Optical signal modulation method, transmitter, and pilot receiving apparatus

Abstract

Embodiments of the present application relate to the technical field of optical communications, and provide an optical signal modulation method, a transmitter, and a pilot receiving apparatus, which are used for improving the problem that pilot crosstalk affects channel state monitoring. The modulation method comprises: modulating at least two pilot signal groups on optical signals in a first wavelength channel, different pilot signal groups in the first wavelength channel being modulated on different frequency bands of the optical signals, and the pilot signal groups comprising at least two pilot signals having a same pilot frequency and phases uniformly arranged in a range of 0 to 2π; and outputting modulated optical signals. The foregoing modulation method can be applied to a wavelength division multiplexing system.

Description

A method for modulating optical signals, a transmitter, and a pilot receiver.

[0001] This application claims priority to Chinese Patent Application No. 202411223295.9, filed with the State Intellectual Property Office of China on September 2, 2024, entitled "A Modulation Method for an Optical Signal, Transmitter and Pilot Receiver", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of optical communication technology, and in particular to a method for modulating optical signals, a transmitter, and a pilot receiver. Background Technology

[0003] In optical fiber communication, wavelength division multiplexing (WDM) systems are commonly used to improve transmission capacity and the utilization efficiency of optical fiber resources. A WDM system includes a transmitter, a receiver, and a transmission link connecting the transmitter and receiver. The transmitter may include multiple transmitters and WDM multiplexers, while the receiver may include a demultiplexer and multiple receivers. The transmission link between the transmitter and receiver is an optical fiber, and amplifiers may also be installed on the transmission link.

[0004] In a wavelength division multiplexing (WDM) system, each transmitter at the transmitting end generates an optical signal in one wavelength channel. The optical signals from multiple wavelength channels generated by multiple transmitters are combined into a single WDM optical signal by a WDM multiplexer. This WDM optical signal is then amplified and transmitted through optical fiber. To ensure reliable operation of the WDM system and reduce interruptions caused by network failures, pilot signals are typically used to monitor the channel status of each wavelength channel in the WDM system.

[0005] However, stimulated Raman scattering (SRS) exists in optical fibers, and it becomes particularly severe under conditions of long-distance and multi-wavelength channel transmission. SRS causes pilot crosstalk in pilot signals; the presence of pilot crosstalk affects the accuracy of monitoring channel status via pilot signals. Summary of the Invention

[0006] This application provides an optical signal modulation method, a transmitter, and a pilot receiver to improve the problem of pilot crosstalk affecting channel status monitoring.

[0007] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0008] In a first aspect, embodiments of this application provide a method for modulating an optical signal, the modulation method comprising:

[0009] At least two pilot signal groups are modulated onto the optical signal in the first wavelength channel; wherein, the first wavelength channel is any wavelength channel in the wavelength division multiplexing system; different pilot signal groups in the first wavelength channel are modulated onto different frequency bands of the optical signal; the pilot signal group includes at least two pilot signals with the same pilot frequency and a phase uniformly distributed in the range of 0 to 2π.

[0010] Output the modulated optical signal.

[0011] In the modulation method provided in this application embodiment, the pilot signals in the pilot signal group adopt the above design. When pilot crosstalk occurs due to SRS, the pilot signals in the same pilot signal group can achieve at least partial cancellation in the crosstalk wavelength channels (other wavelength channels besides the first wavelength channel). Therefore, when the pilot receiving device detects the pilot signal, only the uncancelled part of the pilot signal crosstalked to other wavelength channels can be detected. As a result, the proportion of pilot crosstalk in the detection result will be greatly reduced, or even 0. This can improve the impact of pilot crosstalk on the optical power detection result, and thus improve the accuracy of monitoring the channel status through pilot signals.

[0012] Furthermore, at least two pilot signal groups are modulated onto the optical signal in the first wavelength channel, and all pilot signal groups in the first wavelength channel are modulated onto optical signals of different frequency bands in the first wavelength channel. With this design, when pilot crosstalk occurs due to SRS, pilot signals within the same pilot signal group can cancel out the crosstalk. Different pilot signal groups can also take into account the correlation between pilot crosstalk and wavelength (frequency), separately canceling out pilot crosstalk generated by pilot signals of different frequency bands in the first wavelength channel. This further improves the impact of pilot crosstalk on optical power detection results, and consequently, further enhances the accuracy of monitoring channel status through pilot signals.

[0013] In some embodiments, the pilot frequencies of the pilot signals in different pilot signal groups of the first wavelength channel are the same; in the spectrum of the optical signal, the phase arrangement of the pilot signals in different pilot signal groups of the first wavelength channel has a relationship that causes the pilot signal groups to cancel each other out again.

[0014] Pilot crosstalk is wavelength (frequency) related. When crosstalk occurs in the pilot signal of the first wavelength channel, the degree of crosstalk varies at different frequency points, generally showing a decreasing trend from one end of the frequency range to the other. Therefore, when different pilot signals in the pilot signal group are canceled, perfect cancellation cannot be achieved, and a certain amount of cancellation residue will remain. This cancellation residue will affect the detection results of optical power, thereby affecting the accuracy of monitoring the channel status through pilot signals.

[0015] In the modulation method provided in this application embodiment, by designing the phase and order of the pilot signals in different pilot signal groups, the cancellation residue generated by each pilot signal group can be canceled, that is, the pilot crosstalk is canceled again; thereby further improving the impact of pilot crosstalk on optical power detection results, and thus improving the accuracy of monitoring channel status through pilot signals.

[0016] In some embodiments, the first wavelength channel includes two pilot signal groups, namely the first pilot signal group and the second pilot signal group.

[0017] The first pilot signal group and the second pilot signal group each include two pilot signals, namely the first pilot signal and the second pilot signal; the first pilot signal and the second pilot signal are out of phase.

[0018] In the optical signal spectrum, the first pilot signal and the second pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

[0019] In the modulation method provided in the embodiments of this application, two pilot signals of the same frequency and opposite phase can be used to form an anti-phase pilot pair, and pilot crosstalk can be canceled once within the anti-phase pilot pair; pilot crosstalk between the pairs can be canceled again by two anti-phase pilot pairs with opposite order.

[0020] In some embodiments, in at least one group of pilot signals, the amplitude of the first pilot signal is a first amplitude and is modulated on a frequency band of a first bandwidth in the optical signal; the amplitude of the second pilot signal is a second amplitude and is modulated on a frequency band of a second bandwidth in the optical signal; the product of the first amplitude and the first bandwidth and the product of the second amplitude and the second bandwidth are equal.

[0021] In schemes employing antiphase pilot pairs, a better pilot crosstalk cancellation effect can be achieved by adjusting the amplitude and bandwidth between the pilot signals within the pair.

[0022] In some embodiments, the first amplitude and the second amplitude are equal, and the first bandwidth and the second bandwidth are equal; or, the first amplitude and the second amplitude are not equal, and the first bandwidth and the second bandwidth are not equal.

[0023] In the scheme using anti-phase pilot pairs, a good pilot crosstalk cancellation effect can be achieved by adjusting the amplitude and bandwidth between the pilot signals within the pair; and it can also be applied to different application scenarios.

[0024] In some embodiments, the first wavelength channel includes two pilot signal groups, namely a first pilot signal group and a second pilot signal group; wherein, both the first pilot signal group and the second pilot signal group include three pilot signals, namely a first pilot signal, a second pilot signal and a third pilot signal; the phases of the first pilot signal, the second pilot signal and the third pilot signal are uniformly distributed in the range of 0 to 2π.

[0025] In the optical signal spectrum, the first pilot signal, the second pilot signal, and the third pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

[0026] In the modulation method provided in this application embodiment, each pilot signal group can include a scheme of 3 pilot signals. Intra-group pilot crosstalk is canceled by controlling the phase of the 3 pilot signals, and inter-group pilot crosstalk is canceled by controlling the phase order of the 3 pilot signals in different pilot signal groups. Alternatively, other numbers of pilot signals can be used in the pilot signal group.

[0027] In some embodiments, the first wavelength channel includes three pilot signal groups, namely a first pilot signal group, a second pilot signal group, and a third pilot signal group;

[0028] The first pilot signal group, the second pilot signal group, and the third pilot signal group are arranged sequentially on the spectrum of the optical signal and have the same number of pilot signals.

[0029] In the modulation method provided in the embodiments of this application, three pilot signal groups can be used to achieve the re-cancellation of pilot crosstalk, or other numbers of pilot signal groups can be used.

[0030] In some embodiments, the first pilot signal group includes a first pilot signal and a second pilot signal arranged sequentially on the spectrum of the optical signal; the phases of the first pilot signal and the second pilot signal are a first phase and a second phase, respectively;

[0031] The second pilot signal group includes a third pilot signal and a fourth pilot signal whose spectra are arranged sequentially on the optical signal; the phases of the third pilot signal and the fourth pilot signal are the third phase and the fourth phase, respectively;

[0032] The third pilot signal group includes the fifth and sixth pilot signals whose spectra are arranged sequentially on the optical signal; the phases of the fifth and sixth pilot signals are the fifth phase and the sixth phase, respectively;

[0033] The phase difference between the second phase and the first phase is -π, the phase difference between the fourth phase and the third phase is π, and the phase difference between the sixth phase and the fifth phase is -π.

[0034] When using three pilot signal groups to achieve the cancellation of pilot crosstalk between groups, different anti-phase pilot pairs can be used in each pilot signal group.

[0035] In some embodiments, the first phase, second phase, third phase, fourth phase, fifth phase, and sixth phase are 0, π, 4π / 3, π / 3, 2π / 3, and 5π / 3, respectively. When the pilot signals in the three pilot signal groups adopt the above phase settings, pilot crosstalk can be canceled once within the group, and pilot crosstalk can be canceled again between groups.

[0036] In some embodiments, the bandwidth of the first wavelength channel is an integer multiple of 25 GHz; the bandwidth occupied by the pilot signal on the optical signal is an integer multiple of 6.25 GHz. The modulation method provided in this application embodiment can adapt to wavelength channels with different bandwidths, thus enabling its application in different wavelength division multiplexing systems.

