JPH01211737A - Polarization diversity optical receiver for coherent optical communication - Google Patents

Abstract

PURPOSE:To obtain two local oscillation light beams which have sufficient power by providing a 1/2-wavelength plate and utilizing light beams from both ends of a both-end light emission type semiconductor laser. CONSTITUTION:One local oscillation light (S polarized wave) emitted by one end surface of the both-end light emission type semiconductor laser 7 is changed in polarization state by the 1/2-wavelength plate 14 and has its plane of polarization rotated by 90 deg. to become a P polarized wave. The local oscillation light in the P polarized wave state which is changed in polarization state as mentioned above and local oscillation light emitted by the other end surface of the both-end light emission type semiconductor laser 7 are inputted to a mixing circuit 8, which mixes two kinds of polarized components of signal light sent through an optical fiber 5 by P polarized waves and S polarized waves. Then a detecting circuit 9 detects each polarized wave and a signal composing circuit 10 demodulates, adds, and discriminates them with the input signal. Consequently, the two local oscillation light beams which have sufficient power are obtained.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Conventional technology (Fig. 4) Means for solving the problem to be solved by the invention (Fig. 1) Effect (Fig. 1) ) Embodiment Description of the first embodiment (Fig. 2) Description of the second embodiment (Fig. 3) Effects of the invention [Summary] Regarding a polarization diversity optical receiver for coherent optical communication, local oscillation optical oscillation Even without using a high-output semiconductor laser as a device, by effectively utilizing the light from both ends of a double-ended semiconductor laser, it is possible to generate two
In order to obtain two local oscillation lights, the local oscillation optical oscillator is configured as a double-end emitting type semiconductor laser, and one of the local oscillation lights irradiated from one end surface of the double-end emitting type semiconductor laser is polarized. Local oscillation light polarization state changing means for changing the wave state with respect to the polarization state of the other local oscillation light irradiated from the other end surface of the double-end emitting type semiconductor laser is provided, and the local oscillation light polarization state changing means is provided. The one local oscillation light whose polarization state has been changed by the means and the other local oscillation light irradiated from the other end surface of the double-end emitting semiconductor laser are transmitted through the optical fiber in the mixing circuit. The configuration is such that the two types of polarization components of the signal light are mixed.

[Industrial Application Field] The present invention relates to a polarization diversity optical receiver for coherent heterodyne optical communication.

In recent years, coherent optical communication systems have been in the spotlight, which utilize information such as the amplitude, frequency, and phase of optical carrier waves with increased coherency to derive the ultimate performance of optical communication.

One of the challenges in realizing such a coherent optical communication system is the variation of the polarization state (i.e., when light propagates in an optical fiber, two propagation modes are possible due to the ellipticity of the fiber; When external agitation, such as twisting or bending, is applied to a wave, coupling occurs between the two modes, and the polarization state changes in various ways.) As a countermeasure to this problem, polarization diversity reception method is used. Proposed.

In this polarization diversity reception system, signals of two polarization components are combined, and possible methods for this include an intermediate frequency combining method and a baseband combining method.

Here, the intermediate frequency synthesis method is a method in which the phases of two polarization components are matched in advance and then added and synthesized, and the base-hough 1~ synthesis method is a method in which the two polarization components are detected and then added together. This is a method of synthesis.

By the way, while the intermediate frequency synthesis method is difficult to put into practical use because of the difficulty of phase matching operations, the baseband synthesis method requires two systems of detection circuits but is easy to put into practical use.

[Prior Art] FIG. 4 is a block diagram showing a coherent optical communication system. In FIG. Has a stabilizing device.

Here, for example, a semiconductor laser capable of single mode oscillation is used as the light source. Also, as a light source stabilization device,
If a semiconductor laser is used as described above, for example, one equipped with a temperature control device that controls the temperature of the laser to be constant is used.

Furthermore, the optical modulation circuit performs FSK modulation, ASK modulation, and PSK (including DPSK) modulation on the input signal.

5 is an optical fiber as a transmission medium, and this optical fiber 5
For example, a single-mode optical fiber is used.

