CN111525962B

CN111525962B - Coherent optical receiver, coherent optical processing method, and coherent optical receiving apparatus

Info

Publication number: CN111525962B
Application number: CN201910108027.5A
Authority: CN
Inventors: 赵平; 李良川; 肖新华
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2019-02-02
Filing date: 2019-02-02
Publication date: 2021-09-03
Anticipated expiration: 2039-02-02
Also published as: CN111525962A

Abstract

The application discloses a coherent optical receiver, a coherent optical receiving method and a coherent optical processing system. The coherent optical receiver includes: a first optical Beam Splitter (BS), a second BS, a polarization rotating phase shifter, a first mixer, a second mixer, and a photodetector. Wherein the first BS splits the signal light input to the coherent optical receiver into two signal lights. The two signal lights are inputted to the first and second mixers, respectively. The second BS splits the local oscillator light input to the coherent optical receiver into two local oscillator lights. Inputting the first beam of local oscillator light into a first mixer; and the second beam of local oscillator light is subjected to polarization state rotation and phase shift through the polarization rotation phase shifter and then is input into the second frequency mixer. The first and second mixers respectively mix the inputted light. The mixed output light is output to a photodetector for photoelectric conversion to generate an electrical signal. The coherent light receiver disclosed by the application can realize coherent light receiving irrelevant to the polarization state of local oscillator light, eliminates the influence of polarization state rotation, and effectively improves the coherent light receiving performance.

Description

Coherent optical receiver, coherent optical processing method, and coherent optical receiving apparatus

Technical Field

The present application relates to the field of optical devices, and in particular, to a coherent optical receiver, a coherent optical processing method, and a coherent optical receiving apparatus.

Background

The coherent light transmission technology has the advantages of large transmission capacity, long distance and the like, and can be applied to submarine cables, long-distance backbones and metropolitan area transmission networks. With the rapid increase of the demand of short-distance transmission for high-speed bandwidth, such as large-scale capacity expansion of a data center, the number of internal high-speed switch interconnection ports is increased. The conventional direct detection optical transmission technology cannot balance the transmission bandwidth and distance, and becomes a bottleneck restricting the capacity expansion of a data center. In such a background, the coherent transmission technology becomes a promising alternative technology for short-distance transmission, which can improve the transmission rate and distance of the high-speed switch port in the data center.

A conventional coherent optical transmission system employs two lasers with precisely controlled frequencies, which is costly and difficult to use in a Data Center Network (DCN). The method adopts an asynchronous laser coherence mode, and the system phase noise is large, so that the power consumption of a Digital Signal Processing (DSP) chip is high. This also further hinders the application of such conventional coherent optical transmission systems in DCN scenarios.

Another existing coherent optical transmission system uses homologous coherent optical transmission, i.e., the transmitting end and the receiving end of the system share one laser. At a transmitting end, a laser is divided into two beams by a light beam splitter, one beam is signal light, the other beam is local oscillator light, and the two beams are transmitted to a receiving end through optical fibers respectively. The system does not need a laser with accurately controlled frequency, and has good low-cost potential; the phase noise of the system is low, and the power consumption of the DSP chip is expected to be greatly reduced. However, the homologous coherent optical transmission system generally uses a common optical fiber to transmit the local oscillation light generated by the transmitting end, which may cause the polarization state of the local oscillation light to randomly deflect. Such random deflection may cause the coherent optical receiver at the receiving end to fail to perform optical processing normally, thereby causing signal interruption at the receiving end and failing to acquire service data at the transmitting end. One possible solution is to use expensive polarization maintaining fiber to transmit the local oscillator light generated by the transmitting end, but this will greatly increase the system cost.

Disclosure of Invention

The embodiment of the application provides a coherent light receiver, a coherent light processing method and coherent light receiving equipment, which are used for solving the problem that the coherent light receiver cannot be normal due to polarization state rotation in the prior art.

In a first aspect, embodiments of the present application provide coherent light. The coherent optical receiver includes a first optical Beam Splitter (BS), a second BS, a polarization rotating phase shifter, a first mixer, a second mixer, and a photodetector, wherein: the first BS is configured to split the signal light input to the coherent optical receiver and output a first signal light and a second signal light; the second BS is configured to split the local oscillation light input to the coherent light receiver and output a first local oscillation light and a second local oscillation light; the polarization rotation phase shifter is used for performing 90-degree polarization state rotation and 180-degree phase shift on the second local oscillation light and outputting third local oscillation light; the first frequency mixer is configured to mix the first signal light and the first local oscillator light, and output first mixed light; the second mixer is configured to mix the second signal light and the third local oscillator light, and output second mixed light; the photodetector is configured to perform photoelectric conversion on the first mixed light and the second mixed light to generate an electrical signal.

Through light beam splitting and polarization rotation and phase shift of one local oscillation light, the local oscillation light entering the two frequency mixers is orthogonal, and the coherent light receiver ensures that the local oscillation light cannot be influenced (namely the frequency mixers always have light output) even if the local oscillation light changes in a random polarization state, so that the normal work of the coherent light receiver is ensured.

With reference to the first aspect, in a first specific implementation manner, the second BS and the polarization rotating phase shifter are spatial optical components, and the first BS, the first mixer, and the second mixer are silicon optical components.

With reference to the first aspect, in a second specific implementation manner, the first BS, the second BS, and the polarization rotation phase shifter are spatial optical components, and the first mixer and the second mixer are silicon optical components; the coherent optical receiver further includes a first mirror for reflecting the first signal light or the second signal light.

The two specific designs adopt the space optical assembly to realize the polarization rotation phase shift of the local oscillation light, and the light processing efficiency is higher.

With reference to the first aspect or the first or second specific implementation manner of the first aspect, in a third specific implementation manner, the first BS is a 1 × 2 coupler. The light splitting is performed by a 1-by-2 coupler, and the light splitting performance is better than that of other types of couplers.

With reference to the first aspect or any one of the first to third specific implementation manners of the first aspect, in a fourth specific implementation manner, the coherent optical receiver further includes a first waveguide, a second waveguide, a third waveguide, and a fourth waveguide, where the first waveguide to the fourth waveguide are all multi-polarization waveguides; the first mixer mixes the first signal light and the first local oscillator light, and the second mixer mixes the second signal light and the third local oscillator light, which specifically includes: the first mixer mixes the first signal light and the first local oscillator light after receiving the first signal light and the first local oscillator light through the first waveguide and the third waveguide, respectively; the second mixer mixes the second signal light and the third local oscillator light after receiving the second signal light and the third local oscillator light through the second waveguide and the fourth waveguide, respectively.

