Optical transmission method and device

Abstract

The present application provides an optical transmission method and device for reducing or eliminating phase noise, and relates to the field of communication. A first optical transmission device includes a first circulator and a first receiving module. The first receiving module is coupled to the first circulator. The first circulator is configured to receive a second unmodulated optical signal from a second optical transmission device. The first receiving module is configured to receive a second modulated optical signal from the second optical transmission device and receive the second unmodulated optical signal from the first circulator. The second modulated optical signal is obtained by modulating the first unmodulated optical signal, the second unmodulated optical signal is used to coherence detect the second modulated optical signal, the first unmodulated optical signal and the second unmodulated optical signal are obtained by separating a third unmodulated optical signal, and the third unmodulated optical signal is an optical signal provided from the first optical transmission device to the second optical transmission device.

Description

[Technical field]

[0001] [Related Applications] This application claims priority to Chinese Patent Application No. 202111651329.0, filed with the State Intellectual Property Office of China on December 30, 2021, entitled "OPTICAL TRANSMISSION METHOD AND APPARATUS," which is incorporated herein by reference in its entirety. [Technical field] TECHNICAL FIELD Embodiments of the present application relate to the field of communications, and in particular to an optical transmission method and apparatus. [Background technology]

[0002] In the communication system, a first optical transmission device supplies a third unmodulated optical signal to a second optical transmission device, and the second optical transmission device performs modulation based on the third unmodulated optical signal to obtain a second modulated optical signal. Then, the first optical transmission device receives the second modulated optical signal from the second optical transmission device and performs coherence detection of the second modulated optical signal using local oscillator light. The local oscillator light and the third unmodulated optical signal are obtained by separating the same optical signal on the first optical transmission device side.

[0003] However, the above communication system has a large phase noise. Summary of the Invention

[0004] The present application provides an optical transmission method and apparatus that reduces or eliminates phase noise.

[0005] In order to achieve the aforementioned objectives, the following technical solutions are used in the embodiments of the present application.

[0006] According to a first aspect, an embodiment of the present application provides a first optical transmission device. The device includes a first circulator and a first receiving module. The first receiving module is coupled to the first circulator. The first circulator is configured to receive a second unmodulated optical signal from a second optical transmission device. The first receiving module is configured to receive a second modulated optical signal from the second optical transmission device and receive the second unmodulated optical signal from the first circulator. The second modulated optical signal is obtained by modulating the first unmodulated optical signal, the second unmodulated optical signal is used to coherence detect the second modulated optical signal, the first unmodulated optical signal and the second unmodulated optical signal are obtained by separating a third unmodulated optical signal, and the third unmodulated optical signal is an optical signal provided from the first optical transmission device to the second optical transmission device.

[0007] As a result, the transmission paths of the second modulated optical signal and the second unmodulated optical signal are the same or close to each other. The second modulated optical signal is obtained by modulating the first unmodulated optical signal, and the first unmodulated optical signal and the second unmodulated optical signal are obtained by separating the same optical signal provided by the first optical transmission device, i.e., the third unmodulated optical signal. Furthermore, the transmission paths of the second modulated optical signal and the second unmodulated optical signal are the same or close to each other. Therefore, the two signals have no frequency difference and belong to coherent light. This reduces or eliminates phase noise.

[0008] In a possible design, the first circulator is further coupled to a second circulator. The second optical transmission device includes the second circulator. The first circulator configured to receive the second unmodulated optical signal from the second optical transmission device includes receiving the second unmodulated optical signal from the second circulator and receiving the second unmodulated optical signal.

[0009] In a possible design, the first optical transmission device in the embodiment of the present application further includes a first polarization control module, the first polarization control module is coupled to the first circulator, and the first polarization control module is configured to control the polarization of the second unmodulated optical signal.

[0010] During the transmission process of the second unmodulated optical signal, the polarization state of the second unmodulated optical signal will rotate randomly, which will cause poor coherence detection. The first polarization control module can convert the polarization state of the second unmodulated optical signal into the expected polarization state, thereby realizing normal coherence detection.

[0011] In a possible design, performing coherence detection on the second modulated optical signal using the second unmodulated optical signal includes performing coherence detection on the second modulated optical signal using the second unmodulated optical signal having polarization control.

[0012] In this way, the local oscillator light used for coherence detection is the second unmodulated optical signal that has been subjected to polarization control. The second unmodulated optical signal has high energy in the expected polarization state, so that the effect of random polarization state changes can be eliminated or reduced. Therefore, the accuracy of coherence detection can be improved.

[0013] In a possible design, the first polarization control module is further configured to control the polarization of a first modulated optical signal, the first modulated optical signal being an optical signal transmitted by the first optical transmission device to the second optical transmission device.

[0014] In this way, when the second optical transmission device performs polarization control on the third unmodulated optical signal, the local oscillator light used by the second optical transmission device for coherence detection and the first modulated optical signal are in the same polarization state. After coherence detection, an electrical signal may be obtained without performing polarization separation processing, and target information may be obtained based on the electrical signal. This makes it possible to reduce system power consumption without having to design a separate chip that performs polarization separation, thereby reducing system costs.

[0015] In a possible design, the first optical transmission device in the embodiment of the present application further includes a first transmission module, which is coupled to the first circulator and configured to transmit the first modulated optical signal to the first polarization control module through the first circulator, and the first optical transmission device can provide the first modulated optical signal to the second optical transmission device.

[0016] In a possible design, the first optical transmission device is an optical transmission device on the active antenna unit AAU side, and the second optical transmission device is an optical transmission device on the baseband unit BBU side. Alternatively, the first optical transmission device is an optical transmission device on the BBU side, and the second optical transmission device is an optical transmission device on the AAU side.

[0017] According to a second aspect, an embodiment of the present application provides a second optical transmission device. The device includes a second coupler, a second transmission module, and a second circulator. The second transmission module is coupled to both the second coupler and the second circulator. The second coupler is configured to split the third unmodulated optical signal into at least a first unmodulated optical signal and a second unmodulated optical signal. The third unmodulated optical signal is an optical signal provided by the first optical transmission device. The second transmission module is configured to transmit a second modulated optical signal to the first optical transmission device. The second modulated optical signal is obtained by modulating the first unmodulated optical signal. The second circulator is configured to receive the second unmodulated optical signal from the second coupler and transmit the second unmodulated optical signal to the first optical transmission device. The second unmodulated optical signal is used for coherence detection of the second modulated optical signal.

[0018] In a possible design, the second circulator is further coupled to the first circulator. The first optical transmission device includes the first circulator. Configuring the second circulator to transmit the second unmodulated optical signal to the first optical transmission device includes transmitting the second unmodulated optical signal to the first circulator and transmitting the second unmodulated optical signal.

[0019] In a possible design, the second optical transmission device in the embodiment of the present application further includes a second polarization control module, which is coupled to the second coupler and configured to control the polarization of the third unmodulated optical signal.

[0020] In the transmission process of the third unmodulated optical signal, the polarization state of the third unmodulated optical signal will rotate randomly, which will cause poor coherence detection. The second polarization control module can convert the polarization state of the third unmodulated optical signal into the expected polarization state, so as to realize normal coherence detection.

[0021] In a possible design, the second coupler splitting the third unmodulated optical signal into at least the first unmodulated optical signal and the second unmodulated optical signal includes splitting the polarization-controlled third unmodulated optical signal into at least the first unmodulated optical signal and the second unmodulated optical signal.

[0022] In other words, the first unmodulated optical signal and the second unmodulated optical signal are also optical signals that have been subjected to polarization control.

[0023] In a possible design, the second coupler is further configured to split the polarization-controlled third unmodulated optical signal into a fifth unmodulated optical signal, the fifth unmodulated optical signal being used for coherence detection of the first modulated optical signal, the first modulated optical signal being the optical signal transmitted by the first optical transmission device to the second optical transmission device.

[0024] In this way, the local oscillator light used for coherence detection is the fifth unmodulated optical signal that has been subjected to polarization control. The fifth unmodulated optical signal has high energy in the expected polarization state, so that the effect of random polarization state changes can be eliminated or reduced. Therefore, the accuracy of coherence detection can be improved.

[0025] In a possible design, the second optical transmission device in the embodiment of the present application further includes a second receiving module, which is coupled to both the second circulator and the second coupler, and is configured to receive the first modulated optical signal from the first optical transmission device via the second circulator and receive the fifth unmodulated optical signal from the second coupler, and realize coherence detection of the first modulated optical signal.

[0026] In a possible design, a second polarization control module is coupled to the second transmission module and configured to control the polarization of the third modulated optical signal.

[0027] In this way, when the first optical transmission device performs polarization control on the second unmodulated optical signal, the local oscillator light (i.e., the second unmodulated optical signal) used by the first optical transmission device for coherence detection and the second modulated optical signal are in the same polarization state. After coherence detection, an electrical signal may be obtained without performing polarization separation processing, and target information may be obtained based on the electrical signal. This makes it possible to reduce system power consumption without having to design a separate chip for polarization separation, thereby reducing system costs.

[0028] In a possible design, the second optical transmission device in the embodiment of the present application further includes a third circulator. The second polarization control module is coupled to the second coupler includes the second polarization control module is coupled to the second coupler via the third circulator to realize the unidirectional transmission of the third unmodulated optical signal. The second polarization control module is further coupled to the second transmission module includes the second polarization control module is further coupled to the second transmission module via the third circulator to realize the unidirectional transmission of the second modulated optical signal.

[0029] In a possible design, the first optical transmission device is an optical transmission device on the active antenna unit AAU side, and the second optical transmission device is an optical transmission device on the baseband unit BBU side. Alternatively, the first optical transmission device is an optical transmission device on the BBU side, and the second optical transmission device is an optical transmission device on the AAU side.

[0030] According to a third aspect, an embodiment of the present application provides an optical transmission method, the method being applied to a first optical transmission device. The device includes a first circulator and a first receiving module. The first circulator is coupled to the first receiving module. The method includes: the first circulator receives a second unmodulated optical signal from a second optical transmission device, the first receiving module receives a second modulated optical signal from the second optical transmission device, and receives the second unmodulated optical signal from the first circulator. The second modulated optical signal is obtained by modulating the first unmodulated optical signal, the second unmodulated optical signal is used to coherence detect the second modulated optical signal, the first unmodulated optical signal and the second unmodulated optical signal are obtained by separating a third unmodulated optical signal, and the third unmodulated optical signal is an optical signal provided from the first optical transmission device to the second optical transmission device.

[0031] In a possible design, the first circulator receiving the second unmodulated optical signal from the second optical transmission device includes the first circulator receiving the second unmodulated optical signal from the second circulator, the first circulator further coupled to the second circulator, the second optical transmission device including the second circulator.

