JP2004274539A - Highly nonlinear-resistant optical time division multiplexing transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly nonlinear-resistant OPTDM transmission system for using a transmission system with a nonlinear-resistance and a standard single mode fiber (SSMF) having zero dispersion at a 1.3 μm band so as to transmit an optical time division multiplexing (OTDM) signal of a 1.55 μm band. <P>SOLUTION: The OTDM transmission system includes a light source; a first SSF for transmitting a light outputted from the light source to an optical phase conjugator (OPC); the OPC; and a second SSF for transmitting the light outputted from the OPC. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical time division multiplexing (OTDM) transmission system, and more particularly, to an ultra-high-speed OTDM transmission system having a nonlinear tolerance due to provision of an optical phase conjugator (OPC) in a transmission path. More specifically, transmission of an OTDM signal in a 1.55 μm band using a standard single mode fiber (SSMF) having zero dispersion in a 1.3 μm band by providing an OPC in a transmission path. The present invention relates to an ultra-high-speed OTDM transmission system that has enabled transmission.
[0002]
[Prior art]
Negative dispersion fiber (NDF), reverse dispersion fiber (Reverse Dispersion Fiber; RDF), and mid-span phase conjugation methods have been actively studied to compensate for chromatic dispersion in transmission fibers [see, for example, J.-M. Inoue, H .; Sotobayashi, W.C. Nakajo, H .; Kawaguchi: IEEE Electron. Lett. , 38 (15), 2002, 819-821 (Non-Patent Document 1). ]. It has also been proposed that a phase conjugator (OPC) can also compensate for non-linearities in the fiber [eg, H. et al. Sotobayashi, K .; Kitayama: IEEE / OSA J .; See Lightwave Technology, 17 (12), 1999, 2488-2497. ]. However, the NDF or RDF cannot compensate for the nonlinearity deteriorated by the nonlinearity of the transmission path. In a system using an NDF, the time waveform of a signal light is deteriorated due to self-phase modulation (SPM) when a transmission pulse passes through a fiber due to the effect of the nonlinearity. Therefore, in order to eliminate the influence, the SMF whose core is expanded is mainly used. However, when a high power signal having a short pulse is used for transmission, there is a problem that the influence of nonlinearity cannot be ignored.
In ultra-high-speed OTDM communication, time slots allocated to each bit signal become narrower in time. For this reason, in ultra-high-speed OTDM communication, an ultrashort light pulse is inevitably used as a light source. On the contrary, since the required frequency band is widened, the chromatic dispersion in the fiber which is the transmission line deteriorates the transmission characteristics. Therefore, especially when an OTDM transmission line is used, the chromatic dispersion of the optical fiber must be compensated.
Further, in order to use an SSMF having zero dispersion in the 1.3 μm band and transmit an OTDM signal in the 1.55 μm band, it is necessary to compensate for the chromatic dispersion of the SSMF.
[0003]
[Non-patent document 1]
J. Inoue, H .; Sotobayashi, W.C. Chujo, H .; Kawaguchi: IEEE Electron. Lett. , 38 (15), 2002, 819-821.
[Non-patent document 2]
H. Sotobayashi, K .; Kitayama: IEEE / OSA J .; Lightwave Technology, 17 (12), 1999, 2488-2497.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a transmission system having nonlinear tolerance.
Another object of the present invention is to provide a highly nonlinear proof OTDM transmission system for transmitting an OTDM signal in the 1.55 μm band, particularly using an SSMF having zero dispersion in the 1.3 μm band.
[0005]
[Means for Solving the Problems]
At least one of the above-mentioned problems is solved by the following invention.
(1) An OTDM transmission system including a light source, a first SMF for transmitting light output from the light source to the OPC, an OPC, and a second SMF for transmitting light output from the OPC. It is.
(2) The OTDM transmission system according to (1), wherein the light source is a laser mode-locked laser or a mode-locked semiconductor laser.
(3) The OTDM transmission system according to (1), wherein the light output from the light source is pulsed light.