With reference to the first aspect or any one of the first to the third specific implementation manners of the first aspect, in a fifth specific implementation manner, the coherent optical receiver further includes a first waveguide, a second waveguide, a first transmission unit and a second transmission unit, where the first transmission unit and the second transmission unit respectively include a third waveguide, a fourth waveguide, a first Polarization Beam Splitter (PBS), a Polarization Beam Combiner (PBC), a first single polarization waveguide and a second single polarization waveguide, where the first waveguide to the fourth waveguide are all multi-polarization waveguides, the third waveguide is connected to an input port of the first PBS, two output ports of the first PBS are respectively connected to one end of the first single polarization waveguide and one end of the second single polarization waveguide, and the other end of the first single polarization waveguide and the other end of the second single polarization waveguide are respectively connected to an input port of the PBC A port connection, the PBC and the fourth waveguide being connected, the third waveguide and the fourth waveguide being an optical input waveguide and an optical output waveguide, respectively; the first mixer mixes the first signal light and the first local oscillator light, and the second mixer mixes the second signal light and the third local oscillator light, which specifically includes: the first frequency mixer receives the first signal light and the first local oscillator light through the first waveguide and the first transmission unit respectively, and mixes the first signal light and the first local oscillator light; the second frequency mixer receives the second signal light and the third local oscillator light through the second transmission unit and the second waveguide, and mixes the second signal light and the third local oscillator light; wherein the first waveguide and the second waveguide are both straight waveguides.

The fifth specific implementation manner adopts the design of the single polarization waveguide, so that crosstalk and loss caused by bending and crossing of the dual-mode waveguide are reduced, and the performance of the coherent optical receiver is improved.

Optionally, in an implementation manner of the first aspect or any one of the first aspect, at least two of the first waveguide to the fourth waveguide are provided with a thermal tuning electrode, and the thermal tuning electrode is configured to perform time delay control on light passing through a waveguide corresponding to the thermal tuning electrode. The phase of the light input into the mixer is accurately controlled through the thermal tuning electrode, and the light processing efficiency of the coherent light receiver can be improved.

With reference to the first aspect or any one of the foregoing implementation manners or optional designs of the first aspect, in a sixth specific implementation manner, the coherent light receiver further includes a second mirror; before the first mixer mixes the first signal light and the first local oscillator light, the second reflector reflects the first local oscillator light.

With reference to the first aspect or any one of the foregoing implementation manners or optional designs of the first aspect, in a seventh specific implementation manner, the coherent optical receiver further includes a first lens; before the first mixer mixes the first signal light and the first local oscillator light, the first lens focuses the first local oscillator light.

In combination with the first aspect or any one of the implementations or alternative designs of the first aspect,

with reference to the first aspect or any one of the foregoing implementation manners or optional designs of the first aspect, in an eighth specific implementation manner, the polarization rotation phase shifter includes a second Polarization Beam Splitter (PBS), a third PBS, a third mirror, a fourth mirror, a first half-wave plate, a second half-wave plate, and a 180-degree phase shifter; the polarization rotating phase shifter performs 90-degree polarization rotation and 180-degree phase shift on the second local oscillation light, and outputs third local oscillation light, which specifically includes: after the second PBS performs polarization beam splitting on the second local oscillation light, outputting seventh local oscillation light and eighth local oscillation light; the first half wave plate, the 180-degree phase shifter and the third reflector process the seventh local oscillator light and output ninth local oscillator light, and the second half wave plate and the fourth reflector process the eighth local oscillator light and output tenth local oscillator light, wherein the first half wave plate and the second half wave plate respectively perform 90-degree polarization rotation on the seventh local oscillator light and the eighth local oscillator light; and after the ninth local oscillator light and the tenth local oscillator light are subjected to polarization combination by the third PBS, outputting third polarized light.

Specifically, the smoothness of the processing of the seventh local oscillator light by the first half-wave plate, the 180-degree phase shifter, and the third mirror may be designed as required.

With reference to the eighth specific implementation manner, in a ninth specific implementation manner, the polarization rotating phase shifter further includes a second lens. After the third PBS polarizes and combines the ninth local oscillator light and the tenth local oscillator light, the third PBS outputs the third polarized light, which specifically includes: after the ninth local oscillator light and the tenth local oscillator light are combined in a polarization mode by the third PBS, eleventh local oscillator light is output; the second lens focuses the eleventh local oscillation light and outputs the third polarized light.

With reference to the sixth specific implementation manner, in a tenth specific implementation manner, the polarization rotating phase shifter includes a second Polarization Beam Splitter (PBS), a third PBS, the second mirror, a third mirror, a first half-wave plate, a second half-wave plate, and a 180-degree phase shifter; the polarization rotating phase shifter performs 90-degree polarization rotation and 180-degree phase shift on the second local oscillation light, and outputs third local oscillation light, which specifically includes: after the second PBS performs polarization beam splitting on the second local oscillation light, outputting seventh local oscillation light and eighth local oscillation light; the first half-wave plate, the 180-degree phase shifter and the third reflector process the seventh local oscillator light and output ninth local oscillator light, and the second half-wave plate and the second reflector process the eighth local oscillator light and output tenth local oscillator light, wherein the first half-wave plate and the second half-wave plate respectively rotate the seventh local oscillator light and the eighth local oscillator light by 90-degree polarization states; and after the ninth local oscillator light and the tenth local oscillator light are subjected to polarization combination by the third PBS, generating third polarized light.

Specifically, the order of processing the seventh local oscillation light by the first half-wave plate, the 180-degree phase shifter, and the third mirror may be designed as required.

By using one reflector, the two lights are reflected, the size of a coherent light receiver space optical component is reduced, and the receiver volume can be smaller.

With reference to the tenth possible implementation manner, in an eleventh possible implementation manner, the polarization rotation phase shifter further includes a second lens; after the third PBS polarizes and combines the ninth local oscillator light and the tenth local oscillator light, the third PBS outputs the third polarized light, which specifically includes: after the ninth local oscillator light and the tenth local oscillator light are combined in a polarization mode by the third PBS, eleventh local oscillator light is output; the second lens focuses the eleventh local oscillation light and outputs the third polarized light.

In a second aspect, a method for coherent light processing is disclosed. The method comprises the following steps: carrying out power beam splitting on signal light input into a coherent light receiver to obtain first signal light and second signal light, and carrying out power beam splitting on local oscillator light input into the coherent light receiver to obtain first local oscillator light and second local oscillator light; performing 90-degree polarization state rotation and 180-degree phase shift on the second local oscillation light to obtain third local oscillation light; performing frequency mixing processing on the first signal light and the first local oscillator light to obtain first frequency mixing light, and performing frequency mixing processing on the second optical signal and the third local oscillator light to obtain second frequency mixing light; and performing photoelectric conversion on the first mixed light and the second mixed light to obtain an electric signal.

