 . In case of the laser beam irradiated to the first communication station 10 from the second communication station 20 , the transmission and reception separating unit 22 is arranged in the subsequent stage of the modulator 27 , and arranged in the front-stage of the irradiation/reception coaxial optical system 21 B.

Also, when paying attention to the electrical connection relation, the transmission and reception separating unit 22 is connected with the control device 25 .

The operation of components of the second communication station 20 according to the irradiation/reception coaxial optical system 21 B and the transmission and reception separating unit 22 will be described.

The control device 25 generates an irradiation/reception direction control (IR/Rx DIR CTRL) signal 251 B to control the irradiation direction and reception direction of the irradiation/reception coaxial optical system 21 B. The control device 25 transmits the irradiation/reception direction control signal 251 B to the irradiation/reception coaxial optical system 21 B. The irradiation/reception coaxial optical system 21 B receives the irradiation/reception direction control signal 251 B. The irradiation/reception coaxial optical system 21 B adjusts the irradiation direction/reception direction in response to the irradiation/reception direction control signal 251 B. The irradiation/reception coaxial optical system 21 B receives the laser beam from the adjusted reception direction and also irradiates the laser beam to the adjusted irradiation direction.

The control device 25 generates a transmission/reception separation control (Tx/Rx SEP CTRL) signal 252 . The control device 25 transmits the transmission/reception separation control (Tx/Rx SEP CTRL) signal 252 to the transmission and reception separating unit 22 . The transmission and reception separating unit 22 receives the transmission/reception separation control signal 252 . Therefore, the transmission and reception separating unit 22 switches between two states according to the transmission/reception separation control signal 252 . That is, in a first state, the laser beam received by the irradiation/reception coaxial optical system 21 B is led to the light-attenuating filter 23 . Also, in a second state, the laser beam supplied from the modulator 27 is led to the irradiation/reception coaxial optical system 21 B.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the first embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than in the first embodiment. This leads to the saving of energy which is necessary to remove the obstacle 2 , and the reduction of time to secure a transmission path.

Third Embodiment

FIG. 7 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a third embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 7 has the following different points, compared with the laser communication system according to the first embodiment shown in FIG. 3 . That is, in the present embodiment, the optical axis of the high-power laser beam 15 A 1 and that of the communication laser beam 15 B 1 are coaxialized in the first communication station 10 .

Specifically, the high-power laser irradiation optical system 19 A and the communication laser irradiation optical system 19 B in the first embodiment are unified. The high-power laser irradiation optical system 19 A and the communication laser irradiation optical system 19 B which have been unified corresponds to the coaxial irradiation optical system (COAX IR OP-SYS) 19 C in the third embodiment. In other words, both of the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 which are irradiated from the first communication station 10 are emitted on a coaxial path from the coaxial irradiation optical system 19 C. As a result, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than in the first embodiment, like the second embodiment. This leads to the saving of energy which is necessary to remove the obstacle 2 , and the reduction of time to secure a transmission path.

In the laser communication system 1 in the present embodiment, a coaxialization (COAX) device 18 A and the reflector 17 as an auxiliary optical system are added, compared with the first embodiment. The reflector 17 leads the communication laser beam 15 B 1 emitted from the modulator 16 A, to an input of the coaxialization device 18 A. Note that the reflector 17 is an example and does not exclude an auxiliary optical system of another configuration. The coaxialization device 18 A coaxializes the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 which are supplied from different optical axes, and emits on the identical optical axis. For example, the coaxialization may be realized by using a half prism.

The connection relation of the coaxialization device 18 A will be described.

When paying attention to the optical connection relation, the coaxialization device 18 A is connected with the high-power laser oscillator 15 A, the modulator 16 A and the coaxial irradiation optical system 19 C. In case of the high-power laser beam 15 A 1 emitted from the first communication station 10 , the coaxialization device 18 A is arranged in the subsequent stage of the high-power laser oscillator 15 A and is arranged in the front stage of the coaxial irradiation optical system 19 C. Also, in case of the communication laser beam 15 B 1 emitted from the first communication station 10 , the coaxialization device 18 A is arranged in the subsequent stage of the modulator 16 A through the reflector 17 as the auxiliary optical system, and is arranged in the front stage of the coaxial irradiation optical system 19 C.

Also, when paying attention to the electrical connection relation, the coaxialization device 18 A is connected with the control device 14 .

The connection relation of the coaxial irradiation optical system 19 C will be described. When paying attention to the optical connection relation, the coaxial irradiation optical system 19 C is arranged in the subsequent stage of the coaxialization device 18 A. Also, when paying attention to the electrical connection relation, the coaxial irradiation optical system 19 C is connected with the control device 14 .

The operation of components of the first communication station 10 according to the coaxialization device 18 A and the coaxial irradiation optical system 19 C will be described.

The control device 14 generates a coaxialization control (COAX CTRL) signal 145 A to control the coaxialization of the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 . The control device 14 transmits the coaxialization control signal 145 A to the coaxialization device 18 A. The coaxialization device 18 A receives the coaxialization control signal 145 A. The coaxialization device 18 A adjusts the reception direction of the high-power laser beam 15 A 1 , the reception direction of the communication laser beam 15 B 1 , and the output direction of the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 which are coaxialized, according to the coaxialization control signal 145 A. The coaxialization device 18 A receives the high-power laser beam 15 A 1 emitted from the high-power laser oscillator 15 A, and emits to the coaxial irradiation optical system 19 C. Also, the coaxialization device 18 A receives the communication laser beam 15 B 1 emitted from the modulator 16 A through the reflector 17 as the auxiliary optical system and emits to the coaxial irradiation optical system 19 C.

The control device 14 generates an irradiation direction control (IR-DIR CTRL) signal 146 C to control the irradiation directions of the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 . The control device 14 transmits the irradiation direction control signal 146 C to the coaxial irradiation optical system 19 C. The coaxial irradiation optical system 19 C receives the irradiation direction control signal 146 C. Therefore, the coaxial irradiation optical system 19 C adjusts the irradiation direction of the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 according to the irradiation direction control signal 146 C, and the coaxial irradiation optical system 19 C irradiates the laser beam received from the coaxialization device 18 A to the adjusted irradiation direction.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the first embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than the first embodiment. This leads to the saving of energy which is necessary to remove the obstacle 2 , and the reduction of time to secure a transmission path.

Fourth Embodiment

FIG. 8 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a fourth embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 8 has the following different points, compared with the laser communication system 1 according to the third embodiment shown in FIG. 7 . That is, in the present embodiment, the optical axes of the laser beams transmitted and received by the first communication station 10 are coaxialized.

Specifically, the reception optical system 11 A and the coaxial irradiation optical system 19 C in the third embodiment are unified. The reception optical system 11 A and the coaxial irradiation optical system 19 C which have been unified correspond to an irradiation/reception coaxial optical system (IR/Rx COAX OP-SYS) 11 B in the present embodiment. In other words, in the first communication station 10 , the communication laser beam 26 A irradiated from the second communication station 20 and the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 which are irradiated from the first communication station 10 are received and irradiated by the irradiation/reception coaxial optical system 11 B. As a result, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than in the third embodiment. This leads to further saving of energy which is necessary to remove the obstacle 2 , and further reduction of time to secure a transmission path.

