Wavelength conversion device and wavelength conversion method

Abstract

To increase transmission capacity by suppressing deterioration in signal quality while suppressing nonlinear distortion in wavelength conversion from increasing.SOLUTION: A wavelength conversion device 100 includes: an optical power monitor 112 which monitors optical power variation of input signal light; an excitation light source 115; an optical amplifier 114 which performs intensity modulation on the output of excitation light of the excitation light source 115; a multiplexer 117 which multiplexes the intensity-modulated excitation light with the signal light; a nonlinear optical medium 118 which generates wavelength-converted light of the signal light that the multiplexer 117 outputs based upon nonlinear optical effect; and a control part. The control part performs control to vary the optical power of the excitation light source 115 based upon the optical power variation of the input signal light detected by the optical power monitor 112 and then output the resulting light to the optical modulator 114.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wavelength conversion device and a wavelength conversion method. [Background technology]

[0002] To cope with the ever-increasing traffic in optical networks, the introduction of multiband transmission technology is underway to increase the number of wavelength multiplexing channels and expand transmission capacity. Research into wavelength conversion technology is underway to effectively realize multiband transmission. For example, it is possible to expand the transmission bandwidth by transmitting in a new wavelength band on the transmission line while using an optical transceiver for a band for which development has been progressing. If the optical power input to the wavelength converter installed in the optical transceiver is inappropriate, signal distortion or an increase in linear noise will occur.

[0003] Prior art includes, for example, a technique for suppressing degradation due to additional nonlinear waveform distortion caused by forward pumping by controlling the ratio of the gain generated by forward pumping light and the gain generated by backward pumping light based on the measurement results of the signal light power input to a Raman amplification medium. Another technique involves an optical amplifier monitoring other system characteristics, including the input signal and the optical pump, and incorporating a component for scattering compensation. Another technique involves receiving input light with a monitor photodiode and using power measurements from input and output amplifiers to generate a signal required for stabilizing a current source using a controller, thereby reducing ASE and improving the S / N ratio of the amplifier system. Another technique involves detecting intensity noise at the difference frequency of multiplexed light with a receiver and using the error signal to adjust the drive current characteristics of the pump laser to reduce the error signal (see, for example, Patent Documents 1 to 4 listed below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-131273 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-164664 [Patent Document 3] US Patent Application Publication No. 2004 / 0017603 [Patent Document 4] US Patent Application Publication No. 2004 / 0253001 Summary of the Invention [Problem to be solved by the invention]

[0005] When high optical power is input to a wavelength converter, the conversion efficiency saturates and the converted signal becomes distorted. Therefore, in conventional technology, the input power to the wavelength converter is limited to avoid this nonlinear distortion. However, limiting the input optical power increases the linear noise generated in the downstream optical amplifier.

[0006] As will be explained in more detail later, reducing the input power to the wavelength converter and compensating for the reduced input power with an optical amplifier in the subsequent stage can avoid nonlinear distortion, but this increases the amount of linear noise generated by the optical amplifier. As a result, in conventional technology, either nonlinear or linear noise increases, degrading signal quality.

[0007] In multi-band transmission using wavelength converters of the prior art, simply increasing the number of wavelength multiplexed channels is difficult because the bandwidth is limited by the optical transceiver, optical amplifier, etc., and new optical transceivers and optical amplifiers must be developed to handle the increased bandwidth. Furthermore, the conversion efficiency of wavelength conversion is limited by the characteristics of the nonlinear optical medium, making it difficult to achieve both high efficiency and suppression of nonlinear noise.

[0008] In one aspect, the present invention aims to suppress the increase in nonlinear distortion due to wavelength conversion while suppressing the deterioration of signal quality, thereby enabling an increase in transmission capacity. [Means for solving the problem]

[0009] According to one aspect of the present invention, in a wavelength conversion device including an optical power monitor that monitors optical power fluctuations of input signal light, an excitation light source, an optical modulator that intensity-modulates the output of the excitation light from the excitation light source, a multiplexer that combines the intensity-modulated excitation light with the signal light, a nonlinear optical medium that generates wavelength-converted light of the signal light output by the multiplexer based on a nonlinear optical effect, and a control unit, the control unit is required to perform control such that the optical power of the excitation light from the excitation light source is varied based on the optical power fluctuations of the input signal light detected by the optical power monitor, and output to the optical modulator. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to suppress the increase in nonlinear distortion due to wavelength conversion while suppressing the deterioration of signal quality, thereby achieving an increase in transmission capacity. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a wavelength converter according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram of a wavelength converter according to a second embodiment. [Figure 3] FIG. 3 is a flowchart showing an outline of control of the wavelength converter. [Figure 4] FIG. 4 is a diagram illustrating a first configuration example of a multiband transmission system. [Figure 5] FIG. 5 is a diagram illustrating a second configuration example of a multiband transmission system. [Figure 6] FIG. 6 is a diagram showing an example of the configuration of a wavelength conversion device according to the prior art. [Figure 7] FIG. 7 is a diagram illustrating the occurrence of nonlinear distortion due to saturation of conversion efficiency. [Figure 8A] FIG. 8A is a graph illustrating the amount of nonlinear distortion caused by saturation of conversion efficiency according to the prior art. [Figure 8B] FIG. 8B is a chart illustrating the amount of nonlinear distortion caused by saturation of conversion efficiency according to the embodiment. [Figure 9]FIG. 9 is a chart showing an example of characteristic degradation caused by the prior art. [Figure 10] FIG. 10 is an explanatory diagram of a wavelength converter according to a third embodiment. [Figure 11] FIG. 11 is an explanatory diagram of a wavelength converter according to a fourth embodiment. [Figure 12] FIG. 12 is a diagram illustrating an example of the hardware configuration of a controller of a wavelength converter. [Figure 13] FIG. 13 is a flowchart showing the control details of the wavelength converter. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the disclosed wavelength converter and wavelength conversion method will be described in detail with reference to the drawings. For example, the wavelength converter may be provided in an optical transmitter in a WDM (Wavelength Division Multiplexing) optical transmission system, and may multiplex signal light obtained by wavelength conversion of signal light output from an optical transmitter, output the multiplexed signal light to a transmission line, and transmit the multiplexed signal light to an optical receiving device. Furthermore, for example, the wavelength converter may be provided in an optical receiving device in the optical transmission system, and may generate / extract wavelength-converted signal light corresponding to the optical receiver.

