JP3322653B2 - Optical receiving device used for dark soliton optical communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission system using an optical fiber, and more particularly to an optical receiver used for a long-distance and large-capacity optical communication system using a dark soliton pulse and an optical amplifier.

[0002]

2. Description of the Related Art In the optical fiber communication technology, the super long distance has been progressed by the progress of the optical amplification technology, and it has become possible to cross the Pacific Ocean without using a regenerative repeater. However, in the conventional transmission system, as the transmission speed increases, the influence of the deterioration of the transmission characteristics due to the chromatic dispersion characteristics of the optical fiber and the nonlinear optical effect increases, and there is a limit to the increase in speed and capacity. In recent years, an optical soliton communication system has been spotlighted as a method for overcoming the limitation of high speed due to the wavelength dispersion characteristic and the nonlinear optical effect. The optical soliton communication system actively utilizes the chromatic dispersion characteristics and the nonlinear optical effect of the optical fiber, which are the causes of characteristic deterioration of the conventional transmission system.
This is a method in which pulse broadening due to fiber chromatic dispersion and pulse compression based on non-linear optical effects are balanced to transmit an optical short pulse without changing its shape. When an optical amplifier that compensates for the loss of the optical fiber is used as a repeater, by setting the average power of the relay interval and the average dispersion of the optical fiber to the soliton condition, the waveform change similar to the ideal soliton pulse hardly occurs. No soliton communication is possible.

In high-speed optical soliton communication of about 20 Gb / s, noise of an optical amplifier affects timing jitter of an optical pulse at a receiving end and deteriorates transmission characteristics. In other words, in the optical soliton pulse on which noise is superimposed, the light intensity fluctuates randomly and slightly deviates from the ideal optical soliton pulse form, so that the carrier frequency shift amount fluctuates due to the nonlinear optical effect. Since this is repeated for each repeater, the arrival time of the optical pulse fluctuates randomly while propagating through the optical fiber having a finite dispersion value, thereby causing timing jitter. This phenomenon is called the Gordon House effect, and is a limiting factor of the main transmission characteristics of optical soliton communication. Furthermore, when transmitting a plurality of optical soliton pulses having information, if the interval between adjacent soliton pulses is narrow, the soliton pulses interfere with each other, and a phenomenon of being attracted or repelled is observed. This also results in timing jitter at the receiving end, which is not preferable in terms of application to communication. To suppress soliton pulse interference, the interval between adjacent soliton pulses needs to be widened to some extent. In order to overcome the above-mentioned timing jitter, research on soliton control technology for artificially suppressing timing jitter has been actively conducted, and soliton pulse transmission experiments have progressed rapidly in recent years. one,
The random frequency shift is controlled in the frequency domain using an optical filter, and the other is a method of directly controlling the timing jitter itself in the time domain. However, in the prior art, it is necessary to use an ultra-narrow band optical band-pass filter or complicated processing using an optical modulator inside the repeater, so that practical viewpoints such as long-term reliability of the system are required. Is undesirable. In order to increase the capacity of a long-distance transmission system using an optical amplifier, the transmission line including the optical amplifier should be simplified as much as possible without providing a special mechanism in the transmission line as in the prior art, and It is important that soliton pulses are arranged at high density to transmit an optical signal of high density.

[0004]