In the laser communication system 1 according to the present embodiment, a transmission/reception separating unit 12 A is added, compared with the third embodiment. The transmission/reception separating unit 12 A separates laser beams irradiated from and received by the irradiation/reception coaxial optical system 11 B. The configuration and operation principle of the irradiation/reception coaxial optical system 11 B are same as in the irradiation/reception coaxial optical system 21 B described in the second embodiment. Therefore, further detailed description is omitted.

Moreover, the reflector (REF) 17 and the coaxialization device 18 A according to the present embodiment are different from the case of the third embodiment in the arrangement. That is, in the present embodiment, the coaxialization device 18 A is arranged to directly receive the communication laser beam 15 B 1 emitted from the modulator 16 A, and the reflector 17 as the auxiliary optical system is arranged to lead the high-power laser beam 15 A 1 emitted from the high-power laser oscillator 15 A to the coaxialization device 18 A. However, these differences in the arrangement do not bring an essential change to the effect when coaxializing the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 .

The connection relation of the transmission/reception separating unit 12 A will be described.

When paying attention to the optical connection relation, the transmission/reception separating unit 12 A is connected with the irradiation/reception coaxial optical system 11 B, the reception sensor 13 and the coaxialization device 18 A. In case of the laser beam irradiated to the first communication station 10 from the second communication station 20 , the transmission/reception separating unit 12 A is arranged in the subsequent stage of the irradiation/reception coaxial optical system 11 B, and is arranged in the front-stage of the reception sensor 13 . In case of the laser beam irradiated to the second communication station 20 from the first communication station 10 , the transmission/reception separating unit 12 A is arranged in the subsequent stage of the coaxialization device 18 A, and is arranged in the front stage of the irradiation/reception coaxial optical system 11 B.

Also, when paying attention to the electrical connection relation, the transmission/reception separating unit 12 A is connected with the control device 25 .

The operation of components of the first communication station 10 according to the irradiation/reception coaxial optical system 11 B and the transmission/reception separating unit 12 A will be described.

The control device 14 generates an irradiation/reception direction control (IR/Rx DIR CTRL) signal 141 B to control the irradiation direction and reception direction of the irradiation/reception coaxial optical system 11 B. The control device 14 transmits the irradiation/reception direction control signal 141 B to the irradiation/reception coaxial optical system 11 B. The irradiation/reception coaxial optical system 11 B receives the irradiation/reception direction control signal 141 B. The irradiation/reception coaxial optical system 11 B adjusts the irradiation direction/reception direction according to the irradiation/reception direction control signal 141 B. The irradiation/reception coaxial optical system 11 B receives a laser beam from the adjusted reception direction and also irradiates a laser beam to the adjusted irradiation direction.

The control device 14 generates a transmission/reception separation control (Tx/Rx SEP CTRL) signal 142 A. The control device 14 transmits the transmission/reception separation control signal 142 A to the transmission/reception separating unit 12 A. The transmission/reception separating unit 12 A receives the transmission/reception separation control signal 142 A. Therefore, the transmission/reception separating unit 12 A switches between two states according to the transmission/reception separation control signal 142 A. That is, in a first state, the irradiation/reception coaxial optical system 12 A leads the received laser beam to the reception sensor 13 . Also, in a second state, the irradiation/reception coaxial optical system 12 A leads the laser beam received from the coaxialization device 18 A to the irradiation/reception coaxial optical system 11 B.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the third embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than the first embodiment. This leads to further saving of energy which is necessary to remove the obstacle 2 , and further reduction of time to secure a transmission path.

Fifth Embodiment

FIG. 9 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a fifth embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 9 has the following different points, compared with the laser communication system 1 according to the first embodiment shown in FIG. 3 . That is, in the present embodiment, in the first communication station 10 , the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 are generated by a common laser oscillator.

Specifically, the high-power laser oscillator 15 A and the communication laser oscillator 15 B in the first embodiment are unified. The high-power laser oscillator 15 A and the communication laser oscillator 15 B which have been unified correspond to a high-power/communication laser oscillator 15 C in the present embodiment. In other words, both of the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 which are irradiated from the first communication station 10 are generated by the high-power/communication laser oscillator 15 C, and are emitted on an optical co-axis. As a result, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than the first embodiment, like the second to fourth embodiments. This leads to the saving of energy which is necessary to remove the obstacle 2 , and the reduction of time to secure a transmission path.

The laser communication system 1 in the present embodiment has a modulator 16 B in place of the modulator 16 A in the first embodiment. The modulator 16 B according to the present embodiment operates like the modulator 16 A in the first embodiment regarding the operation to modulate the communication laser beam 15 B 1 . However, the modulator 16 B according to the present embodiment has a feature not to be destroyed even when the high-power laser beam 15 A 1 is supplied. For example, this feature may be realized by the configuration to be switched to a different internal optical system to endure the intensity when the high-power laser beam 15 A 1 is supplied. The switching of such a state may be controlled by the control device 14 .

Also, the laser communication system 1 according to the present embodiment has the coaxial irradiation optical system 19 C in place of the high-power laser irradiation optical system 19 A and the communication laser irradiation optical system 19 B in the first embodiment. The coaxial irradiation optical system 19 C according to the present embodiment is the same as the coaxial irradiation optical system 19 C according to the third embodiment shown in FIG. 7 . Therefore, further detailed description is omitted.

The connection relation of the high-power/communication laser oscillator 15 C will be described. When paying attention to the optical connection relation, the high-power/communication laser oscillator 15 C is arranged in the front stage of the modulator 16 B. Also, when paying attention to the electrical connection relation, the high-power/communication laser oscillator 15 C is connected with the control device 14 .

The connection relation of the modulator 16 B will be described. When paying attention to the optical connection relation, the modulator 16 B is arranged in the subsequent stage of the high-power/communication laser oscillator 15 C, and is arranged in the front stage of the coaxial irradiation optical system 19 C. Also, when paying attention to the electrical connection relation, the modulator 16 B is connected with the control device 14 .

The connection relation with the coaxial irradiation optical system 19 C will be described. When paying attention to the optical connection relation, the coaxial irradiation optical system 19 C is arranged in the subsequent stage of the modulator 16 B. Also, when paying attention to the electrical connection relation, the coaxial irradiation optical system 19 C is connected with the control device 14 .

The operation of components in the first communication station 10 according to the high-power/communication laser oscillator 15 C will be described.

The control device 14 generates an oscillation control (OSC CTRL) signal 143 C to control the oscillation of the high-power laser beam 15 A 1 or the communication laser beam 15 B 1 . The control device 14 transmits the oscillation control signal 143 C to the high-power/communication laser oscillator 15 C. The high-power/communication laser oscillator 15 C receives the oscillation control signal 143 C. The high-power/communication laser oscillator 15 C oscillates and emits the high-power laser beam 15 A 1 or the communication laser beam 15 B 1 to the modulator (MOD) 16 B in response to the oscillation control signal 143 C. The modulator 16 B receives the emitted high-power laser beam 15 A 1 or communication laser beam 15 B 1 .

