Frequency shift correction device for wavelength converter

Abstract

A frequency shift correction device (100-1) for an all-optical wavelength converter (12) provided in an optical cross-connect device (10) of a wavelength multiplexing transmission system (1000) comprises: a detection unit (105) that, when the frequency of idler light, which is wavelength conversion light, is determined from the frequencies of incident signal light and excitation light, detects the frequency shift of the excitation light; and a correction unit (150) that corrects the detected frequency shift of the excitation light. The correction unit (150) performs a setting by shifting from a set excitation light frequency by the detected frequency shift Δf, or by half Δf / 2 of the detected frequency shift Δf.

Description

Frequency deviation correction device for wavelength converter

[0001] The present invention relates to a frequency deviation correction device for a wavelength converter.

[0002] Research and development has been conducted on AO-WC (All Optical Wavelength Conversion) using nonlinear optical media such as periodically poled LiNbO3 (PPLN) (Non-Patent Document 1) and highly nonlinear fiber (Non-Patent Document 2). A multiband optical cross-connect configuration has been proposed in which this AO-WC is added to devices constituting conventional optical cross-connect systems, such as wavelength selective switches (WSSs) and optical amplifiers (Non-Patent Document 3). This configuration allows selection of not only the output direction but also the wavelength band, which is expected to improve the traffic capacity by enabling effective use of wavelength resources.

[0003] Shimpei Shimizu et al., “PPLN-Based Optical Parametric Amplification for Wideband WDM Transmission”, Journal of Lightwave Technology, Vol. 40, Issue 11, June 1, 3374-3384 (2022). Tomoyuki Kato et al., “Whole Band Wavelength Conversion for Wideband Transmission”, in Proc. OFC2021, Paper F1B.1 (2021). Masahiro Nakagawa et al., “Adaptive Link-by-Link Band Allocation: A Novel Adaptation Scheme in Multi-Band Optical Networks”, in Proc. ONDM2021 (2021).

[0004] The nonlinear optical effects that form the principle by which wavelength-converted light is generated in the AO-WC include difference frequency generation (fi = fp - fs, where fi is the frequency of the wavelength-converted light, fp is the frequency of the pump light, and fs is the frequency of the signal light), which is a second-order nonlinear optical effect, and four-wave mixing (fi = 2fp - fs), which is a third-order nonlinear optical effect.The frequency of the idler light (light after conversion), which is wavelength-converted light, is determined from the frequencies of the signal light and pump light that are incident on the nonlinear optical medium.

[0005] Therefore, if a frequency shift Δf occurs in the pump light frequency fp, the frequency of the wavelength-converted light will shift by Δf or 2Δf. Furthermore, this frequency shift of the wavelength-converted light may increase as the number of times the optical signal is wavelength-converted increases. If idler light with a different frequency than expected is transmitted in this way, it may cause signal degradation due to filtering penalties when passing through the WSS in the optical cross-connect unit, or errors may occur when demodulating the signal due to a frequency shift between the signal light and the local light when receiving the optical signal digitally in a coherent manner.

[0006] The present invention has been made in view of the above background, and an object of the present invention is to provide a frequency deviation correction device for a wavelength converter that can correct the frequency deviation of pump light or wavelength-converted light.

[0007] In order to solve the above-mentioned problems, a frequency deviation correction device for a wavelength converter provided in an optical repeater node of an optical transmission system is provided, which is characterized in that when the frequency of idler light, which is wavelength-converted light, is determined from the frequencies of incident signal light and pump light, the device comprises: a detection unit that detects the frequency deviation of the pump light; and a correction unit that corrects the detected frequency deviation of the pump light.

[0008] According to the present invention, it is possible to realize a frequency deviation correction device for a wavelength converter that can correct the frequency deviation of pump light or wavelength-converted light.

[0009] It is a schematic configuration diagram of an optical cross-connect device including a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a detailed configuration diagram of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a detailed configuration diagram of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a detailed configuration diagram of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a diagram for explaining the frequency deviation in wavelength conversion (in the case of four-wave mixing (FWM)). It is a diagram for explaining the frequency deviation in wavelength conversion (in the case of second harmonic generation (SHG) and difference frequency generation (DFG)). It is a diagram for explaining the frequency deviation in wavelength conversion (in the case of DFG). In the frequency deviation correction device for a wavelength converter according to an embodiment of the present invention, when the frequency deviation of the wavelength converter is detected, it is a flowchart for explaining how to correct the frequency deviation by classifying the processing procedures into <detection procedure> and <correction procedure> based on the types of frequency deviations in FIGS. 3A - C. It is a configuration diagram showing a first configuration example of a detection unit of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a configuration diagram showing a second configuration example of a detection unit of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a diagram for explaining the relationship between the wavelength deviation and the optical power by a power meter in a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a configuration diagram showing a third configuration example of a detection unit of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a diagram showing a configuration for specifying the sign of Δf from the optical power measured by a power meter in a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a diagram for explaining a method for specifying the sign of Δf in a method for detecting Δf by a filter and a power meter in a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a diagram for explaining a method for specifying the sign of Δf in a method for detecting Δf by a filter and a power meter in a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a diagram for explaining a method for specifying the sign of Δf in a method for detecting Δf by a filter and a power meter in a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a configuration diagram showing a first configuration example of a detection unit of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention. It is a configuration diagram showing a second configuration example of a detection unit of a frequency deviation correction device for a wavelength converter according to an embodiment of the present invention.FIG. 1 is a configuration diagram showing a third configuration example of a detection unit of a frequency shift correction device for a wavelength converter according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a first configuration example of a detection light removal unit of a frequency shift correction device for a wavelength converter according to an embodiment of the present invention. FIG. 3 is a diagram explaining wavelength setting of detection light in the detection light removal unit and inspection light source of the wavelength converter according to an embodiment of the present invention. FIG. 4 is a configuration diagram showing a second configuration example of a detection light removal unit of a frequency shift correction device for a wavelength converter according to an embodiment of the present invention. FIG. 5 is a configuration diagram showing a third configuration example of a detection light removal unit of a frequency shift correction device for a wavelength converter according to an embodiment of the present invention.

[0010] A frequency offset correction device for a wavelength converter according to an embodiment of the present invention (hereinafter referred to as the "present embodiment") will be described below with reference to the drawings. The frequency offset correction device for a wavelength converter according to this embodiment is applicable to an optical transmission system. FIG. 1 is a schematic diagram of an optical cross-connect device 10 including a frequency offset correction device 100 for a wavelength converter according to an embodiment of the present invention. The optical cross-connect device 10 constitutes an optical node of a wavelength multiplexing transmission system 1000. The wavelength multiplexing transmission system 1000 is an optical transmission system based on dense wave-division multiplexing (DWDM) and digital coherent technology, which multiplexes multiple wavelength signals onto a single optical fiber. The wavelength multiplexing transmission system 1000 includes an optical cross-connect device (OXC) 10, which is an optical node, and Ingress 1-N and Egress 1-N (optical transmission paths) that connect the OXCs 10 together.

