Optical receiver, optical monitoring system, and optical receiving 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

Technical Field

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

Background Art

[0002] In an optical submarine cable system, a branch unit (BU) and an optical add-drop multiplexer (OADM) are installed on the seabed. Some of such optical submarine devices have a function of receiving control light transmitted from an onshore device and returning response light to the onshore device. The response light is a signal including a response signal. The response signal is response data for the control light and is multiplexed with a main signal including user data and transmitted. The main signal is an optical signal including user data, and wavelength division multiplexing (WDM) signal light is mainly used. The wavelength division multiplexed signal light is hereinafter referred to as "WDM light". The following two types are known as methods for multiplexing a response signal with a main signal.

[0003] The first modulation method is a method in which, in an optical submarine device, the drive current of an excitation laser diode is intensity-modulated by a response signal. The excitation laser diode is a light source used in an optical amplifier that amplifies WDM light. In this method, the entire band of the WDM light propagating through the optical submarine cable system is intensity-modulated by the response signal. This modulation method is hereinafter referred to as the "full-wave modulation method", and the optical signal generated by the full-wave modulation method is referred to as the "full-wave modulation signal". In the full-wave modulation method, the modulation degree is set to several percent (%) in order to suppress the influence on the transmission quality of the main signal due to modulation. Here, the modulation degree is the ratio of the power A of the response signal included in the power of the light after modulation to the power B of the light before modulation, that is, A / B.

[0004] The second modulation method uses a dedicated optical carrier used solely for transmitting the response signal, and modulates the intensity of this optical carrier with the response signal. The optical carrier is transmitted by wavelength multiplexing with WDM light. This modulation method will be referred to as the "single-wavelength modulation method" below, 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 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 is a wavelength that 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 the modulation, so the modulation degree of the response carrier can be higher than in the full-wave modulation method. For example, the modulation degree of the response carrier of a single-wavelength modulated signal is several tens of percent.

[0005] Both full-wave modulated signals and single-wavelength modulated signals include response signals from optical submarine equipment. Hereafter, both full-wave modulated signals and single-wavelength modulated signals will be collectively referred to as "response light." Depending on the configuration of the optical submarine cable system, these two types of response light may be used in combination.

[0006] In connection with the present invention, Patent Document 1 describes a wavelength division multiplexing transmission device equipped with a function to adjust the level of an optical signal output from an optical amplifier. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 10-341206 [Overview of the project] [Problems that the invention aims to solve]

[0008] In single-wavelength modulation schemes, the response carrier is combined with WDM light and transmitted from the submarine optical equipment to the land-based equipment. Therefore, even if the modulation index of the response carrier included in the single-wavelength modulated signal is around 40%, the overall modulation index of the single-wavelength modulated signal including the WDM light will be lower, for example, less than 1%. For example, if a single-wavelength modulated signal is received using a photoelectric converter circuit designed for a full-wave modulation signal with a modulation index of around 4%, the power of the response carrier within the power of the single-wavelength modulated signal may fall below the level that the photoelectric converter circuit can receive, potentially preventing the demodulation of the response signal.

[0009] Therefore, in a typical optical receiver, when full-wave modulation and single-wavelength modulation are used together to transmit response light, it was necessary to prepare different photoelectric conversion circuits depending on the modulation method. Specifically, in addition to a photoelectric conversion circuit designed to match the reception level of the full-wave modulation signal, it was necessary to prepare another photoelectric conversion circuit designed to match the reception level of the single-wavelength modulation signal. The photoelectric conversion circuit for the single-wavelength modulation signal is a circuit optimized for lower reception levels so that the response signal can be demodulated even from the response light of a single-wavelength modulation method with a low modulation degree. In other words, in a typical optical receiver, when full-wave modulation and single-wavelength modulation are used together, it is necessary to prepare two types of photoelectric conversion circuits for each method, resulting in a complex and large photoelectric conversion circuit. That is, a problem with typical optical receivers that use full-wave modulation and single-wavelength modulation together is their large size.

