Optical receiver, optical monitor system, and optical reception method

Abstract

This optical receiver comprises: a first optical connection circuit that outputs, to a first path, first response light having an optical level in a first range and having a first response signal multiplexed therein by intensity-modulation of WDM light, and outputs, to a second path, second response light having an optical level in a second range, which does not overlap with the first range, and having a second response signal multiplexed therein by intensity-modulation of an optical carrier having a wavelength different from that of the WDM light; a photoelectric conversion circuit in which the optical reception level enabling output of a response signal from inputted light is within the first range and not within the second range; a level adjustment circuit that is provided in the second path and that adjusts the optical level of light including the second response signal so that the second response signal can be outputted from the photoelectric conversion circuit; and a second optical connection circuit for inputting, to the photoelectric conversion circuit, either the first response light outputted through the first path or the light outputted through the second path.

Description

Optical receiver, optical monitoring system, and optical receiving method

[0001] The present invention relates to an optical receiver and the like.

[0002] In optical submarine cable systems, branching units (BUs) and optical add / drop multiplexers (OADMs) are installed on the seabed. Some of these optical submarine devices have the function of receiving control light transmitted from land-based devices and transmitting response light back to the land-based devices. The response light is a signal containing a response signal. The response signal is response data to the control light, and is transmitted multiplexed with a main signal containing user data. The main signal is an optical signal containing user data, and wavelength division multiplexing (WDM) signal light is mainly used. Wavelength division multiplexing signal light will be referred to as "WDM light" below. The following two methods are known for multiplexing the response signal with the main signal.

[0003] The first modulation method is a method in which the drive current of a pump laser diode in an optical submarine device is intensity-modulated by a response signal. The pump laser diode is a light source used in an optical amplifier that amplifies WDM light. In this method, the entire bandwidth of the WDM light propagating through the optical submarine cable system is intensity-modulated by the response signal. This modulation method will be referred to below as the "full-wave modulation method," and the optical signal generated by the full-wave modulation method will be referred to as the "full-wave modulated signal." In the full-wave modulation method, the modulation depth is set to several percent (%) to suppress the impact of modulation on the transmission quality of the main signal. Here, the modulation depth is the ratio of the power A of the response signal contained in the modulated light power to the power B of the light before modulation, i.e., A / B.

[0004] The second modulation method uses a dedicated optical carrier used only for transmitting the response signal, and intensity-modulates the optical carrier with the response signal. The optical carrier is wavelength-multiplexed with WDM light and transmitted. This modulation method will be referred to below as the "single wavelength modulation method," and the optical signal generated by the single wavelength modulation method will be referred to as the "single wavelength modulated signal." The optical carrier used to generate the single wavelength modulated signal will be referred to below as the "response carrier." The wavelength of the optical carrier used in the single wavelength modulation method is different from that of the WDM light and can be separated from the WDM light using an optical filter or the like. In single wavelength modulation, the WDM light is not affected by modulation, so the modulation depth of the response carrier can be higher than in full-wave modulation. For example, the modulation depth of the response carrier in a single wavelength modulated signal is several tens of percent.

[0005] Both the full-wave modulated signal and the single-wavelength modulated signal include a response signal from the optical submarine equipment. Hereinafter, the full-wave modulated signal and the single-wavelength modulated signal will be collectively referred to as "response light." Depending on the configuration of the optical submarine cable system, the above two types of response light may be used together.

[0006] In relation to the present invention, Patent Document 1 describes a wavelength division multiplexing transmission device having a function of adjusting the level of an optical signal output from an optical amplifier.

[0007] Japanese Patent Application Publication No. 10-341206

[0008] In single-wavelength modulation, the response carrier is multiplexed with WDM light and transmitted from the optical submarine equipment to the onshore equipment. Therefore, even if the modulation depth of the response carrier included in the single-wavelength modulated signal is approximately 40%, the modulation depth of the entire single-wavelength modulated signal including the WDM light may be lower, for example, less than 1%. For example, when a single-wavelength modulated signal is received using an optoelectronic conversion circuit designed for a full-wave modulated signal with a modulation depth of approximately 4%, the power of the response carrier in the single-wavelength modulated signal may be below the level that the optoelectronic conversion circuit can receive, and the response signal may not be demodulated.

[0009] For this reason, in a typical optical receiver, when a full-wave modulation system and a single-wavelength modulation system are mixed to transmit response light, it is necessary to prepare different photoelectric conversion circuits depending on the modulation system. Specifically, in addition to a photoelectric conversion circuit designed to match the reception level of a full-wave modulation signal, it is necessary to prepare another photoelectric conversion circuit designed to match the reception level of a single-wavelength modulation signal. The photoelectric conversion circuit for a single-wavelength modulation signal is a circuit optimized for a lower reception level so that it can demodulate a response signal even from response light of a single-wavelength modulation system with a low modulation depth. In other words, when a typical optical receiver uses a full-wave modulation system and a single-wavelength modulation system together, it is necessary to prepare two photoelectric conversion circuits for each system, which makes the photoelectric conversion circuit complex and large. In other words, a typical optical receiver that uses a mixture of full-wave modulation system and single-wavelength modulation system has the problem of being large in size.

[0010] SUMMARY OF THE INVENTION An object of the present invention is to provide a technique that can suppress an increase in the size of an optical receiver that processes a plurality of response lights in which response signals are multiplexed using different multiplexing methods.