[0037] In some embodiments, in the optical signal spectrum, at least two groups of pilot signals have a guard interval between adjacent pilot signals, the bandwidth of which is 0.5 GHz to 1.5 GHz. This design avoids the situation where, due to the comb filter, pilot signals adjacent to the target frequency band and having a canceling relationship with the pilot signals in the target frequency band are also filtered out when filtering out pilot signals in the target frequency band; thereby improving the signal-to-noise ratio.

[0038] In some embodiments, the first wavelength channel includes groups of pilot signals with different pilot frequencies. This design allows for the detection of pilot signals with different frequencies when the pilot signals are detected by a pilot receiver, thereby enabling the detection of optical power at different locations within the first wavelength channel.

[0039] In some embodiments, the first wavelength channel includes at least 10 groups of pilot signals with different pilot frequencies. This design allows for high-resolution detection of optical power at different locations within the first wavelength channel by detecting pilot signals with at least 10 different pilot frequencies.

[0040] In some embodiments, in the optical signal of the first wavelength channel, the pilot signals in at least two pilot signal groups have the same pilot frequency; on the spectrum of the optical signal, the phase arrangement of the pilot signals in all pilot signal groups with the same pilot frequency has a relationship that causes the pilot signal groups to cancel each other out again.

[0041] This design not only effectively cancels pilot crosstalk but also enables the detection of optical power at different positions in the first wavelength channel.

[0042] In some embodiments, in the optical signal of the first wavelength channel, the pilot frequencies of the two pilot signal groups are the same, namely the first pilot signal group and the second pilot signal group;

[0043] The first pilot signal group and the second pilot signal group each include two pilot signals, namely the first pilot signal and the second pilot signal; the first pilot signal and the second pilot signal are out of phase;

[0044] In the optical signal spectrum, the first pilot signal and the second pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

[0045] Alternatively, both the first pilot signal group and the second pilot signal group include three pilot signals, namely the first pilot signal, the second pilot signal, and the third pilot signal; the phases of the first pilot signal, the second pilot signal, and the third pilot signal are uniformly distributed in the range of 0 to 2π.

[0046] In the optical signal spectrum, the first pilot signal, the second pilot signal, and the third pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

[0047] This design not only effectively cancels pilot crosstalk but also enables the detection of optical power at different positions in the first wavelength channel.

[0048] In some embodiments, each pilot frequency includes the same number of pilot signal groups, and the pilot signal groups have the same pilot signal; on the optical signal spectrum, all pilot signals at each pilot frequency are arranged in the same order, and pilot signals in the same order at different pilot frequencies are grouped together. This design facilitates the filtering out of at least one pilot signal at different pilot frequencies by a pilot receiving device.

[0049] Secondly, embodiments of this application also provide a transmitter, which includes a light source and a modulator. The light source is used to generate an optical signal in a first wavelength channel; the modulator is used to receive the optical signal generated by the light source and perform the modulation method described in the first aspect embodiment.

[0050] In some embodiments, the transmitter further includes a processor configured to send a modulation signal to a modulator according to the modulation method described in the first aspect embodiment, wherein the modulator modulates an optical signal generated by a light source according to the modulation signal.

[0051] The technical effects achievable by the transmitter provided in this application embodiment are the same as those achievable by the modulation method in any of the above embodiments, and will not be repeated here.

[0052] Thirdly, this application also provides a pilot receiving device, which includes a comb filter, a photodetector, and a processor. The comb filter is used to receive the optical signal in the first wavelength channel and filter out the target frequency band portion of the optical signal.

[0053] The photodetector is used to convert the optical signal filtered out by the comb filter into an electrical signal; the processor is connected to the photodetector and is used to determine the optical power in the first wavelength channel based on the electrical signal generated by the photoelectric conversion of the photodetector.

[0054] The optical signal in the first wavelength channel is an optical signal formed by the modulation method described in the first aspect embodiment, and the target frequency band is aligned with one of the pilot signals in at least one group of pilot signals.

[0055] The pilot receiving device provided in this application embodiment is used to perform pilot detection on the optical signal formed by the modulation method described in the first aspect embodiment, thereby achieving the purpose of monitoring the channel status.

[0056] In some embodiments, the comb filter is a Mach-Zehnder interferometer, a Michelson interferometer, an arrayed waveguide grating, or a wavelength selective switch.

[0057] In some embodiments, the target frequency band in the comb filter is specified as an integer multiple of 12.5 GHz. Attached Figure Description

[0058] Figure 1 shows a network architecture diagram of a wavelength division multiplexing system provided by related technologies;

[0059] Figure 2 is a schematic diagram of the transmitter in Figure 1;

[0060] Figure 3 is a schematic diagram of an optical signal and a pilot signal provided by related technologies;

[0061] Figure 4 is a schematic diagram of the pilot receiver device in Figure 1;

[0062] Figure 5 is a schematic diagram of the effect of stimulated Raman scattering on pilot signals provided by related technologies;

[0063] Figure 6 shows the relationship between pilot frequency and pilot crosstalk provided by related technologies;

[0064] Figure 7 shows the relationship between pilot frequency and dispersion provided by related technologies;

[0065] Figure 8 is a flowchart of an optical signal modulation method provided in an embodiment of this application;

[0066] Figure 9 is a flowchart of a transmitter modulation service signal and pilot signal provided in an embodiment of this application;

[0067] Figure 10 is a schematic diagram of a pilot receiving device provided in an embodiment of this application;

[0068] Figure 11 is a schematic diagram of a pilot signal design provided in an embodiment of this application;

[0069] Figure 12 is a schematic diagram of the comb filter provided in the embodiment of this application filtering out the pilot signal in Figure 11;

[0070] Figure 13 is a schematic diagram of another pilot signal design provided in an embodiment of this application;

[0071] Figure 14 is a schematic diagram of the comb filter provided in the embodiment of this application filtering out the pilot signal in Figure 13;

[0072] Figure 15 is a schematic diagram of another pilot signal design provided in an embodiment of this application;

[0073] Figure 16 is a schematic diagram of the comb filter provided in the embodiment of this application filtering out the pilot signal in Figure 15;

[0074] Figure 17 is a schematic diagram of another pilot signal design provided in an embodiment of this application;

[0075] Figure 18 is a schematic diagram of the comb filter provided in the embodiment of this application filtering out the pilot signal in Figure 17;

[0076] Figure 19 is a schematic diagram of another pilot signal design provided in an embodiment of this application;

[0077] Figure 20 is a schematic diagram of the comb filter provided in the embodiment of this application filtering out the pilot signal in Figure 19;

[0078] Figure 21 is a schematic diagram of another pilot signal design provided in an embodiment of this application;

[0079] Figure 22 is a schematic diagram of the comb filter provided in the embodiment of this application filtering out the pilot signal in Figure 21;

[0080] Figure 23 is a schematic diagram of another pilot signal design provided in an embodiment of this application;

[0081] Figure 24 is a schematic diagram of the comb filter provided in the embodiment of this application filtering out the pilot signal in Figure 23. Detailed Implementation

[0082] In optical fiber communication, wavelength division multiplexing (WDM) systems are typically used to improve transmission capacity and the utilization efficiency of optical fiber resources.

[0083] As shown in Figure 1, a wavelength division multiplexing (WDM) system includes a transmitter, a receiver, and a transmission link connecting the transmitter and receiver. The transmitter may include N transmitters (Tx) and a WDM multiplexer, where the N transmitters can be represented as Tx1, Tx2, ..., TxN, and N is a natural number greater than 2. The receiver may include a demultiplexer and N receivers (Rx), where the N receivers can be represented as Rx1, Rx2, ..., RxN. The transmission link between the transmitter and receiver is an optical fiber, and amplifiers, etc., may also be installed on the transmission link.

[0084] As shown in Figure 2, the transmitter in a wavelength division multiplexing (WDM) system may include a light source, a modulator, and a processor (the first processor in Figure 2). The light source generates an optical signal; the processor (the first processor in Figure 2) outputs a modulation signal to the modulator based on the signal to be transmitted, such as a service signal; the modulator modulates the optical signal generated by the light source based on the received modulation signal to form an optical signal in a wavelength channel. In the transmitter, the processor can be a digital signal processor (DSP), a field-programmable gate array (FPGA), or a microcontroller unit (MCU), etc.; and for ease of distinction, the processor in the transmitter will be referred to as the first processor in this paper.

[0085] In a wavelength division multiplexing (WDM) system, each transmitter at the transmitting end generates an optical signal in one wavelength channel, and N transmitters generate optical signals in N wavelength channels. The optical signals in the N wavelength channels are combined into a single WDM optical signal by a WDM multiplexer. This WDM optical signal is then amplified and transmitted through optical fiber. Finally, this WDM optical signal reaches the receiving end, where a demultiplexer separates it into N wavelength channels. These N wavelength channels are then output to N different receivers, each of which processes the input optical signal.

[0086] As described above, wavelength division multiplexing (WDM) systems include multiple wavelength channels that can be transmitted simultaneously. Especially in dense wavelength division multiplexing (DWDM) systems, due to the reduced channel spacing, 40, 80, or even more wavelength channels can be supported. To ensure the reliable operation of the WDM system and reduce interruptions caused by network failures, pilot tones can be used to monitor the channel status of each wavelength channel in the WDM system.

[0087] A pilot signal is a low-amplitude, low-frequency sinusoidal intensity modulated signal superimposed on the optical signal in the wavelength channel at the transmitting end. As shown in Figure 3, the dense black line at the bottom represents the optical signal in the wavelength channel, and the wavy curve above the dense black line represents the pilot signal. Because the pilot signal, when superimposed on the optical signal in the wavelength channel, modulates the top of the optical signal, it can also be called a top-modulation signal.

[0088] For example, the pilot signal can be represented as: Where f is the pilot frequency of the pilot signal, which is usually 30MHz to 40MHz, and m is the modulation depth, which is (maximum power of optical signal - minimum power of optical signal) / average power of optical signal, which is usually 0.01 to 0.2. This is the initial phase.

[0089] Pilot signals can be used to characterize the power of the superimposed optical signal, that is, the optical power of the corresponding wavelength channel. The optical power of the wavelength channel is the basis for channel status monitoring. Therefore, by superimposing pilot signals on the optical signal in the wavelength channel and then detecting the pilot signals, the channel status of the wavelength channel can be monitored.

