JP4552610B2 - Wavelength converter - Google Patents

Description

  The present invention relates to a wavelength converter that generates and outputs output light having a wavelength different from the wavelength of input light, an optical network system that includes the wavelength converter, and an optical transmission system that includes the wavelength converter.

  A wavelength converter is an optical device that outputs output light having a wavelength different from the wavelength of input light (that is, a different optical frequency). In general, in a wavelength converter, input light and excitation light are input to a nonlinear optical medium, and four-wave mixing, which is a kind of nonlinear optical phenomenon, is generated in the nonlinear optical medium, and an output of a new wavelength is generated by this four-wave mixing. Light is generated (see, for example, Patent Document 1 and Patent Document 2).

  Further, the wavelength conversion device is a predetermined wavelength-multiplexed (WDM) signal in which signal components of a plurality of channels having different wavelengths are multiplexed and superimposed so as not to overlap each other along the time axis. It is also possible to perform wavelength conversion as a time-division multiplexing (TDM) signal. As a method for converting the wavelength of a WDM signal into a TDM signal as described above, for example, wavelength conversion methods described in Non-Patent Documents 1 and 2 are known.

  That is, in Non-Patent Document 1, supercontinuum is generated from an input WDM signal, the spectrum of each channel signal is expanded to an extent that they overlap each other, and then sliced by a filter to form a TDM signal. A method of conversion is described. Further, Non-Patent Document 2 uses a device (electro-absorption modulator: EAM) in which an absorption coefficient for input light decreases with respect to light intensity, and continuous light (CW light: CW light: having a wavelength to be converted to a WDM signal. There is described a TDM conversion method that utilizes a characteristic that a waveform of a WDM signal is copied to the CW light by simultaneously injecting continuous-wave light.

When the input light is intensity modulated light, the output light obtained by wavelength conversion is similarly intensity modulated light. From this, the wavelength conversion device can be used, for example, when converting the wavelength of an optical signal transmitted in an optical network system or an optical transmission system.
JP 10-133240 A Japanese Patent Laid-Open No. 2000-081643 H. Sotobayashi et al., “40Gbit / s photonic packet compression and decompression by supercontinuumgeneration” Electronics Letters, Vol. 37, Issue. 2, pp. 110-111, Jan, 2001. JPR Lacey et al., “All-optical WDM to TDM transmultiplexer,” Electronics Letters, Vol. 30, Issue. 19, pp. 1612-1613, Sep, 1994.

  As a result of examining the conventional wavelength converter, the inventors have found the following problems. In other words, in the conventional wavelength converters described in Patent Documents 1 and 2, when the wavelength of the input light changes, the wavelength of the output light also changes. However, in a wavelength conversion device used in a future optical network system or the like, it may be desirable that the wavelength of the output light is constant even if the wavelength of the input light changes.

  In addition, in the wavelength conversion methods described in Non-Patent Documents 1 and 2, the converted signal waveform is deteriorated. Specifically, in the non-patent document 1, since the signal spectrum has the shape of a filter, the signal waveform greatly depends on the shape of the filter. For this reason, it is necessary to change the filter according to the bit rate and modulation format of the signal. Further, in Non-Patent Document 2, since absorption saturation by electric carriers is used, there is an upper limit in response speed, and when high-speed TDM signal conversion is performed, the signal waveform is easily distorted.

  The present invention has been made in order to solve the above-described problem. A wavelength converter capable of stably and constantly changing the wavelength of output light even if the wavelength of input light changes, and an optical network system including the wavelength converter. And an optical transmission system including the wavelength converter.

  The wavelength conversion device according to the present invention is a wavelength conversion device that generates and outputs output light having a wavelength different from the wavelength of the input light, and includes a first wavelength conversion unit and a second wavelength conversion connected in series with each other. A part. The first wavelength conversion unit generates four-wave mixing using the input light and the first excitation light having a single wavelength, generates intermediate light having a new wavelength by the four-wave mixing, and outputs the intermediate light and the input light. To do. The second wavelength conversion unit generates four-wave mixing by the intermediate light and the input light output from the first wavelength conversion unit, and further by the second excitation light, and output light having a new wavelength generated by the four-wave mixing. Is output.

  In this case, it is preferable that the first wavelength conversion unit includes a first excitation light source, a first nonlinear optical medium, and a first optical filter. The first excitation light source outputs first excitation light. The first nonlinear optical medium generates the four-wave mixing by inputting the first pumping light and the input light output from the first pumping light source, and outputs the intermediate light by the four-wave mixing. The first optical filter selectively transmits intermediate light and input light out of the light output from the first nonlinear optical medium. Similarly, the second wavelength converter preferably includes a second excitation light source, a second nonlinear optical medium, and a second optical filter. The second excitation light source outputs second excitation light. The second nonlinear optical medium generates the four-wave mixing by inputting the intermediate light and the input light output from the first wavelength conversion unit, and further the second excitation light output from the second excitation light source. The output light generated by the four-wave mixing is output. The second optical filter selectively transmits output light out of the light output from the second nonlinear optical medium.

  In the wavelength conversion device according to the present invention, the first wavelength conversion device generates four-wave mixing by the first excitation light including the input light and a plurality of channels, and the first wavelength of the new wavelength generated by the four-wave mixing is generated. It is also possible to output the first intermediate light and the second intermediate light. In this case, the second wavelength conversion device generates four-wave mixing by the first intermediate light and the second intermediate light output from the first wavelength conversion unit, and further by the second excitation light, and is generated by the four-wave mixing. The output light having the new wavelength is output.

  Also in this case, the first wavelength conversion unit includes a first excitation light source, a first nonlinear optical medium, and a first optical filter, and the second wavelength conversion unit includes a second excitation light source, a second nonlinear optical medium, And a second optical filter. The first excitation light source outputs first excitation light. The first nonlinear optical medium generates four-wave mixing by inputting the first pumping light output from the first pumping light source and the input light, and the first intermediate light and the second light generated by the four-wave mixing are generated. Output intermediate light. The first optical filter selectively transmits the first intermediate light and the second intermediate light out of the light output from the first nonlinear optical medium. On the other hand, the second excitation light source outputs second excitation light. The second nonlinear optical medium receives four light waves by inputting the first intermediate light and the second intermediate light output from the first wavelength converter, and further the second excitation light output from the second excitation light source. Mixing is generated, and output light generated by the four-wave mixing is output. The second optical filter selectively transmits output light out of the light output from the second nonlinear optical medium.

