Lightwave circuit device

1. Field of the Invention

The present invention relates to a lightwave circuit device, an optical multiplexer, and an optical demultiplexer.

2. Description of the Related Art

As a lightwave circuit device, a coarse wavelength division multiplexing (CWDM) filter that makes use of a planar lightwave circuit (PLC) is disclosed is Kitoh et al., Proceedings of the 2002 IEICE General Conference, C-3-125 (2002), p. 257. With this CWDM filter, a plurality of lattice filters are disposed in tandem. This CWDM filter demultiplexes light of multiplexed wavelength into four lightwaves of different wavelengths.

As another lightwave circuit device, an optical multiplexer or optical demultiplexer in which a plurality of Mach-Zehnder interferometers are connected in a multistage tree is disclosed in Japanese Patent Application No. 2003-149472. Each of the Mach-Zehnder interferometers includes a first optical coupler, two optical waveguides connected to the first optical coupler, and a second optical coupler connected to the two optical waveguides. One of the two optical waveguides functions as a delay circuit.

The wavelengths of lightwaves multiplexed or demultiplexed by one of the above-mentioned lightwave circuit devices are predetermined for each of the lightwave circuit devices. If lightwaves whose wavelengths differ from the predetermined wavelengths are inputted to the above-mentioned lightwave circuit device, such lightwaves cannot be multiplexed. Similarly, if light in which lightwaves whose wavelengths differ from the predetermined wavelengths are multiplexed is inputted to the above-mentioned lightwave circuit device, it is impossible to demultiplex the light into individual lightwaves.

It is an object of the present invention to provide a lightwave circuit device, an optical multiplexer, and an optical demultiplexer with which light can be multiplexed or demultiplexed even when a plurality of lightwaves of varying wavelength are inputted.

To achieve the stated object, a lightwave circuit device having first to third Mach-Zehnder interferometers is provided. The first to third Mach-Zehnder interferometers each have first to third ports, a first optical coupler whose one end is optically coupled to the first port, first and second optical waveguides optically coupled to the other end of the first optical coupler, a second optical coupler optically coupled to each of the first and the second optical waveguides and the second and the third ports, and a first heater provided along at least one of the first and the second optical waveguides. The second port of the first Mach-Zehnder interferometer and the first port of the second Mach-Zehnder interferometer are optically coupled. The third port of the first Mach-Zehnder interferometer and the first port of the third Mach-Zehnder interferometer are optically coupled.

The lightwave circuit device preferably further includes a third optical coupler whose one end is optically coupled to the first port of the first Mach-Zehnder interferometer, third and fourth optical waveguides optically coupled to the other end of the third optical coupler, a fourth optical coupler whose one end is optically coupled to the third and the fourth optical couplers, fifth and sixth optical waveguides optically coupled to the other end of the fourth optical coupler, a fifth optical coupler whose one end is optically coupled to the fifth and the sixth optical waveguides, a second heater provided along at least one of the third and the fourth optical waveguides, and a third heater provided along at least one of the fifth and the sixth optical waveguide. In this case, the lightwave circuit device preferably further includes a fourth port optically coupled to the third optical coupler.

In addition, there is provided an optical multiplexer in which a plurality of first input ports to which a plurality of lightwaves of mutually different wavelengths are inputted, an optical multiplexing circuit (which is the lightwave circuit device of the present invention) that multiplexes the plurality of lightwaves and outputs a first signal light, a second input port to which a second signal light including a lightwave with a different wavelength from the wavelengths of the plurality of lightwaves of the first signal light is inputted, and an output port to which the first and the second signal lights are outputted, are provided on a substrate. The second and the third ports of each of the second and the third Mach-Zehnder interferometers are optically coupled to the plurality of first input ports.

There is further provided an optical demultiplexer in which an input port to which a first signal light including a plurality of lightwaves of mutually different wavelengths and a second signal light including a lightwave having a different wavelength from those of the plurality of lightwaves are inputted, an optical demultiplexing circuit (which is the lightwave circuit device of the present invention) that demultiplexes the first signal light, a first output port to which the second signal light is outputted, and a plurality of second output ports to which each of the plurality of lightwaves that are included in the first signal light and demultiplexed by the optical demultiplexing circuit is outputted, are provided on a substrate. The second and the third ports of each of the second and the third Mach-Zehnder interferometers are optically coupled to the plurality of second output ports.

Advantage of the present invention will become apparent from the following detailed description, which illustrates the best mode contemplated to carry out the invention. The invention is capable of other and different embodiments, the details of which are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the accompanying drawings and description are illustrative in nature, not restrictive.

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numbers refer to similar elements.