[0011] The optical cross-connect device 10 is connected as a relay node for optical signals to optical fibers of Ingress 1 to N and Egress 1 to N, which are routes that bundle together a plurality of optical fibers in an optical network. The optical cross-connect device 10 is used, for example, in a reconfigurable optical add / drop multiplexer (ROADM) that acts as a route switch for optical signals transmitted using various modulation methods such as wavelength division multiplexing in an optical network.

[0012] The optical cross-connect device 10 includes an add / drop function unit 11 (optical multiplexing / demultiplexing unit), an all-optical wavelength converter (AO-WC) 12 (wavelength converter), a wavelength converter frequency deviation correction device 100 that corrects the frequency deviation of the all-optical wavelength converter 12, and a plurality of WSSs 13 that constitute the optical cross-connect unit (enclosed by a dashed line in Figure 1).

[0013] The optical cross-connect device 10 performs processes such as relaying optical signals between OXCs and switching the optical signal routes. The optical cross-connect device 10 can, for example, set any optical path to be added, dropped, or passed through for up to eight transmission paths. In this optical cross-connect device 10, wavelength-multiplexed signal light transmitted from input routes Ingress 1 to N is output to output routes Egress 1 to N via multiple WSSs 13.

[0014] The add / drop functional unit 11 is made up of a multiplexer / demultiplexer and performs processing to multiplex optical signals of different wavelengths and demultiplex the multiplexed optical signals.

[0015] The all-optical wavelength converter 12 converts the wavelength of the wavelength-multiplexed signal light that is route-switched by the optical cross-connect unit. In FIG. 1 , the all-optical wavelength converter 12 on the input side converts an optical signal in the S band (1460-1530 nm wavelength band) to an optical signal in the C band (1530-1565 nm wavelength band), and converts an optical signal in the L band to an optical signal in the C band. The all-optical wavelength converter 12 on the output side converts an optical signal in the C band to an optical signal in the S band, and also converts it to an optical signal in the L band. The all-optical wavelength converter 12 also generates a monitoring wavelength signal from the transmission wavelength signal.

[0016] The frequency deviation correction device 100 is disposed in an all-optical wavelength converter 12 (wavelength converter) that can be installed in an optical cross-connect device 10 (optical repeater node) of a wavelength multiplexing transmission system (optical transmission system). The wavelength converter frequency deviation correction device 100 detects and corrects the frequency deviation of the pump light or the idler light (changed light) of the all-optical wavelength converter 12.

[0017] 1, wavelength converter frequency offset compensation device 100 is installed in each of the input and output all-optical wavelength converters 12, but it may also be connected to only one of the input or output all-optical wavelength converters 12. Furthermore, wavelength multiplexing transmission system 1000 may include optical cross-connect device 10 equipped with wavelength converter frequency offset compensation device 100 and an existing optical cross-connect device that does not include wavelength converter frequency offset compensation device 100. Furthermore, the location where wavelength converter frequency offset compensation device 100 is installed is not limited to optical cross-connect device 10. Configuration examples of wavelength converter frequency offset compensation device 100 will be described later with reference to FIGS. 2A-C.

[0018] WSS13 is an optical switch that not only has the wavelength multiplexing / demultiplexing function of connecting input WDM (Wavelength Division Multiplexing) signals to different output ports for each wavelength, but also has the ability to change the combination of wavelength and output port.By using WSS13, on-site work is not required when changing the transmitting and receiving wavelengths, and path changes can be made quickly by remote operation.

[0019] [Apparatus 100 for Compensating for Frequency Deviation of Wavelength Converter] Figures 2A-C are detailed configuration diagrams of apparatus 100 for compensating for frequency deviation of wavelength converter shown in Figure 1. There are three main configurations of apparatus 100 for compensating for frequency deviation of wavelength converter, and for each of the three main configurations, there are three configuration examples that specifically realize the main configuration. Figures 2A-C show the three main configurations.

[0020] The frequency deviation correcting apparatus 100-1 for a wavelength converter shown in FIG. 2A includes a detecting section 105 that detects the frequency deviation of the pump light, and a correcting section 150 that corrects the detected frequency deviation.

[0021] The wavelength converter frequency deviation correction device 100-2 shown in Figure 2B includes a measurement unit 161 that measures the frequency deviation of the input signal light, a detection unit 108 that detects the frequency deviation of the functional unit wavelength-converted light, and a correction unit 150 that corrects the detected frequency deviation.

[0022] 2C includes an inspection light source 109, a detection unit 108 that detects the frequency deviation of the inspection light source, and a correction unit 150 that corrects the detected frequency deviation. The following describes examples of the configuration.

[0023] 2A includes an optical fiber cable 15, a nonlinear optical medium 101, a pumping light source 102, an optical fiber 15A, an optical multiplexer 103, an optical demultiplexer 104, a detection unit 105, a filter 106, and a correction unit 150. The input signal light may be a single wavelength or a WDM signal light of multiple wavelengths (FIG. 2A shows the case where only one wavelength is input).

[0024] The nonlinear optical medium 101 has nonlinear optical properties and can generate an optical signal with a wavelength different from that of the incident light. As a representative example, any one of highly nonlinear fiber (HNLF), periodically poled lithium niobate (PPLN), and semiconductor optical amplifier (SOA) can be used as the nonlinear optical medium.

[0025] The pumping light source 102 generates pumping light Oe having a predetermined wavelength λe. The pumping light Oe generated by the pumping light source 102 passes through an optical fiber 15A and enters the optical multiplexer 103. The wavelength λe of the pumping light Oe is different from the wavelength λ1 of the input optical signal Oin. The optical intensity of the pumping light Oe is sufficiently greater than that of the input optical signal Oin.

[0026] The optical multiplexer 103 generates light by multiplexing the input optical signal Oin input from the optical fiber cable 15 and the pumping light Oe input from the optical fiber 15A, and sends the generated light to the input end of the nonlinear optical medium 101. The optical demultiplexer 104 demultiplexes the pumping light from the pumping light source 102 and inputs the demultiplexed light to the detection unit 105.

[0027] The detector 105 detects the frequency shift of the pump light when determining the frequency of the idler light, which is wavelength-converted light, from the frequencies of the incident signal light and pump light.

[0028] The correction unit 150 feeds back the frequency shift Δf detected by the detection unit 105 (FB1 indicated by the dashed line in FIG. 2A) and adjusts (corrects) the frequency of the excitation light (symbol a in FIG. 2A).

[0029] The filter 106 filters the output light Oout so as to pass only the outgoing optical signal with wavelength λ2 out of the output light Oout emitted from the output end of the nonlinear optical medium 101. The outgoing optical signal Oo2 with wavelength λ2 is output from the output terminal.

