Optical communication device, point-to-multipoint optical communication system, and method of processing optical signals

Abstract

Disclosed are an optical communication device, a point-to-multipoint optical communication system and a processing method of an optical signal. The device comprises an optical source module and a coherent receiver. The optical source module is configured to provide a local optical signal comprising N single-frequency optical signals with different frequencies; the coherent receiver is configured to receive a target optical signal and the local optical signal, the target optical signal comprising M subcarriers, M≤N; based on the target optical signal and the local optical signal, a plurality of beat signals are obtained, the plurality of beat signals comprising M first beat signals, each first beat signal being obtained by beating one subcarrier and one single-frequency optical signal, and different first beat signals corresponding to different subcarriers and different single-frequency optical signals, the power of a first subcarrier being greater than the power of a second subcarrier, and the power of a single-frequency optical signal corresponding to the first subcarrier being less than the power of a single-frequency optical signal corresponding to the second subcarrier. The device can process subcarriers with large power difference received to obtain electrical signals with close power.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to an optical communication device, a point-to-multipoint (P2MP) optical communication system, and a method for processing optical signals. Background Technology

[0002] P2MP optical communication systems, such as passive optical networks (PON) systems, typically include a central node, an optical distribution network (ODN), and multiple leaf nodes. The central node is connected to the multiple leaf nodes through the ODN.

[0003] In related technologies, multiple leaf nodes transmit burst optical signals to the central node in different time slots. Due to the different path insertion losses from each leaf node to the central node, the power of the burst optical signals received by the central node from different leaf nodes varies. For a P2MP optical communication system based on coherent optical communication technology, the central node includes a coherent receiver and a local oscillator (LO). The LO provides a local optical signal, which is a single-frequency optical signal. The coherent receiver receives the target optical signal and the local optical signal provided by the LO. The target optical signal includes burst optical signals transmitted by multiple leaf nodes. Based on the target optical signal and the local optical signal, the corresponding electrical signal of the target optical signal is obtained. By adjusting the power of the local optical signal, different gains can be applied to the burst optical signals with different powers in the target optical signal, thereby making the power of the electrical signals corresponding to the burst optical signals received in different time slots similar.

[0004] However, when the target optical signal comprises multiple subcarriers, the power of the burst optical signal carried by different subcarriers in the same time slot may differ. In this case, even adjusting the power of the local optical signal cannot eliminate the power difference of the burst optical signal carried by each subcarrier in the same time slot, resulting in higher requirements for the subsequent electrical signal processing module. Summary of the Invention

[0005] This application provides an optical communication device, a P2MP optical communication system, and a method for processing optical signals. The optical communication device can process received burst optical signals with large power differences to obtain electrical signals with similar power, thereby reducing the requirements for the electrical signal processing module.

[0006] In a first aspect, this application provides an optical communication device. The optical communication device includes a light source module and a coherent receiver. The light source module provides a local optical signal, which includes N single-frequency optical signals, each with a different frequency, where N is greater than 1 and is an integer. The coherent receiver receives a target optical signal and the local optical signal. The target optical signal includes M subcarriers, where M is a positive integer and M is less than or equal to N. Based on the target optical signal and the local optical signal, multiple beat frequency signals are obtained. These multiple beat frequency signals include M first beat frequency signals, each of which is obtained by beating one of the M subcarriers with one of the N single-frequency optical signals. Different first beat frequency signals correspond to different subcarriers and different single-frequency optical signals. Among the M subcarriers, the power of the first subcarrier is greater than the power of the second subcarrier, and the power of the first single-frequency optical signal corresponding to the first subcarrier is less than the power of the second single-frequency optical signal corresponding to the second subcarrier. The first subcarrier and the second subcarrier are any two subcarriers out of the M subcarriers.

[0007] By including multiple single-frequency optical signals in the local optical signal, where the number of single-frequency optical signals is greater than or equal to the number of subcarriers in the target optical signal, each subcarrier can beat with a corresponding single-frequency optical signal to obtain a first beat frequency signal. The power of the first beat frequency signal corresponding to the subcarrier can be controlled by adjusting the power of the single-frequency optical signal. When the power of the first subcarrier is greater than the power of the second subcarrier, by making the power of the first single-frequency optical signal corresponding to the first subcarrier less than the power of the second single-frequency optical signal corresponding to the second subcarrier, compared to using single-frequency optical signals of the same power for beating with the first and second subcarriers, the power difference between the first beat frequency signal corresponding to the first subcarrier and the first beat frequency signal corresponding to the second subcarrier can be reduced. This enables a large dynamic range reception in the optical communication device and helps reduce the requirements of subsequent electrical signal processing modules.

[0008] Optionally, the power difference between any two of the M first beat frequency signals is less than a power difference threshold, which can be 0dB-5dB. For example, the power difference threshold could be 1dB, 2dB, or 3dB. Ideally, the power difference between any two first beat frequency signals is zero. This minimizes the power difference between the M first beat frequency signals, reducing the requirements on subsequent electrical signal processing modules.

[0009] Optionally, the frequencies of the M first beat frequency signals are located within the receiving bandwidth of the coherent receiver, and the frequencies of the beat frequency signals other than the M first beat frequency signals are located outside the receiving bandwidth of the coherent receiver.

[0010] Because multiple single-frequency signals exist, each single-frequency signal will beat with a subcarrier in the target optical signal, generating a beat frequency signal. If multiple beat frequency signals corresponding to a subcarrier are all within the receiving bandwidth of the coherent receiver, mutual interference will occur, affecting the receiving performance of the coherent receiver. Therefore, it is necessary to ensure that the frequencies of the beat frequency signals, except for the M-channel first beat frequency signal, are outside the receiving bandwidth of the coherent receiver.

[0011] To obtain the positional relationship between the frequency of the aforementioned beat frequency signal and the receiving bandwidth of the coherent receiver, it is necessary to perform spectral design on the center frequency of each subcarrier and the frequency of each single-frequency optical signal, so that the center frequency of each subcarrier and the frequency of each single-frequency optical signal satisfy the following conditions:

[0012] Condition 1: The interval between the center frequency of the target subcarrier and the frequency of the nearest single-frequency optical signal in the frequency domain is less than the difference between the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier, wherein the target subcarrier is any one of the M subcarriers.

[0013] Condition 2: The interval between the center frequency of the target subcarrier among the M subcarriers and the frequency of the single-frequency optical signal that is the second closest in the frequency domain is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier. The target subcarrier is any one of the M subcarriers; where "second closest" means the second closest.

[0014] Condition 3: The frequency interval between any two adjacent single-frequency optical signals in the frequency domain among the N single-frequency optical signals is greater than the single-side bandwidth of the coherent receiver.

[0015] When a leaf node transmits optical signals using a real-number coherent transmitter, the transmitted optical signal includes subcarriers and corresponding conjugate subcarriers. In this case, the target optical signal also includes a conjugate subcarrier of at least one of the M subcarriers. The interval between the center frequency of the conjugate subcarrier and the frequency of the reference single-frequency optical signal is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the conjugate subcarrier. The reference single-frequency optical signal is the single-frequency optical signal whose center frequency is the second closest in the frequency domain to the center frequency of the subcarrier corresponding to the conjugate subcarrier. This ensures that the frequencies of the beat frequencies of the conjugate subcarriers and other single-frequency optical signals (excluding the single-frequency optical signal whose center frequency is the closest in the frequency domain to its corresponding subcarrier) are outside the receiving bandwidth of the coherent receiver, thus avoiding interference from the beat frequency signals of the conjugate subcarriers to the first beat frequency signal.

[0016] When leaf nodes use real coherent transmitters to send single-carrier real optical signals such as binary phase shift keying (BPSK) or 4-level pulse amplitude modulation (PAM4), the real optical signals contain mutually conjugate symmetrical positive and negative frequency components, which are equivalent to the description of subcarriers and conjugate subcarriers mentioned above. Therefore, the above description based on subcarriers and conjugate subcarriers is also applicable to single-carrier real signals.

[0017] Optionally, the light source module includes a beam combiner and N light-emitting units. Each light-emitting unit provides a single-frequency optical signal. The beam combiner combines the single-frequency optical signals provided by the N light-emitting units into a single signal to obtain the local optical signal. By having the N light-emitting units provide single-frequency optical signals respectively, the power of each single-frequency optical signal can be independently controlled.

[0018] Optionally, the optical communication device further includes a detection module and a control module. The detection module is used to detect the power of each first beat frequency signal, and the control module is used to control the power of the single-frequency optical signal corresponding to each first beat frequency signal based on the power of the first beat frequency signal. This ensures that the power difference between the M first beat frequency signals obtained after beating each subcarrier with its corresponding single-frequency optical signal is small.

[0019] In one possible implementation, the light-emitting unit includes a laser for emitting the single-frequency optical signal. The control module is used to control the temperature of the laser and / or the drive current of the laser to control the power of the single-frequency optical signal emitted by the laser.

[0020] In another possible implementation, the light-emitting unit includes a laser and a power regulator, the power regulator being located in the optical path between the laser and the coherent receiver. The power regulator is used to receive the light beam emitted by the laser and, under the control of the control module, adjust the power of the received light beam to obtain the single-frequency optical signal.

[0021] Through the two implementation methods described above, independent control of the power of each single-frequency optical signal can be achieved.

[0022] Optionally, the detection module is further configured to detect the frequency offset of the single-frequency optical signal, and the control module is further configured to adjust the center frequency of the laser corresponding to the single-frequency optical signal according to the frequency offset detected by the detection module. When the frequency offset of the single-frequency optical signal is too large, it may cause the spectrum of multiple first beat frequency signals to overlap, affecting the data transmission performance. Therefore, it is necessary to detect the frequency offset of the single-frequency optical signal and adjust the center frequency of the laser corresponding to each single-frequency optical signal according to the detected frequency offset.