The control device 14 generates a modulation control (MOD CTRL) signal 144 B to control the modulation of the communication laser beam 15 B 1 . Transmission data is contained in the modulation control signal 144 B, like the modulation control signal 144 A in the first embodiment. In the case that high-power/communication laser oscillator (HP-L/COM-L OSC) 15 C emits the high-power laser beam 15 A 1 , an instruction to carry out the above-mentioned state switching by the modulator 16 B may be contained in the modulation control signal 144 B.

The operation of the coaxial irradiation optical system 19 C according to the present embodiment is same as in the third embodiment. Therefore, further detailed description is omitted.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the first embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than the first embodiment. This leads to the saving of energy which is necessary to remove the obstacle 2 and the reduction of time to secure a transmission path.

Sixth Embodiment

FIG. 10 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a sixth embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 7 has the following different points, compared with the laser communication system 1 according to the fifth embodiment shown in FIG. 9 . That is, in the present embodiment, the optical axes of the laser beams transmitted and received by the first communication station 10 are coaxialized.

Viewing from another point, the laser communication system 1 according to the present embodiment shown in FIG. 7 has the following different points, compared with the laser communication system 1 according to the fourth embodiment shown in FIG. 8 . That is, in the present embodiment, the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 are generated by the common laser oscillator in the first communication station 10 .

In other words, the laser communication system 1 according to the present embodiment is achieved by combining the fourth embodiment shown in FIG. 8 and the fifth embodiment shown in FIG. 9 .

The different points of the present embodiment from the fifth embodiment shown in FIG. 9 will be described. In the present embodiment, the reception optical system 11 A and the coaxial irradiation optical system 19 C in the fifth embodiment are unified. The reception optical system 11 A and the coaxial irradiation optical system 19 C which have been unified correspond to the irradiation/reception coaxial optical system 11 B in the present embodiment. The irradiation/reception coaxial optical system 11 B in the present embodiment is the same as the irradiation/reception coaxial optical system 11 B in the fourth embodiment shown in FIG. 8 in configuration and operation. Therefore, further detailed description is omitted. As a result, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than the first embodiment. This leads to further saving of energy which is necessary to remove the obstacle 2 and further reduction of time to secure a transmission path.

Also, in the laser communication system 1 according to the present embodiment, the transmission/reception separating unit 12 A is added, like the case of the fourth embodiment. The transmission/reception separating unit 12 A according to the present embodiment is the same as the transmission/reception separating unit 12 A in the fourth embodiment shown in FIG. 8 in configuration and operation. Therefore, further detailed description is omitted.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the fifth embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, in the present embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than in the first embodiment. This leads to further saving of energy which is necessary to remove the obstacle 2 and further reduction of time to secure a transmission path.

Seventh Embodiment

FIG. 11 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a seventh embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 11 has the following different points, compared with the laser communication system 1 according to the first embodiment shown in FIG. 3 . That is, in the present embodiment, the first communication station 10 further irradiates a pulse laser beam 15 D 1 .

Specifically, a pulse laser oscillator (P-L OSC) 15 D and a pulse laser irradiation optical system (P-L IR OP-SYS) 19 D are added to the first communication station 10 of the first embodiment. The pulse laser oscillator 15 D can oscillate the pulse laser beam (P-LB) 15 D 1 having a very high output. The pulse laser irradiation optical system 19 D irradiates the oscillated pulse laser beam 15 D 1 to the obstacle 3 of water droplets existing in the direction of the second communication station 20 .

The pulse laser can have a very high output momentarily. Therefore, the pulse laser is suitable for removal of the obstacle 3 of water droplets. However, the pulse laser beam 15 D 1 irradiated from the first communication station 10 does not always reach the reception optical system 21 A of the second communication station 20 , unlike the continuous-wave high-power laser beam 15 A 1 and the communication laser beam 15 B 1 .

The connection relation of the pulse laser oscillator 15 D and the pulse laser irradiation optical system 19 D will be described. When paying attention to the optical connection relation, the pulse laser irradiation optical system 19 D is arranged in the subsequent stage of the pulse laser oscillator 15 D. When paying attention to the electrical connection relation, the pulse laser oscillator 15 D and the pulse laser irradiation optical system 19 D are connected with the control device 14 .

The operation of components of the first communication station 10 according to the pulse laser oscillator 15 D and the pulse laser irradiation optical system 19 D will be described.

The control device 14 generates an oscillation control (OSC CTRL) signal 143 D to control the oscillation of pulse laser beam 15 D 1 . The control device 14 transmits the oscillation control signal 143 D to the pulse laser oscillator 15 D. The pulse laser oscillator 15 D receives the oscillation control signal 143 D. Therefore, in response to the oscillation control signal 143 D, the pulse laser oscillator 15 D oscillates the pulse laser beam 15 D 1 to emit to the pulse laser irradiation optical system 19 D. The pulse laser irradiation optical system 19 D receives the pulse laser beam 15 D 1 .

The control device 14 generates an irradiation direction control signal 146 D to control the irradiation direction of the pulse laser beam 15 D 1 . The control device 14 transmits the irradiation direction control signal 146 D to the pulse laser irradiation optical system 19 D. The pulse laser irradiation optical system 19 D receives the irradiation direction control signal 146 D. Therefore, the pulse laser irradiation optical system 19 D adjusts the irradiation direction of the pulse laser beam 15 D 1 according to the irradiation direction control signal 146 D. The pulse laser irradiation optical system 19 D irradiates the pulse laser beam 15 D 1 to the adjusted irradiation direction.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the first embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, in the present embodiment, the pulse laser beam 15 D 1 suitable for removal of the obstacle 3 of water droplets can be irradiated, in addition to the high-power laser beam 15 A 1 suitable for removal of the obstacle 2 . The removal of the obstacle 3 of water droplets is possible even by the continuous-wave high-power laser beam 15 A 1 . The pulse laser beam 15 D 1 irradiated momentarily has higher applicability. Therefore, the laser communication system 1 according to the present embodiment suits the removal of the obstacle 3 of water droplets in addition to the solid obstacle 2 .

Eighth Embodiment

FIG. 12 is a block circuit diagram showing a configuration example of the laser communication system 1 according to an eighth embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 12 has the following different points, compared with the laser communication system 1 according to the fifth embodiment shown in FIG. 7 . That is, in the present embodiment, the first communication station 10 further irradiates the pulse laser beam 15 D 1 .

Specifically, the pulse laser oscillator 15 D and the reflector 17 as the auxiliary optical system are added to the laser communication system 1 of the fifth embodiment shown in FIG. 7 . Also, the coaxialization device 18 A and the coaxial irradiation optical system 19 C in the fifth embodiment are replaced with a coaxialization (COAX) device 18 B and a coaxial irradiation optical system (COAX IR OP-SYS) 19 E, respectively. The effect of irradiation of the pulse laser beam 15 D 1 is same as in the seventh embodiment shown in FIG. 11 . Therefore, further detailed description is omitted.

The connection relation of the pulse laser oscillator 15 D, the reflector 17 and the coaxial irradiation optical system 19 E will be described. When paying attention to the optical connection relation, the pulse laser oscillator 15 D is connected with the front-stage of the coaxialization device 18 B through the reflector 17 . The coaxial irradiation optical system 19 E is connected with the subsequent stage of the coaxialization device 18 B. Also, when paying attention to the electrical connection relation, the pulse laser oscillator 15 D and the coaxial irradiation optical system 19 E are connected with the control device 14 .