[0013] Example 1 FIG. 1 is a schematic diagram of a wavelength converter according to a first embodiment. The wavelength converter 100 of the first embodiment compensates for nonlinear distortion caused by saturation of conversion efficiency when intensity-modulating pump light of a fundamental wave input to a second-order nonlinear optical medium based on the intensity noise of input signal light. FIG. 1 shows a configuration example of the wavelength converter 100 provided in an optical transmitter, and includes a first polarization wavelength converter 101, a second polarization wavelength converter 102, a polarization beam splitter 103, and a polarization beam splitter 104. In FIG. 1 and subsequent figures, solid lines indicate signal light paths, and dotted lines indicate electrical signal paths. In the overview of FIG. 1, the control unit (controller) that controls the device is omitted, but as will be described later, the control unit (controller) controls the wavelength conversion.

[0014] The polarization beam splitter 103 separates the polarization-multiplexed input signal light, outputs one polarization component of the input signal light to the first polarization wavelength conversion unit 101, and outputs the other polarization component of the input signal light to the second polarization wavelength conversion unit 102.

[0015] The first polarization wavelength conversion unit 101 includes a splitter 111 , an optical power monitor 112 , a low-pass filter 113 , an optical modulator 114 , a pumping light source 115 , a harmonic generator 116 , a multiplexer 117 , and a nonlinear optical medium 118 .

[0016] The splitter 111 splits and outputs the input signal light to the optical power monitor 112 and the multiplexer 117. The optical power monitor 112 monitors the optical power of the input signal light. The low-pass filter 113 outputs the detected low-frequency component of the modulation frequency of the input signal light (the low-speed component of the optical power that fluctuates over time) to the optical modulator 114.

[0017] The optical modulator 114 intensity-modulates the pump light source output of the fundamental wave (for example, a communication wavelength band of 1550 nm) output from the pump light source 115 based on the optical power fluctuation of the input signal light. The harmonic generator 116 generates a harmonic by multiplying the fundamental wave, for example, a doubled pump light. The frequency band of the intensity modulation output by the optical modulator 114 is limited to be lower than the modulation speed of the input signal light.

[0018] The multiplexer 117 multiplexes the input signal light and the optically modulated pump light, and inputs the multiplexed light to the nonlinear optical medium 118. The nonlinear optical medium 118 is an optical medium (second-order nonlinear optical medium) that has a nonlinear optical effect, and generates wavelength-converted light (also called converted light or idler light) by converting the wavelength of the input signal light through the nonlinear optical effect and pump (Raman) amplification.

[0019] An optical fiber, a planar optical waveguide, or the like can be used as the nonlinear optical medium 118. In the case of an optical fiber, when pump light and signal light are multiplexed and input, wavelength-converted light with a wavelength different from that of the signal light is generated by difference frequency generation (or four-wave mixing) due to second-order (or third-order) nonlinear polarization. For example, an optical fiber with a small core cross-sectional area or a high nonlinearity that incorporates an additive with a high nonlinear refractive index can be used.

[0020] In the case of planar optical waveguides, dielectrics with high relative refractive index difference or nonlinear refractive index, such as silicon or compound semiconductors, can be used as the core. Planar optical waveguides using optical crystals such as periodically poled lithium niobate, which has a large second-order nonlinear polarization, can also be used.

[0021] Although the internal configuration of the second polarization wavelength conversion unit 102 is omitted in Figure 1, it has the same internal configuration (splitter 111 to nonlinear optical medium 118) as the first polarization wavelength conversion unit 101, and generates wavelength-converted light for the input signal light of the other polarization component.

[0022] The polarized beam splitter 104 outputs wavelength-converted light obtained by combining the polarized component of the first polarized light wavelength converter 101 and the polarized component of the second polarized light wavelength converter 102 .

[0023] Example 2 FIG. 2 is a schematic diagram of a wavelength converter according to a second embodiment. The wavelength converter 100 according to the second embodiment differs from that according to the first embodiment in the type of pump light source. In the second embodiment, when second harmonic pump light input to a second-order nonlinear optical medium or pump light input to a third-order nonlinear optical medium is intensity-modulated based on the intensity noise of the input signal light, nonlinear distortion caused by saturation of the conversion efficiency is compensated for. In the second embodiment of FIG. 2, the same components as those in the first embodiment of FIG. 1 are denoted by the same reference numerals.

[0024] The wavelength converter 100 in FIG. 2 includes a first polarization wavelength converter 201, a second polarization wavelength converter 202, a polarization beam splitter 103, and a polarization beam splitter 104.

[0025] The first polarization wavelength conversion unit 201 includes a splitter 111 , an optical power monitor 112 , a low-pass filter 113 , an optical modulator 114 , a pumping light source 215 , a multiplexer 117 , and a nonlinear optical medium 118 .

[0026] 2, the pumping light source 215 outputs a pumping light source of a wave twice that of the fundamental wave (for example, 780 nm), and the harmonic generator 116 is omitted. The nonlinear optical medium 118 is a second-order nonlinear optical medium. Alternatively, the pumping light source 215 may be a pumping light source of the fundamental wave, and the nonlinear optical medium 118 may be a third-order nonlinear optical medium.

[0027] (Overview of wavelength conversion device control) Fig. 3 is a flowchart showing an outline of control of a wavelength converter. The control example of Fig. 3 is common to Examples 1 and 2. Here, a control example of the wavelength converter 100 of Example 1 will be described. Signal light is input to the wavelength converter 100 (step S301). This input signal light is split into a first polarization component and a second polarization component by the polarization beam splitter 103 (step S302).