  In the wavelength conversion device according to the present invention, the input light is wavelength-converted by the first wavelength conversion unit, and the intermediate light is output from the first wavelength conversion unit. Subsequently, the input wavelength and the intermediate light are further wavelength-converted in the second wavelength converter, and output light is output from the second wavelength converter. By performing the wavelength conversion twice in this way, the wavelength of the output light becomes constant even if the wavelength of the input light is different. In the wavelength converter according to the present invention, it is preferable that the optical frequency fluctuation of the output light is smaller than the optical frequency fluctuation of the input light. The extinction ratio of output light is preferably larger than the extinction ratio of input light.

  The wavelength conversion device according to the present invention can also convert wavelengths of a plurality of channels of WDM signals having different wavelengths as TDM signals of a predetermined wavelength superimposed so as not to overlap each other along the time axis. .

  An optical network system according to the present invention includes N (N is an integer of 2 or more) optical transmission lines, N optical switches, a first optical multiplexer, N optical delay devices, and a second optical multiplexer. A wave converter, a wavelength conversion device having the above-described structure (a wavelength conversion device according to the present invention), and a signal return means. One of the N optical switches is provided in the middle of each of the N optical transmission lines. The first optical multiplexer combines the optical signals that have arrived from each of the N optical switches, and outputs the combined light to a common optical transmission line. Each of the N optical delay devices is provided corresponding to each of the N optical switches, and delays the optical signal that arrives from the corresponding optical switch. The second optical multiplexer multiplexes the optical signals output from the N optical delay devices. The wavelength converter performs wavelength conversion of the combined light output from the second optical multiplexer. The signal return means returns the optical signal output from the wavelength converter to any one of the N optical transmission lines between the N optical switches and the first optical multiplexer, or to the common optical transmission line.

  In the optical network system according to the present invention, the optical signal transmitted through each optical transmission path and reaching the optical switch is switched at the subsequent transmission destination by the optical switch, and the corresponding optical delay unit and first optical multiplexing are switched. Is transmitted to one of the devices. Each optical signal that has reached the first optical multiplexer is multiplexed by the first optical multiplexer, and the combined light is output to a common optical transmission line. The optical signal that has reached the optical delay device is given a predetermined delay by the optical delay device, is then input to the wavelength conversion device, and is output after wavelength conversion. In the wavelength conversion by this wavelength converter, the optical frequency of the output optical signal is constant regardless of the optical frequency of the input optical signal. The optical signal output from the wavelength converter is returned to any one of the N optical transmission lines between the N optical switches and the first optical multiplexer or to the common optical transmission line by the signal return means.

  When wavelength conversion from a WDM signal to a TDM signal is performed using the wavelength conversion device having the above-described structure, the optical network system according to the present invention, together with the wavelength conversion device, transmits WDM signals that appear intermittently in each channel. It is preferable to provide an optical delay device that inputs and delays each channel so as not to overlap each other along the time axis. In the optical network system having such a configuration, the signal delay in the output channel output from the wavelength converter can be increased by adjusting the signal delay by the optical delay device. Further, the signal delay in the output channel output from the wavelength converter can be narrowed by adjusting the signal delay by the optical delay device.

  Furthermore, the optical transmission system according to the present invention includes an optical transmitter, an optical transmission line, an optical receiver, and a wavelength conversion device (wavelength conversion device according to the present invention) having the above-described structure. The optical transmitter transmits an optical signal. In the optical transmission, an optical signal transmitted from an optical transmitter is transmitted. The optical receiver receives an optical signal propagating through an optical transmission line. The wavelength converter is provided immediately after the optical transmitter and performs wavelength conversion of the optical signal transmitted from the optical transmitter. In such an optical transmission system, even if the chirp of the optical signal output from the optical transmitter is large or the extinction ratio is small, the output light from the wavelength converter is chirp-compensated and waveform-shaped. The transmission distance can be extended.

  In the optical transmission system according to the present invention, the wavelength conversion device may be provided in the middle of the optical transmission path. In this case, even if the chirp of the transmitted optical signal is large or the extinction ratio is small, the output light from the wavelength converter is chirp compensated and the waveform is shaped, so that the signal transmission distance can be extended.

  According to the wavelength converter according to the present invention, the wavelength of the output light can be made constant even when the wavelength of the input light changes.

  Hereinafter, embodiments of the wavelength conversion device, the optical network system, and the optical transmission system according to the present invention will be described in detail with reference to FIGS. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment of wavelength converter)
First, a first embodiment of a wavelength conversion device according to the present invention will be described. FIG. 1 is a diagram showing a configuration of a first embodiment of a wavelength conversion device according to the present invention. The wavelength conversion device 100 according to the first embodiment inputs input light to the incident end 101 and outputs output light having a wavelength different from the wavelength of the input light from the emission end 102. The wavelength conversion device 100 includes a first wavelength conversion unit 110 and a second wavelength conversion unit 120 that are arranged in series between the incident end 101 and the output end 102.

  The first wavelength conversion unit 110 generates four-wave mixing by the input light and the first excitation light, generates intermediate light having a new wavelength by the four-wave mixing, and outputs the intermediate light and the input light. More specifically, the first wavelength conversion unit 110 includes a first excitation light source 111, a first optical coupler 112, a first optical amplifier 113, a first nonlinear optical medium 114, and a first optical filter 115.

The first excitation light source 111 outputs first excitation light having an optical frequency f _pump1 . The first optical coupler 112 multiplexes the input light having the optical frequency f ₀ input through the input terminal 101 and the first excitation light output from the first excitation light source 111. The first optical amplifier 113 receives the input light and the first pump light combined by the first optical coupler 112, and amplifies the input light and the first pump light.

The first nonlinear optical medium 114 generates four-wave mixing by inputting the input light amplified by the first optical amplifier 113 and the first excitation light, and the intermediate light having the optical frequency f ₁ generated by the four-wave mixing. Is output. The first optical filter 115 selectively transmits intermediate light and input light out of the light output from the first nonlinear optical medium 114.

  On the other hand, the second wavelength conversion unit 120 generates four-wave mixing by the intermediate light and input light output from the first wavelength conversion unit 110, and further by the second excitation light, and a new wavelength generated by the four-wave mixing. Output light. More specifically, the second wavelength conversion unit 120 includes a second excitation light source 121, a second optical coupler 122, a second optical amplifier 123, a second nonlinear optical medium 124, and a second optical filter 125.

The second excitation light source 121 outputs second excitation light having an optical frequency f _pump2 . The second optical coupler 122 multiplexes the intermediate light and input light output from the first wavelength conversion unit 110 and the second pumping light output from the second pumping light source 121. The second optical amplifier 123 receives the intermediate light, the input light, and the second pump light combined by the second optical coupler 122, and amplifies the intermediate light, the input light, and the second pump light.

The second nonlinear optical medium 124 receives the intermediate light, the input light, and the second excitation light that are optically amplified by the second optical amplifier 123, and performs four-wave mixing using the intermediate light, the input light, and the second excitation light. And output light having an optical frequency f ₂ generated by the four-wave mixing is output. The second optical filter 125 selectively transmits output light among the light output from the second nonlinear optical medium 124.