The operation of components of the first communication station 10 according to the pulse laser oscillator 15 D and the coaxial irradiation optical system 19 E will be described.

The control device 14 generates an oscillation control signal 143 D to control the oscillation of pulse laser beam 15 D 1 . The control device 14 transmits the oscillation control signal 143 D to the pulse laser oscillator 15 D. The pulse laser oscillator 15 D receives the oscillation control signal 143 D. The pulse laser oscillator 15 D oscillates the pulse laser beam 15 D 1 according to the oscillation control signal 143 D, to emit to the coaxialization device 18 B through the reflector 17 as the auxiliary optical system. The coaxialization device 18 B receives the pulse laser beam 15 D 1 through the reflector 17 .

The control device 14 generates a coaxialization control (COAX CTRL) signal 145 B to control the coaxialization of the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 and the communication laser beam 15 B 1 . The control device 14 transmits the coaxialization control signal 145 B to the coaxialization device 18 B. The coaxialization device 18 B receives the coaxialization control signal 145 B. The coaxialization device 18 B adjusts the reception direction of the high-power laser beam 15 A 1 , the reception direction of the pulse laser beam 15 D 1 , the reception direction of the communication laser beam 15 B 1 , and the irradiation direction of these received laser beams to the coaxial irradiation optical system 19 E on an optical co-axis, according to the coaxialization control signal 145 B. The coaxialization device 18 B receives the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 , and the communication laser beam 15 B 1 from the adjusted reception direction. The coaxialization device 18 B emits each of the high-power laser beams 15 A 1 , the pulse laser beams 15 D 1 and the communication laser beam 15 B 1 to the adjusted coaxial emission direction. The coaxial irradiation optical system 19 E receives the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 and the communication laser beam 15 B 1 .

The control device 14 generates an irradiation direction control (IR-DIR CTRL) signal 146 E to control the irradiation directions of the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 and the communication laser beam 15 B 1 . The control device 14 transmits the irradiation direction control signal 146 E to the coaxial irradiation optical system 19 E. The coaxial irradiation optical system 19 E receives the irradiation direction control signal 146 E. The coaxial irradiation optical system 19 E adjusts the irradiation directions of the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 and the communication laser beam 15 B 1 according to the irradiation direction control signal 146 E. The coaxial irradiation optical system 19 E irradiates the laser beam received from the coaxialization device 18 B to the adjusted irradiation direction.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the fifth embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. Like the case of the fifth embodiment, the area of the hole 2 B to be formed in the obstacle 2 becomes smaller in the present embodiment than in the first embodiment. This leads to the saving of energy which is required to remove the obstacle 2 and the reduction of time to secure a transmission path. Next, like the case of the seventh embodiment, the pulse laser beam 15 D 1 suitable for the removal of the obstacle 3 of water droplets can be irradiated in addition to the high-power laser beam 15 A 1 suitable for the removal of the obstacle 2 in the present embodiment.

The following variation is thought of in the present embodiment. That is, in this variation, only the high-power laser beam 15 A 1 and the pulse laser beam 15 D are coaxialized and are irradiated from the coaxial irradiation optical system 19 E. The communication laser beam 15 B 1 is not coaxialized and is irradiated from another irradiation optical system. In such a case, there is no change in the effect that the obstacle 3 of water droplets can be removed with the pulse laser beam 15 D 1 . Also, the effect can be obtained that the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than in the seventh embodiment.

Ninth Embodiment

FIG. 13 is a block circuit diagram showing a configuration example of the laser communication system 1 according to a ninth embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 9 has the following different points, compared with the laser communication system 1 according to the eighth embodiment shown in FIG. 12 . That is, in the present embodiment, the high-power laser beam 15 A 1 and the pulse laser beam 15 D 1 are generated by the common laser oscillator in the first communication station 10 .

Specifically, the high-power laser oscillator 15 A and the pulse laser oscillator 15 D in the eighth embodiment are unified. The high-power laser oscillator 15 A and the pulse laser oscillator 15 D having been unified correspond to a high-power/pulse laser oscillator (HP-L/P-L OSC) 15 E in the present embodiment. In other words, both of the high-power laser beam 15 A 1 and the pulse laser beam 15 D 1 which are irradiated from the first communication station 10 are generated by the high-power/pulse laser oscillator 15 E and emitted on the optical coaxial path. Moreover, the communication laser beam 15 B 1 is coaxialized by the coaxialization device 18 B with the high-power laser beam 15 A 1 and the pulse laser beam 15 D 1 . As a result, in the present embodiment, like the case of the eighth embodiment shown in FIG. 12 , the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than in the seventh embodiment shown in FIG. 11 . This leads to the saving of energy which is necessary to remove the obstacle 2 and the reduction of time to secure a transmission path. Moreover, because the number of laser oscillators decreases, the configuration of the laser communication system 1 can be simplified.

The connection relation of high-power/pulse laser oscillator 15 E will be described. The high-power/pulse laser oscillator 15 E is connected optically with the front stage of the coaxialization device 18 B and electrically with the control device 14 .

The operation of components of the first communication station 10 according to the high-power/pulse laser oscillator 15 E will be described.

The control device 14 generates an oscillation control (OSC CTRL) signal 143 E to control the oscillation of the high-power laser beam 15 A 1 or the pulse laser beam 15 D 1 . The control device 14 transmits the oscillation control signal 143 E to the high-power/pulse laser oscillator 15 E. The high-power/pulse laser oscillator 15 E receives the oscillation control signal 143 E. The high-power/pulse laser oscillator 15 E oscillates the high-power laser beam 15 A 1 or the pulse laser beam 15 D 1 according to the oscillation control signal 143 E. The high-power/pulse laser oscillator 15 E emits the high-power laser beam 15 A 1 or the pulse laser beam 15 D 1 on the coaxial path to the coaxialization device 18 B.

As the configuration and method of switching the state that high-power/pulse laser oscillator 15 E oscillates the high-power laser beam 15 A 1 or the pulse laser beam 15 D 1 , for example, a method of using a compression device such as so-called “Q switch” is thought of. That is, the identical high-power/pulse laser oscillator 15 E oscillates the pulse laser beam 15 D 1 in the condition that the compression device is optically connected and oscillates the high-power laser beam 15 A 1 as the continuous-wave in the condition that the compression device is optically removed. Here, the installation and removal of the compression device may be controlled through the oscillation control signal 143 E by the control device 14 .

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the first embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, in the present embodiment, like the case of the eighth embodiment shown in FIG. 12 , the area of the hole 2 B to be formed in the obstacle 2 becomes smaller than in the seventh embodiment shown in FIG. 11 . This leads to the saving of energy which is necessary to remove the obstacle 2 and the reduction of time to secure a transmission path. Moreover, because the number of laser oscillators decreases, the configuration of the laser communication system 1 can be simplified.

Tenth Embodiment

FIG. 14 is a block circuit diagram showing a configuration example of the laser communication system 1 according to the tenth embodiment. The laser communication system 1 according to the present embodiment shown in FIG. 14 has the following different points, compared with the laser communication system 1 according to the fifth embodiment shown in FIG. 9 . That is, in the present embodiment, the common laser oscillator generates the pulse laser beam 15 D 1 in the first communication station 10 in addition to the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 .