[0032] In a possible design, the optical transmission method in the embodiment of the present application further includes: a first polarization control module controls the polarization of the second unmodulated optical signal; the first optical transmission device further includes a first polarization control module, and the first polarization control module is coupled to the first circulator.

[0033] In a possible design, performing coherence detection on the second modulated optical signal using the second unmodulated optical signal includes performing coherence detection on the second modulated optical signal using the second unmodulated optical signal having polarization control.

[0034] In a possible design, the optical transmission method in the embodiment of the present application further includes: a first polarization control module controls the polarization of a first modulated optical signal, the first modulated optical signal being an optical signal transmitted by the first optical transmission device to the second optical transmission device.

[0035] In a possible design, the optical transmission method in the embodiment of the present application further includes: the first transmission module transmits the first modulated optical signal to the first polarization control module through the first circulator; the first optical transmission device further includes a first transmission module, and the first transmission module is coupled to the first circulator.

[0036] In a possible design, the first optical transmission device is an optical transmission device on the active antenna unit AAU side, and the second optical transmission device is an optical transmission device on the baseband unit BBU side. Alternatively, the first optical transmission device is an optical transmission device on the BBU side, and the second optical transmission device is an optical transmission device on the AAU side.

[0037] According to a fourth aspect, an embodiment of the present application provides an optical transmission method, the method being applied to a second optical transmission device. The device includes a second coupler, a second transmission module, and a second circulator. The method includes: the second coupler splits the third unmodulated optical signal into at least a first unmodulated optical signal and a second unmodulated optical signal. The third unmodulated optical signal is an optical signal provided by the first optical transmission device. The second transmission module transmits a second modulated optical signal to the first optical transmission device. The second modulated optical signal is obtained by modulating the first unmodulated optical signal. The second circulator receives the second unmodulated optical signal from the second coupler and transmits the second unmodulated optical signal to the first optical transmission device. The second unmodulated optical signal is used for coherence detection of the second modulated optical signal.

[0038] In a possible design, the second circulator transmitting the second unmodulated optical signal to the first optical transmission device includes: the second circulator transmitting the second unmodulated optical signal to the first circulator, the second circulator further coupled to the first circulator, and the first optical transmission device including the first circulator.

[0039] In a possible design, the optical transmission method in the embodiment of the present application further includes: a second polarization control module controls the polarization of the third unmodulated optical signal; the second optical transmission device further includes a second polarization control module, and the second polarization control module is coupled to the second circulator.

[0040] In a possible design, the second coupler splitting the third unmodulated optical signal into at least the first unmodulated optical signal and the second unmodulated optical signal includes: the second coupler splits the polarization-controlled third unmodulated optical signal into at least the first unmodulated optical signal and the second unmodulated optical signal.

[0041] In a possible design, the optical transmission method in the embodiment of the present application further includes: a second coupler splits the third unmodulated optical signal with polarization control into a fifth unmodulated optical signal, which is used for coherence detection of the first modulated optical signal, and the first modulated optical signal is an optical signal transmitted by the first optical transmission device to the second optical transmission device.

[0042] In a possible design, the optical transmission method in the embodiment of the present application further includes: a second receiving module receives the first modulated optical signal from the first optical transmission device via the second circulator and receives the fifth unmodulated optical signal from the second coupler. The device further includes a second receiving module, which is coupled to both the second circulator and the second coupler.

[0043] In a possible design, the optical transmission method in the embodiment of the present application further includes: a second polarization control module controls the polarization of the second modulated optical signal; the second polarization control module is further coupled to the second transmission module.

[0044] In a possible design, the first optical transmission device is an optical transmission device on the active antenna unit AAU side, and the second optical transmission device is an optical transmission device on the baseband unit BBU side. Alternatively, the first optical transmission device is an optical transmission device on the BBU side, and the second optical transmission device is an optical transmission device on the AAU side.

[0045] According to a fifth aspect, an embodiment of the present application provides a computer readable storage medium, the computer readable storage medium storing a program, which when called by a processor performs the method according to the third aspect or any one of the implementations of the third aspect, or performs the method according to the fourth aspect or any one of the implementations of the fourth aspect.

[0046] According to a sixth aspect, an embodiment of the present application provides a computer program product comprising instructions, which when invoked by a processor, cause a method according to the third aspect or any one of the implementations of the third aspect to be performed, or cause a method according to the fourth aspect or any one of the implementations of the fourth aspect to be performed.

[0047] According to a seventh aspect, an embodiment of the present application provides a communication system, the system including a first optical transmission device according to the first aspect or any one of the implementations of the first aspect or the first aspect, and a second optical transmission device according to the second aspect or any one of the implementations of the second aspect or the second aspect.

[0048] For the technical effects brought about by any of the designs of the second to seventh aspects, please refer to the beneficial effects in the corresponding methods described above, and the details will not be described again here. [Brief description of the drawings]

[0049] [Figure 1] FIG. 1 is a diagram of the architecture of a communication system according to an embodiment of the present application.

[0050] [Figure 2A] FIG. 2 is a diagram of another communication system architecture according to an embodiment of the present application.

[0051] [Figure 2B] FIG. 2 is a diagram of yet another communication system architecture according to an embodiment of the present application.

[0052] [Figure 3A]FIG. 2 is a diagram of another communication system architecture according to an embodiment of the present application.

[0053] [Figure 3B] FIG. 2 is a diagram of yet another communication system architecture according to an embodiment of the present application.

[0054] [Figure 4] FIG. 2 is a diagram of yet another communication system architecture according to an embodiment of the present application.

[0055] [Diagram 5] 1 is a schematic flowchart of an optical transmission method according to an embodiment of the present application;

[0056] [Figure 6] 4 is a schematic flow chart of another optical transmission method according to an embodiment of the present application.

[0057] [Figure 7] 4 is a schematic flowchart of yet another optical transmission method according to an embodiment of the present application.

[0058] [Figure 8] 4 is a schematic flowchart of yet another optical transmission method according to an embodiment of the present application.

[0059] [Figure 9] 1 is a schematic flowchart of yet another optical transmission method according to an embodiment of the present application.

[0060] [Figure 10] 4 is a schematic flowchart of yet another optical transmission method according to an embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] In the present specification and the accompanying drawings, the terms "first", "second", etc. are intended to distinguish between different objects or between different processes of the same object, and do not indicate a particular order of objects. Also, the terms "including", "having", or other variations thereof in the present description are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, and optionally includes other steps or units not listed, or optionally includes other inherent steps or units of the process, method, product, or apparatus. In the present embodiment, "a plurality of" includes two or more. In the present embodiment, the words "example" or "for example" and the like are used to represent an example, illustration, or description. Any embodiment or design scheme described as an "example" or "for example" in the present embodiment should not be described as being preferred or having more advantages than another embodiment or design scheme. Rather, the words "example", "for example", etc. are intended to present the relevant concept in a particular way. In the embodiments of this application, "transmission" includes "sending" or "receiving".

[0062] First, in order to facilitate understanding of the embodiments of the present application, a brief description of related art in the present application will be given below.

[0063] 1. Optical modulation, unmodulated optical signals and modulated optical signals

[0064] Optical modulation generally refers to the process of transmitting information on an optical carrier by varying a parameter of the optical carrier, which may include, for example, amplitude, intensity, phase, frequency, etc.

[0065] In the embodiments of the present application, the optical carrier without optical modulation is described as an unmodulated optical signal, for example, laser light emitted by a laser or light provided by another light source, which is not limited in the embodiments of the present application.

[0066] In the embodiments of the present application, an optical signal obtained by optical modulation is described as a modulated optical signal, for example an optical signal obtained by amplitude modulation, intensity modulation, phase modulation or frequency modulation.

[0067] 2. Phase Noise

[0068] Phase noise generally causes a random phase offset of the signal in the time domain, and this phase offset can also be observed in the frequency domain.

[0069] 3. Coherent Optical Transmission Technology

[0070] Coherent optical transmission technology mainly uses a single-frequency coherent light source to transmit more modulation information using multi-dimensional parameters such as phase, frequency, and amplitude, making full use of the optical fiber bandwidth to realize ultra-large-capacity transmission.

[0071] For example, a system that uses coherent optical transmission technology for communication will be described below. FIG 1 is a diagram of an architecture of a conventional communication system 1000 according to an embodiment of the present application. As shown in FIG 1, the communication system 1000 includes a first optical transmission device 110 and a second optical transmission device 120.

[0072] The first optical transmission device 110 includes a laser 111, a coupler 112, a transmission module 113, a circulator 114, a receiving module 115, and a digital signal processing (DSP) module 116. In the first optical transmission device 110, the laser 111 is coupled to the coupler 112, which is further coupled to the transmission module 113, a port of the circulator 114, and the receiving module 115. The transmission module 113 is further coupled to an optical interface 1. Another port of the circulator 114 is coupled to an optical interface 2. Another port of the circulator 114 is coupled to the receiving module 115. The receiving module 115 is further coupled to the DSP module 116.

[0073] The second optical transmission device 120 includes a receiving module 121, a DSP module 122, a coupler 123, a circulator 124, and a transmitting module 125. In the second optical transmission device 120, the receiving module 121 is coupled to the optical interface 3, and the receiving module 121 is further coupled to both the DSP module 122 and the coupler 123. The coupler 123 is further coupled to a port of the circulator 124 and the transmitting module 125, another port of the circulator 124 is coupled to the transmitting module 125, and yet another port of the circulator 124 is coupled to the optical interface 4.

[0074] The optical interface 1 and the optical interface 3 are coupled via a single mode optical fiber 130 , and the optical interface 2 and the optical interface 4 are coupled via a single mode optical fiber 140 .

[0075] For example, the processing process of each element in the first optical transmission device 110 is as follows.

[0076] Laser 111 transmits unmodulated optical signal 1. After coupler 112 receives unmodulated optical signal 1 from laser 111, coupler 112 splits the received unmodulated optical signal 1 into one of the following items: Item 1: Unmodulated optical signal 2, Unmodulated optical signal 3, Unmodulated optical signal 4; Item 2: Unmodulated optical signal 2, Unmodulated optical signal 3; or Item 3: Unmodulated optical signal 3, Unmodulated optical signal 4.

[0077] When an unmodulated optical signal 2 is obtained by the separation, the coupler 112 transmits the unmodulated optical signal 2 to the transmission module 113 as local oscillator light of the transmission module 113. The transmission module 113 modulates the unmodulated optical signal 2 using the information 1 to obtain a first modulated optical signal, and transmits the first modulated optical signal to the second optical transmission device 120 via the optical interface 1 and the single-mode optical fiber 130.

[0078] When the unmodulated optical signal 3 is obtained by the separation, the coupler 112 transmits the unmodulated optical signal 3 to a port of the circulator 114. The circulator 114 transmits the unmodulated optical signal 3 to the optical interface 2 via another port, and transmits it to the second optical transmission device 120 via the single-mode optical fiber 140.

