Method for optical signal transmission, pilot receiver and transmitter

Abstract

The embodiment of the application discloses a kind of optical signal sending method, pilot receiver and transmitter, belong to optical communication technical field.The method comprises the following steps: modulating first pilot signal on the first polarization state of optical signal;Modulate the second pilot signal on the second polarization state of optical signal;Wherein, the phase of first pilot signal and the phase of second pilot signal are different;Output modulated optical signal;Using the application, the interference of pilot signal transferred to other wavelength optical signal in the above Raman power transfer effect can be weakened.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication, and in particular to a method for transmitting optical signals, a pilot receiver and a transmitter. BACKGROUND

[0002] Wavelength division multiplexing (WDM) system can couple multiple optical signals of different wavelengths in the same optical fiber for transmission. At present, WDM system has been widely used in optical communication. In order to make WDM system work stably and reliably, it is necessary to effectively monitor the power of the optical signals transmitted in each wavelength channel of the WDM system to analyze the performance of each wavelength channel.

[0003] At present, the commonly used monitoring method is pilot tone method. In the WDM system, the transmitter transmits optical signals of different wavelengths, and modulates a pilot signal for each wavelength of the optical signal, and the pilot frequency of the pilot signal modulated for the optical signal of different wavelength. The modulated optical signal is transmitted in the optical fiber, and is amplified by an amplifier every certain distance, and part of the amplified optical signal (such as 5% to 10% of the optical signal) is input to the pilot receiver through an optical coupler. For each pilot frequency, the pilot receiver calculates the power of the pilot frequency, and then the power of the corresponding optical signal can be obtained, so as to realize the performance analysis of each wavelength channel in the WDM system.

[0004] However, due to the Raman power transfer effect of the optical fiber, the optical power of the short wavelength optical signal will be transferred to the optical power of the long wavelength optical signal. If the optical signal of wavelength f is dropped at a node, there should be no optical signal of wavelength f transmitted in the optical fiber after the node. However, due to the above-mentioned Raman power transfer effect, the power of the pilot frequency corresponding to the wavelength f is transferred to the long wavelength optical signal. Then, the subsequent pilot receiver can still obtain the power of the pilot frequency corresponding to the wavelength f, and then calculate the power of the optical signal of wavelength f. However, in fact, the optical signal of wavelength f is not transmitted in this section of optical fiber, so that a monitoring error occurs. Therefore, it is urgent to provide a method for reducing the interference of the pilot signal transferred to other wavelength optical signals in the above-mentioned Raman power transfer effect. SUMMARY

[0005] The embodiments of the present application provide a method for transmitting optical signals and a pilot receiver, which can reduce the interference of the pilot signal transferred to other wavelength optical signals in the above-mentioned Raman power transfer effect. The technical solution is as follows:

[0006] In a first aspect, a method for transmitting an optical signal is provided. The method can be implemented by a transmitter in a wavelength division multiplexing system. The method includes: modulating a first pilot signal on a first polarization state of the optical signal; modulating a second pilot signal on a second polarization state of the optical signal; wherein the phase of the first pilot signal and the phase of the second pilot signal are different; and outputting the modulated optical signal.

[0007] In the solution shown in the embodiment of the present application, it is assumed that the optical signal of the first wavelength modulates the pilot signal of the first frequency and the optical signal of the second wavelength modulates the pilot signal of the second frequency. During the optical fiber transmission process, Raman power transfer occurs between the optical signal of the first wavelength and the optical signal of the second wavelength, and part of the power of the optical signal of the first wavelength will be transferred to the power of the optical signal of the second wavelength. Correspondingly, the pilot signal of the first frequency will also be transferred to the optical signal of the second wavelength. If, according to the relevant technology, the pilot signals modulated by the two polarization states of the optical signal are in phase, then when the two in-phase pilot signals of the first frequency are transferred to the second optical signal, the following will occur: Figure 1 The superposition shown in the left figure is the superposition of peaks. However, if the scheme provided by this application is adopted, the pilot signals modulated by the two polarization states of the optical signal are in different phases. Then, when the two pilot signals of different phases of the first frequency are transferred to the second optical signal, the following will occur: Figure 1 The superposition shown in the right figure shows that the peaks are staggered. By comparing Figure 1 From the two cases, it can be seen that in the solution provided by the present application, when Raman power transfer occurs, the power of the pilot signals after superposition is smaller than the power of the pilot signals after superposition in the related art. That is, the solution of the present application can reduce to a certain extent the interference of the pilot signals transferred to optical signals of other wavelengths due to the Raman power transfer effect.

[0008] In a possible implementation manner, the first pilot signal and the second pilot signal are in anti-phase.

[0009] Anti-phase means that the phase is opposite, or the phase difference is 180° (expressed as π in radians).

[0010] Assume that during optical fiber transmission, Raman power transfer occurs between the optical signal of the first wavelength and the optical signal of the second wavelength, and the pilot signal of the first frequency will also be transferred to the optical signal of the second wavelength. If, according to the relevant technology, the pilot signals modulated by the two polarization states of the optical signal are in phase, then when the two in-phase pilot signals of the first frequency are transferred to the second optical signal, the following will occur: Figure 2 The superposition shown in the left figure is the superposition of peaks. However, when the scheme provided by this application is adopted, when the first pilot signal and the second pilot signal are in anti-phase, the two pilot signals of the first frequency with different phases are transferred to the second optical signal, the following will occur: Figure 2The superposition shown in the right figure, i.e. the meeting of the wave crest and the wave trough, causes the two pilot signals to cancel each other out. By comparing the two cases in Figure 2 It can be seen from the above that the scheme provided in the present application can weaken or even eliminate the interference of the pilot signal transferred to other wavelength optical signals due to the Raman power transfer effect to a certain extent.

[0011] In a possible implementation, the pilot signals modulated on the same sub-bands of the first polarization state and the second polarization state are in opposite phases.

[0012] In a possible implementation, the pilot signals modulated on each sub-band of the first polarization state and the pilot signals modulated on each sub-band of the second polarization state are in opposite phases.

[0013] In a possible implementation, the pilot signals modulated on the first sub-band to the Nth sub-band of the first polarization state and the second pilot signals modulated on the first sub-band to the Nth sub-band of the second polarization state are in opposite phases, and the pilot signals modulated on the N+1th sub-band to the last sub-band of the first polarization state and the pilot signals modulated on the N+1th sub-band to the last sub-band of the second polarization state are in opposite phases, where N is a positive integer.

[0014] In a possible implementation, the pilot signals modulated on the Ath sub-band of the first polarization state and the pilot signals modulated on the Ath sub-band of the second polarization state are in opposite phases, and the pilot signals modulated on the Bth sub-band of the first polarization state and the pilot signals modulated on the Bth sub-band of the second polarization state are in opposite phases, where A is an odd number and B is an even number, or A is an even number and B is an odd number.

[0015] In a second aspect, a pilot receiver is provided, which comprises a polarization maintaining power splitter, a first polarization analyzer, a second polarization analyzer, a first photodetector, a second photodetector, and a processor, wherein:

[0016] The polarization maintaining power splitter is configured to receive an input optical signal, and output a first optical signal to the first polarization analyzer and a second optical signal to the second polarization analyzer. The polarization states of the first optical signal, the second optical signal, and the input optical signal are the same, and the powers of the first optical signal and the second optical signal are the same.

[0017] The first polarization analyzer is configured to perform polarization state filtering on the first optical signal and output a third optical signal obtained through the polarization state filtering to the first photodetector. The second polarization analyzer is configured to perform polarization state filtering on the second optical signal and output a fourth optical signal obtained through the polarization state filtering to the second photodetector. The polarization direction of the first polarization analyzer and the polarization direction of the second polarization analyzer are not orthogonal.

[0018] The first photodetector is configured to convert the third optical signal into a first electrical signal and output the first electrical signal to the processor. The second photodetector is configured to convert the fourth optical signal into a second electrical signal and output the second electrical signal to the processor.

[0019] The processor is configured to process the first electrical signal and the second electrical signal to obtain the power corresponding to the pilot frequency of each wavelength of the input optical signal.

[0020] In a possible implementation, the angle between the polarization direction of the first polarizer and the polarization direction of the second polarizer ranges from 40° to 50°. For example, 45°.

[0021] In a possible implementation, the first polarizer is a 0° polarizer, and the second polarizer is a 45° polarizer.

[0022] In a possible implementation, the processor is further configured to determine the RSOP information of the input optical signal according to the first electrical signal and the second electrical signal.