(4) The OTDM transmission system according to (1), wherein the light output from the light source is pulsed light, and a center wavelength of the pulsed light is 1530 nm to 1560 nm or 1570 nm to 1610 nm. The wavelength band of optical communication is mainly limited to the wavelength characteristic of fiber propagation loss and the wavelength band of an optical amplifier. 1530 nm to 1560 nm called C band and 1570 nm to 1610 nm called L band are practical. This is an optical amplifier (fiber amplifier) being developed in this wavelength band. Therefore, it can be implemented in all wavelength bands in principle, but can be implemented more easily in the C and L bands.
(5) The OTDM transmission system according to (1), wherein the light output from the light source is pulsed light having a center wavelength of 1560 nm. The fact that an OTDM transmission system using this light is feasible was also confirmed in Examples.
(6) The OTDM transmission system according to (1), wherein a frequency of the light output from the light source is 5 GHz to 100 GHz. The bit rate of the signal light output from an appropriate light source depends on the performance of the OPC. In the examples, SOA was used. When SOA is used, there is a capability of transmitting 200 km at a bit rate of 80 Gbps (see Non-Patent Document 1). For example, when a highly nonlinear fiber is used as the optical nonlinear medium of the OPC, it can be inferred that if the transmission distance is shortened, transmission exceeding 320 Gbps becomes possible.
(7) The OTDM transmission system according to (1), wherein the light output from the light source is pulse light having a center wavelength of 1560 nm and a pulse width of 3.5 ps generated by a 10 GHz laser mode-locked semiconductor laser. .
(8) The OTDM transmission system according to (1), wherein the first SMF and the second SMF are SMFs having zero dispersion in a 1.3 μm band.
(9) The OTDM transmission system according to (1), wherein the first SMF and the second SMF are 100 km to 200 km, and a total length of the two SMFs is 200 km to 400 km. . The transmission distance (upper limit) changes depending on the bit rate. When the bit rate is 80 Gbps as in the present embodiment, it becomes easier as the transmission distance becomes shorter than 200 km. In such a long-distance transmission system, a repeater (optical amplifier) is preferably provided in the middle of the transmission route.
(10) The OTDM transmission system according to (1), wherein the first SMF is 100 km, and the second SMF is 106 km. This is the length theoretically determined from the dispersion characteristics of the fiber actually used in the embodiment. Therefore, if the physical characteristics of the fibers used are different, if the first SMF length is fixed, the second SMF length must be controlled. Actually, the SMF length is determined so that the product of the secondary dispersion value and the SMF length at the wavelength of the signal light is balanced. In the case of OPC transmission, since the signal light wavelength in the first SMF is different from the wavelength in the second SMF, the SMF length is determined so that the product of the secondary dispersion value and the distance is balanced at each wavelength.
(11) The OTDM transmission system according to (1), wherein the OPC includes a semiconductor optical amplifier (SOA).
(12) The OPC mixes a continuous light source that generates continuous light, signal light having the same center wavelength as the light output from the light source, and continuous light generated from the first continuous light source. The OTDM transmission system according to (1), including a multiplexer and an SOA to which light mixed by the multiplexer is input and in which a four-wave mixing phenomenon is caused.
(13) The OPC includes an SOA, causes signal light output from the light source and passed through the first SMF to cause a four-wave mixing phenomenon in the OPC, inverts the spectrum of the light, and inverts the spectrum. The OTDM transmission system according to the above (1), which outputs light to a second SMF.
(14) The light output from the light source is a pulse light having a center wavelength of 1560 nm, and the pulse light having a center wavelength of 1560 nm and the continuous light having a center wavelength of 1555 nm are input to the phase conjugator. ) Is an OTDM transmission system. As described above, these wavelengths are wavelengths that have been set in consideration of the amplification band and noise characteristics of the optical fiber amplifier and the wavelength characteristics of the optical components, and have actually established communication.
(15) The OTDM transmission system according to (1), wherein the light output from the light source is modulated by a lithium niobate modulator.
(16) The OTDM transmission system according to (1), wherein the light output from the light source is amplified by an erbium-doped fiber amplifier.
[0006]
(17) An OTDM transmission method using the OTDM transmission system according to any one of (1) to (16).