[0030] 2B includes optical fiber cable 15, optical splitter 160 (coupler), measuring unit 161, nonlinear optical medium 101, pumping light source 102, optical fibers 15A and 15B, optical multiplexer 103, filter 106, optical splitter 107 (coupler), detecting unit 108, and correcting unit 150. Components that are the same as those in FIG. 2A are designated by the same reference numerals.

[0031] The measuring unit 161 measures the frequency shift of the input signal light demultiplexed by the optical demultiplexer 160. The optical demultiplexer 107 is connected to the light output side of the filter 106. The output light Oout output from the output end of the nonlinear optical medium 101 is input to the optical demultiplexer 107 via the filter 106. The optical demultiplexer 107 demultiplexes the input light using its wavelength selection characteristics and extracts two types of optical signals. That is, an output optical signal Oo2 with a wavelength λ2 and an output light Oo1 with a wavelength λ1 are output from different output terminals of the optical demultiplexer 107.

[0032] The wavelength λ2 of the outgoing optical signal Oo2 is generated based on the wavelength of the input optical signal Oin, the wavelength λe of the pumping light Oe, and the nonlinear optical characteristics of the nonlinear optical medium 101. The wavelength λ2 of the wavelength-converted outgoing optical signal Oo2 is generated by the input optical signal Oin having a wavelength λ1 passing through the nonlinear optical medium 101 together with the pumping light Oe. In addition, the light emitted from the nonlinear optical medium 101 also contains an optical component having the same wavelength λ1 as before the wavelength conversion.

[0033] The outgoing optical signal Oo2 having a wavelength λ2 output from the optical demultiplexer 107 is sent as a relay output to the downstream optical fiber cable 15. In addition, the outgoing light Oo1 having a wavelength λ1 output from the optical demultiplexer 107 is input to the detection unit 108 via the optical fiber 15B.

[0034] The detector 108 detects the frequency deviation of the idler light when determining the frequency of the idler light, which is wavelength-converted light, from the frequencies of the incident signal light and pump light.

[0035] The corrector 150 feeds back the frequency shift Δf / 2 detected by the detector 105 (FB2 indicated by the dashed line in FIG. 2B) to adjust (correct) the frequency of the excitation light (symbol b in FIG. 2B).

[0036] The frequency shift correction device 100-2 for a wavelength converter shown in Figure 2B has a frequency shift Δf of wavelength-converted light that is twice the frequency shift of the pump light (Figures 3A-C described below), and therefore is able to detect the frequency shift with higher accuracy than when detecting the frequency shift of the pump light (frequency shift correction device 100-1 for a wavelength converter shown in Figure 2A).

[0037] 2C includes optical fiber cable 15, nonlinear optical medium 101, pumping light source 102, inspection light source 109, optical multiplexer 110, optical fibers 15A, 15B, and 15C, optical multiplexer 103, filter 106, optical demultiplexer 107, detector 108, and corrector 150. Components identical to those in FIG. 2B are designated by the same reference numerals.

[0038] The inspection light source 109 generates inspection light Ox with a predetermined wavelength λx. The inspection light Ox generated by the inspection light source 109 passes through an optical fiber 15C and enters the optical multiplexer 110. The wavelength λx of the inspection light Ox is different from the wavelength λe of the pump light Oe and the wavelength λ1 of the input optical signal Oin. The optical intensity of the inspection light Ox is sufficiently greater than that of the input optical signal Oin.

[0039] The optical multiplexer 110 generates light by multiplexing the input optical signal Oin input from the optical fiber cable 15 and the inspection light Ox input from the optical fiber 15B, and sends the light to the input end of the nonlinear optical medium 101.

[0040] The filter 106 transmits only the wavelength-converted light. The detector 108 detects the frequency shift of the wavelength-converted light of the inspection light from the inspection light source when determining the frequency of the idler light, which is wavelength-converted light, from the frequencies of the incident signal light and excitation light.

[0041] The correction unit 150 adjusts (corrects) the frequency of the excitation light (symbol c in FIG. 2C) by feeding back the frequency shift Δf / 2 of the wavelength-converted light of the inspection light detected by the detection unit 108 (FB2 indicated by the dashed line in FIG. 2C).

[0042] In the case of detecting the frequency shift of wavelength-converted light relative to input signal light (wavelength converter frequency shift correction device 100-2 shown in FIG. 2B), when signal light with a wavelength different from or shifted from the expected wavelength is input, it becomes difficult to distinguish whether the frequency shift of the wavelength-converted light is caused by the pump light or the frequency shift of the input signal light. In the wavelength converter frequency shift correction device 100-3 shown in FIG. 2C, a test light source is used to eliminate the frequency shift caused by the frequency shift of the input signal light.

[0043] The operation of the frequency misalignment correction device 100 for a wavelength converter configured as described above will now be described. [Types of Frequency Misalignment and Issues] First, we will explain the three types of frequency misalignment correction device 100 for a wavelength converter (Figs. 2A-C). Figs. 3A-C are diagrams explaining types of frequency misalignment and their issues. Fig. 3A shows the frequency misalignment in wavelength conversion (in the case of four-wave mixing (FWM)), Fig. 3B shows the frequency misalignment in wavelength conversion (in the case of second harmonic generation (SHG) and difference frequency generation (DFG)), and Fig. 3C shows the frequency misalignment in wavelength conversion (in the case of DFG). In Figs. 3A-C, fs is the frequency of the signal light, fp is the frequency of the pump light, fi is the frequency of the wavelength-converted light, and Δf is the frequency misalignment in the pump light.

[0044] In the wavelength conversion shown in FIG. 3A (in the case of four-wave mixing (FWM)), a frequency shift Δf (symbol d in FIG. 3A) of the pump light occurs, and this causes a frequency shift of the wavelength-converted light, fi = 2(fp ± Δf) - fs = (2fp - fs) ± 2Δf.

[0045] In the wavelength conversion shown in Figure 3B (in the case of second harmonic generation (SHG) and difference frequency generation (DFG)), the frequency shift Δf of the pump light (symbol e in Figure 3B) is superimposed on the frequency shift between second harmonic generation (SHG) and difference frequency generation (DFG) (symbol f in Figure 3B), resulting in a frequency shift of 2(fp±Δf).

[0046] In the wavelength conversion (DFG case) and difference frequency generation (DFG) shown in Figure 3C, a frequency shift Δf (symbol g in Figure 3C) occurs in the pump light. Note that in the wavelength conversion (DFG case), a frequency shift of fi = (fp ± Δf) - fs = (fp - fs) ± Δf occurs in the frequency of the wavelength-converted light.

[0047] The AO-WC receives signal light and pump light and generates wavelength-converted light by utilizing second- and third-order nonlinear optical effects. The frequency of the converted light is determined by the frequencies of the signal light and pump light, and if there is a frequency deviation Δf in the pump light frequency fp, the frequency of the converted light will deviate by 2Δf or Δf. Furthermore, this frequency deviation of the converted light may accumulate and increase as the number of times the optical signal passes through the wavelength converter increases.