[0023] In a possible implementation, the processor is further configured to determine the polarization dependent loss (PDL) of the input optical signal according to the first electrical signal and the second electrical signal.

[0024] In a possible implementation, the pilot receiver further includes a third polarizer and a third photodetector, and the third polarizer has a third polarization angle greater than the polarization angle of the polarizer and less than the second polarization angle.

[0025] The polarization maintaining power splitter is further configured to output a fifth optical signal to the third polarizer. The polarization state of the fifth optical signal, the first optical signal, the second optical signal, and the input optical signal is the same, and the powers of the fifth optical signal, the first optical signal, and the second optical signal are the same.

[0026] The third polarizer is configured to perform polarization state filtering on the fifth optical signal and output a sixth optical signal obtained by the polarization state filtering to the third photodetector. The third photodetector is configured to convert the sixth optical signal into a third electrical signal and output the third electrical signal to the processor. The processor is configured to process the first electrical signal, the second electrical signal, and the third electrical signal to obtain the power of the pilot signal corresponding to each wavelength of the input optical signal.

[0027] In a possible implementation, the third polarization angle of the third polarizer is half of the angle between the polarization direction of the first polarizer and the polarization direction of the second polarizer.

[0028] In a possible implementation, the pilot receiver further includes a circular polarization linear polarization converter, a fourth polarizer, and a fourth photodetector.

[0029] The polarization maintaining power splitter is also configured to output a seventh optical signal to the circular-to-linear polarization converter, wherein the polarization states of the seventh optical signal, the first optical signal, the second optical signal and the input optical signal are the same, and the powers of the seventh optical signal, the first optical signal and the second optical signal are the same.

[0030] The circular-to-linear polarization converter is configured to convert an elliptical polarization state in the seventh optical signal into a linear polarization state, and output an eighth optical signal converted to a fourth polarization analyzer.

[0031] The processor is configured to process the first electrical signal, the second electrical signal and the fourth electrical signal to obtain powers corresponding to pilot frequencies of optical signals of each wavelength in the input optical signal.

[0032] In a possible implementation, the circular-to-linear polarization converter is a quarter-wave plate.

[0033] In a possible implementation, the fourth polarization analyzer has the same polarization analyzing angle as the polarization analyzing angle of the first polarization analyzer or the polarization analyzing angle of the second polarization analyzer.

[0034] In a possible implementation, the processor is configured to perform Fourier transform on the first electrical signal to obtain first sub-powers corresponding to pilot frequencies of optical signals of each wavelength in the input optical signal, perform Fourier transform on the second electrical signal to obtain second sub-powers corresponding to the pilot frequencies, and obtain actual powers corresponding to the pilot frequencies according to the first sub-powers and the second sub-powers corresponding to the pilot frequencies.

[0035] In a third aspect, a pilot receiver is provided, and the pilot receiver includes a polarization controller, a polarization beam splitter, a first photodetector, a second photodetector and a processor, wherein:

[0036] The polarization controller is configured to receive an optical signal, depolarize the optical signal, and output the depolarized optical signal to the polarization beam splitter.

[0037] The polarization beam splitter is configured to perform polarization beam splitting on the depolarized optical signal to obtain a first optical signal and a second optical signal, output the first optical signal to the first photodetector, and output the second optical signal to the second photodetector, wherein the first optical signal and the second optical signal are orthogonal.

[0038] The first photodetector is configured to convert the first optical signal into a first electrical signal, and output the first electrical signal to the processor.

[0039] The second photodetector is configured to convert the second optical signal into a second electrical signal and output the second electrical signal to the processor.

[0040] The processor is configured to process the first electrical signal and the second electrical signal to obtain power of a pilot signal corresponding to each wavelength of the input optical signal.

[0041] In a possible implementation, the processor is further configured to:

[0042] determine RSOP information of the input optical signal according to the first electrical signal and the second electrical signal.

[0043] In a possible implementation, the processor is further configured to:

[0044] determine PDL of the input optical signal according to the first electrical signal and the second electrical signal.

[0045] In a fourth aspect, a pilot receiver is provided, and the pilot receiver includes a polarization maintaining power splitter, a polarization rotator, a first polarization beam splitter, a second polarization beam splitter, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, and a processor, where:

[0046] The polarization maintaining power splitter is configured to receive an input optical signal, output a first optical signal to the polarization rotator, and output a second optical signal to the first polarization beam splitter, where the polarization states of the first optical signal, the second optical signal, and the input optical signal are the same, and the powers of the first optical signal and the second optical signal are the same.

[0047] The polarization rotator is configured to perform polarization rotation on the first optical signal to obtain a third optical signal, and send the third optical signal to the second polarization beam splitter.

[0048] The first polarization beam splitter is configured to perform polarization splitting on the second optical signal to obtain a fourth optical signal and a fifth optical signal, output the fourth optical signal to the first photodetector, and output the fifth optical signal to the second photodetector.

[0049] The second polarization beam splitter is configured to perform polarization splitting on the third optical signal to obtain a sixth optical signal and a seventh optical signal, output the sixth optical signal to the third photodetector, and output the seventh optical signal to the fourth photodetector.

[0050] The first photodetector is configured to convert the fourth optical signal into a first electrical signal and output the first electrical signal to the processor.

[0051] The second photodetector is configured to convert the fifth optical signal into a second electrical signal and output the second electrical signal to the processor.

[0052] The third photodetector is configured to convert the sixth optical signal into a third electrical signal and output the third electrical signal to the processor.

[0053] The fourth photodetector is configured to convert the seventh optical signal into a fourth electrical signal and output the fourth electrical signal to the processor.

[0054] The processor is configured to process the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal to obtain powers of pilot signals corresponding to optical signals of each wavelength in the input optical signal.

[0055] In a possible implementation, the polarization rotator is a 45° polarization rotator.

[0056] In a possible implementation, the processor is configured to:

[0057] add the first electrical signal and the second electrical signal to obtain a fifth electrical signal;

[0058] add the third electrical signal and the fourth electrical signal to obtain a sixth electrical signal;

[0059] perform Fourier transform on the fifth electrical signal to obtain first sub-powers corresponding to pilot frequencies of optical signals of each wavelength in the input optical signal;

[0060] perform Fourier transform on the sixth electrical signal to obtain second sub-powers corresponding to the pilot frequencies of the optical signals of each wavelength in the input optical signal;

[0061] for each pilot frequency, obtain an actual power corresponding to the pilot frequency according to the first sub-power and the second sub-power corresponding to the pilot frequency.

[0062] In a possible implementation, the processor is further configured to:

[0063] determine RSOP information of the input optical signal according to the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal.

[0064] In a possible implementation, the processor is further configured to:

[0065] determine PDL of the input optical signal according to the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal.

[0066] In a fifth aspect, a transmitter is provided, the transmitter comprising a signal transmitter and a modulator, wherein:

[0067] the signal transmitter is configured to transmit an optical signal;

[0068] the modulator is configured to modulate a first pilot signal on a first polarization state of the optical signal, modulate a second pilot signal on a second polarization state of the optical signal, wherein a phase of the first pilot signal and a phase of the second pilot signal are different, and output the modulated optical signal. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 is a schematic diagram of a pilot signal provided by an embodiment of the present application;

[0070] Figure 2 is a schematic diagram of a pilot signal provided by an embodiment of the present application;

[0071] Figure 3 is a schematic diagram of a WDM system provided by an embodiment of the present application;

[0072] Figure 4 is a schematic diagram of Raman power transfer provided by an embodiment of the present application;

[0073] Figure 5 is a flowchart of a method for transmitting an optical signal provided by an embodiment of the present application;

[0074] Figure 6 is a schematic diagram of a structure of a transmitter provided by an embodiment of the present application;

[0075] Figure 7 is a schematic diagram of a structure of a transmitter provided by an embodiment of the present application;

[0076] Figure 8 is a schematic diagram of pilot signal inversion provided by an embodiment of the present application;

[0077] Figure 9 is a schematic diagram of pilot signal inversion provided by an embodiment of the present application;

[0078] Figure 10 is a schematic diagram of pilot signal inversion provided by an embodiment of the present application;

[0079] Figure 11 is a schematic diagram of a structure of a pilot receiver provided by an embodiment of the present application;

[0080] Figure 12 is a schematic diagram of a structure of a pilot receiver provided by an embodiment of the present application;

[0081] Figure 13Figure 1 is a structural schematic diagram of a pilot receiver provided by an embodiment of the present application;

[0082] Figure 14 Figure 1 is a structural schematic diagram of a pilot receiver provided by an embodiment of the present application;

[0083] Figure 15 Figure 1 is a structural schematic diagram of a pilot receiver provided by an embodiment of the present application;

[0084] Figure 16 Figure 1 is a structural schematic diagram of a pilot receiver provided by an embodiment of the present application. DETAILED DESCRIPTION

[0085] The embodiment of the present application provides a method for sending an optical signal, which can be applied to a wavelength division multiplexing (WDM) system. Referring to Figure 3 In the WDM system, the sending end can include a plurality of transmitters, such as Tx1, Tx2,..., TxN, and can also include a wavelength division multiplexer. Correspondingly, the receiving end can also include a plurality of receivers, such as Rx1, Rx2, Rx3,..., RxN, and can also include a wavelength division multiplexer. The transmission link between the sending end and the receiving end can be an optical fiber, and amplifiers, power splitters and the like can be arranged on the transmission link.