[0010] (Purpose of the invention) The present invention aims to provide a technology that can suppress an increase in the scale of an optical receiver in an optical receiver that processes multiple response lights in which response signals are multiplexed using different multiplexing methods. [Means for solving the problem]

[0011] The optical receiver of the present invention is A first optical connection means outputs a first response light to a first path, which is light having a first range of light levels and in which a first response signal is multiplexed by intensity modulation of WDM light, and a second response light to a second path, which is light having a second range of light levels that does not overlap with the first range and in which a second response signal is multiplexed by intensity modulation of optical carriers of a different wavelength than the WDM light. A photoelectric conversion means having an optical reception level capable of outputting a response signal from input light that is within the first range and not within the second range, A level adjustment means provided in the second path, which 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, A second optical connection means inputs either the first response light output from the first path or the light output from the second path to the photoelectric conversion means, It is equipped with.

[0012] The light receiving method of the present invention is A first response light, which is light having a first range of light levels and in which a first response signal is multiplexed by intensity modulation of WDM light, is output to a first path. A second response light is output to a second path, which is light having a second range of light levels that does not overlap with the first range, and in which a second response signal is multiplexed by intensity modulation of light carriers of a different wavelength than the WDM light. The optical level of the light including the second response signal is adjusted so that the second response signal can be output from a photoelectric conversion means provided in the second path, whose optical reception level capable of outputting a response signal from the input light is within the first range and not within the second range. Either the first response light output from the first path or the light output from the second path is input to the photoelectric conversion means. The photoelectric conversion means outputs the response signal, Includes instructions. [Effects of the Invention]

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

Brief Description of the Drawings

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

Modes for Carrying Out the Invention

[0015] Embodiments of the present invention will be described below with reference to the drawings. The arrows shown in the drawings illustrate the directions of signals and the like, and are not intended to limit the nature of the signals and the like. Also, in the embodiments and the drawings, the same reference numerals are given to the existing components that are commonly used, and duplicate explanations may be omitted or simplified.

[0016] (First Embodiment) Figure 1 shows an example of the configuration of an optical receiver 100 in a first embodiment of the present invention. The optical receiver 100 includes a first optical connection circuit 110, a second optical connection circuit 120, a level adjustment circuit 130, and an optical / electrical converter (O / E) 140.

[0017] The first optical connection circuit 110 receives response light from outside the optical receiver 100. The response light is either the first response light or the second response light. The first response light is light in which the first response signal is multiplexed by intensity modulation of WDM (Wavelength Division Multiplexing) light. The second response light is light in which the second response signal is multiplexed. The second response signal is multiplexed with WDM light by intensity modulation of an optical carrier of a different wavelength than the WDM light. The optical level of the first response light is in the first range, and the optical level of the second response light is in the 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 the response signal. The response signal is, for example, a signal indicating the 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 connection circuit 110 is a form of optical connection means and can be called the first optical connection means.

[0018] Between the first optical connection circuit 110 and the second optical connection circuit 120, a first path 111 and a second path 112 are arranged in parallel. The second optical connection circuit 120 outputs either the light input from the first path 111 or the light input from the second path 112 to the photoelectric conversion circuit 140. The second optical connection circuit 120 is a form of optical connection means and can be called a second optical connection means.

[0019] The photoelectric conversion circuit 140 receives light input from the second optical connection circuit 120 and outputs the response signal contained in the received light as an electrical signal to the outside of the optical receiver 100. The range of optical reception levels in which the photoelectric conversion circuit 140 can output a response signal from the response light (hereinafter referred to as the "dynamic range") is within the first range and not within the 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 not within the second range. A 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 containing 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 this configuration, can suppress an increase in the size of the optical receiver in an optical receiver that receives optical signals from which response signals have been 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 this 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) Figure 2 shows an example configuration of an optical monitoring system 1 in a second embodiment of the present invention. The optical monitoring system 1 comprises an optical receiver 200 and a monitoring control device 800. The optical receiver 200 comprises optical switches (OSW) 210 and 220, a level adjustment circuit 230, and a photoelectric conversion circuit (O / E) 240. Hereafter, "optical level" will be simply referred to as "level".

