JP2019208111A - Optical receiver and reception method - Google Patents

Abstract

To provide an optical receiver capable of stabilizing reception characteristics by appropriately controlling light power inputted thereto.SOLUTION: An optical receiver in the embodiment comprises light attenuation means 1, separation means 2, photoelectric conversion means 3, and control signal generation means 4. The light attenuation means 1 attenuates light power of inputted signal light. The separation means 2 separates polarization of the signal light whose light power has been attenuated by the light attenuation means 1. The photoelectric conversion means 3 is provided for each of polarization components obtained through the polarization separation performed by the separation means 2 and converts the signal light of each of the polarization components into an electric signal with the use of photoelectric conversion elements connected to a power source via a common power line, before outputting the electric signal. The control signal generation means 4 detects variation in a current flowing through the power line and generates, on the basis of a detection result of the variation in the current, a control signal for controlling the amount of attenuation of the light power by the light attenuation means 1. The light attenuation means 1 attenuates the light power on the basis of the control signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical signal reception technique, and more particularly to a technique for controlling the optical power of a reception signal.

  Digital coherent large-capacity optical communication network systems are widely used. In such an optical communication network system, it is desirable that an optical receiver that receives an optical signal via a transmission line has stable operation and reception characteristics of each element constituting the optical receiver. In order to maintain the reception characteristics, it is necessary to stabilize the reception characteristics by suppressing the failure of each element in the optical receiver and the characteristic fluctuation. For example, in order to suppress failure or characteristics due to input of signal light having strong optical power to each element in the optical receiver, it is necessary to suppress the input optical power to a certain level or less.

  In order to keep the optical power input to each element in the optical receiver below a certain level, for example, a method of attenuating the optical power by providing an optical attenuator at the input unit is used. As a technique for attenuating optical power by providing an optical attenuator in the input unit, for example, a technique as disclosed in Patent Document 1 is disclosed.

  Patent Document 1 relates to an optical transmission device including an optical receiver that performs coherent detection. The optical receiver of the optical transmission device of Patent Document 1 attenuates the optical power of the input optical signal by providing a variable optical attenuator in the input unit. The optical receiver of Patent Document 1 detects the optical power for each photoelectric conversion element based on the electrical signal converted from the signal light in the photoelectric conversion element of each channel when performing coherent detection. The optical receiver of Patent Document 1 controls the optical power output from the variable optical attenuator to the subsequent stage by the control circuit controlling the attenuation amount of the variable optical attenuator based on the detection result for each channel. .

Japanese Patent Laid-Open No. 2006-154297

  However, the technique of Patent Document 1 is not sufficient in the following points. The optical receiver of Patent Document 1 detects the optical power for each photoelectric conversion element, and controls the attenuation amount of the variable optical attenuator based on the individual detection results. Therefore, in order to control the attenuation amount of the variable optical attenuator based on the sum of the input optical powers, a control circuit for determining the attenuation amount of the variable attenuator is required, and the apparatus can be increased in size. For this reason, Patent Document 1 is not sufficient as a technique for appropriately managing the input optical power without stabilizing the device configuration and stabilizing the reception characteristics.

  In order to solve the above-described problems, an object of the present invention is to provide an optical receiver capable of appropriately managing input optical power and stabilizing reception characteristics without complicating the device configuration. Yes.

  In order to solve the above-described problems, the optical attenuating unit, the separating unit, the photoelectric conversion unit, and the control signal generating unit of the present invention are provided. The light attenuating means attenuates the optical power of the input signal light. The separating means polarization separates the signal light whose light power has been attenuated by the light attenuating means. The photoelectric conversion means is provided for each polarization component that has been polarization-separated by the separation means, and the signal light of each polarization component is converted into an electrical signal by the photoelectric conversion element connected to the power source via a common power line. Convert and output. The control signal generation means detects a change in current flowing in the power supply line, and generates a control signal for controlling the attenuation amount of the optical power in the optical attenuation means based on the detection result of the current fluctuation. The light attenuating unit attenuates the optical power based on the control signal.