[0023] Optionally, any one of the M subcarriers includes a burst optical signal transmitted by a leaf node, or includes burst optical signals transmitted by multiple leaf nodes in a time-division multiplexing manner.

[0024] Optionally, the optical communication device can be an optical module, an optical line terminal, an optical transport network device, or a switching device.

[0025] Secondly, a P2MP optical communication system is provided, including a central node, an ODN, and multiple leaf nodes, with intermediate nodes connected to each leaf node via the ODN. The central node includes any of the aforementioned optical communication devices.

[0026] Thirdly, a method for processing optical signals is provided, which can be executed by the aforementioned coherent receiver. The method includes: receiving a local optical signal and a target optical signal, wherein the local optical signal includes N single-frequency optical signals with different frequencies, and the target optical signal includes M subcarriers, where N is greater than 1 and is an integer, and M is a positive integer less than or equal to N; based on the target optical signal and the local optical signal, obtaining multiple beat frequency signals, the multiple beat frequency signals including M first beat frequency signals, each of the M first beat frequency signals being obtained by beating one subcarrier from the M subcarriers with one single-frequency optical signal from the N single-frequency optical signals, and different first beat frequency signals corresponding to different subcarriers and different single-frequency optical signals, wherein among the M subcarriers, the power of the first subcarrier is greater than the power of the second subcarrier, and the power of the first single-frequency optical signal corresponding to the first subcarrier is less than the power of the second single-frequency optical signal corresponding to the second subcarrier. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a P2MP optical communication system provided in an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of another P2MP optical communication system provided in an embodiment of this application;

[0029] Figure 3This is a schematic diagram of another P2MP optical communication system provided in the embodiments of this application;

[0030] Figure 4 This is a schematic diagram of the structure of an optical communication device provided in an embodiment of this application;

[0031] Figure 5 This is a schematic diagram of the structure of another optical communication device provided in an embodiment of this application;

[0032] Figure 6 yes Figure 5 Schematic diagram of a coherent receiver;

[0033] Figure 7 yes Figure 5 A schematic diagram of the signal spectrum during the communication process between the leaf node and the optical communication device;

[0034] Figure 8 This is a schematic diagram of the signal spectrum during the communication process between leaf nodes and optical communication devices in related technologies;

[0035] Figure 9 This is a schematic diagram of another light source module provided in an embodiment of this application;

[0036] Figure 10 This is a schematic diagram of another light source module provided in the embodiments of this application;

[0037] Figure 11 yes Figure 5 Another spectrum diagram of the signal during the communication process between the leaf node and the optical communication device;

[0038] Figure 12 This is a schematic diagram of the structure of another optical communication device provided in an embodiment of this application;

[0039] Figure 13 yes Figure 12 A schematic diagram of the signal spectrum during the communication process between the leaf node and the optical communication device;

[0040] Figure 14 This is a schematic diagram of the structure of a coherent transmitter;

[0041] Figure 15 This is a schematic diagram of another type of coherent transmitter;

[0042] Figure 16 This is a schematic diagram of the structure of another type of coherent transmitter;

[0043] Figure 17 yes Figure 12 Another spectrum diagram of the signal during the communication process between the leaf node and the optical communication device;

[0044] Figure 18yes Figure 12 Another spectrum diagram of the signal during the communication process between the leaf node and the optical communication device;

[0045] Figure 19 yes Figure 12 Another spectrum diagram of the signal during the communication process between the leaf node and the optical communication device;

[0046] Figure 20 This is a schematic flowchart of an optical signal processing method provided in an embodiment of this application. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0048] Figure 1 This is a schematic diagram of the structure of a P2MP optical communication system provided in an embodiment of this application. Figure 1 As shown, the P2MP optical communication system includes a central node P, an optical distribution network (ODN), and multiple leaf nodes MP. The ODN includes a passive optical splitter S (hereinafter referred to as the splitter) for optical power distribution, a trunk fiber connecting the splitter S and the central node P, and branch fibers connecting the splitter S and the leaf nodes MP.

[0049] Figure 1 The example provided illustrates three leaf nodes MP1-MP3 and a beam splitter S comprising one common port and three branch ports. In implementation, the number of branch ports of the beam splitter and the number of connected leaf nodes can be adjusted according to actual needs; this embodiment does not impose any limitations on this.

[0050] Figure 2 This is a schematic diagram of another P2MP optical communication system provided in an embodiment of this application. For example... Figure 2 As shown, the P2MP optical communication system includes a central node P, an ODN, and multiple leaf nodes MP. The ODN includes optical fibers and two cascaded 1:8 optical splitters S.

[0051] The central node P is connected to the common port of the first-stage 1:8 optical splitter S1 via optical fiber. One branch port of the first-stage 1:8 optical splitter S1 is connected to the common port of a second-stage 1:8 optical splitter S2 via optical fiber. The two branch ports of each second-stage 1:8 optical splitter S2 are each connected to a leaf node MP via optical fiber.

[0052] Figure 2The example provided uses a two-stage beam splitter, but more beam splitters can be cascaded. Furthermore, the beam splitter can also be a 1:X beam splitter, where X is any integer other than 8, such as X equal to 2, 3, or 4, etc.

[0053] also, Figure 2 In this embodiment, a portion of the branch ports of the first-stage optical splitter are connected to the second-stage optical splitter, and another portion of the branch ports are connected to the leaf node MP. In other embodiments, all branch ports of the first-stage optical splitter are connected to the second-stage optical splitter. The central node P is connected to the common port of the first-stage 1:8 optical splitter S1 via optical fiber. Each branch port of the first-stage 1:8 optical splitter S1 is connected to the common port of a second-stage 1:8 optical splitter S2 via optical fiber. Each branch port of each second-stage 1:8 optical splitter S2 is connected to a leaf node MP via optical fiber. In this case, the eight second-stage 1:8 optical splitters have a total of 64 branch ports, which can connect to 64 leaf nodes MP.

[0054] When implemented, Figure 1 and Figure 2 The P2MP optical communication system can be applied to optical access networks. The central node P is an optical line terminal (OLT), which typically connects to upstream network-side equipment (such as switches and routers). The leaf nodes MP1-MP3 are optical network units (ONUs) or optical network terminals (ONTs).

[0055] Figure 3 This is a schematic diagram of another P2MP optical communication system provided in the embodiments of this application. For example... Figure 3 As shown, the P2MP optical communication system includes a central node P, an ODN, and multiple leaf nodes MP1-MP3. The ODN comprises Y cascaded 1:2 optical splitters, where Y is an integer greater than 1.

[0056] Each 1:2 splitter includes one common port and two branch ports. The common port of the first-stage 1:2 splitter S1 is connected to the central node P, one branch port of the first-stage 1:2 splitter S1 is connected to the leaf node MP1, and the other branch port of the first-stage 1:2 splitter S1 is connected to the common port of the second-stage 1:2 splitter S2. The common port of the i-th stage splitter is connected to one branch port of the (i-1)-th stage splitter, one branch port of the i-th stage splitter is connected to the leaf node MPi, and the other branch port of the i-th stage splitter is connected to the common port of the (i+1)-th stage splitter. Here, i is an integer, and 1 < i ≤ Y.

[0057] Figure 3The example given uses Y equal to 3, but in practical applications, Y can also equal 4 or 5, etc. Furthermore, Figure 3 The diagram illustrates the number of branch ports per stage of the optical splitter as 2. In practical applications, the number of branch ports of the optical splitter can be more, such as 3, 4, 6 or 8, etc.

[0058] When implemented, Figure 3 The P2MP optical communication system can be applied to optical transport networks, such as metropolitan area aggregation rings. The central node P can be an OTN device or switching device at the aggregation site, and the leaf nodes MP1-MP3 are OTN devices or switching devices at the access sites.

[0059] exist Figure 1-3 In the P2MP optical communication system shown, in the downlink direction, the downlink signal sent by the central node P is transmitted to each leaf node MP through the ODN. The leaf node MP selectively receives downlink data belonging to itself from the downlink signal. In the uplink direction, the uplink signals sent by multiple leaf node MPs are combined by the ODN into a single optical signal and transmitted to the central node P. In the uplink direction, the central node P receives burst optical signals from all leaf node MPs. Due to the different fiber lengths and / or splitter stages between each leaf node MP and the central node P, the corresponding path insertion losses are also different, and the power of the burst optical signals received by the central node P from different leaf node MPs is usually different.

[0060] For example, in Figure 1 In this configuration, the three leaf nodes MP1-MP3 have the same number of splitter stages (single-stage) to the central node P, but the fiber lengths from leaf nodes MP1, MP2, and MP3 to the splitter S increase sequentially. In this case, the path insertion loss of leaf nodes MP1, MP2, and MP3 increases sequentially.

[0061] For example, in Figure 2 In this configuration, there is a first-stage optical splitter between leaf node MP1 and the central node P, and second-stage optical splitters between leaf nodes MP2 and MP3 and the central node P. The total length of the optical fiber between leaf node MP3 and the central node P is the longest, while the total length of the optical fiber between leaf node MP1 and the central node P is the shortest. In this case, the path insertion loss of leaf nodes MP1, MP2, and MP3 increases sequentially.

[0062] For example, in Figure 3In this configuration, there is a first-stage optical splitter between leaf node MP1 and the central node P, a second-stage optical splitter between leaf node MP2 and the central node P, and a third-stage optical splitter between leaf node MP3 and the central node P. The total length of the optical fiber between leaf node MP3 and the central node P is the longest, while the total length of the optical fiber between leaf node MP1 and the central node P is the shortest. In this case, the path insertion loss of leaf nodes MP1, MP2, and MP3 increases sequentially.

[0063] exist Figure 1-3 In the diagram, the height of the rectangular block represents the signal power. It can be seen that the rectangular blocks corresponding to each leaf node MP1-MP3 have the same height, indicating that the signal power transmitted by each leaf node MP1-MP3 is comparable. The signal power received by the central node P from leaf node MP3 is the lowest, while the signal power from leaf node MP1 is the highest.