[0090] In a wavelength division multiplexing (WDM) system, a pilot signal is modulated for the optical signal in each wavelength channel, and the pilot frequency of the pilot signal modulated for the optical signal in different wavelength channels is different. By detecting the pilot signals at different pilot frequencies in the optical fiber, the channel status of each wavelength channel in the WDM system can be monitored.

[0091] Please refer to Figure 1. To detect the pilot signal in the optical fiber, the wavelength division multiplexing (WDM) system also includes a pilot receiver. This receiver can be connected to the optical fiber between the transmitter and receiver via a power divider. The power divider separates a small portion (e.g., 5% to 20%) of the optical signal (WDM optical signal) transmitted in the optical fiber and outputs it to the pilot receiver. For example, a 10:90 power divider can be used to separate 10% of the optical signal in the optical fiber and output it to the pilot receiver.

[0092] As shown in Figure 4, the pilot receiver includes a photodetector (PD) and a processor (the second processor in Figure 4). The photodetector converts the received optical signal (separated from the power divider) into an electrical signal to detect the pilot signal. Since the pilot frequency range of the pilot signal is typically 30MHz to 40MHz, and the pilot frequency is different in different wavelength channels, a low-frequency (usually on the order of MHz) photodetector can be used to simultaneously detect pilot signals in different wavelength channels, offering the advantage of low implementation cost.

[0093] The photodetector transmits the electrical signal generated by photoelectric conversion to the processor (the second processor in Figure 4). Based on the received electrical signal, the processor (the second processor in Figure 4) can obtain pilot signals of different pilot frequencies, thereby obtaining the optical power of different wavelength channels, and thus realizing the monitoring of the channel status of each wavelength channel in the wavelength division multiplexing system.

[0094] In the pilot receiver, the processor can be a digital signal processor (DSP), a field programmable gate array (FPGA), or a microcontroller unit (MCU), etc.; and for ease of distinction, the processor in the pilot receiver is referred to as the second processor in this paper.

[0095] However, stimulated Raman scattering (SRS) exists in optical fibers, and it becomes particularly severe under long-distance and multi-wavelength channel transmission conditions. Due to SRS, power transfer occurs in optical signals across different wavelength channels, leading to crosstalk between them. Pilot signals in different wavelength channels also experience power transfer, causing some of the pilot signal from one wavelength channel to be transferred to other wavelength channels, forming pilot crosstalk.

[0096] Furthermore, when pilot receivers simultaneously detect pilot signals at different pilot frequencies, they can only distinguish the pilot signals based on the pilot frequency, but cannot distinguish the wavelength channel in which the pilot signal is located. That is, they cannot distinguish the non-crosstalk part of the pilot signal in its own wavelength channel and the crosstalk part that has been transferred to other wavelength channels. As a result, the detection results cannot accurately reflect the optical power of the wavelength channel, thus affecting the accuracy of monitoring the channel status through pilot signals.

[0097] The following section will use three adjacent wavelength channels as an example to explain in detail the impact of SRS on pilot signals and channel status monitoring.

[0098] As shown in Figure 5, the three wavelength channels in the wavelength division multiplexing system are the first wavelength channel λ1, the second wavelength channel λ2, and the third wavelength channel λ3. The first pilot signal f1, the second pilot signal f2, and the third pilot signal f3 are modulated on the optical signals in the first wavelength channel λ1, the second wavelength channel λ2, and the third wavelength channel λ3, respectively. The pilot frequencies of the first pilot signal f1, the second pilot signal f2, and the third pilot signal f3 are f1, f2, and f3, respectively, and f1, f2, and f3 are different.

[0099] As shown in the left figure of Figure 5, in the absence of SRS, based on the above description, the pilot receiver can detect the first pilot signal f1, the second pilot signal f2, and the third pilot signal f3, and the detection results can accurately reflect the optical power in the first wavelength channel λ1, the second wavelength channel λ2, and the third wavelength channel λ3; thus, it can better realize the monitoring of the channel status of the wavelength channels in the wavelength division multiplexing system.

[0100] Furthermore, after the optical signal in the first wavelength channel λ1 is lost at a certain node, the pilot receiver can only detect the second pilot signal f2 and the third pilot signal f3, but cannot detect the first pilot signal f1. Therefore, the lost signal of the first wavelength channel λ1 can be monitored based on the detection results of the pilot receiver. Similarly, after the optical signal in the second wavelength channel λ2 or the third wavelength channel λ3 is lost at a certain node, the pilot receiver can also monitor the corresponding lost signal situation.

[0101] As shown in the right figure of Figure 5, when SRS is present, a portion of the power of the optical signal in the first wavelength channel λ1 will be transferred to the second wavelength channel λ2 and the third waveguide channel λ3. Similarly, a portion of the power of the first pilot signal f1 will also be transferred to the second wavelength channel λ2 and the third waveguide channel λ3. Likewise, a portion of the power of the optical signal in the second wavelength channel λ2 will be transferred to the first wavelength channel λ1 and the third waveguide channel λ3, and a portion of the power of the second pilot signal f2 will also be transferred to the first wavelength channel λ1 and the third waveguide channel λ3. Finally, a portion of the power of the optical signal in the third wavelength channel λ3 will be transferred to the first wavelength channel λ1 and the second waveguide channel λ2, and a portion of the power of the third pilot signal f3 will also be transferred to the first wavelength channel λ1 and the second waveguide channel λ2.

[0102] In this situation, when the pilot receiver simultaneously detects the first pilot signal f1, the second pilot signal f2, and the third pilot signal f3, the detected first pilot signal f1 includes both the portion still in the first wavelength channel λ1 (the non-crosstalk portion in this wavelength channel) and the portion transferred to the second wavelength channel λ2 and the third wavelength channel λ3 (the crosstalk portion); the detected second pilot signal f2 includes both the portion still in the second wavelength channel λ2 (the non-crosstalk portion in this wavelength channel) and the portion transferred to the first wavelength channel λ1 and the third wavelength channel λ3 (the crosstalk portion); the detected third pilot signal f3 includes both the portion still in the third wavelength channel λ3 and the portion transferred to the second wavelength channel λ2 and the first wavelength channel λ1. This results in the detection results failing to accurately reflect the optical power in the first wavelength channel λ1, the second wavelength channel λ2, and the third wavelength channel λ3, affecting the accuracy of monitoring the channel status through the pilot signals.

[0103] Furthermore, when the optical signal in the first wavelength channel λ1 is lost at a certain node, part of the first pilot signal f1 is transferred to the second wavelength channel λ2 and the third waveguide channel λ3. This causes the pilot receiver to still detect the first pilot signal f1 (crosstalk portion) when probing the pilot signal, leading to the mistaken assumption that the optical signal in the first wavelength channel λ1 still exists, thus affecting the accuracy of channel status monitoring via pilot signals. Similarly, the same misjudgment will occur when the optical signal in the second wavelength channel λ2 or the third wavelength channel λ3 is lost at a certain node.

[0104] As can be seen from the above description, the influence of SRS will cause pilot crosstalk in the pilot signal, which will affect the accuracy of the monitoring channel status.

[0105] In related technologies, optical band splitting and high-frequency pilot methods are commonly used to improve the above problems. Among them, optical band splitting refers to using a filter device in the pilot receiving device to divide the optical signal (the optical signal separated by the power divider) into N bands, and then using N photodetectors to detect the optical signal in each of the N bands separately.

[0106] The optical banding method can mitigate the impact of pilot crosstalk on channel status monitoring. Its principle is briefly explained below:

[0107] Assuming a wavelength multiplexing system includes M wavelength channels, the optical signal output to the pilot receiver via a power divider contains the optical signals from all wavelength channels, i.e., the optical signals from all M wavelength channels. After optical banding, each band contains only the optical signals from M / N wavelength channels. When using a photodetector to perform pilot detection on the optical signal in one band, only the pilot signals from M / N wavelength channels can be detected. Therefore, for the pilot signal of one wavelength channel, the photodetector can only detect the non-crosstalk portion within that wavelength channel, and the crosstalk portion that crosstalks into other wavelength channels within the same band; it cannot detect the crosstalk portion that crosstalks into wavelength channels in other bands. This shows that using optical banding can reduce the impact of pilot crosstalk on the detection results to 1 / N of the original crosstalk level, thus improving the accuracy of channel status monitoring to some extent.

[0108] However, the effectiveness of the optical banding method is very limited. For example, in a scheme using four bands, the impact of pilot crosstalk on the detection results is reduced to one-quarter of the original crosstalk, or 6 dB, which is not a significant improvement. Furthermore, the optical banding method requires multiple additional filtering devices and photodetectors, leading to a substantial increase in cost.

[0109] The high-frequency pilot method involves increasing the pilot frequency of the pilot signal from 30MHz to 60MHz to 120MHz to 150MHz. Due to the significant walk-off effect during transmission, optical signals in different wavelength channels cannot remain coherently constructive during pilot crosstalk superposition, resulting in a degree of coherent cancellation. This suppresses pilot crosstalk caused by SRS. As shown in Figure 6, with a pilot frequency of 30MHz to 60MHz, significant crosstalk exists, approximately -25dB. After increasing the pilot frequency to 120MHz to 150MHz, the pilot crosstalk decreases from -25dB to -40dB, achieving a suppression effect of 15dB.

[0110] However, as shown in Figure 7, the high-frequency pilot method suffers from severe frequency fading due to dispersion. That is, the power of the high-frequency pilot signal will decrease due to the fiber itself, which will increase the estimation error of optical power and affect the accuracy of channel status monitoring.

[0111] This shows that while the high-frequency pilot method can suppress pilot crosstalk caused by SRS, it also introduces new estimation errors due to frequency fading caused by dispersion, making it difficult to improve overall performance.

[0112] Based on this, embodiments of this application provide a method for modulating optical signals to improve the above-mentioned problems.

[0113] The technical solutions of the embodiments of this application will now be described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them.

[0114] In the following embodiments of this application, the terms "first," "second," etc., are used for descriptive convenience only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0115] In the embodiments of this application, "upper", "lower", "left" and "right" are not limited to the orientation of the components in the accompanying drawings. It should be understood that these directional terms can be relative concepts, used for relative description and clarification, and can change accordingly depending on the orientation of the components in the accompanying drawings.