Heretofore, in optical soliton communication, so-called bright solitons, which transmit short optical pulses in a wavelength band in the anomalous dispersion region of an optical fiber, have been used. On the other hand, a signal obtained by inverting the ON / OFF of the light pulse,
That is, when an optical signal (dark pulse) in which a part of light having a constant intensity is sharply transmitted is transmitted in the normal dispersion region of the optical fiber, the signal intensity and the pulse width of the dark pulse (width of the depression)
It is theoretically known that transmission of the waveform (depression shape) can be performed without deterioration as in the case of the bright soliton if Satisfies a certain relationship (A. Hasegawa and F. Tappert, Ap.
pl. Phys. Lett., Vol.23, pp.171-172, 1973), which is called dark soliton transmission. However, it is necessary to provide an optical phase shift at the center of the dark pulse. FIG.
(A), (b) and (c) show typical examples of bright soliton and dark soliton pulse waveforms (JR Taylor e).
d, Optical Solitons-Theory and Experiment, chap.1
0, Cambridge Univerithy Press, 1992). FIG.
(A) is an example of a bright soliton, and the optical phase is constant. On the other hand, in dark solitons, the light intensity
As shown in (b) and (c), the bright soliton is characterized in that it has a shape in which the light intensity is turned on and off, and in addition, the light phase is shifted. FIG. 12B shows a case where the light in the dent portion is zero (black soliton). In this case, the phase of the light is shifted by π before and after the center value of the dent. FIG. 12C shows half of the intensity of the CW laser beam.
This is the case where the dark pulse is depressed (gray soliton), and the amount of phase shift of light is π / 2. As shown in the figure, A and B are parameters representing the depth of the depression and the relative level of the background light, respectively, where A = B =
1 corresponds to black soliton, and B approaches zero as the level of background light increases. The phase shift amount of the dark soliton is given by Equation 1 using this parameter B.

(Equation 1)

[0005] Compared with bright solitons, dark solitons have features such as that the Gordon house jitter is suppressed to about 70% and that soliton mutual interference is small (YS Kivshar, IEEE J. Quantum Electronic).
s, Vol.29, pp.250-264, 1993). However, since there was no transmitting device and a receiving device having a bright soliton generator to which digital information was added, application of dark solitons to optical communication was not attempted.

According to the present invention, an arrangement of soliton pulses is performed while inverting the light intensity of a normal optical soliton (bright soliton), suppressing mutual interference of dark solitons accompanied by an optical phase shift, and suppressing timing jitter. It is an object of the present invention to provide an optical receiving device which can increase the density and is used for a dark soliton ultra-high speed / large capacity optical transmission system.

[0007]

SUMMARY OF THE INVENTION An optical communication system to which the present invention is applied is an optical transmitter for transmitting a dark soliton pulse optical signal having digital information, and converts the dark soliton pulse optical signal into a return to zero pulse. An optical receiving device for receiving the optical fiber, a transmitting optical fiber connecting the transmitting device and the receiving device, and a plurality of optical amplifier repeaters on the transmitting optical fiber for compensating for the loss of the optical fiber. ,
The transmission optical fiber, at the wavelength of the transmission optical signal,
The average value of the chromatic dispersion value of the entire length of the transmission optical fiber takes a normal dispersion value that is a negative value, and the average value of the chromatic dispersion value of the transmission optical fiber and the optical output intensity of the optical amplification repeater are: It is configured to balance the nonlinear optical effect and the chromatic dispersion effect applied to the transmitted optical signal. An optical transmitter used for transmitting a dark soliton optical signal to be received by the present invention includes: a means for generating an optical pulse signal obtained by adding digital information to a return to zero optical pulse; and a means for generating a constant output light. An optical gate for outputting a logical exclusive OR of two optical input signals; and an optical phase modulator, wherein the return-to-zero digital optical signal and the light having the constant amplitude are transmitted to the exclusive OR optical gate. By converting the light of constant amplitude into an optical pulse signal in which the return-to-zero digital optical signal is turned on and off, and modulating the inverted optical pulse signal by a phase modulator driven at a transmission speed, A method of generating an inverted light pulse signal that gives a phase difference of π or less that is a dark soliton condition to the phase of light before and after the time when the light intensity of the inverted pulse signal is minimized. It has been made. A first optical receiving apparatus according to the present invention includes a means for generating a constant output light, and an optical gate for outputting a logical exclusive OR of two optical input signals. Light having a constant amplitude is incident on an exclusive OR optical gate, and the light having the constant amplitude is converted into a return-to-zero digital optical signal. Is configured. Further, the second optical receiving device splits the on / off inverted optical pulse signal transmitted through the transmission optical fiber, converts one of the optical pulse signals into an electric pulse signal, and then transmits the clock frequency component or the multiplexed signal of the transmission speed. After extracting and amplifying the previous clock frequency component, the other of the transmitted optical pulse signals is passed through the clock frequency signal or the optical modulator modulated at the clock frequency of the transmission speed before multiplexing, and the transmitted optical signal After being converted into a return-to-zero optical signal whose on / off is inverted, the optical signal is received by one or a plurality of optical receivers.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the limiting factors of the transmission characteristics of an optical soliton communication system using an optical amplifier are the timing jitter due to the Gordon House effect and the timing jitter based on the mutual interference between adjacent solitons. In view of this, the dark soliton optical signal to which the present invention is applied is the first
In the optical transmitting terminal, the dark and soliton optical signal is inverted on and off, and the phase of the light is a dark soliton condition before and after the time when the light intensity of the on and off inverted optical pulse signal is minimum. By generating an inverted optical pulse signal having a phase difference of π or less, a high-density dark soliton optical signal is generated, and secondly, by using dark soliton as a transmission signal, mutual interference between adjacent soliton pulses is reduced. Timing jitter based on the Gordon House effect is suppressed. The optical receiving apparatus according to the present invention converts such a dark soliton optical signal into a normal bright soliton, and further receives the signal after the high-density signal is further divided on the time axis. It has the effect of suppressing the influence on the error rate characteristics. This provides a long-distance, large-capacity optical dark soliton communication system capable of transmitting high-density soliton pulses.