[0011] The optical receiver of the present invention comprises: a first optical connection means that outputs to a first path a first response light, the first response light being light having an optical level in a first range and being light into which a first response signal has been multiplexed by intensity-modulating WDM light; and outputs to a second path a second response light, the second response light being light having an optical level in a second range that does not overlap with the first range and being light into which a second response signal has been multiplexed by intensity-modulating an optical carrier of a wavelength different from the WDM light; an optoelectric conversion means that has an optical reception level that is within the first range and not within the second range at which a response signal can be output from input light; a level adjustment means that is provided on the second path and adjusts the optical level of the light including the second response signal so that the second response signal can be output from the optoelectric conversion means; and a second optical connection means that inputs either the first response light output from the first path or the light output from the second path to the optoelectric conversion means.

[0012] The optical receiving method of the present invention includes the steps of: outputting, to a first path, first response light, which is light having an optical level within a first range and into which a first response signal has been multiplexed by intensity-modulating WDM light; outputting, to a second path, second response light, which is light having an optical level within a second range that does not overlap with the first range and into which a second response signal has been multiplexed by intensity-modulating an optical carrier of a wavelength different from the WDM light; adjusting the optical level of the light including the second response signal so that the second response signal can be output from an optoelectric conversion means provided on the second path and having an optical reception level that can output a response signal from input light that is within the first range and not within the second range; inputting either the first response light output from the first path or the light output from the second path into the optoelectric conversion means; and outputting the response signal from the optoelectric conversion means.

[0013] The present invention can suppress an increase in the size of an optical receiver that processes a plurality of response lights in which response signals are multiplexed using different multiplexing methods.

[0014] FIG. 1 is a diagram illustrating a configuration example of an optical receiver according to a first embodiment. FIG. 2 is a diagram illustrating a configuration example of an optical monitoring system according to a second embodiment. FIG. 3 is a diagram illustrating a level adjustment circuit. FIG. 4 is a diagram illustrating a configuration example of a monitoring control device. FIG. 5 is a diagram illustrating a configuration example of an optical monitoring system according to a first modified example of the second embodiment. FIG. 6 is a diagram illustrating a configuration example of an optical monitoring system according to a second modified example of the second embodiment. FIG. 7 is a diagram illustrating a configuration example of an optical monitoring system according to a third embodiment. FIG. 8 is a diagram illustrating a configuration example of an optical monitoring system according to a fourth embodiment. FIG. 9 is a diagram illustrating a configuration example of an optical monitoring system according to a fifth embodiment.

[0015] Embodiments of the present invention will be described below with reference to the drawings. Arrows shown in the drawings are intended to illustrate the direction of signals, etc., and are not intended to limit the nature of the signals, etc. Furthermore, in the embodiments and drawings, previously mentioned components that are commonly used are given the same reference numerals, and duplicate descriptions may be omitted or simplified.

[0016] 1 is a diagram showing an example of the configuration of an optical receiver 100 according to a first embodiment of the present invention. The optical receiver 100 includes a first optical interconnect circuit 110, a second optical interconnect circuit 120, a level adjustment circuit 130, and an optical / electrical converter (O / E) 140.

[0017] Response light is input to the first optical connection circuit 110 from outside the optical receiver 100. The response light is either a first response light or a second response light. The first response light is light obtained by multiplexing a first response signal by intensity-modulating WDM (Wavelength Division Multiplexing) light. The second response light is light obtained by multiplexing a second response signal. The second response signal is multiplexed with WDM light by intensity-modulating an optical carrier having a wavelength different from that of the WDM light. The optical level of the first response light is within a first range, and the optical level of the second response light is within a second range. The first range and the second range do not overlap. The first response signal and the second response signal can be collectively referred to as a response signal. The response signal is, for example, a signal indicating a processing result in an external optical communication device connected to the optical receiver 100, but is not limited to this. The external optical communication device is, for example, an optical submarine device that transmits user data using WDM light, such as a BU or OADM. The first optical connecting circuit 110 is one form of optical connecting means, and can be called first optical connecting means.

[0018] A first path 111 and a second path 112 are arranged in parallel between the first optical interconnection circuit 110 and the second optical interconnection circuit 120. The second optical interconnection circuit 120 outputs one of the light input from the first path 111 and the light input from the second path 112 to the optoelectric conversion circuit 140. The second optical interconnection circuit 120 is one form of optical interconnection means and can be called second optical interconnection means.

[0019] The photoelectric conversion circuit 140 receives light input from the second optical connecting circuit 120 and outputs a response signal included in the received light as an electrical signal to the outside of the optical receiver 100. The range of optical reception levels (hereinafter referred to as the "dynamic range") in which the photoelectric conversion circuit 140 can output a response signal from the response light is within a first range and is not within a second range. In other words, the dynamic range in which the photoelectric conversion circuit 140 can output a response signal from the input light is within the first range and is not within the second range. The photoelectric conversion circuit 120 having such a function is one form of photoelectric conversion means.

[0020] The second path 112 is provided with a level adjustment circuit 130. The level adjustment circuit 130 adjusts the optical level of the light including the second response signal so that the second response signal can be output from the photoelectric conversion circuit 140. The level adjustment circuit 130 is one form of level adjustment means.

