JP2017143485A - Optical receiver and optical receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem of an optical receiver using polarization separation that it is difficult to control the polarization state by simple configuration, without affecting the reception characteristics.SOLUTION: An optical receiver has polarization adjustment means for adjusting the polarization state of first input light, and outputting polarization adjustment light, first polarization separation means for separating the polarization adjustment light into first polarization adjustment light and second polarization adjustment light where the polarization planes are orthogonal each other, second polarization separation means for separating the second input light into first polarization input light and second polarization input light where the polarization planes are orthogonal each other, first optical hybrid interference means for interfering the first polarization adjustment light and first polarization input light and outputting first interference light, second optical hybrid interference means for interfering the second polarization adjustment light and second polarization input light and outputting second interference light, and control means for controlling the polarization adjustment means based on the intensity of the first interference light and the intensity of the second interference light.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical receiver and an optical reception method, and more particularly to an optical receiver and an optical reception method using a coherent optical reception method.

  As the amount of information (traffic) in the Internet increases, there is a demand for further increase in capacity of the backbone transmission system. As a technique for increasing the capacity, there is an optical transmission technique using a plurality of channels such as an optical multilevel modulation system or a polarization multiplexing system.

  In an optical transmission system using a polarization multiplexing system, a set of data signals is transmitted using a set of polarization components that are orthogonal to each other, X polarization and Y polarization. In the optical receiver, a set of data signals is extracted by separating the X polarization and the Y polarization from each other. However, if the orthogonality between the X-polarization channel and the Y-polarization channel deteriorates due to a polarization-dependent loss or the like, the quality of both sets of data signals transmitted through the X-polarization channel and the Y-polarization channel is reduced. There was a problem that it was difficult to maintain.

  A technique for solving such a problem is described in Patent Document 1. The related polarization multiplexed optical receiver described in Patent Document 1 includes a polarization controller, a polarization splitter, a first detector, a second detector, and a control unit.

  Here, the polarization controller controls the polarization state of the polarization multiplexed optical signal. The polarization splitter separates the polarization multiplexed optical signal whose polarization state is controlled by the polarization controller into a first polarization signal and a second polarization signal. The first detector detects the optical power of the first polarization signal. The second detector detects the optical power of the second polarization signal. The control unit controls the polarization controller based on the first optical power signal output from the first detector and the second optical power signal output from the second detector. Yes.

  With such a configuration, in the related polarization multiplexed optical receiver described in Patent Document 1, the polarization of the input polarization multiplexed optical signal is based on both the first and second polarization signals. The state is controlled. Therefore, even if the orthogonality of the first and second polarizations deteriorates, the quality of both polarization channels can be improved comprehensively.

  Patent Document 2 describes a polarization multiplexed optical receiver including a polarization adjustment unit, an optical reception unit, an A / D conversion unit, a digital signal processing unit, and a feedback control unit. In the related polarization multiplexed optical receiver described in Patent Document 2, the feedback control unit generates a control signal based on the quality of the extracted signal data and outputs the control signal to the polarization adjustment unit. As a result, it is possible to compensate for imperfections in the reception state with higher accuracy and realize good transmission characteristics.

  On the other hand, it is important to improve the reception sensitivity with an increase in capacity, and attention is paid to a coherent light reception method with excellent reception sensitivity (see, for example, Patent Documents 3 and 4).

JP 2010-178091 A JP 2013-034065 A JP 2012-050140 A JP 2008-278249 A

  In the coherent light receiving system described above, the signal light is polarized and separated into a vertical polarization plane and a horizontal polarization plane inside the optical receiver, and is mixed with the local oscillation light to receive the coherent light. Therefore, it is desirable that the input signal light ideally has the same optical power on the vertical polarization plane and the horizontal polarization plane. However, since the polarization state of signal light is distorted while propagating in the optical fiber over a long distance, it is difficult to maintain the ideal polarization state.

  At this time, like the related polarization multiplexed optical receiver described in Patent Document 1, the first polarization signal and the second polarization signal separated by the polarization splitter are converted into the first detector and the first polarization signal. If it is configured to detect with two detectors, an optical tap structure is required. For this reason, the number of components of the optical receiver increases and the cost increases. Further, when a part of the optical power is branched for monitoring by the optical tap structure, there is a problem that the optical power used for the reception process of the signal light is reduced and the reception characteristics are deteriorated.