  For each of the first optical amplifier 113 and the second optical amplifier 123, for example, an Er element-doped optical fiber amplifier in which an optical fiber in which an Er element is added to the optical waveguide region is used as an optical amplification medium is suitable. For each of the first nonlinear optical medium 114 and the second nonlinear optical medium 124, for example, an optical fiber having a high nonlinear optical coefficient γ is suitable. The first optical amplifier 113 amplifies each optical component input to the first nonlinear optical medium 114 with a high gain so that four-wave mixing occurs in the first nonlinear optical medium 114 with sufficient efficiency. Similarly, the second optical amplifier 123 amplifies each optical component input to the second nonlinear optical medium 124 with a high gain so that four-wave mixing occurs in the second nonlinear optical medium 124 with sufficient efficiency.

FIG. 2 is a diagram for explaining an arrangement relationship of each optical frequency in the wavelength conversion device 1 according to the first embodiment. In the first wavelength converter 110, the optical frequency _{f 0} of the input light, between the optical frequency _{f PUMP1} of the optical frequency _{f 1} and the first excitation light of the intermediate light, FIG. 2 (a) and the following formula (1) There is a relationship represented by That is, the first wavelength conversion unit 110 outputs intermediate light having the optical frequency f ₁ generated by degenerate four-wave mixing.

On the other hand, the second wavelength converter 120, the optical frequency _{f 0} of the input light, the optical frequency _{f 1} of the intermediate light, between the optical frequency _{f Pump2} of the output light of the optical frequency _{f 2} and the second excitation light, 2 There is a relationship represented by (b) and the following equation (2). That is, the second wavelength conversion unit 120 outputs the output light having the optical frequency f ₂ generated by the non-degenerate four-wave mixing.

Substituting the above equation (1) into the above equation (2) yields the following equation (3). As seen from this equation (3), the optical frequency _{f 2} of the output light is independent of the optical frequency _{f 0} of the input light, the first excitation light optical frequency _{f PUMP1} and the second excitation light of the light frequency _{f Pump2} Depends only on.

  As described above, the wavelength conversion device 100 according to the first embodiment keeps the wavelength of the output light output through the output terminal 102 constant even when the wavelength of the input light input through the input terminal 101 changes. Can be.

FIG. 3 is a diagram for explaining one usage example of the wavelength conversion device 100 according to the first embodiment. FIG. 3A shows the arrangement relationship of the optical frequencies, and FIG. 3B shows how the signals are multiplexed. The input light component input through the input terminal 101 of the wavelength conversion device 100 is one of the optical frequencies f ₀₁ , f ₀₂ and f ₀₃ . Further, the input light components of the optical frequencies f ₀₁ , f ₀₂ and f ₀₃ are input via the input terminal 101 during a certain period, such as a burst signal, but are not input during other periods. . Furthermore, it is assumed that two or more light components of the input light components of the optical frequencies f ₀₁ , f ₀₂ and f ₀₃ are not input simultaneously. In this case, the wavelength converter 100, wavelength-converted input light components of each optical frequency input through the input terminal 101 multiplexes all these as output light having a constant optical frequency f _2. The output light multiplexed in this way is output via the output terminal 102.

  Further, the wavelength conversion device 100 according to the first embodiment can compensate the chirp of the input light and shape the waveform together with the wavelength conversion. FIG. 4 is a diagram for explaining chirp compensation and waveform shaping in the wavelength conversion device 100 according to the first embodiment. FIG. 4A shows temporal changes in the light intensity and optical frequency of input light input via the input terminal 101. FIG. 4B shows temporal changes in the light intensity and the optical frequency of the intermediate light output from the first wavelength conversion unit 110. FIG. 4C shows temporal changes in the light intensity and the optical frequency of the output light output from the output terminal 102.

  When the input light input through the input terminal 101 is, for example, laser light output from a laser diode that is driven by direct modulation, the input light includes pulse rise and pulse as shown in FIG. In addition to the transient chirp phenomenon in which the optical frequency fluctuates at each falling, the adiabatic chirp phenomenon in which the optical frequency varies depending on the light intensity level. By using self-phase modulation, transient chirp can be compensated, but adiabatic chirp cannot be compensated.

  However, in the wavelength conversion device 100 according to the first embodiment, as shown in FIG. 4B, the chirp distribution of the intermediate light is in a state where the chirp distribution of the input light is inverted. Then, as shown in FIG. 4C, the chirp distribution of the output light is in a state where the chirp distributions of the input light and the intermediate light are offset from each other. As described above, the output light output through the output end 102 is an optical component in which the chirp of the input light input through the input end 101 is compensated. Therefore, the optical frequency variation of the output light is smaller than the optical frequency variation of the input light.

  Further, as shown in FIGS. 4A and 4B, the waveform of the intermediate light is similar to the waveform of the input light that is the source of the generation. Then, as shown in FIG. 4C, the waveform of the output light is represented by the product of the waveforms of the input light and the intermediate light that are the sources of the generation. Therefore, the output light output through the output end 102 is a light component in which the waveform of the input light input through the input end 101 is shaped. From this, the extinction ratio of output light becomes larger than the extinction ratio of input light.

  As described above, the chirp is compensated and the signal waveform is shaped, so that the transmission distance can be greatly extended even in an optical transmission system using a laser diode driven by direct modulation.

(Second embodiment of wavelength converter)
Next, a second embodiment of the wavelength conversion device according to the present invention will be described. FIG. 5 is a diagram showing the configuration of the second embodiment of the wavelength conversion device according to the present invention. The wavelength conversion device 200 according to the second embodiment inputs input light via the incident end 201 and outputs output light having a wavelength different from the wavelength of the input light via the emission end 202. The wavelength conversion device 200 includes a first wavelength conversion unit 210 and a second wavelength conversion unit 220 that are arranged in series between the incident end 201 and the emission end 202.

  The first wavelength conversion unit 210 generates four-wave mixing using the input light and the first excitation light, and outputs first intermediate light and second intermediate light having new wavelengths generated by the four-wave mixing. More specifically, the first wavelength conversion unit 210 includes a first excitation light source 211, a first optical coupler 212, a first optical amplifier 213, a first nonlinear optical medium 214, and a first optical filter 215.

The first excitation light source 211 outputs the excitation light components of the optical frequency f _pump11 and the optical frequency f _pump12 as the first excitation light. The first optical coupler 212 multiplexes the input light having the optical frequency f ₀ input via the input terminal 201 and the first excitation light having two wavelengths output from the first excitation light source 211. The first optical amplifier 213 receives the input light and the first excitation light combined by the first optical coupler 212 and amplifies the input light and the first excitation light.