[0021] The optical receiver 100 having such a configuration can suppress an increase in the size of the optical receiver when receiving optical signals in which response signals are multiplexed using different multiplexing methods. This is because the level adjustment circuit 130 adjusts the level of the input optical signal so that the second response signal can be demodulated in the photoelectric conversion circuit 140. With such a configuration, the second response signal can be demodulated from the second response light using the photoelectric conversion circuit 140 whose reception level has been adjusted so that the first response signal can be demodulated from the first response light.

[0022] Second Embodiment Fig. 2 is a diagram showing an example of the configuration of an optical monitoring system 1 according to a second embodiment of the present invention. The optical monitoring system 1 includes an optical receiver 200 and a monitoring control device 800. The optical receiver 200 includes optical switches (OSW) 210 and 220, a level adjustment circuit 230, and an opto-electric conversion circuit (O / E) 240. Note that hereinafter, "optical level" will be simply referred to as "level."

[0023] The optical switches 210 and 220 are both 1x2 optical switches. A response light is input to a common port of the optical switch 210 from outside the optical receiver 200. The response light is an optical signal including a response signal, and is a full-wave modulated signal or a single-wavelength modulated signal transmitted by an optical communication device (not shown). The optical communication device is an optical submarine device such as a BU or OADM. When the optical communication device receives the control light transmitted by the monitor and control device 800, it transmits the response light back to the optical receiver 200. The control light includes a control signal that controls the optical communication device and requests the transmission of a response signal. The response signal, which is a response to the control signal, is multiplexed into the response light using a full-wave modulation method or a single-wavelength modulation method. The full-wave modulation method is a method of intensity-modulating WDM light with a response signal. The single-wavelength modulation method is a method of intensity-modulating an optical carrier (response carrier) with a wavelength different from that of the WDM light with a response signal. Note that in each embodiment of the present application, the full-wave modulated signal and the single-wavelength modulated signal are not input to the optical receiver simultaneously. Moreover, whether the response light is a full-wave modulated signal or a single-wavelength modulated signal differs depending on the optical communication device.

[0024] The common port of the optical switch 210 is connected to an optical transmission device installed outside the optical receiver 200. When the response light input from outside the optical receiver 200 is a full-wave modulated signal, the optical switch 210 outputs the response light to a path 211. When the response light is a single-wavelength modulated signal, the optical switch 210 outputs the response light to a path 212.

[0025] The common port of the optical switch 220 is connected to the photoelectric conversion circuit 240. When the response light is a full-wave modulated signal, the optical switch 220 connects the path 212 to the photoelectric conversion circuit 240. When the response light is a single-wavelength modulated signal, the optical switch 220 connects the output of the level adjustment circuit 230 to the photoelectric conversion circuit 240.

[0026] Path 211 is an optical path that directly connects optical switch 210 and optical switch 220. No optical circuit that changes the properties of the propagating light is arranged on path 211. On the other hand, path 212 is an optical path that connects optical switch 210 and optical switch 220 via level adjustment circuit 230. Level adjustment circuit 230 processes the input single-wavelength modulated signal so that a response signal can be demodulated in photoelectric conversion circuit 240. The level adjustment circuit 230 will be described later.

[0027] The photoelectric conversion circuit 240 converts the light input from path 211 or path 212 via the optical switch 220 into an electrical signal and demodulates the response signal included therein. The dynamic range of the photoelectric conversion circuit 240 is adjusted so that it can demodulate the response signal over the entire power fluctuation range of the full-wave modulated signal input from the optical switch 220. On the other hand, the dynamic range of the photoelectric conversion circuit 240 is not necessarily optimized so that it can demodulate the response signal over the power fluctuation range of the response carrier of the single-wavelength modulated signal input from the optical switch 220. In the single-wavelength modulated signal, the response signal is superimposed on only one response carrier, so the power of the response signal at the power of the response carrier is smaller than the power of the response signal superimposed on the WDM light in the full-wave modulated signal. For example, even if the modulation depth of the full-wave modulated signal is 4% and the modulation depth of the response carrier of the single-wavelength modulated signal is 40%, the optical power of the response signal included in the single-wavelength signal may be converted to a modulation depth of 1% or less in the full-wave modulated signal. In such a case, if an opto-electrical conversion circuit 240 optimized for receiving a full-wave modulated signal is used, there is a risk that the response signal cannot be demodulated from the response carrier of the single-wavelength modulated signal.

[0028] Therefore, in the optical receiver 200 of this embodiment, the response carrier of the single wavelength modulated signal is amplified using the level adjustment circuit 230. By amplifying the response carrier, the photoelectric conversion circuit 240 can demodulate the response signal from both the WDM light and the response carrier within its dynamic range. The demodulated response signal is output to the outside of the optical receiver 200. The response signal may also be input to the monitoring and control device 800.

[0029] FIG. 3 is a diagram illustrating the level adjustment circuit 230. The level adjustment circuit 230 includes optical filters (FIL) 231 and 232 and an optical amplifier (AMP) 233. FIG. 3 schematically illustrates an example of the spectrum of light output from the optical switch 210, with the horizontal axis representing wavelength and the vertical axis representing level (power). In the example spectrum, the white portions schematically indicate fluctuations in the intensity of the spectrum as a result of intensity modulation by the response signal. When the response light is a single-wavelength modulated signal, the optical switch 210 outputs the response light to path 212, and the optical switch 220 connects the optical switch 210 and path 212.