FIG. 1 shows a specific example of an optical transmitter for generating a dark soliton optical signal to which the present invention is applied. 1 is a time division multiplexed bright soliton optical signal generator, and 2 is a CW (cont
inuous wave) laser, 3 is an exclusive OR gate, 4 is an optical phase modulator. The time-division multiplex bright soliton optical signal generator 1 includes a soliton pulse light source 101,
An optical amplifier 102, an optical coupler 103 for dividing a pulse train into four, and optical delay circuits 104, 105, 106, and 10
7, optical intensity modulators 108, 109, 110, 111, an optical coupler 112, and an optical amplifier 113 including an optical band-pass filter for removing noise. The soliton pulse light source 101 generates a soliton pulse train having a pulse width of 10 ps at a wavelength of 1561 nm and a repetition rate of 5 Gb / s. After the soliton pulse train is amplified by the optical amplifier 102,
The optical coupler 103 divides the pulse train into four, sets the delay times of the optical delay circuits 104, 105, 106, and 107 such that the pulse trains are relatively shifted by 0 ps, 25 ps, 50 ps, and 75 ps, respectively. 10
Digital modulation is applied at 9, 110 and 111. The optical intensity modulators 108,
Polarization controllers 128a, 128b, 128c, 12 disposed before 109, 110, 111, respectively.
8d. Optical coupler 1 for four optical signals
At 12, the signal is combined to generate a four-multiplexed bright soliton optical signal. Further, the optical amplifier 113 amplifies the signal light.