The first nonlinear optical medium 214 generates four-wave mixing by inputting the input light amplified by the first optical amplifier 213 and the first pumping light having two wavelengths, and the optical frequency f ₁₁ generated by the four-wave mixing. outputting a first intermediate light and the second intermediate light of optical frequency f ₁₂ of the. The first optical filter 215 selectively transmits the first intermediate light and the second intermediate light among the light output from the first nonlinear optical medium 214.

  The second wavelength conversion unit 220 generates four-wave mixing by the first intermediate light and the second intermediate light output from the first wavelength conversion unit 210, and further by the second excitation light, and a new light generated by the four-wave mixing is generated. Outputs output light with various wavelengths. More specifically, the second wavelength conversion unit 220 includes a second excitation light source 221, a second optical coupler 222, a second optical amplifier 223, a second nonlinear optical medium 224, and a second optical filter 225.

The second excitation light source 221 outputs the second excitation light having the optical frequency f _pump2 . The second optical coupler 222 receives the first intermediate light and the second intermediate light output from the first wavelength conversion unit 210, and further the second excitation light output from the second excitation light source 221. The intermediate light, the second intermediate light, and the second excitation light are combined. The second optical amplifier 223 inputs the first intermediate light, the second intermediate light, and the second excitation light combined by the second optical coupler 222, and the first intermediate light, the second intermediate light, and the second excitation light. Amplify light.

The second nonlinear optical medium 224 generates four-wave mixing by inputting the first intermediate light, the second intermediate light, and the second excitation light amplified by the second optical amplifier 223, and is generated by the four-wave mixing. Output light of optical frequency f ₂ is output. The second optical filter 225 selectively transmits output light among the light output from the second nonlinear optical medium 224.

  For each of the first optical amplifier 213 and the second optical amplifier 223, for example, an Er element-doped optical fiber amplifier in which an optical fiber in which an Er element is added to an optical waveguide region is applied to an optical amplification medium is suitable. For each of the first nonlinear optical medium 214 and the second nonlinear optical medium 224, for example, an optical fiber having a high nonlinear optical coefficient γ is suitable. The first optical amplifier 213 amplifies each signal to be input to the first nonlinear optical medium 214 with high gain so that four-wave mixing occurs with sufficient efficiency in the first nonlinear optical medium 214. Similarly, the second optical amplifier 223 amplifies each signal input to the second nonlinear optical medium 224 with a high gain so that four-wave mixing occurs in the second nonlinear optical medium 224 with sufficient efficiency.

FIG. 6 is a diagram for explaining an arrangement relationship of each optical frequency in the wavelength conversion device 2 according to the second embodiment. In the first wavelength conversion unit 210, the optical frequency f ₀ of the input light, the optical frequency f ₁₁ of the first intermediate light, the optical frequency f ₁₂ of the second intermediate light, and the optical frequencies f _pump11 and f _{pump12 of} the first pumping light. There is a relationship represented by FIG. 6A and the following equation (4). That is, the first wavelength conversion unit 210 outputs intermediate light having an optical frequency f ₁ generated by degenerate four-wave mixing.

On the other hand, in the second wavelength converter 220, the optical frequency _{f 11} of the first intermediate optical, optical frequency _{f 12} of the second intermediate light, between the optical frequency _{f Pump2} optical frequency _{f 2} and a second pumping light of the output light Has a relationship represented by FIG. 6B and the following equation (5). That is, the second wavelength conversion unit 220 outputs output light having an optical frequency f ₂ generated by non-degenerate four-wave mixing.

Substituting the above equation (4) into the above equation (5) yields the following equation (6). As can be seen from this equation (6), the optical frequency f ₂ of the output light does not depend on the optical frequency f ₀ of the input light, and the optical frequencies f pump ₁₁ and f _{pump 12} of the first pump light and the light of the second pump light. It depends only on the frequency f _pump2 .

  The wavelength conversion device 200 according to the second embodiment has the following effects in addition to the same effects as the effects of the wavelength conversion device 100 according to the first embodiment described above. That is, in the wavelength conversion device 100 according to the first embodiment, since the input light is used in the second wavelength conversion unit 120, the output light wavelength cannot be the same as the input light wavelength. In contrast, in the wavelength conversion device 200 according to the second embodiment, since the input light is not used in the second wavelength conversion unit 220, the output light wavelength can be made the same as the input light wavelength.

(First embodiment of optical network system)
Next, a first embodiment of the optical network system according to the present invention will be described. FIG. 7 is a diagram showing the configuration of the first embodiment of the optical network system according to the present invention. The optical network system 1 according to the first embodiment includes N optical transmission lines 11 _{1 to} 11 _N , N optical switches 12 _{1 to} 12 _N , a first optical multiplexer 13, and N optical delay devices 14. comprising ₁ to 14 _N, a second optical multiplexer 15, the wavelength converter 16, an optical coupler 17 and an optical transmission path 18. Here, N is an integer of 2 or more, and n appearing later is an arbitrary integer of 1 or more and N or less.

Each optical transmission line 11 _n transmits an optical signal having an optical frequency f _0n . Each optical switch 12 _n is provided in the optical transmission line 11 _n, the optical signal of the optical frequency f _0n which has propagated through the optical transmission line 11 _n inputs, each optical signal the first optical multiplexer 13 and outputs either to one of the optical delay 14 _n. First optical multiplexer 13, an optical signal multiplexes having propagated through the optical transmission path 11 ₁ to 11 _N respectively the N and outputs the multiplexed light to a common optical transmission path 18.

Each optical delay device 14 _n gives a delay to each optical signal arrived from the corresponding optical switch 12 _n . The second optical multiplexer 15 multiplexes the optical signals output from the _N optical delay devices 14 _{1 to} 14 _N. Wavelength converter 16 performs a wavelength conversion of the multiplexed light output from the second optical multiplexer 15, and outputs the optical signal of the optical frequency f ₂ obtained by the wavelength change. As the wavelength conversion device 16, the wavelength conversion devices 100 and 200 according to the first embodiment or the second embodiment described above are used. The optical coupler 17 returns the optical signal output from the wavelength converter 16 to the common optical transmission line 18.

The optical network system 1 operates as follows. The optical signal having the optical frequency f _0n arriving at the optical switch 12 _n via each optical transmission line 11 _n is switched to the subsequent transmission destination by the optical switch 12 _n , and the corresponding optical delay device 14 _n and the first optical coupling are transmitted. It is transmitted to either one of the wave filters 13. The respective optical signals that have reached the first optical multiplexer 13 are multiplexed by the first optical multiplexer 13, and the combined light is output to the optical transmission line 18.