Specifically, the high-power/communication laser oscillator 15 C according to the fifth embodiment is replaced with a high-power/pulse/communication laser oscillator (HP-L/P-L/COM-L OSC) 15 F which can oscillate the pulse laser beam 15 D 1 . At the same time, it is desirable to replace the modulator 16 B and the coaxial irradiation optical system 19 C in the fifth embodiment with a modulator (MOD) 16 C and a coaxial irradiation optical system (COAX IR OP-SYS) 19 F which endure the intensity of the pulse laser beam 15 D 1 , respectively. As a result, the present embodiment is suitable for the application of removing the obstacle 3 of water droplets by the irradiation of the pulse laser beam 15 D 1 , while keeping the area of the hole 2 B to be formed in the obstacle 2 small.

The connection relation of the high-power laser oscillator 15 F, the pulse/the communication, the modulator 16 C and the coaxial irradiation optical system 19 F will be described. When paying attention to the optical connection relation, the high-power/pulse/communication laser oscillator 15 F is arranged in the front stage of the modulator 16 C and the modulator 16 C is arranged in the front stage of the coaxial irradiation optical system 19 F. When paying attention to the electrical connection relation, the high-power/pulse/communication laser oscillator 15 F, the modulator 16 C and the coaxial irradiation optical system 19 F are connected with the control device 14 .

The operation of components of the first communication station 10 according to the high-power/pulse/communication laser oscillator 15 F, the modulator 16 C and the coaxial irradiation optical system 19 F will be described.

The control device 14 generates an oscillation control (OSC CTRL) signal 143 F to control the oscillation of each laser beam. The control device 14 transmits the oscillation control signal 143 F to the high-power/pulse/communication laser oscillator 15 F. The high-power/pulse/communication laser oscillator 15 F receives the oscillation control signal 143 F. Therefore, the high-power/pulse/communication laser oscillator 15 F oscillates the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 or the communication laser beam 15 B 1 according to the oscillation control signal 143 F. The high-power/pulse/communication laser oscillator 15 F emits the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 or the communication laser beam 15 B 1 on the optical coaxial path to the modulator 16 C. The modulator 16 C receives the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 or the communication laser beam 15 B 1 .

The control device 14 generates a modulation control signal (MOD CTRL) 144 C to control the modulation of the communication laser beam 15 B 1 . The control device 14 transmits the modulation control signal 144 C to the modulator 16 C. The modulator 16 C receives the modulation control signal 144 C. Therefore, the modulator 16 C modulates the communication laser beam 15 B 1 according to the modulation control signal 144 C. The modulator 16 C emits the modulated communication laser beam 15 B 1 , the received high-power laser beam 15 A 1 or the pulse laser beam 15 D 1 on the optical coaxial path to the coaxial irradiation optical system 19 F. The coaxial irradiation optical system 19 F receives the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 or the communication laser beam 15 B 1 .

The control device 14 generates an irradiation direction control (IR-DIR CTRL) signal 146 F to control the irradiation direction of the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 or the communication laser beam 15 B 1 . The control device 14 transmits the irradiation direction control signal 146 F to the coaxial irradiation optical system 19 F. The coaxial irradiation optical system 19 F receives the irradiation direction control signal 146 F. Therefore, the coaxial irradiation optical system 19 F adjusts the irradiation direction of the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 or the communication laser beam 15 B 1 according to the irradiation direction control signal 146 F. The coaxial irradiation optical system 19 F irradiates the high-power laser beam 15 A 1 , the pulse laser beam 15 D 1 or the communication laser beam 15 B 1 to the adjusted irradiation direction.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the fifth embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, the present embodiment can be applied to a case of removing the obstacle 3 of water droplets by the irradiation of the pulse laser beam 15 D 1 while keeping the area of the hole 2 B to be formed in the obstacle 2 small.

Eleventh Embodiment

FIG. 15 is a block circuit diagram showing a configuration example of the laser communication system 1 according to an eleventh embodiment. The laser communication system 1 according to the present embodiment has the following different points, compared with the laser communication system 1 according to the sixth embodiment shown in FIG. 10 . That is, in the present embodiment, the common laser oscillator which generates the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 further generates the pulse laser beam 15 D 1 in the first communication station 10 .

Specifically, the high-power/communication laser oscillator 15 C according to the sixth embodiment is replaced with the high-power/pulse/communication laser oscillator 15 F, which can oscillate the pulse laser beam 15 D 1 . At the same time, it is desirable that the modulator 16 B, the transmission/reception separating unit 12 A and the transmission and reception/reception coaxial optical system 11 B according to the sixth embodiment are replaced with the modulator 16 C, the transmission and reception separating (Tx & Rx SEP) unit 12 B and the coaxial irradiation optical system 19 F to endure the intensity of pulse laser beam 15 D 1 , respectively. As a result, the present embodiment can be applied to remove the obstacle 3 of water droplets by the irradiation of pulse laser beam 15 D 1 , while keeping the area of the hole 2 B to be formed in the obstacle 2 small.

The connection relation of components of the first communication station 10 according to the high-power/pulse/communication laser oscillator 15 F, the modulator 16 C, the transmission and reception separating unit 12 B and the coaxial irradiation optical system 19 F according to the present embodiment will be described.

When paying attention to the optical connection relation, the high-power/pulse/communication laser oscillator 15 F is connected with the modulator 16 C. The modulator 16 C is connected at one end with the high-power/pulse/communication laser oscillator 15 F and is connected at the other end with the transmission/reception separating unit 12 B through the reflector 17 . The transmission/reception separating unit 12 B is connected at one end with the modulator 16 C through the reflector 17 and is connected at another end with the irradiation/reception optical system 11 C, and is connected at another end with the reception sensor 13 .

In case where the first communication station 10 is irradiated with the laser beam from the second communication station 20 , the irradiation/reception optical system 11 C is arranged in the front stage of the transmission and reception separating unit 12 B and the transmission and reception separating unit 12 B is arranged in the front stage of the reception sensor 13 . In case where the second communication station 20 is irradiated with the laser beam from the first communication station 10 , the high-power/pulse/communication laser oscillator 15 F is arranged in the front stage of the modulator 16 C. The modulator 16 C is arranged in the front stage of the transmission and reception separating unit 12 B through the reflector 17 , and the transmission and reception separating unit 12 B is arranged in the front stage of the irradiation/reception optical system 11 C.

Also, when paying attention to the electrical connection relation, the high-power/pulse/communication laser oscillator 15 F, the modulator 16 C, and the transmission and reception separating unit 12 B and the irradiation/reception optical system 11 C are connected with the control device 14 .

The operation of components of the first communication station 10 according to the high-power/pulse/communication laser oscillator 15 F, the modulator 16 C, the transmission/reception separating unit 12 B and the irradiation/reception optical system 11 C will be described.

The operation of the high-power/pulse/communication laser oscillator 15 F and the modulator 16 C according to the present embodiment is same as in the high-power/pulse/communication laser oscillator 15 F and the modulator 16 C according to the tenth embodiment shown in FIG. 14 . Therefore, further detailed description is omitted.