[0048] Furthermore, since the wavelength-converted light passes through the WSS within the MB-OXC, it is expected that a large filtering penalty will occur due to the frequency shift of the wavelength-converted light. Furthermore, when receiving an optical signal digitally with coherence, the frequency shift between the signal light and the local light will cause errors when the signal is demodulated.

[0049] [Operation of Correction Unit 150] The correction unit 150 (FIGS. 2A to 2C) adjusts the frequency of the excitation light by feeding back the frequency deviation detected by the detection units 105 (FIG. 2A) and 108 (FIGS. 2B to 2C).

[0050] The frequency shift is set by shifting the detected frequency by Δf or Δf / 2, focusing on the fact that whether the frequency shift is the same as or twice the frequency shift of the pump light depends on whether the measurement target is pump light or wavelength-converted light, and whether the principle of wavelength conversion is second-order nonlinear optical effect or third-order nonlinear optical effect.

[0051] <Setting by shifting the detected frequency shift Δf from the set excitation light frequency> The correction unit 150 (Figs. 2A-C) sets by shifting the detected frequency shift Δf from the set excitation light frequency. - When Δf is detected by the detection unit 105 (Fig. 2A) that detects the frequency shift of the excitation light - When Δf is detected by the detection unit 108 (Fig. 2B) that detects the frequency shift of the wavelength-converted light - When wavelength conversion by DFG is performed among the detection unit 108 (Fig. 2C) that detects the frequency shift of the wavelength-converted light of the inspection light

[0052] <Setting by shifting the set excitation light frequency by Δf / 2, which is half of the detected frequency shift Δf> The correction unit 150 (FIGS. 2A-C) sets the excitation light frequency by shifting it by Δf / 2, which is half of the detected frequency shift Δf, from the set excitation light frequency. - When Δf is detected by 108 (FIG. 2B), which detects the frequency shift of the wavelength-converted light - When wavelength conversion is performed by FWM or SHG+DFG, among detection unit 108 (FIG. 2C), which detects the frequency shift of the wavelength-converted light of the inspection light

[0053] [Flowchart showing detection procedure and correction procedure] Fig. 4 is a flowchart explaining how to correct a frequency deviation when a frequency deviation in a wavelength converter is detected, by dividing the processing procedure into a "detection procedure" and a "correction procedure" based on the type of frequency deviation shown in Figs. 3A to 3C. The frequency deviation in a wavelength converter is corrected using wavelength converter frequency deviation correction devices 100-1, 100-2, and 100-3 shown in Figs. 2A to 2C.

[0054] <Procedure for detecting frequency deviation of excitation light in wavelength converter frequency deviation correction device 100-1> When the detection unit 105 of the wavelength converter frequency deviation correction device 100-1 shown in Figure 2A detects the frequency deviation Δf of the excitation light (step S1-1), the process proceeds to step S2-1 of the <correction procedure> in Figure 4, following the flow indicated by the white arrow h in Figure 4.

[0055] <Procedure for Detecting Frequency Deviation of Wavelength-Converted Light in Frequency Deviation Compensation Apparatus 100-2 for Wavelength Converter> When the detection unit 108 of the frequency deviation compensation apparatus 100-2 for wavelength converter shown in FIG. 2B detects the frequency deviation Δf of the converted wavelength light (step S1-2), the flow branches into two paths depending on the type of wavelength conversion. That is, if the wavelength conversion is performed by FWM or SHG+DFG (white arrow i in FIG. 4), the flow proceeds to step S2-2 of the <correction procedure> in FIG. 4. On the other hand, if the wavelength conversion is performed by DFG (white arrow j in FIG. 4), the flow proceeds to step S2-3 of the <correction procedure> in FIG. 4.

[0056] <Procedure for Detecting Frequency Deviation of Wavelength-Converted Test Light in Frequency Deviation Compensation Apparatus 100-3 for Wavelength Converter> When the detection unit 108 of the frequency deviation compensation apparatus 100-2 for a wavelength converter shown in FIG. 2B detects the frequency deviation Δf of the wavelength-converted test light (step S1-3), the flow branches into two paths depending on the type of wavelength conversion. That is, if wavelength conversion is performed by FWM or SHG+DFG (white arrow k in FIG. 4), the flow proceeds to step S2-4 of the <correction procedure> in FIG. 4. On the other hand, if wavelength conversion is performed by DFG (white arrow l in FIG. 4), the flow proceeds to step S2-5 of the <correction procedure> in FIG. 4.

[0057] Based on the results of the case-by-case analysis performed by the detection procedure in FIG. 4, the correction procedure described below is performed. In step S2-1 of the correction procedure in FIG. 4, the frequency of the pump light is corrected by Δf. In step S2-2 of the correction procedure in FIG. 4, the measurement unit 161 (FIG. 2B) measures (confirms) the frequency shift of the input signal light. When the frequency shift of the input signal light is confirmed, the process branches into two flows depending on the cause of the frequency shift. That is, if the frequency shift Δf is caused by the frequency shift of the input signal light (white arrow m in FIG. 4), the process proceeds to step S3-1. On the other hand, if there is no frequency shift of the input signal light (white arrow n in FIG. 4), the process proceeds to step S3-2.

[0058] In step S3-1, the frequency of the pump light is not corrected, and in step S3-2, the frequency shift of the pump light is corrected by Δf / 2.

[0059] On the other hand, when checking the frequency shift of the input signal light in step S2-3, the flow branches into two steps depending on the cause of the frequency shift. That is, if the frequency shift Δf is due to the frequency shift of the input signal light (white arrow o in FIG. 4), the flow proceeds to step S3-3. On the other hand, if there is no frequency shift of the input signal light (white arrow p in FIG. 4), the flow proceeds to step S3-4.

[0060] In step S3-3, the frequency of the pump light is not corrected, and in step S3-4, the frequency shift of the pump light is corrected by Δf.

[0061] 4, the frequency shift of the excitation light is corrected by Δf / 2 in step S2-4, which is reached after step S1-3 when the frequency shift Δf of the wavelength-converted light of the test light is detected.In step S2-5, the frequency shift of the excitation light is corrected by Δf.

[0062] Next, a detailed description will be given of specific configuration examples of detectors 105 and 108 of wavelength converter frequency offset correction devices 100-1, 100-2, and 100-3 in Figures 2A to 2C. Corrector 150 of wavelength converter frequency offset correction devices 100-1, 100-2, and 100-3 is the same as in Figures 2A to 2C, and therefore is not shown in the figure.