[0064] In the embodiments of this application, the P2MP optical communication systems shown are all P2MP optical communication systems based on coherent optical communication. In the uplink direction, this P2MP optical communication system supports both time division multiple access (TDMA) and frequency division multiple access (FDMA). Different leaf nodes can occupy different time slots and / or different subcarriers to transmit signals.

[0065] Figure 1-3 In the diagram, horizontal arrows represent time slots, and diagonal arrows represent subcarriers. The dimensions of time slots and subcarriers together form a two-dimensional time-frequency resource table. As long as different leaf nodes occupy different time-frequency resources in the uplink direction, the P2MP optical communication system can function normally.

[0066] Leaf node MP1 transmits a signal via subcarrier f1 in time slot t1, leaf node MP2 transmits a signal via subcarrier f1 in time slot t2, and leaf node MP3 transmits a signal via subcarrier f2 in both time slots t1 and t2. In this case, the communication between leaf nodes MP1 and MP2 is TDMA, and the communication between leaf nodes MP3 and MP1, as well as between leaf nodes MP3 and MP2, is FDMA. This simultaneous presence of TDMA and FDMA can be called Time and Frequency Division Multiple Access (TFDMA).

[0067] In this embodiment, the power difference of burst optical signals from different leaf nodes that the central node needs to support is referred to as the dynamic range. For current access networks, an ODN typically includes two 1:8 splitters plus a 20km fiber length difference, resulting in a 15dB power difference; the output optical power of the leaf nodes themselves also varies, fluctuating within a 5dB range. The maximum dynamic range resulting from the combination of these two factors is 20dB. Therefore, the central node typically needs to support a dynamic range of 15dB-20dB.

[0068] In a P2MP optical communication system employing TFDMA, power differences exist not only between burst optical signals in different time slots but also between burst optical signals on different subcarriers within the same time slot. If the central node directly converts the received burst optical signals into electrical signals, the resulting electrical signals at each leaf node will have different powers. This necessitates that subsequent electrical signal processing modules be able to handle signals with large power differences, placing higher demands on these modules. Typically, electrical signal processing modules include analog-to-digital converters (ADCs). When the power difference between two electrical signals is too large, the higher-power signal may saturate / truncate unnecessarily, incurring nonlinearity costs; the lower-power signal may not fully utilize the ADC's quantization bit width, incurring low-precision quantization costs. For example, with a dynamic range of 20dB, the maximum amplitude difference between electrical signals is 10dB. The quantization bit widths required for higher-power and lower-power signals differ by a factor of 10. Therefore, while avoiding nonlinearity costs associated with higher-power signals, quantization costs are unavoidable. Furthermore, the out-of-band components caused by nonlinear spectral broadening and transmitter noise floor can lead to crosstalk between adjacent subcarriers, and the out-of-band components of high-power electrical signals can also cause crosstalk between low-power electrical signals. These overheads are difficult for electrical signal processing modules to eliminate.

[0069] Therefore, embodiments of this application provide an optical communication device that can amplify and convert received burst optical signals with large power differences to obtain electrical signals with similar power, thereby reducing the requirements on the electrical signal processing module.

[0070] Optionally, the optical communication device provided in this application embodiment can be the aforementioned central node or an optical module disposed in the central node.

[0071] Figure 4 This is a schematic diagram of the structure of an optical communication device provided in an embodiment of this application. Figure 4As shown, the optical communication device includes a light source module 41 and a coherent receiver 42. The light source module 41 provides a local optical signal, which includes N single-frequency optical signals with different frequencies, where N is greater than 1 and is an integer. The coherent receiver 42 receives a target optical signal and the local optical signal. The target optical signal includes M subcarriers, where M is a positive integer and M is less than or equal to N. Beat frequency processing is performed on the M subcarriers and the N single-frequency optical signals to obtain multiple beat frequency signals. These multiple beat frequency signals include M first beat frequency signals, each obtained by beating one subcarrier and one single-frequency optical signal. Different first beat frequency signals correspond to different subcarriers and different single-frequency optical signals. Among the M subcarriers, the power of the first subcarrier is greater than the power of the second subcarrier, and the power of the first single-frequency optical signal corresponding to the first subcarrier is less than the power of the second single-frequency optical signal corresponding to the second subcarrier. The first subcarrier and the second subcarrier are any two subcarriers from the M subcarriers. The first single-frequency optical signal corresponding to the first subcarrier is a single-frequency optical signal obtained by beating the first subcarrier to obtain the corresponding first beat frequency signal. The second single-frequency optical signal corresponding to the second subcarrier is a single-frequency optical signal obtained by beating the second subcarrier to obtain the corresponding first beat frequency signal.

[0072] In this embodiment, the receiving bandwidth of the coherent receiver 42 refers to the spectral range of the optical signal that the coherent receiver can effectively detect and demodulate. In implementation, the receiving bandwidth of the coherent receiver can be determined by the hardware capabilities of the coherent receiver (including the bandwidth of the photoelectric conversion device, the bandwidth of the transimpedance amplifier, and the sampling rate of the ADC, etc.) and subsequent digital signal processing capabilities. For example, the receiving bandwidth of the coherent receiver can be tens to hundreds of GHz on a single side.

[0073] In the embodiments of this application, a single-frequency optical signal refers to an optical signal with a sufficiently narrow linewidth, for example, an optical signal with a linewidth of less than 1 MHz.

[0074] In this embodiment, by including multiple single-frequency optical signals in the local optical signal, and ensuring that the number of single-frequency optical signals is greater than or equal to the number of subcarriers in the target optical signal, each subcarrier can beat with a corresponding single-frequency optical signal to obtain a first beat frequency signal. By controlling the power of this single-frequency optical signal, the power of the first beat frequency signal corresponding to the subcarrier can be controlled. When the power of the first subcarrier is greater than the power of the second subcarrier, by making the power of the first single-frequency optical signal corresponding to the first subcarrier less than the power of the second single-frequency optical signal corresponding to the second subcarrier, compared to using single-frequency optical signals of the same power for beating with the first and second subcarriers, the power difference between the first beat frequency signal corresponding to the first subcarrier and the first beat frequency signal corresponding to the second subcarrier can be reduced. This enables large dynamic range reception in the optical communication device and reduces the requirements for subsequent electrical signal processing modules. Furthermore, the optical communication device does not need to interact with leaf nodes during the large dynamic range reception process, requiring minimal protocol modifications and is easy to implement.

[0075] In implementation, by adjusting the power of the first single-frequency optical signal corresponding to each subcarrier, the power difference between any two of the M first beat frequency signals can be made less than a power difference threshold, that is, the power of the M first beat frequency signals is made close. This power difference threshold can be set according to the performance requirements of the central node, and this application does not impose any restrictions on it. For example, the power difference threshold can be 0dB-5dB. For instance, the power difference threshold could be 1dB, 2dB, or 3dB, etc. Ideally, the power difference between any two first beat frequency signals is equal to 0.

[0076] Optionally, the light source module 41 includes a beam combiner 411 and N light-emitting units 412. Each light-emitting unit 412 is used to provide one single-frequency optical signal. The beam combiner 411 is used to combine the single-frequency optical signals provided by the N light-emitting units 412 into one signal to obtain a local optical signal. By providing single-frequency optical signals by the N light-emitting units respectively, the power of each single-frequency optical signal can be controlled independently.

[0077] In implementation, the light-emitting unit 412 includes at least a laser. In the embodiments of this application, the laser may also be referred to as a local oscillator (LO).

[0078] This application does not limit the type of laser used in its embodiments. Distributed feedback (DFB) lasers, distributed Bragg reflector (DBR) lasers, external cavity lasers (ECL), micro-ring resonator lasers, or other narrow-linewidth fiber lasers can be used.

[0079] In the embodiments of this application, the M subcarriers are transmitted by different leaf nodes in the same time slot. For the same subcarrier, it can be transmitted by the same leaf node or by different leaf nodes in different time slots. That is, the same subcarrier can be transmitted by multiple leaf nodes in a time-division multiplexing manner.

[0080] In this embodiment, the frequencies of the M first beat frequency signals are within the receiving bandwidth of the coherent receiver, while the frequencies of the beat frequency signals other than the M first beat frequency signals are outside the receiving bandwidth of the coherent receiver. Since there are multiple single-frequency signals, each single-frequency signal will beat with a subcarrier in the target optical signal, generating a beat frequency signal. If multiple beat frequency signals corresponding to a subcarrier are all within the receiving bandwidth of the coherent receiver, mutual interference will occur, affecting the receiving performance of the coherent receiver. Therefore, it is necessary to ensure that the frequencies of the beat frequency signals other than the M first beat frequency signals are outside the receiving bandwidth of the coherent receiver.

[0081] To obtain the positional relationship between the frequency of the aforementioned beat frequency signal and the receiving bandwidth of the coherent receiver, it is necessary to perform spectral design on the center frequency of each subcarrier and the frequency of each single-frequency optical signal, so that the center frequency of each subcarrier and the frequency of each single-frequency optical signal satisfy the following conditions:

[0082] Condition 1: The interval between the center frequency of the target subcarrier and the frequency of the nearest single-frequency optical signal in the frequency domain is less than the difference between the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier, wherein the target subcarrier is any one of the M subcarriers.

[0083] Condition 2: The interval between the center frequency of the target subcarrier among the M subcarriers and the frequency of the single-frequency optical signal that is the second closest in the frequency domain is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier. The target subcarrier is any one of the M subcarriers. Here, "second closest" means the second closest.

[0084] Condition 3: The frequency interval between any two adjacent single-frequency optical signals in the frequency domain among the N single-frequency optical signals is greater than the single-side bandwidth of the coherent receiver.