[0086] The transmitter modulates a service signal and a pilot signal on an optical signal, and sends the modulated optical signal. The optical signal is combined into one beam by the wavelength division multiplexer, and is amplified by the amplifier. Then, the optical signal is transmitted by the optical fiber. The optical signal can be amplified by the amplifier at a distance in the transmission process of the optical fiber. For example, an amplifier can be arranged on the optical fiber every 80 kilometers (km) to amplify the optical signal. The amplified optical signal can be split into a part of optical signal by the power splitter to enter the pilot receiver. For example, the power splitter is a 10:90 power splitter, and then 10% of the amplified optical signal can be split by the 10:90 power splitter to enter the pilot receiver. Finally, the optical signal is transmitted to the receiving end, and is separated into N paths of optical signals by the wavelength division multiplexer of the receiving end and is output to the receivers, and the receivers process the input optical signal.

[0087] The pilot signal and the Raman power transfer are briefly described below.

[0088] For example, the three transmitters at the transmitting end can respectively send optical signals with wavelengths of λ1, λ2, and λ3. And the transmitter modulates a pilot signal with a frequency of f1 on the optical signal with a wavelength of λ1, modulates a pilot signal with a frequency of f2 on the optical signal with a wavelength of λ2, and modulates a pilot signal with a frequency of f3 on the optical signal with a wavelength of λ3. When stimulated Raman scattering exists in the optical fiber, Raman power transfer will occur in the optical signal. The power of the optical signal with a wavelength of λ1 will be partially transferred to the optical signals with wavelengths of λ2 and λ3, the power of the optical signal with a wavelength of λ2 will be partially transferred to the optical signals with wavelengths of λ1 and λ3, and the power of the optical signal with a wavelength of λ3 will be partially transferred to the optical signals with wavelengths of λ1 and λ2. Correspondingly, as Figure 4 As shown, the power of the pilot signal with a frequency of f1 will be partially transferred to the optical signals with wavelengths of λ1 and λ2, the power of the pilot signal with a frequency of f2 will be partially transferred to the optical signals with wavelengths of λ1 and λ3, and the power of the pilot signal with a frequency of f3 will be partially transferred to the optical signals with wavelengths of λ1 and λ2.

[0089] In order to reduce the interference of the pilot signal transferred to the optical signal of other wavelengths in the above-mentioned Raman power transfer effect, the embodiment of the present application proposes a method for sending an optical signal, which can be implemented by a transmitter in a WDM system, see Figure 5 , the method may include the following steps:

[0090] Step 501: Acquire a first polarization state and a second polarization state of an optical signal.

[0091] The first polarization state and the second polarization state are orthogonal.

[0092] In practice, a laser in a transmitter emits an optical signal, and then a device capable of bidirectional polarization in the transmitter performs bidirectional polarization on the optical signal to obtain a first polarization state and a second polarization state of the optical signal.

[0093] In different transmitter structures, the devices that implement the bidirectional polarization function may also be different. Several transmitters are listed below for illustration.

[0094] like Figure 6 As shown, the transmitter may include a laser and a dual-polarization IQ modulator. The laser transmits an optical signal, which enters the dual-polarization IQ modulator. The dual-polarization IQ modulator splits the optical signal into a first polarization state and a second polarization state, which are orthogonal to each other.

[0095] like Figure 7As shown, the transmitter comprises a laser, a polarization beam splitter, an IQ modulator, a variable optical attenuator (VOA) and a polarization beam combiner. The laser emits an optical signal, which enters the polarization beam splitter. The polarization beam splitter divides the optical signal into two orthogonal polarization states and outputs them to two IQ modulators respectively.

[0096] Step 502, modulating a first pilot signal in a first polarization state and a second pilot signal in a second polarization state.

[0097] wherein the first pilot signal and the second pilot signal are different in phase.

[0098] In implementation, the transmitter modulates a first pilot signal and a second pilot signal with the same frequency but different phase on two orthogonal polarization states of the optical signal respectively.

[0099] In different transmitter structures, the devices for modulating the pilot signals can also be different.

[0100] In Figure 6 In the transmitter shown, the dual-polarization IQ modulator divides the input optical signal into a first polarization state and a second polarization state, and then performs quadrature amplitude modulation, modulating a pilot signal in the first polarization state and a pilot signal in the second polarization state, and the pilot signals modulated in the first polarization state and the second polarization state are different in phase. For example, the pilot signal modulated in the first polarization state is as follows:

[0101] m*sin(2πf k t+Φ0)

[0102] The pilot signal modulated in the second polarization state is as follows:

[0103] m*sin(2πf k t+Φ0+α)

[0104] wherein m is the modulation depth, f k is the modulation frequency, t is the time, Φ0is the initial phase, and α is the phase difference, and α can be (0, 2π).

[0105] The values of the modulation frequency and the modulation depth of the pilot signal are described exemplarily as follows.

[0106] The modulation frequency of the pilot signal can be between 30 megahertz (MHz) and 40 MHz, and the modulation depth of the pilot signal can be between 0.01 and 0.2.

[0107] The modulation depth is defined as: wherein P max is the maximum power of the optical signal, and P min is the minimum power of the optical signal. is the average power of the optical signal.

[0108] In addition, it should be noted that the dual-bias IQ modulator can also modulate the data to be sent on the first polarization state and the second polarization state. The data to be sent can be service data that the user wants to send.

[0109] In the transmitter as shown in Figure 7 , the IQ modulator modulates the data to be sent on the input polarization state and outputs to the corresponding VOA. Then, the digital signal processor (DSP) controls the two VOAs to modulate the pilot signals on the input optical signals, and the pilot signals modulated by the two VOAs are different in phase.

[0110] In a possible implementation, in order to enable the pilot signals modulated on the two polarization states to be cancelled after being transferred to other optical signals, the pilot signals modulated on the two polarization states of the optical signal can be anti-phase signals, that is, the phases of the two pilot signals differ by 180° (that is, π in radian measure).

[0111] In implementation, the pilot signals modulated on the two polarization states can have various forms of anti-phase, some of which are listed below for illustration.

[0112] Form one,

[0113] As shown in Figure 8 , the pilot signals modulated on each sub-band of the first polarization state are in-phase, the pilot signals modulated on each sub-band of the second polarization state are in-phase, and the pilot signals modulated on each sub-band of the first polarization state are anti-phase with the pilot signals modulated on each sub-band of the first polarization state.

[0114] For example, the pilot signals modulated on each sub-band of the first polarization state are all m*sin(2πf k t+Φ0), the pilot signals modulated on each sub-band of the second polarization state are all m*sin(2πf k t+Φ0+π).

[0115] Form two,

[0116] The pilot signal modulated on the A-th sub-band of the first polarization state is anti-phase with the second pilot signal modulated on the A-th sub-band of the second polarization state, and the first pilot signal modulated on the B-th sub-band of the first polarization state is anti-phase with the second pilot signal modulated on the B-th sub-band of the second polarization state. Wherein, A is an odd number and B is an even number, or A is an even number and B is an odd number.

[0117] For example, the polarization state has k+1 sub-bands, k is even, the value of A can be 1, 3, 5...k+1, and the value of B can be 2, 4, 6...k. Alternatively, the value of A can be 2, 4, 6...k, and the value of B can be 1, 3, 5...k+1. The pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the first polarization state is m*sin(2πf k t+Φ0), and the pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the first polarization state is m*sin(2πf k t+Φ0+π). The pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the second polarization state is m*sin(2πf k t+Φ0+π), and the pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the second polarization state is m*sin(2πf k t+Φ0).

[0118] As shown in the following table, the polarization state has k+1 sub-bands, which are denoted as f0, f0+df, f0+2df...f0+kdf respectively. The pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the first polarization state is opposite to the second pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the second polarization state. The pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the first polarization state is opposite to the pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the second polarization state. Figure 9 As shown in the following table, the polarization state has k+1 sub-bands, which are denoted as f0, f0+df, f0+2df...f0+kdf respectively. The pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the first polarization state is opposite to the second pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the second polarization state. The pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the first polarization state is opposite to the pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the second polarization state.