[0023] Optical switches 210 and 220 are both 1x2 optical switches. A response light is input to the common port of optical switch 210 from outside the optical receiver 200. The response light is an optical signal containing 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 a control light transmitted by the monitoring and control device 800, it sends a response light back to the optical receiver 200. The control light contains a control signal that controls the optical communication device and requests the return of a response signal. The response light is multiplexed with a response signal, which is a reply to the control signal, using either a full-wave modulated method or a single-wavelength modulated method. The full-wave modulated method is a method that modulates the intensity of WDM light with the response signal. The single-wavelength modulated method is a method that modulates the intensity of an optical carrier (response carrier) with a different wavelength than WDM light with the response signal. In each embodiment of this application, the full-wave modulated signal and the single-wavelength modulated signal are not input to the optical receiver simultaneously. Furthermore, whether the response light is a full-wave modulated signal or a single-wavelength modulated signal varies 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. If 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 path 211. If the response light is a single-wavelength modulated signal, the optical switch 210 outputs the response light to 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 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 circuits that change the properties of propagating light are arranged in 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 the response signal can be demodulated in the photoelectric conversion circuit 240. 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 contained in each. The dynamic range of the photoelectric conversion circuit 240 is adjusted so that the response signal can be demodulated 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 the response signal can be demodulated over the power fluctuation range of the response carrier of the single-wavelength modulated signal input from the optical switch 220. In a single-wavelength modulated signal, the response signal is superimposed on only one response carrier, so the power of the response signal in terms of the power of the response carrier is smaller than the power of the response signal superimposed on the WDM light in a full-wave modulated signal. For example, even if the modulation index of the full-wave modulated signal is 4% and the modulation index of the response carrier of the single-wavelength modulated signal is 40%, the optical power of the response signal contained in the single-wavelength signal may be less than 1% when converted to the modulation index of the full-wave modulated signal. In such cases, using the photoelectric conversion circuit 240, which is optimized for receiving full-wave modulated signals, may result in the inability to demodulate the response signal 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] Figure 3 illustrates the level adjustment circuit 230. The level adjustment circuit 230 includes optical filters (FIL) 231 and 232 and an optical amplifier (AMP) 233. Figure 3 schematically shows an example of the spectrum of light output from the optical switch 210, with wavelength on the horizontal axis and level (power) on the vertical axis. In the example spectrum, the white areas schematically show that the intensity of the spectrum fluctuates 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 WDM light from the single-wavelength modulated signal input from the optical switch 210, outputting only the response carriers modulated by the response signal. Since the response carriers have a different wavelength from the WDM light, the optical filter 231 can separate only the response carriers from the response light using a dielectric multilayer film or the like. The response carriers are 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 carriers.

[0031] The optical filter 232 is a narrowband 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 caused by ASE light during demodulation of the response signal can be reduced. However, if the power of the ASE light does not affect the quality of the demodulated response signal, the optical filter 232 may be omitted.

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

[0033] The monitoring and control device 800 transmits a control signal to the optical communication device as a control light. The optical communication device, upon receiving the control light, generates a response signal indicating the content corresponding to the control signal contained in the control light (for example, the result of the control execution). The response signal is converted into response light by the optical communication device using a full-wave modulation method or a single-wavelength modulation method and transmitted to the optical receiver 200.

[0034] The monitoring and control device 800 also retains information on the timing of the transmission of control light to each optical transmission device. In the optical communication device, the reception of control light triggers the transmission of response light. The monitoring and control device 800 also retains information on the modulation scheme of the response light for each optical communication device that transmits the response light. Therefore, the monitoring and control device 800 transmits switching instructions to the optical receiver 200 to switch the optical switches 210 and 220 according to the modulation scheme of the response light of the optical communication device to which the control light is transmitted. The transmission of the switching instructions takes place before the response light from the optical communication device is received by the optical receiver 200. Through this control, when the optical receiver 200 receives the response light corresponding to the control light, it can select either path 211 or 212 according to the modulation scheme of the response light.