  In the receiving method of the present invention, the optical power of the input signal light is attenuated, and the signal light whose optical power is attenuated is subjected to polarization separation. The receiving method of the present invention converts each signal light of each polarization component into an electric signal by a photoelectric conversion element provided for each polarization component separated by polarization and connected to a power source via a common power line. And output. The receiving method of the present invention detects fluctuations in the current flowing through the power supply line, and generates a control signal for controlling the attenuation amount of the optical power based on the detection result of the fluctuation in current. The receiving method of the present invention attenuates optical power based on the control signal.

  According to the present invention, it is possible to appropriately manage the input optical power without complicating the apparatus configuration, and to stabilize the reception characteristics.

It is a figure which shows the outline | summary of a structure of the 1st Embodiment of this invention. It is a figure which shows the outline | summary of a structure of the 2nd Embodiment of this invention. It is a figure which shows the example of a structure of the optical receiver of a structure contrasted with this invention. It is a figure which shows the example of a structure of the optical transmission apparatus using the optical receiver of the 2nd Embodiment of this invention.

(First embodiment)
A first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an outline of the configuration of the optical receiver of this embodiment. The optical receiver of this embodiment includes an optical attenuating unit 1, a separating unit 2, a photoelectric conversion unit 3, and a control signal generating unit 4. The optical attenuating means 1 attenuates the optical power of the input signal light. The separating unit 2 polarization-separates the signal light whose optical power is attenuated by the light attenuating unit 1. The photoelectric conversion means 3 is provided for each polarization component that has been polarization-separated by the separation means 2, and the signal light of each polarization component is electrically converted by the photoelectric conversion element connected to the power source via a common power line. Convert to signal and output. The control signal generation unit 4 detects a change in the current flowing through the power supply line, and generates a control signal for controlling the attenuation amount of the optical power in the optical attenuation unit 1 based on the detection result of the current change. The light attenuating means 1 attenuates the optical power based on the control signal.

  In the optical receiver according to the present embodiment, the control signal generation unit 4 detects fluctuations in the current flowing in the common power supply line that supplies power to the photoelectric conversion element, and controls the attenuation amount of the optical power in the optical attenuation unit 1. Yes. That is, the optical receiver of the present embodiment is based on the detection result of the fluctuation of the current flowing in the common power supply line, and based on the sum of the optical power of the signal light input to the plurality of photoelectric conversion elements, The attenuation amount of the optical power of the signal light can be controlled. Therefore, the optical receiver of the present embodiment is based on the sum of the optical powers input to the optical receiver while controlling the complexity of the device configuration by controlling based on fluctuations in the current flowing in the common power supply line. Thus, the attenuation can be controlled appropriately. As a result, by using the optical receiver of this embodiment, each element is protected by appropriately managing the optical power of the signal light input to each element in the optical receiver, and reception characteristics are stabilized. be able to.

(Second Embodiment)
A second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 shows an outline of the configuration of the optical receiver 100 of the present embodiment. The optical receiver 100 of the present embodiment is used as a module that receives an optical signal by coherent detection in a digital coherent optical communication system.

  The configuration of the optical receiver 100 will be described. The optical receiver 100 according to this embodiment includes an optical receiver 10, a signal processor 20, a local light source unit 30, and a power supply unit 40.

  The optical receiver 10 includes a variable optical attenuator 11, a beam splitter 12, an optical hybrid 13, a photodiode 14, a transimpedance amplifier 15, a resistor 16, and a differential amplifier circuit 17.

  The variable optical attenuator 11 attenuates the optical power of the input optical signal and outputs it. The variable optical attenuator 11 controls the amount of optical power attenuation based on the voltage value of a signal input as a control signal from the differential amplifier circuit 17.

  The variable optical attenuator 11 of this embodiment is configured such that the amount of attenuation of optical power increases as the amplitude value of the voltage of the control signal increases. As the variable optical attenuator 11, for example, a micro electro mechanical systems (MEMS) type optical attenuator is used. Further, the function of the variable optical attenuator 11 of this embodiment corresponds to the optical attenuator 1 of the first embodiment.