Reference numeral 6 denotes a receiving section, which includes a local oscillation light oscillator (local light source) 7 that oscillates local oscillation light, and a signal light transmitted through the optical fiber 5 and the local oscillation light oscillator 7. A mixing circuit 8' that mixes the locally oscillated light (this mixing circuit 8' includes a polarization separation optical fiber coupler 19 that separates the signal light into P polarization and S polarization, and a polarization separation optical fiber coupler 19 that separates the signal light into P polarization and S polarization, and S
a polarization separation optical fiber coupler 19′ that separates into polarization;
a polarization-maintaining optical fiber coupler 20), a detection circuit 9 that receives and detects the mixed output of this mixing circuit 8' with optical receivers 21P and 218, and a detection circuit 9 that corresponds to the input signal from the detected output of this detection circuit 9. A signal synthesis circuit 10 is provided as a demodulation/addition/discrimination circuit for extracting signals.

Here, as the local oscillation light oscillator 7, for example, a double-ended emission type semiconductor laser is used, and the local oscillation light is irradiated from one end face of this semiconductor laser. Note that this local oscillation optical oscillator 7 is also stabilized by controlling the temperature to be constant by a temperature control circuit.

With such a configuration, in principle, coherent optical communication can be performed.

[Problem to be solved by the invention] By the way, in such a polarization diversity optical receiver,
Two local oscillation lights with the same optical frequency are required, but conventionally, a method has been adopted in which the local oscillation light irradiated from one end facet of a semiconductor laser as a local oscillation optical oscillator is separated into two by a polarizing beam splitter. The light emitted from the other end facet of the semiconductor laser is not used.

In this way, in the conventional type, the polarizing beam splitter
Since only the local oscillation light irradiated from one end facet of the semiconductor laser is used as the local oscillation light to be separated into two parts, and the optical output from the other end facet of the semiconductor laser is not used, the power of each local oscillation light is halved. There is a problem with becoming.

Insufficient power of the local oscillation light makes it impossible to achieve the shot noise limit in the optical receiver, and the receiver's SN
This results in a deterioration of the ratio.

Therefore, it is conceivable to prepare a high-output semiconductor laser and achieve the shot noise limit with a margin using just the local oscillation light from one end facet, but at present, there are almost no such high-output semiconductor lasers, Even if it existed, it would be quite expensive.

The present invention aims to solve these problems, and effectively utilizes light from both ends of a double-end emitting type semiconductor laser without using a high-power semiconductor laser as a local oscillation optical oscillator. It is an object of the present invention to provide a polarization diversity optical receiver for coherent optical communication, in which two locally oscillated lights with sufficient power can be obtained.

[Means to solve the problem] FIG. 1 shows a block diagram of the principle of the present invention.

In FIG. 1, reference numeral 1 denotes a transmitter (signal light source), and the transmitter 1 includes a light source, a light modulation circuit, and a light source stabilization device.

Here, for example, a semiconductor laser capable of single mode oscillation is used as the light source. Also, as a light source stabilization device,
If a semiconductor laser is used as described above, for example, one equipped with a temperature control device that controls the temperature of the laser to be constant is used.

Furthermore, the optical modulation circuit performs FSK modulation, ASK modulation, and PSK (including DPSK) modulation on the input signal.

5 is an optical fiber as a transmission medium, and this optical fiber 5
For example, a single mode optical fiber is used.

Reference numeral 6 denotes a receiving section, which includes a local oscillation light oscillator (local light source) 7 that oscillates local oscillation light, and a signal light transmitted through the optical fiber 5 and the local oscillation light oscillator 7. A mixing circuit 8 that mixes the local oscillation light (this mixing circuit 8 includes a polarization separating optical fiber coupler 19 that separates the signal light from the optical fiber 5 into P polarization and S polarization, and a polarization maintaining optical fiber a coupler 20), the mixed output of this mixing circuit 8 is received and detected by the optical receivers 2IP and 218, and a detection circuit 9, and demodulation that extracts a signal corresponding to the above input signal from the detection output of this detection circuit 9. - Equipped with a signal synthesis circuit 10 as an identification circuit.

Here, as the local oscillation optical oscillator 7, a double-end emitting type semiconductor laser (a double-end emitting laser) is used, and this local oscillation optical oscillator 7 is also stabilized by controlling the temperature to be constant by a temperature control circuit. has been modified.

Reference numeral 14 denotes a 1/2 wavelength plate as means for changing the polarization state of the local oscillation light. If the polarization state of the other local oscillation light irradiated from the other end surface of the double-end emitting type semiconductor laser 7 is, for example, S polarization, then the polarization state of this one local oscillation light is rotated by 90 degrees. can be changed to P polarization.