In a specific design, the performing a 90-degree polarization rotation and a 180-degree phase shift on the second local oscillator light to obtain a third local oscillator light specifically includes: carrying out polarization beam splitting on the second local oscillation light to obtain seventh local oscillation light and eighth local oscillation light; performing 90-degree polarization state rotation, 180-degree phase shift and reflection on the seventh local oscillation light to obtain ninth local oscillation light; rotating and reflecting the eighth local oscillator light in a polarization state of 90 degrees to obtain tenth local oscillator light; and after the ninth local oscillator light and the tenth local oscillator light are subjected to polarization combination, the third local oscillator light is obtained.

In another specific design, before performing 90-degree polarization rotation and 180-degree phase shift on the second local oscillation light, the second local oscillation light is further reflected.

In another specific design, the first signal light is reflected before the frequency mixing processing is performed on the first signal light and the first local oscillator light.

In a third aspect, embodiments of the present application disclose a coherent optical receiving device. The apparatus comprises a coherent optical receiver as described in the first aspect or any one of its specific implementations or designs.

In a fourth aspect, the present application discloses a coherent light processing system. The system comprises a transmitting device and a coherent optical receiving device as described in the third aspect. The sending device sends signal light to the coherent light receiving device, or the sending device sends signal light and local oscillator light to the coherent light receiving device.

Compared with the prior art, the coherent light receiving scheme disclosed by the application performs beam splitting processing on the input signal light and the local oscillator light, and further processes the split local oscillator light, so that the local oscillator light input to the frequency mixer is orthogonal in polarization state, the influence of random change of the local oscillator light on a coherent receiver is eliminated, and the performance of the coherent receiver is improved.

Drawings

Embodiments of the present application will now be described in more detail with reference to the accompanying drawings, in which:

fig. 1a is a schematic diagram of a possible application scenario according to an embodiment of the present application;

FIG. 1b is a schematic diagram of another possible application scenario of the embodiment of the present application;

fig. 2 is a schematic structural diagram of a coherent optical receiver provided in the present application;

fig. 3 is a schematic structural diagram of a possible coherent optical receiver according to an embodiment of the present disclosure;

FIG. 4a is a schematic diagram of a possible structure of the polarization rotating phase shifter shown in FIG. 3;

FIG. 4b is a schematic diagram of another possible structure of the polarization rotating phase shifter shown in FIG. 3;

fig. 5 is a schematic structural diagram of another possible coherent optical receiver provided in the embodiments of the present application;

fig. 6 is a schematic structural diagram of another possible coherent optical receiver provided in the embodiments of the present application;

fig. 7 is a schematic structural diagram of a fourth possible coherent optical receiver according to an embodiment of the present application;

FIG. 8 is a schematic diagram of a third possible polarization rotating phase shifter according to an embodiment of the present disclosure;

fig. 9 is a schematic structural diagram of a fifth possible coherent optical receiver according to an embodiment of the present application;

fig. 10 is a flowchart illustrating a method for coherent light reception according to an embodiment of the present application.

Detailed Description

The device form and the application scenario described in the embodiment of the present application are for more clearly illustrating the technical solution of the embodiment of the present invention, and do not limit the technical solution provided by the embodiment of the present invention. As can be known to those skilled in the art, with the evolution of device morphology and the emergence of new scenarios, the technical solution provided in the embodiments of the present application is also applicable to similar technical problems.

It should be noted that the terms "first," "second," and the like in this application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used are interchangeable under appropriate circumstances such that the embodiments described herein are capable of operation in sequences not described in the present application. "and/or" is used to describe the association relationship of the associated objects, meaning that three relationships may exist. For example, a and/or B, may represent: a exists alone, A and B exist simultaneously, and B exists alone. The specific operation methods in the method embodiments may also be applied to the functional description of the relevant components in the apparatus embodiments.

The coherent light receiving technical scheme provided by the application can be applied to different network scenarios, including but not limited to: backbone optical transmission network, optical access network, data center interconnection, short-distance optical interconnection, wireless service forward/backward transmission and the like. Specifically, the technical solution provided by the present application may be used for the receiving side device corresponding to the different networks.

Fig. 1a and 1b show two possible coherent optical transmission systems to which the solution proposed by the present application is applicable.

Fig. 1a shows a homogeneous coherent optical transmission system 100. The system 100 includes a transmission-side apparatus 101 and a reception-side apparatus 102, and optical fibers 103a and 103b connecting these two apparatuses. The transmission-side device 101 includes a data input 1011, a laser 11012, an optical splitter 1013, and a modulator 1014. The light output from the laser 11012 is split into two by the optical splitter 1013, one of which is modulated by the modulator to obtain signal light loaded with service data, and the other is used as local oscillation light. The signal light and the local oscillation light generated by the transmitting side device are transmitted to the receiving side device 102 through the optical fiber. The receiving-end apparatus 102 includes a coherent receiver 1021 and a Digital Signal Processor (DSP) 1022. The former receives signal light and local oscillator light to realize coherent light reception; which processes the electrical signal output by the coherent optical receiver 1021 to obtain traffic data. Since both the signal light and the local oscillator light are generated by the transmitting-side device, the system 100 is referred to as a homologous coherent optical transmission system. It should be noted that the signal light and the local oscillator light may also be transmitted through one optical fiber.

Fig. 1b shows a conventional coherent optical transmission system 200. The system 200 includes a transmission-side device 201, a reception-side device 202, and an optical fiber 203 connecting the two devices. The transmitting side device 201 includes a data input 2011, a laser 12012, and a modulator 1014. The light output from the laser 12012 is modulated by a modulator to obtain signal light loaded with service data, and the signal light is transmitted to the receiving end device 102 through an optical fiber. The receiving end apparatus 202 includes a laser 22022, a coherent receiver 2021 and a DSP 2023. Among them, the laser 22022 and the laser 12012 of the transmission-side device need to keep the frequency the same or substantially the same to achieve coherent light reception.

In the scenario example of fig. 1a, the local oscillator light needs to be transmitted through the optical fiber, which may cause the polarization state to be randomly deflected. This may cause the coherent optical receiver at the receiving end to fail to operate properly. Similarly, the same problem exists if the laser 22022 also needs to be connected via an optical fiber to the coherent optical receiver 2021 in the scenario example of fig. 1 b. In addition, the system shown in FIG. 1b results in higher system cost because of the need for precise frequency control.