Optical signal reaching the optical delay device 14 _n, after the predetermined delay is given by the optical delay device 14 _n, it is wavelength-converted in the wavelength conversion device 16. The wavelength conversion by the wavelength converter 16, regardless of the optical frequency of the input signal, the optical frequency f ₂ of the output signal is constant. The optical signal output from the wavelength converter 16 is returned to the optical transmission line 18 by the optical coupler 17.

As described above, the optical network system 1 according to the first embodiment includes the wavelength conversion device 16 having the same configuration as the wavelength conversion devices 100 and 200 according to the first embodiment or the second embodiment described above. The wavelength conversion device 16 can multiplex optical signals having different wavelengths into signals having a certain wavelength. Note that the optical signal output from the wavelength converter 16 may be returned to the optical transmission line 11 _n between the optical switch 12 _n and the first optical multiplexer 13.

(Second Embodiment of Optical Network System)
The wavelength converters 100 and 200 according to the first and second embodiments described above perform wavelength conversion so that the optical frequency (wavelength) of output light does not depend on the optical frequency (wavelength) of input light. It is said. For example, in the first wavelength conversion device 100, the first wavelength conversion unit 110 generates four-wave mixing with the first excitation light with respect to the input light, and outputs the intermediate light and the input light generated by the four-wave mixing. . Subsequently, in the second wavelength conversion unit 120, the four-wave mixing is generated again by the intermediate light and the input light output from the first wavelength conversion unit 110, and further by the second excitation light. 2 Intermediate light (output light) is output.

  What can be said from this feature is that when the input signal (input light) is a WDM signal in which signals of a plurality of channels having different wavelengths are multiplexed, which signal component (wavelength) is used by using the wavelength converters 100 and 200. Component) is also converted to a specific wavelength. As an example utilizing this feature, it has already been described that wavelength resources can be made highly efficient by converting burst signals having different wavelengths into one specific wavelength (see FIG. 3).

However, the wavelength converters 100 and 200 according to the first and second embodiments can be applied to CW signals that are transmitted in a steady manner instead of in a burst form. FIG. 8 shows an example in which wavelength conversion is performed on a pulse signal train of a plurality of channels having different wavelengths. 8A is similar to the above-described FIG. 3A, the input optical signal of the optical frequencies f ₀₁ , f ₀₂ , f ₀₃ and f ₀₄ , the output signal of the optical frequency f ₂ , and the optical frequency f The arrangement _| positioning relationship of the excitation light component of _pump1 and _fpump2 is shown.

Signals of each channel (optical frequency _{f 01, f 02, f 03} and _{f 04),} as shown in FIG. 8 (b), has a specific bit rate, one bit period determined by the bit rate ( It is a pulse-like signal that is narrower than T _b ). These input signals are adjusted in timing so that they do not overlap each other before the WDM multiplexing. After WDM multiplexing in this state, when wavelength conversion is performed by the wavelength converters 100 and 200 according to the first embodiment and the second embodiment, all converted pulses are arranged on the same time axis without overlapping. Therefore (the output signal of the optical frequency f ₂ shown in FIG. 8B), the WDM signal is converted into a TDM signal.

  In the above description, application to a 4-channel WDM signal has been described. However, the number of signal channels is not particularly limited as long as it is 2 channels or more. In FIG. 8, the bit rates of the signal channels are all the same, but different bit rates may be used between the signal channels as long as the period of all the pulse trains satisfies the relationship of an integral multiple of a specific value. Good.

The wavelength conversion from the WDM signal to the TDM signal as described above can be realized by an optical network system having a configuration as shown in FIG. FIG. 9 is a diagram showing the configuration of the second embodiment of the optical network system according to the present invention. The optical network system 1A according to the second embodiment includes N optical transmission lines 11 _{1 to} 11 _{N through} which signals of respective channels propagate, N optical delay devices 14 _{1 to} 14 _N , and N optical signals. Amplifiers 19 _{1 to} 19 _N , an optical multiplexer 15, and a wavelength converter 16 are provided. Note that any of the wavelength conversion devices 100 and 200 according to the first embodiment and the second embodiment can be applied to the wavelength conversion device 16.

In the optical network system ₁ </ b> A according to the second embodiment, before the optical signal multiplexer 15 multiplexes the pulse-like signal sequence that has propagated through the _N transmission lines 11 _{1 to} 11 _N , the optical delay device 14 _1. The timing is adjusted so as not to overlap each other by ˜14 _N. Thereafter, these timing-adjusted signals are wavelength-multiplexed by the optical multiplexer 15, and the combined light (WDM signal) is converted into a TDM signal by the wavelength converter 16. Since it is necessary to increase the power of each signal before it is input to the wavelength converter 16, optical amplifiers 19 _{1 to} 19 _N are arranged between the optical delay devices 14 _{1 to} 14 _N and the optical multiplexer 15. Has been. The optical amplifier may be disposed between the multiplexer 15 and the wavelength conversion device 16. In particular, as shown in FIG. 9, when the optical amplifiers 19 _{1 to} 19 _N are arranged immediately before the optical multiplexer 15, optical noise generated in these optical amplifiers 19 _{1 to} 19 _N is generated in the optical multiplexer 15. Since it is removed, it is preferable. Furthermore, since it is necessary to narrow the pulse width of each signal so as not to overlap, the waveform shaping may be performed using a short fiber or the like.

  As described above, in the conversion from the WDM signal to the TDM signal, the frequency resources can be effectively used by collecting the signals having a relatively low bit rate from the terminal into one channel and sending them to the trunk network. Such a technology can be an important technology in the future, but when the signal has a very high bit rate such as 160 Gbit / s, high-speed signal generation by electrical means is impossible, and by optical means. Signal generation is powerful.

  Several examples of WDM / TDM conversion in all signal channels have been reported. One is to generate supercontinuum, which broadens the spectrum of each pulse so as to overlap each other, and then overlaps each other. Is a conversion method for obtaining a TDM signal by cutting out the signal with a filter. The details are described in Non-Patent Document 1 described above, but the signal waveform after conversion largely depends on the characteristics of the filter to be cut out, so it is necessary to change the filter to be used depending on the signal.

  Further, as another example, by inputting a CW light having a specific wavelength simultaneously with a pulsed WDM signal to a medium having a characteristic that an absorption coefficient decreases with respect to the intensity of the input light, the WDM signal is incident on the CW light. A conversion method using copying of the shape is also conceivable. The details are described in Non-Patent Document 2 described above. However, since the saturation characteristic of absorption by an electric carrier is used, the influence of the electric band limitation is not a little. It will be distorted.

  In contrast to the conversion methods described in Non-Patent Documents 1 and 2, in the wavelength conversion device according to the present invention, since the filter is only used to block unnecessary signals, the band of the filter is sufficiently wide for the signals. Will have no effect. Further, since the TDM signal is generated without using electrical means, there is no electrical speed limitation.

