Light receiver

1. Field of the Invention

The present invention relates to a light receiver which reproduces and outputs a light clock signal synchronized with the light signal data row inputted by using a light saturable absorber, and the light data row.

2. Description of the Related Art

FIG. 11 is a light digital reproduction apparatus shown on B-12-21, 1999, by Ohtani (KDD) et al. in a great spring meeting of “The Institute of Electronics, Information and Communication Engineers (IEICE)”, and the saturable absorption characteristic of the electric field absorption type light modulator (hereinafter, written as EA modulator, EA is an abbreviation for Electro-Absorption) is utilized. When the light input signal and the light clock pulse generated by the light pulse generator are inputted into the light saturable absorber, because the absorption saturation occurs when the input signal has the sufficient intensity corresponding to the characteristic of the light saturable absorber, the light pulse generated by the light pulse generator passes when the input light signal is “1”, and when the input light signal is “0”, it is absorbed and coding occurs. At this time, it is necessary that the light clock pulse which is the reproduced output light source, is in timed relationship with the input signal pulse in the optimum phase condition in the saturable absorber in which coding is conducted. In the conventional example, the clock electric signal in timed relationship with the repeated frequency of the input light signal data row is extracted from the light absorption current taken out from the electrode of the EA modulator which is the saturable absorber, and by the electric clock signal, the light modulator is driven, and the light clock pulse in timed relationship with the light input signal is generated.

In the coding of the light signal by the light signal using the light saturable absorber, it is necessary that the synchronization of both the light signals in the light saturable absorber is established, and the optimum phase relationship is always kept for them. In this case, as in the conventional example, when the process in which the synchronization clock electric signal is extracted once from the clock signal, and the clock electric signal is electrically/light converted, is passed through, because it is difficult that the phase variation in the clock signal path is intrinsically compensated for, and the same high speed operation as the light signal speed is required for the electric circuit, there is a problem that cost becomes high.

A light receiver according to the first invention has: a light clock pulse generation light source to control the repeated frequency of a light clock pulse by the input current or input voltage; a wave-branching means for wave-branching the light from the clock pulse generation light source into the first light and the second light, each having a wavelength λ 2 ; an output means for outputting the first light wave-branched by the wave-branching means to the output terminal of the light clock; a wave-composing means for wave-composing the second light wave-branched by the wave-branching means with the signal light, which has a wavelength λ 1 , inputted from the input terminal; a light saturable absorber which absorbs the light wave-composed by the wave-composing means and outputs the photo current, and in which a light absorption coefficient is decreased corresponding to the light input level; an optical filter which separates the light with wavelength λ 1 and the light with wavelength λ 2 , which are outputted from the light saturable absorber; a dither signal source for modulating the phase of the light pulse generated from the clock pulse generation light source by the dither signal; and a phase controller for controlling so that the phase of the light source generated by the light clock pulse generation light source and the phase of the signal light inputted from the input terminal are in timed relationship with 0°, according to the output of the light saturable absorber which generates the photo current, and the output of the dither signal source.

A light receiver corresponding to the second invention, which comprising: a light clock pulse generation light source to control the repeated frequency of a light clock pulse by the input current or input voltage; a wave-branching means for wave-branching the light from the clock pulse generation light source into the first light (wavelength λ 2 ) and the second light (wavelength λ 2 ); an output means for outputting the first light wave-branched by the wave-branching means to the output terminal of the light clock; a wave-composing means for wave-composing the second light wave-branched by the wave-branching means with the signal light (wavelength λ 1 ) inputted from the input terminal; a light saturable absorber whose light absorption coefficient is decreased corresponding to the light input level of the wave-composed light signal; an optical filter which separates the light of wavelength λ 1 and the light or wavelength λ 2 outputted from the light saturable absorber; a light receiving unit to electrically convert the separated light by the optical filter; a dither signal source for modulating the phase of the light pulse generated from the clock pulse generation light source by the dither signal; and a phase controller for controlling so that the phase of the light source generated by the light clock pulse generation light source and the phase of the signal light inputted from the input terminal are in timed relationship with 0°, according to the output of the light saturable absorber which generates the photo current, and the output of the dither signal source.

The light receiver according to the third invention, has a light variable delay unit to control a delay amount by the input current or the input voltage, and a dither signal source to modulate the light input signal by the dither signal.

The light receiver according to the fourth invention, has a light variable delay unit to control a delay amount by the input current or the input voltage, and a dither signal source to modulate the light input signal by the dither signal.