To solve the above-mentioned problems of the prior art, the present application provides a new coherent optical receiver. The coherent light receiver has signal light and local oscillator light as input and electrical signal as output. The output electrical signal includes service data, and the final service data can be obtained by further processing the output electrical signal. The coherent light receiver can process local oscillation light into two beams of light with orthogonal polarization states, so that the problem that the normal work of the receiver is influenced due to the random change of the polarization states of the local oscillation light is solved. By adopting the coherent light receiver, a coherent light transmission system can adopt a conventional optical fiber to realize normal coherent light reception so as to acquire service data. In addition, compared with a scheme adopting a polarization maintaining optical fiber, the technical scheme provided by the application greatly reduces the cost of a coherent optical transmission system.

Fig. 2 is a schematic structural diagram of a coherent optical receiver according to the present application. The coherent optical receiver 300 includes two optical Beam Splitters (BS) (301 and 302), a polarization rotating phase shifter 303, two mixers (304 and 305), and a photodetector (306). These components may be silicon optical components or space optical components. Correspondingly, the connection relationship in the figures may indicate that there is a direct or indirect physical connection, and may also indicate a spatial position relationship (i.e., there is no physical connection). This is not a limitation of the present application. Reference may be made in detail to further embodiments described hereinafter.

The BS 301 is configured to split the signal light input to the coherent optical receiver 300 and output two signal lights (hereinafter referred to as a first signal light and a second signal light). The BS 302 is configured to split the local oscillator light input to the coherent optical receiver 300 and output two local oscillator lights (hereinafter referred to as a first local oscillator light and a second local oscillator light). It should be noted that the BS may also be referred to as an optical splitter, which splits the power of the input light to obtain two beams.

The polarization rotation phase shifter 303 is configured to perform 90-degree polarization rotation and 180-degree phase shift on the second local oscillation light, and output a third local oscillation light. It should be noted that a 270 degree polarization rotation for light in one direction is equivalent to a 90 degree polarization rotation in the opposite direction. Both rotations result in the formation of a polarization state orthogonality between the input light and the output light. It should be noted that the requirements for the polarization state angle or the phase shift angle are not the same and are strictly equal. Angles that approximate the requirements are also understood to fall within the scope of the embodiments of the present application.

The

mixers

304 and 305 are used to mix two input lights and output the mixed lights. Specifically, the mixer 304 performs a mixing process on the first signal light and the first local oscillator light, and outputs mixed light. The mixer 305 performs mixing processing on the second signal light and the third local oscillation light, and outputs mixed light. The mixer according to the present application is an optical mixer for coherent optical communication. Those skilled in the art will appreciate that the mixers may be implemented by spatial optics or silicon optical materials, etc., such as Multimode interferometer (MMI) mixers, coupler array mixers, etc. Unless otherwise stated, the mixer used in the existing coherent optical communication and the new mixer realized later with the development of optical materials can be used in the coherent optical receiver proposed in the present application. The mixed light may be referred to as a light component or other name. This is not limited in this application. The set of mixed light output by the two mixers carries customer data. For the subsequent processing of these mixed lights, the client data transmitted from the transmitting device can be obtained.

The photodetector 306 photoelectrically converts the mixed light output from the

mixers

304 and 305 to generate an electric signal.

The coherent optical receiver shown in fig. 2 makes the local oscillator lights entering the two mixers orthogonal by splitting the light and performing polarization rotation and phase shift on one local oscillator light, thereby ensuring that the output of the mixers (i.e. always there is optical output) is not affected even if the local oscillator light changes in a random polarization state, and ensuring the normal operation of the coherent optical receiver.

Embodiments of the present application will be described in further detail below with reference to the more accompanying drawings based on the above described common aspects related to coherent optical receivers. It should be noted that, unless otherwise specified, the specific description of some technical features in one embodiment may also be applied to explain that other embodiments refer to the corresponding technical features. For example, the description of a specific structure of a photodetector in one embodiment may be applicable to corresponding photodetectors in other embodiments. As another example, the specific implementation of the polarization rotating phase shifter in one embodiment may be applied to the polarization rotating phase shifter in other embodiments. Further, to clearly illustrate the relationship of components in different embodiments, the present application uses the same or similar reference numbers to identify functionally the same or similar components in different embodiments. It should be noted that, in the description of the embodiment of the apparatus in the present application, the description from the optical flow direction is for more clearly describing the technical solution, and the limitation of the apparatus itself is not understood.

Fig. 3 is a schematic structural diagram of a possible coherent optical receiver according to an embodiment of the present disclosure. The coherent optical receiver 400 includes two BSs (301 and 405), a polarization rotating phase shifter 303, two mixers (304 and 305), four balanced detectors (404a, 404b, 404c, and 404d), antireflection films (403a and 403b), and a plurality of waveguides (not numbered in the figure). Note that the BS 405 and the polarization rotating phase shifter 303 are spatial optical components (reference numeral 402); BS 301,

mixers

304 and 305 are silicon optical components (reference numeral 401). The lines with arrows in fig. 3 and other subsequent figures indicate the flow direction of light. Specifically, the light may be signal light, local oscillator light, or light output after being mixed.

The BS 301 in the silicon optical module 401 and the input and output ends of the two mixers are connected to waveguides, and the two devices are connected through waveguides. Unless otherwise specified, the waveguides in silicon optical package 401 are generally multi-polarization waveguides. The silicon optical subassembly 401 may be made of one or more materials such as silicon, germanium, silicon dioxide, silicon nitride, III-V, etc. Optionally, the silicon optical assembly 401 includes polished or plated optical antireflection films disposed on both sides of the silicon optical assembly 401. Such as 403a and 403b shown in fig. 3. The anti-reflection film can improve the light transmittance, so that the performance of the coherent light receiver is improved. The BS 301 may specifically be a 1 x 2 coupler. The 1 x 2 coupler may in particular be an evanescent wave coupler or an MMI splitter.

In this embodiment, the number of output ports of the mixer is 4. The mixed light output from a pair of output ports of each mixer is input to a balanced detector. A balanced detector is one type of photodetector. The photoelectric conversion device comprises two input ports and an output port, photoelectric conversion and differential processing can be carried out on two input lights, and an electric signal is output. In fig. 2, a total of four electrical signals are output from the 4 balanced detectors for further signal processing. It should be noted that the 4 balanced detectors in fig. 2 may also be replaced by 8 Photo Detectors (PDs) and 4 differential circuits. Specifically, each balanced detector is replaced with 2 PDs and one differential circuit. Wherein the inputs of the two PDs receive the two output lights of one mixer, respectively; the outputs of the two PDs are connected to two input ports of the differential circuit, respectively. The differential circuit performs differential processing on the electric signals output by the two PDs and outputs one electric signal. Alternatively, the 4 balanced detectors in fig. 2 may be replaced by a detector array to perform photoelectric conversion to obtain a set of electrical signals.