Then, one locally oscillated light (P polarized wave) whose polarization state has been changed by the half-wave plate 14 and the other locally oscillated light (S
The mixing circuit 8 converts the two types of polarization components (P polarization, S polarization) of the signal light transmitted through the optical fiber 5 into
[Function] With this configuration, one local oscillation light (S polarized wave) irradiated from one end surface of the double-end emitting semiconductor laser 7 is
The polarization state is changed by the /2 wavelength plate 14, the polarization plane is rotated by 90 degrees, and it becomes P polarization, and then the local oscillation light in the P polarization state whose polarization state is changed in this way. The locally oscillated light (S polarization) of the other beam j irradiated from the other end face of the double-end emitting type semiconductor laser 7 is input to the mixing circuit 8, and is transmitted through the optical fiber 5 by the mixing circuit 8. Two types of polarization components of the signal light (P polarization.

S polarization).

Thereafter, each polarized wave is detected by a detection circuit 9, and then demodulated and added to the input signal and discriminated by a signal synthesis circuit 10.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

(a) Description of the first embodiment Fig. 2 is a block diagram showing the first embodiment of the present invention. belongs to.

Now, in this FIG. 2, reference numeral 6 denotes a polarization diversity optical receiver as a receiving section, and this polarization diversity optical receiver 6 includes a local oscillation optical oscillator 72 and a local oscillation optical polarization state changing means 1/1. Two-wavelength plate 14. Mixed circuit 8.
Detection circuit 9. Demodulation/addition/discrimination circuit (signal synthesis circuit) 1
0, addition circuit 11. It has a control circuit 12.

Here, as the local oscillation light oscillator 7, a double-end emission type semiconductor laser (both-end emission type laser) is used, whereby local oscillation light is oscillated from both end surfaces of the double-end emission type semiconductor laser 7. There is.

In this case, the double-end emitting type semiconductor laser 7 is designed and manufactured so that the power ratio of both locally oscillated lights is equal.

Note that the light source stabilization device 1 configured as a temperature control device
8, the laser temperature is controlled to be constant.

Further, the 1/2 wavelength plate 14 is a double-end emitting type semiconductor laser 7.
The polarization plane of one local oscillation light irradiated from one end face is 9
If the polarization state of the other locally oscillated light irradiated from the other end surface of the double-end emitting semiconductor laser 7 is, for example, S polarization, then the polarization state of this one locally oscillated light is It can be changed to P polarization.

Further, the mixing circuit 8 receives the signal light P which has been subjected to FSX modulation or ASK modulation and has been transmitted through the optical fiber 5.
It mixes two types of local oscillation light (P polarization, S polarization) from the local oscillation light oscillation bag M7 for each of the two types of polarization components of si, and separates the signal light Psi from the optical fiber 5. It is provided with a polarization-separating optical fiber coupler 19 that emits waves, and a polarization-maintaining optical fiber coupler 20 that maintains each of the p and s polarization states.

Note that one local oscillation light (S polarization) irradiated from one end surface of the double-end emitting type semiconductor laser 7 is changed in polarization state by the 172-wave plate 14 and becomes P polarization. The local oscillation light in the P polarization state whose polarization state has been changed by the change in the polarization state and the other local oscillation light (S polarization) irradiated from the other end surface of the double-end emitting semiconductor laser 7 are input to the mixing circuit 8. Therefore, there is no need for the polarization separation optical fiber coupler 19' that separates the locally oscillated light as in the conventional case.

The detection circuit 9 detects the signals of each polarization component from the mixing circuit 8, and includes photoelectric conversion circuits 21P and 21S configured as a double-balanced optical receiver, and a post amplifier 22.
P, 22S, and bandpass filters 23P, 23S.

Here, the photoelectric conversion circuits 21P and 21S are circuits that receive optical signals and convert them into electrical signals, and the post amplifier 22P,
228 is a circuit that amplifies the electrical output from the photoelectric conversion circuits 2LP and 21S, and the bandpass filters 23P and 23S filter only the required frequency band to generate the intermediate frequency signal eP+.
This is a circuit that outputs eS.