The light receiver according to the fifth invention has: the first light circulator which outputs the inputted light signal to the light saturable absorber, and outputs the light pulse reproduced in the light saturable absorber; the second light circulator to terminate the light signal outputted from the light saturable absorber, and output the light clock pulse to the light saturable absorber; a light clock pulse generation light source to control the repeated frequency of a light clock pulse by the input current or input voltage; a wave-branching means for wave-branching the light from the clock pulse generation light source into the first light and the second light; an output means for outputting the first light clock wave-branched by the wave-branching means to the output terminal; a reproduction means for outputting the second light clock wave-branched by the wave-branching means from the second light circulator to the light saturable absorber, wherein the light saturable absorber outputs the reproduced light signal through the first light circulator; and a phase controller for controlling so that the phase of the light source generated by the light clock pulse generation light source is in timed relationship with the phase of the signal light inputted from the input terminal, according to the output of the light saturable absorber to generate the photo current and the output of the dither signal source.

The light receiver according to the sixth invention has: the first light circulator to output the inputted signal light to the light saturable absorber; the second light circulator to terminate the light signal outputted from the light saturable absorber; a light clock pulse generation light source to control the repeated frequency of a light clock pulse by the input current or input voltage; a wave-branching means for wave-branching the light from the light clock pulse generation light source into the first light and the second light; an output means for outputting the first light wave-branched by the wave-branching means to the output terminal of the light clock; a light saturable absorber to output the second light clock wave-branched by the wave-branching means to the first light circulator; a light receiving unit to wave-branch the light signal from the first light circulator and to electrically convert it; and a phase controller for controlling so that the phase of the light source generated by the light clock pulse generation light source is in timed relationship with the phase of the signal light inputted from the input terminal, according to the output of the light receiving unit and the output of the dither signal source.

The light receiver according to the seventh invention has: a light variable delay unit to control a delay amount by the input current or the input voltage; and a dither signal source to modulate the phase of the light input signal by the dither signal.

The light receiver according to the eighth invention has: a light variable delay unit to control a delay amount by the input current or the input voltage; and a dither signal source to modulate the light input signal by the phase of the dither signal.

In the light receiver according to the ninth invention, the repeated frequency of the light clock pulse generation light source is 1/n (n is a natural number) of the input light signal bit rate.

FIG. 1 is a block diagram showing an embodiment 1.

FIG. 2 is a block diagram showing an embodiment 2.

FIG. 3 is a block diagram showing an embodiment 3.

FIG. 4 is a block diagram showing an embodiment 4.

FIG. 5 is a block diagram showing an embodiment 5.

FIG. 6 is a block diagram showing an embodiment 6.

FIG. 7 is a block diagram showing an embodiment 7.

FIG. 8 is a block diagram showing an embodiment 8.

FIG. 9 is a block diagram showing an embodiment 9.

FIG. 10 is a block diagram showing an example of the structure of a light pulse generator.

FIG. 11 is a block diagram showing the structure of the conventional example.

The present invention will be described in detail with reference to the accompanying drawings. In the drawings, each heavy line or arrow represents a flow of a light signal, and each thin line or arrow represents a flow of an electrical signal.

FIG. 1 is a structural block diagram showing a light receiver according to the present invention. In FIG. 1, numeral 1 a is a light data input terminal, numerals 2 a and 2 b are light wave-composing and branching units, numeral 3 a is a light saturable absorber, numeral 4 a is an optical band pass filter (OBPF), numeral 5 a is a light data output terminal, numeral 6 a is a light clock output terminal, numeral 7 a is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 a is a low pass filter (LPF), numeral 9 a is a reversible or irreversible amplifier, numeral 10 a is a synchronous detector, numeral 11 a is a loop filter, numeral 12 a is a low frequency dither signal source, and numeral 13 a is a current/voltage adder.

As light wave-composing and branching units 2 a and 2 b , a photo coupler, plane light waveguide path, wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 a , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 a is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation.

Next, the operation of FIG. 1 will be described. When the light clock pulse and the sufficiently intensive input signal light are inputted into the light saturable absorber, because the light clock pulse is coded by the signal light, the light absorption current taken out from the electrode includes the phase difference signal of two light signals. That is, because the light saturable absorber can be operated as the phase comparator of the light signal input and the electric signal output, when it is combined with the light pulse generator by which the repeated frequency can be electrically changed, the phase synchronous operation can be easily conducted in the same manner as the PLL in the general electric circuit.