[0119] As shown in the following table, the polarization state has k+1 sub-bands, which are denoted as f0, f0+df, f0+2df...f0+kdf respectively. The pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the first polarization state is opposite to the second pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the second polarization state. The pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the first polarization state is opposite to the pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the second polarization state.

[0120] As shown in the following table, the polarization state has k+1 sub-bands, which are denoted as f0, f0+df, f0+2df...f0+kdf respectively. The pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the first polarization state is opposite to the second pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the second polarization state. The pilot signal modulated on the 2nd, 4th, 6th...kth sub-band of the first polarization state is opposite to the pilot signal modulated on the 1st, 3rd, 5th...k+1st sub-band of the second polarization state.

[0121] For example, the polarization state has k+1 sub-bands, and the pilot signal modulated on the 1st to Nth sub-band of the first polarization state is m*sin(2πf k t+Φ0), and the pilot signal modulated on the 1st to Nth sub-band of the second polarization state is m*sin(2πf k t+Φ0+π). The pilot signal modulated on the N+1th to k+1th sub-band of the first polarization state is m*sin(2πf k t+Φ0+π), and the pilot signal modulated on the N+1th to k+1th sub-band of the second polarization state is m*sin(2πfk t+Φ0).

[0122] As shown in Figure 10 , the polarization state has k+1 sub-bands, respectively denoted as: f0, f0+df, f0+2df...f0+kdf. The pilot signals modulated on the first to Nth sub-bands of the first polarization state are opposite to the pilot signals modulated on the first to Nth sub-bands of the second polarization state. The pilot signals modulated on the N+1th to k+1th sub-bands of the first polarization state are opposite to the pilot signals modulated on the N+1th to k+1th sub-bands of the second polarization state.

[0123] Step 503, transmitting the modulated optical signal.

[0124] In implementation, after modulating the data and pilot signals to be transmitted, the transmitter outputs the modulated optical signal to the wavelength division multiplexer.

[0125] In order to cooperate with the method for transmitting optical signal provided in the embodiments of the present application, so that the opposite pilot signals can be detected, the embodiments of the present application also correspondingly provide several pilot receivers.

[0126] Referring to Figure 11 , the pilot receiver comprises a polarization maintaining power divider, a first polarization analyzer, a second polarization analyzer, a first photoelectric detector, a second photoelectric detector and a processor.

[0127] The relationship between the polarization direction of the polarization analyzer and the polarization direction of the optical signal will be briefly described below.

[0128] When the polarization direction of the polarization state is parallel to the polarization direction of the polarization analyzer, the polarization state can pass through the polarization analyzer completely. When the polarization direction of the polarization state is orthogonal (perpendicular) to the polarization direction of the polarization analyzer, the polarization state cannot pass through the polarization analyzer. With the angle between the polarization direction of the polarization state and the polarization direction of the polarization analyzer changing from 0° to 90°, the signal strength of the polarization state passing through the polarization analyzer becomes weaker and weaker. When the angle between the polarization direction of the polarization state and the polarization direction of the polarization analyzer is 45°, only half of the polarization state can pass through the polarization analyzer.

[0129] In implementation, the first polarization state and the second polarization state of the optical signal can be rotated during transmission, and the following situation can occur: the included angle (acute angle) between the polarization direction of the polarization state and the polarization direction of the polarizer is 45°. In this case, if the conventional two polarizers with orthogonal polarization directions are used for polarization filtering, each polarizer will output half of the first polarization state and half of the second polarization state to the corresponding photodetector, and accordingly, each photodetector corresponding to the polarizer will receive half of the first pilot signal and half of the second pilot signal. In the case that the pilot signals modulated on the two polarization states are anti-phase, the two pilot signals received by the photodetector will cancel each other out, and the final pilot signal power is 0.

[0130] In order to avoid the above problems and enable the photodetector to detect the pilot signal, in the embodiment of the present application, the polarization direction of the first polarizer and the polarization direction of the second polarizer are not orthogonal.

[0131] In the embodiment of the present application, referring to Figure 11 Because two polarizers are provided, the polarization maintaining power splitter needs to divide the input optical signal into two paths, and in this case, the polarization maintaining power splitter is a 1:1 polarization maintaining power splitter.

[0132] The polarization maintaining power splitter receives the input optical signal and performs polarization maintaining power splitting on the input optical signal, outputs the first optical signal to the first polarizer, and outputs the second optical signal to the second polarizer. The first optical signal and the second optical signal obtained after polarization maintaining power splitting are the same, and the polarization states of the two optical signals are the same as the polarization state of the input optical signal, and the powers of the two optical signals are each half of the power of the input optical signal.

[0133] The first polarizer performs polarization state filtering on the first optical signal and outputs the third optical signal obtained by polarization state filtering to the first photodetector. The second polarizer performs polarization state filtering on the second optical signal and outputs the fourth optical signal obtained by polarization state filtering to the second photodetector.

[0134] The first photodetector converts the third optical signal into a first electrical signal and outputs the first electrical signal to the processor. The second photodetector converts the fourth optical signal into a second electrical signal and outputs the second electrical signal to the processor.

[0135] The processor processes the first electrical signal and the second electrical signal to obtain the power of the pilot signal of each wavelength optical signal in the input optical signal.

[0136] Specifically, the processing of the processor can be as follows:

[0137] Suppose the first electrical signal is s1(t) and the second electrical signal is s2(t).

[0138] First, the processor performs Fourier transform on s1(t) to obtain each pilot frequency f k The corresponding first sub-power is:

[0139]

[0140] The processor also performs Fourier transform on s2(t) to obtain each pilot frequency f k The corresponding second sub-power is:

[0141]

[0142] Then, for each pilot frequency f k , the first sub-power and the second sub-power are first squared and summed, and then square rooted, so as to obtain the actual power of the pilot frequency f k .

[0143]

[0144] Here, the pilot frequency f k corresponds to the actual power, which is the power of the pilot signal with the pilot frequency f k modulated on the optical signal with the wavelength λ k in the input optical signal.

[0145] In a possible implementation, in order to make the electrical signals output by the first photodetector and the second photodetector in an orthogonal relationship, the included angle between the polarization direction of the first polarizer and the polarization direction of the second polarizer can be 45°.

[0146] In the case where the included angle between the polarization direction of the first polarizer and the polarization direction of the second polarizer is 45°, assuming that the amplitude of the electrical signal output by the first photodetector is cos 2 (θ)-sin 2 (θ)=cos(2θ), the amplitude of the electrical signal output by the second photodetector is cos 2 (θ+45°)-sin2(θ+45°)=cos(2θ+90°)=sin(2θ). Wherein, θ is the included angle between the polarization direction of the input polarizer after the two orthogonal polarization states are combined and the polarization direction of the first polarizer.

[0147] In a possible implementation, the detection angle of the first polarizer is 0°, and the detection angle of the second polarizer is 45°.

[0148] The polarizer with the detection angle of 0° can also be referred to as a 0° polarizer, and the polarizer with the detection angle of 45° can also be referred to as a 45° polarizer.

[0149] In the case that the first polarizer is a 0° polarizer, the θ in the above cos(2θ) and sin(2θ) is the polarization angle of the combined two orthogonal polarization states of the input polarizer.

[0150] In a possible implementation, the first polarizer and the second polarizer are both fiber-type polarizers.

[0151] In a possible implementation, the polarization-maintaining power splitter is a polarization-maintaining fiber coupler.

[0152] In a possible implementation, referring to Figure 12 In addition to the first polarizer and the second polarizer, the pilot receiver provided by the embodiments of the present application can further include N polarizers, and correspondingly, the pilot receiver can further include N photodetectors, and the N polarizers and the N photodetectors correspond to each other in one-to-one correspondence.

[0153] The N polarizers have different polarization angles, and the polarization angles of the N polarizers are greater than the polarization angle of the first polarizer and less than the polarization angle of the second polarizer.

[0154] In a possible implementation, the polarization angles of the N polarizers can be respectively wherein, θ1 is the polarization angle of the first polarizer, θ2 is the polarization angle of the second polarizer, and θ is the polarization angle of the N polarizer. is the included angle between the polarization direction of the first polarizer and the polarization direction of the second polarizer.