[0028] The first polarization component is output to the first polarization wavelength converter 101, which performs the control of steps S303 to S307. First, the optical power monitor 112 detects the optical power of a portion of the signal light split by the splitter 111 (step S303). Next, the low-speed component of the signal light is extracted by the low-pass filter 113 (step S304).

[0029] Next, the optical modulator 114 modulates the output of the pump light source 115 based on the fluctuations in the optical power of the signal light (step S305). For example, the optical modulator 114 performs intensity modulation on the pump light in response to fluctuations in the optical power of the input signal light. Next, the multiplexer 117 multiplexes the modulated pump light and the signal light, and inputs the multiplexed light to the nonlinear optical medium 118 (step S306). The nonlinear optical medium 118 generates converted light based on the modulated pump light and the signal (step S307).

[0030] The second polarization component is output to the second polarization wavelength converter 102, and the control of steps S313 to S317 is performed. The control of steps S313 to S317 performed by the second polarization wavelength converter 102 is the same as the control of steps S303 to S307 performed by the first polarization wavelength converter 101.

[0031] Then, the converted light of the first polarization component output by the first polarization wavelength converter 101 in step S307 and the converted light of the second polarization component output by the second polarization wavelength converter 102 in step S317 are output to the polarization beam splitter 104. The polarization beam splitter 104 multiplexes the first polarization component and the second polarization component (step S308). Then, the wavelength converter 100 outputs the converted light after multiplexing (step S309). The control contents of the control example of the wavelength converter 100 of the second embodiment are also the same as those shown in FIG. 3.

[0032] In the wavelength conversion device of the embodiment, the intensity-modulated output of pump light is controlled based on the fluctuation of the optical power of the input signal light. For example, the input optical power of the pump light is controlled to fluctuate (increase or decrease) in the same way as the fluctuation (increase or decrease) of the optical power of the input signal light. This makes it possible to respond to the fluctuation of the optical power of the input signal light, keep the output power of the pump light close to a constant level, suppress saturation of the conversion efficiency, and suppress nonlinear noise (and linear noise) and degradation of signal quality.

[0033] (About multi-band transmission systems) Fig. 4 is a diagram showing a first example of a configuration of a multiband transmission system. Here, we will explain a configuration example of a multiband transmission system in which the number of wavelength multiplexed channels is increased to expand transmission capacity. In the system configuration example of Fig. 4, a transmitter 410 and a receiver 420 transmit signal light in three different wavelength bands, for example, the L-band, C-band, and S-band of WDM.

[0034] The transmitting device 410 includes a plurality of L-band transmitters 401a, a plurality of C-band transmitters 401b, a plurality of S-band transmitters 401c, an L-band wavelength multiplexer 402a, a C-band wavelength multiplexer 402b, and an S-band wavelength multiplexer 402c. The transmitting device 410 also includes an L-band optical amplifier 403a, a C-band optical amplifier 403b, an S-band optical amplifier 403c, and a wavelength multiplexer 404. The wavelength multiplexer 404 outputs signal light of each of the L, C, and S bands to a transmission path 430.

[0035] The receiving device 420 includes a wavelength demultiplexer 405, an L-band optical amplifier 406a, a C-band optical amplifier 406b, and an S-band optical amplifier 406c. It also includes an L-band wavelength demultiplexer 407a, a C-band wavelength demultiplexer 407b, an S-band wavelength demultiplexer 407c, and a plurality of L-band receivers 408a, a plurality of C-band receivers 408b, and a plurality of S-band receivers 408c. The plurality of receivers 408 convert the input signal light into electrical signals and output them.

[0036] 4, the bandwidth is limited by the optical transmitter 401, optical receiver 408, optical amplifiers 403 and 406, etc. for each band. In order to wavelength-multiplex more channels than the number of channels limited by these individual bands, it becomes necessary to use optical components such as optical transmitters and receivers and optical amplifiers for additional bands, which increases costs.

[0037] Fig. 5 is a diagram showing a second configuration example of a multiband transmission system. Fig. 5 shows an example in which the wavelength converters 100 of the above-mentioned first and second embodiments (Figs. 1 and 2) are applied to a multiband transmission system. The wavelength converters 100 are disposed in a transmitting device 510 and a receiving device 520, respectively, and transmit signal light via a transmission path 530.

[0038] 5, a transmitting device 510 and a receiving device 520 transmit signal light in three different wavelength bands, for example, the L-band, C-band, and S-band of WDM. The transmitting device 510 includes a plurality of C-band transmitters 501, a C-band wavelength multiplexer 502, a C-band optical amplifier 503, and a wavelength multiplexer 504. The plurality of transmitters 501 convert input electrical signals into signal light with wavelengths in the C-band (first wavelength band) and output the converted signal light.

[0039] The transmitting device 510 includes a wavelength converter 100-1 that converts the C-band signal light into the L-band (second wavelength band), and a wavelength converter 100-2 that converts the C-band signal light into the S-band (third wavelength band).

[0040] The receiving device 520 includes a wavelength demultiplexer 505, a C-band optical amplifier 506, a C-band wavelength demultiplexer 507, and a plurality of C-band receivers 508. The plurality of receivers 508 converts the input signal light of the C-band wavelength into an electrical signal and outputs it.

[0041] The receiver 520 includes a wavelength converter 100-3 that converts the signal light in the L band into the C band, and a wavelength converter 100-4 that converts the signal light in the S band into the C band.

[0042] The wavelength converters 100-1 and 100-2 provided in the transmitting device 510 can be applied with the configuration shown in the first embodiment (FIG. 1) or the second embodiment (FIG. 2) as they are. The wavelength converters 100-3 and 100-4 provided in the receiving device 520 can be applied with the configuration described in the first embodiment (FIG. 1) or the second embodiment (FIG. 2).