In the condition that the ordinary PLL using the analog phase comparator establishes the phase synchronization, because the signal phase of the two signals whose phases are compared, is shifted by 90°, in FIG. 1, by the structure in which a slight phase modulation is added to the control signal of the light clock pulse by using the low frequency dither Signal source, and after the unnecessary high frequency component of the electric signal obtained from the saturable absorber electrode is removed by the low pass filter 8 a , it is synchronous-detected and inputted into the loop filter, the phase comparison characteristic is equivalently differentiated, and the phase synchronization is established under the condition that the phase difference of two light signals is 0°. According to the operations described above, because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, the embodiment shown in FIG. 1 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high speed electric circuit is not necessary.

FIG. 2 is a structural block diagram showing a light receiver according to the present invention. In FIG. 2, numeral 1 b is a light data input terminal, numerals 2 c , 2 d and 2 e are light wave-composing and branching units, numeral 3 b is a light saturable absorber, numeral 4 b is an optical band pass filter (OBPF), numeral 5 b is a light data output terminal, numeral 6 b is a light clock output terminal, numeral 7 b is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 b is a low pass filter(LPF), numeral 9 b is a reversible or irreversible amplifier, numeral 10 b is a synchronous detector, numeral 11 b is a loop filter, numeral 12 b is a low frequency dither signal source, numeral 13 b is a current/voltage adder, and numeral 14 a is a light receiving unit to conduct the photo-electric conversion.

As light wave-composing and branching units 2 c , 2 d and 2 e , a photo coupler, plane light waveguide path, wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 b , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 b is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation.

Next, the operation of FIG. 2 will be described. The operation of the present embodiment 2 is the same as the embodiment 1 in FIG. 1 except that the phase difference signal of the light signal and the light clock pulse light source is detected in such a manner that a portion of the reproduced light data output outputted from the saturable absorber is photo-electrically converted by the light receiving unit 14 a , and because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, in the same manner as in the embodiment 1 in FIG. 1, the present embodiment 2 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high sped electric circuit is not necessary.

FIG. 3 is a structural block diagram showing a light receiver according to the present invention. In FIG. 3, numeral 1 c is a light data input terminal, numerals 2 f and 2 g are light wave-composing and branching units, numeral 3 c is a light saturable absorber, numeral 4 c is an optical band pass filter (OBPF), numeral 5 c is a light data output terminal, numeral 6 c is a light clock output terminal, numeral 7 c is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 c is a low pass filter(LPF), numeral 9 c is a reversible or irreversible amplifier, numeral 10 c is a synchronous detector, numeral 11 c is a loop filter, numeral 12 c is a low frequency dither signal source, and numeral 15 a is a light delay unit in which the delay amount can be controlled by the input current or voltage.

As light wave-composing and branching units 2 f and 2 g , a photo coupler, plane light waveguide path, or wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 c , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 c is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation. The light delay line 15 a can be easily procured from the market.

The operation of the present embodiment is the same as in the embodiment in FIG. 1, except that the phase modulation for the synchronization establishment at the optimum phase is superimposed on the input signal light side by using the light delay line, and in contrast to a fact that, in the embodiment 1 in FIG. 1, unnecessary phase modulation component is superimposed on the reproduced light data output and the clock output according to circumstances, in the embodiment 3 in FIG. 3, the input light signal light, which is finally discarded, is phase modulated, thereby, the reproduced light signal output and clock light output, which have lesser phase jitter, can be obtained. According to the above description, in the same manner as in the embodiment 1, because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, the present embodiment 2 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high speed electric current is not necessary.

FIG. 5 is a structural block diagram showing a light receiver according to the present invention. In FIG. 5, numeral 1 e is a light data input terminal, numeral 2 k is a light wave-composing and branching unit, numeral 3 e is a light saturable absorber, numeral 5 e is a light data output terminal, numeral 6 e is a light clock output terminal, numeral 7 e is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 e is a low pass filter (LPF), numeral 9 e is a reversible or irreversible amplifier, numeral 10 e is a synchronous detector, numeral 11 e is a loop filter, numeral 12 e is a low frequency dither signal source, numeral 13 c is a current/voltage adder, and numeral 16 a and 16 b are a light circulators.

As light wave-composing and branching units 2 h , 2 i and 2 j , a photo coupler, plane light waveguide path, or wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 d , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 d is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation. The light delay line 15 b can be easily procured from the market.

Next, the operation of FIG. 4 will be described.