[0116] In the embodiments of this application, unless the context otherwise requires, the term "comprising" is interpreted as open and encompassing throughout the specification and claims, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "exemplarily," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this application. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples.

[0117] As used herein, “about,” “approximately,” or “approximately” includes the stated value and the average value within an acceptable range of deviation from the given value, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the given quantity (i.e., the limitations of the measurement system).

[0118] As used herein, “parallel,” “perpendicular,” and “equal” include the described situation and situations that are similar to the described situation, within an acceptable range of deviation, which is determined by those skilled in the art taking into account the measurement under discussion and the error associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, “parallel” includes absolute parallelism and approximate parallelism, where an acceptable range of deviation for approximate parallelism may be, for example, within 5°; “perpendicular” includes absolute perpendicularity and approximate perpendicularity, where an acceptable range of deviation for approximate perpendicularity may also be, for example, within 5°; “equal” includes absolute equality and approximate equality, where an acceptable range of deviation for approximate equality may be, for example, a difference between the two equals being less than or equal to 5% of either one.

[0119] It should be understood that when a layer or element is referred to as being on another layer or substrate, it can mean that the layer or element is directly on the other layer or substrate, or that there is an intermediate layer between the layer or element and the other layer or substrate.

[0120] Exemplary embodiments are described in this application with reference to cross-sectional views and / or plan views and / or equivalent circuit diagrams, which are idealized exemplary drawings. In the drawings, the thickness of layers and regions is enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as being limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing processes. For example, etched regions shown as rectangular would typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0121] This application provides a modulation method for optical signals, which can be applied in the aforementioned wavelength division multiplexing (WDM) system and executed in the transmitter at the transmitting end. Specifically, the modulation method can be applied to the optical signal using a modulator. For ease of description and understanding, the modulation method provided in this application uses one wavelength channel in a WDM system as an example to illustrate the scheme. Modulation methods for optical signals in other wavelength channels in a WDM system can be referred to the description of that wavelength channel.

[0122] As shown in Figure 8, the modulation method may include:

[0123] Step S100: Modulate at least two pilot signal groups onto the optical signal in the first wavelength channel.

[0124] In this system, the first wavelength channel is any wavelength channel in the wavelength division multiplexing system. At least two pilot signal groups are modulated onto the optical signal in the first wavelength channel. Each pilot signal group includes at least two pilot signals with the same pilot frequency and a phase uniformly distributed in the range of 0 to 2π. Here, the uniform distribution of the phase of the pilot signals in the pilot signal group in the range of 0 to 2π means that, assuming there are x (x is a natural number greater than or equal to 2) pilot signals in the pilot signal group, the x pilot signals have x different phases, and these x phases are all in the range of 0 to 2π; and when the x phases are arranged in ascending order, the difference between two adjacent phases is 2π / X.

[0125] Furthermore, the uniform distribution mentioned above can be a strictly uniform distribution or an approximately uniform distribution, as long as the deviation of the approximation is within an acceptable range in the field.

[0126] For example, the pilot signal group may include two pilot signals, namely a first pilot signal and a second pilot signal. The first pilot signal and the second pilot signal have the same pilot frequency and the same phase, namely a first phase and a second phase, respectively. The first phase and the second phase are uniformly distributed in the range of 0 to 2π, for example, they can be 0 and π, or they can be π / 2 and 3π / 2, respectively. That is, the difference between the second phase and the first phase is π, and the first pilot signal and the second pilot signal are a pair of signals with the same frequency but opposite phase.

[0127] Another example is that the pilot signal group may include three pilot signals, namely a first pilot signal, a second pilot signal, and a third pilot signal. The first pilot signal, the second pilot signal, and the third pilot signal have the same pilot frequency and the phases are a first phase, a second phase, and a third phase, respectively. For example, they can be 0, 2π / 3, and 4π / 3, or they can be π / 3, π, and 5π / 3, respectively.

[0128] Pilot signal groups may also include other numbers of pilot signals, which will not be listed here.

[0129] Within the same pilot signal group, different pilot signals are modulated onto optical signals of different frequency bands in the first wavelength channel. The modulation depth, amplitude, and occupied bandwidth of the pilot signals can be the same or different.

[0130] The pilot signals in the pilot signal group adopt the above design. When pilot crosstalk occurs due to SRS, the pilot signals in the same pilot signal group can achieve at least partial cancellation in the crosstalk wavelength channels (other wavelength channels besides the first wavelength channel). Therefore, when the pilot receiving device detects the pilot signal, it can only detect the uncancelled part of the pilot signal that has crosstalked to other wavelength channels. As a result, the proportion of pilot crosstalk in the detection result will be greatly reduced, or even 0. This can improve the impact of pilot crosstalk on the optical power detection result, and thus improve the accuracy of monitoring the channel status through pilot signals.

[0131] To improve the cancellation effect of pilot signals in the same pilot signal group in the wavelength channel of crosstalk when pilot crosstalk occurs due to SRS, the modulation depth, amplitude, and occupied bandwidth of the pilot signals in the pilot signal group can be adjusted. For example, the modulation depth of different pilot signals in the same pilot signal group can be controlled to be the same, and the product of amplitude and occupied bandwidth can be controlled to be equal.

[0132] For example, different pilot signals in the same pilot signal group have the same modulation depth, amplitude, and occupied bandwidth.

[0133] Another example is that different pilot signals in the same pilot signal group have the same modulation depth but different amplitudes and different bandwidths. However, for different pilot signals, the product of amplitude and bandwidth is the same.

[0134] This design allows pilot signals in the same pilot signal group to achieve most or even all cancellation in the wavelength channel of the crosstalk when pilot crosstalk occurs due to SRS. This can further improve the impact of pilot crosstalk on optical power detection results, and thus further improve the accuracy of monitoring channel status through pilot signals.

[0135] As described above, the pilot signal design in the pilot signal group can mitigate the impact of pilot crosstalk on channel status monitoring results. However, when pilot crosstalk occurs due to SRS, it is correlated with wavelength (frequency). Specifically, the larger the frequency interval, the greater the crosstalk. That is, (refer to the right side of Figure 5) when the frequency interval between the first and second wavelength channels is smaller than the frequency interval between the first and third wavelength channels, the portion of the pilot signal from the first wavelength channel that crosstalks into the third wavelength channel will be greater than the portion that crosstalks into the second wavelength channel. Furthermore, since the first wavelength channel itself has a certain bandwidth, the pilot signal crosstalk at different frequency points also varies. For example, when the frequency interval between the first frequency point and the second wavelength channel in the first wavelength channel is greater than the frequency interval between the second frequency point and the second wavelength channel, the portion of the pilot signal at the first frequency point that crosstalks into the second wavelength channel will be greater than the portion of the pilot signal at the second frequency point that crosstalks into the second wavelength channel.

[0136] Therefore, when crosstalk occurs in the pilot signal of the first wavelength channel, the degree of crosstalk varies at different frequency points, generally showing a decreasing trend from one end of the frequency range to the other. Based on this, in the modulation method provided in this application embodiment, at least two pilot signal groups are modulated on the optical signal of the first wavelength channel, and all pilot signal groups in the first wavelength channel are modulated on optical signals of different frequency bands in the first wavelength channel. The pilot frequencies of different pilot signal groups can be the same or different; the number of pilot signals they contain can be the same or different. With this design, when pilot crosstalk occurs due to SRS, the pilot signals in the same pilot signal group can cancel each other out. It can also take into account the correlation between pilot crosstalk and wavelength (frequency), and cancel out the crosstalk generated by pilot signals of different frequency bands in the first wavelength channel respectively. This can further improve the impact of pilot crosstalk on optical power detection results, and further improve the accuracy of monitoring channel status through pilot signals.

[0137] In the modulation method of this application embodiment, the pilot frequency range of the pilot signal is 0.1MHz to 60MHz. Furthermore, in order to distinguish between different wavelength channels, there should be no pilot signals with the same pilot frequency between different wavelength channels.

[0138] The optical signal in the first wavelength channel is generated by a transmitter at the transmitting end. The transmitter modulates the service signal and pilot signal onto the optical signal in the first wavelength channel. For example, as shown in Figure 9, when the transmitter modulates the service signal and pilot signal onto the optical signal in the first wavelength channel, the modulation process may include:

[0139] Step S10: Convert the service signal into a frequency domain signal using Fourier transform.

[0140] Among them, the service signal is the signal that the wavelength division multiplexing system needs to transmit through the first wavelength channel, and the service signal is a time-domain signal.

[0141] Step S20: Divide the frequency domain signal into multiple sub-frequency domain signals according to the pilot signal.

[0142] In step S20, the frequency domain signal can be divided into multiple sub-frequency domain signals according to the frequency range corresponding to the pilot signals, based on the number of pilot signals and the bandwidth occupied by each pilot signal. For example, if the bandwidth of the first wavelength channel is 100 GHz and a total of 4 pilot signals are set, with each pilot signal occupying 25 GHz, the frequency domain signal can be divided into four equal parts to form 4 sub-frequency domain signals with a bandwidth of 25 GHz.

[0143] Step S30: Convert each sub-frequency domain signal into a sub-service signal using inverse Fourier transform.

[0144] Step S40: Merge the corresponding sub-service signals and pilot signals to form a first merged signal, and merge different first merged signals to form a second merged signal.

[0145] As can be seen from the above description, the sub-service signals and pilot signals have a corresponding relationship in the spectrum, and the sub-service signals and pilot signals in the same frequency range will be combined to form the first combined signal.

[0146] Step S50: Control the modulator to perform modulation according to the second combined signal.

[0147] By performing the steps S10 to S50 described above, the transmitter can modulate the service signal and the pilot signal onto the optical signal in the first wavelength channel.

[0148] In addition, the transmitter can also modulate the service signal and the pilot signal on the optical signal in the first wavelength channel in other ways. For example, the service signal can be modulated on the optical signal in the first wavelength channel first, and then the pilot signal can be modulated.

[0149] Step S200: Output the modulated optical signal.

[0150] After step S100, the transmitter modulates the service signal and pilot signal onto the optical signal in the first wavelength channel; then it outputs the optical signal to the wavelength division multiplexer; the wavelength division multiplexer combines the optical signals in multiple wavelength channels generated by different transmitters in the transmitting end into a wavelength division multiplexed optical signal, which is then transmitted through optical fiber.