[0035] Figure 4 shows an example configuration of the monitoring and control device 800. The monitoring and control device 800 comprises a first transmitting circuit 801, a second transmitting circuit 802, and a database 803. The first transmitting circuit 801 transmits control light to the optical transmission device. The control light is an optical signal that includes an instruction requesting the transmission of 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 the transmission of the control light. The second transmitting circuit 802 transmits switching instructions for the optical switches 210 and 220 to the optical receiver 200. The transmission of the switching instructions takes place before the response light from the optical communication device arrives at the optical receiver 200. As a result, the optical receiver 200 can distribute the response light to either path 211 or path 212 depending on the type of response light. Both the first transmitting circuit 801 and the second transmitting circuit 802 are forms of transmitting means. The first transmitting circuit 801 can be called the first transmitting means, and the second transmitting circuit 802 can be called the second transmitting means.

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

[0037] On the other hand, consider the case where the optical communication device, which is the destination of the control light from the monitoring and control device 800, transmits a response signal to the optical receiver 200 using a single-wavelength modulation scheme. In this case, the monitoring 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 then adjusted by the optical amplifier 233 to a value within the dynamic range of the photoelectric conversion circuit 240. 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 it can suppress an increase in the size of the optical receiver in an optical receiver that processes multiple response lights in which response signals are multiplexed by different multiplexing methods. Furthermore, when the optical receiver 200 transmits the demodulated response signal from 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 similarly in the following first and second modifications.

[0039] (First modified example of the second embodiment) Figure 5 shows 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 in place 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 in place 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 as described in Figure 3.

[0041] In the level adjustment circuit 230A, the response carrier output from the optical filter 232 is amplified by optical amplifiers 233 and 234. Since the optical receiver 201 is equipped with optical amplifier 234 in addition to optical amplifier 233, the response carrier can be further amplified even when the gain of 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, for example, when the response carrier level is lower. The level adjustment circuit 230A may also be equipped with an optical filter at the output of optical amplifier 234 to remove ASE light generated in optical amplifier 234.

[0042] (Second modification of the second embodiment) Figure 6 shows an example 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 Figure 2 in that it includes an optical switch 810.

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

[0044] The optical monitoring system 3, equipped with an optical switch 810, can transmit control light to each of the multiple optical communication devices and receive response light from each optical communication device.

[0045] (Third embodiment) Figure 7 shows an example configuration of an optical monitoring system 4 in a third embodiment of the present invention. The optical monitoring system 4 comprises an optical receiver 300 and a monitoring control device 800. Compared to the optical receiver 200, the optical receiver 300 is equipped with an optical coupler (CPL) 310 instead of an optical switch 210. That is, the optical receiver 300 comprises an optical coupler 310, an optical switch 220, a level adjustment circuit 230, and a photoelectric conversion circuit 240. The configuration and function of the optical switch 220, the level adjustment circuit 230, and the photoelectric conversion circuit 240 are the same as those of the optical receiver 200.

[0046] Optical coupler 310 is a 1x2 optical coupler with a branching ratio of 1:1. Response light is input to optical coupler 310 from outside the optical receiver 300. Regardless of whether the input response light is a full-wave modulated signal or a single-wavelength modulated signal, optical coupler 310 outputs the signal to both paths 211 and 212 with power corresponding to the branching ratio of 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] If the input response light is a full-wave modulated signal, the optical switch 220 inputs the light propagated through path 211 to the photoelectric conversion circuit 240. If the input response light is a single-wavelength modulated signal, the optical switch 220 inputs the light output from level adjustment circuit 230 to the photoelectric conversion circuit 240. The optical switch 220 may be controlled by the monitoring and control device 800.

[0049] The optical monitoring system 4 and optical receiver 300, having this configuration, can suppress an increase in the size of the optical receiver in an optical receiver that receives each optical signal from which the response signal has been multiplexed using different multiplexing methods. This is 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 is equipped with 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 is equipped with two optical switches. In addition, the level adjustment circuit 230A provided in the optical receiver 201 may be used instead of the level adjustment circuit 230.