[0085] When the center frequencies of each subcarrier and the frequencies of each single-frequency optical signal satisfy condition one, the frequency of the first beat signal generated by beating each subcarrier with the single-frequency optical signal that is closest in the frequency domain is within the receiving bandwidth of the coherent receiver. When the center frequencies of each subcarrier and the frequencies of each single-frequency optical signal satisfy condition two, the frequency of the beat signal generated by beating each subcarrier with the single-frequency optical signal that is not closest in the frequency domain is outside the receiving bandwidth of the coherent receiver. When the frequencies of each single-frequency optical signal satisfy condition three, the frequency of the beat signal generated by beating any two single-frequency optical signals is outside the receiving bandwidth of the coherent receiver.

[0086] Figure 5 This is a schematic diagram of another optical communication device provided in an embodiment of this application. Figure 5 As shown, the optical communication device includes a light source module 51 and a coherent receiver 52. The light source module 51 provides a local optical signal, which includes two single-frequency optical signals with different frequencies. The coherent receiver 52 receives a target optical signal and the local optical signal. The target optical signal includes two subcarriers; it performs beat frequency processing on the two subcarriers and the two single-frequency optical signals to obtain four beat frequency signals. These four beat frequency signals include two first beat frequency signals and two second beat frequency signals. The frequencies of the two first beat frequency signals are within the receiving bandwidth of the coherent receiver, and the power of the two first beat frequency signals is equal. The optical carriers and single-frequency optical signals corresponding to the two first beat frequency signals are different. The frequencies of the two second beat frequency signals are outside the receiving bandwidth of the coherent receiver.

[0087] Figure 5 The coherent receiver in this example is a standard coherent receiver. Figure 6 This is a schematic diagram of a standard coherent receiver. (For example...) Figure 6As shown, a standard coherent receiver includes a polarization beamsplitter, a beam splitter, two 90° mixers, and four photoelectric conversion circuits. The polarization beamsplitter splits the target optical signal into a first polarization state and a second polarization state, where both are linearly polarized light with perpendicular polarization directions. The beam splitter splits the local optical signal into two sub-optical signals. A 90° mixer mixes the first polarization state optical signal and one sub-optical signal to obtain two orthogonal first optical intermediate frequency (IF) signals. The two photoelectric conversion circuits are connected to the two outputs of the 90° mixer to perform photoelectric conversion on the two IF signals, obtaining two orthogonal digital electrical signals XI and XQ. Another 90° mixer is used to mix the optical signal of the second polarization state with another sub-optical signal to obtain two orthogonal second optical intermediate frequency signals. Two other photoelectric conversion circuits are connected to the two output terminals of the 90° mixer respectively to perform photoelectric conversion on the two second optical intermediate frequency signals to obtain two orthogonal digital electrical signals YI and YQ.

[0088] For example, each photoelectric conversion circuit includes a balanced photodetector (BPD), a trans-impedance amplifier (TIA), and an ADC. The input of the TIA is connected to the output of the BPD, and the output of the TIA is connected to the input of the ADC.

[0089] Optionally, the light source module 51 includes a beam combiner 511 and two light-emitting units 512. Each light-emitting unit 512 is used to provide one single-frequency optical signal. The beam combiner 511 is used to combine the single-frequency optical signals provided by the two light-emitting units 512 into one to obtain a local optical signal.

[0090] Optionally, such as Figure 5 As shown, the optical communication device also includes a detection module 53 and a control module 54. The detection module 53 is used to detect the power of each first beat frequency signal, and the control module 54 is used to control the power of the single-frequency optical signal corresponding to each first beat frequency signal based on the power of each first beat frequency signal determined by the detection module 53. In this way, the power difference between the M first beat frequency signals obtained after each subcarrier beats with the corresponding single-frequency optical signal can be minimized.

[0091] In one possible implementation, when the power difference between the two first beat frequency signals exceeds the aforementioned power difference threshold, the power of the single-frequency optical signal corresponding to the first beat frequency signal with lower power is increased and / or the power of the single-frequency optical signal corresponding to the first beat frequency signal with higher power is decreased. In practice, the power of the single-frequency optical signal can be adjusted according to a set step size. For example, the set step size could be 0.1 dB, etc.

[0092] In another possible implementation, the power of each subcarrier can be determined first based on the power of each first beat frequency signal and the power of each single-frequency optical signal; then, the target power of the single-frequency optical signal corresponding to the power of the subcarrier can be determined based on the power of each subcarrier and the mapping relationship between the power range of the subcarrier and the power of the single-frequency optical signal; finally, the power of the single-frequency optical signal can be adjusted according to the determined target power.

[0093] The light-emitting unit 512 includes a laser and a power regulator. The power regulator is located in the optical path between the laser and the coherent receiver 52 and is electrically connected to the control module 54. The power regulator is used to receive the light beam emitted by the laser and, under the control of the control module 54, adjust the power of the received light beam to obtain a single-frequency optical signal.

[0094] In practice, the detection module 53 detects the power of each first beat frequency signal in real time, and then the control module 54 calculates the power required by the single-frequency optical signal at the current moment (i.e. the gain required by each subcarrier), and controls the power of the corresponding single-frequency optical signal through the power regulator.

[0095] Alternatively, the power regulator can be a variable optical attenuator (VOA) or a semiconductor optical amplifier (SOA).

[0096] For example, the detection module 53 may include a digital signal processing (DSP) module. The control module 54 includes, but is not limited to, a DSP or a microcontroller unit (MCU). In implementation, the detection module 53 and the control module 54 may be integrated on the same physical chip, or they may be two separate physical chips.

[0097] Figure 7 yes Figure 5 The diagram shows the signal processing procedure of the optical communication device. Figure 5 (a)-(e) in the text represent respectively Figure 7 The location for spectrum acquisition of each signal. Figure 7 In the diagram, the vertical axis represents power; the greater the signal height, the greater the signal power. Solid lines represent single-frequency optical signals, and dashed lines represent frequency points (where there is no signal). In the following text, "spectrum" is short for the optical signal spectrum, and "electric spectrum" is short for the electrical signal spectrum.

[0098] Figure 7 Part (a) is the spectrum of the subcarriers transmitted by leaf node MP1. Figure 7 Part (b) is the spectrum of the subcarriers transmitted by leaf node MP2. The center frequency of the transmitting laser of leaf node MP1 is set to 193.3 THz, and leaf node MP1 transmits the left subcarrier with 193.3 THz as the reference point; the center frequency of the transmitting laser of leaf node MP2 is set to 193.5 THz, and leaf node MP2 transmits the right subcarrier with 193.5 THz as the reference point.

[0099] like Figure 5 As shown, the fiber length connected to leaf node MP1 is greater than that connected to leaf node MP2. Therefore, the insertion loss of the path corresponding to leaf node MP1 is larger. Consequently, in the target optical signal received by the coherent receiver of the optical communication device, the power of the subcarrier from leaf node MP1 is lower than the power of the subcarrier from leaf node MP2. Figure 7 As shown in part (c).

[0100] Figure 7 Part (d) is the spectrum of the local optical signal. For example... Figure 7 As shown in section (d), the frequency of the first single-frequency optical signal corresponding to the subcarrier transmitted by leaf node MP1 is 193.3 THz. That is, the center frequency of the laser in one light-emitting unit is set to 193.3 THz, aligned with the center frequency of the transmitting laser in leaf node MP1; the center frequency of the laser in the other light-emitting unit is set to 193.5 THz, aligned with the center frequency of leaf node MP2. The power of the first single-frequency optical signal corresponding to the subcarrier transmitted by leaf node MP1 is greater than the power of the second single-frequency optical signal corresponding to the subcarrier transmitted by leaf node MP2.

[0101] The coherent receiver detects the beat frequency between the single-frequency optical signal and the subcarrier, which can be viewed as the subcarrier undergoing down-conversion with the frequency of the single-frequency optical signal as a reference point. In this embodiment, since there are two single-frequency optical signals, the electrical signal actually detected by the coherent receiver is the superposition of the beat frequencies of the target optical signal and the two single-frequency optical signals, respectively, resulting in the following electrical spectrum: Figure 7 As shown in part (e).

[0102] The beat frequency results between the target optical signal and the first single-frequency optical signal are beat frequency signals 2 and 4, and the beat frequency results between the target optical signal and the second single-frequency optical signal are beat frequency signals 1 and 3. Note that beat frequency signals 1 and 2 correspond to the left subcarrier from leaf node MP1, and beat frequency signals 3 and 4 correspond to the right subcarrier from leaf node MP2. Furthermore, the beat frequency results between the first single-frequency optical signal and the second single-frequency optical signal are... Figure 7 The solid arrows in the diagram represent the signals. The beat frequencies of each subcarrier in both the single-frequency optical signal and the target optical signal are eliminated by the coherent receiver itself.

[0103] Figure 7 In section (e), the trapezoidal dashed box represents the receiving bandwidth of the coherent receiver. From Figure 7 As can be seen from part (e), the frequencies of beat frequency signals 2 and 3 are within the receiving bandwidth of the coherent receiver, while the frequencies of beat frequency signals 1 and 4 are outside the receiving bandwidth. Therefore, based on the above spectrum design, it is possible to ensure that only beat frequency signals 2 and 3 are within the receiving bandwidth of the coherent receiver, while beat frequency signals 1 and 4 are outside the receiving bandwidth. In other words, the coherent receiver ultimately detects only beat frequency signals 2 and 3. In the coherent receiver, the single-frequency optical signal can linearly amplify the optical carrier. Therefore, the power of beat frequency signals 2 and 3 can be controlled by the power of the first and second single-frequency optical signals, respectively. This allows the power of the first beat frequency signal corresponding to the subcarriers from leaf nodes MP1 and MP2 to be leveled on the electrical spectrum of the coherent receiver, thus achieving the reception of subcarriers with large power differences.