  The beam splitter 12 polarization-separates the input optical signal and outputs it. The beam splitter 12 includes a beam splitter 12-1 that separates an optical signal by polarization and a beam splitter 12-2 that separates a local light by polarization. The beam splitter 12-1 separates the polarization of the optical signal input from the communication path, outputs the X polarization to the optical hybrid 13-1, and sends the Y-shaped wave to the optical hybrid 13-2. In addition, the beam splitter 12-2 polarization-separates light input from the local light source unit 30, outputs X-polarized light to the optical hybrid 13-1, and sends Y-shaped waves to the optical hybrid 13-2. Further, the function of the beam splitter 12 of the present embodiment corresponds to the separating unit 2 of the first embodiment.

  The optical hybrid 13 combines the input optical signal and the local light by causing them to interfere with each other through two paths whose phases are different by 90 degrees. The optical hybrid 13-1 has two phases of the X-wave component of the optical signal input from the beam splitter 12-1 and the X-polarized component of the local light input from the beam splitter 12-2 that are 90 degrees different from each other. Combine on the route.

  The optical hybrid 13-1 uses an I-phase (Quadrature) component signal and an I-phase (Quadrature) component signal generated by combining the optical signal and the local light with a path that is 90 degrees out of phase. 1 and to the photodiode 14-2.

  The optical hybrid 13-2 includes two components whose phases are different from each other by 90 degrees between the Y polarization component of the optical signal input from the beam splitter 12-1 and the Y polarization component of the local light input from the beam splitter 12-2. Combine on the route. The optical hybrid 13-2 uses an I-phase component signal and a Q-phase component signal generated by combining an optical signal and local light through a path whose phase is 90 degrees different from each other, and outputs a photodiode 14-3 and a photodiode 14-4. Send to.

  The photodiode 14 converts the input optical signal into an electric signal, and outputs it as a current signal to the transimpedance amplifier 15 connected to the anode side. The photodiode 14 of the present embodiment is formed as a balanced photodiode. Each photodiode 14 is connected to a power supply unit 40.

  The photodiode 14-1 and the photodiode 14-2 convert the optical signal of the X polarization I-phase component and the Q-phase component input from the optical hybrid 13-1 into an electrical signal, and the transimpedance amplifier 15-1. Output to the transimpedance amplifier 15-2. The photodiode 14-3 and the photodiode 14-4 convert the Y-polarized I-phase component and Q-phase optical signals input from the optical hybrid 13-2 into electrical signals, and the transimpedance amplifier 15-3. Output to the transimpedance amplifier 15-4. The function of the photodiode 14 of the present embodiment corresponds to the photoelectric conversion means 3 of the first embodiment.

  The resistor 16 is provided between the power supply unit 40 and each photodiode 14. The resistance value of the resistor 16 is set so that the differential amplifier circuit 17 can detect the fluctuation of the current flowing through the power supply line as the fluctuation of the voltage.

  The differential amplifier circuit 17 is connected to both ends of the resistor 16 and amplifies and outputs a voltage signal based on the voltage difference between both ends of the resistor 16. The differential amplifier circuit 17 is configured using an operational amplifier. The differential amplifier circuit 17 amplifies the output signal so that the amplitude of the voltage of the output signal becomes an amplitude suitable for the control of the variable optical attenuator 11. The amplification factor in the differential amplifier circuit 17 is set in advance so that the amplitude of the voltage of the output signal becomes an amplitude suitable for the control of the variable optical attenuator 11. Further, the differential amplifier circuit 17 of the present embodiment corresponds to the control signal generating unit 4 of the first embodiment.

  The transimpedance amplifier 15 converts the current signal input from the photodiode 14 into a voltage signal and outputs the voltage signal to the signal processing unit 20. The transimpedance amplifier 15 corresponds to each photodiode 14, and four transimpedance amplifiers 15-1, transimpedance amplifier 15-2, transimpedance amplifier 15-3, and transimpedance amplifier 15-4 are provided.