FIG. 1 is a schematic diagram of an optical module equipped with the lightwave circuit device according to the present invention;

FIG. 2 is a schematic diagram of a first embodiment pertaining to the lightwave circuit device according to the present invention;

FIG. 3 is a graph illustrating an example of the transmission spectrum of light traveling from four input ports P 1 to a port r 1 in the lightwave circuit device of the first embodiment;

FIGS. 4A and 4B are graphs illustrating an example of the transmission spectrum of light traveling from the port r 1 to an output port P 3 or P 4 in the lightwave circuit device of the first embodiment, with FIG. 4A being when a switch is set to output the signal light S 1 to the output port P 3 , and FIG. 4B being when the switch is set to output the signal light S 1 to the output port P 4 ;

FIG. 5 is a schematic diagram of a second embodiment pertaining to the lightwave circuit device according to the present invention;

FIG. 6 is a graph illustrating an example of the transmission spectrum of light traveling from an input port P 13 to output ports P 11 and P 12 in the lightwave circuit device of the second embodiment;

FIG. 7 is a schematic diagram of a third embodiment pertaining to the lightwave circuit device according to the present invention;

FIG. 8 is a schematic diagram of a fourth embodiment pertaining to the lightwave circuit device according to the present invention;

FIGS. 9A and 9B are graphs illustrating an example of the transmission spectrum of light traveling from an input port P 33 to the output port P 11 or P 32 in the lightwave circuit device of the fourth embodiment, with FIG. 9A being when a switch is set to output the signal light S 3 to the output port P 11 , and FIG. 9B being when the switch is set to output the signal light S 1 to the output port P 11 ;

FIG. 10 is a block diagram of an optical add/drop apparatus equipped with the lightwave circuit device of the first embodiment and the lightwave circuit device of the second embodiment;

FIGS. 11A and 11B are block diagrams of a wavelength division multiplexing transmission system equipped with a plurality of the optical add/drop apparatus of FIG. 10 , with FIG. 11A being when the transmission path A is operating normally, and FIG. 11B being when an obstruction has occurred in the transmission path A;

FIG. 12 is a block diagram of an optical add/drop apparatus equipped with the lightwave circuit device of the third embodiment and the lightwave circuit device of the fourth embodiment; and

FIG. 13 is a block diagram of a wavelength division multiplexing transmission system equipped with a plurality of the optical add/drop apparatus of FIG. 12 .

First Embodiment

FIG. 1 is a schematic diagram of an optical module 1 equipped with the lightwave circuit device according to the present invention. The optical module 1 is used, for example, in a CWDM system or a dense wavelength division multiplexing (DWDM) system.

The lightwave circuit device 10 of the first embodiment is, for example, a planar waveguide type element made of a silica-based material, and has a substrate 16 made of a silica-based material, for example. Optical waveguides, optical couplers, Mach-Zehnder interferometers, optical switches, and the like are provided to the substrate 16 . Therefore, it can be said that lightwave circuits are integrated on the substrate 16 in the lightwave circuit device 10 . Optical fiber arrays 2 are connected at both ends 16 a of the substrate 16 . A reinforcing member 4 is provided on the surface of the substrate 16 at both ends 16 a , and the reinforcing members 4 are also connected to the optical fiber arrays 2 . The ends 6 a of optical fibers 6 are fixed to the optical fiber arrays 2 . The optical axes of the lightwave circuits and the optical fibers 6 are aligned.

A plurality of wires 12 are electrically connected to the surface of the substrate 16 . The other ends of the wires 12 are fixed to a wiring board 8 so as to form terminals 12 a . A control unit equipped with electrical circuits for controlling the lightwave circuit device 10 can be connected to the terminals 12 a . The lightwave circuit device 10 , the reinforcing members 4 , the optical fiber arrays 2 , the wires 12 , the wiring board 8 , and the ends 6 a of the optical fibers 6 are covered with a molding 14 made of resin, for example. The terminals 12 a project outward from the molding 14 .

FIG. 2 is a schematic diagram of a first embodiment pertaining to the lightwave circuit device according to the present invention. The lightwave circuit device 10 of the first embodiment has an optical multiplexing circuit 20 , and functions as an optical multiplexer. The optical multiplexing circuit 20 includes first to third Mach-Zehnder interferometers M 1 to M 3 provided to the substrate 16 .

A first port r 1 is provided to one end M 1 a of the Mach-Zehnder interferometer M 1 , and a second port r 2 and a third port r 3 are provided to the other end M 1 b . One end C 1 a of a first optical coupler C 1 is optically coupled to the port r 1 . A first optical waveguide (also called an arm) w 1 and a second optical waveguide w 2 are optically coupled to the other end C 1 b of the optical coupler C 1 . One end C 2 a of a second optical coupler C 2 is optically coupled to the optical waveguides w 1 and w 2 . The ports r 2 and r 3 are optically coupled to the other end C 2 b of the optical coupler C 2 . First heaters H 11 and H 1 are provided to the optical waveguides w 1 and w 2 , respectively.

A first port r 4 is provided to one end M 2 a of the Mach-Zehnder interferometer M 2 , and a second port r 5 and a third port r 6 are provided to the other end M 2 b . A first port r 7 is provided to one end M 3 a of the Mach-Zehnder interferometer M 3 , and a second port r 8 and a third port r 9 are provided to the other end M 3 b . The internal structure of the Mach-Zehnder interferometer M 2 and the Mach-Zehnder interferometer M 3 is the same as the internal structure of the Mach-Zehnder interferometer M 1 . The port r 2 of the Mach-Zehnder interferometer M 1 is optically coupled to the port r 4 of the Mach-Zehnder interferometer M 2 . The port r 3 of the Mach-Zehnder interferometer M 1 is optically coupled to the port r 7 of the Mach-Zehnder interferometer M 3 .