[0051] (Fourth embodiment) Figure 8 shows an example configuration of an optical monitoring system 5 in a fourth embodiment of the present invention. The optical monitoring system 5 comprises an optical receiver 400 and a monitoring control device 800. The optical receiver 400 comprises an optical coupler 410, an optical switch 220, a level adjustment circuit 430, and a photoelectric conversion circuit 240. Compared to the optical receiver 300, the optical receiver 400 is equipped with an optical coupler 410 instead of an optical coupler 310, and a level adjustment circuit 430 instead of a level adjustment circuit 230. The configuration and function of the optical switch 220 and the photoelectric conversion circuit 240 are the same as those of the optical receivers 200 and 300.

[0052] The optical coupler 410 is an unequal branch 1x2 optical coupler. In this embodiment, the optical coupler 410 has a branch ratio of 90%:10% (10dB optical coupler), but the branch ratio is not limited to this. The optical coupler 410 receives response light 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 paths 211 and 212. On the branch side of the optical coupler 410, the side with the smaller branch ratio (i.e., the side with the larger branch loss) is connected to path 211, and the side with the larger branch ratio (i.e., the side with the smaller branch loss) is connected to path 212. In this embodiment, the optical coupler 410 is a 10dB optical coupler. Therefore, the pass-through loss from the input side of the optical coupler 410 to path 211 is approximately 10 dB, and the pass-through loss from the input side of the optical coupler 410 to path 212 is approximately 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, when the response light is a full-wave modulated signal, the full-wave modulated WDM light is blocked by the optical filter 231. Since 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 amplification.

[0054] The operation of the optical switch 220 is the same as that of the optical receivers 200 and 300. That is, if the response light input to the optical receiver 400 is a full-wave modulated signal, the optical switch 220 inputs the light propagated along path 211 to the photoelectric conversion circuit 240. If the response light is a single-wavelength modulated signal, the optical switch 220 inputs the response carrier propagated along path 212 to the photoelectric conversion circuit 240. The optical switch 220 may be controlled by the monitoring and control device 800.

[0055] In this embodiment, the optical coupler 410 is an unequal branch optical coupler. Therefore, the power of the response light branched to path 211 is different from the power of the response light branched to path 212. In this embodiment, the branching loss to path 212, which has a larger branching ratio, is about 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 when the full-wave modulated signal propagates through path 211 is about 9 dB smaller compared to 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 photoelectric conversion circuit 240 and the power of the response carrier. As a result, when both of these powers fall within the dynamic range of the photoelectric conversion circuit 240, the photoelectric conversion circuit 240, which has a dynamic range for receiving the full-wave modulated signal, can demodulate the response signal not only from the full-wave modulated signal but also from the response carrier. The branching ratio of the optical coupler 410 is set so that the photoelectric conversion circuit 240 can demodulate the response signal regardless of 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, the control circuit can be simplified compared to the optical receiver 200. Furthermore, by using an unequal branch optical coupler 410, the optical receiver 400 can reduce the difference between the power of the response carrier of the single-wavelength modulated signal input to the photoelectric conversion circuit 240 and the power of the full-wave modulated signal. Therefore, the optical receiver 400 enables demodulation of 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 response light at a higher level to path 212 than to path 211. In other words, the optical coupler 410 performs the function of the level adjustment circuit 130 described in Figure 1. The optical monitoring system 5 and optical receiver 400 with such a configuration can suppress an increase in the size of the optical receiver in each optical receiver that receives optical signals multiplexed by different multiplexing methods.

[0057] (Fifth embodiment) Figure 9 shows an example configuration of an optical monitoring system 6 in a fifth embodiment of the present invention. The optical monitoring system 6 comprises an optical receiver 500 and a monitoring control device 800. The optical receiver 500 comprises a WDM filter 510, an optical switch 220, a level adjustment circuit 530, and a photoelectric conversion circuit 240. Compared to the optical receiver 200, the optical receiver 500 includes a WDM filter 510 instead of an optical switch 210, and a level adjustment circuit 530 instead of a level adjustment circuit 230. The configuration and function of the optical switch 220 and the photoelectric conversion circuit 240 are the same as 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 composed of a dielectric multilayer filter or a Wavelength Selective Switch (WSS). The response light is input to the WDM filter 510 from outside the optical receiver 500. The WDM filter 510 outputs the light in the WDM light wavelength band to path 211 and the light in the response carrier wavelength band to path 212. That is, the optical path from the input to path 211 in the WDM filter 510 functions as an optical bandpass filter that transmits only the wavelength of the WDM light. The optical path from the input to path 212 in the WDM filter 510 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 carriers 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 carriers. 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 this configuration, can suppress an increase in the size of the optical receiver in an optical receiver that receives each optical signal multiplexed by different multiplexing methods. Also, like optical receivers 300 and 400, optical receiver 500 only requires one optical switch. Therefore, the control circuit can be simplified compared to optical receiver 200. Furthermore, since the WDM filter 510 includes the function of a narrowband filter for 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 may also be described as follows, but are not limited thereto.