  The signal processing unit 20 demodulates the signal by performing reception processing such as distortion correction, polarization separation, decoding, and error correction of the received signal. The signal processing unit 20 includes an analog / digital conversion element in the input unit. The signal processing unit 20 is configured by a DSP (Digital Signal Processor). The signal processing unit 20 may be configured using a semiconductor device other than a DSP such as an FPGA (Field Programmable Gate Array). The reception processing of the signal processing unit 20 may be performed by a general-purpose processor such as a CPU (Central Processing Unit) executing a computer program.

  The local light source unit 30 combines the optical signal transmitted through the communication path and generates local light used when generating an intermediate frequency optical signal. The local light source unit 30 includes a semiconductor laser and outputs light having a frequency set based on the frequency of an optical signal transmitted through a communication path. The local light source unit 30 has a wavelength of light to be output so that the local light wavelength can be changed based on the wavelength of the received optical signal assigned to the optical receiver 100 based on the wavelength design of the optical communication system. It may be variable.

  The power supply unit 40 is a DC power supply that supplies current to each photodiode 14. The power supply unit 40 supplies current to each photodiode 14 via a common power supply line. The cathode of each photodiode 14 is connected to a power supply line from the power supply unit 40. Further, a resistor 16 is provided on the power supply line connecting the power supply unit 40 and the cathode of each photodiode 14.

  The operation of the optical receiver 100 of this embodiment will be described. The signal light transmitted through the communication path and input to the optical receiver 100 is sent to the variable optical attenuator 11. When the signal light is input, the variable optical attenuator 11 attenuates the optical power of the signal light and sends it to the beam splitter 12-1. The variable optical attenuator 11 attenuates the signal light so that the amount of attenuation corresponds to the amplitude value of the voltage of the signal input from the differential amplifier circuit 17. The attenuation amount in the variable optical attenuator 11 is set so as to increase as the amplitude value of the voltage of the signal input from the differential amplifier circuit 17 increases.

  When the attenuated signal light is input, the beam splitter 12-1 separates the signal light into X-polarized and Y-polarized optical signals. When the signal light is polarized and separated, the beam splitter 12-1 outputs the X-shaped wave signal light to the optical hybrid 13-1, and outputs the Y-shaped wave signal light to the optical hybrid 13-2.

  Further, the local light source unit 30 interferes with an optical signal transmitted via a communication path, and outputs local light used when generating an optical signal having an intermediate frequency. The local light output from the local light source unit 30 is sent to the beam splitter 12-2. When local light is input, the beam splitter 12-2 separates the local light into X-polarized and Y-polarized optical signals. When polarization of the local light is separated, the beam splitter 12-1 outputs the local light of the X-shaped wave to the optical hybrid 13-1, and outputs the local light of the Y-shaped wave to the optical hybrid 13-2.

  When the signal light and the local light are input, the optical hybrid 13-1 and the optical hybrid 13-2 cause the signal light input from the beam splitter 12-1 and the local light input from the beam splitter 12-2 to interfere with each other. The intermediate frequency signal corresponding to the I-phase component and the Q-phase component is generated. The optical hybrid 13-1 sends the generated intermediate frequency optical signal to the photodiode 14-1 and the photodiode 14-2. In addition, the optical hybrid 13-2 sends the generated intermediate-frequency optical signal to the photodiode 14-3 and the photodiode 14-4.

  When an optical signal is input, each photodiode 14 converts the input optical signal into an electrical signal and sends it to the signal processing unit 20. When an electrical signal converted from an optical signal is input, the signal processing unit 20 converts the input signal into a digital signal and performs demodulation processing. The signal processing unit 20 outputs the demodulated signal to an optical transmission device provided with the optical receiver 100.

  A bias voltage is applied to each photodiode 14 that converts an optical signal into an electric signal by a power supply unit 40. The current flowing through the common power supply line connecting the power supply unit 40 and the photodiode 14 varies depending on the optical power of the optical signal incident on each photodiode 14. Therefore, the current flowing through the common power supply line varies depending on the total optical power of the optical signals incident on all the photodiodes 14.