[0063] [Specific Configuration Examples of Detector 105 of Wavelength Converter Frequency Deviation Compensation Apparatus 100-1] First, specific configuration examples of detector 105 of wavelength converter frequency deviation compensation apparatus 100-1 of FIG. 2A will be described with reference to FIGS. 5 to 10C. Specific configuration examples of detector 105 of wavelength converter frequency deviation compensation apparatus 100-1 include a first configuration example (FIG. 5) that uses a coupler and a wavemeter, a second configuration example (FIG. 6) that uses a coupler, a filter, and a power meter, and a third configuration example (FIG. 8) that uses a coupler, a local light source, an O / E converter, and an electrical spectrum analyzer. Details of a method for detecting Δf using a filter and a power meter will also be described (FIGS. 9 to 10C).

[0064] <First Configuration Example of Detector 105 of Wavelength Converter Frequency Deviation Compensation Apparatus 100-1> Figure 5 is a configuration diagram showing a first configuration example of detector 105 of wavelength converter frequency deviation compensation apparatus 100-1. Components that are the same as those in Figure 2A are assigned the same reference numerals. Wavelength converter frequency deviation compensation apparatus 100-1 shown in Figure 5 includes optical fiber cable 15, nonlinear optical medium 101, pumping light source 102, optical fiber 15A, optical multiplexer 103, optical demultiplexer 104, detector 105, and filter 106. Detector 105 is composed of wavemeter 120.

[0065] The frequency deviation correction device 100-1 of the wavelength converter shown in FIG. 5 splits the signal using an optical splitter 104 (coupler), and measures the wavelength of the pumping light using a wavemeter 120 to determine fp+Δf.

[0066] Frequency offset correcting apparatus 100-1 for a wavelength converter shown in FIG. 5 can directly measure Δf, and therefore can specify Δf with high accuracy by using a measuring instrument with high resolution.

[0067] <Second Configuration Example of Detector 105 of Wavelength Converter Frequency Deviation Compensation Apparatus 100-1> Figure 6 is a configuration diagram showing a second configuration example of detector 105 of wavelength converter frequency deviation compensation apparatus 100-1. Components that are the same as those in Figure 2B are assigned the same reference numerals. Wavelength converter frequency deviation compensation apparatus 100-1 shown in Figure 6 includes an optical fiber cable 15, a nonlinear optical medium 101, a pumping light source 102, an optical fiber 15A, an optical multiplexer 103, an optical demultiplexer 104, a detector 105, and a filter 106. The detector 105 includes a filter 121 and a power meter 122.

[0068] In the wavelength converter frequency deviation correction device 100-1 shown in FIG. 6, the optical power is measured by a power meter 122 arranged after a filter 121 that splits the wavelength of the pumping light using an optical splitter 104 (coupler) and transmits the wavelength of the pumping light.

[0069] Fig. 7 is a diagram illustrating the relationship between wavelength shift and optical power measured by the power meter 122. The solid line in Fig. 7 indicates the transmission band of the filter, and the dashed line in Fig. 7 indicates the waveform of the measured wavelength. When a wavelength shift occurs as indicated by arrow q in Fig. 7 relative to the transmission band of the filter shown by the solid line in Fig. 7, the optical power received by the power meter 122 becomes weaker.

[0070] The wavelength converter frequency offset corrector 100 - 1 measures or estimates the relationship between Δf and the received power in advance, and determines Δf from the optical power measured by the power meter 122 .

[0071] However, although the magnitude of the wavelength shift can be estimated, the sign of Δf cannot be identified using only one power meter 122. For this reason, in this embodiment, the sign is identified by testing the cases where the wavelength shift is changed by +Δf and −Δf from the value set when adjusting the pump light frequency (described later).

[0072] The frequency deviation correcting apparatus 100-1 for a wavelength converter shown in FIG. 6 does not use an expensive measuring instrument, and therefore can be realized inexpensively.

[0073] <Third Configuration Example of Detector 105 of Wavelength Converter Frequency Deviation Compensation Apparatus 100-1> Figure 8 is a configuration diagram showing a third configuration example of detector 105 of wavelength converter frequency deviation compensation apparatus 100-1. Components that are the same as those in Figure 2C are assigned the same reference numerals. The wavelength converter frequency deviation compensation apparatus 100-1 shown in Figure 8 includes an optical fiber cable 15, a nonlinear optical medium 101, a pumping light source 102, an optical fiber 15A, an optical multiplexer 103, an optical demultiplexer 104, a detector 105, and a filter 106. The detector 105 includes a local light source 131, an optical multiplexer 132, an O / E converter 133, and an electrical spectrum analyzer 134.

[0074] In the wavelength converter frequency deviation correction device 100-1 shown in FIG. 8, the beat signal generated when the optical splitter 104 (coupler) splits the light and combines it with a laser beam set to the wavelength of the pump light is received by an electrical spectrum analyzer 134, and Δf is measured.

[0075] As in the second configuration example described above, since the sign of Δf cannot be identified, the case where the value is changed to +Δf or −Δf from the value set when adjusting the excitation light frequency is tried and identified.

[0076] As in the first configuration example, the wavelength converter frequency deviation correction device 100-1 shown in Figure 8 can directly measure Δf, and therefore, by using a high-resolution measuring instrument, it is possible to determine Δf with high accuracy.

[0077] <Details of Δf Detection Method Using Filter and Power Meter> Next, the Δf detection method using a filter and power meter will be described in detail. Fig. 9 is a diagram showing a configuration for identifying the sign of Δf from the optical power measured by a power meter. The same components as in Fig. 6 are assigned the same reference numerals. Frequency deviation correction device 100-1 for wavelength converter shown in Fig. 9 includes optical fiber cable 15, nonlinear optical medium 101, pumping light source 102, optical fiber 15A, optical multiplexer 103, optical demultiplexer 104, detection unit 105, and filter 106.

[0078] The detecting unit 105 includes an optical multiplexer 123, a filter 121, a power meter 122, a filter 124, and a power meter 125. The detecting unit 105 shown in Fig. 9 has two sets of combinations: one set consisting of a filter 121 and a power meter 122, and the other set consisting of a filter 124 and a power meter 125. A method of detecting Δf using the filter and power meter configured in Fig. 9 will be described later with reference to Fig. 10C.

[0079] 10A-C are diagrams illustrating a method for identifying the sign of Δf in a Δf detection method using a filter and a power meter. The solid lines in FIGS. 10A-C show the filter transmission band, and the dashed lines in FIGS. 10A-C show the waveform of the measured wavelength. FIGS. 10A-B show a method for identifying the sign of Δf when there is a single combination of a filter and a power meter. When there is a single combination of a filter and a power meter, this method can be applied to the detection unit 105 shown in FIG. 6.

[0080] As indicated by arrow q in Figure 10A, the transmission band of filter #1 is set to a width of 0.1 nm or the like, centered on λp. The method for identifying the sign of Δf shown in Figure 10A involves measuring or estimating the relationship between Δf and received power in advance, and identifying Δf from the measured power. Furthermore, since it is not possible to identify the sign of Δf, the sign of the frequency shift is identified by testing the cases where the excitation light frequency is adjusted to +Δf and -Δf from the value set.