By power splitting, the BS 405 splits the local oscillator light into two local oscillator lights, wherein one of the two local oscillator lights is input into a waveguide connected to one input end of the mixer 304; the other beam is input to a polarization rotating phase shifter 303. There are various implementations of the polarization rotating phase shifter 303. This is further described below in conjunction with fig. 4a and 4 b.

Fig. 4a is a schematic diagram of a possible structure of the polarization rotating phase shifter shown in fig. 3. Polarization rotating phase shifter 800 includes two Polarization Beam Splitters (PBSs) (801 and 802), two half-wave plates (802 and 803), two mirrors (804 and 805), phase shifter 806, and lens 808. The PBS801 is configured to split input light into polarization components, and output two lights have orthogonal polarization states. The PBS 807 is used to combine the two input beams and output them. PBS 807 may also be referred to as PBC, i.e., to achieve polarization combining. Two half-wave plates are used to achieve 90 degree polarization state rotation of the light. Phase shifter 806 is used to achieve a 180 degree phase shift of the light. The lens 808 is used for focusing, and can improve the light transmission performance. It should be noted that the lens 808 is an optional device. Alternatively, another lens may be placed before the PBS801 to focus the local oscillator light input to the polarization rotating phase shifter before subsequent processing. It should be noted that the half-wave plate may be replaced by two quarter-wave plates.

The following describes the processing of the input local oscillator light by the polarization rotating phase shifter 800 with reference to specific components. Specifically, the local oscillation light is polarized and split by the PBS801 and then split into local oscillation light a and local oscillation light B. Then, the local oscillation light a is subjected to polarization rotation, reflection, and phase shift processing in order via the half-wave plate 802, the mirror 805, and the phase shifter 806, and then local oscillation light C is generated. The local oscillation light B is processed by a half-wave plate 803 and a reflecting mirror 804 in sequence to generate local oscillation light D. Finally, the local oscillation light C and the local oscillation light D are polarized and combined by the PBS 807 and focused by the lens 808, and then local oscillation light E is generated. The local oscillator light E is input to a waveguide connected to the other input of the mixer 305.

Fig. 4b is a schematic diagram of another possible structure of the polarization rotating phase shifter shown in fig. 3. Polarization rotating phase shifter 900 includes the same components as polarization rotating phase shifter 800 of FIG. 4 a. The main difference is that half-wave plate 901 of polarization rotating phase shifter 900 is located between mirror 805 and phase shifter 806; and a half-wave plate 802 corresponding to polarization rotating phase shifter 800 is located between PBS801 and mirror 805. The local oscillator light processing input to the polarization rotating phase shifter 900 is similar to that described in fig. 4a, and is not repeated here. The only difference is that the PBS801 outputs one of the light with its polarization state rotated after reflection by the mirror.

In general, the order of processing for the polarization rotation, reflection, and phase shifter of the local oscillator light may be switched in one optical processing branch between the two PBSs (i.e., PBSs 801 and 807). Similarly, the order of processing for the polarization rotation and reflection of the local oscillator light on the other optical processing branch may also be reversed. Accordingly, the relative position of the devices can be correspondingly adjusted. Fig. 4a and 4b only give two examples of these. This is not to be taken in any way limiting by the present application.

The mirrors of fig. 4a and 4b may be reflective flat mirrors or mirror mirrors.

By using the coherent optical receiver shown in fig. 3 or any one of the specific manners shown in fig. 3, the polarization state orthogonality of the local oscillator light input to the two mixers can be achieved by processing the local oscillator light, so that the coherent optical receiver can be ensured to achieve normal operation independent of the polarization state. In addition, the efficiency of realizing polarization rotation phase shift of light by adopting the spatial optical component is higher. Therefore, the local oscillator light is processed and mixed by the space optical component and the silicon optical component, so that the optical processing efficiency can be improved, namely the performance of the coherent optical receiver is improved.

Fig. 5 is a schematic structural diagram of another possible coherent optical receiver according to an embodiment of the present application. The coherent optical receiver 500 includes two BSs (301 and 302), a polarization rotating phase shifter 303, two mixers (304 and 305), four balanced detectors (404a, 404b, 404c and 404d), antireflection films (403a and 403b), four retarders (501 and 504), and a plurality of waveguides (not shown in the figure). The descriptions of the introduction and alternatives of other components, other than the delayers, can be found in the description of fig. 2-4b and will not be repeated here.

The coherent optical receiver 500 differs from the coherent optical receiver 400 shown in fig. 3 in that a delay is provided on 4 waveguides in the silicon optical module to which the input ends of the mixers are connected. Specifically, the temperature of the waveguide can be changed by arranging the thermal tuning electrode on the corresponding waveguide and controlling the current or voltage of the thermal tuning electrode, so that the delay control of the light passing through the waveguide corresponding to the thermal tuning electrode is realized. The advantage of adding a delay is that the phases of the light entering the mixer can be controlled more accurately so that they are in phase with each other when entering the mixer, thereby improving the efficiency of subsequent signal processing.

It should be noted that the coherent optical receiver 500 including 4 time delays is only a specific example. In a specific implementation, any two or any three of the 4 waveguides shown in fig. 5 can be selected to set the retarders, so as to achieve the purpose of controlling the phase. For example, only 502 and 503 may be provided, and delay control is realized by fewer delay units, thereby saving cost. As another example, 502-504 may be provided. The present application is not limited in this respect.

The coherent optical receiver structure shown in fig. 5 can ensure that coherent optical receiving processing is not affected by random variation of local oscillator light, and has performance guarantee. In addition, the light receiving and processing efficiency is improved by arranging the delayer.

Fig. 6 is a schematic structural diagram of another possible coherent optical receiver according to an embodiment of the present application. The coherent optical receiver 600 includes two BSs (301 and 405), a Polarization rotating phase shifter 303, two mixers (304 and 305), four balanced detectors (404a, 404b, 404c and 404d), two PBSs (601 and 602), two Polarization Beam Combiners (PBCs) (603 and 604), and 4 single Polarization waveguides (dashed lines, not numbered, within the waveguide assembly 401' in fig. 6) and a plurality of waveguides (not numbered in the figure). Descriptions of the introduction and alternatives of other components, in addition to the two PBSs (601 and 602), the two PBCs (603 and 604), and the 4 single polarization waveguides, may be found in the descriptions of fig. 2-4b and will not be repeated here. It should be noted that the silicon optical module 401' in this embodiment does not include an antireflection film. It should be noted that the PBC is also a PBS in nature, and only the number and direction of the light inputs and outputs are different. Specifically, the PBS inputs one light and outputs two lights with two orthogonal polarization states; and PBC is to input two lights to be combined and output as one light.