  Furthermore, very high bit rate signals such as 160 Gbit / s have very low dispersion tolerance. In addition, if a chirp remains in the signal, even a small amount of dispersion may be distorted greatly. On the other hand, the wavelength converter according to the present invention also has an effect of compensating for chirp, so that it is possible to generate a TDM signal having a relatively high dispersion tolerance.

(First Embodiment of Optical Transmission System)
Next, a first embodiment of the optical transmission system according to the present invention will be described. FIG. 10 is a diagram showing the configuration of the first embodiment of the optical transmission system according to the present invention. The optical transmission system 2 according to the first embodiment includes optical transmission paths 23 ₁ to 23 _M , optical amplifiers 24 _{1 to} 24 _M, and wavelength conversion, which are sequentially arranged between an optical transmitter 21 and an optical receiver 22. A device 25 is provided. M is an integer of 2 or more. As the wavelength conversion device 25, the wavelength conversion devices 100 and 200 according to the first embodiment or the second embodiment described above are used.

The optical signal output from the optical transmitter 21 is wavelength-converted by a wavelength conversion device 25 provided immediately after the optical transmitter 21. The optical signal output from the wavelength converter 25, the optical transmission line ₂₃ 1 ~ 23 _M propagated, after being amplified by the optical amplifier ₂₄ 1 to 24 _M provided in the middle, received by the optical receiver 22 Is done.

  As described above, the wavelength converter 25 can perform chirp compensation and waveform shaping of the optical signal output from the optical transmitter 21. Therefore, even when the chirp of the optical signal output from the optical transmitter 21 is large or the extinction ratio is small, as in the case where a direct-modulation drive laser diode is applied to the optical transmitter 21, the wavelength conversion device Since the optical signal output from 25 is chirp-compensated and waveform-shaped, the optical transmission system 2 according to the first embodiment can extend the signal transmission distance.

(Second Embodiment of Optical Transmission System)
Next, a second embodiment of the optical transmission system according to the present invention will be described. FIG. 11 is a diagram showing the configuration of the second embodiment of the optical transmission system according to the present invention. The optical transmission system according to the second embodiment 3, arranged in this order between the optical transmitter 31 and optical receiver 32, the optical transmission path ₃₃ to 333 _4, the optical amplifier ₃₄ 1 to 34 ₄ and the wavelength converting A device 35 is provided. As the wavelength converter 35, the wavelength converters 100 and 200 according to the first embodiment or the second embodiment described above are used.

Optical signal output from the optical transmitter 31, after the optical transmission path ₃₃ to 333 ₄ propagated and amplified by the optical amplifier ₃₄ 1 to 34 ₄ provided in the middle, is received in the optical receiver 32 The The optical signal transmitted from the optical transmitter 31 to the optical receiver 32 is wavelength-converted by a wavelength converter 35 provided in the middle of the optical transmission path between the optical transmitter 31 and the optical receiver 32.

  As described above, the wavelength converter 35 can perform chirp compensation and waveform shaping of the optical signal that has propagated through the optical transmission line. Therefore, even when the chirp of the transmitted optical signal is large or the extinction ratio is small as in the case where a laser diode of direct modulation drive is applied to the optical transmitter 31, Even when a modulator is applied, even if a chirp is generated due to a nonlinear effect (for example, self-phase modulation or cross-phase modulation) in the transmission path on the way, it is output from the wavelength converter 35. The optical signal is chirp compensated and waveform shaped. Therefore, the optical transmission system 3 according to the second embodiment can also extend the signal transmission distance.

  The chirp possessed by the optical signal generally causes the signal waveform to deteriorate due to the chromatic dispersion of the optical transmission line. However, if the chromatic dispersion of the optical transmission line is negative, the waveform of the optical signal may be sharpened, which may contribute to an improvement in reception sensitivity in the optical receiver 32. However, even if the chromatic dispersion of the optical transmission line is negative, if the absolute value of the chromatic dispersion is too large, the signal waveform deteriorates.

Therefore, the wavelength dispersion of the optical transmission path 33 _1, 33 ₂ between the optical transmitter 31 and the wavelength conversion device 35 is a negative, moderately improved chirp of optical signals by this period of the optical transmission path 33 _1, 33 ₂ It is preferable to keep it. If the chirp of the optical signal is subsequently removed by the wavelength converter 35, the signal waveform can be prevented from deteriorating and the signal transmission distance can be extended.

Further, in order to suppress the deterioration of the signal waveform due to the nonlinear optical phenomenon, the optical signal is transmitted by the phase modulator 36 provided immediately after the optical transmitter 31 as in the optical transmission system 3A shown in FIG. You may deliberately give a chirp. FIG. 12 is a diagram illustrating a configuration of a modification of the optical transmission system according to the second embodiment. Also in this case, if the chirp of the optical signal is appropriately improved by the optical transmission paths 33 ₁ and 33 _{2 and then} the chirp of the optical signal is removed by the wavelength conversion device 35, the deterioration of the signal waveform can be suppressed. Transmission distance can be extended.

Next, a more specific embodiment of the wavelength conversion device according to the present invention will be described. FIG. 13 is a diagram showing the configuration of a specific example of the wavelength converter according to the present invention. The wavelength conversion device 300 shown in FIG. 13 has a configuration equivalent to the configuration of the wavelength conversion device 100 according to the first embodiment described above. The wavelength conversion device 300 is used together with the signal light source 330. This signal light source 330 includes a laser diode of 2.5 Gb / s direct modulation drive, and outputs an optical signal having an optical frequency f ₀ = 193.4 THz.

  The wavelength converter 300 includes a first pumping light source 311, a first optical coupler 312, a first optical amplifier 313, a first nonlinear optical medium 314, as components corresponding to the first wavelength converting unit 110 in the first embodiment. Optical couplers 315a and 315b and optical filters 315c and 315d are provided.

The first excitation light source 311 outputs the first excitation light having an optical frequency f _pump1 = 193.8 THz. The first optical coupler 312 multiplexes the optical signal output from the signal light source 330 and the first excitation light output from the first excitation light source 311. The first optical amplifier 313 receives the optical signal combined with the first optical coupler 312 and the first pumping light, and amplifies the optical signal and the first pumping light. The first optical amplification receiver 313 outputs amplified light having a power of 17 dBm.

The first nonlinear optical medium 314 generates four-wave mixing by inputting the optical signal amplified by the first optical amplifier 313 and the first pumping light, and the optical frequency f ₁ = 194 generated by the four-wave mixing. Outputs 2 THz intermediate light. As the first nonlinear optical medium 314, a highly nonlinear optical fiber having a length of 500 m is used.