The demodulation/addition/discrimination circuit 10 receives the detection output e of the detection circuit 9.
It has a demodulation function that extracts a signal corresponding to the transmitted human signal from P+ es, and includes delay detection circuits 24P and 24S.
, addition circuit 25, low-pass filter 26, identification circuit 27
have.

Here, the delay detection circuits 24P and 24S have delay circuits 24P-1 and 24S-1 that branch signals and delay one of them, but each delay circuit 24. P-1,248-1
The delay time in FSX (ASK) is set to approximately 0.

Further, the adder circuit 25 includes each delay detection circuit 24P.

This is a circuit that adds and synthesizes the outputs Vp and Vs of the 24S.

Further, the low-pass filter 26 is a circuit that removes noise in unnecessary bands, and the identification circuit 27 is a circuit that identifies 0 and 1 information from a signal and extracts a signal corresponding to the transmission input signal. Note that the identification circuit 27 detects 0.0 from the input signal. li
It also has the ability to extract timing signals for different uses.

By the way, the addition circuit 11 includes a bandpass filter 23P,
The detection output es+epfz of each polarized wave component from 23S is added, and an adder 13 is provided for this purpose.
Furthermore, this adder circuit 11 includes an automatic gain control circuit (AGC circuit) 1 that adjusts the output gain after addition in the adder 13.
It has 5.

Further, the control circuit 12 controls the oscillation frequency of the local oscillation optical oscillation bag W7 based on the addition output of the addition circuit 11. For this purpose, the control circuit 12 controls the frequency of the signal obtained by the addition circuit 11. a frequency discrimination circuit 16 that discriminates and outputs a corresponding voltage signal, and this frequency discrimination circuit 16
It is configured as an automatic frequency control circuit (AFC circuit) including a drive circuit 17 which converts the output of the circuit into a current signal and inputs the signal to the oscillation frequency control input terminal of the local oscillation optical oscillator 7.

By the way, in this FIG. 2, ``■'' is a transmitting section, and this transmitting section 1 has a light source 2, a light source stabilizing device 4, and an amplifier 28.

Here, as the light source 2, for example, a semiconductor laser capable of single mode oscillation is used. Moreover, if a semiconductor laser is used as the light source stabilizing device 4 in this way,
For example, a device having a temperature control device that controls the temperature of the laser at a constant level is used.

Furthermore, the amplifier 28 amplifies the input signal (data) and applies a current signal IAC to the oscillation frequency control end of the light source 2. Furthermore, the amplifier 28 amplifies the input signal (data) and applies a current signal IAC to the oscillation frequency control end of the light source 2.
DC is also supplied.

This performs optical modulation and performs ASK on the input signal.
Modulation (pulse amplitude modulation) or FSX modulation (pulse frequency modulation) can be performed.

Further, in FIG. 2, 5 is an optical fiber as a transmission medium.

With the above configuration, one locally oscillated light (S polarized wave) irradiated from one end surface of the double-ended semiconductor laser 7 is 1/2
The polarization state is changed by the wavelength plate 14 to become P polarization, and then the locally oscillated light in the P polarization state whose polarization state has been changed in this way and the double-ended emission type semiconductor laser 7
The other local oscillation light (S polarization) emitted from the other end surface is input to the mixing circuit 8, and the mixing circuit 8 combines the two types of polarization components of the signal light transmitted through the optical fiber 5. (P polarization, S polarization).

Thereafter, each polarized wave is detected by the detection circuit 9, and further demodulated, added to, and identified by the input signal by the demodulation/addition/identification circuit 1o.

In this way, in this first embodiment, even without using a high-output semiconductor laser as the local oscillation optical oscillator, sufficient light can be generated by effectively utilizing the light from both ends of the double-end emitting type semiconductor laser 7. Two locally oscillated lights with high power can be obtained, and since a half-wave plate 14 is used to rotate one of the local oscillated lights from the double-end emitting type semiconductor laser 7 by 90 degrees, polarization can be achieved with low loss. The wave state can be changed, and as a result, the power deficiency of the local oscillator light can be sufficiently compensated, and a sufficient shot noise limit can be achieved at the receiver, so that the deterioration of the signal-to-noise ratio of the receiver can be avoided. It never invites.