[0155] In the case that the pilot receiver further includes the N polarizers, the polarization-maintaining power splitter needs to perform polarization-maintaining power splitting on the input optical signal, and output N+2 optical signals, and the powers of the N+2 optical signals are and the polarization states of the N+2 optical signals are the same as the polarization state of the input optical signal.

[0156] For example, N=1, and in addition to the first polarizer and the second polarizer, the pilot receiver further includes a third polarizer, and correspondingly, the pilot receiver further includes a third photodetector corresponding to the third polarizer. The polarization angle of the third polarizer is 22.5°.

[0157] In the pilot receiver shown in Figure 12 , the processor can receive electrical signals output from the N+2 photodetectors. For each electrical signal, the processor performs Fourier transform on the electrical signal to obtain sub-powers corresponding to each pilot frequency. Then, for each pilot frequency, the processor squares and sums the sub-powers corresponding to the pilot frequency obtained by the Fourier transform, and then takes the square root to obtain the actual power corresponding to the pilot frequency.

[0158] In a possible implementation, referring to Figure 13In order to enable the pilot receiver to receive the pilot signal modulated on the polarization state when the polarization state is rotated into a special polarization state during transmission, the pilot receiver provided by the embodiment of the application further comprises a circular polarization linear polarization converter, a fourth polarizer and a fourth photodetector.

[0159] The special polarization state will be described briefly below.

[0160] In the case where the polarization state is changed from linear polarization to original polarization, it is assumed that the amplitude of the electrical signal output by the first photodetector is cos 2 (θ)-sin 2 (θ), and the amplitude of the electrical signal output by the second photodetector is The amplitude of the electrical signal output by the fourth photodetector is [sin 2 (θ+φ)-cos 2 (θ+φ)]sinδ. Wherein φ is the included angle between the polarization direction of the fourth polarizer and the polarization direction of the first polarizer. δ is the ellipticity after the combination of the two orthogonal polarization states input into the polarizer. When θ=45° and δ=90°, the amplitude of the electrical signal output by the first photodetector is cos 2 (θ)-sin 2 (θ), and the amplitude of the electrical signal output by the second photodetector is Both are 0, and only the amplitude of the electrical signal output by the fourth photodetector is [sin 2 (θ+φ)-cos 2 (θ+φ)]sinδ is not 0. This is the special polarization state described above. It can be seen that in this case, the first photodetector and the second photodetector have no electrical signal output.

[0161] In the case where the pilot receiver further comprises the circular polarization linear polarization converter, the fourth polarizer and the fourth photodetector, the polarization maintaining power splitter needs to perform polarization maintaining power splitting on the input optical signal, and output three optical signals, which are output to the first polarizer, the second polarizer and the circular polarization linear polarization converter respectively. The power of the three optical signals is one third of the power of the input optical signal, and the polarization states of the three optical signals are the same as the polarization state of the input optical signal.

[0162] The polarization maintaining power splitter performs polarization state conversion on the received optical signal. If the input polarization state is linear polarization state, the polarization state is converted into circular polarization state for output. If the input polarization state is circular polarization state, the polarization state is converted into linear polarization state for output.

[0163] In addition, the circular polarization linear polarization converter, the fourth polarizer and the fourth photodetector described above can also be arranged on the basis of the pilot receiver shown in Figure 12 , see Figure 14 .

[0164] In a possible implementation, the fourth polarizing angle is the same as the first polarizing angle or the second polarizing angle.

[0165] In a possible implementation, the circular polarization linear polarization converter is a quarter-wave plate.

[0166] In a possible implementation, in the receiver structure shown in FIG. 1, the first light-emitting device and the second light-emitting device are arranged in a same plane. Figure 11 With the receiver structure shown in FIG. 1, monitoring of the rotation of state of polarization (RSOP) and polarization dependent loss (PDL) can also be implemented. The monitoring of the RSOP and the PDL is described below.

[0167] I. Monitoring of the RSOP

[0168] The first photodetector outputs a first electrical signal to the processor, and the second photodetector outputs a second electrical signal to the processor. The processor calculates a ratio of the first electrical signal to the second electrical signal. If the ratio of the first electrical signal to the second electrical signal changes over time, it is determined that the RSOP occurs, that is, the polarization angle of the state of polarization changes over time.

[0169] Specifically, a derivative of the ratio of the first electrical signal to the second electrical signal with respect to time can be calculated as the RSOP information, to represent the time-domain change of the polarization angle of the state of polarization.

[0170] II. Monitoring of the PDL

[0171] The first photodetector outputs a first electrical signal to the processor, and the second photodetector outputs a second electrical signal to the processor. It is assumed that the amplitude of the first electrical signal is cos 2 (θ)-sin 2 (θ), and the amplitude of the second electrical signal is where θ is an included angle between a polarization direction of the combined two orthogonal states of polarization and a polarization direction of the first polarizer, and in the case where the first polarizer is a 0° polarizer, θ is a polarization angle of the combined two orthogonal states of polarization. is an included angle between the polarization direction of the first polarizer and the polarization direction of the second polarizer, and in the case where the second polarizer is a 45° polarizer,

[0172] The processor compares the power of the first electrical signal with the power of the second electrical signal according to a monitoring period, to determine the PDL.

[0173] Specifically, in each monitoring period, the processor obtains the maximum power of the first electrical signal in the monitoring period, and the first power of the second electrical signal when the first electrical signal is at the maximum power in the monitoring period. The condition for judging that the input optical signal has no polarization-dependent loss is that if the first electrical signal is at the maximum power P max1 in the monitoring period, the first power is Then it can be determined that the two polarization states have no polarization-dependent loss.

[0174] In each monitoring period, the processor also obtains the maximum power of the second electrical signal in the monitoring period, and the second power of the first electrical signal when the second electrical signal is at the maximum power in the monitoring period. The condition for judging that the input optical signal has no polarization-dependent loss is that if the second electrical signal is at the maximum power P max2 in the monitoring period, the second power is Then it can be determined that the two polarization states have no polarization-dependent loss.

[0175] When any of the above two conditions for judging that the input optical signal has no polarization-dependent loss is met, it is determined that the input optical signal has no polarization-dependent loss, and when neither of the above two conditions for judging that the input optical signal has no polarization-dependent loss is met, it is determined that the input optical signal has polarization-dependent loss.

[0176] In a possible implementation, under the receiver structure shown in Figure 12 , the monitoring of polarization rotation and polarization-dependent loss can also be implemented. Hereinafter, taking N=1 as an example, the monitoring of polarization rotation and polarization-dependent loss under the receiver structure shown in Figure 12 is described respectively.

[0177] I. Monitoring polarization rotation

[0178] The first photodetector outputs the first electrical signal to the processor, the second photodetector outputs the second electrical signal to the processor, and the third photodetector outputs the third electrical signal. Then, according to any two of the first electrical signal, the second electrical signal and the third electrical signal, it is determined whether the polarization state has polarization rotation over time.

[0179] Specifically, the processor calculates the ratio of any two of the first electrical signal, the second electrical signal and the third electrical signal. If the ratio changes over time, it is determined that the polarization state has polarization rotation over time.

[0180] Specifically, the derivative of the ratio of any two electrical signals with respect to time can be calculated as polarization rotation information to represent the time-domain change of the polarization angle of the polarization state.

[0181] For example, the processor calculates the ratio of the first electrical signal and the second electrical signal. If the ratio of the first electrical signal and the second electrical signal changes over time, it is determined that the polarization state changes over time has a polarization rotation.

[0182] II. Monitoring polarization dependent loss

[0183] The first photodetector outputs a first electrical signal to the processor, the second photodetector outputs a second electrical signal to the processor, and the third photodetector outputs a third electrical signal to the processor. Assuming that the amplitude of the first electrical signal is cos 2 (θ) - sin 2 (θ), the amplitude of the second electrical signal is cos (θ) - sin 2 (θ), and the amplitude of the third electrical signal is cos 2 (θ + σ) - sin (θ + σ). Wherein σ is the included angle between the polarization direction of the third polarizer and the polarization direction of the first polarizer, and σ is in the range of (0°, 45°). In the case of the third polarizer being a 22.5° polarizer, σ = 22.5°.

[0184] The processor compares the power of the first electrical signal, the power of the second electrical signal, and the power of the third electrical signal according to a monitoring period, to determine the polarization dependent loss.

[0185] Specifically, in each monitoring period, the processor obtains the maximum power of the first electrical signal in the monitoring period, the first power of the second electrical signal when the first electrical signal is at the maximum power in the monitoring period, and the third power of the third electrical signal when the first electrical signal is at the maximum power in the monitoring period. The condition for determining that the input optical signal has no polarization dependent loss is that if the first electrical signal is at the maximum power P max1 in the monitoring period, the first power is and the third power is [cos 2 (σ) - sin 2 (σ)] * P max1 , it can be determined that the input optical signal has no polarization dependent loss.