The optical couplers 315a and 315b and the optical filters 315c and 315d constitute a first optical filter. The optical coupler 315a splits the light output from the first nonlinear optical medium 314 into two, outputs one of the branched light to the optical filter 315c, and outputs the other to the optical filter 315d. Optical filter 315c, of the light having arrived from the optical coupler 315a, for selectively transmitting the optical signal of the optical frequency f _0. The optical filter 315d selectively transmits the intermediate light having the optical frequency f ₁ out of the light reaching from the optical coupler 315a. The optical filters 315c and 315d have a transmission bandwidth approximated by a 2nd super-Gaussian function, as well as having a transmission bandwidth of 75 GHz. The optical coupler 315b combines the optical signal transmitted through the optical filter 315c and the intermediate light transmitted through the optical filter 315d.

  In addition, the wavelength conversion device 300 includes, as components corresponding to the second wavelength conversion unit 120 in the first embodiment, a second excitation light source 321, a second optical coupler 322, a second optical amplifier 323, and a second nonlinear optical medium. 324 and a second optical filter 325.

Second pumping light source 321 outputs a second excitation light optical frequency _{f pump2} = 194.0THz. The second optical coupler 322 combines the intermediate light and the optical signal output from the optical coupler 315b with the second pumping light output from the second pumping light source 321. The second optical amplifier 323 amplifies the intermediate light and the optical signal combined by the second optical coupler 322, and further the second pumping light. The second optical amplifier 323 outputs amplified light having a power of 15 dBm.

The second nonlinear optical medium 324 receives the intermediate light amplified by the second optical amplifier 323, the optical signal, and the second pumping light to generate four-wave mixing, and the optical frequency f ₂ generated by the four-wave mixing. = Output light of 193.6 THz. The second nonlinear optical medium 324 is a highly nonlinear optical fiber having a length of 500 m. The second optical filter 325 is an optical component that selectively transmits output light out of the light output from the second nonlinear optical medium 324, has a transmission bandwidth of 75 GHz, and is approximated by a 2nd super-Gaussian function. Transmission characteristics.

FIG. 14 shows an optical spectrum in the wavelength converter 300 shown in FIG. FIG. 14A shows a spectrum of light output from the first nonlinear optical medium 314. FIG. 14B shows a spectrum of light output from the second nonlinear optical medium 324. As this was shown in FIG. 14, the light output from the first nonlinear optical medium 314, in addition to the first pump light component of the signal components and the optical frequency f _PUMP1 optical frequency f _0, the optical frequency f ₁ Of intermediate light components. The light output from the second nonlinear optical medium 324 includes an optical frequency f in addition to the signal component at the optical frequency f ₀ , the intermediate light component at the optical frequency f ₁ , and the second excitation light component at the optical frequency f _pump2 . ₂ output light components are included.

FIG. 15 is a graph showing the waveform of each signal and the optical frequency variation in the wavelength conversion device 300 shown in FIG. FIG. 15A shows the waveform and optical frequency variation of the optical signal having the optical frequency f ₀ output from the signal light source 330. FIG. 15B shows the waveform and optical frequency variation of the intermediate light having the optical frequency f ₁ output from the optical coupler 315b. FIG. 15C shows the waveform of the output light of the optical frequency f ₂ output from the optical filter 325 and the optical frequency fluctuation. As shown in FIG. 15, the optical signal output from the signal light source 330 has an extinction ratio of 7.5 dB, and both transient chirp and adiabatic chirp are recognized. The intermediate light has the same extinction ratio as that of the optical signal, but the chirp is inverted compared to the optical signal. The output light has a reduced intensity low level to improve the extinction ratio, and adiabatic chirp is suppressed.

  FIG. 16 is an eye pattern of an optical signal after transmission in the optical transmission system using the wavelength conversion device 300 shown in FIG. FIG. 16A shows an eye pattern of an optical signal after an optical signal output from a direct modulation drive laser diode is directly transmitted through a single-mode optical fiber having a length of 150 km without using the wavelength converter 300. . FIG. 16B shows the light after the optical signal output from the direct modulation drive laser diode is wavelength-converted and chirp-compensated by the wavelength converter 300 and transmitted through a single-mode optical fiber having a length of 150 km. It is an eye pattern of a signal. As can be seen from FIG. 16, when the optical signal is chirp-compensated by the wavelength converter 300, the waveform deterioration of the optical signal after being transmitted through the optical fiber having a length of 150 km is suppressed.

  According to the wavelength conversion device of the present invention, the wavelength of the output light can be made constant even when the wavelength of the input light changes, and can be applied to an optical network system or an optical transmission system.

It is a figure which shows the structure of 1st Embodiment of the wavelength converter which concerns on this invention. It is a figure for demonstrating the arrangement | positioning relationship of each optical frequency in the wavelength converter which concerns on 1st Embodiment. It is a figure for demonstrating the usage example of the wavelength converter which concerns on 1st Embodiment. It is a figure for demonstrating chirp compensation and waveform shaping in the wavelength converter which concerns on 1st Embodiment. It is a figure which shows the structure of 2nd Embodiment of the wavelength converter which concerns on this invention. It is a figure for demonstrating the arrangement | positioning relationship of each optical frequency in the wavelength converter which concerns on 2nd Embodiment. 1 is a diagram showing a configuration of a first embodiment of an optical network system according to the present invention. FIG. It is a figure for demonstrating concretely the wavelength conversion from a WDM signal to a TDM signal. FIG. 3 is a diagram showing a configuration of a second embodiment of an optical network system according to the present invention. It is a figure which shows the structure of 1st Embodiment of the optical transmission system concerning this invention. It is a figure which shows the structure of 2nd Embodiment of the optical transmission system which concerns on this invention. It is a figure which shows the structure of the modification of the optical transmission system which concerns on 2nd Embodiment. It is a figure which shows the structure of the specific example of the wavelength converter which concerns on this invention. It is an optical spectrum in the wavelength converter shown by FIG. It is a graph which shows the waveform of each signal channel and the optical frequency fluctuation | variation in the wavelength converter shown by FIG. It is an eye pattern of the optical signal after transmission in the optical transmission system using the wavelength converter shown in FIG.