[0151] As described above, the optical signal in the first wavelength channel includes at least two pilot signal groups, each of which comprises at least two pilot signals with the same pilot frequency and a phase uniformly distributed within the range of 0 to 2π. In this case, when using a pilot receiving device from related technologies to detect all pilot signals, the pilot signals in the pilot signal groups have a cancellation relationship, which may result in the pilot signals being undetectable or the detection result deviating significantly from the actual result.

[0152] Based on this, the present application embodiment further improves the pilot receiving device. As shown in Figure 10, the pilot receiving device provided in this application embodiment includes a comb filter, a photodetector, and a second processor. The comb filter has a passband and a stopband arranged in the spectrum. During operation, the comb filter receives the optical signal separated from the power divider, filters out the portion of the optical signal located in the passband, and blocks the portion located in the stopband. The bandwidth of the passband in the comb filter and its position in the spectrum form a target frequency band, enabling the comb filter to filter out the portion of the optical signal located in the target frequency band. By designing the bandwidth and position of the passband and stopband in the comb filter in the spectrum, different target frequency bands can be formed, thereby achieving different filtering purposes to match different application scenarios.

[0153] For the optical signal generated by the above modulation method, the target frequency band can be aligned with one pilot signal from at least one pilot signal group in the first wavelength channel by designing a comb filter, thereby achieving the purpose of filtering out one pilot signal from at least one pilot signal group. When filtering out pilot signals from different pilot signal groups simultaneously, it is necessary to ensure that the pilot signals filtered from different pilot signal groups do not have a canceling relationship. For example, the filtered pilot signals can have different pilot frequencies; or, for example, if the filtered pilot signals have the same pilot frequency, their phases should be in the same quadrant, that is, both should be in the interval of 0 to π / 2, π / 2 to π, π to 3π / 2, or 3π / 2 to 0.

[0154] The comb filter outputs the filtered optical signal (the optical signal located in the target frequency band) to a photodetector. The photodetector detects the pilot signal in the optical signal and then outputs the detection result (electrical signal) to a second processor. Based on the detection result of the photodetector and the design parameters of the comb filter, the second processor can obtain the optical power in the first wavelength channel, thereby achieving the purpose of monitoring the channel status.

[0155] In the pilot receiving device provided in the embodiments of this application, the comb filter is implemented using devices such as a wavelength selective switch, a Mach-Zehnder interferometer, a Michelson interferometer, or an interferometer implemented using an arrayed waveguide grating.

[0156] As described above, pilot crosstalk is correlated with wavelength (frequency). When crosstalk occurs in the pilot signal of the first wavelength channel, the degree of crosstalk varies at different frequency points, generally showing a decreasing trend from one end of the frequency range to the other. Therefore, when different pilot signals in the pilot signal group are canceled, perfect cancellation cannot be achieved, and a certain amount of cancellation residue will remain. This cancellation residue will affect the detection results of optical power, thereby affecting the accuracy of monitoring the channel status through pilot signals.

[0157] Based on this, this application also provides another modulation method. The difference between this method and the modulation method described above is that, in step S100, at least two pilot signal groups are modulated onto the optical signal in the first wavelength channel. All pilot signal groups in the first wavelength channel have the same pilot frequency, and the phase arrangement of the pilot signals in all pilot signal groups on the spectrum of the optical signal in the first wavelength channel has a relationship that allows the pilot signal groups to cancel each other out again. As described above, the pilot signals in each pilot signal group have a certain amount of cancellation residue during cancellation. The re-cancellation relationship between pilot signal groups means that by designing the phase and order of the pilot signals in different pilot signal groups, the cancellation residue generated by each pilot signal group can also be canceled out, i.e., re-cancellation is achieved; thereby further improving the impact of pilot crosstalk on the optical power detection results, and thus improving the accuracy of monitoring the channel status through pilot signals.

[0158] In some embodiments, two pilot signal groups, namely a first pilot signal group and a second pilot signal group, are modulated onto the optical signal in the first wavelength channel. The first pilot signal group and the second pilot signal group have the same pilot signal, but the pilot signals in the first pilot signal group and the second pilot signal group are arranged in opposite phase order on the spectrum of the optical signal in the first waveguide channel.

[0159] It should be noted that the ordering of pilot signals on the spectrum of the optical signal in the first wavelength channel mentioned in this article refers to the fact that different pilot signals occupy different frequency ranges on the optical signal in the first wavelength channel, and the different pilot signals are ordered from small to large frequency.

[0160] For information on the pilot signals contained in the first and second pilot signal groups, please refer to the description of pilot signal groups and pilot signals above.

[0161] In some embodiments, both the first pilot signal group and the second pilot signal group include two pilot signals, namely a first pilot signal and a second pilot signal, which form a signal pair with the same frequency but opposite phase. In the optical signal spectrum in the first waveguide channel, the first pilot signal and the second pilot signal in the first pilot signal group and the second pilot signal group are arranged in opposite order.

[0162] For example, as shown in Figure 11, there are two adjacent wavelength channels in the frequency range of 193 THz to 193.1 THz, namely the first wavelength channel and the second wavelength channel. The bandwidth of the first wavelength channel and the second wavelength channel is 50 GHz, and the frequency range is simply represented as 0 GHz to 50 GHz and 50 GHz to 100 GHz, respectively.

[0163] When modulating the optical signal in the first wavelength channel, a first pilot signal is modulated in a frequency band ranging from 0 GHz to 12.5 GHz, which can be expressed as m*sin(2πf1t+π); a second pilot signal, which is in the same frequency but out of phase with the first pilot signal, is modulated in a frequency band ranging from 12.5 GHz to 25 GHz, which can also be expressed as m*sin(2πf1t). The modulated first and second pilot signals together form the first pilot signal group.

[0164] A second pilot signal is modulated in a frequency band ranging from 25 GHz to 37.5 GHz, and the second pilot signal can be expressed as m*sin(2πf1t); a first pilot signal is modulated in a frequency band ranging from 37.5 GHz to 50 GHz, and the first pilot signal can be expressed as m*sin(2πf1t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0165] When modulating the optical signal in the second wavelength channel, a first pilot signal is modulated in a frequency band ranging from 50 GHz to 62.5 GHz, which can be expressed as m*sin(2πf²t+π); a second pilot signal, which is in the same frequency but out of phase with the first pilot signal, is modulated in a frequency band ranging from 62.5 GHz to 75 GHz, which can also be expressed as m*sin(2πf²t). The modulated first and second pilot signals together form the first pilot signal group.

[0166] A second pilot signal is modulated in a frequency band ranging from 75 GHz to 87.5 GHz, and the second pilot signal can be expressed as m*sin(2πf²t); a first pilot signal is modulated in a frequency band ranging from 87.5 GHz to 100 GHz, and the first pilot signal can be expressed as m*sin(2πf²t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0167] It can be seen that in this example, both the first and second wavelength channels are modulated with two pilot signal groups, each of which includes two pilot signals of the same frequency but opposite phase; and, in the two pilot signal groups in each wavelength channel, the first and second pilot signals are ordered in opposite directions on the optical signal spectrum.

[0168] Furthermore, the pilot frequencies of the four pilot signals in the first wavelength channel are all f1, and the pilot frequencies of the four pilot signals in the second wavelength channel are all f2. Moreover, the four pilot signals in the same wavelength channel are evenly distributed across the spectrum, with each pilot signal occupying the same bandwidth of 12.5 GHz.

[0169] When using a pilot receiver to receive and detect the above-mentioned pilot signals, the same pilot signals in the two pilot signal groups in each wavelength channel can be filtered out by designing the target frequency band in the comb filter, that is, filtering out all the first pilot signals or all the second pilot signals.

[0170] In this example, as shown in Figure 12, the comb filter can adopt a 25 GHz passband specification, with target frequency bands of 12.5 GHz to 37.5 GHz and 62.5 GHz to 87.5 GHz; it is used to filter out all the second pilot signals. The photodetector and the second processor can obtain the optical power of the first wavelength channel and the second wavelength channel based on the optical signals filtered out by the comb filter, thereby achieving the purpose of monitoring the channel status.

[0171] As another example, as shown in Figure 13, there are two adjacent wavelength channels within a 50 GHz bandwidth, namely the first wavelength channel and the second wavelength channel. The bandwidth of both the first and second wavelength channels is 25 GHz, and their frequency ranges are simply represented as 0 GHz to 25 GHz and 25 GHz to 50 GHz, respectively.

[0172] When modulating the optical signal in the first wavelength channel, a first pilot signal is modulated in a frequency band ranging from 0 GHz to 6.25 GHz, which can be expressed as m*sin(2πf1t+π); a second pilot signal, which is in the same frequency but out of phase with the first pilot signal, is modulated in a frequency band ranging from 6.25 GHz to 12.5 GHz, which can also be expressed as m*sin(2πf1t). The modulated first and second pilot signals together form the first pilot signal group.

[0173] A second pilot signal is modulated in a frequency band ranging from 12.5 GHz to 18.75 GHz, and the second pilot signal can be expressed as m*sin(2πf1t); a first pilot signal is modulated in a frequency band ranging from 18.75 GHz to 25 GHz, and the first pilot signal can be expressed as m*sin(2πf1t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0174] When modulating the optical signal in the second wavelength channel, a first pilot signal is modulated in a frequency band ranging from 25 GHz to 31.25 GHz, which can be expressed as m*sin(2πf²t+π); a second pilot signal, which is in the same frequency but out of phase with the first pilot signal, is modulated in a frequency band ranging from 31.25 GHz to 37.5 GHz, which can also be expressed as m*sin(2πf²t). The modulated first and second pilot signals together form the first pilot signal group.

[0175] A second pilot signal is modulated in a frequency band ranging from 37.5 GHz to 43.75 GHz, and the second pilot signal can be expressed as m*sin(2πf²t); a first pilot signal is modulated in a frequency band ranging from 43.75 GHz to 50 GHz, and the first pilot signal can be expressed as m*sin(2πf²t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0176] It can be seen that in this example, both the first and second wavelength channels are modulated with two pilot signal groups, each of which includes two pilot signals of the same frequency but opposite phase; and, in the two pilot signal groups in each wavelength channel, the first and second pilot signals are ordered in opposite directions on the optical signal spectrum.