Time-division multiplexed bright soliton optical signal
To port P of exclusive OR optical gate 3₁ Incident on
And port P_Two Of CW laser 2 with wavelength of 1558 nm
When power light is incident, the CW laser light is
Scoursive OR output, that is, the output of a bright soliton optical signal
The port P is converted to an optical pulse signal_Three Or
Output from Exclusive or optical gate to nonlinear light
Figure 2 shows an example of a loop mirror (Sagnac interferometer)
Shown in The exclusive OR optical gate is an optical amplifier 11
4. Polarization controllers 115 and 119, optical coupler 11
7, 120, 121, optical isolators 116, 122,
124, the optical bandpass filter 123 and the nonlinear optical filter.
IB118. The branching ratio of the optical coupler 120 is
1: 1. Port P ₁ To 20Gb / s time division multiple
A double bright soliton optical signal is input and
After amplifying the average power to about 13 dBm,
Troller 115, optical isolator 116, optical coupler 1
The light enters the nonlinear optical fiber 118 via the optical fiber 17. Light
The fiber 118 has a chromatic dispersion of about 1558 nm.
A dispersion-shifted single-mode optical fiber
And the length is about 10 km. On the other hand, CW laser light
Auto P_Two Incident, optical isolator 122, optical cup
Through the optical coupler 118 and the optical coupler 120.
Incident on. The polarization controller 119 controls the optical coupler 12
If the polarization states of the two output lights 1 are kept the same,
To P₁ If there is no optical input from the
Signal and counterclockwise optical signal are_Two Return to the direction
Optical coupler 121, optical bandpass filter 123,
Port P through optical isolator 124_3aOutput from
You. Port P₁ The bright soliton optical signal from the CW
When the laser beam enters the same polarization state as the laser beam, the optical fiber
The effect causes a change in the refractive index according to the magnitude of the light intensity
Counter-clockwise CW laser by cross-phase modulation
The phase change according to the intensity of the bright soliton optical signal only for light
A key is added. Peak power of bright soliton optical signal
Set the phase change due to mutual phase modulation to π
Then, it corresponds to the peak power of the bright soliton optical signal.
Time to go to port P_Two The incident CW laser light
All ports P_3bOutput to port P_3aThe output to
CW laser light with inverted intensity of bright soliton optical signal
An optical signal (dark pulse) in which a part of is depressed is output.
That is, port P_3aThe light signal from is a bright soliton light
Logical exclusive OR of signal and CW laser light
Output, and port P_3bThe light output to the
And will be. 20 dark pulse light signals
Gb / s modulated by the optical phase modulator 4
To shift the phase by π at the center of the optical signal
As a result, a transmission optical signal for dark soliton transmission is obtained.

FIG. 6 shows how dark solitons are generated.
You. FIG. 6A shows a time division multiplexed bright soliton optical signal emission.
Light output from raw device 1, (b) Exclusive or light
CW laser beam incident on gate 3, (c) Exclude
Port P of Shibu-or optical gate 3 _Three Light signal from (d)
Is a dark soliton optical signal after passing through the optical phase modulator 4.
You. Also, the light intensity at the center of dark solitons is not necessarily
Since it does not need to be zero, the output of the optical amplifier 114 is
Even if it is lowered quickly to generate an optical signal that does not reach zero,
Good. In this case, the amount of phase shift by the optical phase modulator 4
May be set to π or less. In addition, the above nonlinear optical loop
Controlling the polarization controller 119 in the mirror (FIG. 2);
The polarization states of the two outputs of the 3 dB coupler 120
By making them orthogonal, the exclusive OR optical gate 3
Port P of_3aAnd port P_3bOutput to both
Port P_3bFrom
Dark soliton with inverted light signal intensity
Ton light signals can also be extracted. In this specific example,
Non-linear optical loop mixer as optical gate 3
The optical fiber in the Ra (Sagnac interferometer)
Optical fiber, but two polarization-maintaining optical fibers of the same length
Fibers are used with fibers connected with their main axes orthogonal.
The bright soliton optical signal to the polarization-maintaining fiber.
By entering at 45 degrees to the main axis,
The same brightness is used regardless of the polarization state of the CW laser light.
An optical signal with inverted soliton intensity can be extracted.
Wear.

The exclusive OR optical gate 3 includes:
By utilizing the mutual gain saturation phenomenon in which the gain of the other wavelength is modulated in accordance with the incident light intensity of one wavelength when the gain of the semiconductor optical amplifier is saturated, as shown in FIG. 3, through the optical coupler 117a. CW laser light and bright soliton optical signal (work as pump light) to semiconductor optical amplifier 129
Is incident, and only the wavelength component of the CW laser light is passed through the optical bandpass filter 123a, whereby a dark light signal similar to that described above can be generated.

Further, as shown in FIG. 4, a Mach-Zehnder interferometer is constituted by nonlinear optical fibers 130 and 131 having the same length, a CW laser beam is input via a polarization controller 119a, and a bright soliton optical signal (pump light) is input. ) Via the optical amplifier 114a, the polarization controller 115a, and the optical coupler 117b, it is possible to generate a dark optical signal similar to the above.