[0079] When an unmodulated optical signal 4 is obtained by the separation, the coupler 112 transmits the unmodulated optical signal 4 to the receiving module 115 as local oscillator light of the receiving module 115, as shown by the dashed arrow in Fig. 1. Furthermore, the circulator 114 receives a second modulated optical signal from the optical interface 2, and transmits the second modulated optical signal to the receiving module 115, as shown by the solid arrow in Fig. 1. The receiving module 115 obtains an electric signal 2 by performing coherence detection on the second modulated optical signal using the unmodulated optical signal 4, and transmits the electric signal 2 to the DSP module 116. The DSP module 116 performs sampling, analog-to-digital conversion, and digital signal processing on the electric signal 2 to obtain information 2.

[0080] The processing process of each element in the second optical transmission device 120 is as follows.

[0081] When the first optical transmission device 110 transmits the unmodulated optical signal 3 to the second optical transmission device 120 via the single-mode optical fiber 140, the circulator 124 receives the unmodulated optical signal 3 via the optical interface 4 and transmits the unmodulated optical signal 3 to the coupler 123. The coupler 123 splits the unmodulated optical signal 3 into one of the following items: Item 1: unmodulated optical signal 5, unmodulated optical signal 6; Item 2: Unmodulated optical signal 5. That is, the unmodulated optical signal 3 is used as the unmodulated optical signal 5; or Item 3: Unmodulated optical signal 6. That is, the unmodulated optical signal 3 is used as the unmodulated optical signal 6.

[0082] When an unmodulated optical signal 5 is obtained by the separation, the coupler 123 transmits the unmodulated optical signal 5 to the receiving module 121 as local oscillator light of the receiving module 121. When the first optical transmission device 110 transmits a first modulated optical signal to the second optical transmission device 120 via the single mode optical fiber 130, the receiving module 121 receives the first modulated optical signal via the optical interface 3. The receiving module 115 performs coherence detection of the first modulated optical signal using the unmodulated optical signal 5 to obtain an electrical signal 1, and transmits the electrical signal 1 to the DSP module 116. The DSP module 116 performs sampling, analog-to-digital conversion, and digital signal processing on the electrical signal 1 to obtain information 1.

[0083] When an unmodulated optical signal 6 is obtained by the separation, the coupler 123 transmits the unmodulated optical signal 6 to the transmission module 125 as local oscillator light of the transmission module 125. The transmission module 125 modulates the unmodulated optical signal 6 using the information 2 to obtain a second modulated optical signal, and transmits the second modulated optical signal to the circulator 124. The circulator 124 transmits the second modulated optical signal to the first optical transmission device 110 via the optical interface 4 and the single-mode optical fiber 140, as shown by the solid arrow in FIG.

[0084] It should be noted that FIG. 1 is only used as a possible implementation example to describe an example of the configuration and operation process of a conventional communication system, and does not limit the embodiments of the present application.

[0085] In conclusion, when the second optical transmission device 120 transmits the second modulated optical signal to the first optical transmission device 110 via the single-mode optical fiber 140, it can be seen that for the second modulated optical signal, the optical signal used for coherence detection is the unmodulated optical signal 4. However, when the distance between the first optical transmission device 110 and the second optical transmission device 120 is long, the difference in the transmission path length between the unmodulated optical signal 4 and the second modulated optical signal becomes large, and the unmodulated optical signal 4 and the second modulated optical signal become unrelated to each other. This results in increased phase noise.

[0086] In view of this, an embodiment of the present application provides a communication system. As shown in FIG. 2A, a communication system 2000 provided in the embodiment of the present application includes a first optical transmission device 210 and a second optical transmission device 220. For example, the first optical transmission device 210 and the second optical transmission device 220 are coupled to each other via an optical fiber. For example, an optical interface 1 of the first optical transmission device 210 is coupled to an optical interface 3 of the second optical transmission device 220 via a single-mode optical fiber 230, and an optical interface 2 of the first optical transmission device 210 is coupled to an optical interface 4 of the second optical transmission device 220 via a single-mode optical fiber 240.

[0087] For example, the first optical transmission device 210 may be realized as an optical transmission device on the baseband unit (BBU) side, for example, an optical module that can be coupled to the BBU. The second optical transmission device 220 may be realized as an optical transmission device on the active antenna unit (AAU) side, for example, an optical module that can be coupled to the AAU. Alternatively, conversely, the first optical transmission device 210 may be realized as an optical transmission device on the AAU side, for example, an optical module that can be coupled to the AAU. The second optical transmission device 220 may be realized as an optical transmission device on the BBU side, for example, an optical module that can be coupled to the BBU. Note that, with the development of technology, the AAU and the BBU may be named differently, or may be other devices capable of implementing the functions of the AAU and the BBU. The names of the AAU and the BBU are not limited in the embodiment of the present application. Similarly, the first optical transmission device 210 and the second optical transmission device 220 may be named differently, or may be realized as optical transmission devices on the other device side. This is not limited in the embodiment of the present application.

[0088] There may be two signal transmission directions between the first optical transmission device 210 and the second optical transmission device 220. Specifically, the transmission from the first optical transmission device 210 to the second optical transmission device 220 may be called the first transmission direction, and the transmission from the second optical transmission device 220 to the first optical transmission device 210 may be called the second transmission direction. For example, when an AAU and a BBU are realized, the process in which the BBU transmits a modulated optical signal to the AAU may be called downlink transmission. Also, the process in which the AAU transmits a modulated optical signal to the BBU may be called uplink transmission. In the embodiment of the present application, regarding the modulated optical signal, the modulated optical signal transmitted in the first transmission direction is called the first modulated optical signal. The modulated optical signal transmitted in the second transmission direction is called the second modulated optical signal.

[0089] 2A, in the first optical transmission device 210, the first optical transmission device 210 includes a first circulator 214 and a first receiving module 216, as shown by solid line blocks in FIG. 2A. The first circulator is coupled to the first receiving module 216. For example, a port of the first circulator 214 is coupled to the first receiving module 216 via a polarization maintaining optical fiber or an optical waveguide.

[0090] The first circulator 214 can realize unidirectional signal transmission. For example, the first circulator 214 may be a three-port component. For example, the three ports of the first circulator 214 are indicated as port A, port B, and port C, respectively, and the first circulator 214 realizes unidirectional signal transmission by sending a signal received at port A through port B, sending a signal received at port B through port C, and sending a signal received at port C through port A. Note that, in the embodiment of the present application, the three-port component is merely an example for explaining the first circulator 214. Of course, the first circulator 214 may have other numbers of ports as long as unidirectional signal transmission can be realized. The specific implementation of the first circulator 214 is not limited to the embodiment of the present application.

[0091] In an embodiment of the present application, the first circulator 214 is configured to receive an unmodulated optical signal 7 from the second optical transmission device 220. For example, taking FIG. 2A as an example, the first circulator 214 is configured to receive an unmodulated optical signal 7 from the second optical transmission device 220 via the optical interface 1 and a single-mode optical fiber 230.

[0092] Also, taking FIG. 2A as an example, when the second optical transmission device 220 includes the second circulator 221, the first circulator 214 is coupled to the second circulator 221. For example, the first circulator 214 is coupled to the second circulator 221 via the optical interface 1, the single mode optical fiber 230, and the optical interface 3. The first circulator 214 is configured to receive the unmodulated optical signal 7 from the second circulator 221 via the optical interface 1, the single mode optical fiber 230, and the optical interface 3, as shown by the dashed arrow in FIG. 2A. For the second circulator 221, please refer to the description of the second optical transmission device 220. Details will not be described again here.

[0093] The first receiving module 216 can convert an optical signal into an electrical signal. The first receiving module 216 can also be called a receiver or a coherent receiver. In the embodiment of the present application, only a receiving module is used as an example for explanation. For example, the first receiving module 216 can be realized as an integrated coherent receiver (ICR). Coherence means that the first receiving module 216 can recover amplitude information and phase information.

[0094] In an embodiment of the present application, the first receiving module 216 is configured to receive the second modulated optical signal from the second optical transmission device 220. For example, taking FIG. 2A as an example, the first receiving module 216 is configured to receive the second modulated optical signal from the second optical transmission device 220 via the optical interface 2 and the single-mode optical fiber 240.

[0095] Optionally, when the first optical transmission device 210 includes a fourth circulator 215 and the second optical transmission device 220 includes a third circulator 225, as shown in FIG. 2A, the first receiving module 216 is coupled to the fourth circulator 215, which is coupled to the third circulator 225 via the optical interface 2, the single-mode optical fiber 240, and the optical interface 4. The first receiving module 216 is configured to receive the second modulated optical signal from the third circulator 225 via the fourth circulator 215, the optical interface 2, and the single-mode optical fiber 240, as shown by the thick solid arrow in FIG. 2A. The first receiving module 216 is further configured to receive the unmodulated optical signal 7 from the first circulator 214. The unmodulated optical signal 7 is subjected to coherence detection with respect to the second modulated optical signal to obtain the electrical signal 2.

[0096] The second modulated optical signal is obtained by modulating the unmodulated optical signal 6. For details, see the description of the second transmission module 226. The unmodulated optical signal 6 and the unmodulated optical signal 7 are obtained by splitting the unmodulated optical signal 3. For details, see the description of the second coupler 224.

[0097] The unmodulated optical signal 3 is an optical signal supplied from the first optical transmission device 210 to the second optical transmission device 220, as indicated by the thin solid arrow in FIG. 2A.

[0098] Optionally, Fig. 2A is further used as an example. The first optical transmission device 210 includes a laser 211, a first coupler 212, and a fourth circulator 215, as shown by dashed blocks in Fig. 2A. The first coupler 212 is coupled to both the laser 211 and the fourth circulator 215. For example, the first coupler 212 is coupled to the laser 211 via a polarization-maintaining optical fiber or optical waveguide, and the first coupler 212 is coupled to the fourth circulator 215 via a polarization-maintaining optical fiber or optical waveguide.

[0099] For example, laser 211 may provide a continuous wave with a wavelength λ, which may be in the O band from about 1260 nanometers (nm) to about 1360 nm, or the C / L band from about 1530 nm to about 1625 nm. Laser 211 may be a distributed feedback (DFB) laser without temperature or other wavelength control. In this case, laser 211 is referred to as an uncooled laser and may have a linewidth greater than 100 kilohertz (kHz) up to 1 megahertz (MHz) or more. Alternatively, laser 211 is an external cavity laser (ECL) with a narrow linewidth.

[0100] In the embodiment of the present application, the laser 211 is configured to transmit an unmodulated optical signal 1. The unmodulated optical signal 1 is used for modulation or coherence detection of an optical signal. It should be understood that in the embodiment of the present application, the example of a laser providing the unmodulated optical signal 1 is used for illustration purposes only. Of course, another device may provide the light source instead. This is not limited in the embodiment of the present application.