[0177] Furthermore, the pilot frequencies of the four pilot signals in the first wavelength channel are all f1, and the pilot frequencies of the four pilot signals in the second wavelength channel are all f2. Moreover, the four pilot signals in the same wavelength channel are evenly distributed across the spectrum, with each pilot signal occupying the same bandwidth of 6.25 GHz.

[0178] When using a pilot receiver to receive and detect the aforementioned pilot signals, the same pilot signals in the two pilot signal groups within each wavelength channel can be filtered out by designing the target frequency band in the comb filter; that is, all first pilot signals or all second pilot signals can be filtered out. In this example, as shown in Figure 14, the comb filter can adopt a 12.5 GHz passband specification, with target frequency bands of 6.25 GHz to 18.75 GHz and 31.25 GHz to 43.75 GHz; it is used to filter out all second pilot signals. The photodetector and the second processor can obtain the optical power of the first and second wavelength channels based on the optical signals filtered out by the comb filter, thereby achieving the purpose of channel status monitoring.

[0179] As another example, as shown in Figure 15, there are two adjacent wavelength channels within a bandwidth of 150 GHz, namely the first wavelength channel and the second wavelength channel. The bandwidth of both the first wavelength channel and the second wavelength channel is 75 GHz, and the frequency ranges are simply represented as 0 GHz to 75 GHz and 75 GHz to 150 GHz, respectively.

[0180] When modulating the optical signal in the first wavelength channel, a first pilot signal is modulated in a frequency band ranging from 0 GHz to 12.5 GHz, which can be expressed as m*sin(2πf1t+π); a second pilot signal is modulated in a frequency band ranging from 12.5 GHz to 37.5 GHz, which can be expressed as m*0.5*sin(2πf1t). The second pilot signal is in the same frequency and out of phase with the first pilot signal. The amplitudes of the first and second pilot signals are the first amplitude and the second amplitude, respectively, with the first amplitude being twice the second amplitude. The bandwidths occupied by the first and second pilot signals are the first bandwidth and the second bandwidth, respectively, with the second bandwidth being twice the first bandwidth. The product of the first amplitude and the first bandwidth and the product of the second amplitude and the second bandwidth are equal. The modulated first and second pilot signals constitute the first pilot signal group.

[0181] A second pilot signal is modulated in a frequency band ranging from 37.5 GHz to 62.5 GHz, and the second pilot signal can be expressed as m*0.5*sin(2πf1t); a first pilot signal is modulated in a frequency band ranging from 62.5 GHz to 75 GHz, and the first pilot signal can be expressed as m*sin(2πf1t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0182] For the second wavelength channel, a first pilot signal is modulated in a frequency band ranging from 75 GHz to 87.5 GHz, and the first pilot signal can be expressed as m*sin(2πf²t+π); a second pilot signal is modulated in a frequency band ranging from 87.5 GHz to 112.5 GHz, and the second pilot signal can be expressed as m*0.5*sin(2πf²t). The modulated first and second pilot signals constitute the first pilot signal group.

[0183] A second pilot signal is modulated in a frequency band ranging from 112.5 GHz to 137.5 GHz, and the second pilot signal can be expressed as m*0.5*sin(2πf²t); a first pilot signal is modulated in a frequency band ranging from 137.5 GHz to 150 GHz, and the first pilot signal can be expressed as m*sin(2πf²t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0184] It can be seen that in this example, both the first and second wavelength channels are modulated with two pilot signal groups, each of which includes two pilot signals of the same frequency but opposite phase; and, in the two pilot signal groups in each wavelength channel, the first and second pilot signals are ordered in opposite directions on the optical signal spectrum.

[0185] Furthermore, the pilot frequencies of the four pilot signals in the first wavelength channel are all f1, and the pilot frequencies of the four pilot signals in the second wavelength channel are all f2. Within the same group of pilot signals, the amplitudes and bandwidths occupied by the first and second pilot signals are different, but the product of their amplitudes and bandwidths is equal.

[0186] When using a pilot receiver to receive and detect the aforementioned pilot signals, the passband of the comb filter can be designed to filter out the identical pilot signals in the two pilot signal groups within each wavelength channel, i.e., to filter out all first pilot signals or all second pilot signals. In this example, as shown in Figure 16, the comb filter can be a 50GHz specification, with target frequency bands of 12.5GHz to 62.5GHz and 87.5GHz to 137.5GHz, used to filter out all second pilot signals. The photodetector and the second processor can obtain the optical power of the first and second wavelength channels based on the optical signals filtered out by the comb filter, thereby achieving the purpose of channel status monitoring.

[0187] As can be seen from the above three examples, the modulation method provided in this application embodiment can be applied to wavelength channels with bandwidth that is an integer multiple of 25 GHz, and the specifications of the comb filter can be half or more than half the bandwidth of the wavelength channel; it has the advantages of good applicability and can match a variety of different application scenarios.

[0188] Because the passband and stopband of a comb filter are typically not perfectly rectangular spectra, pilot signals adjacent to the target frequency band are easily filtered out along with the target frequency band pilot signals. However, pilot signals adjacent to the target frequency band usually have a canceling relationship with the pilot signals in the target frequency band. This results in the simultaneous filtering out of canceling pilot signals, affecting the signal-to-noise ratio of pilot signal detection, and consequently affecting the accuracy of optical power detection and channel status monitoring. For example, in the examples shown in Figures 11 and 12, the comb filters range from 12.5 GHz to 37.5 GHz and from 62.5 GHz to 87.5 GHz. However, due to the comb filter, while filtering out the second pilot signals in the frequency ranges of 12.5GHz to 37.5GHz and 62.5GHz to 87.5GHz, it also filters out the first pilot signals near the frequencies of 12.5GHz, 37.5GHz, 62.5GHz, and 87.5GHz. The first and second pilot signals are in-phase and out-of-phase signals with a canceling relationship, which affects the signal-to-noise ratio of the photodetector's detection of the second pilot signal, and thus affects the accuracy of optical power detection and channel status monitoring.

[0189] Based on this, in some embodiments, when modulating the pilot signal on the optical signal of the first wavelength channel, a certain bandwidth of guard interval is reserved in the spectrum of the optical signal. That is, adjacent pilot signals have a certain guard interval in the spectrum, and the pilot signal is not modulated in the guard interval, thereby achieving the purpose of setting the interval between adjacent pilot signals. This design can effectively isolate adjacent pilot signals in the spectrum of the optical signal, so that when a pilot receiving device filters out a certain pilot signal, adjacent pilot signals will not be filtered out, improving the signal-to-noise ratio of pilot signal detection, and improving the accuracy of optical power detection and channel status monitoring.

[0190] The guard interval can be located at one end or both ends of the pilot signal in the optical signal spectrum. The bandwidth of the guard interval can be from 0.5 GHz to 1.5 GHz, and its specific size can be determined according to the bandwidth of the first wavelength channel, the number of pilot signals, and the bandwidth of the pilot signals.

[0191] For example, as shown in Figure 17, there are two adjacent wavelength channels within a bandwidth of 100 GHz, namely the first wavelength channel and the second wavelength channel. The bandwidth of both the first wavelength channel and the second wavelength channel is 50 GHz, and the frequency range is simply represented as 0 GHz to 50 GHz and 50 GHz to 100 GHz, respectively.

[0192] When modulating the optical signal in the first wavelength channel, a first pilot signal is modulated in a frequency band ranging from 0.5 GHz to 12 GHz, and the first pilot signal can be expressed as m*sin(2πf1t+π); a second pilot signal, which has the same frequency but is out of phase with the first pilot signal, is modulated in a frequency band ranging from 13 GHz to 24.5 GHz, and the second pilot signal can be expressed as m*sin(2πf1t). The first and second pilot signals modulated above constitute the first pilot signal group.

[0193] A second pilot signal is modulated in a frequency band ranging from 25.5 GHz to 37 GHz, and the second pilot signal can be expressed as m*sin(2πf1t); a first pilot signal is modulated in a frequency band ranging from 38 GHz to 49.5 GHz, and the first pilot signal can be expressed as m*sin(2πf1t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0194] When modulating the optical signal in the second wavelength channel, a first pilot signal is modulated in a frequency band ranging from 50.5 GHz to 62 GHz, which can be expressed as m*sin(2πf²t+π); a second pilot signal, which is in the same frequency but out of phase with the first pilot signal, is modulated in a frequency band ranging from 63 GHz to 74.5 GHz, which can also be expressed as m*sin(2πf²t). The modulated first and second pilot signals together form the first pilot signal group.

[0195] A second pilot signal is modulated in a frequency band ranging from 75.5 GHz to 87 GHz, and the second pilot signal can be expressed as m*sin(2πf²t); a first pilot signal is modulated in a frequency band ranging from 88 GHz to 99.5 GHz, and the first pilot signal can be expressed as m*sin(2πf²t+π). The modulated second pilot signal and the first pilot signal together form a second pilot signal group.

[0196] It can be seen that in this example, both the first and second wavelength channels are modulated with two pilot signal groups, each of which includes two pilot signals of the same frequency but opposite phase; and, in the two pilot signal groups in each wavelength channel, the first and second pilot signals are ordered in opposite directions on the optical signal spectrum.

[0197] Furthermore, the pilot frequencies of the four pilot signals in the first wavelength channel are all f1, and the pilot frequencies of the four pilot signals in the second wavelength channel are all f2. Moreover, the four pilot signals in the same wavelength channel are evenly distributed across the spectrum, meaning they occupy the same bandwidth of 11.5 GHz. There is a 0.5 GHz guard interval at both ends of the pilot signals.

[0198] When using a pilot receiver to receive and detect the aforementioned pilot signals, as shown in Figure 18, the comb filter can adopt a 25 GHz passband specification, with target frequency bands of 12.5 GHz to 37.5 GHz and 62.5 GHz to 87.5 GHz; it is used to filter out all the second pilot signals. The photodetector and the second processor can obtain the optical power of the first wavelength channel and the second wavelength channel based on the optical signal filtered out by the comb filter, thereby achieving the purpose of monitoring the channel status.