The lightwave circuit device 10 is also equipped with four first input ports P 1 to which a plurality of lightwaves having mutually different wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are inputted. The ports r 5 , r 6 , r 8 , and r 9 of the Mach-Zehnder interferometers M 2 and M 3 are optically coupled to the input ports P 1 via optical waveguides. When lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are inputted to the input ports P 1 , these lightwaves are inputted to the ports r 5 , r 6 , r 8 , and r 9 , respectively. The optical multiplexing circuit 20 multiplexes the lightwaves inputted to the ports r 5 , r 6 , r 8 , and r 9 , and outputs a first signal light S 1 in which lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are multiplexed from the port r 1 of the Mach-Zehnder interferometer M 1 .

In the Mach-Zehnder interferometers M 1 to M 3 , heaters H 1 , H 11 , H 2 , H 21 , H 3 , and H 31 are provided along the optical waveguides. These heaters are electrically connected to the respective wires 12 ( FIG. 1 ). By applying a desired voltage to the terminals 12 a , the refractive index of the heated portion of the optical waveguides w 2 , w 1 , w 4 , w 3 , w 6 , and w 5 can be adjusted. As a result, the phase differential φ 1 between lightwaves passing through the optical waveguides w 2 and w 1 , the phase differential φ 2 between lightwaves passing through the optical waveguides w 4 and w 3 , and the phase differential φ 3 between lightwaves passing through the optical waveguides w 6 and w 5 can each be controlled. An alternate configuration is possible in which the phase differentials φ 1 , φ 2 , and φ 3 are controlled by providing only the heaters H 1 , H 2 , and H 3 , or in which the phase differentials φ 1 , φ 2 , and φ 3 are controlled by providing only the heaters H 11 , H 21 , and H 31 .

Therefore, even when the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 of lightwaves inputted to the lightwave circuit device 10 vary, by setting desired phase differentials φ 1 , φ 2 , and φ 3 , it is possible to multiplex a plurality of lightwaves that have wavelength intervals determined by the phase differentials and a differential order. For instance, when using a plurality of lightwaves whose wavelengths are entirely shifted from the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 to the long or short wavelength side, the plurality of lightwaves can still be multiplexed by the lightwave circuit device 10 . The manner in which the phase differential is controlled will be described in detail below.

The lightwave circuit device 10 preferably includes an optical switch SW on the substrate 16 . The optical switch SW has a third optical coupler C 7 , and the port r 1 of the Mach-Zehnder interferometer M 1 is optically coupled via an optical waveguide to one end C 7 b of the optical coupler C 7 . Third and fourth optical waveguides w 7 and w 8 are optically coupled to the other end C 7 a of the optical coupler C 7 . One end C 8 b of a fourth optical coupler C 8 is optically coupled to the optical waveguides w 7 and w 8 . Fifth and sixth optical waveguides w 9 and w 10 are optically coupled to the other end C 8 a of the optical coupler C 8 . One end C 9 b of a fifth optional coupler C 9 is optically coupled to the optical waveguides w 9 and w 10 . Second heaters H 4 and H 41 are provided along the optical waveguides w 7 and w 8 , respectively. Third heaters H 51 and H 5 are provided along the optical waveguides w 9 and w 10 , respectively.

When the lightwave circuit device 10 is equipped with the optical switch SW, a phase differential φ 4 between lightwaves passing through the optical waveguides w 7 and w 8 and a phase differential φ 5 between lightwaves passing through the optical waveguides w 10 and w 9 can be controlled by the heaters H 4 , H 41 , H 5 , and H 51 . As a result, it is possible to switch the path of the signal light passing through the optical couplers C 7 , C 8 , and C 9 and the optical waveguides w 7 to w 10 . Alternatively, the phase differentials φ 4 and φ 5 may be controlled by providing only the heaters H 4 and H 5 , or the phase differentials φ 4 and φ 5 may be controlled by providing only the heaters H 41 and H 51 .

In the lightwave circuit device 10 that is equipped with the optical switch SW, the heaters H 1 , H 11 , H 2 , H 21 , H 3 , H 31 , H 4 , H 41 , H 5 , and H 51 can all be controlled together. That is, the optical multiplexing circuit 20 and the optical switch SW can be controlled simultaneously. This improves control over the signal light passing through the lightwave circuit device 10 . Furthermore, since the optical switch SW is provided to the substrate 16 , the lightwave circuit device 10 is more compact and less expensive.

The lightwave circuit device 10 preferably includes a second input port P 2 (fourth port) that is optically coupled via an optical waveguide to one end C 7 b of the optical coupler C 7 on the side of the port r 1 . The input port P 2 is provided to the substrate 16 . In this case, for example, a second signal light S 2 including monitoring light having a wavelength of λ m that is different from any of the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 can be inputted to the input port P 2 .