[0104] In related technologies, the local optical signal received by a coherent receiver consists of only a single-frequency optical signal. Figure 8 This is a schematic diagram illustrating the processing of the target optical signal by a coherent receiver when the local optical signal consists of only a single-frequency optical signal. For example... Figure 8 As shown in parts (a) and (b), the center frequency of the single-frequency optical signal is 193.4 THz, and the center frequency of the lasers at the leaf nodes MP1 and MP2 is also 193.4 THz. Figure 8 Part (c) is the spectrum of the target optical signal received by the coherent receiver. Figure 8 Part (d) is the spectrum of the local optical signal. Figure 8 Part (e) is the electrical spectrum of the beat frequency signal obtained by the coherent receiver. From Figure 8 As can be seen from part (e), the power of the beat frequency signal on the electric spectrum cannot be leveled out.

[0105] contrast Figure 7 and Figure 8 It can be seen that the main differences between the embodiments of this application and related technologies are: 1) In the embodiments of this application, the coherent receiver uses multiple light-emitting units, each light-emitting unit corresponding to one subcarrier, and the subcarrier power electrical domain leveling is achieved by controlling the power of the single-frequency optical signal provided by the light-emitting unit. 2) Through spectrum design, by utilizing the bandwidth limitation of the coherent receiver itself, it is ensured that the beat frequency signal (i.e., the first beat frequency signal) of each subcarrier with only one single-frequency optical signal falls within the receiving bandwidth of the coherent receiver. The beat frequency signal between any two single-frequency optical signals and the beat frequency signal between a single-frequency optical signal and other subcarriers fall outside the receiving bandwidth of the coherent receiver.

[0106] In this embodiment, each subcarrier is transmitted by one leaf node in the same time slot, and different subcarriers are transmitted by different leaf nodes. The same subcarrier is transmitted by the same leaf node or by multiple leaf nodes using time-division multiplexing, that is, multiple leaf nodes transmit optical signals through the subcarrier in different time slots.

[0107] Figure 9 This is a schematic diagram of another light source module provided in an embodiment of this application. For example... Figure 9 As shown, the detection module 53 is also used to detect the frequency offset of each single-frequency optical signal; the control module 54 is also used to adjust the center frequency of the laser corresponding to the single-frequency optical signal according to the frequency offset detected by the detection module 53.

[0108] When the center frequency of the laser has a frequency offset, the first beat frequency signal received by the coherent receiver may overlap, leading to a degradation in the receiver's performance. Therefore, it is necessary to detect and control the center frequency of the laser to stabilize the frequency of the single-frequency optical signal output by the laser, thereby avoiding frequency overlap in the first beat frequency signal received by the coherent receiver.

[0109] This application does not limit the method by which the detection module detects the frequency offset of the single-frequency optical signal; any related technology can be used. For example, the frequency offset can be estimated by analyzing the phase information of the first beat frequency signal. Another example is that the single-frequency optical signal can be optically mixed with a highly stable reference light source, and the frequency offset of the single-frequency optical signal can be determined based on the frequency change of the resulting beat frequency signal.

[0110] Optionally, the control module 54 is used to adjust the temperature of the laser and / or the drive current of the laser to adjust the center frequency of the laser. This can be achieved by heating the laser with a heater or cooling the laser with a semiconductor cooler.

[0111] It should be noted that for lasers with small center frequency offsets during operation, there is no need to detect the frequency offset of the single-frequency optical signal through a detection module or adjust the center frequency of the corresponding laser through a control module. For example, for ECLs, the center frequency of a coherent ECL can be locked to the dense wavelength division multiplexing (DWDM) frequency grid points specified by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) standard. Typically, the frequency offset does not exceed ±1.5 GHz, and as long as a guard interval greater than 3 GHz is provided, subcarrier overlap will not occur. Therefore, when the laser is an ECL, there is no need to detect the frequency offset of the single-frequency optical signal through a detection module or adjust the center frequency of the corresponding laser through a control module.

[0112] Figure 10 This is a schematic diagram of another light source module provided in an embodiment of this application. Figure 8 and Figure 9 The difference in the light source module is that, Figure 10 In this configuration, the light-emitting unit includes lasers (i.e., LO1 and LO2) but does not include a power regulator. The lasers are used to emit single-frequency optical signals; the control module 54 is electrically connected to the lasers and is used to control the temperature of the lasers and / or the drive current of the lasers to control the power of the single-frequency optical signals emitted by the lasers.

[0113] Optionally, the control module 54 is also used to control the frequency of the single-frequency optical signal emitted by the laser. In implementation, the control module can control the power and frequency of the single-frequency optical signal emitted by the laser by controlling the temperature of the laser and / or the drive current of the laser.

[0114] Figure 7 In this configuration, the center frequencies of the lasers emitting at leaf nodes MP1 and MP2 are equal to the center frequencies of the two lasers in the light source module, which are also equal to the center frequencies of the single-frequency optical signal. This controls the spectrum of the target optical signal received by the coherent receiver. In practical applications, the center frequencies of the lasers emitting at leaf nodes MP1 and MP2 can be set to other frequency values, achieving the same result. Figure 7 The spectrum of the target optical signal shown in section (c).

[0115] Figure 11 Part (a) is the spectrum of the subcarriers transmitted by leaf node MP1. Figure 11 Part (b) is the spectral diagram of the subcarriers transmitted by the leaf node MP2. For example... Figure 11As shown in parts (a) and (b), the center frequency of the transmitting laser of leaf node MP1 is set to 193.27THz, and leaf node MP1 directly transmits a baseband single-carrier signal with a single-sided bandwidth of 30GHz (double-sided bandwidth of 60GHz, which is only for illustration; in practice, the frequency guard interval can also be included in the single-sided bandwidth required by the signal); the center frequency of the transmitting laser of leaf node MP2 is set to 193.53THz, and leaf node MP2 also transmits a baseband single-carrier signal with a single-sided bandwidth of 30GHz.

[0116] Figure 11 Part (c) is the spectrum of the target optical signal received by the central node P. Figure 5 The spectrum shown in part (c) is the same. Figure 11 Part (d) is the spectrum of the local optical signal, and... Figure 5 The spectrum shown in part (d) is the same. Figure 11 Part (e) is the electrical spectrum of the beat frequency signal obtained by the coherent receiver, and... Figure 5 The spectrum shown in part (e) is the same. It can be seen that as long as the spectrum of the target optical signal received by the coherent receiver is as shown... Figure 11 As shown in part (c), by combining it with the corresponding local optical signal, the electrical spectrum of the required beat frequency signal can be obtained.

[0117] exist Figure 7 In the illustrated embodiment, if the single-sided bandwidth of the subcarrier transmitted by the leaf node is 30 GHz, then the transmitting laser of the leaf node needs to support a single-sided bandwidth of 60 GHz. And... Figure 11 In the illustrated embodiment, the transmitting laser at the leaf node needs to support a single-sided bandwidth of 30 GHz. Therefore, it can be seen that... Figure 11 In the illustrated embodiment, the requirements for the laser transmitter at the leaf node are relatively low.

[0118] Figure 12 This is a schematic diagram of another optical communication device provided in an embodiment of this application. Figure 5 The difference in the optical communication device shown is that, Figure 12 The light source module 51 of the optical communication device includes four light-emitting units 512. Correspondingly, the local optical signal provided by the light source module 51 includes four single-frequency optical signals. The four light-emitting units 512 correspond to four subcarriers respectively, and control the power of the corresponding single-frequency optical signal to flatten the power of the subcarriers on the spectrum within the receiving bandwidth of the coherent receiver, that is, to flatten the power of each first beat frequency signal.

[0119] The following is combined with Figure 13 The working process of the optical communication device will be explained. For ease of understanding, this embodiment will continue to use the [previous method / method]. Figure 5The embodiment shown illustrates how the center frequency of the laser at the leaf node is aligned with the center frequency of the laser in the corresponding light-emitting unit.

[0120] Figure 13 Parts (a)-(d) are the spectra of the subcarriers emitted by leaf nodes MP1-MP4, respectively. Figure 13 In sections (a)-(d), the dashed lines with arrows indicate the frequency points where the center frequency of the transmitting receiver of the leaf nodes is located, and the blank trapezoids indicate the unused frequency band of that subcarrier. The four leaf nodes MP1-MP4 transmit subcarriers 1-4 respectively. The center frequencies of the transmitting lasers of leaf nodes MP1-MP4 are 193.1THz, 193.3THz, 193.5THz and 193.7THz respectively.

[0121] Figure 13 Part (e) is the spectrum of the target optical signal received by the coherent receiver. For example... Figure 13 As shown in part (e), in the target optical signal, the power of subcarriers 1-4 increases sequentially.

[0122] Figure 13 Part (f) is the spectrum of the local optical signal. For example... Figure 13 As shown in section (f), the local optical signal includes four single-frequency optical signals with frequencies of 193.1 THz, 193.3 THz, 193.5 THz, and 193.7 THz, respectively. It can be seen that in this embodiment, the center frequencies of the transmitting lasers at the leaf nodes MP1-MP4 are aligned with the center frequencies of the corresponding single-frequency optical signals. The power of the four single-frequency optical signals decreases sequentially.

[0123] Figure 13 Part (g) shows the electrical spectrum of the beat frequency signal generated by the coherent receiver. After subcarriers 1-4 beat with the four single-frequency optical signals, theoretically each subcarrier will generate four beat frequency signals (which can be called images), and the power of each beat frequency signal is proportional to the power of each single-frequency optical signal. However, within the receiving bandwidth of the coherent receiver, only one beat frequency signal from each subcarrier will appear, and each beat frequency signal corresponds to a different single-frequency optical signal. Specifically, in this embodiment, the beat frequency signals 1-4 on the electrical spectrum within the receiving bandwidth of the coherent receiver originate from leaf nodes MP1-MP4, and their power corresponds to the power of the four single-frequency optical signals, respectively.