[0101] For example, the first coupler 212 can split the input optical signal to obtain at least one optical signal. For example, the first coupler 212 can equally split the input optical signal to obtain two beams of optical signals. It should be understood that the number of split optical beams and the split ratio are not limited to the embodiment of the present application. The coupler may also be called an optical splitter, a splitter, etc. In the embodiment of the present application, only the coupler is used as an example for explanation.

[0102] In an embodiment of the present application, the first coupler 212 is configured to receive the unmodulated optical signal 1 from the laser 211 and separate the unmodulated optical signal 1. The separation result includes any one of the following items:

[0103] The first items are an unmodulated optical signal 2 and an unmodulated optical signal 3. The first coupler 212 is configured to split the unmodulated optical signal 1 into the unmodulated optical signal 2 and the unmodulated optical signal 3 based on a specific ratio. The ratio used by the first coupler 212 to perform the splitting may be a preset value or may be a value determined based on a reference coefficient. For example, the reference coefficient includes a transmission distance between the first optical transmission device 210 and the second optical transmission device 220.

[0104] The second item is the unmodulated optical signal 3. That is, the unmodulated optical signal 1 is not separated and is used as the unmodulated optical signal 3 as it is.

[0105] Regarding the above separation result, if an unmodulated optical signal 2 is obtained by separation, the unmodulated optical signal 2 is used to modulate a first modulated optical signal, and the modulated optical signal is transmitted in the first transmission direction. For details, refer to FIG. 1 or the description of the first transmission module 213. Details will not be described again here.

[0106] Regarding the above separation result, if an unmodulated optical signal 3 is obtained by separation, the unmodulated optical signal 3 is used for modulation of the second modulated optical signal and coherence detection. For details, refer to the description of the second transmitting module 226 and the first receiving module 216.

[0107] It should be noted that the first coupler 212 in FIG. 2A does not provide the local oscillator light, ie, the unmodulated optical signal 4, directly to the first receiver module 216, as compared to the coupler 112 in FIG.

[0108] For example, the fourth circulator 215 can realize unidirectional signal transmission. For example, the fourth circulator 215 may be a three-port component. For details, please refer to the description of the first circulator 214. The details will not be described again here.

[0109] In an embodiment of the present application, the fourth circulator 215 is configured to receive the unmodulated optical signal 3 from the first coupler 212 and transmit the unmodulated optical signal 3 to the second optical transmission device 220. For example, continuing to refer to FIG. 2A , a port of the fourth circulator 215 is configured to receive the unmodulated optical signal 3 from the first coupler 212. Another port of the fourth circulator 215 is configured to transmit the unmodulated optical signal 3 to the third circulator 225 via the optical interface 2, the single mode optical fiber 240, and the optical interface 4.

[0110] It can be seen that when the first optical transmission device 210 includes a laser 211, a first coupler 212 and a fourth circulator 215, the unmodulated optical signal 3 can be separated and transmitted under the cooperation of the three components, and the first optical transmission device 210 can provide the unmodulated optical signal 3 to the second optical transmission device 220.

[0111] 2A only uses the coupling relationship between the laser 211, the first coupler 212, and the fourth circulator 215 as an example to describe the generation and transmission of the unmodulated optical signal 3. Of course, the first optical transmission device may have other components or coupling relationships between components to realize the function of generating and transmitting the unmodulated optical signal 3. This is not limited to the embodiment of the present application.

[0112] Optionally, the first optical transmission device 210 further includes a first DSP module 217, as shown by a dashed line in Fig. 2A. The first DSP module 217 is coupled to the first receiving module 216. For example, the first DSP module 217 is coupled to the first receiving module 216 via an electrical coupling cable. The first DSP module 217 is configured to receive the electrical signal 2 from the first receiving module 216 and determine the information 2 based on the electrical signal 2. For details, please refer to the description of Fig. 1. The details will not be described again here.

[0113] 1, the local oscillator light of the first receiving module 216 in FIG. 2A, i.e., the unmodulated optical signal 7, is provided by the first circulator 214. The unmodulated optical signal 7 is obtained after the unmodulated optical signal 3 is separated by the second coupler 224, and the unmodulated optical signal 3 is the optical signal separated by the first coupler 212. That is, the local oscillator light of the first receiving module 216 is not an optical signal directly separated by the first coupler 212, but an optical signal separated by the first coupler 212, passed through the second optical transmission device 220, and then fed back to the first optical transmission device 210.

[0114] In the first optical transmission device 210, only the first DSP module 217 is used as an example of a component capable of processing the electrical signal 2. Of course, the first optical transmission device 210 may have other components or coupling relationships between components to realize the processing function of the electrical signal 2. This is not limited to the embodiment of the present application.

[0115] In the first optical transmission device 210, both the second modulated optical signal and the unmodulated optical signal 7 are from the second optical transmission device 220. Therefore, the transmission paths of the second modulated optical signal and the unmodulated optical signal 7 are the same or close to each other. The second modulated optical signal is obtained by modulating the unmodulated optical signal 6, and the unmodulated optical signal 6 and the unmodulated optical signal 7 are obtained by separating the same optical signal, i.e., the unmodulated optical signal 3, supplied from the first optical transmission device 210. Furthermore, the transmission paths of the second modulated optical signal and the unmodulated optical signal are the same or close to each other. Therefore, the two signals have no frequency difference and belong to coherent light. This reduces or eliminates phase noise.

[0116] 2A, in the second optical transmission device 220, the second optical transmission device 220 includes a second coupler 224, a second circulator 221, and a second transmission module 226. The second coupler 224 is coupled to both the second circulator 221 and the second transmission module 226. For example, an output port of the second coupler 224 is coupled to a port of the second circulator 221 via a polarization-maintaining optical fiber or optical waveguide. Another output port of the second coupler 224 is coupled to the second transmission module 226 via a polarization-maintaining optical fiber or optical waveguide.

[0117] The second coupler 224 can also split the input optical signal. For example, for a specific implementation of the second coupler 224, please refer to the description of the first coupler 212. The details will not be described again here.

[0118] In the embodiment of the present application, the second coupler 224 is configured to split the unmodulated optical signal 3. For the ratio used when the second coupler 224 performs the splitting, please refer to the description of the first coupler 212. A detailed description will be omitted here. Note that the ratio used when the second coupler 224 performs the splitting may be the same as or different from the ratio used when the first coupler 212 performs the splitting. This is not limited in the embodiment of the present application.

[0119] Optionally, the second optical transmission device 220 further includes a third circulator 225, as shown by a dashed block in FIG. 2A. The third circulator 225 can also realize unidirectional signal transmission. For example, the third circulator 225 may be a three-port component. For specific implementation, please refer to the description of the first circulator 214. Details will not be described again here. For example, the coupling relationship between the third circulator 225 and the second coupler 224 is as follows: the input port of the second coupler 224 is coupled to a port of the third circulator 225 through a polarization-maintaining optical fiber or optical waveguide, and the other port of the third circulator 225 is coupled to the optical interface 4 through a polarization-maintaining optical fiber or optical waveguide. In an embodiment of the present application, the third circulator 225 is configured to receive the unmodulated optical signal 3 from the fourth circulator 215 via the optical interface 4, the single-mode optical fiber 240 and the optical interface 2, and transmit the unmodulated optical signal 3 to the second coupler 224, which receives the unmodulated optical signal 3.

[0120] For example, the separation result of the second coupler 224 includes one of the following items:

[0121] The first items are unmodulated optical signal 5, unmodulated optical signal 6, and unmodulated optical signal 7.

[0122] The second item is the unmodulated optical signal 5. That is, the unmodulated optical signal 3 is not separated and is used as the unmodulated optical signal 5 as it is.

[0123] The third item is an unmodulated optical signal 6 and an unmodulated optical signal 7 .

[0124] When the unmodulated optical signal 5 is obtained by the splitting, the unmodulated optical signal 5 is used for coherence detection of the first modulated optical signal. For details, please refer to FIG. 1 or the description of the second receiving module 222. The details will not be described again here.

[0125] If the unmodulated optical signal 6 is obtained by the splitting, the second coupler 224 is configured to transmit the unmodulated optical signal 6 to the second transmission module 226. The unmodulated optical signal 6 is used to modulate the second modulated optical signal. For details, please refer to the description of the second transmission module 226. The details will not be described again here.

[0126] When the unmodulated optical signal 7 is obtained by the separation, the second coupler 224 is configured to send the unmodulated optical signal 7 to the second circulator 221. The unmodulated optical signal 7 is provided to the first optical transmission device 210 to perform coherence detection of the second modulated optical signal. For details, please refer to the description of the second receiving module 216. The details will not be described again here. For example, FIG. 2A is used as an example. The second circulator 221 is configured to send the unmodulated optical signal 7 to the first circulator 214 via the optical interface 3, the single-mode optical fiber 230, and the optical interface 1, as shown by the dashed arrow in FIG. 2A.

[0127] It should be noted that the second coupler 224 in Fig. 2A can further split the unmodulated optical signal 7 compared to the coupler 123 in Fig. 1. For details, please refer to the description of the splitting result of the second coupler 224.

[0128] The second transmission module 226 can convert an electrical signal into an optical signal. The second transmission module 226 may also be called a transmitter or a modulator. In the embodiment of the present application, only the transmission module is used as an example for explanation. For example, the second transmission module 226 may be realized as a polarization multiplexed in-phase and quadrature (IQ) modulator. For example, the second transmission module 226 uses amplitude information and phase information to modulate the unmodulated optical signal, for example, using high-order quadrature amplitude modulation (QAM), to generate a modulated optical signal of a specific wavelength based on the electrical signal. It should be noted that the second transmission module 226 may alternatively perform modulation using other suitable modulation formats. This is not limited in the embodiment of the present application.

[0129] In the embodiment of the present application, the second transmitting module 226 is configured to transmit a second modulated optical signal to the first optical transmission device 210. The second modulated optical signal is obtained after the unmodulated optical signal 6 is modulated. Further taking FIG. 2A as an example, the second transmitting module 226 is configured to transmit the second modulated optical signal to the first optical transmission device 210 via the optical interface 4.

[0130] Optionally, if the second optical transmission device 220 includes a third circulator 225, further using FIG. 2A as an example, an output port of the second transmission module 226 is coupled to a port of the third circulator 225 via a polarization-maintaining optical fiber or optical waveguide. The second transmission module 226 is configured to transmit the second modulated optical signal to the third circulator 225. The third circulator 225 is configured to transmit the second modulated optical signal to the optical interface 4, and the second modulated optical signal is transmitted to the first optical transmission device 210 via the single-mode optical fiber 240, as shown by the thick solid arrow in FIG. 2A.

[0131] The second circulator 221 can realize unidirectional signal transmission. For example, the second circulator 221 may be a three-port component. For specific implementation, please refer to the description of the first circulator 214. Details will not be described again here.