The coherent optical receiver 600 differs from the coherent optical receiver 400 shown in fig. 3 in that the two waveguides (multi-polarization) where there is a crossover at the two mixer inputs in the silicon optical package 401' are replaced by a PBS, two single polarization waveguides, and a PBC structure, respectively. The other two waveguides at the two mixer inputs do not cross any other waveguides. In particular, the other two waveguides can be designed as straight waveguides. For simplicity of description, the structure consisting of one PBS, two single polarization waveguides, and one PBC is simply referred to as a transmission unit. It will be appreciated that this embodiment differs from the embodiment shown in fig. 3 in that both crossed waveguides of the silicon optical component 401' in fig. 3 are replaced by a transmission unit structure.

The processing procedure of the transmission unit for light is described by taking the signal light output by BS 301 as an example. The signal light a output from BS 301 is input to PBS 601, and is divided into signal light B and signal light C having orthogonal polarization states. The two signal lights are respectively transmitted through single polarization waveguides and then input into the PBC 604. The signal lights B and C are combined into a signal light D, which is input to the mixer 305. The processing procedures for the local oscillation light are similar and are not described in detail.

It should be noted that only one of the crossed waveguides may be replaced. That is, only one of the waveguides is replaced with the structure of the transmission unit. This also improves the performance of the coherent optical receiver to some extent relative to the coherent optical receiver 400 shown in fig. 3.

Optionally, similar to the embodiment shown in fig. 5, in this embodiment, a time delay device may also be introduced to the waveguide of the waveguide assembly 401', so as to implement accurate phase control on the light input into the mixer, and improve the performance of the coherent optical receiver.

Coherent optical receiver 600 has the advantages associated with the coherent optical receiver shown in fig. 3. In addition, compared with the coherent optical receiver 400 shown in fig. 3, the coherent optical receiver 600 provided in this embodiment reduces crosstalk and loss caused by bending and crossing of the dual-mode waveguide through an alternative crossed waveguide design, and improves the optical processing efficiency of the coherent optical receiver.

Fig. 7 is a schematic structural diagram of a fourth possible coherent optical receiver according to an embodiment of the present application. The coherent optical receiver 700 includes two BSs (301 and 405), a polarization rotating phase shifter 303, two mixers (304 and 305), four balanced detectors (404a, 404b, 404c, and 404d), a mirror 701, and a lens 702 and a plurality of waveguides (not numbered in the figure). The descriptions of the introduction and alternatives of other components, other than the mirror 701 and the lens 702, can be found in the descriptions of fig. 2-4b and will not be repeated here.

The coherent optical receiver 600 differs from the coherent optical receiver 400 shown in fig. 3 in that the spatial optical component 402' further comprises a mirror 701 and a lens 702. One beam of local oscillation light output by the PBS 405 is reflected by the mirror 701, focused by the lens, and then input to the mixer 305. That is, before the mixer 305 performs the mixing process on the beam of local oscillation light, the local oscillation light also needs to undergo mirror reflection and/or lens focusing process.

In this embodiment, the polarization rotating phase shifter 303 may be designed according to the variations described in fig. 4a or 4b or related to these figures. Alternatively, the polarization rotating phase shifter 303 can also be designed in accordance with the third approach provided in fig. 8.

Fig. 8 is a schematic structural diagram of a third possible polarization rotating phase shifter according to an embodiment of the present application. As shown in fig. 8, polarization rotating phase shifter 1000 includes two PBSs (801 and 802), two half-wave plates (802 and 803), two mirrors (803 and 701), and phase shifter 1001. The reflecting mirror 701 is a reflecting mirror in the space optical module 402' shown in fig. 7. That is, the mirror is used to reflect two light paths. The design can reduce the number of the reflecting mirrors and the size of the polarization rotation phase shifter.

The processing of the input local oscillator light by the polarization rotating phase shifter 1000 is basically the same as the structure shown in fig. 4a, and is not described herein again. The main difference is that between PBS801 and PBS 807, the light is processed by 180 degree phase shift, polarization rotation and reflection in sequence. It should be noted that, similar to fig. 4a and b, the order of light processing between the PBS801 and the PBS 802 may be designed. Namely, the corresponding spatial relative positions of the devices are specifically designed according to actual needs.

The coherent optical receiver 700 of the present embodiment has the same technical advantages as the coherent optical receiver shown in fig. 3. Furthermore, the coherent optical receiver 700 presented in this embodiment may reduce the size of the spatial optical components by alternative polarization rotating phase shifter designs.

Fig. 9 is a schematic structural diagram of a fifth possible coherent optical receiver according to an embodiment of the present application. The coherent optical receiver 1100 includes two BSs (1101 and 302), mirrors 1105, a lens 1104, a polarization rotation phase shifter 303, two mixers (304 and 305) and four balanced detectors (404a, 404b, 404c, and 404d), antireflection films (403a and 403b), and a plurality of waveguides (not numbered in the figure). It should be noted that the

BSs

1101 and 302, and the polarization rotating phase shifter 303 are spatial optical components (reference numeral 1102). The

mixers

304 and 305 are silicon optical components (reference number 1103). The lines with arrows in fig. 9 indicate the flow direction of light. Specifically, the light may be signal light, local oscillator light, or light output after being mixed. The descriptions of the introduction and alternatives of other components, other than the mirror 1105 and the lens 1104, can be found in the descriptions of fig. 2-8 and will not be repeated here.

The coherent optical receiver 1100 differs from the coherent optical receiver 400 shown in fig. 3 in that the optical splitter BS1101 for signal light is also a spatial optical device. Specifically, the BS1101 performs power splitting on input signal light, one of which is focused by a lens 1104 and then input to the mixer 304 through a waveguide; the other beam is reflected by the mirror 1105 and then input to the mixer 305 through the waveguide. It should be noted that the lens 1104 is optional. That is, the signal light may need to be subjected to mirror reflection and/or lens transmission processing before the mixer mixes the corresponding signal light. Further, optionally, a lens may be placed before the BS1101 to realize focusing of the signal light input to the coherent optical receiver.

Optionally, similar to the embodiment shown in fig. 5, in this embodiment, a time delay device may also be introduced to the waveguide of the waveguide assembly 1103, so as to implement accurate phase control on the light input into the mixer, and improve the performance of the coherent optical receiver.

It should be noted that, in the present embodiment, the waveguide is an optional component. That is, the local oscillator light or the signal light output from the spatial optical component may be directly input into the input port of the mixer by a proper design. Similarly, the mixed light output from the output end of the mixer can be directly output to the balanced detector without adding additional waveguide. The advantage of adding waveguides is that the transmission efficiency of light can be improved. Alternatively, the crossed waveguides connecting the mixers may be replaced by a design as in fig. 6. The present application is not limited thereto.