[0007]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the OTDM transmission system 1 according to the first embodiment of the present invention includes a light source 2, a first SMF 3 for transmitting light output from the light source to the OPC, and an OPC 4. An OTDM transmission system having a second SMF 5 for transmitting the light output from the OPC. It is to be noted that the provision of the optical amplifiers 6 and 7 for amplifying light and the autocorrelator 8 for observing output light as shown in FIG. 1 is another preferred embodiment of the present invention. is there.
[0008]
(light source)
The light source 2 used in the OTDM transmission system of the present invention is preferably a laser mode-locked laser or a laser mode-locked semiconductor laser.
[0009]
The light output from the light source is more preferably, for example, mode-locked pulsed light, and preferably 1560 nm as the center wavelength of the light output from the light source, and the frequency of the light output from the light source is , Preferably 5 GHz to 100 GHz, more preferably 7 GHz to 20 GHz, and particularly preferably 10 GHz.
More specifically, the light output from the light source is a pulsed light having a center wavelength of 1560 nm and a pulse width of 3.5 ps generated by a 10 GHz mode-locked semiconductor laser. In the embodiment, the SOA was used as a phase conjugator. For example, when a highly nonlinear fiber is used as the optical nonlinear medium of the phase conjugator, it is considered that if the transmission distance is shortened, transmission exceeding 320 Gbps becomes possible.
[0010]
(Single mode fiber)
The single mode fiber (SMF) is not particularly limited as long as it can transmit light. Examples of the SMF include a first SMF and a second SMF having zero dispersion in a 1.3 μm band. In the OTDM transmission system of the present invention, four-wave mixing is caused by providing the OPC in the transmission path, and the 1.55-μm band OTDM signal is transmitted using SSMF having zero dispersion in the 1.3 μm band. It is possible to do.
[0011]
As the SMF, for example, one or both of the first SMF and the second SMF are 110 ± 10 μm as Aeff (effective area: effective sectional area of the core). ² May be used. Since the nonlinearity is proportional to the light intensity (density), such a core-expanded SMF is less likely to cause nonlinearity by enlarging the cross-sectional area of the core so that the optical power is not concentrated at the center of the optical fiber. However, transmission can be performed without causing nonlinearity without using the core expansion SMF.
[0012]
The length of the SMF is preferably one or both of the first SMF and the second SMF is 100 km to 1000 km, and the total length of the two SMFs is 200 km to 2000 km, more preferably Is one or both of the first SMF and the second SMF is 100 km to 200 km, and the total length of the two SMFs is 200 km to 400 km, and particularly preferably, the first SMF is 100 km, The second SMF is 106 km. According to the OTDM transmission system of the present invention, information can be transmitted over long distances by compensating for dispersion. If the first fiber length and the dispersion value are known, the signal light wavelength, and the CW light wavelength in the OPC are determined, the optimum second fiber length is determined. As described above, these wavelengths are wavelengths that are set in consideration of the amplification band and noise characteristics of the optical fiber amplifier and the wavelength characteristics of the optical components, and that have actually established communication.
[0013]
(Optical phase conjugator)
The optical phase conjugator (OPC) is not particularly limited as long as it can output phase conjugate light by the four-wave mixing phenomenon, and a known OPC can be used.
As OPC, for example, Watanabe, T.W. Naito, and T.M. Chikama, "Compensation of chromatic dispersion as a single-mode fiber by optical phase conjugation," IEEE Photo. Technol. Lett. , 1993, 5, (1), p. 92-95. , And R.I. M. Jopson, A. H. Gnauck and R.A. M. Delosier, "Compensation of fibrous chromatographic dispersion by spectral inversion," IEEE Electron. Lett. , 1993, 29, (7), p. 576-578. May be a configuration using an optical fiber as described in C. Thatham, G .; Sherlock, and L.M. D. Westbrook, "Compensation fiber chromatic dispersion by optical phase composition in a semiconductor conductor laser amplifier," IEEE Electron. Lett. , 1993,29, (21), pp. 1851-1852, and U.S.A. Feiste, R .; Ludwig, C.I. Schmidt, E .; Dietrich, S.M. Diez, H .; J. Ehrke, E .; Patzak, H .; G. FIG. Weber, and T.W. Merker, "80-Gb / s transmission over 106-km standard-fiber using optical phase conjugation in a Sagnac-interferometer," IEEE Photon. Technol. Lett. , 1999, 11, (8) pp. It may be one using SOA as described in 1063-1065. Among them, OPC using SOA is desirable from the viewpoints of small size, light weight, low cost, and excellent stability.