  The differential amplifier circuit 17 is connected to both ends of the resistor 16 on the power supply line, and the voltage across the resistor is applied to the input terminal of the operational amplifier of the differential amplifier circuit 17. That is, the differential amplifier circuit 17 detects the fluctuation of the current flowing through the resistor 16 on the power supply line as the fluctuation of the voltage across the resistor. The differential amplifier circuit 17 generates a signal obtained by amplifying a voltage signal based on the voltage difference between the input terminals, and outputs the generated signal to the variable optical attenuator 11. The variable optical attenuator 11 attenuates and outputs the input signal light based on the voltage value of the voltage signal input as a control signal from the differential amplifier circuit 17.

  FIG. 3 is a diagram illustrating an example of the configuration of an optical receiver having a configuration compared with the optical receiver 100 of the present embodiment. The optical receiver of FIG. 3 includes a beam splitter in front of the variable optical attenuator, branches a part of the signal input to the optical receiver, and measures the optical power of the signal input to the optical detector. Yes. 3 controls the attenuation amount in the variable optical attenuator in the control circuit based on the measurement result of the optical power in the photodetector, and the optical power of the signal light output from the variable optical attenuator is controlled. Control is in progress. In the optical receiver configured as shown in FIG. 3, since a part of the optical power of the signal light used for coherent reception is branched for measurement, the signal light may be deteriorated during coherent detection, and the reception quality may be deteriorated. There is. Further, in the optical receiver having the configuration as shown in FIG. 3, since the branching beam splitter, the optical power measuring instrument, and the control circuit are required, the apparatus may be increased in size.

  On the other hand, the optical receiver 100 of the present embodiment detects optical power based on the current flowing through the photodiode 14 that is a photoelectric conversion element, and therefore can suppress signal degradation during coherent detection. Further, the optical receiver 100 of the present embodiment controls the control amount of the variable optical attenuator 11 by converting the fluctuation of the current flowing through the power supply line into the voltage signal in the differential amplifier circuit 17 and amplifying and outputting the voltage signal. A voltage signal is generated. Therefore, the optical receiver 100 of the present embodiment can suppress the increase in size and complexity of the device.

  The optical power detected by converting the current into voltage by the differential amplifier circuit 17 of the present embodiment is based on the signal light transmitted through the communication path and the optical power of the local light. However, since local light fluctuation is small in optical power fluctuation, the attenuation of optical power in the variable optical attenuator 11 can be controlled based on the fluctuation in voltage detected by the differential amplifier circuit 17. Moreover, it is good also as a structure which measures the optical power of the local light output from the local light source part 30, and reflects it in attenuation amount. In the case of such a configuration, for example, the optical power attenuation in the variable optical attenuator 11 based on the fluctuation of the optical power calculated from the fluctuation of the signal line current by the control circuit and the fluctuation of the optical power of the local light. The amount is controlled.

  In the optical receiver 100 of the present embodiment, the fluctuation of the current flowing through the power supply line that supplies power to each photodiode 14 is detected as the amplitude of the voltage value by the resistor 16 and the differential amplifier circuit 17. Therefore, the optical receiver 100 according to the present embodiment is based on the sum of the optical powers of the signal lights input to the plurality of photoelectric conversion elements, based on the detection result of the fluctuation of the current flowing through the common power supply line. The current can be detected by converting it into a voltage. The optical receiver 100 of this embodiment amplifies the detected voltage fluctuation of the common power supply line in the differential amplifier circuit 17 and controls the attenuation amount of the optical power in the variable optical attenuator 11. Therefore, the optical receiver 100 of this embodiment controls the optical power of the signal light output from the variable optical attenuator 11 to the subsequent stage based on the total sum of the input optical powers without requiring a complicated control circuit. can do. As a result, by using the optical receiver 100 of the present embodiment, each element can be managed by appropriately managing the optical power of the signal light input to each element in the optical receiver 100 without complicating the device configuration. Can be protected and reception characteristics can be stabilized.