Output ports P 3 and P 4 are optically coupled via optical waveguides to the other end C 9 a of an optical coupler C 9 which is on the opposite side from the optical waveguides w 9 and w 10 . The signal lights S 1 , S 2 can be outputted to either of the output ports P 3 and P 4 as desired by controlling the heater of the optical switch SW.

A specific example of the lightwave circuit device 10 will now be described. In this specific example, the optical waveguides w 1 to w 10 include a core and a cladding that covers the core. The cladding is composed of overcladding and undercladding. The optical couplers C 1 to C 9 are optical directional couplers. The heaters are thin-film resistors provided on the surface of the overcladding of the optical waveguide. The use of a heater allows the refractive index of the core and cladding to be changed.

As for waveguide parameters, a specific refractive index differential Δn for the core to the cladding is 1.5% and the core size is 4.5×4.5 μm. As for the lightwave circuit parameters, a diffraction order m 1 of the optical waveguide w 1 when the wavelength is λ 0 is 18.85, a diffraction order m 2 of the optical waveguide w 3 is 9.425, a diffraction order m 3 of the optical waveguide w 5 is 9.175, a diffraction order m 4 for the optical waveguide w 7 is 37.7, and a diffraction order m 5 of the optical waveguide w 9 is −75.4. The coupling coefficients k 1 , k 2 , . . . , k 7 of the optical couplers C 1 , C 2 , . . . , C 7 are each 0.5, the coupling coefficient k 8 of the fourth optical coupler C 8 is 0.3, and the coupling coefficient k 9 of the optical coupler C 9 is 0.1.

The effective refractive index n eff and the arm length differentials ΔL 1 , ΔL 2 , ΔL 3 , ΔL 4 , and ΔL 5 , which are obtained by subtracting the length of the optical waveguides w 2 , w 4 , w 6 , w 8 , and w 10 from the length of the optical waveguides w 1 , w 3 , w 5 , w 7 , and w 9 satisfy the following equation:

n eff ×L i =λ 0 ×m i ( i= 1, 2, 3, 4, 5)  (1)

The heaters H 1 , H 11 , H 2 , H 21 , H 3 , and H 31 are used to control the phase differentials φ 1 , φ 2 , and φ 3 to be 45°, 22.5°, and 22.5°, respectively. Here, the phase differential is expressed as a positive value when the phase of the light passing through the optical waveguides w 2 , w 4 , and w 6 is delayed compared to the phase of the light passing through the optical waveguides w 1 , w 3 , and w 5 .

FIG. 3 is a graph illustrating an example of the transmission spectrum of light traveling from the four input ports P 1 to the port r 1 in the lightwave circuit device of the first embodiment. The horizontal axis of the graph indicates the wavelength of the light, while the vertical axis indicates the loss (dB). The symbols “♦”, “▴”, “▪”, and “x” each indicate the transmission spectrum of lightwaves passing through r 5 , r 6 , r 8 , and r 9 , respectively. The wavelengths λ 1 , λ 2 , λ 3 , and λ 4 that give the minimum loss in each transmission spectrum are 1470 nm, 1550 nm, 1510 nm, and 1590 nm, respectively. Therefore, lightwaves that have wavelengths of 1470 nm, 1550 nm, 1510 nm, and 1590 nm and pass through r 5 , r 6 , r 8 , and r 9 are multiplexed, and are outputted as the wavelength division multiplexed signal light S 1 from the port r 1 .

FIGS. 4A and 4B are graphs illustrating an example of the transmission spectrum of light traveling from the port r 1 to the output port P 3 or P 4 in the lightwave circuit device of the first embodiment. The horizontal axis of the graph indicates the wavelength of the light, while the vertical axis indicates the loss (dB).

FIG. 4A illustrates the case when a switch is set to output the signal light S 1 to the output port P 3 , where the heaters H 4 , H 41 , H 5 , and H 51 are used to control the phase differentials φ 4 and φ 5 to be −90° and 180°, respectively. Here, the phase differential is expressed as a positive value when the phase of the light passing through the optical waveguides w 8 and w 10 is delayed compared to the phase of the light passing through the optical waveguides w 7 and w 9 . The spectrum indicated as P 3 is the transmission spectrum of light traveling from the port r 1 to the output port P 3 , and the spectrum indicated as P 4 is the transmission spectrum of light traveling from the port r 1 to the output port P 4 . The loss at the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 is the minimum in the spectrum P 3 .

FIG. 4B illustrates the case when the switch is set to output the signal light S 1 to the output port P 4 , where the phase differentials φ 4 and φ 5 are controlled to be −90° and 180°, respectively. The spectrum indicated as P 3 is the transmission spectrum of light traveling from the port r 1 to the output port P 3 , and the spectrum indicated as P 4 is the transmission spectrum of light traveling from the port r 1 to the output port P 4 . The loss at the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 is the minimum in the spectrum P 4 .