  On the other hand, the related polarization multiplexed optical receiver described in Patent Document 2 is configured to generate a control signal based on the quality of the extracted signal data, so that there is a limit in responsiveness.

  As described above, the optical receiver using polarization separation has a problem that it is difficult to accurately control the polarization state with a simple configuration without affecting the reception characteristics.

  The object of the present invention is that it is difficult to accurately control the polarization state with a simple configuration without affecting the reception characteristics in an optical receiver using polarization separation, which is the problem described above. An object of the present invention is to provide an optical receiver and an optical receiving method that solve the problem.

  The optical receiver of the present invention adjusts the polarization state of the first input light and outputs the polarization adjustment light, and the first polarization whose polarization planes are orthogonal to each other. The first polarization separation means for separating the adjustment light and the second polarization adjustment light, and the second input light are separated into the first polarization input light and the second polarization input light whose polarization planes are orthogonal to each other. A second polarization separation unit, a first optical hybrid interference unit that outputs the first interference light by causing the first polarization adjustment light and the first polarization input light to interfere with each other; Second optical hybrid interference means for outputting the second interference light by interfering with the second polarization input light, and polarization adjustment means based on the intensity of the first interference light and the intensity of the second interference light Control means for controlling.

  The optical reception method of the present invention adjusts the polarization state of the first input light to generate polarization adjustment light, and the polarization adjustment light is converted into the first polarization adjustment light and the first polarization adjustment light whose polarization planes are orthogonal to each other. The second input light is separated into the two polarization adjustment lights, the first polarization adjustment light and the first polarization are separated into the first polarization input light and the second polarization input light whose planes of polarization are orthogonal to each other. The first interference light is generated by causing the input light to interfere, and the second interference light is generated by causing the second polarization adjustment light and the second polarization input light to interfere with each other. The amount of adjustment of the polarization state is controlled based on the intensity of the second interference light.

  According to the optical receiver and the optical receiving method of the present invention, in a configuration using polarization separation, the polarization state can be accurately controlled with a simple configuration without affecting reception characteristics.

It is a block diagram which shows the structure of the optical receiver which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the optical receiver which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the optical receiver which concerns on the 3rd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the direction of the arrow in a drawing shows an example and does not limit the direction of the signal between blocks.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of an optical receiver 100 according to the first embodiment of the present invention.

  The optical receiver 100 according to this embodiment includes a polarization adjustment unit 110, a first polarization separation unit 120, a second polarization separation unit 130, a first optical hybrid interference unit 140, and a second optical hybrid interference. Means 150 and control means 160 are provided.

  The polarization adjustment unit 110 adjusts the polarization state of the first input light S11 and outputs the polarization adjustment light. The first polarization separation unit 120 separates the polarization adjustment light into first polarization adjustment light and second polarization adjustment light whose polarization planes are orthogonal to each other. The second polarization separation unit 130 separates the second input light S12 into first polarization input light and second polarization input light whose polarization planes are orthogonal to each other.

  The first optical hybrid interference unit 140 causes the first polarization adjustment light and the first polarization input light to interfere with each other and outputs the first interference light S21. The second optical hybrid interference unit 150 causes the second polarization adjustment light and the second polarization input light to interfere with each other and outputs the second interference light S22. Then, the control unit 160 controls the polarization adjusting unit 110 based on the intensity of the first interference light S21 and the intensity of the second interference light S22.

  Thus, the optical receiver 100 of this embodiment is configured to control the polarization adjusting unit 110 based on the intensity of the first interference light S21 and the intensity of the second interference light S22. Therefore, it is not necessary to separately provide a light branching structure for monitoring. As a result, according to the optical receiver 100 of the present invention, in a configuration using polarization separation, the polarization state can be accurately controlled with a simple configuration without affecting reception characteristics.

  As described above, the polarization adjusting unit 110 controls the polarization state of the first input light S11. Accordingly, the polarization adjusting unit 110 causes the first input light polarization component, which is one polarization component of the first input light S11, and the second input light polarization orthogonal to the first input light polarization component. An input light power ratio that is a ratio of light powers of wave components can be adjusted.

  Further, the control means 160 can be configured to control the polarization adjusting means 110 so that the intensity of the first interference light S21 and the intensity of the second interference light S22 are substantially equal.