[0014]
As an SOA used for the OPC, an SOA including a non-linear medium for generating phase conjugate light can be used. As the SOA, a known SOA such as an optical fiber, a bulk SOA, and a multiple quantum well SOA as described in Applied Physics Vol. 63, No. 12, pp. 1219-1226 (1994) can be used. Among these, a polarization independent bulk type SOA is preferable as the SOA.
In the present invention, the SOA used specifically is SOA manufactured by Applied Optics.
[0015]
As an example of the OPC of the present invention, as shown in FIG. 2, a continuous light source 11 that generates continuous light, a signal light having the same center wavelength as the light output from the light source, and the first continuous light source One includes a multiplexer 12 for mixing the generated continuous light and an SOA 13 in which light mixed by the multiplexer is input and a four-wave mixing phenomenon occurs. Preferably, an optical filter 16 is provided between the optical amplifier 15 and the multiplexer 12, and an optical filter 17 is provided between the optical amplifier 14 and the multiplexer 12. Preferably, the optical filter 16 is a bandpass filter having a center wavelength of 1560 nm and a bandwidth of 5 nm, and the optical filter 17 is preferably a bandpass filter having a center wavelength of 1555 nm and a bandwidth of 1 nm. According to such an OPC, a four-wave mixing phenomenon is caused in the light output from the light source and input to the OPC through the first SMF, and the spectrum of the light is inverted. Output from the second SMF. Note that, as shown in FIG. 2, an optical amplifier such as an erbium-doped fiber amplifier is installed downstream of the continuous light source 14 and / or at a position 15 for amplifying signal light, which is another preferred embodiment of the present invention. is there.
[0016]
The multiplexer is not particularly limited as long as light from one or more optical communication paths can be mixed or distributed to one or more optical communication paths. As the multiplexer, a known multiplexer such as a half mirror, a beam splitter such as a polarization beam splitter, or a fiber coupler can be used.
[0017]
As an OTDM transmission system using such an OPC, specifically, light output from a light source is pulse light having a center wavelength of 1560 nm, and a continuous light having a center wavelength of 1560 nm and a center wavelength of 1555 nm are provided to a phase conjugator. And continuous light of the same. With such a system using light, desirable phase conjugate light can be obtained. As described above, these wavelengths are wavelengths that have been set in consideration of the amplification band and noise characteristics of the optical fiber amplifier and the wavelength characteristics of the optical components and have actually established communication.
[0018]
(4 light wave mixing phenomenon)
Hereinafter, the four-wave mixing phenomenon will be described.
When two lights having different wavelengths (strong light is pump light (frequency fp) and weak light is probe light (frequency fq)) are injected into a nonlinear medium, the pump light is the center of the pump light, and the probe light is the target frequency position. Then, a new light (signal light (frequency fs)) is output. These frequencies have a relationship of fs = 2fp−fq. The pump light is modulated by the beat between the pump light and the probe light, and signal light is generated. The light mixing phenomenon involving these four light waves (the pump light appears twice and is counted as two) is a phenomenon called a four light wave mixing phenomenon. In order for four-wave mixing to occur, the nonlinear effect must respond to the difference frequency fd = fp-fq between the two input lights. When fd is less than several GHz, the main optical nonlinear effect is a change in the number of carriers due to interband transition. This frequency region is called near-degenerate four-wave mixing (NDFWM). As fd further increases, the change in the number of carriers no longer follows, and the non-linear effect whose expiration is within the band becomes the main mechanism. The region where fd is from several 100 GHz to several THz is called highly non-degenerate four-wave mixing (HNDFWM).