[0043] According to this multiband transmission system, the transmitting device 510 and the receiving device 520 can increase the number of WDM wavelength multiplexed channels and expand the transmission capacity by using multiple transmitters 501 and receivers 508. The transmitting device 510 and the receiving device 520 are each provided with wavelength converters 100 (100-1 to 100-4) to convert the wavelength of the signal light.

[0044] This allows the transmitter 501, receiver 508, optical amplifiers 503 and 506, wavelength multiplexer 502, and wavelength demultiplexer 507 of the transmitting device 510 and the receiving device 520 to be constructed inexpensively using optical components of a common wavelength band (C band).

[0045] (Prior art and its problems) 6 is a diagram showing an example of the configuration of a wavelength converter according to the prior art. The conventional wavelength converter 600 includes a splitter 601, an optical power monitor 602, a controller 603, a look-up table (LUT) 604, an optical amplifier 605, a wavelength converter 606, and an optical amplifier 607. The optical amplifier 605 may be a variable optical attenuator, and reduces the input power to the wavelength converter 606.

[0046] An input signal light is split by a splitter 601 to an optical power monitor 602 and an optical amplifier 605. The optical power monitor 602 monitors the optical power of the input signal light and outputs the result to a controller 603. The controller 603 adjusts the output power of the upstream optical amplifier 605 in accordance with the optical power of the input signal light set in a setting table 604, and inputs the adjusted output power to a wavelength converter 606. The downstream optical amplifier 607 compensates for the adjusted output power.

[0047] 6, when the optical power of the input signal light to the wavelength converter 606 is sufficiently lower than the power of the pump light, the optical power transition from the pump light to the signal light and the idler light (wavelength-converted light) is very small. In this case, the nonlinear distortion added to the idler light generated as a phase conjugate light of the input signal light can be ignored.

[0048] On the other hand, when the input signal light power to the wavelength converter 606 is no longer at a level sufficiently lower than the pump light power, the optical power transition of the pump light to the signal light and idler light becomes large, so the optical power of the pump light attenuates and the conversion efficiency saturates.

[0049] Since the instantaneous optical attenuation of pump light depends on the instantaneous optical power of input signal light, when the input signal light has an intensity-modulated component, the conversion efficiency is saturated instantaneously and nonlinear distortion is added to the converted signal.

[0050] The above process occurs similarly for second-order and third-order nonlinearities, although the thresholds are different because the absolute values ​​of the nonlinear polarizations are different. The saturation level of the conversion efficiency and the amount of nonlinear distortion are correlated. Therefore, the amount of nonlinear distortion can be estimated by monitoring the input and output power of the wavelength converter 606. However, when the wavelength converter 606, whose transmittance and conversion efficiency change over time, is operated in the saturation region, it is impossible to separate the change in the input signal state from the change in the wavelength converter characteristics over time. For example, control using the LUT 604 cannot respond to the change in the input signal state and the change in the wavelength converter characteristics over time.

[0051] 6, if the input power to wavelength converter 606 is reduced and the reduced input power is compensated for by optical amplifier 607 at the subsequent stage, nonlinear distortion can be avoided, but this increases the amount of linear noise generated by optical amplifier 607. As a result, in the conventional technology, nonlinear noise or linear noise increases, degrading signal quality.

[0052] FIG. 7 is a diagram illustrating the occurrence of nonlinear distortion due to saturation of conversion efficiency. FIG. 7(a) is a diagram illustrating second-order nonlinearity. Sj ) does not include nonlinear components. Second-order nonlinear pump light V p(2) has twice the frequency of the fundamental pump light (for example, 780 nm). When these input signal light and pump light are input to a second-order nonlinear medium, the WDM signal and the generated idler light (wavelength-converted light, V Ij ) nonlinear distortion components due to ASE light are added to each channel, degrading the signal-to-noise ratio.

[0053] Fig. 7(b) is an explanatory diagram of the third-order nonlinearity. Sj ) does not include nonlinear components. The input signal light and the third-order nonlinear pump light V p(3) When the third-order nonlinear medium is input, the WDM signal and the generated idler light (wavelength-converted light, V Ij ) nonlinear distortion components due to ASE light are added to each channel, degrading the signal-to-noise ratio.

[0054] (Differences in the amount of nonlinear distortion due to saturation of conversion efficiency) Figure 8A is a graph illustrating the amount of nonlinear distortion caused by saturation of conversion efficiency in the conventional technology. The signal light input optical power in Figure 8A(a) changes over time (times t1 and t2). In contrast, as shown in Figure 8A(b), in the conventional technology, the pump light input optical power remains constant regardless of changes in the signal light input optical power.

[0055] As a result, as shown in Fig. 8A(c), the pump light output power tends to be low (high saturation) at time t1 and high (low saturation) at time t2. The idler light output power shown in Fig. 8A(d) has a waveform different from the waveform of the input signal light shown in Fig. 8A(a). The idler light output power in Fig. 8A(d) has an output waveform in which the change in the waveform of the input signal light is small.

[0056] FIG. 8B is a graph illustrating the amount of nonlinear distortion caused by saturation of conversion efficiency according to an embodiment. The signal light input optical power in FIG. 8B(a) changes over time (times t1 and t2). In the embodiment, as shown in FIG. 8B(b), the pump light input optical power is changed in the same direction as the change in the signal light input optical power. The time-averaged value of the pump light input optical power is substantially the same as the constant pump light input optical power shown in the conventional example (FIG. 8A(b)). The pump light corresponds to the low-frequency component of the input signal light extracted by the low-pass filter 113, and is intensity-modulated by the modulator 114, with the frequency band of the intensity modulation being limited to be lower than the modulation speed of the input signal light.

[0057] As a result, the pump light output power remains almost constant as shown in Fig. 8B(c), and the idler light output power shown in Fig. 8B(d) maintains the waveform of the input signal light shown in Fig. 8A(a) and exhibits a similar change.