In the optical fiber, the plane of polarization of the signal light rotates according to the intensity of the pump light due to the optical Kerr effect. If this is used, the optical Kerr shutter shown in FIG. 5 is also used as an exclusive OR optical gate. can do. The polarization planes of the bright soliton optical signal serving as pump light applied via the optical amplifier 114b, the polarization controller 115b, and the optical coupler 117c are connected to two polarization plane preserving fibers 125 and 126 of the same length with their main axes orthogonal to each other. When the CW laser beam is incident at an angle of 45 degrees from the main axis via the polarization controller 119b while being made to coincide with the main axis of the optical fiber, the plane of polarization of the CW laser light rotates according to the intensity of the bright soliton optical signal. By taking out only the CW laser light modulated by the optical bandpass filter 123c at the optical fiber output end, and inputting the passing polarization plane to the polarizer 127 whose polarization plane matches the polarization plane of the input CW laser light, A dark optical signal obtained by inverting the ON / OFF of the bright soliton optical signal is obtained. According to this specific example,
After converting the optically multiplexed bright soliton optical signal into a dark soliton optical signal and transmitting it, the receiving side can separate and receive the optical signal before multiplexing. In this case,
Because processing can be performed with the array density of light pulses reduced,
There is an effect that the influence of the timing jitter included in the transmitted optical signal on the bit error rate can be easily suppressed.

[0015]

(Embodiment 1) FIG. 7 shows an embodiment of an optical receiver according to the present invention. The receiving apparatus includes an exclusive OR optical gate 200, a CW laser 201, an optical coupler 202,
Light receiving element 203, narrow band pass filter 204, frequency divider 205, optical demultiplexer 206, optical receiver 2
07, 208, 209 and 210. The exclusive OR gate 200 has 20 time-division multiplexed 20
The Gb / s dark soliton optical signal and the output of the CW laser 201 are incident, and the CW laser light is converted into a time division multiplexed bright soliton optical signal in which the dark soliton optical signal is turned on and off. The time division multiplexed optical signal is branched into two by the optical coupler 202. A part of the branched optical signal is converted into an electric signal by the light receiving element 203,
The clock frequency component of Gb / s is extracted, and the frequency divider 205
Thus, the clock frequency is converted to a clock frequency before multiplexing of 5 Gb / s. The other of the branched signal lights and the 5 Gb / s clock signal are input to the optical demultiplexer and separated into four 5 Gb / s bright soliton optical signals.
7, 208, 209 and 210 to reproduce data. The optical demultiplexer 206 uses four electro-absorption optical modulators to synchronize with the optical signal before multiplexing at 25 ps.
This can be realized by forming an optical gate having a width. Further, optical demultiplexing may be performed using the optical AND operation of the nonlinear optical loop mirror shown in FIG.

(Embodiment 2) FIG. 8 shows another embodiment of the optical receiver according to the present invention. In the first embodiment shown in FIG. 7, the dark solitons are converted into bright solitons and then separated by the optical demultiplexer 206. In the present embodiment, the dark solitons are converted into bright solitons. And optical demultiplexing are performed at the same time. The time division multiplexed dark soliton optical signal is split into two by the optical coupler 202 through the optical amplifier 102a. A part of the branched optical signal is converted into an electric signal by the light receiving element 203, a clock frequency component of 20 Gb / s is extracted by the narrow band filter 204, and 5 G is extracted by the frequency divider 205.
The signal is converted into a clock frequency before b / s multiplexing and amplified by the narrow band amplifier 211. The other of the branched signal lights is divided into four and four electroabsorption optical modulators 216, 217, 218, 2
It is incident on 19. Each optical modulator has a microwave delay circuit 2
The 5G, wherein the delay time is adjusted so as to synchronize with the optical signal before multiplexing at 12, 213, 214, and 215, respectively.
It is driven by a sinusoidal voltage having a clock frequency of b / s, and forms an optical gate having a period of 100 ps and a width approximately equal to the pulse width of the bright soliton optical signal. When the multiplexed optical signal passes through the optical modulator, an optical gate waveform is output as it is at a constant intensity where there is no dark pulse, so that a bright pulse is formed. Where a dark pulse exists, the gate waveform has a dark pulse. If the shape is the inverse of the on / off state, the output will be zero. Further, no signal is output from the other three optical signal trains because the optical modulator is in the OFF state. Therefore, the output of each optical modulator is obtained by inverting the on / off state of the multiplex dark pulse and separating it as a bright soliton pulse signal before multiplexing. Four systems of 5 Gb / s bright soliton optical signals are amplified by optical amplifiers 220, 221, 222, and 223.
The light enters the optical receivers 207, 208, 209 and 210, respectively, and reproduces data.