Thus, the signal lights S 1 , S 2 can be outputted to either of the output ports P 3 and P 4 as desired by controlling the heaters H 4 , H 41 , H 5 , and H 51 . Accordingly, the heaters H 4 , H 41 , H 5 , and H 51 , the optical couplers C 7 , C 8 , and C 9 , and the optical waveguides w 7 to w 10 function as the optical switch SW. Furthermore, the optical switch SW suppresses cross-talk between adjacent lightwaves among the lightwaves having the wavelength λ 1 , λ 2 , λ 3 , and λ 4 . Therefore, with the lightwave circuit device 10 equipped with an optical switch SW, there is no need to add a separate filter circuit for suppressing cross-talk, and the lightwave circuit device 10 that is more compact and less expensive can be obtained.

Second Embodiment

FIG. 5 is a schematic diagram of a second embodiment pertaining to the lightwave circuit device according to the present invention. A lightwave circuit device 10 a in this second embodiment is, for example, a planar waveguide type lightwave circuit device made of a silica-based material. The lightwave circuit device 10 a has an optical demultiplexing circuit 30 and functions as an optical demultiplexer. The optical demultiplexing circuit 30 includes Mach-Zehnder interferometers M 1 , M 2 , and M 3 provided to a substrate 16 . The port r 2 of the Mach-Zehnder interferometer M 1 is optically coupled to the port r 4 of the Mach-Zehnder interferometer M 2 . The port r 3 of the Mach-Zehnder interferometer M 1 is optically coupled to the port r 7 of the Mach-Zehnder interferometer M 3 .

The lightwave circuit device 10 a preferably includes an optical switch SW that is optically coupled to the port r 1 of the Mach-Zehnder interferometer M 1 . Input ports P 13 and P 14 are optically coupled via optical waveguides to one end C 9 a of the optical coupler C 9 of the optical switch SW. A first output port P 12 (fourth port) that is provided to the substrate 16 is optically coupled via an optical waveguide to one end C 7 b of the optical coupler C 7 of the optical switch SW. A plurality of second output ports P 11 are optically coupled via optical waveguides to the ports r 5 , r 6 , r 8 , and r 9 of the Mach-Zehnder interferometers M 2 and M 3 .

In the lightwave circuit device 10 a , a first signal light S 1 in which a plurality of lightwaves having mutually different wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are multiplexed, and a second signal light S 2 including a monitoring light λ m are inputted to the input port P 13 . The signal light S 1 and the signal light S 2 are inputted to the optical switch SW, and the signal light S 1 and the signal light S 2 are separated from one another by controlling the heater of this optical switch SW. The signal light S 1 is inputted to the optical demultiplexing circuit 30 , and is demultiplexed into a plurality of lightwaves of wavelengths λ 1 , λ 2 , λ 3 , and λ 4 by the optical demultiplexing circuit 30 . As a result, lightwaves of the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 included in the signal light S 1 are separately outputted from the four output ports P 11 . Meanwhile, the signal light S 2 is outputted as the monitoring light λ m from the output port P 12 .

With each of the Mach-Zehnder interferometers M 1 to M 3 here, a heater is provided along at least one of the optical waveguides. With the lightwave circuit device 10 a equipped with these Mach-Zehnder interferometers M 1 to M 3 , the heaters H 1 , H 11 , H 2 , H 21 , H 3 , and H 31 can be used to control the phase differentials φ 1 , φ 2 , and φ 3 in the Mach-Zehnder interferometers M 1 to M 3 . Therefore, with the lightwave circuit device 10 a , even if the wavelengths of the lightwaves λ 1 , λ 2 , λ 3 , and λ 4 included in the signal light S 1 are changed, by setting the desired phase differentials φ 1 , φ 2 , and φ 3 , it is possible to demultiplex the signal light including the plurality of lightwaves if they have wavelength intervals determined by the phase differentials and a differential order.

A specific example of the lightwave circuit device 10 a will now be described. FIG. 6 is a graph illustrating an example of the transmission spectrum of light traveling from an input port P 13 to output ports P 11 and P 12 in the lightwave circuit device of the second embodiment. The horizontal axis of the graph indicates the wavelength of the light, while the vertical axis indicates the loss (dB). The spectrum indicated as P 11 is the spectrum of light traveling from the input port P 13 to the output port P 11 , and the spectrum indicated as P 12 is the spectrum of light traveling from the input port P 13 to the output port P 12 .

In this example, the wavelength λ m of the monitoring light is set at 1610 nm. The values of the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 , the optical waveguide parameters, and the lightwave circuit parameters are all the same as in the first embodiment. It can be seen from the graph of FIG. 6 that the loss is the minimum at the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 at the output port P 11 . Thus, lightwaves having wavelengths of λ 1 , λ 2 , λ 3 , and λ 4 are each outputted from the output ports P 11 . Meanwhile, it can be seen that the loss is the minimum at the wavelength λ m at the output port P 12 . Also, at the output port P 12 , the loss is the minimum when the wavelength is 1470 nm, 1530 nm, or 1570 nm. Therefore, the wavelength λ m of the monitoring light may be set at 1470 nm, 1530 nm, or 1570 nm. Thus, with the lightwave circuit device 10 a , signal light including a plurality of mutually different lightwaves, a monitoring light, or the like can be used as the second signal light.