[0019]
The wavelength of the continuous light (pump light) is preferably from 1530 nm to 1560 nm, more preferably from 1540 nm to 1560 nm, and still more preferably from 1550 nm to 1560 nm. The intensity of the continuous light is preferably 23 to 26 dBm. The conversion efficiency of the FWM is proportional to the square of the intensity of the continuous pump light, and is proportional to the intensity of the signal light. However, when the signal light intensity is increased, the intensity cannot be increased because the converted light is deteriorated due to the pattern effect peculiar to the SOA. Therefore, to increase the efficiency, the pump light intensity must be increased, but if it is too high, the SOA is destroyed. Therefore, the above range is preferable as the intensity of the pump light.
[0020]
(Input signal light)
The input signal light input to the phase conjugator of the present invention is not particularly limited as long as it is an optical signal used for optical communication, and known light can be used. It is a small signal, more preferably a signal that matches the ITU grid. The light intensity is preferably -3 dBm to 3 dBm, more preferably -1 dBm to 3 dBm, and still more preferably 0 dBm to 3 dBm.
[0021]
(Optical modulator)
The light output from the light source is preferably modulated by a lithium niobate (LN) modulator. The LN modulator includes an intensity modulator, a phase modulator, a polarization modulator, and the like. The basic phenomenon used by the modulator is an electro-optic effect. The electro-optic effect is a phenomenon in which the refractive index of a medium changes when a voltage is applied to the medium. The change in the refractive index is converted into a phase change of light passing through the medium. The phase modulator uses the electro-optic effect as it is.
[0022]
(Optical amplifier)
Light output from the light source is preferably amplified by an erbium-doped fiber amplifier. That is, it is a preferred embodiment of the present invention that the light output from the light source is amplified by the optical amplifier and then transmitted to the OPC. Examples of such an optical amplifier include a semiconductor laser amplifier and an optical fiber amplifier, and among these, an optical fiber amplifier is more preferable, and an erbium-doped fiber amplifier (EDFA) is more preferable. It is. The EDFA has a wide bandwidth that can be amplified, and an amplification band of 0.03 μm or more is obtained in the 1.55 μm band. When this is converted into a frequency band, it becomes about 3.7 THz. The EDFA also has an advantage that it does not depend on the polarization plane of incident light. In the optical fiber communication, a 1.55 μm band is generally used. Therefore, an EDFA is preferable as the optical amplifier, but a neodymium-doped fiber amplifier is preferable in the optical communication using the 1.33 μm band.
The optical amplifiers specifically used in the present invention are EAD-40C and EAD-500C manufactured by IPGL Laser.
[0023]
(Optical time division multiplexing)
Optical time division multiplexing (OTDM) is a communication multiplexing method as described below. First, an analog signal is converted into a digital signal (pulse) by an encoder in advance. The converted pulses are arranged so that the time positions are shifted for each channel so that the pulses do not overlap. The multiplexing number is determined based on the number of times the original pulse sequence based on the time position. When the transmitting side divides each optical signal at regular time intervals and transmits it, the receiving side restores the signal for each line. OTDM is a technique for transmitting a large amount of information in this way.
[0024]
The highly nonlinear OTDM transmission system of the present invention can transmit a signal with a large power and little deterioration of the signal light (a small time extension of the pulse), that is, a high-quality signal. Since the temporal dispersion is small, the time slot can be small. Thus, the highly nonlinear OTDM transmission system of the present invention enables OTDM communication.
[0025]
【Example】
(Embodiment 1) FIG. 1 shows a schematic diagram of a transmission system using a medium distance OPC which is an experimental system of Embodiment 1.
As shown in FIG. 1, in this embodiment, an OPC transmission apparatus uses an optical phase SOA as described in Non-Patent Document 1 as an optical phase mixer and a standard SMF of 200 km as a transmission line. . A 1560 nm Gaussian Fourier limit (Fourier transform limited) 3.5 ps optical pulse generated by a 10 GHz mode-locked semiconductor laser was used as the transmitted optical signal. At the midpoint of the transmission fiber, the optical spectrum of the signal pulse was wavelength shifted to 1550-nm, and the spectrum was inverted using an optical phase mixer based on four-wave mixing in the SOA. Then, the transmitted light pulse was measured using an autocorrelator (autocorrelator) and an optical spectrum analyzer (spectrum analyzer: spectroscope). At 1550 nm, the dispersion and dispersion slope of SMF are -16.8 ps / nm / km and 0.057 ps / nm, respectively. ² / Km. To compensate for second order dispersion in the SMF, the product of the second order dispersion fiber length in the first and second half fibers was balanced. 4 to 6 show the influence of the transmission power on the pulse width expansion factor (pulse broadening factor), the pulse waveform (autocorrelation), and the optical spectrum.