  Here, the first input light S11 can be signal light transmitted from the transmission side, and the second input light S12 can be local oscillation light transmitted from a local oscillation light source. Not limited to this, the first input light S11 may be a local oscillation light transmitted from a local oscillation light source, and the second input light S12 may be a signal light transmitted from the transmission side.

  Next, the optical reception method of this embodiment will be described.

  In the optical receiving method of the present embodiment, first, the polarization adjustment light is generated by adjusting the polarization state of the first input light. Subsequently, the polarization adjustment light is separated into first polarization adjustment light and second polarization adjustment light whose polarization planes are orthogonal to each other. Further, the second input light is separated into first polarized input light and second polarized input light whose polarization planes are orthogonal to each other. Thereafter, the first polarization adjustment light and the first polarization input light are caused to interfere with each other to generate a first interference light, and the second polarization adjustment light and the second polarization input light are caused to interfere with each other to generate a second interference light. Is generated. Then, the amount of adjustment of the polarization state is controlled based on the intensity of the first interference light and the intensity of the second interference light.

  Here, the generation of the polarization adjustment light described above is performed by controlling the polarization state of the first input light, and the first input light polarization component which is one polarization component of the first input light. Adjusting the input optical power ratio, which is the ratio of the optical power of the second input optical polarization component orthogonal to the first input optical polarization component.

  Further, the control of the adjustment amount of the polarization state described above includes the control of the adjustment amount of the polarization state so that the intensity of the first interference light and the intensity of the second interference light are substantially equal. can do.

  As described above, according to the optical receiver 100 and the optical reception method of the present embodiment, in a configuration using polarization separation, the polarization state can be accurately controlled with a simple configuration without affecting reception characteristics. Can do.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing a configuration of an optical receiving apparatus 1000 according to the second embodiment of the present invention.

  The optical receiver 1000 according to the present embodiment includes a coherent optical receiver 200, a local oscillation light source 300, and a digital signal processing unit 400. The local oscillation light source 300 transmits local oscillation light S32 as the second input light. The digital signal processing unit 400 converts the electrical signal output from the coherent optical receiver 200 into a digital signal, performs signal processing, and generates a demodulated signal.

  The coherent optical receiver 200 includes a polarization control element 210 as polarization adjustment means, a first polarization beam splitter 220 as first polarization separation means, and a second polarization as second polarization separation means. A wave beam splitter 230 is provided.

  The polarization control element 210 receives the signal light (first input light) S31 transmitted from the transmission side, and changes the polarization state of the input signal light. The polarization control element 210 can be configured by combining wave plates. A first polarization beam splitter (PBS) 220 performs polarization separation on signal light whose polarization state has been changed. The second polarization beam splitter 230 separates the polarization of the local oscillation light S32.

  The coherent optical receiver 200 further includes a first optical hybrid unit (first optical hybrid interference unit) 240, a second optical hybrid unit (second optical hybrid interference unit) 250, a monitor unit 261 as a detection unit, And a polarization controller (polarization controller) 262. Here, the monitor unit (detection unit) 261 and the polarization control unit (polarization control unit) 262 constitute a control unit. The first optical hybrid unit 240 and the second optical hybrid unit 250 cause the signal light subjected to polarization separation and the local oscillation light subjected to polarization separation to interfere with each other and output interference light.

  The configuration of the coherent optical receiver 200 so far is the same as the configuration of the optical receiver 100 according to the first embodiment.

  The coherent optical receiver 200 of the present embodiment is further provided with a photoelectric conversion means. The photoelectric conversion means photoelectrically converts the first interference light output from the first optical hybrid unit 240 to generate a first electrical signal, and outputs the second interference light output from the second optical hybrid unit 250. A second electrical signal is generated by photoelectric conversion.

  Here, the photoelectric conversion means may include a photodiode 271 that receives interference light and a transimpedance amplifier (TIA) 272. The transimpedance amplifier 272 converts the output current output from the photodiode 271 into a voltage signal.

  At this time, the monitor unit 261 detects the first monitor signal from the first electric signal, and detects the second monitor signal from the second electric signal. The polarization control unit (polarization control means) 262 controls the polarization control element 210 based on the first monitor signal and the second monitor signal.