[0062] (Note 1) A first optical connection means outputs a first response light to a first path, which is light having a first range of light levels and in which a first response signal is multiplexed by intensity modulation of WDM light, and a second response light to a second path, which is light having a second range of light levels that does not overlap with the first range and in which a second response signal is multiplexed by intensity modulation of optical carriers of a different wavelength than the WDM light. A photoelectric conversion means having an optical reception level capable of outputting a response signal from input light that is within the first range and not within the second range, A level adjustment means provided in the second path, which 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, A second optical connection means inputs 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 equipped with the following features.

[0063] (Note 2) The first optical connection means and the second optical connection means include an optical switch that selects either the first path or the second path. The level adjustment means is An optical filter that transmits light including the second response signal, and Includes an optical amplifier that amplifies the light including the second response signal output from the optical filter, The optical receiver described in Appendix 1.

[0064] (Note 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 either the first path or the second path. The level adjustment means is An optical filter that transmits light including the second response signal, and Includes an optical amplifier that amplifies the light including the second response signal output from the optical filter, The optical receiver described in Appendix 1.

[0065] (Note 4) The first optical connection means includes an unequal branching optical coupler that branches both the first response light and the second response light into the first path and the second path with different branching ratios. The second optical connection means includes an optical switch that selects either the first path or the second path. The level adjustment means includes an optical filter that transmits light including the second response signal, The optical receiver described in Appendix 1.

[0066] (Note 5) The first optical connection means includes a demultiplexer that outputs the first response light to the first path and the light containing the response signal included in the second response light to the second path. The second optical connection means includes an optical switch that selects either the first path or the second path. The level adjustment means includes an optical amplifier that amplifies the light including the second response signal input from the demultiplexer. Optical receiver as described in Appendix 1 or 2.

[0067] (Note 6) At least one of the first optical connection means and the second optical connection means is an optical receiver as described in any one of Appendix 1 to 5, which is controlled in response to an external switching instruction.

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

[0069] (Note 8) The optical switch is provided to select the fiber pair connecting the optical receiver and the optical transmission device. The monitoring and control device inputs the control light to the selected fiber pair. The optical receiver receives the first response light or the second response light from the selected fiber pair. The optical monitoring system described in Appendix 7.

[0070] (Note 9) The aforementioned monitoring and control device is A first transmitting means for transmitting a control light to an optical transmission device that requests the 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 the transmission of the control light, A second transmitting means transmits a switching instruction for the optical switch provided 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 the timing of the transmission of the control light and the correspondence between the optical transmission device and the type of response light. Equipped with, The optical monitoring system described in Appendix 7.

[0071] (Note 10) A first response light, which is light having a first range of light levels and in which a first response signal is multiplexed by intensity modulation of WDM light, is output to a first path. A second response light is output to a second path, which is light having a second range of light levels that does not overlap with the first range, and in which a second response signal is multiplexed by intensity modulation of light carriers of a different wavelength than the WDM light. The optical level of the light including the second response signal is adjusted so that the second response signal can be output from a photoelectric conversion means provided in the second path, whose optical reception level capable of outputting a response signal from the input light is within the first range and not within the second range. Either the first response light output from the first path or the light output from the second path is input to the photoelectric conversion means. The photoelectric conversion means outputs the response signal, Optical reception method.

[0072] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the embodiments described above. Various modifications can be made to the configuration and details of the present invention that will be understood by those skilled in the art 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 onshore optical transmission systems. Each embodiment also discloses embodiments of optical receivers, optical monitoring systems, optical receiving methods, monitoring and control devices, and monitoring and control methods.