[0186] In each monitoring period, the processor also obtains the maximum power of the second electrical signal in the monitoring period, the second power of the first electrical signal when the second electrical signal is at the maximum power in the monitoring period, and the fourth power of the third electrical signal when the second electrical signal is at the maximum power in the monitoring period. The condition for determining that the input optical signal has no polarization dependent loss is that if the second electrical signal is at the maximum power P max2 in the monitoring period, the second power is and the fourth power is , it can be determined that the input optical signal has no polarization dependent loss.

[0187] In each monitoring period, the processor also acquires the maximum power of the third electrical signal in the monitoring period, the fifth power of the first electrical signal when the third electrical signal is at the maximum power in the monitoring period, and the sixth power of the second electrical signal when the third electrical signal is at the maximum power in the monitoring period. The condition that the input optical signal does not have polarization-dependent loss is determined as: if the second electrical signal is at the maximum power P max3 in the monitoring period, the fifth power is [cos 2 (-σ)-sin 2 (-σ)]*P max3 , and the sixth power is , then it is determined that the input optical signal does not have polarization-dependent loss.

[0188] When any one of the above three conditions that the input optical signal does not have polarization-dependent loss is met, it is determined that the input optical signal does not have polarization-dependent loss, and when none of the above three conditions that the input optical signal does not have polarization-dependent loss is met, it is determined that the input optical signal has polarization-dependent loss.

[0189] In a possible implementation, under the pilot receiver structure shown in Figure 13 and Figure 14 , the polarization rotation and polarization-dependent loss can also be monitored. The processing of monitoring the polarization rotation and the polarization-dependent loss under the pilot receiver structure shown in Figure 13 is similar to the processing of monitoring the polarization rotation and the polarization-dependent loss under the pilot receiver structure shown in Figure 14 , and only the implementation of monitoring the polarization rotation and the polarization-dependent loss under the pilot receiver structure shown in Figure 13 will be described below.

[0190] The monitoring of the polarization rotation is the same as or similar to the monitoring of the polarization rotation under the receiver structure shown in Figure 11 , and will not be described here. The monitoring of the polarization-dependent loss will be described below.

[0191] The first photodetector outputs the first electrical signal to the processor, the second photodetector outputs the second electrical signal to the processor, and the fourth photodetector outputs the fourth electrical signal to the processor. In the case of considering a special polarization state, it is assumed that the amplitude of the first electrical signal is cos 2 (θ)-sin 2 (θ), the amplitude of the second electrical signal is , and the amplitude of the fourth electrical signal is [sin 2 (θ+φ)-cos 2 (θ+φ)]sinδ.

[0192] The processor compares the power of the first electrical signal, the power of the second electrical signal and the power of the fourth electrical signal according to a monitoring period to determine the polarization dependent loss.

[0193] Specifically, in each monitoring period, the processor acquires the maximum power of the first electrical signal in the monitoring period, the first power of the second electrical signal when the first electrical signal is at the maximum power in the monitoring period, and the seventh power of the fourth electrical signal when the first electrical signal is at the maximum power in the monitoring period. The condition that the input optical signal does not have polarization dependent loss is that if the first electrical signal is at the maximum power P max1 in the monitoring period, the first power is and the seventh power is [sin 2 (φ)-cos 2 (φ)]sinδ*P max1 , then it can be determined that the input optical signal does not have polarization dependent loss.

[0194] In each monitoring period, the processor further acquires the maximum power of the second electrical signal in the monitoring period, the second power of the first electrical signal when the second electrical signal is at the maximum power in the monitoring period, and the eighth power of the fourth electrical signal when the second electrical signal is at the maximum power in the monitoring period. The condition that the input optical signal does not have polarization dependent loss is that if the second electrical signal is at the maximum power P max2 in the monitoring period, the second power is and the eighth power is 0, then it can be determined that the input optical signal does not have polarization dependent loss.

[0195] In each monitoring period, the processor further acquires the maximum power of the fourth electrical signal in the monitoring period, the ninth power of the first electrical signal when the fourth electrical signal is at the maximum power in the monitoring period, and the tenth power of the second electrical signal when the fourth electrical signal is at the maximum power in the monitoring period. The condition that the input optical signal does not have polarization dependent loss is that if the fourth electrical signal is at the maximum power P max4 in the monitoring period, the ninth power is [cos 2 (-φ)-sin 2 (-φ)]*P max4 and the tenth power is 0, then it can be determined that the input optical signal does not have polarization dependent loss.

[0196] When any one of the above three conditions that the input optical signal does not have polarization dependent loss is met, it is determined that the input optical signal does not have polarization dependent loss, and when none of the above three conditions that the input optical signal does not have polarization dependent loss is met, it is determined that the input optical signal has polarization dependent loss.

[0197] The embodiment of the present application further provides a pilot receiver, referring to Figure 15 The pilot receiver comprises a polarization controller, a polarization beam splitter, a first photodetector, a second photodetector and a processor.

[0198] In implementation, the polarization controller receives an input optical signal, disturbs or locks the polarization of the input optical signal, and outputs the disturbed or locked optical signal to the polarization beam splitter.

[0199] The disturbance is random disturbance on the input optical signal, which changes the polarization direction of the polarization state of the input optical signal.

[0200] The locking is locking the polarization direction of the polarization state of the input optical signal, and outputting the polarization state with a fixed polarization direction.

[0201] Both the disturbance and the locking are to avoid the polarization direction of the polarization state of the input optical signal being 45°, therefore, the polarization controller also needs to ensure that the polarization angle of the polarization state output by the polarization controller is not 45° in the case of locking.

[0202] The polarization beam splitter performs polarization splitting on the disturbed or locked optical signal, and obtains orthogonal first and second optical signals, and outputs the first optical signal to the first photodetector and the second optical signal to the second photodetector.

[0203] The first photodetector converts the first optical signal into a first electrical signal and outputs the first electrical signal to the processor. The second photodetector converts the second optical signal into a second electrical signal and outputs the second electrical signal to the processor.

[0204] The processor processes the first and second electrical signals to obtain the power of the pilot signal of each wavelength optical signal in the input optical signal. It should be noted that the specific processing of the processor is the same as that of the processor in the pilot receiver shown in Figure 11 Therefore, the specific processing of the processor in the pilot receiver shown in

[0205] In a possible implementation manner, under the structure of the receiver shown in Figure 15 The polarization-dependent loss can be monitored.

[0206] The processor judges the polarization-dependent loss according to the power of the first and second electrical signals in a monitoring period.

[0207] Specifically, in each monitoring period, the processor obtains the maximum power of the first electrical signal in the monitoring period, and the power of the second electrical signal when the first electrical signal is at the maximum power in the monitoring period. The condition for judging that the input optical signal has no polarization-dependent loss is that if the first electrical signal is at the maximum power in the monitoring period, the second electrical signal is also at the maximum power in the monitoring period, and the two maximum powers are the same, it is determined that the input optical signal has no polarization-dependent loss.

[0208] In each monitoring period, the processor obtains the maximum power of the second electrical signal in the monitoring period, and the power of the first electrical signal when the second electrical signal is at the maximum power in the monitoring period. The condition for judging that the input optical signal has no polarization-dependent loss is that if the second electrical signal is at the maximum power in the monitoring period, the first electrical signal is also at the maximum power in the monitoring period, and the two maximum powers are the same, it is determined that the input optical signal has no polarization-dependent loss.

[0209] When any one of the above two conditions for judging that the input optical signal has no polarization-dependent loss is met, it is determined that the input optical signal has no polarization-dependent loss, and when neither of the above two conditions for judging that the input optical signal has no polarization-dependent loss is met, it is determined that the input optical signal has polarization-dependent loss.

[0210] The embodiment of the present application also provides a pilot receiver, which refers to Figure 16 The pilot receiver comprises a polarization maintaining power divider, a polarization rotator, a first polarization beam splitter, a second polarization beam splitter, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, and a processor.

[0211] In implementation, the following situation may occur in the process of optical signal transmission in an optical fiber: the optical signal is subjected to polarization rotation, and the polarization angle of the first polarization state or the second polarization state after polarization rotation is 45°. In this case, if the optical signal is directly subjected to polarization beam splitting by a polarization beam splitter, half of the first polarization state and half of the second polarization state are contained in each optical signal output by the polarization beam splitter. Thus, after each optical signal is input to a photodetector, the opposite-phase pilot signals modulated on the two polarization states are offset, so that the processor cannot calculate the power of the pilot signal.