The operation of transmission/reception separating unit 12 B according to the present embodiment is different in the following points from that of the transmission/reception separating unit 12 A according to the sixth embodiment shown in FIG. 10 . That is, the pulse laser beam 15 D 1 is irradiated to the irradiation/reception optical system 11 C, in addition to the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 . The other operation of the transmission/reception separating unit 12 B according to the present embodiment is same as in the sixth embodiment. Therefore, further detailed description is omitted.

The operation of the irradiation/reception optical system 11 C according to the present embodiment is different in the following points from that of the irradiation/reception coaxial optical system 11 B according to the sixth embodiment shown in FIG. 10 . That is, the pulse laser beam 15 D 1 is irradiated in addition to the high-power laser beam 15 A 1 and the communication laser beam 15 B 1 . The other operation of the irradiation/reception optical system 11 C according to the present embodiment is same as in the sixth embodiment. Therefore, further detailed description is omitted.

The remaining configuration of the laser communication system 1 according to the present embodiment and each step of the laser communication method according to the present embodiment are same as in the first embodiment. Therefore, further detailed description is omitted.

The effect of the present embodiment will be described. As mentioned above, while keeping the area of the hole 2 B to be formed in the obstacle 2 small, the present embodiment can be applied to the application of removing the obstacle 3 of water droplets by irradiation of the pulse laser beam 15 D 1 .

Twelfth Embodiment

Each step of the laser communication method using the laser communication system 1 of the first to eleventh embodiments shown in FIG. 3 and FIG. 6 to FIG. 15 has been described with reference to the flow chart shown in FIG. 4 . Another variation of the laser communication method using the laser communication system 1 of the first to eleventh embodiments will be described below as a twelfth embodiment, with reference to FIG. 16 and FIG. 17A to FIG. 17D .

The laser communication method according to the present embodiment is different in the following points from the first embodiment shown in FIG. 4 . That is, in the sixth step S 106 of the first embodiment, the output level of the laser beam is changed rapidly to the low output level for communication from the high-power level of removing the obstacle 2 . However, in the present embodiment, the first communication station 10 drops the output level of the high-power laser beam 15 A 1 step-by-step. The second communication station 20 raises the transmittance of the light-attenuating filter 23 step-by-step. These step-by-step adjustments are realized by repeating the processing of the fourth step S 204 to the seventh step S 207 .

FIG. 16 is a flow chart showing a configuration example of the laser communication method according to the twelfth embodiment. The flow chart of FIG. 16 contains 10 steps of a 0 th step S 200 to the ninth step S 209 . The flow chart of FIG. 16 begins from the 0 th step S 200 . After the 0 th step S 200 , a first step S 201 is executed.

At the first step S 201 , the second communication station 20 protects the reception sensor 24 by the light-attenuating filter 23 . The first step S 201 according to the present embodiment is the same as the first step S 101 in the first embodiment shown in FIG. 4 . Therefore, further detailed description is omitted. After the first step S 201 , a second step S 202 is executed.

At the second step S 202 , the first communication station 10 irradiates the high-power laser beam 15 A 1 and removes the obstacle 2 . The second step S 202 according to the present embodiment is the same as the second step S 102 in the first embodiment shown in FIG. 4 . Therefore, further detailed description is omitted. FIG. 17A is a diagram showing an example of state that the laser communication system 1 according to the twelfth embodiment removes the obstacle 2 with the high-power laser beam 15 A 1 . After the second step S 202 , a third step S 203 is executed.

At the third step S 203 , the second communication station 20 detects the high-power laser beam 15 A 1 . The third step S 203 according to the present embodiment is the same as the third step S 103 , like the first embodiment shown in FIG. 4 . Therefore, further detailed description is omitted. After the third step S 203 , a fourth step S 204 is executed.

At the fourth step S 204 , the second communication station 20 transmits a detection signal to the first communication station 10 . The fourth step S 204 according to the present embodiment is the same as the fourth step S 104 in the first embodiment shown in FIG. 4 . Therefore, further detailed description is omitted. FIG. 17B is a diagram showing an example of state that the second communication station 20 of the laser communication system 1 according to the twelfth embodiment detects the high-power laser beam 15 A 1 and transmits the communication laser beam 26 A containing the detection signal. After the fourth step S 204 , a fifth step S 205 is executed.

At the fifth step S 205 , the first communication station 10 receives the detection signal. The fifth step S 205 according to the present embodiment is the same as the fifth step S 105 in the first embodiment shown in FIG. 4 . Therefore, further detailed description is omitted. Next, after the fifth step S 205 , a sixth step S 206 is executed.

At the sixth step S 206 , the first communication station 10 drops the output level of the high-power laser beam 15 A 1 step-by-step. When detecting that the intensity of the high-power laser beam 15 A 1 received by the reception sensor 24 dropped, the second communication station 20 raises the transmittance of the light-attenuating filter 23 step-by-step according to the intensity drop. As a specific method of raising the transmittance of the light-attenuating filter 23 step-by-step, a plurality of light-attenuating filters 23 with the different transmittances are prepared previously, and may be exchanged one after another. Or, a polarizing filter is used as the light-attenuating filter 23 , and an angle between the polarization direction of the polarizing filter and the polarization direction of the high-power laser beam 15 A 1 may be change step-by-step. FIG. 17C is a diagram showing an example of state that the first communication station 10 of the laser communication system 1 according to the twelfth embodiment drops the output level of the high-power laser beam step-by-step and the second communication station 20 raises the transmittance of the light-attenuating filter step-by-step. After the sixth step S 206 , a seventh step S 207 is executed.

At the seventh step S 207 , it is determined whether or not the intensity level of the high-power laser beam 15 A 1 is fallen to the intensity level of the communication laser beam 15 B 1 . This determination may be carried out by the first communication station 10 which adjusts the intensity level of the high-power laser beam 15 A 1 or the second communication station 20 which receives the high-power laser beam 15 A 1 . As a result of the determination, if the intensity level of the high-power laser beam 15 A 1 drops to the intensity level of the communication laser beam 15 B 1 (YES), an eighth step S 208 is executed after the seventh step S 207 . In the other case (NO), a fourth step S 204 is executed after the seventh step S 207 .

At the eighth step S 208 , the first communication station 10 and the second communication station 20 start the high-speed communication using the communication laser beam 15 B 1 . FIG. 17D is a diagram showing an example of state that the second communication station 20 of the laser communication system 1 according to the twelfth embodiment detects the output level of the communication laser beam and starts the high-speed communication. A ninth step S 209 is executed after the eighth step S 208 , and the flow chart of FIG. 16 ends.

As described above, in the laser communication system 1 and the laser communication method according to the present embodiment, the confirmation of securement of the transmission path between the communication stations is carried out by the following scheme:

(1) The reception sensor 24 is protected by the light-attenuating filter 23 until the transmission path is established (the first step S 201 ).

(2) After passing through the obstacle 2 (the second step S 202 ), the detection signal is transmitted to the first communication station 10 (the fourth step S 204 ), when the second communication station 20 receives the high-power laser beam 15 A 1 (the third step S 203 ).

(3) When receiving the detection signal from the second communication station 20 (the fifth step S 205 ), the first communication station 10 drops the intensity level of the laser beam to be outputted by a constant level for each step (the sixth step S 206 ).