Third Embodiment

FIG. 7 is a schematic diagram of a third embodiment pertaining to the lightwave circuit device according to the present invention. A lightwave circuit device 10 b of this third embodiment is, for example, a planar waveguide type lightwave circuit device made of a silica-based material. The lightwave circuit device 10 b has an optical multiplexing circuit 20 provided to a substrate 16 , and functions as an optical multiplexer. The lightwave circuit device 10 b includes four first input ports P 1 to which lightwaves having a plurality of mutually different wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are inputted. Also, the lightwave circuit device 10 b preferably includes an optical switch SW that is optically coupled via an optical waveguide to the port r 1 of the Mach-Zehnder interferometer M 1 .

A second input port P 22 (fourth port) provided to the substrate 16 is optically coupled via an optical waveguide to one end C 7 b , which is on the side of the port r 1 , of the optical coupler C 7 of the optical switch SW. In this case, a second signal light S 3 including a plurality of lightwaves having mutually different wavelengths λ 5 , λ 6 , λ 7 , and λ 8 can be inputted to the input port P 22 , for example. The wavelengths λ 5 , λ 6 , λ 7 , and λ 8 are all different from the wavelength λ 1 , λ 2 , λ 3 , and λ 4 .

Output ports P 23 and P 24 are optically coupled via optical waveguides to one end C 9 a of the optical coupler C 9 of the optical switch SW. When the optical switch SW is used, the signal lights S 1 , S 3 can be outputted from either of the output ports P 23 and P 24 as desired.

With each of the Mach-Zehnder interferometers M 1 to M 3 here, a heater is provided along at least one of the optical waveguides. With a lightwave circuit device 10 b thus equipped with the Mach-Zehnder interferometers M 1 to M 3 , the phase differentials φ 1 , φ 2 , and φ 3 in the Mach-Zehnder interferometers M 1 to M 3 can be controlled by using the heaters H 1 , H 11 , H 2 , H 21 , H 3 , and H 31 . Therefore, with the lightwave circuit device 10 b , just as with the lightwave circuit device 10 , even if the wavelengths of the lightwaves λ 1 , λ 2 , λ 3 , and λ 4 are changed, by setting the desired phase differentials φ 1 , φ 2 , and φ 3 , it is possible to multiplex a plurality of lightwaves having wavelength intervals determined by the phase differentials and a diffraction order.

Fourth Embodiment

FIG. 8 is a schematic diagram of a fourth embodiment pertaining to the lightwave circuit device according to the present invention. A lightwave circuit device 10 c of this fourth embodiment is, for example, a planar waveguide type lightwave circuit device made of a silica-based material. The lightwave circuit device 10 c has an optical demultiplexing circuit 30 , and functions as an optical demultiplexer.

The lightwave circuit device 10 c preferably includes an optical switch SW that is optically coupled to the port r 1 of the Mach-Zehnder interferometer M 1 . Input ports P 33 and P 34 are optically coupled via optical waveguides to one end C 9 a of the optical coupler C 9 of the optical switch SW. A first output port P 32 (fourth port) provided to a substrate 16 is optically coupled via an optical waveguide to one end C 7 b , which is on the side of the port r 1 , of the optical coupler C 7 of the optical switch SW.

With this fourth embodiment, the signal lights S 1 and S 3 are inputted to the input port P 33 and then inputted to the optical switch SW. The signal light S 1 includes lightwaves having wavelengths of λ 1 , λ 2 , λ 3 , and λ 4 , while the signal light S 3 includes lightwaves having wavelengths of λ 5 , λ 6 , λ 7 , and λ 8 that are all different from the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 . The signal lights S 1 and S 3 are separated by the optical switch SW into the signal light S 1 and the signal light S 3 . Under a predetermined phase differentials φ 4 and φ 5 of the optical switch SW, the signal light S 1 is inputted to the optical demultiplexing circuit 30 and demultiplexed into a plurality of lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 , which are separately outputted from the output ports P 11 . Meanwhile, the signal light S 3 is outputted from the output port P 32 . The signal lights S 1 , S 3 may instead be inputted to the input port P 34 . In this case, the signal light S 3 is demultiplexed by the optical demultiplexing circuit 30 by adjusting the phase differentials φ 1 , φ 2 , and φ 3 , and outputted separately from the output ports P 11 . Meanwhile, the signal light S 1 is outputted from the output port P 32 .

With each of the Mach-Zehnder interferometers M 1 to M 3 here, a heater is provided along at least one of the optical waveguides. With a lightwave circuit device 10 c equipped with these Mach-Zehnder interferometers M 1 to M 3 , the heaters H 1 , H 11 , H 2 , H 21 , H 3 , and H 31 can be used to control the phase differentials φ 1 , φ 2 , and φ 3 in the Mach-Zehnder interferometers M 1 to M 3 . Therefore, with the lightwave circuit device 10 c , just as with the lightwave circuit device 10 a , even if the wavelengths of the lightwaves λ 1 , λ 2 , λ 3 , and λ 4 included in the signal light S 1 are changed, by setting the desired phase differentials φ 1 , φ 2 , and φ 3 , it is possible to demultiplex signal light including a plurality of lightwaves having wavelength intervals determined by the phase differentials and differential order.