[0081] As indicated by the arrow q in Figure 10B, the transmission band of filter #1 is set at a position offset from λp to the positive or negative side (here, offset from λp to the positive side) with a width of 0.1 nm or the like. The method for determining the sign of Δf shown in Figure 10B involves measuring or estimating the relationship between Δf and received power in advance, and determining Δf from the measured power. Because the filter transmission band is set in advance to a position offset from λp to the positive side, the sign of Δf can be determined from the measured power. If the frequency deviation from λp is small, the sign of the frequency deviation can be determined.

[0082] The method for determining the sign of Δf shown in FIG. 10C uses two combinations of filters and power meters. When two combinations of filters and power meters are used, the detection unit 105 shown in FIG. 9 is applied. As indicated by arrows q1 and q2 in FIG. 10C, the transmission bands of filter #1 and filter #2 are set to widths of 0.1 nm on the left and right of λp. The method for determining the sign of Δf shown in FIG. 10C measures or estimates the relationship between Δf and received power in advance, and determines Δf from the measured power. Since a frequency shift occurs in the direction where the power after passing through the filter is larger on the left and right, the sign of the frequency shift is determined. The configuration of frequency shift correction device 100-1 for a wavelength converter and a method for detecting the frequency shift of wavelength-converted light have been described above.

[0083] Next, the configuration of the frequency deviation correcting device 100-2 for a wavelength converter and a method for detecting the frequency deviation of wavelength-converted light will be described.

[0084] [Specific Configuration Examples of Detector 108 in Wavelength Converter Frequency Deviation Compensation Apparatus 100-2] First, specific configuration examples of detector 108 in wavelength converter frequency deviation compensation apparatus 100-1 of Fig. 2B will be described with reference to Figs. 11 to 13. Specific configuration examples of detector 108 in wavelength converter frequency deviation compensation apparatus 100-2 include a first configuration example (Fig. 11) that uses a coupler and a wavemeter, a second configuration example (Fig. 12) that uses a coupler, a filter, and a power meter, and a third configuration example (Fig. 13) that uses a coupler, a local light source, an O / E converter, and an electrical spectrum analyzer.

[0085] <First Configuration Example of Detector 108 of Wavelength Converter Frequency Deviation Compensation Apparatus 100-2> Figure 11 is a configuration diagram showing a first configuration example of detector 108 of wavelength converter frequency deviation compensation apparatus 100-2. Components that are the same as those in Figures 2B and 5 are assigned the same reference numerals. Wavelength converter frequency deviation compensation apparatus 100-2 shown in Figure 11 includes optical fiber cable 15, optical demultiplexer 160, measurement unit 161, nonlinear optical medium 101, pumping light source 102, optical fibers 15A and 15B, optical multiplexer 103, filter 106, optical demultiplexer 107, detector 108, and compensation unit 150 (not shown). Detector 108 is composed of wavemeter 120.

[0086] The frequency deviation correction device 100-2 of the wavelength converter shown in FIG. 11 splits the signal using an optical splitter 107 (coupler), and measures the wavelength of the pumping light using a wavemeter 120 to determine fi+Δf.

[0087] Frequency offset correcting apparatus 100-2 for a wavelength converter shown in FIG. 11 can directly measure Δf, and therefore can specify Δf with high accuracy by using a measuring instrument with high resolution.

[0088] <Second Configuration Example of Detector 108 of Wavelength Converter Frequency Deviation Compensation Apparatus 100-2> Figure 12 is a configuration diagram showing a second configuration example of detector 108 of wavelength converter frequency deviation compensation apparatus 100-2. Components that are the same as those in Figures 2B and 6 are assigned the same reference numerals. Frequency deviation compensation apparatus 100-2 of a wavelength converter shown in Figure 12 includes optical fiber cable 15, optical demultiplexer 160, measuring unit 161, nonlinear optical medium 101, pumping light source 102, optical fibers 15A and 15B, optical multiplexer 103, filter 106, optical demultiplexer 107, detector 108, and compensation unit 150 (not shown).

[0089] In the wavelength converter frequency offset correction device 100-2 shown in Figure 12, optical power is measured using a power meter 122 located after a filter 121 that splits the pump light wavelength using an optical splitter 107 (coupler). The relationship between Δf and the received power is measured or estimated in advance, and Δf is determined from the measured power. Furthermore, since the sign of Δf cannot be determined, as described in Figure 10A, the sign is determined by trying +Δf and -Δf from the value set when adjusting the pump light frequency.

[0090] The frequency deviation correcting apparatus 100-2 for a wavelength converter shown in FIG. 12 does not use an expensive measuring instrument, and therefore can be realized inexpensively.

[0091] <Third Configuration Example of Detector 108 of Wavelength Converter Frequency Deviation Compensation Apparatus 100-2> Figure 13 is a configuration diagram showing a third configuration example of detector 108 of wavelength converter frequency deviation compensation apparatus 100-2. Components that are the same as those in Figures 2C and 8 are assigned the same reference numerals. Frequency deviation compensation apparatus 100-2 of a wavelength converter shown in Figure 13 includes optical fiber cable 15, optical demultiplexer 160, measuring unit 161, nonlinear optical medium 101, pumping light source 102, testing light source 109, optical multiplexer 110, optical fibers 15A, 15B, and 15C, optical multiplexer 103, filter 106, optical demultiplexer 107, detector 108, and compensation unit 150 (not shown).

[0092] In the wavelength converter frequency deviation correction device 100-2 shown in FIG. 13, the beat signal generated when the optical splitter 107 (coupler) splits the light and combines it with laser light set to the wavelength of the pump light is received by an electrical spectrum analyzer 134, and Δf is measured.

[0093] As in the second configuration example described above, since the sign of Δf cannot be identified, the case where the value is changed to +Δf or −Δf from the value set when adjusting the excitation light frequency is tried and identified.

[0094] The wavelength converter frequency deviation correction device 100-2 shown in FIG. 13 can directly measure Δf, as in the first configuration example, and therefore can determine Δf with high accuracy by using a high-resolution measuring instrument.

[0095] An effect common to the wavelength converter frequency deviation correction device 100-2 shown in Figures 11 to 13 is that the frequency deviation Δf of the wavelength-converted light is twice the frequency deviation of the pump light, making it easier to detect the frequency deviation with higher accuracy than when detecting the frequency deviation of the pump light (the wavelength converter frequency deviation correction device 100-1 shown in Figures 5, 6, and 8).

[0096] 11 to 13, optical demultiplexer 107 (coupler) is arranged before filter 106 that extracts wavelength-converted light, but optical demultiplexer 107 (coupler) may be arranged before or after filter 106. The configuration of frequency deviation correction device 100-2 for a wavelength converter and the method for detecting the frequency deviation of wavelength-converted light have been described above.

[0097] Next, the configuration of the frequency deviation correcting device 100-3 for a wavelength converter and a method for detecting the frequency deviation of wavelength-converted light will be described.