[0058] (Example of characteristic degradation due to conventional technology) Figure 9 is a graph showing an example of characteristic degradation due to conventional technology. Figure 9(a) shows the conversion efficiency as a function of input optical power. In Figure 9(a), the triangle (dotted line characteristics) represents the case when the input optical power is for a single channel, and the circle (solid line characteristics) represents the case when the input optical power is for multiple channels (64 channels). In either case, it has been observed that as the input signal optical power increases, the conversion efficiency (output optical power of the converted signal) decreases, and once the saturation level reaches approximately 1 dB, signal degradation in wavelength conversion becomes noticeable.

[0059] In conventional technology, when wavelength-converting a signal light with an input optical power of 18 dBm, for example, the conversion efficiency saturation is about 2 dB, resulting in significant signal degradation during wavelength conversion. To suppress this signal degradation during wavelength conversion, it is necessary to lower the input optical power to, for example, about 13 dBm, which corresponds to a conversion efficiency saturation of 0.5 dB. In conventional technology, in order to suppress linear noise increase throughout the entire node, including wavelength conversion, if the input power to wavelength converter 606 is limited, the loss must be compensated for by the downstream optical amplifier 607.

[0060] Figure 9(b) shows the noise figure versus input optical power. It shows the change in noise figure with input signal optical power when the input optical power to wavelength converter 606 is limited to 13 dBm or less, assuming a conversion efficiency of 0 dB in the configuration of the conventional technology (Figure 6) and a noise figure of 6 dB for optical amplifier 605 and wavelength converter 606.

[0061] 9(b) shows the dotted line characteristics when a variable optical attenuator is installed before wavelength converter 606, and the solid line characteristics when optical amplifier 605 is installed before wavelength converter 606. Generally, at an input optical power of 18 dBm (0 dBm / ch for 64 channels), when a variable optical attenuator is installed before (dotted line characteristics), the noise figure deteriorates by about 5 dB compared to lower power, and when an optical amplifier is installed before (solid line characteristics), the noise figure deteriorates by about 9 dB compared to lower power. In contrast, by applying the embodiment, it is possible to suppress these 5 dB or 9 dB deteriorations.

[0062] Example 3 10 is an explanatory diagram of a wavelength converter according to a third embodiment. In this third embodiment, the general configuration described in the first embodiment (FIG. 1) is detailed, including a controller, and components similar to those in FIG. 1 are designated by the same reference numerals.

[0063] An input signal light is input to the polarization beam splitter 103 via a variable optical attenuator 1001. The polarization beam splitter 103 separates the polarization-multiplexed input signal light, outputs one polarization component of the input signal light to the first polarization wavelength converter 101, and outputs the other polarization component of the input signal light to the second polarization wavelength converter 102.

[0064] In the first polarization wavelength converter 101, the splitter 111 splits and outputs the input signal light to the optical power monitor (input signal light power monitor) 112 and the multiplexer 117. The optical power monitor (input signal light power monitor) 112 monitors the optical power of the input signal light and outputs the monitor value to the controller 1020. The low-pass filter 113 outputs the detected low-frequency component of the input signal light (the low-speed component of the optical power that fluctuates over time) to the optical attenuator 1002. The optical attenuator 1002 attenuates the output of the low-pass filter 113 by an attenuation amount based on the control of the controller 1020, and outputs the output to the optical modulator 114.

[0065] Under the control of the controller 1020, the pumping light source 115 controls the pumping light source output of a fundamental wave (for example, a communication wavelength band of 1550 nm) in response to fluctuations in the optical power of the input signal light, and outputs it to the optical modulator 114. The optical modulator 114 intensity-modulates the input signal light using the pumping light source output output from the pumping light source 115. The harmonic generator 116 generates a harmonic wave obtained by multiplying the fundamental wave, for example, a doubled wave pumping light.

[0066] The splitter 1003 splits the output of the harmonic generator 116 and outputs it to the multiplexer 117 and the input pump light power monitor 1004. The pump light power detected by the input pump light power monitor 1004 is output to the controller 1020.

[0067] The multiplexer 117 multiplexes the input signal light and the optically modulated pump light, and inputs the multiplexed light to the nonlinear optical medium 118. The nonlinear optical medium 118 generates wavelength-converted light (converted light, idler light) by converting the wavelength of the input signal light through the nonlinear optical effect and pump (Raman) amplification.

[0068] The demultiplexer 1005 demultiplexes the wavelength-converted light output from the nonlinear optical medium 118. The wavelength-converted light having the pumping light wavelength is output to the splitter 1006, and the wavelength-converted light (output signal light) is output to the splitter 1009.

[0069] The splitter 1006 splits and outputs the optical power of the pump light wavelength to a pump light noise power monitor 1007 and an output pump light power monitor 1008. The optical power of the pump light noise detected by the pump light noise power monitor 1007 and the optical power of the output pump light detected by the output pump light power monitor 1008 are output to a controller 1020.

[0070] The splitter 1009 splits and outputs the wavelength-converted light (output signal light) to an output signal light power monitor 1010 and the polarization beam splitter 104. The output signal light power monitor 1010 detects the optical power of the wavelength-converted light (output signal light) and outputs the detected power to a controller 1020.

[0071] The polarization beam splitter 104 polarization-combines one polarization output from the first polarization wavelength converter 101 and the other polarization output from the second polarization wavelength converter 102, and outputs the result to the optical amplifier 1011. The optical amplifier 1011 optically amplifies the wavelength-converted light (output signal light) after polarization combining under the control of the controller 1020.

[0072] The controller 1020 controls the attenuation amount of the optical attenuator 1002 and the pumping light output power of the fundamental wave pumping light source 115 based on the detected outputs of the monitors (input signal light power, input pumping light power, pumping light noise power, output pumping light power, output signal light power), and also controls the optical amplification amount of the optical amplifier 1011.

[0073] Example 4 Fig. 11 is an explanatory diagram of a wavelength converter according to a fourth embodiment. In this fourth embodiment, the general configuration described in the second embodiment (Fig. 2) is detailed, including a controller, and the same components as those in Figs. 1 and 2 are denoted by the same reference numerals.