  2 shows a configuration in which the monitor unit 261 detects the output current output from the photodiode 271 as a monitor signal. Not limited to this, the monitor unit 261 may be configured to detect the voltage signal output from the transimpedance amplifier 272 as a monitor signal.

  FIG. 2 shows a case where the first optical hybrid unit 240 and the second optical hybrid unit 250 output the first interference light and the second interference light including the in-phase component and the quadrature phase component, respectively. The case where the photodiode 271 has a balanced receiver structure is shown.

  Next, the operation of the optical receiving apparatus 1000 according to the present embodiment will be described.

  As described above, the coherent optical receiver 200 according to the present embodiment has a configuration in which the polarization control element 210 is provided on the optical path of the input signal light S31 and before the first polarization beam splitter 220. Yes. Therefore, by changing the adjustment amount of the polarization state of the polarization control element 210, it is possible to change the ratio of the optical power of the input signal light S31 in the vertical polarization plane to the horizontal polarization plane. is there.

  In the coherent optical receiver 200, the signal light mixed with the local oscillation light after polarization separation is input to the photodiode 271. The monitor unit 261 monitors the output current of the photodiode 271 and outputs a monitor signal to the polarization control unit 262.

  The polarization control unit 262 constantly monitors whether the optical power of the interference light input to each photodiode 271 is equal based on the monitor signal acquired from the monitor unit 261. When the polarization state of the input signal light S31 changes, the optical power input to each photodiode 271 is biased. When the polarization control unit 262 detects the deviation of the optical power, the polarization control unit 262 changes the adjustment amount of the polarization state of the polarization control element 210 so that the optical power input to each photodiode 271 becomes equal. In the example shown in FIG. 2, the polarization controller 262 controls the monitor signal values obtained from the four balanced receiver structure photodiodes to be all equal.

  By such control, the optical power of the vertical polarization plane and the optical power of the horizontal polarization plane of the interference light input to the photodiode 271 can be equalized.

  As described above, according to the optical receiving apparatus 1000 of the present embodiment, in the configuration using polarization separation, the polarization state can be accurately controlled with a simple configuration without affecting the reception characteristics.

  Further, by adjusting the polarization state of the input signal light, the reception range in coherent light reception can be expanded. The reason will be described below.

  With respect to the range of signal light power that can be input in the coherent light receiving system, an upper limit and a lower limit are respectively defined. That is, an upper limit is defined in order to prevent destruction of the devices constituting the coherent optical receiver. In addition, a lower limit is defined so that signal processing can be normally performed in the digital signal processing unit. At this time, the signal light input to the coherent optical receiver is in a state where the optical power of the vertical polarization plane and the optical power of the horizontal polarization plane are mixed, and the optical power is biased to one of the polarization planes. is there. Considering such a case, it is necessary to set a narrow range of signal light power that can be input.

  However, according to the optical receiving apparatus 1000 of the present embodiment, the polarization state of the input signal light is adjusted, and the optical power of the vertical polarization plane and the horizontal polarization plane of the interference light input to the photodiode 271 are changed. Can be even. As a result, it is possible to expand the reception range in coherent light reception.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 3 is a block diagram showing a configuration of an optical receiver 2000 according to the third embodiment of the present invention.

  The optical receiver 2000 according to the present embodiment includes a coherent optical receiver 200, a local oscillation light source 300, and a digital signal processing unit 400. The local oscillation light source 300 transmits local oscillation light S32 as the first input light. The digital signal processing unit 400 converts the electrical signal output from the coherent optical receiver 200 into a digital signal, performs signal processing, and generates a demodulated signal.

  The coherent optical receiver 200 includes a polarization control element 210 as polarization adjustment means, a first polarization beam splitter 220 as first polarization separation means, and a second polarization as second polarization separation means. A wave beam splitter 230 is provided.

  Here, in the optical receiver 2000 according to the present embodiment, the polarization control element 210 receives the local oscillation light S32 transmitted from the local oscillation light source 300 as the first input light, and the polarization state of the local oscillation light S32 The configuration is changed. On the other hand, the signal light S31 transmitted from the transmission side is directly input to the second polarization beam splitter 230 as the second input light. The first polarization beam splitter 220 is configured to depolarize the local oscillation light whose polarization state has been changed, and the second polarization beam splitter 230 is configured to depolarize the signal light S31.