[0098] [Specific Configuration Example of the Detection Light Remover 140 of the Wavelength Converter Frequency Misalignment Correction Apparatus 100-3] First, specific configuration examples of the detection light remover 140 of the wavelength converter frequency misalignment correction apparatus 100-3 of FIG. 2B will be described with reference to FIGS. 14 to 17. The specific configuration example of the detection light remover 140 of the wavelength converter frequency misalignment correction apparatus 100-3 is similar to the first configuration example (FIG. 11) of the wavelength converter frequency misalignment correction apparatus 100-2 using a coupler and a wavemeter. It is also similar to the second configuration example (FIG. 12) of the wavelength converter frequency misalignment correction apparatus 100-2 using a coupler, a filter, and a power meter, and to the third configuration example (FIG. 13) of the wavelength converter frequency misalignment correction apparatus 100-2 using a coupler, a local light source, an O / E converter, and an electrical spectrum analyzer.

[0099] <First Configuration Example of the Sensing Light Remover 140 of the Wavelength Converter Frequency Shift Correction Apparatus 100-3> Figure 14 is a configuration diagram showing a first configuration example of the sensing light remover 140 of the wavelength converter frequency shift correction apparatus 100-3. Components that are the same as those in Figure 2C are assigned the same reference numerals. The wavelength converter frequency shift correction apparatus 100-3 shown in Figure 14 includes an optical fiber cable 15, a nonlinear optical medium 101, a pumping light source 102, an inspection light source 109, an optical multiplexer 110, optical fibers 15A, 15B, and 15C, an optical multiplexer 103, the sensing light remover 140, a detector 108, and a correction unit 150 (not shown).

[0100] The detection light removal unit 140 is a functional unit that detects the frequency shift of the wavelength-converted light of the inspection light. In the first configuration example, the detection light removal unit 140 is a WSS (wavelength selective switch) 141, which replaces the filter 106 and optical demultiplexer 107 of the frequency shift correction device 100-3 for wavelength converters shown in FIG. 2C .

[0101] The detection light removal unit 140 sets a port from which the wavelength-converted light of the WSS 141 is output and a port from which the inspection light is output. This removes the detection light and transmits only the wavelength-converted light. The detection light removal unit 140 sets the wavelength of the detection light to a wavelength range that excludes the range of wavelengths that can be assumed before and after wavelength conversion and the excitation light wavelength (λp) within the wavelength range in which wavelength band conversion is possible. Alternatively, it can be set to a wavelength that is not being used at that moment within the wavelength range that can be assumed before wavelength conversion.

[0102] In the wavelength converter frequency offset correction device 100-3, the detector 108 detects the wavelength offset of the detection light. The detector 108 is the same as that used in the wavelength converter frequency offset correction device 100-2 shown in FIGS. 11-13. Therefore, the detector 108 can achieve the same effect as that of the wavelength converter frequency offset correction device 100-2 shown in FIGS. 11-13. That is, when the detector 108 uses a wavemeter 120, or when a local light source, an O / E converter, and an electrical spectrum analyzer are used, Δf can be measured directly, and therefore Δf can be determined with high accuracy by using a high-resolution measuring instrument. Furthermore, when the detector 108 uses a filter and a power meter, expensive measuring instruments are not used, and therefore it can be implemented inexpensively.

[0103] Fig. 15 is a diagram illustrating wavelength setting of the detection light in the detection light removal unit 140 and the inspection light source 109. The thick solid line frame indicated by the symbol r in Fig. 15 indicates the range of wavelengths that can be assumed before wavelength conversion, and the thick dashed line frame indicated by the symbol s in Fig. 15 indicates the range of wavelengths that can be assumed after wavelength conversion. Within these ranges, the shaded area indicated by the symbol t in Fig. 15 indicates the wavelength of the detection light. The wavelength of the detection light is set to a wavelength range (shaded area in Fig. 15) that excludes the range of wavelengths that can be assumed before and after wavelength conversion and the excitation light wavelength (λp) within the range in which wavelength band conversion is possible.

[0104] The frequency deviation correcting apparatus 100-3 for a wavelength converter shown in FIG. 14 can eliminate the frequency deviation caused by the frequency deviation of the input signal light by using a test light source.

[0105] <Second Configuration Example of the Sensing Light Remover 140 of the Wavelength Converter Frequency Shift Correction Apparatus 100-3> Figure 16 is a configuration diagram showing a second configuration example of the sensing light remover 140 of the wavelength converter frequency shift correction apparatus 100-3. The same components as those in Figure 13 are assigned the same reference numerals. The wavelength converter frequency shift correction apparatus 100-3 shown in Figure 16 includes an optical fiber cable 15, a nonlinear optical medium 101, a pumping light source 102, an inspection light source 109, an optical multiplexer 110, optical fibers 15A, 15B, and 15C, an optical multiplexer 103, the sensing light remover 140, a detector 108, and a correction unit 150 (not shown).

[0106] In the second configuration example, the detection light removal unit 140 includes an optical demultiplexer 142 (coupler) and a filter 143. A WDM coupler may be used instead of the optical demultiplexer 142 and the filter 143. The wavelength converter frequency deviation correction device 100-3 shown in Fig. 16 transmits only the wavelength-converted light using the filter 143 or the WDM coupler.

[0107] The frequency deviation correcting apparatus 100-3 for a wavelength converter shown in FIG. 16 can eliminate the frequency deviation caused by the frequency deviation of the input signal light by using a test light source.

[0108] <Third Configuration Example of the Sensing Light Remover 140 of the Wavelength Converter Frequency Shift Correction Apparatus 100-3> Figure 17 is a configuration diagram showing a third configuration example of the sensing light remover 140 of the wavelength converter frequency shift correction apparatus 100-3. The same components as those in Figure 13 are assigned the same reference numerals. The wavelength converter frequency shift correction apparatus 100-3 shown in Figure 17 includes an optical fiber cable 15, a nonlinear optical medium 101, a pumping light source 102, an inspection light source 109, an optical multiplexer 110, optical fibers 15A, 15B, and 15C, an optical multiplexer 103, the sensing light remover 140, a detector 108, and a correction unit 150 (not shown).

[0109] In the third configuration example, the detection light removal unit 140 includes an optical demultiplexer 142 (coupler) and an optical amplifier 144. The frequency deviation correction device 100-3 of a wavelength converter shown in Fig. 17 sets the wavelength of the test light so that it is outside the amplification band of the optical amplifier 144. In other words, the detection light is removed by bringing the wavelength of the test light outside the amplification band of the optical amplifier 144.

[0110] The frequency offset compensation device 100-3 for a wavelength converter shown in Fig. 17 can eliminate frequency offsets caused by frequency offsets of input signal light by using a test light source. In particular, the frequency offset compensation device 100-3 for a wavelength converter shown in Fig. 17 can eliminate detection light without installing any additional equipment by sharing the test light source with an optical amplifier that amplifies wavelength-converted light.