Note that when the detection output eS+ ep from the detection circuit 9 is fed back and the oscillation frequency of the double-end emitting type semiconductor laser 7 is controlled, these detection output information es+ ep
are added and synthesized, and the output gain after this addition is adjusted by the automatic gain control circuit (AGC circuit) 15.
The signal is inputted to the control input terminal of the double-end emitting type semiconductor laser 7 via the frequency discrimination circuit 16 and the drive circuit 17 . As a result, this double-end emitting type semiconductor laser 7 is feedback-controlled so as to have a required oscillation frequency.

(b) Description of the second embodiment Fig. 3 is a block diagram showing the second embodiment of the present invention. It is.

Now, in this FIG. 3, 6 is a polarization diversity optical receiver of ~19- as a receiver, and this polarization diversity optical receiver bag M6 is a local oscillation optical oscillator configured as a double-end emitting type semiconductor laser. 7° 1/2 wavelength plate 14 as local oscillation light polarization state changing means. Mixed circuit 8. Detection circuit 9. In addition to the demodulation/addition/discrimination circuit (signal synthesis circuit) 10, it has an addition circuit 11 and a control circuit 12.

Here, local oscillation optical oscillator (double-end emission type semiconductor laser) 7.1/2 wavelength plate 14. Mixed circuit 8. Detection circuit 9. Demodulation/addition/discrimination circuit 10. Since the control circuit 12 is substantially the same as that in the first embodiment described above, detailed explanation thereof will be omitted.

By the way, the addition circuit 11 includes a bandpass filter 23P,
The detection output es+ep of each polarized wave component from 23S is added, and an adder 13 is provided for this purpose, but this addition circuit 11 also includes a doubler 29 that doubles the output frequency after addition. , and an automatic gain control circuit (AGC circuit) 15 that adjusts the output gain of this doubler 29.

Here, the difference from the first embodiment described above is that it has a doubler 29, and by using this doubler 29, it is possible to cancel out the spread of the spectrum due to the phase information of the intermediate frequency signal. .

In addition, the delay circuit 24P- of the delay detection circuit 24P, 24S
The delay time at 1,248-1 is set to 1 bit for DPSK.

By the way, in this FIG. 3, 1 is a transmitting section for DPSK, and this transmitting section 1 includes a light source 2, an optical modulation circuit 3, a light source stabilizing device 4, a waveform shaping circuit 30, an amplifier 31, and a differential encoding circuit. It has a circuit 32 and a crystal oscillator 33.

Here, as the light source 2, for example, a semiconductor laser capable of single mode oscillation is used. Moreover, if a semiconductor laser is used as the light source stabilizing device 4 in this way,
For example, a device having a temperature control device that controls the temperature of the laser at a constant level is used.

Furthermore, the differential encoding circuit 32 receives the reference signal and the input signal (data) from the crystal oscillator 33, differentially encodes it, and outputs it. The signal is input to the optical modulation circuit 3 via the waveform shaping circuit 30.

This performs optical modulation and converts the input signal into DPS.
It is possible to perform K modulation.

Note that 5 is an optical fiber as a transmission medium.

With the above configuration, one locally oscillated light (S polarized wave) irradiated from one end surface of the double-ended semiconductor laser 7 is 1/2
The polarization state is changed by the wavelength plate 14 to become P polarization, and then the locally oscillated light in the P polarization state whose polarization state has been changed in this way and the double-ended emission type semiconductor laser 7
The other locally oscillated light (S polarization) emitted from the other end surface is input to the mixing circuit 8, and the mixing circuit 8 converts the DPSK-modulated signal light transmitted through the optical fiber 5. It is mixed with two types of polarization components (P polarization and S polarization).

Thereafter, each polarized wave is detected by a detection circuit 9, and further demodulated, added to, and identified by the input signal by a demodulation/addition/discrimination circuit 10.

In this way, in the case of the second embodiment as well, without using a high-output semiconductor laser as the local oscillation optical oscillator, by effectively utilizing the light from both ends of the double-end emitting type semiconductor laser 7, A half-wave plate 1 that can obtain two local oscillation lights with sufficient power and further rotate one of the local oscillation lights from the double-end emitting type semiconductor laser 7 by 90°.
4, it is possible to change the polarization state with low loss, and as a result, it is possible to sufficiently compensate for the lack of power of the local oscillation light and sufficiently achieve the shot noise limit in the optical receiver. , it does not cause deterioration of the signal-to-noise ratio of the receiver.