[0132] In an embodiment of the present application, the second circulator 221 is configured to receive the unmodulated optical signal 7 from the second coupler 224 and transmit the unmodulated optical signal 7 to the first optical transmission device 210. For example, as shown in FIG. 2A , the second circulator 221 is configured to transmit the unmodulated optical signal 7 to the first optical transmission device 210 via the optical interface 3.

[0133] Optionally, when the first optical transmission device 210 includes the first circulator 221, the second circulator 221 is coupled to the first circulator 214. The second circulator 221 is configured to transmit the unmodulated optical signal 7 to the first circulator 214. For example, the second circulator 221 is configured to transmit the unmodulated optical signal 7 to the first circulator 214 via the optical interface 3, the single-mode optical fiber 230, and the optical interface 1, as shown by the dashed arrow in FIG. 2A. The second unmodulated optical signal is used for coherence detection of the second modulated optical signal. For details, please refer to the description of the second receiving module 216. The details will not be described again here.

[0134] In the second optical transmission device 220, the second modulated optical signal and the unmodulated optical signal 7 are transmitted to the first optical transmission device 210. Therefore, the transmission paths of the second modulated optical signal and the unmodulated optical signal 7 are the same or close to each other. The second modulated optical signal is obtained by modulating the unmodulated optical signal 6, and the unmodulated optical signal 6 and the unmodulated optical signal 7 are obtained by separating the same optical signal, i.e., the unmodulated optical signal 3, supplied from the first optical transmission device 210. Furthermore, the transmission paths of the second modulated optical signal and the unmodulated optical signal are the same or close to each other. Therefore, there is no frequency difference between the two signals and they belong to coherent light. This reduces or eliminates phase noise.

[0135] In the above, the coupling relationship and function of each component is described in terms of modulation, transmission, and demodulation, using only the second modulated optical signal as an example. Optionally, in the above, the coupling relationship and function of each component is described in terms of modulation, transmission, and coherence detection, using only the first modulated optical signal as an example.

[0136] Optionally, the first optical transmission device 210 further includes a first transmission module 213, as shown by a dashed block in FIG. 2A. The first transmission module 213 can also convert an electrical signal into an optical signal. For details, please refer to the description of the second transmission module 226. Details will not be described again here. For example, the coupling relationship between the first transmission module 213 and other components is as follows: the first transmission module 213 is coupled to both the first coupler 212 and the first circulator 214. For example, the first transmission module 213 is coupled to the first coupler 212 via a polarization-maintaining optical fiber or optical waveguide, and the first transmission module 213 is coupled to the first circulator 214 via a polarization-maintaining optical fiber or optical waveguide.

[0137] In the embodiment of the present application, the function of the first transmitting module 213 is described as follows.

[0138] When the first coupler 212 obtains the unmodulated optical signal 2 by separation, the first transmission module 213 receives the unmodulated optical signal 2 from the first coupler 212 and modulates the unmodulated optical signal 2 to obtain a first modulated optical signal. For details, please refer to the description of FIG. 1. Details will not be described again here. Note that in the embodiment of the present application, only the first transmission module 213 is taken as an example to explain the coupling relationship between the first transmission module 213 and other components to realize the function of generating the first modulated optical signal. Of course, the first optical transmission device 210 may alternatively have other components or coupling relationships between components to realize the function of generating the first modulated optical signal 2. This is not limited to the embodiment of the present application.

[0139] Furthermore, in an embodiment of the present application, the first circulator 214 is further configured to receive the first modulated optical signal from the first transmission module 213 and transmit the first modulated optical signal to the second optical transmission device 220. For example, the first circulator 214 is configured to transmit the first modulated optical signal to the second circulator 221 via the optical interface 1, the single-mode optical fiber 230, and the optical interface 3, as shown by the thick solid arrow in FIG. 2B.

[0140] Optionally, in the second optical transmission device 220, the second circulator 221 is further configured to receive the first modulated optical signal from the first optical transmission device 210 and send the first modulated optical signal to the second receiving module 222. For example, the second circulator 221 is configured to receive the first modulated optical signal from the first circulator 214 via the optical interface 3 and send the first modulated optical signal to the second receiving module 222.

[0141] Optionally, the second optical transmission device 220 further includes a second receiving module 222, as shown by a dashed block in FIG. 2A. The second receiving module 222 can also convert an optical signal into an electrical signal. For example, for a specific implementation of the second receiving module 222, please refer to the description of the first receiving module 216. Details will not be described again here. For example, the coupling relationship between the second receiving module 222 and other components is as follows: the second receiving module 222 is coupled to both the second coupler 224 and the second circulator 221. For example, the second receiving module 222 is coupled to the second coupler 224 via a polarization-maintaining optical fiber or optical waveguide, and the second receiving module 222 is coupled to the second circulator 221 via a polarization-maintaining optical fiber or optical waveguide.

[0142] In the embodiment of the present application, the function of the second receiving module 222 is described as follows.

[0143] The second receiving module 222 is configured to receive the first modulated optical signal from the second circulator 221. After the second coupler 224 obtains the unmodulated optical signal 5 by separation, the unmodulated optical signal 5 is used to perform coherence detection on the first modulated optical signal. For example, the second receiving module 222 performs coherence detection on the first modulated optical signal using the unmodulated optical signal 5 to obtain the electrical signal 1. For details, please refer to the description of FIG. 1. The details will not be described again here.

[0144] In the embodiment of the present application, only the second receiving module 222 is taken as an example to explain the coupling relationship between the second receiving module 222 and other components to realize the function of receiving the second modulated optical signal. Of course, the second optical transmission device 220 may alternatively have other components or coupling relationships between components to realize the function of receiving the second modulated optical signal. This is not limited to the embodiment of the present application.

[0145] Optionally, the second optical transmission device 220 further includes a second DSP module 223, as shown by a dashed block in Fig. 2A. The second DSP module 223 is coupled to the second receiving module 222. For example, the second DSP module 223 is coupled to the second receiving module 222 via an electrical coupling cable. The second DSP module 223 is configured to receive the electrical signal 1 from the second receiving module 222 and determine the information 1 based on the electrical signal 1. For details, please refer to the description of Fig. 1. The details will not be described again here.

[0146] In the second optical transmission device 220, only the second DSP module 223 is used as an example of a component capable of processing the electrical signal 1. Of course, the second optical transmission device 220 may have other components or coupling relationships between components to realize the processing function of the electrical signal 1. This is not limited to the embodiment of the present application.

[0147] It can be seen that based on the coupling relationships and functions of the above components, the functions of modulation, transmission and coherence detection of the first modulated optical signal can be realized.

[0148] In some embodiments, as shown in FIG. 3A, the first optical transmission device 210 further includes a first polarization control (automatic polarization controller, APC) module 218, as shown by a thick solid block in FIG. 3A. The polarization control module is a polarization state control component, which can convert any dynamically changing input polarization state into any expected output polarization state. For example, the polarization control module changes the polarization state by utilizing the birefringence phenomenon of crystals, and obtains polarized light of the expected polarization state by utilizing a specific synthesis method and control algorithm. The synthesis method can include the number of wave plates coupled in series and the relative orientation relationship between the wave plates. The control algorithm can include dynamically changing the orientation and birefringence relative position difference of the wave plates at high speed. The polarization control module is also called a polarization controller. In the embodiment of the present application, only the polarization control module is used as an example for explanation.

[0149] For example, the coupling relationship between the first polarization control module 218 and other components is as follows. The first polarization control module 218 is coupled to the first circulator 214. For example, referring to FIG. 3A, the first polarization control module 218 is coupled to the first circulator 214 via a polarization-maintaining optical fiber or optical waveguide, and the first polarization control module 218 is coupled to the optical interface 1 via a polarization-maintaining optical fiber or optical waveguide. In addition, the first polarization control module 218 may be arranged on the second optical transmission device 220 side instead of the first optical transmission device 210 side. For example, the second circulator 221 is coupled to the optical interface 3 via the first polarization control module 218 (not shown in FIG. 3A). This is not limited to the embodiment of the present application.

[0150] As shown in Fig. 3A, the first polarization control module 218 and the first receiver module 216 may be independent components. Also, the first polarization control module 218 and the first receiver module 216 may be integrated. For example, the first polarization control module 218 is an internal component of the first receiver module 216, although not shown in Fig. 3A.

[0151] The function of the first polarization control module 218 is described as follows. The first polarization control module 218 is configured to control the polarization of the unmodulated optical signal 7. For example, the first polarization control module 218 is configured to convert the polarization state of the unmodulated optical signal 7 to a desired polarization state after receiving the unmodulated optical signal 7 through the optical interface 1. The desired polarization state may be the same as the polarization state of the second modulated optical signal. And the first polarization control module 218 is configured to transmit the polarization-controlled unmodulated optical signal 7 to the first receiving module 216 through the first circulator 214.

[0152] In addition, the optical interface 1 and the optical interface 3 are usually coupled through a polarization-maintaining optical fiber so that the unmodulated optical signal 7 has sufficient energy in a constant polarization state as much as possible, and the coherence detection can be performed normally. However, in practical applications, the polarization-maintaining optical fiber may be affected by other application environment changes such as extrusion processing, trampling, and stretching during installation. As a result, the function of maintaining the polarization state of the polarization-maintaining optical fiber is reduced. In this case, the polarization state of the unmodulated optical signal 7 transmitted through the polarization-maintaining optical fiber rotates randomly. This causes poor coherence detection. However, the first polarization control module 218 can convert the polarization state of the unmodulated optical signal 7 into the expected polarization state, thereby realizing normal coherence detection.

[0153] In this case, performing coherence detection on the second modulated optical signal using the unmodulated optical signal 7 includes: performing coherence detection on the second modulated optical signal using the unmodulated optical signal 7 with polarization control. For example, FIG. 3A is further used as an example. When the second optical transmission device 220 transmits the unmodulated optical signal 7 to the first optical transmission device 210, the first receiving module 216 receives the unmodulated optical signal 7 with polarization control from the first circulator 214, and provides it as a local oscillator light to perform coherence detection on the second modulated optical signal.

[0154] In this way, the local oscillator light used for coherence detection is the polarization-controlled unmodulated optical signal 7. Since the unmodulated optical signal 7 has high energy in the expected polarization state, the effect of random polarization state changes can be eliminated or reduced, and the accuracy of coherence detection can be improved.