[0124] The four leaf nodes MP1-MP4 transmit subcarriers 1-4 respectively. Furthermore, the center frequency of the laser at the leaf node's transmitting end is aligned with the center frequency of the laser in the light source module (i.e., the center frequency of the single-frequency optical signal). These two conditions ensure that the beat frequency signals corresponding to subcarriers 1-4 within the coherent receiver's receiving bandwidth do not overlap. In this embodiment, firstly, the coherent receiver's receiving bandwidth must be wide enough to cover subcarriers 1-4; secondly, the coherent receiver's receiving bandwidth cannot be too wide, as it must be able to filter out the aforementioned non-target beat frequency items (non-target beat frequency items are beat frequency signals other than the first beat frequency signal). Typically, the receiving bandwidth of the coherent receiver is fixed, so it is generally achieved by reasonably selecting the spectral spacing between the single-frequency optical signals: the beat frequency signals (x≠y) of the subcarrier from leaf node MPx and the single-frequency optical signal LOy, as well as the beat frequencies of the single-frequency optical signal LOx and the single-frequency optical signal LOy (x≠y), do not fall within the coherent receiver's receiving bandwidth. In the embodiments of this application, the beat frequency of the single-frequency optical signal LOx and its own, and the beat frequency of the subcarrier from the leaf node MPx and its own, are eliminated by the detection principle of the coherent receiver, which is the same as that of the classic coherent receiver.

[0125] Therefore, in the embodiments of this application, the spectral distribution between each subcarrier and the single-frequency optical signal satisfies the following relationship so that the spectral distribution of the beat frequency signal generated by the coherent receiver satisfies: the frequency of the beat frequency signal of each single-frequency optical signal with only one subcarrier is within the receiving bandwidth of the coherent receiver, and the frequency of the beat frequency signal with other subcarriers or single-frequency optical signals is outside the receiving bandwidth of the coherent receiver.

[0126] 1. The interval between the center frequency of the target subcarrier and the frequency of the nearest single-frequency optical signal in the frequency domain is less than the difference between the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier. Here, the target subcarrier is any subcarrier in the target optical signal.

[0127] for example, Figure 13 In this context, the single-frequency optical signal closest to the frequency of subcarrier 1 from leaf node MP1 is LO1. To ensure that the beat frequency signal between subcarrier 1 from leaf node MP1 and the single-frequency optical signal LO1 falls within the receiving bandwidth of the coherent receiver, the left edge of the beat frequency signal must fall to the right of the left edge of the receiving bandwidth of the coherent receiver. Similarly, all subcarriers must satisfy this condition, thus ensuring that the frequency of each first beat frequency signal is within the receiving bandwidth of the coherent receiver.

[0128] 2. The frequency between the center frequency of the target subcarrier and the frequency of the next closest single-frequency optical signal in the frequency domain is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier.

[0129] for example, Figure 13In the context of MP2, subcarrier 2 has the closest single-frequency optical signal LO2 in the frequency domain, and the second closest single-frequency optical signal LO1. Therefore, in the electrical spectrum, the beat frequency signal between subcarrier 2 and LO1 needs to be filtered out by the receiving bandwidth of the coherent receiver. Among all the images from subcarrier 2 (i.e., beat frequency signals other than the first beat frequency signal), the image closest to the 0 frequency (i.e., the point with a frequency of 0) can be filtered out, thus filtering out all other images from subcarrier 2. This requires that the left edge of the spectrum of this beat frequency signal falls to the right of the right edge of the receiving bandwidth of the coherent receiver. Clearly, the interval between the center frequency of this beat frequency image and the 0 frequency is the interval between the center frequency of subcarrier 2 and the frequency of the single-frequency optical signal LO1. This ensures that all beat frequency signals except the first beat frequency signal are outside the receiving bandwidth of the coherent receiver.

[0130] 3. The minimum spacing between single-frequency optical signals is greater than the single-side bandwidth of the coherent receiver. This is to ensure that the beat frequency signal (e.g., between any two single-frequency optical signals) is within a certain range. Figure 13 The frequency (indicated by the solid arrow in section (g)) falls outside the receiving bandwidth of the coherent receiver.

[0131] In this embodiment, the frequency interval between any two adjacent single-frequency optical signals is equal, meaning that the frequencies of all single-frequency optical signals are arranged at equal intervals. In other embodiments, the frequencies of the individual single-frequency optical signals may also be arranged in a non-equal-interval manner.

[0132] It should be noted that, with Figure 11 The illustrated embodiments are similar, in obtaining Figure 13 In the case of the spectral distribution shown in part (e), the center frequency of the transmitting laser of the leaf node can be adjusted to reduce the bandwidth requirement of the transmitting laser of the leaf node. For example, if leaf node MP1 actually only transmits subcarrier 1, the center frequency of the transmitting receiver of leaf node MP1 can be set to the center frequency of subcarrier 1, and then the baseband single-carrier signal can be transmitted.

[0133] exist Figure 5 and Figure 12 In this model, each leaf node uses a standard coherent transmitter to transmit subcarriers. The following section combines... Figure 14 The structure of a standard coherent transmitter is described. For example... Figure 14As shown, a standard coherent transmitter includes a laser, a beam splitter, four modulation circuits, two IQ modulators, and a polarization coupler. Each modulation circuit includes a digital-to-analog converter (DAC) and a modulation driver. Each modulation circuit receives one digital signal; the digital signals received by the four modulation circuits correspond to orthogonal signals with X-polarization (XQ signals), in-phase signals with X-polarization (XI signals), orthogonal signals with Y-polarization (YQ signals), and in-phase signals with Y-polarization (YI signals), respectively. The laser emits a beam, and the beam splitter divides the emitted beam into two sub-beams. One IQ modulator modulates one sub-beam using the XI and XQ signals to obtain an X-polarized modulated optical signal; the other IQ modulator modulates the other sub-beam using the YI and YQ signals to obtain a Y-polarized modulated optical signal. The polarization coupler combines the X-polarized and Y-polarized modulated optical signals into an optical carrier and transmits this carrier.

[0134] In addition to leaf nodes employing standard coherent transmitters, the optical communication apparatus provided in this disclosure is also applicable to leaf nodes employing non-standard coherent transmitters (also known as simplified coherent transmitters). In this case, the cost of the leaf nodes can be reduced. In practical applications, within the same P2MP optical communication system, some leaf nodes may employ standard coherent transmitters, while others may employ non-standard coherent transmitters. These non-standard coherent transmitters may include one or more types mentioned below.

[0135] In practice, non-standard coherent transmitters primarily reduce the number of dimensions of the transmitted signal, thereby decreasing the corresponding number of hardware channels. Regardless of the number of dimensions of the signal transmitted by the coherent transmitter, a standard coherent receiver is capable of handling four dimensions; therefore, standard coherent receivers are used in optical communication devices.

[0136] Figure 15 and Figure 16 These are schematic diagrams of a non-standard coherent transmitter. For example... Figure 15 As shown, this non-standard coherent transmitter is a single-polarized real-number transmitter, which includes a laser, a modulator, and a modulation circuit. The modulation circuit receives the XI signal, a single-polarized real-number signal. The laser provides the beam, and the modulator modulates the XI signal onto the beam to obtain and output a subcarrier. Compared to a standard coherent transmitter, the four modulation circuits are simplified to one.

[0137] like Figure 16As shown, this non-standard coherent transmitter is a dual-polarized real-number transmitter, comprising a laser, a beam splitter, two modulation circuits, two modulators, and a polarization coupler. Each modulation circuit receives one single-polarized real-number signal; the single-polarized real-number signals received by the two modulation circuits correspond to the XI signal and the YI signal, respectively. The laser emits a beam, and the beam splitter divides the emitted beam into two sub-beams. One modulator modulates one sub-beam using the XI signal to obtain an X-polarized modulated optical signal; the other modulator modulates the other sub-beam using the YI signal to obtain a Y-polarized modulated optical signal. The polarization coupler combines the X-polarized and Y-polarized modulated optical signals into an optical carrier and transmits this carrier. Compared to a standard coherent transmitter, the four modulation circuits are simplified to two.

[0138] In addition, there exists a non-standard coherent transmitter that transmits only single-polarization complex signals. Compared to the standard coherent transmitter, the four modulation circuits are simplified to two.

[0139] The following is combined with Figure 17-19 An example is provided for transmitting subcarriers using a non-standard coherent transmitter.

[0140] Figure 17 Based on Figure 5 The diagram illustrates the signal change process of the optical communication device shown. Figure 5 In the process, leaf nodes MP1-MP2 transmit subcarrier 1 and subcarrier 2 respectively, with a bilateral bandwidth of 60GHz (single-sided bandwidth of 30GHz).

[0141] Figure 17 In parts (a) and (b), the dashed arrows indicate the center frequency of the laser at the leaf node. Although it is real-number modulation, the modulator is biased at the NULL point (the point with the lowest output power when there is no modulation), and the final transmitted signal is a zero-mean signal with no DC component. In practical applications, leaf node MP1 transmits subcarrier 1 and its conjugate symmetrical conjugate subcarrier 1'; leaf node MP2 transmits subcarrier 2 and its conjugate symmetrical conjugate subcarrier 2'. This is because a real-number transmitter can only transmit real-number signals, and real-number signals are conjugate symmetrical in the frequency domain. Simultaneously transmitting subcarrier 1 and conjugate subcarrier 1' ensures that the signal transmitted by the transmitter is a real number in the time domain, while subcarrier 1 and conjugate subcarrier 1' can themselves be complex subcarriers. Furthermore, since subcarrier 1 and conjugate subcarrier 1' do not overlap in the frequency domain, information from subcarrier 1 or conjugate subcarrier 1' can be extracted separately through filtering. Subcarrier 1 and conjugate subcarrier 1' transmit identical information, so only one subcarrier needs to be extracted. The same applies to leaf node MP2. In this embodiment, the first beat frequency signal corresponding to subcarriers 1 and 2 is extracted; the beat frequency signals corresponding to conjugate subcarriers 1' and 2' are located outside the receiving bandwidth of the coherent receiver.