[0026]
(Comparative Example 1)
As shown in FIG. 3, an experiment was performed using a 200 km fiber (4 sets of 36.7 km SMF and 13.3 km NDF) transmission system as a transmission line for NDF setting. This transmission system uses a Gaussian 2.9ps optical pulse 10 GHz laser mode-locked semiconductor laser of 1535.8 nm as a light source 22, EDFAs as amplifiers 23 and 24, and Aeff: 110 as SMFs 25, 26, 27 and 28. ± 10μm ² SMF with an effective core of The zero dispersion wavelength and dispersion slope of one span (SMF + NDF) are 1532.7 nm and 0.009 ps / nm at 1535.8 nm, respectively. ² / Km. In the figure, 29 to 32 represent NDFs, and 33 represents an autocorrelator.
[0027]
FIG. 4 shows the pulse width expansion rate after transmission. In the figure, black circles represent the pulse width enlargement rate of the first embodiment, and white circles represent the pulse width enlargement rate of the comparative example 1. From FIG. 4, it can be seen that the pulse width expansion rate exceeds 1 in both Example 1 and Comparative Example 1, and that the pulse width is expanded by transmission. However, the pulse width expansion rate in Example 1 is smaller than that in Comparative Example 1. From this, it can be seen that the transmission system using OPC can suppress the dispersion of the pulse compared to the transmission system using NDF. Note that the pulse width expansion rate is standardized using an initial pulse width before transmission.
[0028]
FIG. 5 shows a change in the pulse waveform in the time domain when the transmission power is changed. FIG. 5A shows a change in the pulse waveform in Comparative Example 1, and FIG. 5B shows a change in the pulse waveform in Example 1. In the figure, BtoB represents a back-to-back, that is, a pulse waveform of a signal before transmission. In both Example 1 and Comparative Example 1, the pulse waveform is wider than the pulse waveform of the signal before transmission. However, in the case of Example 1 (FIG. 5B), a constant pulse waveform was maintained irrespective of the transmission power as compared with that of Comparative Example 1 (FIG. 5A), There is little deviation from the pulse waveform.
[0029]
FIG. 6 shows a change in the pulse waveform in the wavelength region when the transmission power is changed. FIG. 6A shows a change in the pulse waveform in Comparative Example 1, and FIG. 6B shows a change in the pulse waveform in Example 1. From FIG. 6, it can be seen that the example 1 has less change in the pulse waveform than the comparative example 1.
[0030]
As described above, in the first embodiment in which OPC is used, the pulse width expansion degree hardly changes. However, the pulse waveform has changed compared to the initial pulse. This is considered to be due to third-order dispersion in the fiber because OPC cannot compensate for dispersion. Conversely, in Comparative Example 1 in which NDF is used, the pulse width expands and the spectrum changes, and when the transmission power exceeds 5 dBm, the pulse temporally has a tail (trapezoidal shape). These results are believed to be caused by the SPM effect. On the other hand, when OPC is used, no influence of nonlinearity is observed.
In conclusion, it has been found that OPC can compensate for non-linearities in the fiber, and therefore has a large tolerance for non-linearities in medium-range OPC transmission lines.
[0031]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the transmission system which can compensate the signal deteriorated by the nonlinearity of the transmission path can be provided.
According to the present invention, it is possible to provide a transmission system for transmitting an OTDM signal in a 1.55 μm band using a standard SSMF having a zero dispersion in a 1.3 μm band.
[Brief description of the drawings]
FIG. 1 is a diagram schematically illustrating an OTDM transmission system according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing an example of an OPC of the present invention.
FIG. 3 is a diagram schematically illustrating an OTDM transmission system using an NDF in Comparative Example 1.