(Embodiment 3) FIG. 9 shows still another embodiment of the optical receiver according to the present invention. The difference from the third embodiment is that the saturable absorbers 224, 225, 226 and 227 are connected after the optical modulators 216, 217, 218 and 219. In the third embodiment, where there is a dark pulse, the gate waveform is set to a shape in which the on / off of the dark pulse is inverted, and the output is set to zero. However, when there is timing jitter in the dark pulse or when the gate waveform is In the case of deviation from the shape, a residual error component is output. In this embodiment, the absorption coefficient changes according to the light intensity (the absorption coefficient decreases as the light intensity increases).
The saturable absorbers 224, 225, 226, and 227 can remove the residual error component, remove errors due to timing jitter, and improve the extinction ratio of the optical signal.

FIG. 10 is a diagram for explaining the operation of the dark soliton light receiving apparatus (Embodiment 4). 10A is a time-division multiplexed dark soliton optical signal, FIG. 10B is an optical gate waveform formed by an electro-absorption optical modulator modulated by a frequency-divided synchronous clock,
(C) is an optical gate output waveform, and (d) is a bright soliton optical signal after passing through a saturable absorption element.

FIG. 11 shows a specific example of an optical communication system using the optical receiver according to the present invention. Reference numeral 5 denotes an n-multiplexed dark soliton optical transmitter, 6 denotes an n-multiplexed dark soliton optical receiver, and 7 denotes an optical transmission line composed of an optical fiber and an optical amplifier for compensating for the loss of the optical fiber. In this embodiment, the transmission speed before multiplexing is 5 Gb / s, and the multiplicity is n = 4. The four-multiplexed dark soliton optical transmitting device 5 is realized by the optical transmitting device (the first embodiment) and the optical receiving device (the fourth embodiment) according to the present invention described above. The total length of the transmission optical fiber 8 in the optical transmission line 7 is about 9000 km, and the average chromatic dispersion is -0.0 in a normal dispersion value.
It is set to 5 ps / km / nm. 300 optical amplifying repeaters 9 each using an erbium-doped fiber for compensating the loss of the optical fiber are installed every about 30 km. The pulse width of the transmission dark pulse is 10 ps, and the average optical output power of each optical amplification repeater is set to 3 dBm so that the section average optical power of each span satisfies the soliton condition. The average value of the timing jitter of dark solitons after 9000 km transmission is 4.8 ps, and error-free reception cannot be performed as it is. However, in the present embodiment, reception is achieved with an error rate of 10 ⁻⁹ or less because a receiving device that is hardly affected by timing jitter is used.

[0020]

As described in detail above, the present invention provides
It is possible to realize a dark soliton optical receiving apparatus and an optical communication system using the same that has almost no timing jitter limitation. In addition, since a simple optical transmission line combining an optical fiber and an optical amplifier can be used, reliable ultra-high-speed and long-distance optical communication becomes possible. It has a remarkable effect for realizing.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a dark soliton optical transmission device to which the present invention is applied.

FIG. 2 is a diagram showing an exclusive OR optical gate using a nonlinear optical loop mirror (Sagnac interferometer) used in the present invention.

FIG. 3 is a diagram showing an exclusive OR optical gate using a semiconductor optical amplifier used in the present invention.

FIG. 4 is a diagram showing an exclusive OR optical gate using a nonlinear Mach-Zehnder interferometer used in the present invention.

FIG. 5 is a diagram showing an exclusive or optical gate using an optical car shutter used in the present invention.