(4) The second communication station 20 raises the transmittance of the light-attenuating filter 23 by the constant level for each step according to the drop of the intensity level (the sixth step S 206 ).

(5) If the intensity level of the laser beam irradiated from the first communication station 10 drops to the same level as the output level of the communication laser beam (the seventh step S 207 ), the high-speed communication is started (the eighth step S 208 ).

In this way, in the present embodiment, by changing the transmittance of the light-attenuating filter 23 step-by-step, it is possible to prevent more surely that the reception sensor 24 of the second communication station 20 is damaged by the high-power laser beam 15 A 1 .

Especially, such protection is effective when the second communication station 20 cannot be distinguished between the drop of the reception level when the transmission path in which the spatial laser communication is carried out between the first communication station 10 and the second communication station 20 is covered by the obstacle 2 and the drop of the output level of the laser beam by the adjustment of the first communication station 10 . That is, if a step-by-step change is not carried out, when an obstruction factor is removed after the output level of the laser beam received by the second communication station 20 drops with the obstruction factor such as the obstacle 2 , there is a fear that the high-power laser beam 15 A 1 is incident directly on the reception sensor 24 so that the reception sensor 24 is damaged. As in the present embodiment, in case where a step-by-step change is carried out, if the output level of the received laser beam rapidly drops after the reception signal is transmitted, it is possible to determine that the high-power laser beam 15 A 1 was obstructed. Therefore, the protected state of the reception sensor 24 is maintained by the light-attenuating filter 23 , and when the obstruction factor is removed, the reception sensor 24 can be protected from the high-power laser beam 15 A 1 .

Thirteenth Embodiment

Another variation of the laser communication method using the laser communication system 1 of any of the first to eleventh embodiments will be described as a thirteenth embodiment, with reference to FIG. 18A , FIG. 18B , and FIG. 19A to FIG. 19D .

The laser communication method according to the present embodiment is different in the following points from the case of the twelfth embodiment shown in FIG. 16 . That is, in the twelfth embodiment, the second communication station 20 transmits the detection signal at the fourth step S 204 , and when the first communication station 10 receives this detection signal at the fifth step S 205 , at the sixth step S 206 , the first communication station 10 drops the output level of the high-power laser beam 15 A 1 step-by-step and the second communication station 20 raises the transmittance of the light-attenuating filter 23 step-by-step. However, in the present embodiment, the second communication station 20 transmits the detection signal at the fourth step S 304 , and after the first communication station 10 receives the detection signal at the fifth step S 305 , further communication is carried out between the first communication station 10 and the second communication station 20 . Then, the step-by-step change is carried out in the output level of the high-power laser beam 15 A 1 and the transmittance of the light-attenuating filter 23 . This further communication is executed in the sixth step S 306 to the ninth step S 309 .

FIG. 18A and FIG. 18B show the flow chart showing a configuration example of the laser communication method according to the thirteenth embodiment. The flow chart of FIG. 18A and FIG. 18B contains 14 steps of a 0 th step S 300 to a thirteenth step S 313 . The flow chart of FIG. 18A and FIG. 18B begins from the 0 th step S 300 . After the 0 th step S 300 , a first step S 301 is executed.

At the first step S 301 , the second communication station 20 protects the reception sensor 24 by the light-attenuating filter 23 . The first step S 301 according to the present embodiment is the same as the first step S 201 of the twelfth embodiment shown in FIG. 16 . Therefore, further detailed description is omitted. After the first step S 301 , a second step S 302 is executed.

At the second step S 302 , the first communication station 10 irradiates the high-power laser beam 15 A 1 and removes the obstacle 2 . The second step S 302 according to the present embodiment is the same as the second step S 202 of the twelfth embodiment shown in FIG. 16 . Therefore, further detailed description is omitted. FIG. 19A is a diagram showing an example of state that the laser communication system 1 according to the thirteenth embodiment removes the obstacle 2 with the high-power laser beam 15 A 1 . After the second step S 302 , a third step S 303 is executed.

At the third step S 303 , the second communication station 20 detects the high-power laser beam 15 A 1 . The third step S 303 according to the present embodiment is the same as the third step S 203 of the twelfth embodiment shown in FIG. 16 . Therefore, further detailed description is omitted. After the third step S 303 , a fourth step S 304 is executed.

At the fourth step S 304 , the second communication station 20 transmits the first detection signal to the first communication station 10 . The fourth step S 304 according to the present embodiment is the same as the fourth step S 204 of the twelfth embodiment shown in FIG. 16 . Therefore, further detailed description is omitted. FIG. 19B is a diagram showing an example of state that the second communication station 20 of the laser communication system 1 according to the thirteenth embodiment detects the high-power laser beam 15 A 1 and transmits the communication laser beam 26 A which contains the first detection signal. After the fourth step S 304 , a fifth step S 305 is executed.

At the fifth step S 305 , the first communication station 10 receives the first detection signal. The fifth step S 305 according to the present embodiment is the same as the fifth step S 205 of the twelfth embodiment shown in FIG. 16 . Therefore, further detailed description is omitted. Next, a sixth step S 306 is executed after the fifth step S 305 .

At the sixth step S 306 , the first communication station 10 changes the output level of the high-power laser beam 15 A 1 in a specific pattern. This specific pattern may be, for example, a pattern in which a lighting-up state of a predetermined output level and a going-out state is repeated in a predetermined interval, or may be a pattern in which an output level is changed step-by-step or continuously between the plurality of output levels. In any case, it is desirable that data showing this specific pattern is previously stored in the control device 25 and the storage unit (not shown) such that the second communication station 20 can detect the change of the output level of the high-power laser beam 15 A 1 . After the sixth step S 306 , a seventh step S 307 is executed.

At the seventh step S 307 , the second communication station 20 detects the specific pattern of the change of the output level of the high-power laser beam 15 A 1 . After the seventh step S 307 , an eighth step S 308 is executed.

At the eighth step S 308 , the second communication station 20 transmits the second detection signal to the first communication station 10 . This second detection signal is transmitted as the communication laser beam 26 A, like the first detection signal transmitted at the fourth step S 304 . After the eighth step S 308 , a ninth step S 309 is executed.

At the ninth step S 309 , the first communication station 10 receives the second detection signal. After the ninth step S 309 , a tenth step S 310 is executed.

At the tenth step S 310 , the first communication station 10 drops the output level of the high-power laser beam 15 A 1 step-by-step. The second communication station 20 raises the transmittance of the light-attenuating filter 23 step-by-step. The method of raising the transmittance of the light-attenuating filter 23 step-by-step is same as in the sixth step S 206 shown in FIG. 16 . Therefore, further detailed description is omitted. FIG. 19C is a diagram showing an example of state that the first communication station 10 of the laser communication system 1 according to the thirteenth embodiment drops the output level of the high-power laser beam step-by-step, and the second communication station 20 raises the transmittance of the light-attenuating filter 23 step-by-step. After the tenth step S 310 , an eleventh step S 311 is executed.

At the eleventh step S 311 , it is determined whether or not the intensity level of the high-power laser beam 15 A 1 drops to the intensity level of the communication laser beam 15 B 1 . The eleventh step S 311 according to the present embodiment is same as seventh step S 207 according to the twelfth embodiment shown in FIG. 16 . Therefore, further detailed description is omitted. As the result of the determination, if the intensity level of the high-power laser beam 15 A 1 has dropped to the intensity level of the communication laser beam 15 B 1 (YES), a twelfth step S 312 is executed after the eleventh step S 311 . In the other case (NO), the fourth step S 304 is executed after the eleventh step S 311 .