A specific example of the lightwave circuit device 10 c will now be described. FIGS. 9A and 9B are graphs illustrating an example of the transmission spectrum of light traveling from the input port P 33 to the output port P 11 or P 32 in the lightwave circuit device of the fourth embodiment. The horizontal axis of the graph indicates the wavelength of the light, while the vertical axis indicates the loss (dB). In this example, the wavelengths λ 1 , λ 2 , λ 3 , λ 4 , λ 5 , λ 6 , λ 7 , and λ 8 are 1470 nm, 1550 nm, 1510 nm, 1590 nm, 1610 nm, 1530 nm, 1490 nm, and 1570 nm. The optical waveguide parameters and the lightwave circuit parameters are the same as in the first embodiment.

FIG. 9A illustrates when a switch is set such that the signal light S 3 is outputted to the output port P 11 . The spectrum indicated as P 11 is the loss spectrum of light traveling from the input port P 33 to the output port P 11 , and the spectrum indicated as P 32 is the loss spectrum of light traveling from the output port P 33 to the output port P 32 .

With the lightwave circuit device 10 c , for example, the heaters H 1 to H 5 , H 11 , H 21 , H 31 , H 41 , and H 51 are used to control the phase differential φ 1 to be −45°, the phase differential φ 2 to be −22.5°, the phase differential φ 3 to be −22.5°, the phase differential φ 4 to be 90°, and the phase differential φ 5 to be −180°. With the spectrum P 11 , the loss is the minimum at the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 , and lightwaves having the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 are outputted from the output port P 11 . With the spectrum P 32 , the loss is the minimum at the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 , and lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are outputted from the output port P 32 .

FIG. 9B illustrates when the switch is set such that signal light S 1 is outputted to the output port P 11 . The spectrum indicated as P 11 is the spectrum of light traveling from the input port P 34 to the output port P 11 , and the spectrum indicated as P 32 is the spectrum of light traveling from the input port P 34 to the output port P 32 .

With the lightwave circuit device 10 c , the phase differential φ 1 is controlled to be 45°, the phase differential φ 2 to be 22.5°, the phase differential φ 3 to be 22.5°, the phase differential φ 4 to be −90°, and the phase differential φ 5 to be 180°. With the spectrum P 11 , the loss is the minimum at the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 , and lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are outputted from the output port P 11 . With the spectrum P 32 , the loss is the minimum at the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 , and lightwaves having the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 are outputted from the output port P 32 .

As discussed above, when the optical switch SW is used, either the signal light S 1 or S 3 can be selectively inputted to the optical demultiplexing circuit 30 and demultiplexed.

Optical Add/Drop Apparatus and Wavelength Multiplexing Transmission System

FIG. 10 is a block diagram of an optical add/drop apparatus equipped with the lightwave circuit device 10 of the first embodiment and the lightwave circuit device 10 a of the second embodiment. A transmission path A, which is used ordinarily, and a transmission path B, which is used as a back-up, are respectively connected to the input ports P 13 and P 14 , of the lightwave circuit device 10 a . The transmission paths A and B are also respectively connected to the output ports P 3 and P 4 , of the lightwave circuit device 10 . The transmission paths A and B constitute a cable having two optical fibers, for example. Ordinarily, the monitoring light having a wavelength of λ m and the first signal light S 1 , in which a plurality of lightwaves having different wavelengths of λ 1 , λ 2 , λ 3 , and λ 4 are multiplexed, pass through the transmission path A.

First, the first signal light S 1 and the monitoring light are inputted to the input port P 13 of the lightwave circuit device 10 a , and demultiplexed by the lightwave circuit device 10 a . Lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are outputted from the plurality of output ports P 11 . Meanwhile, the monitoring light having a wavelength λ m is outputted from the output port P 12 of the lightwave circuit device 10 a , and inputted to a monitor photo diode (PD). Each lightwave is then passed through an add/drop through component 42 , and then inputted to the plurality of input ports P 1 of the lightwave circuit device 10 . With this lightwave circuit device 10 , the lightwaves are multiplexed and become the first signal light S 1 . The monitoring light is used for determining light-receiving level by the monitor PD, outputted from a monitoring light-use laser diode (LD) (not shown), and inputted to the input port P 2 of the lightwave circuit device 10 . After this, the first signal light S 1 and the monitoring light are multiplexed and then outputted from the output port P 3 of the lightwave circuit device 10 .

If there should be some kind of obstruction in the transmission path A, and the transmission path A is no longer able to transmit the first signal light S 1 and the monitoring light, the monitoring light will not reach the monitor PD. As a result, the obstruction in the transmission path A will be detected. If this happens, first a control unit HC controls the heaters H 4 , H 41 , H 5 , and H 51 of the lightwave circuit device 10 based on the electrical signals from the monitor PD, and changes the phase differentials φ 4 and φ 5 of the lightwave circuit device 10 , shifting from the state shown in FIG. 4A to the state shown in FIG. 4B . As a result, the first signal light S 1 and the monitoring light pass through the transmission path B.