FIG. 6 is an explanatory diagram of dark soliton transmission optical pulse signal generation.

FIG. 7 is a diagram illustrating a dark soliton light receiving device 1 according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a dark soliton light receiving device 2 according to a second embodiment of the present invention.

FIG. 9 is a diagram illustrating a dark soliton light receiving device 3 according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating an operation of the dark soliton light receiving apparatus according to the second embodiment of the present invention.

FIG. 11 is a diagram illustrating an optical communication system realized by using the present invention.

FIG. 12 is a waveform diagram showing a typical example of the waveforms of a conventional bright soliton and dark soliton pulse.

[Explanation of symbols]

Reference Signs List 1 time division multiplex bright soliton optical signal generator 2,201 CW laser 3,200 exclusive OR optical gate 4 optical phase modulator 5 n-multiplexed dark soliton optical transmitter 6 n-multiplexed dark soliton optical receiver 7 optical transmission line 8 Optical fiber for transmission 9 Optical amplifier repeater 101 Soliton pulse light source 102, 102a, 113, 114, 114a, 114
b, 220, 221, 222, 223 Optical amplifier 103, 112, 117, 117a, 117b, 12
0, 121, 202 Optical couplers 104, 105, 106, 107 Optical delay lines 108, 109, 110, 111 Optical intensity modulators 115, 115a, 115b, 119, 119a, 11
9b Polarization controller 116, 122, 124 Optical isolator 118, 130, 131 Nonlinear optical fiber 123, 123a, 123b, 123c Optical bandpass filter 125, 126 Polarization-preserving nonlinear optical fiber 127 Polarizer 128 Polarization controller 129 Semiconductor optical amplifier 203 Light receiving element 204 Narrow band filter 205 Divider 206 Optical demultiplexer 207,208,209,210 Optical receiver 211 Narrow band amplifier 212,213,214,215 Microwave delay circuit 216,217,218,219 Electroabsorption light Modulator 224, 225, 226, 227 Supersaturated absorption element

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shu Yamamoto 2-2-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside Keididi Co., Ltd. (72) Inventor Shigeyuki Akiba 2-2-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo (56) References JP-A-3-185430 (JP, A) JP-A-2-96718 (JP, A) JP-A-5-241220 (JP, A) JP-A-3-17633 ( JP, A) JP-A-2-113736 (JP, A) JP-A-55-90146 (JP, A) JP-A-5-284117 (JP, A) JP-A-2-116151 (JP, U) Electronic communication Ed., Introduction to New Version Laser, Japan Society of Electronics and Communication Engineers, March 25, 1979, first edition, p. 87-88 (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 G02F 1/35

Claims (8)