[0142] Since subcarriers 1 and 2 are both complex subcarriers, if they are dual-biased signals, there is no rate loss under the same receiving bandwidth of the coherent receiver. However, if they are single-biased signals, the rate drops to half. That is, converting a dual-biased signal to a single-biased signal at the leaf node will result in a rate reduction, while converting a complex signal to a real signal at the leaf node will not. From another perspective, to achieve a rate reduction when converting a complex signal to a real signal at the leaf node, the cost would be doubling the minimum device bandwidth required for the transmitter at the leaf node, and also doubling the minimum device bandwidth originally required at the central node. However, using the above spectrum design, the minimum device bandwidth required for the optical communication device at the central node remains unchanged.

[0143] like Figure 17 As shown in part (a), the right edge of subcarrier 1 transmitted by leaf node MP1 is aligned with the center frequency of the first single-frequency optical signal, 193.3 THz. Considering the 60 GHz subcarrier bilateral bandwidth, the center frequency of the laser at the transmitting end of leaf node MP1 is located at 193.24 THz. Figure 17 As shown in section (b), the settings for leaf node MP2 are similar to those for leaf node MP1. Since each leaf node only supports signals with conjugate symmetry in the transmission frequency domain, the center frequency of its transmitting laser is fixed.

[0144] This embodiment also has requirements for spectrum design, namely, that the input of the coherent receiver should show the following: Figure 17 The spectral distributions shown in parts (c) and (d) are as follows. Note that we ultimately resolve beat frequency signals 1 and 2. Figure 17 In part (e), the solid line portion within the rectangular dashed box, if we only consider the spectral position relationship corresponding to the beat frequency signal shown by the solid line, then the spectral design of this embodiment... Figure 5 The spectrum design of the illustrated embodiment is the same.

[0145] Figure 17 In sections (a)-(c), solid lines represent subcarriers, and dashed lines represent conjugate subcarriers introduced by using a real-coherent transmitter. Each subcarrier and the single-frequency optical signal must satisfy the following conditions:

[0146] 1. The interval between the center frequency of the target subcarrier and the frequency of the nearest single-frequency optical signal in the frequency domain is less than the difference between the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier. Here, the target subcarrier is any subcarrier in the target optical signal. This ensures that the frequency of each first beat frequency signal lies within the receiving bandwidth of the coherent receiver.

[0147] 2. The frequency between the center frequency of the target subcarrier and the frequency of the second closest single-frequency optical signal in the frequency domain is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier. This ensures that all beat frequency signals except the first beat frequency signal are outside the receiving bandwidth of the coherent receiver.

[0148] 3. The interval between any two adjacent single-frequency optical signals is greater than the single-side bandwidth of the coherent receiver. This ensures that the frequency of the beat frequency signal between any two single-frequency optical signals is outside the receiving bandwidth of the coherent receiver.

[0149] In this embodiment, if the target subcarrier has a corresponding conjugate subcarrier, the spectral spacing between the conjugate subcarrier and the second nearest single-frequency optical signal is greater than the spectral spacing between the target subcarrier and the second nearest single-frequency optical signal. It is possible that the conjugate subcarrier might be closer to the second nearest single-frequency optical signal than the target subcarrier, requiring that the beat frequency signals of all subcarriers and the second nearest single-frequency optical signal be filtered out by the receiving bandwidth of the coherent receiver. Therefore, after introducing the conjugate subcarrier, the conjugate subcarrier also needs to meet the following conditions:

[0150] 4. The interval between the center frequency of each conjugate subcarrier and the frequency of the reference single-frequency optical signal is greater than the sum of the single-side bandwidth of the coherent receiver and the single-side bandwidth of the conjugate subcarrier. The reference single-frequency optical signal is the single-frequency optical signal whose center frequency is the second closest in the frequency domain to the center frequency of the subcarrier corresponding to that conjugate subcarrier. This ensures that the frequencies of the beat frequencies of the conjugate subcarriers and other single-frequency optical signals (excluding the single-frequency optical signal whose center frequency is the closest to its corresponding subcarrier) are all outside the receiving bandwidth of the coherent receiver, thus preventing interference from the beat frequencies of the conjugate subcarriers to the first beat frequency signal.

[0151] Since conjugate subcarriers appear in pairs, the definition of the nearest and second-nearest single-frequency optical signals here is based on the target subcarrier.

[0152] In this embodiment, the frequency of the beat frequency signal between the conjugate subcarrier and the nearest single-frequency optical signal is also outside the receiving bandwidth of the coherent receiver, but this is not a necessary condition. In other embodiments, in the case of multiple subcarriers, it may be necessary for the frequency of the beat frequency signal between some of the conjugate subcarriers and the nearest single-frequency optical signal to be within the receiving bandwidth of the coherent receiver.

[0153] Even if the frequency of the beat frequency signal between the conjugate subcarrier and the nearest single-frequency optical signal falls within the receiving bandwidth of the coherent receiver, the conjugate subcarrier can be filtered out by a digital filter as long as there is no spectral overlap. Furthermore, when the subcarrier power difference within the receiving bandwidth of the coherent receiver is small, the beat frequency between the subcarrier and the non-nearest LO can be filtered out by a digital filter. When the power difference of the first beat frequency signal within the receiving bandwidth of the coherent receiver is large, a dilemma arises: either saturation / truncation of the high-power beat frequency signal or loss of quantization accuracy of the low-power beat frequency signal. Therefore, essentially, we want the power of the first beat frequency signal within the receiving bandwidth of the coherent receiver to be similar. In the embodiments of this application, by controlling the power of the single-frequency optical signal, it can be ensured that the power of the first beat frequency signal between all target subcarriers and the nearest single-frequency optical signal is similar. Since conjugate subcarriers and target subcarriers appear in pairs, their powers are naturally similar (this is guaranteed by the spectral symmetry of the real-time signal), so the beat frequency signal between the conjugate subcarrier and the nearest single-frequency optical signal falling within the receiving bandwidth of the coherent receiver does not cause the aforementioned problems.

[0154] If designed according to condition 4 above, it can be further compressed. Figure 17 The spectral spacing in the spectrum, thus, may result in... Figure 18 The spectral distribution in the coherent receiver indicates that beat frequencies outside the receiver's bandwidth overlap. However, since the coherent receiver actually needs to detect the first beat frequency signal within its receiver bandwidth, it does not concern itself with whether beat frequencies outside the receiver bandwidth overlap.

[0155] When leaf nodes transmit single-carrier real-valued optical signals such as BPSK and PAM4 using a real-valued coherent transmitter, the real-valued optical signal contains mutually conjugate symmetrical positive and negative frequency components, which is equivalent to the description of subcarriers and conjugate subcarriers mentioned above. Therefore, the above description based on subcarriers and conjugate subcarriers also applies to single-carrier real-valued signals. In this case, the coherent receiver can extract the positive frequency component (or negative frequency component), and then the optical communication device can obtain the negative frequency component (or positive frequency component) based on the conjugate symmetry relationship between the positive and negative frequency components. Finally, the complete information is obtained based on the positive and negative frequency components.

[0156] For example, when leaf node MP1 uses a real-valued coherent transmitter to transmit a subcarrier with a center frequency of 193.24 THz and a bilateral bandwidth of 120 GHz, and the real-valued optical signal carried by this subcarrier is a PAM4 signal, the position of the left half of this subcarrier is... Figure 17 The position of the conjugate subcarrier 1' in part (a) corresponds to the position of the right half of the subcarrier. Figure 17 The position of subcarrier 1 in part (a) corresponds to this. The coherent receiver can extract the frequency component corresponding to the right half of the subcarrier.

[0157] In this case, the interval between the center frequency of the right half of the subcarrier and the frequency of the nearest single-frequency optical signal in the frequency domain is less than the difference between the single-sided bandwidth of the coherent receiver and half of the single-sided bandwidth of the subcarrier; the interval between the center frequency of the right half of the subcarrier and the frequency of the second nearest single-frequency optical signal in the frequency domain is less than the sum of the single-sided bandwidth of the coherent receiver and half of the single-sided bandwidth of the subcarrier.

[0158] Figure 19 yes Figure 12 This diagram illustrates the signal processing procedure of a mid-light communication device. It can also be extended to cases with more than two target subcarriers. Similarly, if there are N subcarriers, N single-frequency optical signals are used. Figure 19 An example with 4 subcarriers is given, where each subcarrier corresponds to a leaf node. Figure 19 The arrows in sections (a)-(d) indicate the center frequency of the laser at the leaf node, and the dashed lines without arrows indicate the frequency position of the nearest corresponding single-frequency optical signal (as opposed to the previous ones). Figure 19 (The frequency positions of the single-frequency optical signals shown in part (f) are the same). Leaf nodes MP1-MP4 transmit subcarriers 1-4 respectively, and the nearest single-frequency optical signals corresponding to subcarriers 1-4 are LO1-LO4 respectively. Finally, the spectrum of the target optical signal at the entrance of the coherent receiver is as follows: Figure 19 As shown in section (e), the coherent receiver receives the first beat frequency signals of subcarriers 1-4 and single-frequency optical signals LO1-LO4 within its receiving bandwidth, respectively. Figure 19 As shown in the real part within the dashed box in part (g), the power of the first beat frequency optical signal on the electrical spectrum can be adjusted by controlling the power of the corresponding single-frequency optical signal.

[0159] Furthermore, the frequencies of the conjugate subcarriers 2' and 3', and the beat frequencies of the single-frequency optical signals LO2 and LO3, respectively, are also within the receiving bandwidth of the coherent receiver, and they overlap with each other. Since the conjugate subcarriers 2' and 3' contain exactly the same information as the target subcarriers 2 and 3, we only need to resolve the information of subcarriers 2 and 3. This overlap effectively reduces bandwidth waste.