[0155] Optionally, the first polarization control module 218 is further configured to control the polarization of the first modulated optical signal. The first modulated optical signal is an optical signal transmitted by the first optical transmission device 210 to the second optical transmission device 220. For details, please refer to the description of FIG. 2B. Details will not be described again here. For example, still using FIG. 3A as an example, the first circulator 214 is further configured to send the first modulated optical signal to the first polarization control module 218. The first polarization control module 218 is configured to control the polarization of the first modulated optical signal so that the polarization-controlled first modulated optical signal has more energy in the expected polarization direction. The polarization-controlled first modulated optical signal and the polarization-controlled unmodulated optical signal 3 may be in the same polarization state. Also on the second optical transmission device 220 side, when polarization control is performed on the unmodulated optical signal 3, the local oscillator light (i.e., the unmodulated optical signal 5) used by the second receiving module 222 to perform coherence detection and the first modulated optical signal are in the same polarization state. In this way, after the second receiving module 222 performs coherence detection, the electrical signal 1 can be acquired. The second DSP module 223 can acquire the information 1 based on the electrical signal 1 and does not need to perform polarization separation processing, so that the system power consumption is reduced and there is no need to design individual chips. This helps reduce system costs.

[0156] It should be noted that if the coherent communication system 2000 includes the first polarization control module 218, the single mode optical fiber 230 may be replaced with other coupling materials, such as common fiber, to reduce system costs.

[0157] In some embodiments, the second optical transmission device 220 further includes a second polarization control module 227, as shown by a thick solid block in Fig. 3B. For the polarization control module, please refer to the description of the first polarization control module 218. The details will not be described again here.

[0158] For example, the coupling relationship between the second polarization control module 227 and other components is described as follows.

[0159] The second polarization control module 227 is coupled to the second coupler 224. For example, see FIG. 3B. The second polarization control module 227 is coupled to the second coupler 224 via the third circulator 225. Also, the second polarization control module 227 may be arranged on the first optical transmission device 210 side, not on the second optical transmission device 220 side. For example, the fourth circulator 215 is coupled to the optical interface 2 via the second polarization control module 227 (not shown in FIG. 3B). This is not limited to the embodiment of the present application.

[0160] As shown in Fig. 3B, the second polarization control module 227 and the second receiver module 222 may be independent components. Also, the second polarization control module 227 and the second receiver module 222 may be integrated. For example, the second polarization control module 227 is an internal component of the second receiver module 222, although it is not shown in Fig. 3B.

[0161] The function of the second polarization control module 227 is explained as follows.

[0162] The second polarization control module 227 is configured to control the polarization of the unmodulated optical signal 3. For example, the second polarization control module 227 is configured to receive the unmodulated optical signal 3 via the optical interface 4 and convert the polarization state of the unmodulated optical signal 3 to a desired polarization state. The desired polarization state may be the same as the polarization state of the unmodulated optical signal 3 on the first optical transmission device 210 side, or may be a polarization state in another direction. This is not limited in the embodiment of the present application.

[0163] In this case, the second coupler 224 is configured to split the polarization-controlled unmodulated optical signal 3. For example, the second coupler 224 is configured to receive the polarization-controlled unmodulated optical signal 3 from the second polarization control module 227 via the third circulator 225, and then split the unmodulated optical signal 3. For example, the second coupler 224 is configured to split the polarization-controlled unmodulated optical signal 3 into at least the unmodulated optical signal 6 and the unmodulated optical signal 7. In another example, the second coupler 224 is configured to split the polarization-controlled unmodulated optical signal 3 into at least the unmodulated optical signal 6, the unmodulated optical signal 7, and the unmodulated optical signal 5. In another example, the second coupler 224 is configured to split the polarization-controlled unmodulated optical signal 3 into the unmodulated optical signal 5. For the unmodulated optical signal 6, see the description of the second transmission module 226. For the unmodulated optical signal 7, see the description of the second circulator 221. The unmodulated optical signal 5 is used for coherence detection of the first modulated optical signal. For details, please refer to the description of the second receiving module 222. Details will not be described again here. Since the unmodulated optical signal 6, the unmodulated optical signal 7, and the unmodulated optical signal 5 are obtained by separating the unmodulated optical signal 3 that has been subjected to polarization control, the unmodulated optical signal 6, the unmodulated optical signal 7, and the unmodulated optical signal 5 have the same polarization state as the unmodulated optical signal 3 that has been subjected to polarization control, and are also optical signals that have been subjected to polarization control.

[0164] The second receiving module 222 is configured to receive the first modulated optical signal from the first optical transmission device 210. As shown in FIG. 3B, the second receiving module 222 is configured to receive the first modulated optical signal from the first circulator 214 via the second circulator 221. The first modulated optical signal is obtained by modulating the unmodulated optical signal 2. For details, please refer to the description of the first transmission module 213. The unmodulated optical signal 2 and the unmodulated optical signal 3 are obtained by splitting the same optical signal (i.e., the unmodulated optical signal 1). For details, please refer to the description of the first coupler 212. The details will not be described again here. For example, the second receiving module 222 is configured to perform coherence detection on the first modulated optical signal, for example, using the unmodulated optical signal 5.

[0165] In this way, the local oscillator light used for coherence detection is the polarization-controlled unmodulated optical signal 5. Since the unmodulated optical signal 5 has high energy in the expected polarization state, the effect of random polarization state changes can be eliminated or reduced, and the accuracy of coherence detection can be improved.

[0166] Optionally, the second polarization control module 227 is further coupled to the second transmission module 226 via a third circulator 225. For example, as shown in FIG. 3B, the third circulator 225 has three ports respectively coupled to the second coupler 224, the second transmission module 226, and the second polarization control module 227.

[0167] The second polarization control module 227 is further used to control the polarization of the second modulated optical signal. For example, as shown in FIG. 3B, when the unmodulated optical signal 6 is obtained by the separation, the second coupler 224 is configured to transmit the unmodulated optical signal 6 to the second transmission module 226 to modulate the second modulated optical signal. For details, refer to the description of the second transmission module 226. Details will not be described again here. In addition, the second polarization control module 227 is configured to receive the second modulated optical signal from the second transmission module 226 via the third circulator 225, control the polarization of the second modulated optical signal, and transmit the polarization-controlled second modulated optical signal to the fourth circulator 215 of the first optical transmission device 210.

[0168] In this way, in the first receiving module 216, the modulated optical signal used for coherence detection is an optical signal that has been subjected to polarization control, and has a larger energy in the expected polarization direction. The second modulated optical signal that has been subjected to polarization control and the unmodulated optical signal 7 that has been subjected to polarization control may be in the same polarization state. When the unmodulated optical signal 7 is also subjected to polarization control on the first optical transmission device 210 side, the local oscillator light (i.e., the unmodulated optical signal 7) used by the first receiving module 216 to perform coherence detection and the second modulated optical signal are in the same polarization state. In this way, after the first receiving module 216 performs coherence detection, the electrical signal 2 can be obtained. The first DSP module 217 can obtain the information 2 based on the electrical signal 2, and does not need to perform polarization separation processing, thereby reducing system power consumption.

[0169] It should be noted that if the coherent communication system 2000 includes the second polarization control module 227, the single mode optical fiber 240 may be replaced with other coupling materials, such as common fiber, to reduce system costs.

[0170] In some embodiments, as shown in FIG. 4, the first optical transmission device 210 further includes a first polarization control module 218, and the second optical transmission device 220 further includes a second polarization control module 227. For the coupling relationship and function of the first polarization control module 218 with other components, please refer to the description of FIG. 3A. For the coupling relationship and function of the second polarization control module 227 with other components, please refer to the description of FIG. 3B. Details will not be described again here. For the unmodulated optical signal, in the communication system shown in FIG. 4, the polarization of the unmodulated optical signal in the first transmission direction (i.e., the unmodulated optical signal 3) can be controlled, and the polarization of the unmodulated optical signal in the second transmission direction (i.e., the unmodulated optical signal 7) can also be controlled, which can eliminate or reduce the influence of random polarization state changes and help improve the coherence detection performance of the system. 4, the polarization of the first modulated optical signal in the first transmission direction can be controlled, and the polarization of the second modulated optical signal in the second transmission direction can also be controlled, so that neither of the two optical transmission devices (i.e., the first optical transmission device 210 and the second optical transmission device 220) needs to perform polarization separation processing, which helps reduce system costs.

[0171] An embodiment of the present application further provides a coherent optical transmission method 5000. The method is applicable to the communication system 2000 shown in Figure 2A, Figure 2B, Figure 3A, Figure 3B or Figure 4. As shown in Figure 5, the optical transmission method 5000 includes the following steps:

[0172] S501: The first optical transmission device 210 transmits an unmodulated optical signal 3 to the second optical transmission device 220. In response, the second optical transmission device 220 receives the unmodulated optical signal 3 from the first optical transmission device 210.

[0173] 2A, in the first optical transmission device 210, the fourth circulator 215 transmits the unmodulated optical signal 3 to the third circulator 225 via the optical interface 2, the single-mode optical fiber 240, and the optical interface 4. Correspondingly, in the second optical transmission device 220, the third circulator 225 receives the unmodulated optical signal 3 via the optical interface 4.

[0174] For example, see Fig. 2A. In the first optical transmission device 210, the process of generating the unmodulated optical signal 3 is as follows.

[0175] The laser 211 generates an unmodulated optical signal 1. The first coupler 212 receives the unmodulated optical signal 1 from the laser 211 and separates the unmodulated optical signal 1 to obtain a separation result. The separation result includes one of the following items: Item 1: Unmodulated optical signal 2, Unmodulated optical signal 3; or Item 2: Unmodulated optical signal3.

[0176] For the result of the separation, see the description of the first coupler 212. Details will not be described again here. When the unmodulated optical signal 2 is obtained by separation, the first optical transmission device 210 executes the description of S511. When the unmodulated optical signal 3 is obtained by separation, the first coupler 212 transmits the unmodulated optical signal 3 to the fourth circulator 215, and then transmits the unmodulated optical signal 3 to the second optical transmission device 220.

[0177] S502: The second optical transmission device 220 demultiplexes the unmodulated optical signal 3.

[0178] For example, see Figure 2A. The second coupler 224 receives the unmodulated optical signal 3 from the third circulator 225 and separates the unmodulated optical signal 3 to obtain a separation result. The separation result includes one of the following items: Item 1: unmodulated optical signal 5, unmodulated optical signal 6, unmodulated optical signal 7; Item 2: an unmodulated optical signal 5; or Item 3: Unmodulated optical signal 6, unmodulated optical signal 7.

[0179] For the result of the separation, see the description of the second coupler 224 in FIG. 2A. Details will not be described again here. When an unmodulated optical signal 5 is obtained by separation, the second optical transmission device 220 executes S513. When an unmodulated optical signal 6 is obtained by separation, the second optical transmission device 220 executes S503. When an unmodulated optical signal 7 is obtained by separation, the second optical transmission device 220 executes S505. S503 and S505 are described as follows.

[0180] S503: The second optical transmission device 220 modulates the unmodulated optical signal 6 to obtain a second modulated optical signal.

[0181] For example, see Fig. 2A. The second transmitting module 226 receives the unmodulated optical signal 6 from the second coupler 224 and modulates the unmodulated optical signal 6 to obtain a second modulated optical signal. For details, see the description of the second transmitting module 226 in Fig. 2A. The details will not be described again here.