[0111] [Effects] As described above, the frequency deviation correction device 100-1 (FIGS. 2A, 5, 6, 8) of the wavelength converter (all-optical wavelength converter 12) (FIG. 1) provided in the optical repeater node (optical cross-connect device 10) (FIG. 1) of the optical transmission system (wavelength multiplexing transmission system 1000) (FIG. 1) includes a detection unit 105 (FIGS. 2A, 5, 6, 8) that detects the frequency deviation of the excitation light and a correction unit 150 (FIG. 2A) that corrects the detected frequency deviation of the excitation light when determining the frequency of idler light, which is wavelength-converted light, from the frequencies of incident signal light and excitation light.

[0112] In this way, the deviation of the frequency of the pump light or the wavelength-converted light from the desired frequency can be measured and fed back to the frequency setting of the pump light, thereby correcting the frequency deviation of the wavelength-converted light.

[0113] A frequency deviation correction device 100-2 (FIGS. 2B, 11-13) of a wavelength converter (all-optical wavelength converter 12) (FIG. 1) provided in an optical repeater node (optical cross-connect device 10) (FIG. 1) of an optical transmission system (wavelength multiplexing transmission system 1000) (FIG. 1), which, when determining the frequency of idler light, which is wavelength-converted light, from the frequencies of incident signal light and pump light, is provided with a detection unit 108 (FIGS. 2B, 11-13) that detects the frequency deviation of the idler light, and a correction unit 150 (FIG. 2B) that corrects the detected frequency deviation of the idler light.

[0114] In this way, the deviation of the frequency of the pump light or the wavelength-converted light from the desired frequency can be measured and fed back to the frequency setting of the pump light, thereby correcting the frequency deviation of the wavelength-converted light. Furthermore, by measuring the frequency deviation of the wavelength-converted light, which is twice the frequency deviation of the pump light, it is possible to identify the frequency deviation of the pump light with high accuracy.

[0115] A frequency deviation correction device 100-3 (FIGS. 2C, 14, 16, 17) for a wavelength converter (all-optical wavelength converter 12) (FIG. 1) provided in an optical repeater node (optical cross-connect device 10) (FIG. 1) of an optical transmission system (wavelength multiplexing transmission system 1000) (FIG. 1) includes a test light source 109 (FIGS. 2C, 14, 16, 17), and when determining the frequency of idler light, which is wavelength-converted light, from the frequencies of incident signal light and pump light, includes a detection unit 108 (FIGS. 2C, 14, 16, 17) that detects a frequency deviation of wavelength-converted light of test light from the test light source, and a correction unit 150 (FIG. 2C) that corrects the detected frequency deviation of the wavelength-converted light of the test light.

[0116] In this way, the deviation of the frequency of the excitation light or the wavelength-converted light from the desired frequency can be measured and fed back to the frequency setting of the excitation light to correct the frequency deviation of the wavelength-converted light. Furthermore, by measuring the frequency deviation of the wavelength-converted light, which is twice the frequency deviation of the excitation light, it is possible to identify the frequency deviation of the excitation light with high accuracy. In particular, by using detection light, it is possible to measure the frequency deviation of the wavelength-converted light that is caused only by the frequency deviation of the excitation light.

[0117] In wavelength converter frequency deviation correction devices 100, 100-1, 100-2, and 100-3 (FIGS. 1, 2A-C, 5, 6, 8, 11-14, 16, and 17), correction unit 150 sets a frequency deviation from the set excitation light frequency by the detected frequency deviation Δf or half the detected frequency deviation Δf, Δf / 2.

[0118] The present invention focuses on the fact that whether the frequency shift is the same as or twice as large as the frequency shift of the pump light depends on whether the measurement target is pump light or wavelength-converted light, and whether the principle of wavelength conversion is second-order nonlinear optical effect or third-order nonlinear optical effect. By doing so, it is possible to correct (adjust) and identify the frequency shift of the pump light or the wavelength-converted light with high accuracy.

[0119] Furthermore, among the processes described in the above embodiments, all or part of the processes described as being performed automatically can be performed manually, or all or part of the processes described as being performed manually can be performed automatically using known methods. In addition, the processing procedures, control procedures, specific names, and information including various data and parameters shown in the above documents and drawings can be changed as desired unless otherwise specified. Furthermore, the components of each device shown in the drawings are functionally conceptual and do not necessarily have to be physically configured as shown. In other words, the specific form of distribution and integration of each device is not limited to that shown in the drawings, and all or part of the devices can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0120] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be implemented by software that causes a processor to interpret and execute programs that implement the respective functions. Information such as programs, tables, and files that implement the respective functions may be stored in a memory, a recording device such as a hard disk or a solid-state drive (SSD), or a recording medium such as an integrated circuit (IC) card, a secure digital (SD) card, or an optical disk.

[0121] 10 Optical cross-connect device (optical repeater node) 11 Add / Drop function unit (optical multiplexing / demultiplexing unit) 12 All-optical wavelength converter (wavelength converter) 13 WSS 15 Optical fiber cable 15A, 15B, 15C Optical fiber 101 Nonlinear optical medium 102 Pumping light source 103 Optical multiplexer 104, 122, 160 Optical demultiplexer (coupler) 105, 108 Detection unit 106, 121 Filter 109 Inspection light source 100, 100-1, 100-2, 100-3 Frequency deviation correction device for wavelength converter 110 Optical multiplexer 120 Wavelength meter 122 Power meter 140 Detection light removal unit 144 Optical amplifier 150 Correction unit 161 Measurement unit 1000 Wavelength multiplexing transmission system (optical transmission system)

Claims

1. A frequency deviation correction device for a wavelength converter provided in an optical repeater node of an optical transmission system, comprising: a detection unit that detects the frequency deviation of the pump light when determining the frequency of idler light, which is wavelength-converted light, from the frequencies of incident signal light and pump light; and a correction unit that corrects the detected frequency deviation of the pump light.

2. A frequency deviation correction device for a wavelength converter provided in an optical repeater node of an optical transmission system, comprising: a detection unit that detects the frequency deviation of the idler light, which is wavelength-converted light, when the frequency of the idler light is determined from the frequencies of the incident signal light and pump light; and a correction unit that corrects the detected frequency deviation of the idler light.

3. A frequency deviation correction device for a wavelength converter provided in an optical repeater node of an optical transmission system, comprising: a test light source; a detection unit that detects the frequency deviation of the wavelength-converted light of the test light from the test light source when determining the frequency of idler light, which is wavelength-converted light, from the frequencies of incident signal light and pump light; and a correction unit that corrects the detected frequency deviation of the wavelength-converted light of the test light.

4. A frequency deviation correction device for a wavelength converter described in any one of claims 1 to 3, characterized in that the correction unit sets a frequency deviation from the set excitation light frequency by the detected frequency deviation or half the detected frequency deviation.

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