At the twelfth step S 312 , the first communication station 10 and the second communication station 20 start the high-speed communication using the communication laser beam 15 B 1 . FIG. 19D is a diagram showing an example of state that the first communication station 10 and the second communication station 20 in the laser communication system 1 according to the thirteenth embodiment start the high-speed communication. After the twelfth step S 312 , a thirteenth step S 313 is executed and the flow chart of FIG. 18 ends.

As described above, in the laser communication system 1 and the laser communication method according to the present embodiment, the confirmation of securement of the transmission path between the communication stations is carried out in the following method:

(1) Until the transmission path is established, the reception sensor 24 is protected by the light-attenuating filter 23 (the first step S 301 ).

(2) After passing through the obstacle 2 (the second step S 302 ), the second communication station 20 receives the high-power laser beam 15 A 1 (the third step S 303 ), transmits the first detection signal to the first communication station 10 (the fourth step S 304 ).

(3) When receiving the first detection signal from the second communication station 20 (the fifth step S 205 ), the first communication station 10 changes the intensity level of the laser beam to be outputted in the specific pattern (the sixth step S 306 ).

(4) When detecting a change of the laser beam in the specific pattern (the seventh step S 307 ), the second communication station 20 transmits the second detection signal to the first communication station 10 (the eighth step S 308 ).

(5) When receiving the second detection signal (the ninth step S 309 ), the first communication station 10 drops the intensity level of the laser beam to be outputted step-by-step in a constant level for each step (the tenth step S 310 ).

(6) The second communication station 20 raises the transmittance of the light-attenuating filter 23 step-by-step in a constant level for each step, according to the drop of the output level of the laser beam (the tenth step S 310 ).

(7) The above-mentioned (3)-(6) is repeated, and when the intensity level of the laser beam irradiated by the first communication station 10 drops to the intensity level for the communication laser beams (the eleventh step S 311 ), the high-speed communication is started (the twelfth step S 312 ).

In this way, in the present embodiment, since the timing to change the transmittance of the light-attenuating filter 23 step-by-step is clearly defined based on the communication, the reception sensor 24 can be protected more surely.

The present invention which was accomplished by the inventors has been specifically described based on the embodiments. However, the present invention is not limited to the embodiments. Various changes or modification can be carried out in a range without deviate from the gist of the present invention. Also, the features described in the embodiments can be freely combined in a range without technical contradiction.

1 : laser communication system

10 : first communication station (1 st COM-STA)

11 A: reception optical system (Rx OP-SYS)

11 B: irradiation/reception coaxial optical system (IR/Rx COAX OP-SYS)

11 C: irradiation/reception coaxial optical system (IR/Rx COAX OP-SYS)

12 A: transmission and reception separating (Tx & Rx SEP) unit

12 B: transmission and reception separating (Tx & Rx SEP) unit

13 : reception (Rx) sensor

131 : reception (Rx) signal

14 : control (CTRL) devices

141 A: reception direction control (Rx-DIR CTRL) signal

141 B: irradiation/reception direction control (IR/Rx DIR CTRL) signal

141 C: irradiation/reception direction control (IR/Rx DIR CTRL) signal

142 A transmission and reception separation control (Tx & Rx SEP CTRL) signal

142 B: transmission and reception separation control (Tx & Rx SEP CTRL) signal

143 A: oscillation control (OSC CTRL) signal

143 B: oscillation control (OSC CTRL) signal

143 C: oscillation control (OSC CTRL) signal

143 D: oscillation control (OSC CTRL) signal

143 E: oscillation control (OSC CTRL) signal

143 F: oscillation control (OSC CTRL) signal

144 A: modulation control (MOD CTRL) signal

144 B: modulation control (MOD CTRL) signal

144 C: modulation control (MOD CTRL) signal

145 A: coaxialization control (COAX CTRL) signal

145 B: coaxialization control (COAX CTRL) signal

146 A: irradiation direction control (IR-DIR CTRL) signal

146 B: irradiation direction control (IR-DIR CTRL) signal

146 C: irradiation direction control (IR-DIR CTRL) signal

146 D: irradiation direction control (IR-DIR CTRL) signal

146 E: irradiation direction control (IR-DIR CTRL) signal

146 F: irradiation direction control (IR-DIR CTRL) signal

15 A: high-power laser oscillator (HP-L OSC)

15 A 1 high-power laser beam (HP-LB)

15 A 2 : communication laser beam (COM-LB)

15 B: communication laser oscillator (COM-L OSC)

15 B 1 : communication laser beam (COM-LB)

15 C high-power/communication laser oscillator (HP-L/COM-L OSC)

15 D: pulse laser oscillator (P-L OSC)

15 D 1 : pulse laser beam (P-LB)

15 E: high-power/pulse laser oscillator (HP-L/P-L OSC)

15 F: high-power/pulse/communication laser oscillator (HP-L/P-L/COM-L OSC)

16 A: modulator (MOD)

16 B: modulator (MOD)

16 C: modulator (MOD)

17 : reflector (REF)

18 A: coaxialization (COAX) device

18 B: coaxialization (COAX) device

19 A: high-power laser irradiation optical system (HP-L IR OP-SYS)

19 B: communication laser irradiation optical system (COM-L IR OP-SYS)

19 C: coaxial irradiation optical system (COAX IR OP-SYS)

19 D: pulse laser irradiation optical system (P-L IR OP-SYS)

19 E: coaxial irradiation optical system (COAX IR OP-SYS)

19 F: coaxial irradiation optical system (COAX IR OP-SYS)

20 : second communication station (2 nd COM-STA)

21 A: reception optical system (Rx OP-SYS)

21 B: irradiation/reception coaxial optical system (IR/Rx COAX OP-SYS)

22 : transmission and reception separating (Tx & Rx SEP) unit

23 : light-attenuating (LA) filter

24 : reception (Rx) sensor

241 : reception (Rx) signal

25 : control (CTRL) device

251 A: reception direction control (Rx-DIR CTRL) signal

251 B: irradiation/reception direction control (IR/Rx DIR CTRL) signal

252 : transmission and reception separation control (Tx/Rx SEP CTRL) signal

253 : transmittance control (TM CTRL) signal

254 : oscillation control (OSC CTRL) signal

255 : modulation control (MOD CTRL) signal

256 : irradiation direction control (IR-DIR CTRL) signal

26 : communication laser oscillator (COM-L OSC)

26 A: communication laser beam (COM-LB)

27 : modulator (MOD)

28 : irradiation optical systems (IR OP-SYS)

2 : obstacle

2 A: irradiation (IR) part

2 B: hole

3 : obstacle

100 : first communication station (1 st COM-STA)

200 : second communication station (2 nd COM-STA)

300 : communication laser beam (COM-LB)

400 : high-power laser irradiation (HP-L IR) apparatus

410 : high-power laser oscillator (HP-L OSC)

420 : irradiation optical system (IR OP-SYS)

430 : high-power laser beam (HP-LB)

500 : target

510 : irradiation (IR) part