Furthermore, when the detection output O3+ep from the detection circuit 9 is fed back to control the oscillation frequency of the double-ended emission type semiconductor laser 7, these detection output information es+eP are added and synthesized, and the output after this addition is a doubler. -29 cancels the spread of the spectrum due to the phase information of the intermediate frequency signal, and after that, the output gain of the doubler -29 is adjusted by the automatic gain control circuit (AGC circuit) 15, and then the frequency discrimination circuit 16 and the drive The signal is inputted through the circuit 17 to the control input terminal of the double-end emitting type semiconductor laser 7 . As a result, the double-end emitting type semiconductor laser 7 is subjected to fee 1 to back control so as to have the required oscillation frequency.

[Effects of the Invention] As described in detail above, according to the polarization diversity optical receiver for coherent optical communication of the present invention, a double-end emission type optical receiver can be used without using a high-power semiconductor laser as a local oscillation optical oscillator. By effectively utilizing the light from both ends of the semiconductor laser, two local oscillation lights with sufficient power can be obtained, and the polarization state of one local oscillation light from the double-end emitting semiconductor laser can be changed. Since the local oscillation light polarization state changing means is used to change the polarization state of the other local oscillation light, the polarization state can be changed with low loss, and as a result, the power shortage of the local oscillation light can be avoided. Since the shot noise limit in the photoreceiver can be sufficiently achieved by sufficiently compensating, there is an advantage that the signal-to-noise ratio of the receiver does not deteriorate.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram showing the first embodiment of the invention, Fig. 3 is a block diagram showing the second embodiment of the invention, and Fig. 4 is a block diagram of the conventional example. It is a diagram. In the figure, 1 is a transmitter, 2 is a light source, 3 is an optical modulation circuit, 4 is a light source stabilization device, 5 is an optical fiber, 6 is a polarization diversity optical receiver as a receiver, 7 is a double-end emitting type semiconductor laser A local oscillation optical oscillator configured as: 8 is a mixing circuit, 9 is a detection circuit, 10 is a demodulation/addition/discrimination circuit (signal synthesis circuit), 11 is an addition circuit, 12 is a control circuit, 13 is an adder, 14 15 is an automatic gain control circuit (AGC circuit); 16 is a frequency discrimination circuit; 17 is a drive circuit; 18 is a light source stabilization device; 19 is a polarization device. Separation optical fiber coupler, 20 is a polarization maintaining optical fiber coupler, 21P, 21S are photoelectric conversion circuits, 22P, 223 are pos I-amplifiers, 23P, 23S are band pass filters, 24P, 24S
is a delay detection circuit, 24P-1, 243-1 is a delay circuit, 25 is an addition circuit, 26 is a low-pass filter, 27 is an identification circuit, 28 is an amplifier, 29 is a doubler-1, 30 is a waveform shaping circuit, 31 is an amplifier, 32 is a differential encoding circuit, and 33 is a crystal oscillator.

Claims (2)

[Claims] (1) Local oscillation optical oscillator that oscillates local oscillation light (7)
and a mixing circuit (8) that mixes each of the two types of polarization components of the signal light transmitted through the optical fiber (5) with the local oscillation light from the local oscillation light oscillator (7); A detection circuit (9) that detects the signals of each polarization component from the circuit (8), and a signal synthesis circuit (10) that extracts a signal corresponding to the input signal from the detection output from the detection circuit (9). Polarization diversity optical receiver for coherent optical communication equipped with
), the local oscillation optical oscillator (7) is configured as a double-end emitting type semiconductor laser, and the polarization state of one local oscillation light irradiated from one end surface of the double-end emitting type semiconductor laser (7) is determined from the two ends. local oscillation light polarization state changing means (
14) is provided, and the local oscillation light polarization state changing means (
The one local oscillation light whose polarization state has been changed in step 14) and the other local oscillation light irradiated from the other end surface of the double-end emitting semiconductor laser (7) are mixed in the mixing circuit (8). A polarization diversity optical receiver for coherent optical communication, characterized in that two types of polarization components of signal light transmitted through the optical fiber (5) are mixed. (2) The coherent optical communication device according to claim 1, wherein the locally oscillated light polarization state changing means (14) is configured as a half-wave plate that rotates the polarization plane of the one locally oscillated light by 90 degrees. Polarization diversity optical receiver.