[0074] In the fourth embodiment, the optical attenuator 1002 located after the low-pass filter 113 may be an optical amplifier. In the fourth embodiment, similar to the second embodiment (FIG. 2), the pumping light source 215 is a pumping light source of a second harmonic of the fundamental wave, and the harmonic generator 116 is omitted. The nonlinear optical medium 118 is a second-order nonlinear optical medium. Alternatively, the pumping light source 215 may be a pumping light source of the fundamental wave, and the nonlinear optical medium 118 may be a third-order nonlinear optical medium.

[0075] The controller 1020 controls the attenuation amount of the optical attenuator 1002 (or the optical amplification amount of the optical amplifier) ​​based on the detected outputs of the monitors (input signal light power, input pumping light power, pumping light noise power, output pumping light power, output signal light power), as in the third embodiment. It also controls the pumping light output power of the pumping light source 215 and the optical amplification amount of the optical amplifier 1011.

[0076] (Controller configuration example) 12 is a diagram showing an example of the hardware configuration of a controller of a wavelength converter, showing an example of the configuration of a controller 1020 corresponding to the control unit of the wavelength converter shown in FIGS.

[0077] 12, the controller 1020 includes a processor 1201 such as a CPU (Central Processing Unit), a memory 1202, a network IF 1203, a recording medium IF 1204, and a recording medium 1205. The components are connected to each other via a bus 1200.

[0078] Here, the processor 1201 is a control unit that controls the entire wavelength conversion device 100. The processor 1201 may have multiple cores. The memory 1202 has, for example, a read-only memory (ROM), a random access memory (RAM), and a flash ROM. Specifically, for example, the flash ROM stores a control program, the ROM stores an application program, and the RAM is used as a work area for the processor 1201. The programs stored in the memory 1202 are loaded into the processor 1201, causing the processor 1201 to execute the coded processes.

[0079] The network IF 1203 serves as an interface between the network NW and the control unit (controller 1020), and controls input and output of information between the wavelength converter 100 and the outside.

[0080] The recording medium IF 1204 controls reading / writing of data from / to the recording medium 1205 under the control of the processor 1201. The recording medium 1205 stores data written under the control of the recording medium IF 1204.

[0081] In addition to the above-mentioned components, the control unit (controller 1020) may be connectable to, for example, an input device, a display, etc. via an IF.

[0082] 12 can realize the functions of the wavelength converter 100 by executing a program. The controller 1020 may also be configured with an FPGA (Field-Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a DSP (Digital Signal Processor).

[0083] (Flowchart showing details of control of wavelength conversion device) Fig. 13 is a flowchart showing details of control of the wavelength converter. The control content common to the third embodiment (Fig. 10) and the fourth embodiment (Fig. 11) will be described using Fig. 13. The control shown in Fig. 13 is the processing content of the control unit (controller 1020) of the wavelength converter 100, and the control unit starts the processing when the wavelength converter 100 is initially set or when a change occurs in each monitored value.

[0084] First, the control unit calculates the input signal light power monitor value P SI and the output signal light power monitor value P detected by the output signal light power monitor 1010. SO The control unit also acquires the input pump light power monitor value P PI and the output pump light power monitor value P detected by the output pump light power monitor 1008. PO is acquired (step S1301).

[0085] Next, the control unit calculates the input signal light power monitor value P SI to the target conversion efficiency value CE T , and the target pump light attenuation value PD T Next, the control unit determines the conversion efficiency CE=P SO / P SI and the pump light attenuation PD=P PO / P PI is calculated (step S1303).

[0086] Next, the control unit sets the calculated conversion efficiency CE as a conversion efficiency target value CE T (step S1304). As a result of the comparison, the conversion efficiency CE is compared with the conversion efficiency target value CE T If it is greater than or equal to (step S1304: CE≧CE T ), the control unit proceeds to the process of step S1305. On the other hand, if the conversion efficiency CE is equal to or greater than the conversion efficiency target value CE T If it is less than (step S1304: CE <CE T ), the control unit proceeds to the process of step S1307.

[0087] In step S1305, the control unit calculates the pump light noise power monitor value P N Next, the control unit acquires the pump light noise power monitor value P N The excitation light noise target value P NT (step S1306). As a result of the comparison, the pump light noise power monitor value P N is the photonic noise target value P NT If it is less than or equal to (Step S1306:P N ≦P NT ), the control unit ends the above processing. Meanwhile, the pump light noise power monitor value P N is the photonic noise target value P NT If it exceeds (step S1306: P N >P NT ), the control unit proceeds to the process of step S1309.

[0088] In step S1307, the control unit sets the calculated pump light attenuation amount PD to the pump light attenuation target value PD T (step S1307). As a result of the comparison, the pump light attenuation PD is compared with the pump light attenuation target value PD T If PD≧PD (step S1307: T ), the control unit adjusts the output power of the pump light source 115 (step S1308), and the process returns to step S1301. T If it is less than (step S1307: PD <PD T ), the control unit performs a process to adjust the amount of attenuation of the variable optical attenuator 1001 and the gain of the optical amplifier 1011 (step S1311). After this, the control unit returns to the process of step S1301.

[0089] In step S1309, the control unit compares the loop count i of the process execution with a predetermined target loop count N (step S1309). If, as a result of the comparison, the loop count i is less than the target loop count N (step S1309: i < N), the control unit adjusts the output power of the optical attenuator (or optical amplifier) 1002 (step S1310) and returns to the process of step S1305. In this loop process, the excitation light noise power monitor value P N becomes the start-up light noise target value P NT The output power of the optical attenuator (or optical amplifier) 1002 is adjusted so as to be less than or equal to the following. On the other hand, if the loop count i reaches the target loop count N (step S1309: i = N), the control unit proceeds to the process of step S1311.