  The coherent optical receiver 200 further includes a first optical hybrid unit (first optical hybrid interference unit) 240, a second optical hybrid unit (second optical hybrid interference unit) 250, a monitor unit 261 as a detection unit, And a polarization controller (polarization controller) 262. Here, the monitor unit (detection unit) 261 and the polarization control unit (polarization control unit) 262 constitute a control unit. The first optical hybrid unit 240 and the second optical hybrid unit 250 cause the signal light subjected to polarization separation and the local oscillation light subjected to polarization separation to interfere with each other and output interference light.

  The coherent optical receiver 200 further includes photoelectric conversion means. The photoelectric conversion means photoelectrically converts the first interference light output from the first optical hybrid unit 240 to generate a first electrical signal, and outputs the second interference light output from the second optical hybrid unit 250. A second electrical signal is generated by photoelectric conversion.

  Here, the photoelectric conversion means may include a photodiode 271 that receives interference light and a transimpedance amplifier (TIA) 272. The transimpedance amplifier 272 converts the output current output from the photodiode 271 into a voltage signal.

  At this time, the monitor unit 261 detects the first monitor signal from the first electric signal, and detects the second monitor signal from the second electric signal. The polarization control unit (polarization control means) 262 controls the polarization control element 210 based on the first monitor signal and the second monitor signal.

  FIG. 3 shows a configuration in which the monitor unit 261 detects the voltage signal output from the transimpedance amplifier 272 as a monitor signal. Not limited to this, the monitor unit 261 may be configured to detect the output current output from the photodiode 271 as a monitor signal.

  FIG. 3 shows a case where the first optical hybrid unit 240 and the second optical hybrid unit 250 respectively output the first interference light and the second interference light including the in-phase component and the quadrature phase component. The case where the photodiode 271 has a balanced receiver structure is shown.

  Next, the operation of the optical receiving apparatus 1000 according to the present embodiment will be described.

  As described above, the coherent optical receiver 200 according to the present embodiment is on the optical path of the local oscillation light S32 transmitted from the local oscillation light source 300, and in front of the first polarization beam splitter 220, the polarization control element. 210 is provided. Therefore, by changing the adjustment amount of the polarization state of the polarization control element 210, it is possible to change the ratio of the optical power of the vertical polarization plane and the optical power of the horizontal polarization plane of the local oscillation light S32.

  In the coherent optical receiver 200, the signal light mixed with the local oscillation light after polarization separation is input to the photodiode 271. The transimpedance amplifier 272 converts the output current of the photodiode 271 into a voltage signal. The monitor unit 261 monitors the voltage signal output from the transimpedance amplifier 272 and outputs the monitor signal to the polarization control unit 262.

  The polarization control unit 262 constantly monitors whether the optical power of the interference light input to each photodiode 271 is equal based on the monitor signal acquired from the monitor unit 261. When the polarization state of the input signal light S31 changes, the optical power input to each photodiode 271 is biased. When the polarization control unit 262 detects the deviation of the optical power, the polarization control unit 262 changes the adjustment amount of the polarization state of the polarization control element 210 so that the optical power input to each photodiode 271 becomes equal. Thereby, the ratio of the optical power of the vertical polarization plane and the optical power of the horizontal polarization plane of the local oscillation light S32 is changed. In the example shown in FIG. 3, the polarization controller 262 performs control so that the monitor signal values obtained from the four balanced receiver structure photodiodes are all equal.

  By such control, the optical power of the vertical polarization plane and the optical power of the horizontal polarization plane of the interference light input to the photodiode 271 can be equalized.

  As described above, according to the optical receiving apparatus 2000 of the present embodiment, in a configuration using polarization separation, the polarization state can be accurately controlled with a simple configuration without affecting reception characteristics.

  Further, by adjusting the polarization state of the local oscillation light S32, the reception range in coherent light reception can be expanded. The reason will be described below.

  With respect to the range of signal light power that can be input in the coherent light receiving system, an upper limit and a lower limit are respectively defined. That is, an upper limit is defined in order to prevent destruction of the devices constituting the coherent optical receiver. In addition, a lower limit is defined so that signal processing can be normally performed in the digital signal processing unit. At this time, the signal light input to the coherent optical receiver is in a state where the optical power of the vertical polarization plane and the optical power of the horizontal polarization plane are mixed, and the optical power is biased to one of the polarization planes. is there. Considering such a case, it is necessary to set a narrow range of signal light power that can be input.