The operation of the present embodiment 4 is the same as in the embodiment in FIG. 2, except that the phase modulation for the synchronization establishment at the optimum phase is superimposed on the input signal light side by using the light delay line, and in contrast to a fact that, in the embodiment 2 in FIG. 2, unnecessary phase modulation component is superimposed on the reproduced light data output and the clock output according to circumstances, in the embodiment 4 in FIG. 4, because the input light signal light, which is finally discarded, is phase modulated, thereby, the reproduced light signal output and clock light output, which have lesser phase jitter, can be obtained. According to the above description, in the same manner as in the embodiment 2, because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, the present embodiment 4 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high sped electric circuit is not necessary.

FIG. 5 is a structural block diagram showing a light receiver according to the present invention. In FIG. 5, numeral 1 e is a light data input terminal, numeral 2 k is a light wave-composing and branching unit, numeral 3 e is a light saturable absorber, numeral 5 e is a light data output terminal, numeral 6 e is a light clock output terminal, numeral 7 e is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 e is a low pass filter(LPF), numeral 9 e is a reversible or irreversible amplifier, numeral 10 e is a synchronous detector, numeral 11 e is a loop filter, numeral 12 e is a low frequency dither signal source, numeral 13 e is a current/voltage adder, and numeral 16 a and 16 b are a light circulators.

As a light wave-composing and branching unit 2 k , a photo coupler, plane light waveguide path, or wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 e , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 e is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation.

Next, the operation of FIG. 5 will be described. Although, in the embodiment in FIG. 1, the light signal and the light clock pulse are inputted into the saturable absorber from the same direction, FIG. 5 is structured such that these are inputted from the reverse direction, and by using the light circulator, not the optical filter, the light signal and the light clock pulse are separated. The other operations are the same as those in the embodiment 1 in FIG. 1 . In the structure in FIG. 5, because the operations in the embodiment 1 in FIG. 1 can be realized by the smaller number of the light wave-composing and branching units, the photoelectric power of the signal light can be effectively utilized. According to the operations as described above, because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, the present embodiment 5 as shown in FIG. 5 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high sped electric circuit is not necessary.

FIG. 6 is a structural block diagram showing a light receiver according to the present invention. In FIG. 6, numeral 1 g is a light data input terminal, numeral 2 m and 2 n are light wave-composing and branching units, numeral 3 g is a light saturable absorber, numeral 5 g is a light data output terminal, numeral 6 g is a light clock output terminal, numeral 7 g is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 g is a low pass filter (LPF), numeral 9 g is a reversible or irreversible amplifier, numeral 10 g is a synchronous detector, numeral 11 g is a loop filter, numeral 12 g is a low frequency dither signal source, numeral 13 d is a current/voltage adder, numeral 14 c is a light receiving unit to conduct the photoelectric conversion, and numeral 16 e and 16 f are a light circulators.

As light wave-composing and branching units 2 m and 2 n , a photo coupler, plane light waveguide path, or wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 g , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 g is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation.

Next, the operation of FIG. 6 will be described. Although, in the embodiment 2 in FIG. 2, the light signal and the light clock pulse are inputted into the saturable absorber from the same direction, FIG. 6 is structured such that these are inputted from the reverse direction, and by using the light circulator, not the optical filter, the light signal and the light clock pulse are separated. The other operations are the same as those in the embodiment 2 in FIG. 2 . In the structure in FIG. 6, because the operations in the embodiment 2 in FIG. 2 can be realized by the smaller number of the light wave-composing and branching units, the photoelectric power of the signal light can be effectively utilized. According to the operations as described above, because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, the present embodiment 6 as shown in FIG. 6 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high sped electric circuit is not necessary.

FIG. 7 is a structural block diagram showing a light receiver according to the present invention. In FIG. 7, numeral if is a light data input terminal, numeral 21 is a light wave-composing and branching unit, numeral 3 f is a light saturable absorber, numeral 5 f is a light data output terminal, numeral 6 f is a light clock output terminal, numeral 7 f is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 f is a low pass filter(LPF), numeral 9 f is a reversible or irreversible amplifier, numeral 10 f is a synchronous detector, numeral 11 f is a loop filter, numeral 12 f is a low frequency dither signal source, numeral 15 c is a light delay unit in which the delay amount can be controlled by the input current or voltage, and numeral 16 c and 16 d are a light circulators.

As a light wave-composing and branching unit 21 , a photo coupler, plane light waveguide path, or wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 f , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 f is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation. The light delay line 15 c can be easily procured from the market.