[0090] The wavelength conversion device according to the embodiment described above includes an optical power monitor that monitors the optical power fluctuation of the input signal light, an excitation light source, an optical modulator that intensity-modulates the output of the excitation light of the excitation light source, a multiplexer that multiplexes the excitation light intensity-modulated on the signal light, a non-linear optical medium that generates wavelength-converted light of the signal light output by the multiplexer based on the non-linear optical effect, and a control unit. The control unit performs control to vary the optical power of the excitation light of the excitation light source based on the optical power fluctuation of the input signal light detected by the optical power monitor and output it to the optical modulator. For example, the control unit performs control to increase or decrease the output of the excitation light source in the same manner corresponding to the increase or decrease of the detection output of the optical power fluctuation of the input signal light detected by the optical power monitor. Thereby, it is possible to respond to the fluctuation of the optical power of the input signal light, suppress the saturation of the conversion efficiency of wavelength conversion, and suppress the deterioration of non-linear noise and signal quality.

[0091] Further, the wavelength conversion device may include a low-pass filter that passes the low-frequency components of the input signal light, and the optical modulator may limit the frequency band of the intensity modulation to be lower than the modulation speed of the signal light. Thereby, the frequency band of the intensity modulation can be limited to be lower than the modulation speed of the input signal light, the saturation of the conversion efficiency can be suppressed, and the deterioration of non-linear noise and signal quality can be suppressed.

[0092] The wavelength conversion device may further include an optical power monitor that detects the output power of the wavelength-converted light and the input / output optical power of the pump light, a variable optical attenuator that can adjust the optical power of the signal light input to the device, and an optical amplifier that optically amplifies the wavelength-converted light output from the device. The control unit calculates the conversion efficiency of the wavelength signal light based on the optical power of the input signal light and the optical power of the output signal light, calculates the attenuation of the pump light based on the input / output power of the pump light, and adjusts the optical power of the pump light or the attenuation of the variable optical attenuator and the gain of the optical amplifier to achieve a target conversion efficiency. This allows the pump light power for wavelength conversion to be appropriately adjusted, thereby improving the conversion efficiency of wavelength conversion.

[0093] The wavelength conversion device may further include an optical power monitor that detects the noise power of the pump light from the output of the nonlinear optical medium, and an optical attenuator that attenuates the optical power of the signal light input to the optical modulator. The control unit may adjust the attenuation of the optical attenuator so that the noise power of the pump light becomes a predetermined target noise power of the pump light. This reduces the noise power of the wavelength-converted light, thereby enabling appropriate output power to be obtained.

[0094] In addition, in the wavelength conversion device, the nonlinear optical medium may be a second-order nonlinear optical medium, the pumping light source may output pumping light of a fundamental wave in the communication wavelength band, and the modulated output of the optical modulator may be output to a multiplexer via a second-order harmonic generator that generates a second-order harmonic. In addition, in the wavelength conversion device, the nonlinear optical medium may be a second-order nonlinear optical medium, and the pumping light source may output pumping light of a double wave of the fundamental wave in the communication wavelength band. Furthermore, in the wavelength conversion device, the nonlinear optical medium may be a third-order nonlinear optical medium, and the pumping light source may output pumping light of a fundamental wave in the communication wavelength band. In this way, wavelength conversion can be performed using a pumping light source according to the type of nonlinear optical medium.

[0095] The wavelength conversion device may further include a polarization beam splitter that performs polarization separation on the signal light input to the device and polarization combination on the wavelength-converted light output from the device, thereby enabling appropriate wavelength conversion for each polarization of the polarization-multiplexed signal light.

[0096] The following additional notes are provided regarding the above-described embodiment.

[0097] (Supplementary Note 1) A wavelength conversion device including an optical power monitor that monitors fluctuations in the optical power of input signal light, a pumping light source, an optical modulator that intensity-modulates the output of pumping light from the pumping light source, a multiplexer that multiplexes the intensity-modulated pumping light with the signal light, a nonlinear optical medium that generates wavelength-converted light of the signal light output by the multiplexer based on a nonlinear optical effect, and a control unit, The control unit fluctuating the optical power of the pumping light from the pumping light source based on the fluctuation in the optical power of the input signal light detected by the optical power monitor, and outputting the pumping light to the optical modulator; A wavelength conversion device characterized by performing control.

[0098] (Supplementary Note 2) The control unit A wavelength conversion device as described in Appendix 1, characterized in that the output of the pumping light source is controlled to increase or decrease in response to an increase or decrease in the detected output of the optical power fluctuation of the input signal light detected by the optical power monitor.

[0099] (Supplementary Note 3) A low-pass filter is included which passes a low frequency component of the input signal light and outputs it to the optical modulator; 2. The wavelength conversion device according to claim 1, wherein the optical modulator limits the frequency band of the intensity modulation to be lower than the modulation speed of the signal light.

[0100] (Supplementary Note 4) Further, an optical power monitor for detecting the output power of the wavelength-converted light and the input / output optical power of the pumping light, a variable optical attenuator that can freely change the optical power of the signal light input to the device; an optical amplifier that optically amplifies the wavelength-converted light output from the device; The control unit calculating a conversion efficiency of the wavelength signal light based on the optical power of the input signal light and the output signal light; calculating an attenuation amount of the pumping light based on an input / output power of the pumping light; 2. A wavelength conversion device according to claim 1, characterized in that the optical power of the pumping light is adjusted, or the attenuation of the variable optical attenuator and the gain of the optical amplifier are adjusted to achieve a predetermined target conversion efficiency.

[0101] (Supplementary Note 5) further comprising an optical power monitor for detecting the noise power of the pumping light from the output of the nonlinear optical medium; an optical attenuator that attenuates the optical power of the signal light input to the optical modulator; The control unit 2. The wavelength conversion device according to claim 1, wherein the attenuation of the optical attenuator is adjusted so that the noise power of the pumping light becomes a predetermined target noise power of the pumping light.