By using the coherent optical receiver shown in fig. 9 or any one of the specific manners shown in fig. 9, the local oscillator light input to the two mixers can be processed to realize polarization state orthogonality, so that the coherent optical receiver can realize normal operation independent of the polarization state. In addition, the spatial optical component and the silicon optical component are used for respectively realizing the processing and the frequency mixing of the signal light and the local oscillator light, so that the optical processing efficiency can be improved, namely the performance of the coherent optical receiver is improved.

Fig. 10 is a flowchart illustrating a method for coherent light reception according to an embodiment of the present application. Specifically, the method comprises the following steps:

step 1201, dividing a signal light input into a coherent light receiver to output a first signal light and a second signal light, and dividing a local oscillation light input into the coherent light receiver to output a first local oscillation light and a second local oscillation light;

specifically, the device for splitting the signal light or the local oscillator light input to the coherent optical receiver may be a spatial optical splitter or a splitter made of other materials, such as: a silicon optical device.

Step 1203: performing 90-degree polarization state rotation and 180-degree phase shift on the second local oscillation light to obtain third local oscillation light;

specifically, the third local oscillator light may be obtained by polarization rotation and phase shift processing of the device shown in fig. 4a, 4b, or 8. For example, performing 90-degree polarization rotation and 180-degree phase shift on the second local oscillator light to obtain a third local oscillator light specifically includes: carrying out polarization beam splitting on the second local oscillator light to obtain two beams of local oscillator light; performing 90-degree polarization state rotation, 180-degree phase shift and reflection on one beam to obtain fourth local oscillation light; rotating and reflecting the other beam in a polarization state of 90 degrees to obtain fifth local oscillation light; and after the fourth local oscillation light and the fifth local oscillation light are subjected to polarization combination, the third local oscillation light is obtained.

As another example, optionally, before performing 90-degree polarization rotation and 180-degree phase shift on the second local oscillator light, the second local oscillator light is further reflected and/or focused. Other specific processing steps are described in the related figures, and are not described in detail herein.

Step 1205: performing frequency mixing processing on the first signal light and the first local oscillator light to obtain first frequency mixing light, and performing frequency mixing processing on the second optical signal and the third local oscillator light to obtain second frequency mixing light;

in particular, the mixing process may be implemented by the apparatus of fig. 3, 5, 6 or 9 or by alternatives mentioned for the aforementioned apparatus embodiments. For example, prior to mixing, it may be necessary to pass through lenses, mirrors, PBS, PBC, and/or different types of waveguide processing (e.g., focusing, reflecting, transmitting, etc.), and the like. This is not limited in this application. For a detailed description of the implementation and related processing, reference may be made to related apparatus embodiments, which are not described herein in detail.

Step 1207: and performing photoelectric conversion on the first mixed light and the second mixed light to output electric signals.

Specifically, the photoelectric conversion may be realized by the device mentioned in fig. 3 or the aforementioned apparatus embodiment. For a detailed description of the implementation and related processing, reference may be made to related apparatus embodiments, which are not described herein in detail.

By the processing in the above method, the local oscillator light can be processed into two polarized lights with orthogonal polarization states, and then the frequency mixing processing is performed. The method can be applied to a coherent light receiver or a device or a system of the coherent light receiver, ensures that the performance of the coherent light receiver is not influenced by the random change of the polarization state of local oscillator light, and always ensures the normal working state.

The embodiment of the present application further provides a receiving side device, where the receiving side device includes the coherent optical receiver according to any of the foregoing apparatus embodiments. Specifically, the receiving-side device may further include other components such as a DSP, a Trans-Impedance Amplifier (TIA), an Analog-to-Digital Converter (ADC), and the like, for further processing the electrical signal output by the coherent optical receiver.

The embodiment of the present application further provides a coherent optical transmission system, which includes a sending-side device and a receiving-side device including the coherent optical receiver according to any of the foregoing apparatus embodiments. Specifically, the laser generating the local oscillation light may be in the transmitting-side device or in the receiving-side device.

Finally, it should be noted that: the above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A coherent optical receiver comprising a first optical beam splitter BS, a second BS, a polarization rotating phase shifter, a first mixer, a second mixer, and a photodetector, wherein:

the first BS is configured to split the signal light input to the coherent optical receiver and output a first signal light and a second signal light;

the second BS is configured to split the local oscillation light input to the coherent light receiver and output a first local oscillation light and a second local oscillation light;

the polarization rotation phase shifter is configured to perform 90-degree polarization state rotation and 180-degree phase shift on the second local oscillator light, and output a third local oscillator light, where the first local oscillator light and the third local oscillator light are orthogonal in polarization state before entering the first mixer and the second mixer;

the first frequency mixer is configured to mix the first signal light and the first local oscillator light, and output first mixed light;

the second mixer is configured to mix the second signal light and the third local oscillator light, and output second mixed light;

the photodetector is configured to perform photoelectric conversion on the first mixed light and the second mixed light to generate an electrical signal.

2. The coherent optical receiver of claim 1, wherein the second BS and the polarization rotating phase shifter are spatial optical components and the first BS, the first mixer, and the second mixer are silicon optical components.

3. The coherent optical receiver of claim 1, wherein the first BS, the second BS, and the polarization rotating phase shifter are spatial optical components, and the first mixer and the second mixer are silicon optical components; the coherent optical receiver further includes a first reflecting mirror, and the first reflecting mirror reflects the first signal light before the first mixer mixes the first signal light and the first local oscillation light.

4. The coherent optical receiver according to claim 2 or 3, further comprising a first waveguide, a second waveguide, a third waveguide, and a fourth waveguide, the first waveguide to the fourth waveguide each being a multi-polarization waveguide; the first mixer mixes the first signal light and the first local oscillator light, and the second mixer mixes the second signal light and the third local oscillator light, which specifically includes:

the first mixer mixes the first signal light and the first local oscillator light after receiving the first signal light and the first local oscillator light through the first waveguide and the third waveguide, respectively;

the second mixer mixes the second signal light and the third local oscillator light after receiving the second signal light and the third local oscillator light through the second waveguide and the fourth waveguide, respectively.

5. The coherent optical receiver according to claim 4, wherein any at least two of the first waveguide to the fourth waveguide are provided with a thermo-modulation electrode for delay control of light passing through the waveguide corresponding to the thermo-modulation electrode.