[0030] The optical filter 231 removes the WDM light from the single wavelength modulated signal input from the optical switch 210 and outputs only the response carrier modulated by the response signal. Because the response carrier has a different wavelength from the WDM light, the optical filter 231 can separate only the response carrier from the response light using a dielectric multilayer film or the like. The response carrier is amplified by the optical amplifier 233. The gain of the optical amplifier 233 is set so that the photoelectric conversion circuit 240 can demodulate the response signal from the response carrier.

[0031] The optical filter 232 is a narrow-band optical bandpass filter that removes ASE (Amplified Spontaneous Emission) generated in the optical amplifier 233. By using the optical filter 232, the influence of noise due to ASE light can be reduced when the response signal is demodulated. Note that if the power of the ASE light is at a level that does not affect the quality of the demodulated response signal, the optical filter 232 may be omitted.

[0032] As described above, the optical switches 210 and 220 select the path 211 when the optical signal input to the optical switch 210 is a full-wave modulated signal, and select the path 212 when the optical signal input to the optical switch 210 is a single-wavelength modulated signal. The control (switching instruction) for the optical switches 210 and 220 may be performed by the monitor and control device 800 as described below.

[0033] The monitoring and control device 800 transmits a control signal to the optical communication device as control light, and the optical communication device that receives the control light generates a response signal indicating the content (e.g., the result of control execution) corresponding to the control signal included in the control light. The response signal is converted into response light using full-wave modulation or single-wavelength modulation in the optical communication device and transmitted to the optical receiver 200.

[0034] The monitoring and control device 800 also holds information on the timing at which the control light is transmitted to each optical transmission device. The reception of the control light triggers the transmission of a response light in the optical communication device. The monitoring and control device 800 also holds information on the modulation method of the response light for each optical communication device that transmits the response light. Therefore, the monitoring and control device 800 transmits a switching instruction to the optical receiver 200 to switch the optical switches 210 and 220 according to the modulation method of the response light of the optical communication device to which the control light is to be transmitted. The transmission of the switching instruction is performed before the optical receiver 200 receives the response light from the optical communication device. Through this control, the optical receiver 200 can select the path 211 or 212 according to the modulation method of the response light when it receives the response light corresponding to the control light.

[0035] FIG. 4 illustrates an exemplary configuration of the monitoring and control device 800. The monitoring and control device 800 includes a first transmission circuit 801, a second transmission circuit 802, and a database 803. The first transmission circuit 801 transmits control light to the optical transmission device. The control light is an optical signal including an instruction to transmit a full-wave modulated signal (first response light) or a single-wavelength modulated signal (second response light). The database 803 stores the correspondence between the optical transmission device and the type of response light (whether the response light is a full-wave modulated signal or a single-wavelength modulated signal). The database 803 also stores the timing of transmission of the control light. The second transmission circuit 802 transmits a switching instruction for the optical switches 210 and 220 to the optical receiver 200. The switching instruction is transmitted before the response light from the optical communication device arrives at the optical receiver 200. This allows the optical receiver 200 to distribute the response light to the path 211 or the path 212 depending on the type of the response light. The first transmission circuit 801 and the second transmission circuit 802 are both a form of transmission means. Note that the first transmission circuit 801 can be called the first transmission means, and the second transmission circuit 802 can be called the second transmission means.

[0036] Consider a case where an optical communication device to which the monitor and control device 800 transmits a control light signal transmits a response signal to the optical receiver 200 using full-wave modulation. In this case, before the response light to the transmitted control light is received by the optical receiver 200, the monitor and control device 800 switches the optical switches 210 and 220 to the path 211 side. Because the response light is a full-wave modulated signal, the photoelectric conversion circuit 240 can photoelectrically convert the response light as is and demodulate the response signal.

[0037] On the other hand, consider a case where an optical communication device, which is the destination of the control light from the monitor and control device 800, transmits a response signal to the optical receiver 200 using the single wavelength modulation method. In this case, the monitor and control device 800 switches the optical switches 210 and 220 to the path 212 side before the response light arrives at the optical receiver 200. As a result, the response carrier is amplified in the level adjustment circuit 230. The power of the response carrier is set to a value within the dynamic range of the photoelectric conversion circuit 240 by the optical amplifier 233. Therefore, the photoelectric conversion circuit 240 can demodulate the response signal by photoelectrically converting the amplified response carrier.

[0038] As described above, the optical receiver 200 and the optical monitoring system 1 including the same can suppress an increase in the size of the optical receiver that processes multiple response lights in which response signals are multiplexed using different multiplexing methods. Note that, when the optical receiver 200 transmits the response signal demodulated by the photoelectric conversion circuit 240 to the monitoring control device 800, the database 803 may store the received response signal. This effect can also be obtained in the first and second modifications described below.

[0039] 5 is a diagram showing an example of the configuration of an optical monitoring system 2 which is a first modification of the second embodiment of the present invention. The optical monitoring system 2 includes an optical receiver 201 instead of the optical receiver 200 of the optical monitoring system 1. The optical receiver 201 differs from the optical receiver 200 in that it includes a level adjustment circuit 230A instead of the level adjustment circuit 230.