[0102] (Supplementary Note 6) The nonlinear optical medium is a second-order nonlinear optical medium, the pumping light source outputs pumping light of a fundamental wave in a communication wavelength band; 2. The wavelength conversion device according to claim 1, wherein the modulated output of the optical modulator is output to the multiplexer via a second harmonic generator that generates a second harmonic.

[0103] (Supplementary Note 7) The nonlinear optical medium is a second-order nonlinear optical medium, 2. The wavelength conversion device according to claim 1, wherein the pumping light source outputs pumping light that is a second harmonic of a fundamental wave in a communication wavelength band.

[0104] (Supplementary Note 8) The nonlinear optical medium is a third-order nonlinear optical medium, 2. The wavelength conversion device according to claim 1, wherein the pumping light source outputs pumping light of a fundamental wave in a communication wavelength band.

[0105] (Appendix 9) The wavelength conversion device according to appendix 1, further comprising a polarization beam splitter that performs polarization separation of the signal light input to the device and polarization combination of the wavelength-converted light output from the device.

[0106] (Supplementary Note 10) A wavelength conversion method for a wavelength conversion device including an optical power monitor that monitors optical power fluctuations of input signal light, a pumping light source, an optical modulator that intensity-modulates the output of pumping light from the pumping light source, a multiplexer that multiplexes the intensity-modulated pumping light with the signal light, a nonlinear optical medium that generates wavelength-converted light of the signal light output from the multiplexer based on a nonlinear optical effect, and a control unit, The control unit fluctuating the optical power of the pumping light from the pumping light source based on the fluctuation in the optical power of the input signal light detected by the optical power monitor, and outputting the pumping light to the optical modulator; A wavelength conversion method characterized by controlling [Explanation of symbols]

[0107] 100 Wavelength conversion device 101,201 First polarization wavelength conversion unit 102,202 Second polarization wavelength conversion unit 103,104 Polarization beam splitter 111, 1003, 1006, 1009 splitter 112 Optical Power Monitor 113 Low-pass filter 114 Optical Modulator 115,215 Excitation light source 116 Harmonic Generator 117 Multiplexer 118 Nonlinear Optical Media 410,510 Transmitting equipment 420,520 receiving device 1001 Variable Optical Attenuator 1002 Optical attenuator (or optical amplifier) 1004 Input pump optical power monitor 1005 Duplexer 1007 Pump Optical Noise Power Monitor 1008 Output pump light power monitor 1010 Output signal optical power monitor 1011 Optical Amplifier 1020 Controller (control unit) 1201 processor 1202 memory 1205 Recording Media NW Network

Claims

1. A wavelength conversion device including an optical power monitor that monitors fluctuations in the optical power of input signal light, a pumping light source, an optical modulator that intensity-modulates the output of pumping light from the pumping light source, a multiplexer that multiplexes the intensity-modulated pumping light with the signal light, a nonlinear optical medium that generates wavelength-converted light of the signal light output by the multiplexer based on a nonlinear optical effect, and a control unit, The control unit fluctuating the optical power of the pumping light from the pumping light source based on the fluctuation in the optical power of the input signal light detected by the optical power monitor, and outputting the pumping light to the optical modulator; A wavelength conversion device characterized by performing control.

2. The control unit 2. A wavelength conversion device according to claim 1, wherein the output of the pumping light source is controlled to increase or decrease in response to an increase or decrease in the detected output of the optical power fluctuation of the input signal light detected by the optical power monitor.

3. a low-pass filter that passes a low frequency component of the input signal light and outputs it to the optical modulator; 2. The wavelength conversion device according to claim 1, wherein the optical modulator limits the frequency band of the intensity modulation to be lower than the modulation rate of the signal light.

4. an optical power monitor for detecting the output power of the wavelength-converted light and the input and output optical powers of the pumping light; a variable optical attenuator that can freely change the optical power of the signal light input to the device; an optical amplifier that optically amplifies the wavelength-converted light output from the device; The control unit calculating a conversion efficiency of the wavelength signal light based on the optical power of the input signal light and the output signal light; calculating an attenuation amount of the pumping light based on an input / output power of the pumping light; 2. The wavelength conversion device according to claim 1, wherein the optical power of the pumping light or the attenuation of the variable optical attenuator and the gain of the optical amplifier are adjusted to achieve a predetermined target conversion efficiency.

5. an optical power monitor for detecting the noise power of the pumping light from the output of the nonlinear optical medium; an optical attenuator that attenuates the optical power of the signal light input to the optical modulator; The control unit 2. The wavelength conversion device according to claim 1, wherein the attenuation of the optical attenuator is adjusted so that the noise power of the pumping light becomes a predetermined target noise power of the pumping light.

6. the nonlinear optical medium is a second-order nonlinear optical medium, the pumping light source outputs pumping light of a fundamental wave in a communication wavelength band; 2. The wavelength conversion device according to claim 1, wherein the modulated output of said optical modulator is output to said multiplexer via a second harmonic generator that generates a second harmonic.

7. the nonlinear optical medium is a second-order nonlinear optical medium, 2. The wavelength conversion device according to claim 1, wherein the pumping light source outputs pumping light that is a second harmonic of a fundamental wave in a communication wavelength band.

8. the nonlinear optical medium is a third-order nonlinear optical medium; 2. The wavelength conversion device according to claim 1, wherein the pumping light source outputs pumping light of a fundamental wave in a communication wavelength band.

9. A wavelength conversion method for a wavelength conversion device including an optical power monitor that monitors optical power fluctuations of input signal light, a pumping light source, an optical modulator that intensity-modulates the output of pumping light from the pumping light source, a multiplexer that multiplexes the intensity-modulated pumping light with the signal light, a nonlinear optical medium that generates wavelength-converted light of the signal light output from the multiplexer based on a nonlinear optical effect, and a control unit, The control unit fluctuating the optical power of the pumping light from the pumping light source based on the fluctuation in the optical power of the input signal light detected by the optical power monitor, and outputting the pumping light to the optical modulator; A wavelength conversion method characterized by controlling

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