[0199] Please continue referring to Figure 18. Due to the guard interval, in the optical signal spectrum of the first wavelength channel, the frequency ranges occupied by the first pilot signal and the second pilot signal in the first pilot signal group are 0.5 GHz to 12 GHz and 13 GHz to 24.5 GHz, respectively; and the frequency ranges occupied by the second pilot signal and the first pilot signal in the second pilot signal group are 25.5 GHz to 37 GHz and 38 GHz to 49.5 GHz, respectively. In the optical signal spectrum of the second wavelength channel, the frequency ranges occupied by the first pilot signal and the second pilot signal in the first pilot signal group are 50.5 GHz to 62 GHz and 63 GHz to 74.5 GHz, respectively; and the frequency ranges occupied by the second pilot signal and the first pilot signal in the second pilot signal group are 75.5 GHz to 87 GHz and 88 GHz to 99.5 GHz, respectively. Therefore, when the target frequency bands of the comb filter are 12.5 GHz to 37.5 GHz and 62.5 GHz to 87.5 GHz, even if the passband and stopband of the comb filter are not perfectly rectangular, pilot signals adjacent to the target frequency band can be avoided. This improves the signal-to-noise ratio of pilot signal detection, and enhances the accuracy of optical power detection and channel status monitoring.

[0200] In some embodiments, both the first pilot signal group and the second pilot signal group include three pilot signals, namely a first pilot signal, a second pilot signal, and a third pilot signal, with the first pilot signal, the second pilot signal, and the third pilot signal having phases of a first phase, a second phase, and a third phase, respectively. The first phase, the second phase, and the third phase are uniformly distributed in the range of 0 to 2π. In the optical signal spectrum in the first waveguide channel, the first pilot signal, the second pilot signal, and the third pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

[0201] For example, as shown in Figure 19, the bandwidth of the first wavelength channel is 75 GHz, and the frequency range is simply expressed as 0 GHz to 75 GHz.

[0202] When modulating the optical signal in the first wavelength channel, a first pilot signal is modulated in a frequency band ranging from 0 GHz to 12.5 GHz, which can be represented as m*sin(2πf1t); a second pilot signal is modulated in a frequency band ranging from 12.5 GHz to 25 GHz, which can be represented as m*sin(2πf1t+2π / 3); and a third pilot signal is modulated in a frequency band ranging from 25 GHz to 37.5 GHz, which can be represented as m*sin(2πf1t+4π / 3). The modulated first, second, and third pilot signals constitute the first pilot signal group.

[0203] A third pilot signal is modulated in a frequency band ranging from 37.5 GHz to 50 GHz. The second pilot signal can be expressed as m*sin(2πf1t+4π / 3). A second pilot signal is modulated in a frequency band ranging from 50 GHz to 62.5 GHz. The second pilot signal can be expressed as m*sin(2πf1t+2π / 3). A first pilot signal is modulated in a frequency band ranging from 62.5 GHz to 75 GHz. The modulated third, second, and first pilot signals constitute the second pilot signal group.

[0204] As can be seen from this, in this example, the first wavelength channel modulation has two pilot signal groups, each of which includes three pilot signals: a first pilot signal, a second pilot signal, and a third pilot signal. The three pilot signals have the same pilot frequency and their phases are uniformly distributed in the range of 0 to 2π. Furthermore, in the spectrum of the optical signal in the first wavelength channel, the first pilot signal, the second pilot signal, and the third pilot signal in the two pilot signal groups are arranged in reverse order.

[0205] In addition, the pilot frequencies of the six pilot signals in the first wavelength channel are all f1, and they are evenly distributed on the spectrum. Each pilot signal occupies the same bandwidth, which is 12.5 GHz.

[0206] When using a pilot receiver to receive and detect the above-mentioned pilot signals, the same pilot signals in the two pilot signal groups in the first wavelength channel can be filtered out by designing the target frequency band in the comb filter, that is, all the first pilot signals, the second pilot signals, or the third pilot signals can be filtered out.

[0207] In this example, as shown in Figure 20, the comb filter can adopt a 25 GHz passband specification, with a target frequency band of 25 GHz to 50 GHz, to filter out all the third pilot signals. The photodetector and the second processor can obtain the optical power of the first wavelength channel based on the optical signal filtered out by the comb filter, thereby achieving the purpose of monitoring the channel status.

[0208] In some embodiments, three pilot signal groups are modulated onto the optical signal in the first wavelength channel, namely, a first pilot signal group, a second pilot signal group, and a third pilot signal group. The first pilot signal group, the second pilot signal group, and the third pilot signal group have the same number of pilot signals. Regarding the pilot signals included in the first pilot signal group, the second pilot signal group, and the third pilot signal group, refer to the description of pilot signal groups and pilot signals above.

[0209] On the optical signal of the first wavelength channel, by controlling the phase and order of the pilot signals in each pilot signal group, the cancellation residue generated by the three pilot signal groups can be canceled again.

[0210] For example, as shown in Figure 21, the bandwidth of the first wavelength channel is 75 GHz, and the frequency range is simply expressed as 0 GHz to 75 GHz.

[0211] When modulating the optical signal in the first wavelength channel, a first pilot signal is modulated in a frequency band ranging from 0 GHz to 12.5 GHz, which can be expressed as m*sin(2πf1t); a second pilot signal is modulated in a frequency band ranging from 12.5 GHz to 25 GHz, which can be expressed as m*sin(2πf1t+π); the first and second pilot signals modulated above form a first pilot signal group.

[0212] A third pilot signal is modulated in a frequency band ranging from 25 GHz to 37.5 GHz, and the third pilot signal can be expressed as m*sin(2πf1t+4π / 3); a fourth pilot signal is modulated in a frequency band ranging from 37.5 GHz to 50 GHz, and the fourth pilot signal can be expressed as m*sin(2πf1t+π / 3); the modulated third and fourth pilot signals form a second pilot signal group.

[0213] A fifth pilot signal is modulated in a frequency band ranging from 50 GHz to 62.5 GHz, and the fifth pilot signal can be expressed as m*sin(2πf1t+2π / 3); a sixth pilot signal is modulated in a frequency band ranging from 62.5 GHz to 75 GHz, and the sixth pilot signal can be expressed as m*sin(2πf1t+5π / 3). The modulated fifth and sixth pilot signals together form the third pilot signal group.

[0214] As can be seen from this, in this example, the first wavelength channel modulation has three pilot signal groups, each of which includes two pilot signals with the same pilot frequency but out of phase. The pilot frequencies of the six pilot signals in the first wavelength channel are all f1, and they are evenly distributed on the spectrum. Each pilot signal occupies the same bandwidth, which is 12.5 GHz.

[0215] When using a pilot receiver to receive and detect the aforementioned pilot signals, the pilot signal in at least one pilot signal group in the first wavelength channel can be filtered out by designing the target frequency band in the comb filter.

[0216] In this example, as shown in Figure 22, the comb filter can adopt a 12.5 GHz passband specification, with target frequency bands of 0 GHz to 12.5 GHz and 37.5 GHz to 50 GHz, and is used to filter out the first pilot signal and the fourth pilot signal. The photodetector and the second processor can obtain the optical power of the first wavelength channel based on the optical signal filtered out by the comb filter, thereby achieving the purpose of monitoring the channel status.

[0217] This application also provides another modulation method, which differs from the modulation method in the above embodiments in that, in step S100, at least two pilot signal groups are modulated onto the optical signal in the first wavelength channel; wherein, all pilot signal groups in the first wavelength channel are modulated onto optical signals in different frequency bands. Each pilot signal group includes at least two pilot signals with the same pilot frequency, and the pilot signals in the same pilot signal group have a cancellation relationship. Furthermore, the pilot frequencies are different in all pilot signal groups in the first wavelength channel.

[0218] This design allows for the detection of pilot signals with different pilot frequencies when the pilot signal is detected by the pilot receiver, thereby enabling the detection of optical power at different positions in the first wavelength channel.

[0219] In the modulation method provided in this application embodiment, each pilot signal group can be configured with pilot signals as described in the above embodiments. At each pilot frequency, one pilot signal group can be modulated, or at least two pilot signal groups can be modulated. When modulating at least two pilot signal groups at the same pilot frequency, the pilot signal groups can be designed to cancel each other out again, as described in the above embodiments.

[0220] For different pilot frequencies, the number of pilot signal groups, the pilot signals in the pilot signal groups, and the bandwidth they occupy can be the same or different. Pilot signals at the same pilot frequency can be concentrated on the spectrum of the optical signal in the first wavelength channel, or they can be interspersed with pilot signals at other pilot frequencies.

[0221] The number of pilot signal groups and the number of different pilot frequencies in the first wavelength channel can be determined based on the resolution of optical power detection in the first wavelength channel. The bandwidth occupied by each pilot signal, each pilot signal group, and each pilot signal group at each pilot frequency can be determined based on factors such as the bandwidth of the first wavelength channel, the number of pilot frequencies, the number of pilot signal groups at the same pilot frequency, and the number of pilot signals in the pilot signal group.

[0222] In some embodiments, the first wavelength channel has at least 10 groups of pilot signals with different pilot frequencies. This design allows for high-resolution detection of optical power at different locations within the first wavelength channel by detecting pilot signals with at least 10 different pilot frequencies.

[0223] In some embodiments, for different pilot frequencies, the number of pilot signal groups, the pilot signals in the pilot signal groups, and the bandwidth occupied are all the same; and the pilot signals in different pilot frequencies are all arranged in the same order, with pilot signals in the same order in the same pilot signal group being arranged in a concentrated manner.

[0224] For example, as shown in Figure 23, the bandwidth of the first wavelength channel is 100 GHz, and the frequency range is simply expressed as 0 GHz to 100 GHz.

[0225] When modulating the optical signal in the first wavelength channel, 25 pilot signals with different pilot frequencies are modulated in 25 frequency bands ranging from 0 GHz to 1 GHz, 1 GHz to 2 GHz, ..., 24 GHz to 25 GHz. These 25 pilot signals can be represented as m*sin(2πf1t+π), m*sin(2πf2t+π), ..., m*sin(2πf... 25 t+π).

[0226] The second pilot signal is modulated at 25 pilot frequencies across 25 frequency bands: 25 GHz to 26 GHz, 26 GHz to 27 GHz, ..., 49 GHz to 50 GHz. These 25 pilot frequencies can be represented as m*sin(2πf1t), m*sin(2πf2t), ..., m*sin(2πf... 25 The first pilot signal and the second pilot signal, which are modulated to the same pilot frequency band as described above, constitute the first pilot signal group.