[0040] The level adjustment circuit 230A includes optical filters 231 and 232, and optical amplifiers 233 and 234. When the response light input from outside the optical receiver 201 is a single-wavelength modulated signal, the optical switch 210 switches the optical path to path 212 so that the response light is input to the level adjustment circuit 230A. The functions of the optical filter 231, optical amplifier 233, and optical filter 232 of the level adjustment circuit 230 are the same as those described in FIG. 3 .

[0041] In the level adjustment circuit 230A, the response carrier output from the optical filter 232 is amplified in optical amplifiers 233 and 234. Since the optical receiver 201 includes the optical amplifier 234 in addition to the optical amplifier 233, the response carrier can be further amplified even when the gain of the optical amplifier 233 alone is insufficient. The amplified response carrier is input to the optical switch 220. As a result, it is possible to demodulate the response signal from the single-wavelength modulated signal in the photoelectric conversion circuit 240, even when the response carrier level is lower, for example. Note that the level adjustment circuit 230A may include an optical filter at the output of the optical amplifier 234 to remove ASE light generated in the optical amplifier 234.

[0042] (Second Modification of Second Embodiment) Fig. 6 is a diagram showing an example of the configuration of an optical monitoring system 3 which is a second modification of the second embodiment of the present invention. The optical monitoring system 3 differs from the optical monitoring system 1 shown in Fig. 2 in that it includes an optical switch 810.

[0043] The optical switch 810 selects a downstream optical fiber through which control light transmitted from the monitor and control device 800 is transmitted to an optical communication device and an upstream optical fiber through which response light to the control light is transmitted. The optical switch 810 is connected to multiple optical communication devices, and each optical communication device is connected to the optical switch 810 via a fiber pair (FP). One fiber pair includes two optical fibers, one of which is used as a downstream optical fiber and the other as an upstream optical fiber. These fiber pairs are connected to the optical switch 810 as an FP group 820. The optical switch 810 selects an optical communication device to be controlled on a fiber pair basis. The control light transmitted by the monitor and control device 800 is transmitted to the optical transmission device to be controlled via one optical fiber of the selected fiber pair. The optical transmission device that receives the control light transmits response light to the optical receiver 200 via the other optical fiber of the selected fiber pair.

[0044] The optical monitoring system 3 includes the optical switch 810, and is therefore capable of transmitting control light to each of a plurality of optical communication devices and receiving response light from each of the optical communication devices.

[0045] 7 is a diagram showing an example of the configuration of an optical monitoring system 4 according to a third embodiment of the present invention. The optical monitoring system 4 includes an optical receiver 300 and a monitoring control device 800. Compared to the optical receiver 200, the optical receiver 300 includes an optical coupler (CPL) 310 instead of the optical switch 210. That is, the optical receiver 300 includes the optical coupler 310, an optical switch 220, a level adjustment circuit 230, and an opto-electrical conversion circuit 240. The configurations and functions of the optical switch 220, the level adjustment circuit 230, and the opto-electrical conversion circuit 240 are similar to those of the optical receiver 200.

[0046] The optical coupler 310 is a 1×2 optical coupler with a branching ratio of 1:1. Response light is input to the optical coupler 310 from outside the optical receiver 300. Whether the input response light is a full-wave modulated signal or a single-wavelength modulated signal, the optical coupler 310 outputs the signal to both paths 211 and 212 with power according to the branching ratio of the optical coupler 310.

[0047] The level adjustment circuit 230 blocks the wavelength of the WDM light and transmits and amplifies only the wavelength of the response carrier. Therefore, even if the response light input from the optical coupler 310 is a full-wave modulated signal, the full-wave modulated WDM light is not output from the level adjustment circuit 230.

[0048] When the input response light is a full-wave modulated signal, the optical switch 220 inputs the light that has propagated through the path 211 to the photoelectric conversion circuit 240. When the input response light is a single-wavelength modulated signal, the optical switch 220 inputs the light output from the level adjustment circuit 230 to the photoelectric conversion circuit 240. The optical switch 220 may be controlled by the monitor and control device 800.

[0049] The optical monitoring system 4 and the optical receiver 300 having such a configuration can suppress an increase in the size of the optical receiver that receives optical signals in which response signals are multiplexed using different multiplexing methods, because the level adjustment circuit 230 adjusts the level of the input optical signal so that the second response signal can be demodulated in the photoelectric conversion circuit 240.

[0050] Furthermore, the optical receiver 300 includes only one optical switch. Therefore, the configuration of the optical switch and its control circuit can be simplified compared to the optical receiver 200, which includes two optical switches. Note that the level adjustment circuit 230 may be replaced by the level adjustment circuit 230A included in the optical receiver 201.

[0051] 8 is a diagram showing an example of the configuration of an optical monitoring system 5 according to a fourth embodiment of the present invention. The optical monitoring system 5 includes an optical receiver 400 and a monitoring control device 800. The optical receiver 400 includes an optical coupler 410, an optical switch 220, a level adjustment circuit 430, and an opto-electric conversion circuit 240. Compared to the optical receiver 300, the optical receiver 400 includes the optical coupler 410 instead of the optical coupler 310, and the level adjustment circuit 430 instead of the level adjustment circuit 230. The configurations and functions of the optical switch 220 and the opto-electric conversion circuit 240 are similar to those of the optical receivers 200 and 300.