FIG. 4 is a diagram illustrating a pulse width expansion rate after transmission.
FIG. 5 is a diagram illustrating a change in a pulse waveform in a time domain when a transmission power is changed. FIG. 5A shows a change in the pulse waveform in Comparative Example 1, and FIG. 5B shows a change in the pulse waveform in Example 1.
FIG. 6 is a diagram illustrating a change in a pulse waveform in a wavelength region when a transmission power is changed. FIG. 6A shows a change in the pulse waveform in Comparative Example 1, and FIG. 6B shows a change in the pulse waveform in Example 1.
[Explanation of symbols]
1 OTDM transmission system
2 Light source
3 First single mode fiber (SMF)
4 Optical phase conjugator (OPC)
5. Second single mode fiber (SMF)
6 Optical amplifier
7 Optical amplifier
8 Autocorrelator
11 Continuous light source
12 Optical coupler
13. Semiconductor Optical Amplifier (SOA)
14 Optical amplifier
15 Optical amplifier
16 Optical filter
17 Optical Filter

Claims (17)

A light source,
A first single mode fiber for transmitting light output from the light source to an optical phase conjugator;
An optical phase conjugator;
A second single mode fiber for transmitting the light output from the optical phase conjugator,
Optical time division multiplex transmission system. The optical time division multiplex transmission system according to claim 1, wherein the light source is a laser mode-locked laser or a mode-locked semiconductor laser. The optical time division multiplex transmission system according to claim 1, wherein the light output from the light source is pulsed light. The optical time-division multiplex transmission system according to claim 1, wherein the light output from the light source is pulsed light, and a center wavelength of the pulsed light is 1530 nm to 1560 nm or 1570 nm to 1610 nm. The optical time division multiplex transmission system according to claim 1, wherein the light output from the light source is pulse light having a center wavelength of 1560 nm. The optical time division multiplex transmission system according to claim 1, wherein the frequency of the light output from the light source is 5 GHz to 100 GHz. The optical time-division multiplexing transmission system according to claim 1, wherein the light output from the light source is pulsed light having a center wavelength of 1560 nm and a pulse width of 3.5 ps generated by a 10 GHz laser mode-locked semiconductor laser. The optical time division multiplex transmission system according to claim 1, wherein the first single mode fiber and the second single mode fiber are single mode fibers having zero dispersion in a 1.3 µm band. The optical time division according to claim 1, wherein the first single mode fiber and the second single mode fiber have a length of 100 km to 200 km, and a total length of the two single mode fibers is 200 km to 400 km. Multiplex transmission system. The optical time division multiplex transmission system according to claim 1, wherein the first single mode fiber is 100 km, and the second single mode fiber is 106 km. The optical time division multiplex transmission system according to claim 1, wherein the optical phase conjugator includes a semiconductor optical amplifier. The optical phase conjugator,
A continuous light source for generating continuous light,
A multiplexer that mixes signal light having the same center wavelength as light output from the light source and continuous light generated from the first continuous light source,
A semiconductor optical amplifier in which light mixed by the multiplexer is input and a four-wave mixing phenomenon is caused;
The optical time division multiplex transmission system according to claim 1. The optical phase conjugator includes a semiconductor optical amplifier,
A four-wave mixing phenomenon is caused in the light output from the light source and input to the optical phase conjugator through the first single mode fiber, the spectrum of the light is inverted, and the light having the inverted spectrum is converted to the second light. Output to a single-mode fiber
The optical time division multiplex transmission system according to claim 1. The light output from the light source is a pulse light having a center wavelength of 1560 nm,
The optical time-division multiplexing transmission system according to claim 1, wherein continuous light having a center wavelength of 1560 nm and continuous light having a center wavelength of 1555 nm are input to the phase conjugator. The optical time division multiplex transmission system according to claim 1, wherein the light output from the light source is modulated by a lithium niobate modulator. The optical time division multiplex transmission system according to claim 1, wherein the light output from the light source is amplified by an erbium-doped fiber amplifier. An optical time division multiplex transmission method using the optical time division multiplex transmission system according to any one of claims 1 to 16.

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