[0212] In order to compensate for the problem caused by the above situation, in the pilot receiver provided by the embodiment of the present application, the input optical signal of the pilot receiver first enters the polarization maintaining power divider, the polarization maintaining power divider performs polarization maintaining power division on the input optical signal, outputs a first optical signal to the polarization rotator, and outputs a second optical signal to the first polarization beam splitter. The first optical signal and the second optical signal obtained after polarization maintaining power division are the same, and the polarization states of the two optical signals are the same as the polarization state of the input optical signal, and the powers of the two optical signals are each half of the power of the input optical signal.

[0213] The polarization rotator performs polarization rotation on the first optical signal to obtain a third optical signal, and sends the third optical signal to the second polarization beam splitter. The first polarization beam splitter performs polarization splitting on the second optical signal to obtain a fourth optical signal and a fifth optical signal, and outputs the fourth optical signal to the first photodetector and outputs the fifth optical signal to the second photodetector.

[0214] In this way, even if the polarization angle of the first polarization state or the second polarization state is 45°, the polarization rotator performs polarization rotation on the received optical signal, so that the output optical signal no longer has a polarization state with a polarization angle of 45°. Therefore, the last processor can effectively calculate the power of the pilot signal.

[0215] The second polarization beam splitter performs polarization splitting on the third optical signal to obtain a sixth optical signal and a seventh optical signal, and outputs the sixth optical signal to the third photodetector and outputs the seventh optical signal to the fourth photodetector.

[0216] The first photodetector converts the fourth optical signal into a first electrical signal and outputs the first electrical signal to the processor. The second photodetector is configured to convert the fifth optical signal into a second electrical signal and output the second electrical signal to the processor. The third photodetector converts the sixth optical signal into a third electrical signal and outputs the third electrical signal to the processor. The fourth photodetector converts the seventh optical signal into a fourth electrical signal and outputs the second electrical signal to the processor.

[0217] The processor processes the first electrical signal, the second electrical signal, the third electrical signal and the fourth electrical signal to obtain the power of the pilot signal of each wavelength optical signal in the input optical signal.

[0218] In implementation, the processor sums the first electrical signal and the second electrical signal to obtain a fifth electrical signal, and sums the third electrical signal and the fourth electrical signal to obtain a sixth electrical signal. Then, the processor performs Fourier transform on the fifth electrical signal to obtain a first sub-power corresponding to each pilot frequency. And performs Fourier transform on the sixth electrical signal to obtain a second sub-power corresponding to each pilot frequency. Finally, for each pilot frequency, square sum the first sub-power and the second sub-power corresponding to the pilot frequency, and then take the square root to obtain the actual power corresponding to the pilot frequency.

[0219] In a possible implementation, the polarization rotator is a 45° polarization rotator, that is, the polarization rotator can rotate the polarization state of the optical signal by 45° and then output.

[0220] In addition, the polarization rotator can also be a polarization rotator with other angles, for example, between 40° and 50°.

[0221] In a possible implementation, inFigure 16 Under the receiver structure shown, monitoring of polarization rotation and polarization dependent loss can be realized. The monitoring of polarization rotation and polarization dependent loss is described below respectively.

[0222] I. Monitoring of polarization rotation

[0223] The first electrical signal and the second electrical signal are monitored as a group, and the third electrical signal and the fourth electrical signal are monitored as a group. The monitoring method for each group is the same as that of the polarization rotation monitoring of the pilot receiver shown above, and is not described here in detail. Figure 11

[0224] II. Monitoring of polarization dependent loss

[0225] The processor compares the power of the first electrical signal, the power of the second electrical signal, the power of the third electrical signal and the power of the fourth electrical signal according to the monitoring period to determine the polarization dependent loss.

[0226] Specifically, in each monitoring period, the processor obtains the maximum power of the first electrical signal in the monitoring period, the first power of the second electrical signal when the first electrical signal is at the maximum power in the monitoring period, the second power of the third electrical signal when the first electrical signal is at the maximum power in the monitoring period, and the third power of the fourth electrical signal when the first electrical signal is at the maximum power in the monitoring period. The condition for determining that the input optical signal does not have polarization dependent loss is that if the first electrical signal is at the maximum power in the monitoring period, the second electrical signal is also at the maximum power in the monitoring period and the two maximum powers are the same, and the second power and the third power are 0, then it is determined that the input optical signal does not have polarization dependent loss.

[0227] In each monitoring period, the processor also obtains the maximum power of the second electrical signal in the monitoring period, the fourth power of the first electrical signal when the second electrical signal is at the maximum power in the monitoring period, the fifth power of the third electrical signal when the second electrical signal is at the maximum power in the monitoring period, and the sixth power of the fourth electrical signal when the second electrical signal is at the maximum power in the monitoring period. The condition for determining that the input optical signal does not have polarization dependent loss is that if the second electrical signal is at the maximum power in the monitoring period, the first electrical signal is also at the maximum power in the monitoring period and the two maximum powers are the same, and the fifth power and the sixth power are 0, then it is determined that the input optical signal does not have polarization dependent loss.

[0228] ​In each monitoring period, the processor further acquires a maximum power of the third electrical signal in the monitoring period, a seventh power of the second electrical signal when the third electrical signal is at the maximum power in the monitoring period, an eighth power of the second electrical signal when the third electrical signal is at the maximum power in the monitoring period, and a ninth power of the fourth electrical signal when the third electrical signal is at the maximum power in the monitoring period. The condition for determining that the input optical signal does not have polarization-dependent loss is that if the third electrical signal is at the maximum power in the monitoring period, the fourth electrical signal is also at the maximum power in the monitoring period and the two maximum powers are the same, and the eighth power and the ninth power are 0, then it is determined that the input optical signal does not have polarization-dependent loss.

[0229] In each monitoring period, the processor further acquires a maximum power of the fourth electrical signal in the monitoring period, a tenth power of the first electrical signal when the fourth electrical signal is at the maximum power in the monitoring period, an eleventh power of the third electrical signal when the second electrical signal is at the maximum power in the monitoring period, and a twelfth power of the fourth electrical signal when the second electrical signal is at the maximum power in the monitoring period. The condition for determining that the input optical signal does not have polarization-dependent loss is that if the fourth electrical signal is at the maximum power in the monitoring period, the third electrical signal is also at the maximum power in the monitoring period and the two maximum powers are the same, and the eleventh power and the twelfth power are 0, then it is determined that the input optical signal does not have polarization-dependent loss.

[0230] When any one of the above four conditions for determining that the input optical signal does not have polarization-dependent loss is met, it is determined that the input optical signal does not have polarization-dependent loss, and when none of the above four conditions for determining that the input optical signal does not have polarization-dependent loss is met, it is determined that the input optical signal has polarization-dependent loss.

[0231] Those skilled in the art can understand that all or part of the steps of the above-mentioned embodiments can be completed by hardware, or by programs instructing relevant hardware to complete, and the programs can be stored in a computer readable storage medium, which can be a read-only memory, a magnetic disk or an optical disk.

[0232] The above only describes one embodiment of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for transmitting an optical signal, characterized in that: The method comprises: modulating a first pilot signal on a first polarization state of the optical signal; modulating a second pilot signal on a second polarization state of the optical signal, wherein the pilot signals modulated on the same sub-band of the first polarization state and the second polarization state are in anti-phase; Output a modulated optical signal, wherein the modulated optical signal carries the first pilot signal and the second pilot signal.

2. The method according to claim 1, characterized in that The pilot signals modulated on the same sub-band of the first polarization state and the second polarization state are in opposite phases, comprising: The pilot signals modulated on each sub-frequency band of the first polarization state and the pilot signals modulated on each sub-frequency band of the second polarization state are both in opposite phases.

3. The method according to claim 1, characterized in that The pilot signals modulated on the same sub-band of the first polarization state and the second polarization state are in opposite phases, comprising: The pilot signal modulated on the first sub-band to the Nth sub-band of the first polarization state is inversely phased to the second pilot signal modulated on the first sub-band to the Nth sub-band of the second polarization state, and the pilot signal modulated on the last sub-band of the N+1th sub-band of the first polarization state is inversely phased to the pilot signal modulated on the last sub-band of the N+1th sub-band of the second polarization state, where N is a positive integer.

4. The method according to claim 1, wherein The pilot signals modulated on the same sub-band of the first polarization state and the second polarization state are in opposite phases, comprising: The pilot signal modulated on the Ath sub-band of the first polarization state is in phase with the pilot signal modulated on the Ath sub-band of the second polarization state, and the pilot signal modulated on the Bth sub-band of the first polarization state is in phase with the pilot signal modulated on the Bth sub-band of the second polarization state, where A is an odd number and B is an even number, or A is an even number and B is an odd number.