[0052] The optical coupler 410 is a 1x2 optical coupler with unequal branching. In this embodiment, the optical coupler 410 has a branching ratio of 90%:10% (10 dB optical coupler), but the branching ratio is not limited to this. Response light is input to the optical coupler 410 from outside the optical receiver 400. Regardless of whether the input response light is a full-wave modulated signal or a single-wavelength modulated signal, the optical coupler 410 outputs the signal to both path 211 and path 212. Furthermore, the branching side of the optical coupler 410 has a smaller branching ratio (i.e., a larger branching loss) connected to path 211, and a larger branching ratio (i.e., a smaller branching loss) connected to path 212. In this embodiment, the optical coupler 410 is a 10 dB optical coupler. Therefore, the transmission loss from the input side of the optical coupler 410 to the path 211 is about 10 dB, and the transmission loss from the input side of the optical coupler 410 to the path 212 is about 0.5 dB.

[0053] The level adjustment circuit 430 includes an optical filter 231. The optical filter 231 transmits only light of the wavelength of the response carrier. Therefore, if the response light is a full-wave modulated signal, the full-wave modulated WDM light is blocked by the optical filter 231. Because the level adjustment circuit 430 does not include an optical amplifier, the response carrier output from the optical filter 231 is input to the optical switch 220 without being amplified.

[0054] The operation of the optical switch 220 is similar to that of the optical receivers 200 and 300. That is, when the response light input to the optical receiver 400 is a full-wave modulated signal, the optical switch 220 inputs the light propagating through the path 211 to the photoelectric conversion circuit 240. When the response light is a single-wavelength modulated signal, the optical switch 220 inputs the response carrier propagating through the path 212 to the photoelectric conversion circuit 240. The optical switch 220 may be controlled by the monitor and control device 800.

[0055] In this embodiment, the optical coupler 410 is an unequal branching optical coupler. Therefore, the power of the response light branched to path 211 differs from the power of the response light branched to path 212. In this embodiment, the branching loss to path 212, which has a higher branching ratio, is approximately 9 dB smaller than the branching loss to path 211. Therefore, the difference between the power of the response carrier input to the level adjustment circuit 430 and the power of the full-wave modulated signal propagating through path 211 is approximately 9 dB smaller than the configuration using the optical switch 210 exemplified in the second embodiment, etc. In other words, by using the optical coupler 410, the optical receiver 400 can reduce the difference between the power of the full-wave modulated signal input to the opto-electrical conversion circuit 240 and the power of the response carrier. As a result, when both powers fall within the dynamic range of the opto-electrical conversion circuit 240, the response signal can be demodulated not only from the full-wave modulated signal but also from the response carrier using the opto-electrical conversion circuit 240, which has a dynamic range for receiving the full-wave modulated signal. The branching ratio of the optical coupler 410 is set so that the photoelectric conversion circuit 240 can demodulate the response signal whether the response light is a full-wave modulated signal or a single-wavelength modulated signal.

[0056] Like the optical receiver 300, the optical receiver 400 requires only one optical switch. Therefore, compared to the optical receiver 200, the control circuit can be simplified. Furthermore, by using the optical coupler 410, which is an unequal branching optical coupler, the optical receiver 400 can reduce the difference between the power of the response carrier of the single-wavelength modulated signal input to the opto-electrical conversion circuit 240 and the power of the full-wave modulated signal. Therefore, the optical receiver 400 can demodulate the response signal without providing an optical amplifier in the level adjustment circuit 430. In the optical receiver 400, the optical coupler 410 distributes a higher level response light to path 212 than path 211. That is, the optical coupler 410 performs the function of the level adjustment circuit 130 described in FIG. 1 . The optical monitoring system 5 and optical receiver 400 configured as described above can suppress an increase in the size of the optical receiver when receiving optical signals in which response signals are multiplexed using different multiplexing methods.

[0057] 9 is a diagram showing an example of the configuration of an optical monitoring system 6 according to a fifth embodiment of the present invention. The optical monitoring system 6 includes an optical receiver 500 and a monitoring control device 800. The optical receiver 500 includes a WDM filter 510, an optical switch 220, a level adjustment circuit 530, and an opto-electrical conversion circuit 240. Compared to the optical receiver 200, the optical receiver 500 includes the WDM filter 510 instead of the optical switch 210, and the level adjustment circuit 530 instead of the level adjustment circuit 230. The configurations and functions of the optical switch 220 and the opto-electrical conversion circuit 240 are similar to those of the optical receiver 200.

[0058] The WDM filter 510 is an optical demultiplexer that separates the input response light by wavelength. The WDM filter 510 may be configured with a dielectric multilayer filter or a wavelength selective switch (WSS). Response light is input to the WDM filter 510 from outside the optical receiver 500. The WDM filter 510 outputs, of the input response light, light in the wavelength band of the WDM light to the path 211 and light in the wavelength band of the response carrier to the path 212. That is, the optical path from the input of the WDM filter 510 to the path 211 functions as an optical bandpass filter that transmits only the wavelength of the WDM light. The optical path from the input of the WDM filter 510 to the path 212 functions as an optical bandpass filter that transmits only the wavelength of the response carrier of the single-wavelength modulated signal.