Explanation of symbols

1 ... optical network system, 2,3,3a ... optical transmission _{system, 11 1 ~11 N, 18,23 1} ~23 M, 33 1 ~33 4 ... optical transmission line, ₁₂ 1 to 12 N _... optical switch, 13 ... first optical multiplexer, ₁₄ 1 to 14 N _... optical delay device, 15 ... second optical multiplexer, 16,25,35,100,200,300 ... wavelength converter, 17 ... optical coupler, 21 and 31 ... Optical transmitter, 22, 32 ... Optical receiver, 19 ₁ , 19 ₂ , to 19 _N , 24 _{1 to} 24 _M , 34 _{1 to} 34 ₄ ... Optical amplifier, 36 ... Phase modulator, 101, 201 ... Incident end , 102, 202 ... emitting end, 110, 210 ... first wavelength converter, 111, 211, 311 ... first excitation light source, 112, 212, 312 ... first optical coupler, 113, 213, 313 ... first light Amplifier 114, 214, 314 ... first nonlinear Shape optical medium, 115, 215 ... first optical filter, 120, 220 ... second wavelength conversion unit, 121, 221, 321 ... second excitation light source, 122, 222, 322 ... second optical coupler, 123, 223, 323... Second optical amplifier 124 224 324 Second nonlinear optical medium 125 225 325 Second optical filter 315a 315b Optical coupler 315c 315d Optical filter 330 Signal light source

Claims (14)

A wavelength converter that outputs output light having a wavelength different from the wavelength of input light,
A first wavelength conversion unit that generates four-wave mixing by input light and first excitation light of a single wavelength, generates intermediate light of a new wavelength by the four-wave mixing, and outputs the intermediate light together with the input light; ,
Second light is generated by the four-wave mixing by the intermediate light and the input light output from the first wavelength conversion unit, and further by the second excitation light, and output light having a new wavelength generated by the four-wave mixing is output. The wavelength converter provided with the wavelength converter. The first wavelength conversion unit generates four-wave mixing by inputting a first excitation light source that outputs the first excitation light, and the first excitation light and the input light output from the first excitation light source. A first nonlinear optical medium that outputs the intermediate light generated by the four-wave mixing, and a first that selectively transmits the intermediate light and the input light among the lights output from the first nonlinear optical medium. Including an optical filter,
The second wavelength conversion unit outputs a second excitation light source that outputs the second excitation light, the intermediate light and the input light that are output from the first wavelength conversion unit, and further, is output from the second excitation light source. The second excitation light is input to generate four-wave mixing, and the second nonlinear optical medium that outputs the output light generated by the four-wave mixing, and the light output from the second nonlinear optical medium The wavelength conversion device according to claim 1, further comprising a second optical filter that selectively transmits the output light. A wavelength converter that outputs output light having a wavelength different from the wavelength of input light,
A first wavelength conversion unit that generates four-wave mixing using input light and first excitation light including a plurality of channels, and outputs first intermediate light and second intermediate light having new wavelengths generated by the four-wave mixing;
Four-wave mixing is generated by the first intermediate light and the second intermediate light output from the first wavelength conversion unit, and further by the second excitation light, and output light having a new wavelength generated by the four-wave mixing is generated. The wavelength converter provided with the 2nd wavelength conversion part to output. The first wavelength conversion unit performs four-wave mixing by inputting the first excitation light source that outputs the first excitation light, the first excitation light output from the first excitation light source, and the input light. A first nonlinear optical medium that generates and outputs the first intermediate light and the second intermediate light generated by the four-wave mixing, and the first intermediate light and the first intermediate light out of the light output from the first nonlinear optical medium, and A first optical filter that selectively transmits the second intermediate light,
The second wavelength conversion unit includes a second excitation light source that outputs the second excitation light, the first intermediate light and the second intermediate light output from the first wavelength conversion unit, and the second excitation light. Four-wave mixing is generated by inputting the second excitation light output from the light source, and the second nonlinear optical medium that outputs the output light generated by the four-wave mixing is output from the second nonlinear optical medium. The wavelength conversion device according to claim 3, further comprising: a second optical filter that selectively transmits the output light out of the output light. The wavelength converter according to claim 1 or 3, wherein the wavelength of the output light is constant regardless of the wavelength of the input light. 4. The wavelength conversion device according to claim 1, wherein an optical frequency variation of the output light is smaller than an optical frequency variation of the input light. 5. The wavelength conversion device according to claim 1 or 3, wherein an extinction ratio of the output light is larger than an extinction ratio of the input light. The wavelength conversion is performed on each of signals of a plurality of channels having different wavelengths as signals of an output channel of a predetermined wavelength superimposed so as not to overlap each other along the time axis. Wavelength converter. An optical delay unit that includes a plurality of channels having different wavelengths, inputs input light in which each channel signal appears intermittently, and delays the signals of each channel so as not to overlap each other along the time axis;
By wavelength-converting each of the signals of the plurality of channels adjusted by the optical delay unit as a signal of an output channel of a predetermined wavelength so that signal generation times between the channels do not overlap along the time axis, An optical network system comprising the wavelength conversion device according to claim 1 or 3, wherein the signal existence probability is increased. An optical delay unit that includes a plurality of channels having different wavelengths, inputs input light in which each channel signal appears intermittently, and delays the signals of each channel so as not to overlap each other along the time axis;
By wavelength-converting each of the signals of the plurality of channels adjusted by the optical delay unit as a signal of an output channel of a predetermined wavelength so that signal generation times between the channels do not overlap along the time axis, An optical network system comprising the wavelength converter according to claim 1 or 3, wherein the signal interval is narrowed. N optical transmission lines (N is an integer of 2 or more);
N optical switches provided one by one in the middle of each of the N optical transmission lines;
A first optical multiplexer that multiplexes optical signals arriving from each of the N optical switches and outputs the combined light to a common optical transmission line;
N optical delay devices that are provided one by one for each of the N optical switches and that output a delayed optical signal that has arrived from the corresponding optical switch;
A second optical multiplexer for multiplexing the optical signals output from the N optical delay devices;
The wavelength conversion device according to claim 1 or 3, wherein wavelength conversion of the multiplexed light output from the second optical multiplexer is performed.
A signal for returning the multiplexed light output from the wavelength converter to any one of the N optical transmission lines positioned between the N optical switches and the first optical multiplexer or to the common optical transmission line An optical network system comprising return means. N optical transmission lines (N is an integer of 2 or more);
N optical delay units that are provided one by one in the middle of each of the N optical transmission lines and give a delay to an optical signal of a corresponding wavelength;
An optical multiplexer for multiplexing the optical signals output from the N optical delay devices;
The optical network system provided with the wavelength converter of Claim 1 or Claim 3 which performs wavelength conversion of the multiplexed light output from the said optical multiplexer. An optical transmitter for transmitting an optical signal;
An optical transmission path for transmitting an optical signal transmitted from the optical transmitter;
An optical receiver for receiving an optical signal transmitted through the optical transmission path;
The optical transmission system provided with the wavelength converter of Claim 1 or Claim 3 provided immediately after the said optical transmitter, and performing wavelength conversion of the optical signal sent from the said optical transmitter. An optical transmitter for transmitting an optical signal;
An optical transmission path for transmitting an optical signal transmitted from the optical transmitter;
An optical receiver for receiving an optical signal transmitted through the optical transmission path;
The optical transmission system provided with the wavelength converter of Claim 1 or Claim 3 provided in the middle of the said optical transmission path, and performing wavelength conversion of the optical signal which propagates the said optical transmission path.

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