  The optical receiver 100 of the second embodiment is used as a module that receives an optical signal in an optical transmission device of a digital coherent optical communication system. A plurality of optical receivers 100 may be provided in one optical transmission device. FIG. 4 shows an example of the configuration of an optical transmission apparatus 200 including N optical receivers 100 according to the second embodiment (N is an integer). In the optical transmission device 200 of FIG. 4, a wavelength division multiplexed signal input from a transmission path is branched by a branching unit configured by a beam splitter or the like, and each optical receiver 100 performs reception processing. With such a configuration, the optical receiver 100 according to the second embodiment is used as a receiver of the optical signal of each channel included in the wavelength multiplexed signal in the optical transmission apparatus 200 that receives the wavelength multiplexed signal. Can do. The optical transmission device 200 may further include an optical transmitter that transmits an optical signal.

DESCRIPTION OF SYMBOLS 1 Optical attenuation means 2 Separation means 3 Photoelectric conversion means 4 Control signal generation means 10 Optical receiving part 11 Variable optical attenuator 12 Beam splitter 13 Optical hybrid 14 Photodiode 15 Transimpedance amplifier 16 Resistance 17 Differential amplification circuit 20 Signal processing part 30 Local light source unit 40 Power source unit 100 Optical receiver 101 Demultiplexing unit 200 Optical transmission device

Claims (10)

A light attenuating means for attenuating the optical power of the input signal light;
Separating means for polarization-separating the signal light with the optical power attenuated by the optical attenuation means;
The signal light of each of the polarization components is converted into an electrical signal by a photoelectric conversion element provided for each polarization component separated by polarization by the separation means and connected to a power source via a common power line. Photoelectric conversion means for outputting;
Control signal generating means for detecting fluctuations in the current flowing through the power line and generating a control signal for controlling the attenuation amount of the optical power in the optical attenuating means based on the detection result of the fluctuations in the current;
The optical receiver is configured to attenuate the optical power based on the control signal. And further comprising a combining means for combining the signal light for each of the polarization components separated by the separating means and the local light through paths whose phases are different from each other by 90 degrees,
2. The optical receiver according to claim 1, wherein the photoelectric conversion element of the photoelectric conversion unit converts the signal light respectively output from the paths whose phases are different from each other by 90 degrees into the electric signal. Further comprising monitoring means for monitoring the optical power of the local light,
3. The optical receiver according to claim 2, wherein the control signal generation unit generates the control signal based on a detection result of the current variation and the optical power of the local light.   The optical receiver according to claim 1, wherein the control signal generation unit converts a current flowing through the power supply line into a voltage signal, and generates a signal obtained by amplifying the voltage signal as the control signal. . A plurality of optical receivers according to any one of claims 1 to 4,
An optical transmission device comprising: a demultiplexing unit for branching a wavelength multiplexed signal received via a transmission line and inputting the branched signal light to each of the optical receivers. Attenuates the optical power of the input signal light,
Polarization separation of the signal light attenuated the optical power,
Provided for each polarization component that has undergone polarization separation, the photoelectric conversion element connected to the power supply via a common power line converts the signal light of each of the polarization components into an electrical signal and outputs it,
Detecting a variation in the current flowing through the power line, and generating a control signal for controlling the attenuation amount of the optical power based on the detection result of the variation in the current;
A receiving method, wherein the optical power is attenuated based on the control signal. The separated signal light for each polarization component and local light are respectively combined by paths whose phases are different from each other by 90 degrees,
The receiving method according to claim 6, wherein the photoelectric conversion element converts the signal light output from the path into the electric signal. Monitoring the optical power of the local light,
The receiving method according to claim 7, wherein the control signal is generated based on a detection result of the current fluctuation and an optical power of the local light.   8. The receiving method according to claim 6, wherein a current flowing through the power supply line is converted into a voltage signal, and a signal obtained by amplifying the voltage signal is generated as the control signal. Wavelength multiplexed signal received via the transmission line is separated into signal light of each channel,
Optical power is attenuated for each of the separated signal lights, the signal light that has attenuated the optical power is polarized and separated, and the signal light of each of the polarization components is converted into an electrical signal by the photoelectric conversion element. The reception method according to claim 6, wherein:

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