Next, the operation of FIG. 7 will be described. Although, in the embodiment 3 in FIG. 3, the light signal and the light clock pulse are inputted into the saturable absorber from the same direction, FIG. 7 is structured such that these are inputted from the reverse direction, and by using the light circulator, not the optical filter, the light signal and the light clock pulse are separated. The other operations are the same as those in the embodiment 3 in FIG. 3 . In the structure in FIG. 7, because the operations in the embodiment 3 in FIG. 13 can be realized by the smaller number of the light wave-composing and branching units, the photoelectric power of the signal light can be effectively utilized. According to the operations as described above, because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, the present embodiment 7 as shown in FIG. 7 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high sped electric circuit is not necessary.

FIG. 8 is a structural block diagram showing a light receiver according to the present invention. In FIG. 8, numeral 1 h is a light data input terminal, numerals 2 o and 2 p are light wave-composing and branching units, numeral 3 h is a light saturable absorber, numeral 5 h is a light data output terminal, numeral 6 h is a light clock output terminal, numeral 7 h is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 h is a low pass filter(LPF), numeral 9 h is a reversible or irreversible amplifier, numeral 10 h is a synchronous detector, numeral 11 h is a loop filter, numeral 12 h is a low frequency dither signal source, numeral 14 d is a light receiving unit to conduct the photoelectric conversion, numeral 15 d is a light delay unit in which the delay amount can be controlled by the input current or voltage, and numeral 16 g and 16 h are a light circulators.

As light wave-composing and branching units 2 o and 2 p , a photo coupler, plane light waveguide path, or wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 h , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 h is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation. The light delay line 15 d can be easily procured from the market.

Next, the operation of FIG. 8 will be described. Although, in the embodiment 4 in FIG. 4, the light signal and the light clock pulse are inputted into the saturable absorber from the same direction, FIG. 8 is structured such that these are inputted from the reverse direction, and by using the light circulator, not the optical filter, the light signal and the light clock pulse are separated. The other operations are the same as those in the embodiment 4 in FIG. 4 . In the structure in FIG. 8, because the operations in the embodiment 4 in FIG. 4 can be realized by the smaller number of the light wave-composing and branching units, the photoelectric power of the signal light can be effectively utilized. According to the operations as described above, because the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse are simultaneously conducted in one light saturable absorber, the present embodiment 8 as shown in FIG. 8 operates as the light receiver (light 3 R receiver) in which the phase adjustment is not necessary, and the high sped electric circuit is not necessary.

FIG. 9 is a structural block diagram showing a light receiver according to the present invention. In FIG. 9, numeral 1 i is a light data input terminal, numerals 2 q and 2 r are light wave-composing and branching units, numeral 3 i is a light saturable absorber, numeral 4 e is an optical band pass filter (OBPF), numeral 5 i is a light data output terminal, numeral 6 i is a light clock output terminal, numeral 7 i is a light pulse generator which can change the repeated frequency by the input current/voltage, numeral 8 i is a low pass filter (LPF), numeral 9 i is a reversible or irreversible amplifier, numeral 10 i is a synchronous detector, numeral 11 i is a loop filter, numeral 12 i is a low frequency dither signal source, and numeral 13 e is a current/voltage adder.

As light wave-composing and branching units 2 q and 2 r , a photo coupler, plane light waveguide path, or wavelength multiple wave-composing and branching unit, can be used. The light saturable absorber, numeral 3 i , is, for example, an EA modulator, or semiconductor light amplifier. The light pulse generator 7 i is, for example, a mode lock laser by which the pulse repeated frequency can be changed by the injection current or impressed voltage, or as shown in FIG. 10, a unit which is structured by the combination of an electric VCO, light modulator, and light source, can be used. In the latter structure, although it is necessary to use the high speed electric clock signal, it is not necessary to compensate for the phase variation.

Next, the operation of FIG. 9 will be described. In FIG. 9, the repeated frequency of the light clock pulse generation light source is 1/n (n is a natural number) of the bit rate of the signal light in the embodiment 1 in FIG. 1 . Because the phase comparison operation of the saturable absorber can be conducted in the same manner, also in such the case, the embodiment 9 shown in FIG. 9 conducts the phase comparison of both the light signals and the coding of the light clock pulse by the light signal pulse simultaneously in one light saturable absorber, and operates as the light receiver (light 3 R receiver) which conducts the separation of the multiple light signal, reproduction of the dividing light clock pulse, and the separated light pulse reproduction.