(57) [Claims] An optical receiver for use in a dark soliton optical communication system for transmitting a dark soliton optical pulse signal which is an on / off inverted optical signal of a bright soliton optical signal in which digital information is added to a return to zero optical pulse. An input terminal for receiving an optical pulse signal; a constant-amplitude light generating means for outputting light of a constant amplitude; receiving the dark soliton light pulse signal and the output of the constant-amplitude light generating means, Optical gate means having an output function of a logical exclusive OR of two optical inputs for converting a return to zero optical pulse obtained by inverting the on / off state of the dark soliton optical pulse signal into an optical pulse signal obtained by adding digital information; An electrical pulse signal obtained by adding digital information to the return to zero optical pulse output from the optical gate means Optical receiving apparatus for use in dark soliton optical communication system characterized by comprising an optical receiver for converting the scan signal. 2. A dark soliton optical communication system for transmitting a time-division multiplexed dark soliton optical pulse signal, which is an optical signal obtained by time division multiplexing a plurality of bright soliton optical signals obtained by adding digital information to return-to-zero optical pulses and on / off inverted. An optical receiver used in a system, comprising: an input terminal for receiving the time-division multiplexed dark soliton optical pulse signal; a constant-amplitude light generating means for outputting light of a constant amplitude; the time-division multiplexed dark soliton optical pulse signal; Receiving the output of the amplitude light means, converting the light of the constant amplitude into a time-division multiplexed optical pulse signal obtained by adding digital information to a return-to-zero optical pulse obtained by inverting the ON / OFF of the time-division multiplexed dark soliton optical pulse signal; Optical gating means having a logical exclusive OR output function of two optical inputs; Frequency dividing means for dividing a clock electric signal having a clock frequency of a return to zero light pulse before multiplexing from a time division multiplexed light pulse signal obtained by adding digital information to a return to zero light pulse; A time-division multiplexed optical signal obtained by adding digital information to a return to zero optical pulse and the clock electric signal output from the frequency dividing means are input, and a plurality of optical signals respectively synchronized with a plurality of return to zero optical signals before being multiplexed. An optical demultiplexer for separating a pulse signal; and an optical receiver for converting a plurality of optical pulse signals obtained by adding digital information to the return zero optical pulse output from the optical demultiplexer into a plurality of electric pulse signals. An optical receiver for use in a dark soliton optical communication system. 3. A dark soliton optical communication system for transmitting a time division multiplexed dark soliton optical pulse signal which is an on / off inverted optical signal obtained by time division multiplexing a bright soliton optical signal obtained by adding digital information to a return to zero optical pulse. In the optical receiver used, an input terminal for receiving the time-division multiplexed dark soliton optical pulse signal, and a clock electric signal having a clock frequency of the return-to-zero optical pulse before multiplexing are separated from the time-division multiplexed on / off inverted optical signal. A frequency dividing means, and a clock before multiplexing by modulating the time-division multiplexed dark soliton optical pulse signal with a plurality of clock electric signals each having a required delay to the clock electric signal output from the frequency dividing means. Simultaneously divides the frequency and converts it to a return-to-zero optical pulse with inverted on / off, A plurality of optical modulators for obtaining a plurality of optical pulse signals obtained by adding digital information to a return to zero optical pulse obtained by inverting the on / off state of the time division multiplexed dark soliton optical pulse signal; and a return to zero output of the optical modulator. An optical receiver for use in a dark soliton optical communication system, comprising: an optical receiver that converts a plurality of optical pulse signals obtained by adding digital information to optical pulses to a plurality of electric pulse signals. 4. A dark soliton optical communication system for transmitting a time division multiplexed dark soliton optical pulse signal which is an on / off inverted optical signal obtained by time division multiplexing a bright soliton optical signal obtained by adding digital information to a return to zero optical pulse. An input terminal for receiving the time-division multiplexed dark soliton optical pulse signal, and a clock electric signal having a clock frequency of the return-to-zero optical pulse before multiplexing from the time-division multiplexed dark soliton optical pulse signal. A frequency dividing means for dividing, and a clock before multiplexing by modulating the time division multiplexed on / off inverted optical signal with a plurality of clock electric signals each having a required delay to the clock electric signal output from the frequency dividing means. Simultaneously divides the frequency and converts it to a return-to-zero optical pulse with inverted on / off, A plurality of optical modulators for obtaining a plurality of optical pulse signals obtained by adding digital information to a return toe zero optical pulse obtained by inverting the on / off of the time division multiplexed on / off inverted optical signal; and a return tow of outputs of the plurality of optical modulators. A plurality of absorption means having supersaturated absorption characteristics in which the absorption coefficient decreases as the light intensity increases in order to absorb residual error components from a plurality of light pulse signals obtained by adding digital information to the zero light pulse; An optical receiver for use in a dark soliton optical communication system, comprising: an optical receiver that converts a plurality of optical pulse signals obtained by adding digital information to an output return-to-zero optical pulse to a plurality of electric pulse signals. 5. The optical receiver according to claim 1, wherein the optical gate means is a non-linear optical fiber loop mirror. 6. The optical receiver according to claim 1, wherein the optical gate means is a nonlinear optical fiber car shutter. 7. The optical receiver according to claim 1, wherein said optical gate means is a nonlinear optical Mach-Zehnder interferometer. 8. The optical receiver according to claim 1, wherein said optical gate means is a semiconductor optical amplifier.