[0182] S504: The second optical transmission device 220 transmits a second modulated optical signal to the first optical transmission device 210. In response, the first optical transmission device 210 receives the second modulated optical signal from the second optical transmission device 220.

[0183] 2A, the second transmission module 226 transmits the second modulated optical signal to the third circulator 225, and the third circulator 225 transmits the second modulated optical signal to the optical interface 4, so that the second modulated optical signal is transmitted to the fourth circulator 215 of the first optical transmission device 210 via the single-mode optical fiber 240. Correspondingly, the fourth circulator 215 receives the second modulated optical signal via the optical interface 2.

[0184] S505: The second optical transmission device 220 transmits the unmodulated optical signal 7 to the first optical transmission device 210. In response, the first optical transmission device 210 receives the unmodulated optical signal 7 from the second optical transmission device 220.

[0185] 2A, the second coupler 224 transmits the unmodulated optical signal 7 to the second circulator 221, which then transmits the unmodulated optical signal 7 to the optical interface 3, so that the unmodulated optical signal 7 is transmitted to the first circulator 214 of the first optical transmission device 210 via the single-mode optical fiber 230. Correspondingly, the first circulator 214 receives the unmodulated optical signal 7 via the optical interface 1.

[0186] Optionally, for the first optical transmission device 210, after S504 and S505, S506 is performed.

[0187] S506: The first optical transmission device 210 performs coherence detection of the second modulated optical signal using the unmodulated optical signal 7.

[0188] For example, see FIG. 2A. The first receiving module 216 receives the unmodulated optical signal 7 from the first circulator 214, and uses the unmodulated optical signal 7 as a local oscillator light. The first receiving module 216 further receives the second modulated optical signal from the fourth circulator 215, and performs coherence detection on the second modulated optical signal using the unmodulated optical signal 7 to obtain an electrical signal 2. For details, see the description of the first receiving module 216 in FIG. 2A. Then, the first DSP module 217 processes the electrical signal 2 to obtain information 2. For details, see the description of the first DSP module 217 in FIG. 2A. The details will not be described again here.

[0189] In the optical transmission method 5000, in the embodiment of the present application, the second optical transmission device 220 transmits the second modulated optical signal and the unmodulated optical signal 7 to the first optical transmission device 210. Therefore, the transmission paths of the second modulated optical signal and the unmodulated optical signal 7 are the same or close to each other. The second modulated optical signal is obtained by modulating the unmodulated optical signal 6, and the unmodulated optical signal 6 and the unmodulated optical signal 7 are obtained by separating the same optical signal, i.e., the unmodulated optical signal 3, supplied from the first optical transmission device 210. Furthermore, the transmission paths of the second modulated optical signal and the unmodulated optical signal are the same or close to each other. Therefore, the two signals have no frequency difference and belong to coherent light. This reduces or eliminates phase noise.

[0190] The above only describes the second modulated optical signal in terms of modulation, transmission and demodulation. Optionally, the above also describes the first modulated optical signal in terms of modulation, transmission and coherence detection. Please refer to FIG. 6. The coherent optical transmission method 5000 in the embodiment of the present application further includes:

[0191] S511: The first optical transmission device 210 modulates the unmodulated optical signal 2 to obtain a first modulated optical signal.

[0192] For example, see Fig. 2A. After the unmodulated optical signal 2 is obtained by splitting, the first transmitting module 213 receives the unmodulated optical signal 2 from the first coupler 212 and modulates the unmodulated optical signal 2 to obtain a first modulated optical signal. For details, please refer to the description of the first transmitting module 213 in Fig. 2A. The details will not be described again here.

[0193] S512: The first optical transmission device 210 transmits a first modulated optical signal to the second optical transmission device 220. In response, the second optical transmission device 220 receives the first modulated optical signal from the first optical transmission device 210.

[0194] 2A, the first transmission module 213 transmits the first modulated optical signal to the first circulator 214, and the first circulator 214 transmits the first modulated optical signal to the optical interface 1, so that the first modulated optical signal is transmitted to the second circulator 221 of the second optical transmission device 220 via the single-mode optical fiber 230. Correspondingly, the second circulator 221 receives the first modulated optical signal via the optical interface 3.

[0195] S513: The second optical transmission device 220 performs coherence detection of the first modulated optical signal using the unmodulated optical signal 5.

[0196] For example, see Fig. 2A. The second receiving module 222 receives the unmodulated optical signal 5 from the second coupler 224 and uses the unmodulated optical signal 5 as a local oscillator light. The second receiving module 222 further receives the first modulated optical signal from the second circulator 221 and performs coherence detection on the first modulated optical signal using the unmodulated optical signal 5 to obtain an electrical signal 1. Then, the second DSP module 223 processes the electrical signal 1 to obtain information 1.

[0197] In some embodiments, as shown in FIG. 7, the coherent optical transmission method 5000 in the embodiment of the present application further includes:

[0198] S520: The first optical transmission device 220 controls the polarization of the unmodulated optical signal 7.

[0199] For example, see Fig. 3A. After receiving the unmodulated optical signal 7 through the optical interface 1, the first polarization control module 218 converts the polarization state of the unmodulated optical signal 7 into an expected polarization state. For details, please refer to the description of the first polarization control module 218 in Fig. 3A. The details will not be described again here.

[0200] When S520 is executed, S506 may be replaced by S506a.

[0201] S506a: The first optical transmission device 210 performs coherence detection on the second modulated optical signal using the unmodulated optical signal 7 that has been subjected to polarization control.

[0202] For example, the first receiving module 216 receives the polarization-controlled unmodulated optical signal 7 from the first polarization control module 218 via the first circulator 214, and performs coherence detection on the second modulated optical signal using the unmodulated optical signal 7 as a local oscillator light.

[0203] In this way, the local oscillator light used for coherence detection is the polarization-controlled unmodulated optical signal 7. Since the unmodulated optical signal 7 has high energy in the expected polarization state, the effect of random polarization state changes can be eliminated or reduced, and the accuracy of coherence detection can be improved.

[0204] Optionally, as shown in FIG. 8 , the coherent optical transmission method 5000 in the embodiment of the present application further includes the following steps:

[0205] S521: The first optical transmission device 220 controls the polarization of the first modulated optical signal.

[0206] For example, see Fig. 3A. After generating the first modulated optical signal, the first transmission module 213 transmits the first modulated optical signal to the first polarization control module 218 via the first circulator 214. The first polarization control module 218 is configured to control the polarization of the first modulated optical signal such that the polarization-controlled first modulated optical signal has more energy in the expected polarization direction.

[0207] When S521 is executed, S512 may be replaced with S512a.

[0208] S512a: The first optical transmission device 210 transmits the first modulated optical signal that has been subjected to polarization control to the second optical transmission device 220. In response, the second optical transmission device 220 receives the first modulated optical signal that has been subjected to polarization control from the first optical transmission device 210.

[0209] 3A, the first polarization control module 218 transmits the polarization-controlled first modulated optical signal via the optical interface 1 and the single mode optical fiber 230. Correspondingly, the second circulator 221 receives the polarization-controlled first modulated optical signal via the optical interface 3 and provides the polarization-controlled first modulated optical signal to the second receiver module 222.

[0210] Also on the second optical transmission device 220 side, when polarization control is performed on the unmodulated optical signal 3, the local oscillator light (i.e., the unmodulated optical signal 5) used by the second receiving module 222 to perform coherence detection and the first modulated optical signal are in the same polarization state. In this way, after the second receiving module 222 performs coherence detection, the electrical signal 1 can be acquired. The second DSP module 223 can acquire the information 1 based on the electrical signal 1 and does not need to perform polarization separation processing, thereby reducing system power consumption.

[0211] In some embodiments, as shown in FIG. 9, the optical transmission method 5000 in the embodiment of the present application further includes the following steps:

[0212] S530: The second optical transmission device 220 controls the polarization of the unmodulated optical signal 3.

[0213] For example, see Fig. 3B. After receiving the unmodulated optical signal 3 through the optical interface 4, the second polarization control module 227 converts the polarization state of the unmodulated optical signal 3 into an expected polarization state. For details, please refer to the description of the second polarization control module 227 in Fig. 3B. The details will not be described again here.

[0214] When S530 is executed, S502 may be replaced by S502a.

[0215] S502a: The second optical transmission device 220 demultiplexes the unmodulated optical signal 3 that has been subjected to polarization control.

[0216] Since the unmodulated optical signal 6, the unmodulated optical signal 7, and the unmodulated optical signal 5 are obtained by separating the unmodulated optical signal 3 that has been subjected to polarization control, the unmodulated optical signal 6, the unmodulated optical signal 7, and the unmodulated optical signal 5 are in the same polarization state as the unmodulated optical signal 3 that has been subjected to polarization control.

[0217] Optionally, in the second optical transmission device 220, when the unmodulated optical signal 5 is obtained by demultiplexing, S513 may be replaced with S513a.

[0218] S513a: The second optical transmission device 220 performs coherence detection on the first modulated optical signal by using the unmodulated optical signal 5 that has been subjected to polarization control.

[0219] For example, the second receiving module 222 further receives the first modulated optical signal from the first optical transmission device 210 via the second circulator 221, and performs coherence detection on the first modulated optical signal using the polarization-controlled unmodulated optical signal 5. For details, see the description of the second receiving module 222 in FIG. 3B. The details will not be described again here.

[0220] In this way, the local oscillator light used for coherence detection is the polarization-controlled unmodulated optical signal 5. Since the unmodulated optical signal 5 has high energy in the expected polarization state, the effect of random polarization state changes can be eliminated or reduced, improving the accuracy of coherence detection.

[0221] Optionally, as shown in FIG. 10 , the optical transmission method 5000 in the embodiment of the present application further includes:

[0222] S531: The second optical transmission device 220 controls the polarization of the second modulated optical signal.

[0223] For example, see Fig. 3B. After generating the second modulated optical signal, the second transmission module 226 transmits the second modulated optical signal via the third circulator 225 to the second polarization control module 227. The second polarization control module 227 controls the polarization of the second modulated optical signal so that the polarization-controlled second modulated optical signal has more energy in the expected polarization direction.

[0224] When S531 is executed, S504 may be replaced with S504a.

[0225] S504a: The second optical transmission device 220 transmits the second modulated optical signal on which polarization control has been performed to the first optical transmission device 210. In response, the first optical transmission device 210 receives the second modulated optical signal on which polarization control has been performed from the second optical transmission device 220.

[0226] 3B, the second polarization control module 227 transmits the polarization-controlled second modulated optical signal via the optical interface 4 and the single mode optical fiber 240. Correspondingly, the fourth circulator 215 receives the polarization-controlled second modulated optical signal via the optical interface 2 and provides the polarization-controlled second modulated optical signal to the first receiving module 216.