FIGS. 11A and 11B are block diagrams of a wavelength multiplexing transmission system equipped with a plurality of the optical add/drop apparatus of FIG. 10 . FIG. 11A illustrates the case when the transmission path A is operating normally, and FIG. 11B when an obstruction has occurred in the transmission path A. In this example, three optical add/drop apparatus 40 are connected in an annular shape via the transmission paths A and B. In the state in FIG. 11A , the first signal light S 1 and the monitoring light having a wavelength λ m are passing through the transmission path A. When an obstruction in the transmission path A is detected, the optical add/drop apparatus 40 are controlled such that the first signal light S 1 and the monitoring light will pass through the transmission path B.

FIG. 12 is a block diagram of an optical add/drop apparatus 50 equipped with the lightwave circuit device 10 b of the third embodiment and the lightwave circuit device 10 c of the fourth embodiment. Lightwaves having mutually different wavelengths λ 1 to λ 8 are inputted to the input port P 33 of the lightwave circuit device 10 c , and of these plurality of lightwaves, those having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are demultiplexed by the lightwave circuit device 10 c . As a result, lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are outputted from the plurality of output ports P 11 . These lightwaves pass through an add/drop through component 52 , after which they are inputted to the plurality of input ports P 1 of the lightwave circuit device 10 b. Meanwhile, the lightwaves having the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 are outputted from the output port P 32 of the lightwave circuit device 10 c and inputted to the input port P 22 of the lightwave circuit device 10 b . the lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are multiplexed by this lightwave circuit device 10 b . Further, lightwaves having wavelengths of λ 5 , λ 6 , λ 7 , and λ 8 are multiplexed with the above lightwaves, and the lightwaves λ 1 to λ 8 are outputted to the output port P 23 of the lightwave circuit device 10 b.

Here, it is also possible to control the heaters of the lightwave circuit devices 10 b and 10 c so that lightwaves having the wavelengths of λ 5 , λ 6 , λ 7 , and λ 8 pass through the add/drop through component 52 . In this case, these lightwaves are outputted from the output ports P 11 of the lightwave circuit device 10 c and pass through the add/drop through component 52 , after which they are separately inputted to the input ports P 1 of the lightwave circuit device 10 b . Meanwhile, lightwaves having the wavelengths of λ 1 , λ 2 , λ 3 , and λ 4 are outputted from the output port P 32 of the lightwave circuit device 10 c and inputted to the input port P 22 of the lightwave circuit device 10 b.

FIG. 13 is a block diagram of a wavelength multiplexing transmission system equipped with a plurality of the optical add/drop apparatus of FIG. 12 . In this example, an add/drop node 1 , an add/drop node 2 , and a main node are connected in an annular shape via the transmission path A. The above-mentioned optical add/drop apparatus 50 is used as the add/drop node 1 and the add/drop node 2 . In the add/drop node 1 , lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 pass through the add/drop through component 52 , while lightwaves having the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 are outputted from the output port P 32 and inputted to the input port P 22 . In the add/drop node 2 , lightwaves having the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 pass through the add/drop through component 52 , while lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 are outputted from the output port P 32 and inputted to the input port P 22 . Either the lightwaves having the wavelengths λ 1 , λ 2 , λ 3 , and λ 4 or the lightwaves having the wavelengths λ 5 , λ 6 , λ 7 , and λ 8 can be selectively outputted from the transmission path A by controlling the heaters of the lightwave circuit devices 10 b and 10 c.

With a conventional wavelength multiplexing transmission system, a spare optical add/drop apparatus is usually provided only in case the main. optical add/drop apparatus should break down. Also, a conventional optical add/drop apparatus is designed so that only one type of lightwave passes through the add/drop through component. Consequently, if different lightwaves are to pass through the add/drop through components of two optical add/drop apparatus, for example, two types of optical add/drop apparatus have to be provided. However, when the above-mentioned optical add/drop apparatus 50 is used, the lightwaves that pass through the add/drop through component can be changed by controlling the heaters. Accordingly, with a wavelength multiplexing transmission system equipped with the optical add/drop apparatus 50 , only one type of optical add/drop apparatus need be provided as a spare.

While this invention is described in connection with what is presently considered to be the most practical and preferred embodiments, the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

For instance, the number of Mach-Zehnder interferometers in the optical multiplexing circuit or optical demultiplexing circuit is not limited to three. Mach-Zehnder interferometers can be connected in the form of an n-stage tree (where n is a natural number). In this case, the number of Mach-Zehnder interferometers is 2 n −1, that is, it is (1+2+2 2 + . . . +2 n−1 ). The number of the plurality of input ports P 1 is 2 n . The lightwave circuit device 10 of the optical module 1 can also be substituted with the lightwave circuit device 10 a , lightwave circuit device 10 b , or lightwave circuit device 10 c.

The entire disclosure of Japanese Patent Application No. 2004-173093 filed on Jun. 10, 2004, including specification, claims, drawings, and summary are incorporated herein by reference in its entirety.