[0227] The second pilot signal is modulated at 25 different pilot frequencies across 25 frequency bands: 50GHz to 51GHz, 51GHz to 52GHz, ..., 74GHz to 75GHz. The second pilot signal at each of the 25 pilot frequencies can be expressed as m*sin(2πf)25 t), m*sin(2πf 24 t),...,m*sin(2πf1t).

[0228] The first pilot signal is modulated at 25 different pilot frequencies across 25 frequency bands: 75GHz to 76GHz, 76GHz to 77GHz, ..., 99GHz to 100GHz. The first pilot signal at each of the 25 pilot frequencies can be expressed as m*sin(2πf) 25 t+π), m*sin(2πf) 24 t+π), ..., m*sin(2πf1t+π). The first pilot signal and the second pilot signal with the same modulated pilot frequency band as described above constitute the first pilot signal group.

[0229] Therefore, in this example, the first wavelength channel modulates 50 pilot signal groups at 25 different pilot frequencies. Each pilot frequency includes two pilot signal groups, and each pilot signal group includes two pairs of signals with the same frequency but opposite phase. The pilot signals in the two pilot signal groups are arranged in reverse order. The first wavelength channel has a total of 100 pilot signals, which are evenly distributed across the spectrum. Each pilot signal occupies the same bandwidth, which is 1 GHz.

[0230] When using a pilot receiver to receive and detect the aforementioned pilot signals, at least one pilot signal at each pilot frequency in the first wavelength channel can be filtered out by designing the target frequency band in the comb filter. In this example, as shown in Figure 24, the comb filter can be a 50GHz specification, with a target frequency band of 25GHz to 75GHz, used to filter out two second pilot signals at all pilot frequencies. The photodetector and the second processor can obtain the optical power at 25 points in the first wavelength channel based on the optical signals filtered out by the comb filter.

[0231] This application also provides a transmitter, which is applied to the transmitting end of a wavelength division multiplexing (WDM) system, and includes a light source and a modulator. The light source is used to generate an optical signal in a first wavelength channel; the modulator is used to receive the optical signal generated by the light source and execute the modulation method described in the above embodiments.

[0232] In some embodiments, the transmitter further includes a processor; the processor is configured to send a modulation signal to a modulator, the modulation signal being formed according to the method content of step S100 of the modulation method described in the above embodiments; the modulator modulates the light signal generated by the light source according to the received modulation signal.

[0233] This application also provides a wavelength division multiplexing (WDM) system, which uses the pilot receiver and transmitter provided in the above embodiments.

[0234] The transmitter and wavelength division multiplexing system provided in this application have the same technical effects as the modulation method in any of the above embodiments, and will not be described again here.

[0235] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for modulating an optical signal, characterized in that, The modulation method includes: At least two pilot signal groups are modulated onto the optical signal in the first wavelength channel; wherein the first wavelength channel is any wavelength channel in the wavelength division multiplexing system; the at least two pilot signal groups are respectively modulated onto different frequency bands of the optical signal; the pilot signal group includes at least two pilot signals with the same pilot frequency and a phase uniformly distributed in the range of 0 to 2π. The modulated optical signal is output.

2. The modulation method according to claim 1, characterized in that, The pilot frequencies of the pilot signals in the at least two pilot signal groups are the same; In the spectrum of the optical signal, the phase arrangement of the pilot signals in the at least two pilot signal groups has a relationship that causes the pilot signal groups to cancel each other out again.

3. The modulation method according to claim 2, characterized in that, The at least two pilot signal groups include two pilot signal groups, namely a first pilot signal group and a second pilot signal group; The first pilot signal group and the second pilot signal group each include two pilot signals, namely a first pilot signal and a second pilot signal; the first pilot signal and the second pilot signal are out of phase. On the spectrum of the optical signal, the first pilot signal and the second pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

4. The modulation method according to claim 3, characterized in that, In at least one of the pilot signal groups, the amplitude of the first pilot signal is a first amplitude and is modulated on a frequency band of a first bandwidth in the optical signal; the amplitude of the second pilot signal is a second amplitude and is modulated on a frequency band of a second bandwidth in the optical signal; the product of the first amplitude and the first bandwidth and the product of the second amplitude and the second bandwidth are equal.

5. The modulation method according to claim 4, characterized in that, The first amplitude and the second amplitude are equal, and the first bandwidth and the second bandwidth are equal; Alternatively, the first amplitude and the second amplitude are not equal, and the first bandwidth and the second bandwidth are not equal.

6. The modulation method according to claim 2, characterized in that, The at least two pilot signal groups include two pilot signal groups, namely a first pilot signal group and a second pilot signal group; The first pilot signal group and the second pilot signal group each include three pilot signals, namely a first pilot signal, a second pilot signal, and a third pilot signal; the phases of the first pilot signal, the second pilot signal, and the third pilot signal are uniformly distributed in the range of 0 to 2π. On the spectrum of the optical signal, the first pilot signal, the second pilot signal, and the third pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

7. The modulation method according to claim 2, characterized in that, The at least two pilot signal groups include three pilot signal groups, namely a first pilot signal group, a second pilot signal group, and a third pilot signal group; The first pilot signal group, the second pilot signal group, and the third pilot signal group are arranged sequentially on the spectrum of the optical signal and have the same number of pilot signals.

8. The modulation method according to claim 7, characterized in that, The first pilot signal group includes a first pilot signal and a second pilot signal arranged sequentially on the spectrum of the optical signal; the phases of the first pilot signal and the second pilot signal are a first phase and a second phase, respectively; The second pilot signal group includes a third pilot signal and a fourth pilot signal arranged sequentially on the spectrum of the optical signal; the phases of the third pilot signal and the fourth pilot signal are the third phase and the fourth phase, respectively; The third pilot signal group includes a fifth pilot signal and a sixth pilot signal arranged sequentially on the spectrum of the optical signal; the phases of the fifth pilot signal and the sixth pilot signal are the fifth phase and the sixth phase, respectively; Wherein, the phase difference between the second phase and the first phase is -π, the phase difference between the fourth phase and the third phase is π, and the phase difference between the sixth phase and the fifth phase is -π.

9. The modulation method according to claim 8, characterized in that, The first phase, the second phase, the third phase, the fourth phase, the fifth phase, and the sixth phase are 0, π, 4π / 3, π / 3, 2π / 3, and 5π / 3, respectively.

10. The modulation method according to any one of claims 1 to 9, characterized in that, The bandwidth of the first wavelength channel is an integer multiple of 25 GHz; The pilot signal occupies a bandwidth that is an integer multiple of 6.25 GHz on the optical signal.

11. The modulation method according to any one of claims 1 to 9, characterized in that, In the spectrum of the optical signal, there is a guard interval between adjacent pilot signals in the at least two pilot signal groups, and the bandwidth of the guard interval is 0.5 GHz to 1.5 GHz.

12. The modulation method according to claim 1, characterized in that, The at least two pilot signal groups include pilot signal groups with different pilot frequencies.

13. The modulation method according to claim 12, characterized in that, The at least two pilot signal groups include at least 10 different pilot signal groups with different pilot frequencies.

14. The modulation method according to claim 12 or 13, characterized in that, In the optical signal of the first wavelength channel, the pilot frequencies of the pilot signals in at least two of the pilot signal groups are the same; In the spectrum of the optical signal, the phase arrangement of the pilot signals in all pilot signal groups with the same pilot frequency has a relationship that causes the pilot signal groups to cancel each other out again.

15. The modulation method according to claim 14, characterized in that, In the optical signal of the first wavelength channel, the pilot frequencies of the two pilot signal groups are the same, namely the first pilot signal group and the second pilot signal group; The first pilot signal group and the second pilot signal group each include two pilot signals, namely a first pilot signal and a second pilot signal; the first pilot signal and the second pilot signal are out of phase. In the spectrum of the optical signal, the first pilot signal and the second pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order; Alternatively, both the first pilot signal group and the second pilot signal group include three pilot signals, namely a first pilot signal, a second pilot signal, and a third pilot signal; the phases of the first pilot signal, the second pilot signal, and the third pilot signal are uniformly distributed in the range of 0 to 2π. On the spectrum of the optical signal, the first pilot signal, the second pilot signal, and the third pilot signal in the first pilot signal group and the second pilot signal group are arranged in reverse order.

16. The modulation method according to claim 14, characterized in that, Each pilot frequency includes the same number of pilot signal groups, and the pilot signal groups have the same pilot signal; In the spectrum of the optical signal, all the pilot signals at each pilot frequency are arranged in the same order, and the pilot signals in the same order at different pilot frequencies are arranged in a group.

17. A transmitter, characterized in that, The transmitter includes: A light source, said light source being used to generate an optical signal in a first wavelength channel; and A modulator, the modulator being configured to receive an optical signal generated by the light source and to perform the modulation method according to any one of claims 1 to 16.

18. The transmitter according to claim 17, characterized in that, The transmitter further includes a processor; the processor is configured to send a modulation signal to the modulator according to the modulation method of any one of claims 1 to 16, the modulator modulating the optical signal generated by the light source according to the modulation signal.

19. A pilot receiver, characterized in that, The pilot receiver includes a comb filter, a photodetector, and a processor; The comb filter is used to receive the optical signal in the first wavelength channel and filter out the target frequency band portion of the optical signal. The photodetector is used to convert the optical signal filtered out by the comb filter into an electrical signal; as well as The processor is connected to the photodetector and is used to determine the optical power in the first wavelength channel based on the electrical signal generated by the photoelectric conversion of the photodetector. Wherein, the optical signal in the first wavelength channel is an optical signal formed by the modulation method according to any one of claims 1 to 16, and the target frequency band is aligned with one of the pilot signals in at least one group of pilot signals.

20. The pilot receiver according to claim 19, characterized in that, The comb filter is a Mach-Zehnder interferometer, a Michelson interferometer, an arrayed waveguide grating, or a wavelength selective switch.

21. The pilot receiving device according to claim 19 or 20, characterized in that, The target frequency band in the comb filter is an integer multiple of 12.5 GHz.

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