6. The coherent optical receiver according to any one of claims 2 or 3, further comprising a first waveguide, a second waveguide, a first transmission unit and a second transmission unit, wherein the first transmission unit and the second transmission unit respectively comprise a third waveguide, a fourth waveguide, a first polarization beam splitter PBS, a polarization beam combiner PBC, a first single polarization waveguide and a second single polarization waveguide, wherein the first waveguide to the fourth waveguide are all multi-polarization waveguides, the third waveguide is connected to an input port of the first PBS, two output ports of the first PBS are respectively connected to one end of the first single polarization waveguide and one end of the second single polarization waveguide, the other end of the first single polarization waveguide and the other end of the second single polarization waveguide are respectively connected to an input port of the PBC, the output port of the PBC is connected with the fourth waveguide, and the third waveguide and the fourth waveguide are respectively an optical input waveguide and an optical output waveguide; the first mixer mixes the first signal light and the first local oscillator light, and the second mixer mixes the second signal light and the third local oscillator light, which specifically includes:

the first frequency mixer receives the first signal light and the first local oscillator light through the first waveguide and the first transmission unit, and then mixes the first signal light and the first local oscillator light;

the second mixer mixes the second signal light and the third local oscillator light after receiving the second signal light and the third local oscillator light through the second transmission unit and the second waveguide, respectively;

the first waveguide and the second waveguide do not intersect.

7. The coherent optical receiver of any of claims 2-3, further comprising a second mirror; before the first mixer mixes the first signal light and the first local oscillator light, the second reflector reflects the first local oscillator light.

8. The coherent optical receiver of any of claims 2-3, further comprising a first lens; before the first mixer mixes the first signal light and the first local oscillator light, the first lens focuses the first local oscillator light.

9. The coherent optical receiver of any of claims 2-3, wherein the polarization rotating phase shifter comprises a second Polarization Beam Splitter (PBS), a third PBS, a third mirror, a fourth mirror, a first half wave plate, a second half wave plate, and a 180 degree phase shifter; the polarization rotating phase shifter performs 90-degree polarization rotation and 180-degree phase shift on the second local oscillation light, and outputs third local oscillation light, which specifically includes:

after the second PBS performs polarization beam splitting on the second local oscillation light, outputting seventh local oscillation light and eighth local oscillation light;

the first half wave plate, the 180-degree phase shifter and the third reflector process the seventh local oscillator light and output ninth local oscillator light, and the second half wave plate and the fourth reflector process the eighth local oscillator light and output tenth local oscillator light, wherein the first half wave plate and the second half wave plate respectively perform 90-degree polarization rotation on the seventh local oscillator light and the eighth local oscillator light;

and after the ninth local oscillator light and the tenth local oscillator light are subjected to polarization combination by the third PBS, third polarized light is output.

10. The coherent optical receiver of claim 9, wherein the third mirror and the fourth mirror are reflective flat mirrors or mirror bodies.

11. The coherent optical receiver according to claim 9, wherein the processing of the seventh local oscillator light by the first half-wave plate, the 180-degree phase shifter, and the third mirror specifically includes:

the first half wave plate, the 180-degree phase shifter and the third reflector sequentially process the seventh local oscillation light; or, the first half wave plate, the third reflector and the 180-degree phase shifter sequentially process the seventh local oscillator light; or, the 180-degree phase shifter, the first half-wave plate, and the third mirror sequentially process the seventh local oscillation light.

12. The coherent optical receiver of claim 9, wherein the polarization rotating phase shifter further comprises a second lens; after the third PBS polarizes and combines the ninth local oscillator light and the tenth local oscillator light, the third PBS outputs the third polarized light, which specifically includes:

after the ninth local oscillator light and the tenth local oscillator light are combined in a polarization mode by the third PBS, eleventh local oscillator light is output;

the second lens focuses the eleventh local oscillation light and outputs the third polarized light.

13. The coherent optical receiver of claim 7, wherein the polarization rotating phase shifter comprises a second Polarization Beam Splitter (PBS), a third PBS, the second mirror, a third mirror, a first half-wave plate, a second half-wave plate, and a 180 degree phase shifter; the polarization rotating phase shifter performs 90-degree polarization rotation and 180-degree phase shift on the second local oscillation light, and outputs third local oscillation light, which specifically includes:

the first half-wave plate, the 180-degree phase shifter and the third reflector process the seventh local oscillator light and output ninth local oscillator light, and the second half-wave plate and the second reflector process the eighth local oscillator light and output tenth local oscillator light, wherein the first half-wave plate and the second half-wave plate respectively rotate the seventh local oscillator light and the eighth local oscillator light by 90-degree polarization states;

and after the ninth local oscillator light and the tenth local oscillator light are subjected to polarization combination by the third PBS, third polarized light is generated.

14. The coherent optical receiver of claim 13, wherein the second mirror and the third mirror are mirror mirrors or bulk mirrors.

15. The coherent optical receiver according to claim 13 or 14, wherein the processing of the seventh local oscillator light by the first half wave plate, the 180-degree phase shifter and the third mirror specifically includes:

16. The coherent optical receiver of claim 13, wherein the polarization rotating phase shifter further comprises a second lens; after the third PBS polarizes and combines the ninth local oscillator light and the tenth local oscillator light, the third PBS outputs the third polarized light, which specifically includes:

17. A method of coherent light processing, the method comprising:

carrying out power beam splitting on signal light input into a coherent light receiver to obtain first signal light and second signal light, and carrying out power beam splitting on local oscillator light input into the coherent light receiver to obtain first local oscillator light and second local oscillator light;

performing 90-degree polarization rotation and 180-degree phase shift on the second local oscillator light to obtain third local oscillator light, wherein the first local oscillator light and the third local oscillator light are orthogonal in polarization state before frequency mixing processing;

performing frequency mixing processing on the first signal light and the first local oscillator light to obtain first frequency mixing light, and performing frequency mixing processing on the second signal light and the third local oscillator light to obtain second frequency mixing light;

and performing photoelectric conversion on the first mixed light and the second mixed light to obtain an electric signal.

18. The method according to claim 17, wherein the performing a 90-degree polarization rotation and a 180-degree phase shift on the second local oscillator light to obtain a third local oscillator light specifically includes:

carrying out polarization beam splitting on the second local oscillation light to obtain seventh local oscillation light and eighth local oscillation light;

performing 90-degree polarization state rotation, 180-degree phase shift and reflection on the seventh local oscillation light to obtain ninth local oscillation light;

rotating and reflecting the eighth local oscillator light in a polarization state of 90 degrees to obtain tenth local oscillator light;

and after the ninth local oscillator light and the tenth local oscillator light are subjected to polarization combination, the third local oscillator light is obtained.

19. The method of claim 17 or 18, wherein the second local oscillator light is also reflected prior to 90 degree polarization rotation and 180 degree phase shift of the second local oscillator light.

20. The method of claim 17, wherein the first signal light is reflected before the mixing process is performed on the first signal light and the first local oscillator light.