[0059] The level adjustment circuit 530 includes an optical amplifier 233 and an optical filter 232. The optical amplifier 233 amplifies the response carrier separated by the WDM filter 510. The gain of the optical amplifier 233 is set so that the photoelectric conversion circuit 240 can demodulate the response signal from the response carrier. The optical filter 232 removes ASE generated in the optical amplifier 233. If the power of the ASE light is low enough not to affect the quality of the response signal, the optical filter 232 may be omitted.

[0060] The optical monitoring system 6 and optical receiver 500 having such a configuration can suppress an increase in the size of the optical receiver, which receives optical signals in which response signals are multiplexed using different multiplexing methods. Furthermore, like the optical receivers 300 and 400, the optical receiver 500 requires only one optical switch. Therefore, the control circuit can be simplified compared to the optical receiver 200. Furthermore, because the WDM filter 510 includes a narrowband filter function for the path 212, a narrowband filter is not required in the level adjustment circuit 530, and the configuration of the level adjustment circuit 530 can be simplified.

[0061] The embodiments of the present invention can be described as follows, but are not limited to these.

[0062] (Supplementary Note 1) An optical receiver comprising: a first optical connection means that outputs, to a first path, first response light, which is light having an optical level in a first range and is light into which a first response signal is multiplexed by intensity-modulating WDM light, and outputs, to a second path, second response light, which is light having an optical level in a second range that does not overlap with the first range and is light into which a second response signal is multiplexed by intensity-modulating an optical carrier of a wavelength different from the WDM light; a photoelectric conversion means that has an optical reception level at which a response signal can be output from input light that is within the first range and not within the second range; a level adjustment means that is provided on the second path and that adjusts the optical level of light including the second response signal so that the second response signal can be output from the photoelectric conversion means; and a second optical connection means that inputs either the first response light output from the first path or the light output from the second path to the photoelectric conversion means.

[0063] (Supplementary Note 2) An optical receiver as described in Supplementary Note 1, wherein the first optical connection means and the second optical connection means include an optical switch that selects one of the first path and the second path, and the level adjustment means includes an optical filter that transmits light that includes the second response signal, and an optical amplifier that amplifies the light that includes the second response signal output from the optical filter.

[0064] (Supplementary Note 3) An optical receiver as described in Supplementary Note 1, wherein the first optical connection means includes an optical coupler that branches both the first response light and the second response light into the first path and the second path, the second optical connection means includes an optical switch that selects one of the first path and the second path, and the level adjustment means includes an optical filter that transmits light that includes the second response signal, and an optical amplifier that amplifies the light that includes the second response signal output from the optical filter.

[0065] (Supplementary Note 4) The optical receiver described in Supplementary Note 1, wherein the first optical connection means includes an unequal branching optical coupler that branches both the first response light and the second response light to the first path and the second path at different branching ratios; the second optical connection means includes an optical switch that selects one of the first path and the second path; and the level adjustment means includes an optical filter that transmits light including the second response signal.

[0066] (Supplementary Note 5) An optical receiver as described in Supplementary Note 1 or 2, wherein the first optical connection means includes a demultiplexer that outputs the first response light to the first path and outputs light including the response signal included in the second response light to the second path, the second optical connection means includes an optical switch that selects one of the first path and the second path, and the level adjustment means includes an optical amplifier that amplifies the light including the second response signal input from the demultiplexer.

[0067] (Supplementary Note 6) The optical receiver according to any one of Supplementary Notes 1 to 5, wherein at least one of the first optical connecting means and the second optical connecting means is controlled in response to an external switching instruction.

[0068] (Supplementary Note 7) An optical monitoring system comprising: an optical receiver according to Supplementary Note 6, which receives the first response light and the second response light transmitted by an optical transmission device; and a monitoring control device which transmits control light to the optical transmission device, requesting transmission of the first response light or the second response light, and transmits the switching instruction to the optical receiver.

[0069] (Supplementary Note 8) An optical monitoring system according to Supplementary Note 7, further comprising an optical switch for selecting a fiber pair connecting the optical receiver and the optical transmission device, wherein the monitoring and control device inputs the control light to the selected fiber pair, and the optical receiver receives the first response light or the second response light from the selected fiber pair.

[0070] (Supplementary Note 9) The optical monitoring system according to Supplementary Note 7, wherein the monitoring and control device comprises: a first transmitting means for transmitting control light to an optical transmission device, the control light requesting transmission of the first response light or the second response light; a database for storing correspondence between the optical transmission device and the type of response light and the timing of transmission of the control light; and a second transmitting means for transmitting to the optical receiver, before the first response light or the second response light arrives at the optical receiver, a switching instruction for an optical switch provided in the optical receiver, according to the timing of transmission of the control light and the correspondence between the optical transmission device and the type of response light.

[0071] (Supplementary Note 10) An optical receiving method comprising: outputting, to a first path, first response light, which is light having an optical level in a first range and into which a first response signal has been multiplexed by intensity-modulating WDM light; outputting, to a second path, second response light, which is light having an optical level in a second range not overlapping with the first range and into which a second response signal has been multiplexed by intensity-modulating an optical carrier of a wavelength different from the WDM light; adjusting the optical level of the light including the second response signal so that the second response signal can be output from a photoelectric conversion means provided on the second path and having an optical reception level at which a response signal can be output from input light that is within the first range and not within the second range; inputting either the first response light output from the first path or the light output from the second path into the photoelectric conversion means; and outputting the response signal from the photoelectric conversion means.