[0227] In this way, the second modulated optical signal subjected to polarization control and the unmodulated optical signal 7 subjected to polarization control may be in the same polarization state. When the unmodulated optical signal 7 is also subjected to polarization control on the first optical transmission device 210 side, the local oscillator light (i.e., the unmodulated optical signal 7) used by the first receiving module 216 to perform coherence detection and the second modulated optical signal are in the same polarization state. In this way, the first receiving module 216 can obtain the electrical signal 2 after performing coherence detection. The first DSP module 217 can obtain the information 2 based on the electrical signal 2 and does not need to perform polarization separation processing, thereby reducing system power consumption.

[0228] The above description is merely a specific implementation of the present application, and is not intended to limit the protection scope of the present application. Any modifications or replacements within the technical scope disclosed in the present application shall be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A first optical transmission device, a first circulator configured to receive a second unmodulated optical signal from a second optical transmission device; a first receiving module coupled to the first circulator and configured to receive a second modulated optical signal from the second optical transmission device and to receive the second unmodulated optical signal from the first circulator, the second modulated optical signal being obtained by modulating a first unmodulated optical signal, the second unmodulated optical signal being used to perform coherence detection on the second modulated optical signal, the first unmodulated optical signal and the second unmodulated optical signal being obtained by separating a third unmodulated optical signal, the third unmodulated optical signal being an optical signal supplied from the first optical transmission device to the second optical transmission device; An apparatus comprising:

2. the first circulator is further coupled to a second circulator, the second optical transmission device including the second circulator; 2. The apparatus of claim 1, wherein the first circulator being configured to receive a second unmodulated optical signal from a second optical transmission device comprises receiving the second unmodulated optical signal from the second circulator.

3. 3. The apparatus of claim 1, further comprising a first polarization control module coupled to the first circulator, the first polarization control module configured to control the polarization of the second unmodulated optical signal.

4. 4. The apparatus of claim 3, wherein using the second unmodulated optical signal to perform coherence detection on the second modulated optical signal comprises using the second unmodulated optical signal with polarization control to perform coherence detection on the second modulated optical signal.

5. 5. The apparatus of claim 3, wherein the first polarization control module is configured to control the polarization of a first modulated optical signal, the first modulated optical signal being an optical signal transmitted by the first optical transmission device to the second optical transmission device.

6. 6. The apparatus of claim 5, further comprising: a first transmission module coupled to the first circulator and configured to transmit the first modulated optical signal through the first circulator to the first polarization control module.

7. The first optical transmission device is an optical transmission device on an active antenna unit (AAU) side, and the second optical transmission device is an optical transmission device on a baseband unit (BBU) side, or 7. The device according to claim 1, wherein the first optical transmission device is an optical transmission device on a BBU side, and the second optical transmission device is an optical transmission device on an AAU side.

8. A second optical transmission device, a second coupler configured to split the third unmodulated optical signal into at least the first unmodulated optical signal and the second unmodulated optical signal, the third unmodulated optical signal being an optical signal provided from a first optical transmission device; a second transmission module coupled to the second coupler and configured to transmit a second modulated optical signal to the first optical transmission device, the second modulated optical signal being obtained by modulating the first unmodulated optical signal; and a second circulator coupled to the second coupler to receive the second unmodulated optical signal from the second coupler and to transmit the second unmodulated optical signal to the first optical transmission device, the second unmodulated optical signal being used for coherence detection of the second modulated optical signal; and An apparatus comprising:

9. the second circulator is further coupled to a first circulator, and the first optical transmission device includes the first circulator; 9. The apparatus of claim 8, wherein the second circulator being configured to transmit the second unmodulated optical signal to the first optical transmission device comprises transmitting the second unmodulated optical signal to the first circulator.

10. 10. The apparatus of claim 8 or 9, further comprising: a second polarization control module coupled to the second coupler and configured to control the polarization of the third unmodulated optical signal.

11. 11. The apparatus of claim 10, wherein the second coupler splitting the third unmodulated optical signal into at least a first unmodulated optical signal and a second unmodulated optical signal comprises splitting the third unmodulated optical signal with polarization control into at least the first unmodulated optical signal and the second unmodulated optical signal.

12. 12. The apparatus of claim 10 or 11, wherein the second coupler is further configured to split the third unmodulated optical signal having undergone polarization control into a fifth unmodulated optical signal, the fifth unmodulated optical signal being used for coherence detection of the first modulated optical signal, and the first modulated optical signal being the optical signal transmitted by the first optical transmission device to the second optical transmission device.

13. 13. The apparatus of claim 12, further comprising: a second receiver module coupled to both the second circulator and the second coupler and configured to receive the first modulated optical signal from the first optical transmission device via the second circulator and to receive the fifth unmodulated optical signal from the second coupler.

14. The apparatus of any one of claims 10 to 13, wherein the second polarization control module is further coupled to the second transmission module and configured to control the polarization of the second unmodulated optical signal.

15. further comprising a third circulator; the second polarization control module being coupled to the second coupler includes the second polarization control module being coupled to the second coupler via the third circulator; 15. The apparatus of claim 14, wherein the second polarization control module being further coupled to the second transmission module comprises the second polarization control module being further coupled to the second transmission module via the third circulator.

16. The first optical transmission device is an optical transmission device on an active antenna unit (AAU) side, and the second optical transmission device is an optical transmission device on a baseband unit (BBU) side, or The device according to any one of claims 8 to 15, wherein the first optical transmission device is an optical transmission device on a BBU side, and the second optical transmission device is an optical transmission device on an AAU side.

17. An optical transmission method, the method being applied to a first optical transmission device, the device including a first circulator and a first receiving module, the method comprising: receiving, by the first circulator, a second unmodulated optical signal from a second optical transmission device; receiving, by the first receiving module, a second modulated optical signal from the second optical transmission device and receiving the second unmodulated optical signal from the first circulator, wherein the second modulated optical signal is obtained by modulating a first unmodulated optical signal, the second unmodulated optical signal is used to perform coherence detection on the second modulated optical signal, the first unmodulated optical signal and the second unmodulated optical signal are obtained by separating a third unmodulated optical signal, and the third unmodulated optical signal is an optical signal supplied from the first optical transmission device to the second optical transmission device; The method includes:

18. receiving a second unmodulated optical signal from a second optical transmission device by the first circulator, 18. The method of claim 17, comprising the step of receiving, by the first circulator, the second unmodulated optical signal from a second circulator, the first circulator being further coupled to the second circulator, and the second optical transmission device including the second circulator.

19. The method comprises: controlling the polarization of the second unmodulated optical signal with a first polarization control module, the apparatus further comprising: the first polarization control module coupled to the first circulator; 19. The method of claim 17 or 18, further comprising:

20. 20. The method of claim 19, wherein using the second unmodulated optical signal to perform coherence detection on the second modulated optical signal comprises using the second unmodulated optical signal with polarization control to perform coherence detection on the second modulated optical signal.

21. The method comprises: a step of controlling polarization of a first modulated optical signal by the first polarization control module, the first modulated optical signal being an optical signal transmitted from the first optical transmission device to the second optical transmission device; 21. The method of claim 19 or 20, further comprising:

22. The method comprises: transmitting the first modulated optical signal to the first polarization control module via the first circulator by a first transmission module, the apparatus further including the first transmission module, the first transmission module being coupled to the first circulator; 22. The method of claim 21 further comprising:

23. The first optical transmission device is an optical transmission device on an active antenna unit (AAU) side, and the second optical transmission device is an optical transmission device on a baseband unit (BBU) side, or The method according to any one of claims 17 to 22, wherein the first optical transmission device is an optical transmission device on a BBU side, and the second optical transmission device is an optical transmission device on an AAU side.

24. An optical transmission method, the method being applied to a second optical transmission device, the device including a second coupler, a second transmission module, and a second circulator, the method comprising: splitting the third unmodulated optical signal into at least a first unmodulated optical signal and a second unmodulated optical signal by the second coupler, the third unmodulated optical signal being an optical signal provided from a first optical transmission device; transmitting a second modulated optical signal to the first optical transmission device by the second transmission module, the second modulated optical signal being obtained by modulating the first unmodulated optical signal; receiving, by the second circulator, the second unmodulated optical signal from the second coupler and transmitting the second unmodulated optical signal to the first optical transmission device, the second unmodulated optical signal being used for coherence detection of the second modulated optical signal; The method includes:

25. The step of transmitting the second unmodulated optical signal to the first optical transmission device by the second circulator includes:

25. The method of claim 24, comprising the step of transmitting the second unmodulated optical signal by the second circulator to a first circulator, the second circulator being further coupled to the first circulator, and the first optical transmission device including the first circulator.

26. The method comprises: controlling the polarization of the third unmodulated optical signal with a second polarization control module, the apparatus further comprising: the second polarization control module coupled to the second coupler; 26. The method of claim 24 or 25, further comprising:

27. The step of splitting the third unmodulated optical signal into at least a first unmodulated optical signal and a second unmodulated optical signal by the second coupler includes:

27. The method of claim 26, comprising splitting the third unmodulated optical signal with polarization control by the second coupler into at least the first unmodulated optical signal and the second unmodulated optical signal.

28. The method comprises: a step of splitting the third unmodulated optical signal, which has been subjected to polarization control, into a fifth unmodulated optical signal by the second coupler, the fifth unmodulated optical signal being used for coherence detection of a first modulated optical signal, and the first modulated optical signal being an optical signal transmitted from the first optical transmission device to the second optical transmission device; 28. The method of claim 26 or 27, further comprising:

29. The method comprises: receiving, by a second receiving module, the first modulated optical signal from the first optical transmission device via the second circulator and the fifth unmodulated optical signal from the second coupler, the device further including a second receiving module, the second receiving module being coupled to both the second circulator and the second coupler; 30. The method of claim 28, further comprising:

30. The method according to any one of claims 26 to 29, further comprising a step of controlling the polarization of the second modulated optical signal by the second polarization control module, the second polarization control module being further coupled to the second transmission module.

31. The first optical transmission device is an optical transmission device on an active antenna unit (AAU) side, and the second optical transmission device is an optical transmission device on a baseband unit (BBU) side, or The method according to any one of claims 24 to 30, wherein the first optical transmission device is an optical transmission device on a BBU side, and the second optical transmission device is an optical transmission device on an AAU side.

32. A computer-readable storage medium, the computer-readable storage medium storing a program, the program being capable of executing the method according to any one of claims 17 to 23 or claims 24 to 31 when called by a processor.

33. A computer program product comprising instructions which, when invoked by a processor, perform the method of any one of claims 17 to 23 or claims 24 to 31.

34. A communication system comprising: a first optical transmission device according to any one of claims 1 to 7; and a second optical transmission device according to any one of claims 8 to 16.

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