5. A pilot receiver, characterized in that: The pilot receiver includes a polarization-maintaining power splitter, a first polarization analyzer, a second polarization analyzer, a first photodetector, a second photodetector, and a processor, wherein: The polarization-maintaining power splitter is configured to receive an input optical signal and output a first optical signal to the first polarization analyzer and output a second optical signal to the second polarization analyzer, wherein the first optical signal, the second optical signal, and the input optical signal have the same polarization state, and the first optical signal and the second optical signal have the same power; The first polarization analyzer is configured to perform polarization state filtering on the first optical signal and output a third optical signal obtained by polarization state filtering to the first photodetector; The second polarization analyzer is used to perform polarization state filtering on the second optical signal and output a fourth optical signal obtained by polarization state filtering to the second photodetector, wherein the polarization direction of the first polarization analyzer is not orthogonal to the polarization direction of the second polarization analyzer; The first photodetector is configured to convert the third optical signal into a first electrical signal and output the first electrical signal to the processor; the second photodetector, configured to convert the fourth optical signal into a second electrical signal, and output the second electrical signal to the processor; The processor is used to process the first electrical signal and the second electrical signal to obtain the power corresponding to the pilot frequency of the optical signal of each wavelength in the input optical signal, and the pilot signals on the same sub-band of the first polarization state and the second polarization state of the input optical signal are in reverse phase.

6. The pilot receiver according to claim 5, characterized in that The angle between the polarization direction of the first analyzer and the polarization direction of the second analyzer is in the range of 45°±5°.

7. The pilot receiver according to claim 5 or 6, characterized in that: The processor is further configured to: Polarization state rotation (RSOP) information of the input optical signal is determined according to the first electrical signal and the second electrical signal.

8. The pilot receiver according to claim 5 or 6, characterized in that: The processor is further configured to: A polarization dependent loss (PDL) of the input optical signal is determined according to the first electrical signal and the second electrical signal.

9. The pilot receiver according to claim 5 or 6, characterized in that: The pilot receiver further includes a third polarization analyzer and a third photodetector, wherein the polarization angle of the third polarization analyzer is greater than the polarization angle of the polarization analyzer and smaller than the second polarization angle; The polarization-maintaining power splitter is further configured to output a fifth optical signal to the third analyzer, wherein the fifth optical signal, the first optical signal, the second optical signal, and the input optical signal have the same polarization state, and the fifth optical signal, the first optical signal, and the second optical signal have the same power; The third polarization analyzer is configured to perform polarization state filtering on the fifth optical signal and output a sixth optical signal obtained by polarization state filtering to the third photodetector; the third photodetector is configured to convert the sixth optical signal into a third electrical signal and output the third electrical signal to the processor; The processor is configured to process the first electrical signal, the second electrical signal, and the third electrical signal to obtain the power corresponding to the pilot frequency of the optical signal of each wavelength in the input optical signal.

10. The pilot receiver according to claim 5 or 6, characterized in that: The pilot receiver further includes a circular polarization and linear polarization converter, a fourth polarization analyzer and a fourth photodetector; The polarization-maintaining power splitter is further configured to output a seventh optical signal to the circular polarization and linear polarization converter, wherein the seventh optical signal, the first optical signal, the second optical signal, and the input optical signal have the same polarization state, and the seventh optical signal, the first optical signal, and the second optical signal have the same power; The circular polarization-linear polarization converter is configured to convert the elliptical polarization state in the seventh optical signal into a linear polarization state, and output the converted eighth optical signal to the fourth analyzer; The fourth analyzer is configured to convert the eighth optical signal into a fourth electrical signal and output the fourth electrical signal to the processor; The processor is configured to process the first electrical signal, the second electrical signal, and the fourth electrical signal to obtain the power of the pilot signal corresponding to the optical signal of each wavelength in the input optical signal.

11. The pilot receiver according to claim 10, wherein: The circular polarization and linear polarization converter is a quarter wave plate.

12. The pilot receiver according to claim 10, wherein: The analyzing angle of the fourth analyzer is the same as the analyzing angle of the first analyzer or the analyzing angle of the second analyzer.

13. The pilot receiver according to claim 5 or 6, characterized in that: The processor is configured to: Performing Fourier transform on the first electrical signal to obtain a first sub-power corresponding to a pilot frequency of an optical signal of each wavelength in the input optical signal; Performing Fourier transform on the second electrical signal to obtain a second sub-power corresponding to the pilot frequency of the optical signal of each wavelength in the input optical signal; For each pilot frequency, the actual power corresponding to the pilot frequency is obtained according to the first sub-power and the second sub-power corresponding to the pilot frequency.

14. A pilot receiver, characterized in that: The pilot receiver includes a polarization-maintaining power splitter, a polarization rotator, a first polarization beam splitter, a second polarization beam splitter, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, and a processor, wherein: The polarization-maintaining power splitter is configured to receive an input optical signal, and output a first optical signal to the polarization rotator, and output a second optical signal to the first polarization beam splitter, wherein the first optical signal, the second optical signal, and the input optical signal have the same polarization state, and the first optical signal and the second optical signal have the same power; The polarization rotator is configured to perform polarization rotation on the first optical signal to obtain a third optical signal, and send the third optical signal to the second polarization beam splitter; the first polarization beam splitter is configured to perform polarization splitting on the second optical signal to obtain a fourth optical signal and a fifth optical signal, and output the fourth optical signal to the first photodetector and output the fifth optical signal to the second photodetector; the second polarization beam splitter is configured to perform polarization splitting on the third optical signal to obtain a sixth optical signal and a seventh optical signal, and output the sixth optical signal to the third photodetector and output the seventh optical signal to the fourth photodetector; The first photodetector is configured to convert the fourth optical signal into a first electrical signal and output the first electrical signal to the processor; the second photodetector, configured to convert the fifth optical signal into a second electrical signal, and output the second electrical signal to the processor; the third photodetector is configured to convert the sixth optical signal into a third electrical signal and output the third electrical signal to the processor; the fourth photodetector is configured to convert the seventh optical signal into a fourth electrical signal and output the fourth electrical signal to the processor; The processor is configured to process the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal to obtain the power of the pilot signal corresponding to the optical signal of each wavelength in the input optical signal, wherein the pilot signals on the same sub-band of the first polarization state and the second polarization state of the input optical signal are in opposite phases.

15. The pilot receiver according to claim 14, wherein: The processor is further configured to: RSOP information of the input optical signal is determined according to the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal.

16. The pilot receiver according to claim 14 or 15, characterized in that: The processor is further configured to: A PDL of the input optical signal is determined according to the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal.

17. A pilot receiver, characterized in that: The pilot receiver includes a polarization controller, a polarization beam splitter, a first photodetector, a second photodetector, and a processor, wherein: The polarization controller is configured to receive an input optical signal, scramble the optical signal, and output the scrambled optical signal to the polarization beam splitter; The polarization beam splitter is configured to perform polarization splitting on the scrambled optical signal to obtain a first optical signal and a second optical signal, output the first optical signal to the first photodetector, and output the second optical signal to the second photodetector, wherein the first optical signal and the second optical signal are orthogonal; The first photodetector is configured to convert the first optical signal into a first electrical signal and output the first electrical signal to the processor; the second photodetector, configured to convert the second optical signal into a second electrical signal and output the second electrical signal to the processor; The processor is used to process the first electrical signal and the second electrical signal to obtain the power of the pilot signal corresponding to the optical signal of each wavelength in the input optical signal, and the pilot signals on the same sub-band of the first polarization state and the second polarization state of the input optical signal are in opposite phases.

18. The pilot receiver according to claim 17, wherein: The processor is further configured to: RSOP information of the input optical signal is determined according to the first electrical signal and the second electrical signal.

19. The pilot receiver according to claim 17 or 18, characterized in that: The processor is further configured to: A PDL of the input optical signal is determined according to the first electrical signal and the second electrical signal.

20. A transmitter, characterized in that: The transmitter includes a signal transmitter and a modulator, wherein: The signal transmitter is used to send an optical signal; The modulator is configured to modulate a first pilot signal on a first polarization state of the optical signal, modulate a second pilot signal on a second polarization state of the optical signal, and output a modulated optical signal, wherein the pilot signals modulated on the same sub-band of the first polarization state and the second polarization state are in anti-phase, and the modulated optical signal carries the first pilot signal and the second pilot signal.

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