[0072] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that are understandable to those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. For example, the present invention can be applied not only to optical submarine cable systems but also to terrestrial optical transmission systems. Each embodiment also discloses an optical receiver, an optical monitoring system, an optical receiving method, a monitoring control device, and a monitoring control method.

[0073] Furthermore, the configurations described in the respective embodiments are not necessarily mutually exclusive, and the functions and effects of the present invention may be achieved by a configuration that combines all or part of the above-described embodiments.

[0074] Some or all of the functions and procedures of the optical receiver described in each of the above embodiments may be realized by a central processing unit (CPU) included in the optical receiver or monitoring control device in each embodiment executing a program. The program is recorded on a tangible and non-transitory recording medium. The recording medium may be, but is not limited to, a semiconductor memory or a fixed magnetic disk device.

[0075] 1-6 Optical monitoring system 100, 200, 201, 300, 400, 500 Optical receiver 111 First path 112 Second path 130, 230, 230A, 430, 530 Level adjustment circuit 140, 240 Photoelectric conversion circuit 210, 220 Optical switch 211, 212 Path 231, 232 Optical filter 233, 234 Optical amplifier 310, 410 Optical coupler 510 WDM filter 530 Level adjustment circuit 800 Monitoring and control device 801 First transmission circuit 802 Second transmission circuit 803 Database 810 Optical switch 820 FP group

Claims

1. outputting a first response light, which is light having an optical level in a first range and is light into which a first response signal is multiplexed by intensity-modulating WDM (Wavelength Division Multiplexing) light, to a first path; outputting, to a second path, second response light, which is light having an optical level in a second range not overlapping with the first range and is light into which a second response signal has been multiplexed by intensity-modulating an optical carrier having a wavelength different from that of the WDM light; a first optical connection means; a photoelectric conversion means for converting input light into a response signal at an optical reception level that is within the first range and not within the second range; a level adjusting means provided on the second path for adjusting the optical level of light including the second response signal so that the second response signal can be output from the photoelectric conversion means; a second optical connection means for inputting either the first response light output from the first path or the light output from the second path to the photoelectric conversion means; An optical receiver comprising:

2. the first optical connecting means and the second optical connecting means each include an optical switch that selects one of the first path and the second path; The level adjustment means an optical filter that transmits light including the second response signal; and an optical amplifier that amplifies light including the second response signal output from the optical filter; 2. The optical receiver according to claim 1.

3. the first optical connection means includes an optical coupler that branches both the first response light and the second response light into the first path and the second path, the second optical connection means includes an optical switch that selects one of the first path and the second path; The level adjustment means an optical filter that transmits light including the second response signal; and an optical amplifier that amplifies light including the second response signal output from the optical filter; 2. The optical receiver according to claim 1.

4. the first optical connection means includes an unequal branching optical coupler that branches the first response light and the second response light into the first path and the second path at different branching ratios, the second optical connection means includes an optical switch that selects one of the first path and the second path; the level adjustment means includes an optical filter that transmits light including the second response signal.

2. The optical receiver according to claim 1.

5. the first optical connection means includes a demultiplexer that outputs the first response light to the first path and outputs light including the response signal included in the second response light to the second path; the second optical connection means includes an optical switch that selects one of the first path and the second path; the level adjusting means includes an optical amplifier that amplifies the light including the second response signal input from the demultiplexer; 3. An optical receiver according to claim 1 or 2.

6. 3. The optical receiver according to claim 1, wherein at least one of said first optical connecting means and said second optical connecting means is controlled in response to an external switching instruction.

7. an optical receiver according to claim 6 , which receives the first response light and the second response light transmitted from an optical transmission device; a monitoring and control device that transmits control light to the optical transmission device to request transmission of the first response light or the second response light, and transmits the switching instruction to the optical receiver.

8. an optical switch for selecting a fiber pair connecting the optical receiver and the optical transmission device; the monitor and control device inputs the control light into the selected fiber pair; the optical receiver receives the first response light or the second response light from the selected fiber pair; 8. An optical monitoring system according to claim 7.

9. The monitoring and control device includes: a first transmitting means for transmitting a control light to the optical transmission device, the control light requesting transmission of the first response light or the second response light; a database that stores the correspondence between the optical transmission device and the type of response light, and the timing of transmitting the control light; a second transmitting means for transmitting a switching instruction for an optical switch included in the optical receiver to the optical receiver before the first response light or the second response light arrives at the optical receiver, in accordance with a timing of transmitting the control light and a correspondence between the optical transmission device and the type of the response light; Equipped with 8. An optical monitoring system according to claim 7.

10. outputting a first response light, which is light having an optical level in a first range and is light into which a first response signal is multiplexed by intensity-modulating WDM (Wavelength Division Multiplexing) light, to a first path; outputting, to a second path, second response light, which is light having an optical level in a second range not overlapping with the first range and is light into which a second response signal is multiplexed by intensity-modulating an optical carrier having a wavelength different from that of the WDM light; adjusting the optical level of light including the second response signal so that the second response signal can be output from a photoelectric conversion means provided on the second path and having an optical reception level at which a response signal can be output from input light that is within the first range and not within the second range; inputting either the first response light output from the first path or the light output from the second path into the photoelectric conversion means; outputting the response signal from the photoelectric conversion means; Optical receiving method.