[0160] In this embodiment, 4 / 5 of the coherent receiver's receiving bandwidth is used to receive subcarriers, and these subcarriers can all be complex signals. Figure 18 In the illustrated embodiment, the entire receiving bandwidth of the coherent receiver is used to receive the target subcarrier. As the number of subcarriers increases, the phenomenon of bandwidth loss caused by the beat frequency signal corresponding to the conjugate subcarrier within the receiving bandwidth of this coherent receiver becomes increasingly severe. However, by allowing the conjugate subcarriers to overlap, the bandwidth utilization of the coherent receiver can still be higher than 1 / 2.

[0161] It should be noted that if this method is not used, directly in Figures 5 to 13 Based on the corresponding embodiment, if the complex signal is converted into a real signal, the bandwidth utilization of the coherent receiver drops to 1 / 2. The above analysis of the bandwidth utilization of the coherent receiver does not consider polarization. If the polarization changes from dual-polarization to single-polarization, the bandwidth utilization of the coherent receiver will decrease by another 1 / 2.

[0162] The spectrum design requirement in this embodiment is still to make the target optical signal... Figure 17 The spectrum shown indicates that the frequencies of each subcarrier and the single-frequency optical signal still need to meet certain requirements. Figure 17 The corresponding conditions.

[0163] It should be noted that, Figure 17 and Figure 19 The example provided illustrates the concept of each subcarrier having a corresponding conjugate subcarrier. In other embodiments, only some subcarriers may have corresponding conjugate subcarriers. That is, in a P2MP optical communication system, some leaf nodes may use standard coherent transmitters, while other leaf nodes may use real-valued transmitters.

[0164] It should be noted that, Figure 12 In the text, (a)-(g) represent respectively Figures 17-19 The acquisition location of the signal spectrum corresponding to the letter in the text.

[0165] This application also provides a method for processing optical signals, which can be implemented by a coherent receiver in the aforementioned optical communication device. Figure 20 This is a schematic flowchart illustrating an optical signal processing method provided in an embodiment of this application. Figure 20 As shown, the method includes:

[0166] In 201, local optical signals and target optical signals are received.

[0167] The local optical signal includes N single-frequency optical signals with different frequencies, and the target optical signal includes M subcarriers, where N is greater than 1 and N is an integer, and M is a positive integer and M is less than or equal to N.

[0168] In 202, multiple beat frequency signals are obtained based on the target optical signal and the local optical signal.

[0169] These multiple beat frequency signals include M first beat frequency signals. Each first beat frequency signal is obtained by beating one subcarrier and one single-frequency optical signal, and different first beat frequency signals correspond to different subcarriers and different single-frequency optical signals. Among the M subcarriers, the power of the first subcarrier is greater than the power of the second subcarrier, and the power of the first single-frequency optical signal corresponding to the first subcarrier is less than the power of the second single-frequency optical signal corresponding to the second subcarrier.

[0170] Optionally, the frequencies of the M first beat frequency signals are located within the receiving bandwidth of the coherent receiver, and the frequencies of the beat frequency signals other than the M first beat frequency signals are located outside the receiving bandwidth of the coherent receiver.

[0171] Optionally, the interval between the center frequency of the target subcarrier and the frequency of the single-frequency optical signal that is closest to it in the frequency domain among the M subcarriers is less than the difference between the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier, and the target subcarrier is any one of the M subcarriers; the interval between the center frequency of the target subcarrier and the frequency of the second closest single-frequency optical signal in the frequency domain among the M subcarriers is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier, and the target subcarrier is any one of the M subcarriers; the frequency interval between any two adjacent single-frequency optical signals in the frequency domain among the N single-frequency optical signals is greater than the single-sided bandwidth of the coherent receiver.

[0172] Optionally, the target optical signal further includes a conjugate subcarrier of at least one of the M subcarriers, wherein the interval between the center frequency of each conjugate subcarrier and the frequency of the reference single-frequency optical signal is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the conjugate subcarrier, wherein the reference single-frequency optical signal is a single-frequency optical signal whose center frequency is the second closest to that of the subcarrier corresponding to the conjugate subcarrier in the frequency domain.

[0173] Optionally, any one of the M subcarriers includes a burst optical signal transmitted by a leaf node, or includes burst optical signals transmitted by multiple leaf nodes in a time-division multiplexing manner.

[0174] It should be noted that the optical signal processing method provided in the above embodiments and the optical communication device embodiments belong to the same concept. For details of its implementation process, please refer to the optical communication device embodiments, which will not be repeated here.

[0175] The descriptions of the optical communication devices corresponding to the above figures each have their own emphasis. For parts not described in detail in a certain embodiment of an optical communication device, please refer to the relevant descriptions in other embodiments.

[0176] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application pertains. The terms “first,” “second,” “third,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar terms mean that the elements or objects preceding “comprising” or “including” encompass the elements or objects listed following “comprising” or “including” and their equivalents, and do not exclude other elements or objects. The “multiple” mentioned in the embodiments of this application refers to two or more. A and / or B indicate three possibilities: A; B; and A and B.

[0177] The above is merely one embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An optical communication device, characterized by, include: A light source module is used to provide a local optical signal, which includes N single-frequency optical signals, the N single-frequency optical signals having different frequencies, wherein N is greater than 1 and N is an integer; A coherent receiver is used to receive a target optical signal and a local optical signal. The target optical signal includes M subcarriers, where M is a positive integer and M is less than or equal to N. Based on the target optical signal and the local optical signal, multiple beat frequency signals are obtained. The multiple beat frequency signals include M first beat frequency signals. Each of the M first beat frequency signals is obtained by beating one of the M subcarriers with one of the N single-frequency optical signals. Different first beat frequency signals correspond to different subcarriers and different single-frequency optical signals. Among the M subcarriers, the power of the first subcarrier is greater than the power of the second subcarrier, and the power of the first single-frequency optical signal corresponding to the first subcarrier is less than the power of the second single-frequency optical signal corresponding to the second subcarrier.

2. The optical communication device of claim 1, wherein, The frequencies of the M-channel first beat frequency signals are within the receiving bandwidth of the coherent receiver, while the frequencies of the beat frequency signals other than the M-channel first beat frequency signals are outside the receiving bandwidth of the coherent receiver.

3. The optical communication device of claim 2, wherein, The interval between the center frequency of the target subcarrier and the frequency of the single-frequency optical signal that is closest to it in the frequency domain among the M subcarriers is less than the difference between the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier, and the target subcarrier is any one of the M subcarriers. The interval between the center frequency of the target subcarrier and the frequency of the second closest single-frequency optical signal in the frequency domain is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the target subcarrier. The target subcarrier is any one of the M subcarriers. The frequency interval between any two adjacent single-frequency optical signals in the frequency domain among the N single-frequency optical signals is greater than the single-side bandwidth of the coherent receiver.

4. The optical communication device of claim 3, wherein, The target optical signal also includes a conjugate subcarrier of at least one of the M subcarriers. The interval between the center frequency of the conjugate subcarrier and the frequency of the reference single-frequency optical signal is greater than the sum of the single-sided bandwidth of the coherent receiver and the single-sided bandwidth of the conjugate subcarrier. The reference single-frequency optical signal is a single-frequency optical signal whose center frequency is the second closest to that of the subcarrier corresponding to the conjugate subcarrier in the frequency domain.

5. The optical communication device according to any one of claims 1 to 3, characterized in that, The light source module includes a beam combiner and N light-emitting units. Each of the N light-emitting units is used to provide one single-frequency optical signal; The beam combiner is used to combine the single-frequency optical signals provided by the N light-emitting units into one channel to obtain the local optical signal.

6. The optical communication device according to claim 5, characterized in that, The optical communication device further includes a detection module and a control module. The detection module is used to detect the power of each first beat frequency signal, and the control module is used to control the power of the single-frequency optical signal corresponding to each first beat frequency signal based on the power of each first beat frequency signal.

7. The optical communication device according to claim 6, characterized in that, The light-emitting unit includes a laser, which is used to emit the single-frequency optical signal; The control module is used to control the temperature of the laser and / or the driving current of the laser, so as to control the power of the single-frequency optical signal emitted by the laser.

8. The optical communication device according to claim 6, characterized in that, The light-emitting unit includes a laser and a power regulator, with the power regulator located in the optical path between the laser and the coherent receiver; The power regulator is used to receive the beam emitted by the laser and, under the control of the control module, adjust the power of the received beam to obtain the single-frequency optical signal.

9. The optical communication device according to any one of claims 6 to 8, characterized in that, The detection module is also used to detect the frequency offset of the single-frequency optical signal, and the control module is also used to adjust the center frequency of the laser corresponding to the single-frequency optical signal according to the frequency offset detected by the detection module.

10. The optical communication device according to any one of claims 1 to 4 and claims 6 to 8, characterized in that, Any one of the M subcarriers includes a burst optical signal transmitted by a leaf node, or includes burst optical signals transmitted by multiple leaf nodes in a time-division multiplexing manner.

11. A point-to-multipoint optical communication system, characterized in that, include: The device comprises a central node, an optical distribution network (ODN), and multiple leaf nodes, wherein an intermediate node is connected to the multiple leaf nodes through the ODN, and the central node includes the optical communication device according to any one of claims 1 to 10.

12. A method for processing optical signals, characterized in that, The method includes: The system receives local optical signals and target optical signals, wherein the local optical signals include N single-frequency optical signals with different frequencies, and the target optical signals include M subcarriers, wherein N is greater than 1 and N is an integer, and M is a positive integer and M is less than or equal to N. Based on the target optical signal and the local optical signal, multiple beat frequency signals are obtained. The multiple beat frequency signals include M first beat frequency signals. Each of the M first beat frequency signals is obtained by beating one subcarrier from the M subcarriers and one single-frequency optical signal from the N single-frequency optical signals. Different first beat frequency signals correspond to different subcarriers and different single-frequency optical signals. Among the M subcarriers, the power of the first subcarrier is greater than the power of the second subcarrier, and the power of the first single-frequency optical signal corresponding to the first subcarrier is less than the power of the second single-frequency optical signal corresponding to the second subcarrier.

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