[0073] Furthermore, the configurations described in each embodiment are not necessarily mutually exclusive. The operation 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 implemented by a central processing unit (CPU) in the optical receiver or monitoring and control device in each embodiment executing a program. The program is recorded on a fixed, tangible and non-transitory recording medium. Semiconductor memory or fixed magnetic disk devices may be used as the recording medium, but are not limited to these. [Explanation of symbols]

[0075] 1-6 Optical Monitoring System 100, 200, 201, 300, 400, 500 Optical Receivers 111 The first route 112 Second Route 130, 230, 230A, 430, 530 Level Adjustment Circuit 140, 240 Photoelectric Conversion Circuit 210, 220 Optical switches Routes 211 and 212 231, 232 Light filters 233, 234 Optical amplifier 310, 410 Optical Coupler 510 WDM filter 530 Level Adjustment Circuit 800 Monitoring and Control Device 801 First Transmitter Circuit 802 Second Transmitter Circuit 803 Database 810 Optical switch 820 FP group

Claims

1. A first response light, which is light having a first range of light levels and in which a first response signal is multiplexed by intensity modulation of WDM (Wavelength Division Multiplexing) light, is output to a first path. The second response light, which is light having a second range of light levels that does not overlap with the first range, and in which a second response signal is multiplexed by intensity modulation of light carriers of a different wavelength than the WDM light, is output to the second path. First optical connection means, A photoelectric conversion means having an optical reception level capable of outputting a response signal from input light that is within the first range and not within the second range, A level adjustment means provided in the second path, which 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, A second optical connection means inputs 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 equipped with the following features.

2. 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. The level adjustment means is An optical filter that transmits light including the second response signal, and The optical amplifier includes an optical amplifier that amplifies the light, which includes the second response signal output from the optical filter, The optical receiver described in 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 either the first path or the second path. The level adjustment means is An optical filter that transmits light including the second response signal, and The optical amplifier includes an optical amplifier that amplifies the light, which includes the second response signal output from the optical filter, The optical receiver described in claim 1.

4. The first optical connection means includes an unequal branch optical coupler that branches both the first response light and the second response light into the first path and the second path with different branching ratios. The second optical connection means includes an optical switch that selects either the first path or the second path. The level adjustment means includes an optical filter that transmits light including the second response signal, The optical receiver described in claim 1.

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

6. The optical receiver according to claim 1 or 2, wherein at least one of the first optical connection means and the second optical connection 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 by the optical transmission device, An optical monitoring system comprising: a monitoring control device that transmits a control light requesting the transmission of the first response light or the second response light to the optical transmission device, and transmits the switching instruction to the optical receiver.

8. The optical switch is provided to select the fiber pair connecting the optical receiver and the optical transmission device. The monitoring and control device inputs the control light to the selected fiber pair. The optical receiver receives the first response light or the second response light from the selected fiber pair. The optical monitoring system described in claim 7.

9. The aforementioned monitoring and control device is A first transmitting means for transmitting a control light to the optical transmission device that requests the 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 the transmission of the control light, A second transmitting means transmits the switching instruction to the optical receiver before the first response light or the second response light arrives at the optical receiver, depending on the timing of the transmission of the control light and the correspondence between the optical transmission device and the type of response light. Equipped with, The optical monitoring system described in claim 7.

10. A method for receiving light used in an optical receiver, By the first optical connection means, A first response light, which is light having a first range of light levels and in which a first response signal is multiplexed by intensity modulation of WDM (Wavelength Division Multiplexing) light, is output to a first path. A second response light is output to a second path, which is light having a second range of light levels that does not overlap with the first range, and in which a second response signal is multiplexed by intensity modulation of light carriers of a different wavelength than the WDM light. By means of level adjustment, The optical level of the light including the second response signal is adjusted so that the second response signal can be output from a photoelectric conversion means provided in the second path, whose optical reception level capable of outputting a response signal from the input light is within the first range and not within the second range. By the second optical connection means, Either the first response light output from the first path or the light output from the second path is input to the photoelectric conversion means. The photoelectric conversion means outputs the response signal. Optical reception method.

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