  However, according to the optical receiver 2000 of this embodiment, the optical power of the vertical polarization plane and the horizontal polarization plane of the interference light input to the photodiode 271 is adjusted by adjusting the polarization state of the local oscillation light S32. Can be made even. As a result, it is possible to expand the reception range in coherent light reception.

  The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the invention described in the claims, and it is also included within the scope of the present invention. Not too long.

DESCRIPTION OF SYMBOLS 100 Optical receiver 110 Polarization adjustment means 120 1st polarization separation means 130 2nd polarization separation means 140 1st optical hybrid interference means 150 2nd optical hybrid interference means 160 Control means 200 Coherent optical receiver 210 Polarization control element 220 First polarization beam splitter 230 Second polarization beam splitter 240 First optical hybrid unit 250 Second optical hybrid unit 261 Monitor unit 262 Polarization control unit 271 Photodiode 272 Transimpedance amplifier 300 Local oscillation light source 400 Digital signal processing unit 1000, 2000 Optical receiver S11 First input light S12 Second input light S21 First interference light S22 Second interference light S31 Signal light S32 Local oscillation light

Claims (10)

Polarization adjustment means for adjusting the polarization state of the first input light and outputting the polarization adjustment light;
First polarization separation means for separating the polarization adjustment light into first polarization adjustment light and second polarization adjustment light whose polarization planes are orthogonal to each other;
Second polarization separation means for separating the second input light into first polarization input light and second polarization input light whose polarization planes are orthogonal to each other;
First optical hybrid interference means for causing the first polarization adjustment light and the first polarization input light to interfere with each other and outputting first interference light;
Second optical hybrid interference means for outputting the second interference light by causing the second polarization adjustment light and the second polarization input light to interfere with each other;
An optical receiver comprising: control means for controlling the polarization adjusting means based on the intensity of the first interference light and the intensity of the second interference light. The polarization adjusting means controls a polarization state of the first input light, thereby controlling a first input light polarization component that is one polarization component of the first input light, and the first input light. The optical receiver according to claim 1, wherein an input optical power ratio that is a ratio of optical powers of the second input optical polarization component orthogonal to the input optical polarization component is adjusted. The optical receiver according to claim 1, wherein the control unit controls the polarization adjusting unit so that an intensity of the first interference light and an intensity of the second interference light are substantially equal. Photoelectric conversion means for photoelectrically converting the first interference light to generate a first electrical signal, and photoelectrically converting the second interference light to generate a second electrical signal;
The control means includes
Detecting means for detecting a first monitor signal from the first electrical signal and detecting a second monitor signal from the second electrical signal;
The optical receiver according to any one of claims 1 to 3, further comprising: polarization control means for controlling the polarization adjusting means based on the first monitor signal and the second monitor signal. The optical receiver according to claim 4, wherein the photoelectric conversion means includes a photodiode and a transimpedance amplifier. The first input light is signal light transmitted from the transmission side,
The optical receiver according to any one of claims 1 to 5, wherein the second input light is a local oscillation light transmitted from a local oscillation light source. The first input light is a local oscillation light transmitted from a local oscillation light source,
The optical receiver according to any one of claims 1 to 5, wherein the second input light is signal light transmitted from a transmission side. An optical receiver according to claim 4 or 5,
A local oscillation light source for transmitting local oscillation light which is one of the first input light and the second input light;
An optical receiver comprising: digital signal processing means for converting the first electric signal and the second electric signal into digital signals, performing signal processing, and generating a demodulated signal. Adjusting the polarization state of the first input light to generate polarization-adjusted light;
The polarization adjustment light is separated into first polarization adjustment light and second polarization adjustment light whose polarization planes are orthogonal to each other;
Separating the second input light into first polarized input light and second polarized input light whose planes of polarization are orthogonal to each other;
Causing the first polarization adjustment light and the first polarization input light to interfere with each other to generate a first interference light;
Causing the second polarization adjustment light and the second polarization input light to interfere with each other to generate a second interference light;
An optical reception method for controlling an adjustment amount of the polarization state based on the intensity of the first interference light and the intensity of the second interference light. The control of the adjustment amount of the polarization state includes controlling the adjustment amount of the polarization state so that the intensity of the first interference light and the intensity of the second interference light are substantially equal. 9. The optical receiving method described in 9.

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