Signal conversion system and signal conversion method

Abstract

The present application relates to the technical field of signal processing, and particularly relates to a signal conversion system and a signal conversion method. The conversion system comprises a constellation compression unit and a vector shift unit. Firstly, the constellation compression unit receives an input quadrature phase shift keying signal, performs constellation compression processing on constellation points on a constellation diagram corresponding to the quadrature phase shift keying signal, compresses the constellation points on the constellation diagram to a straight line, and obtains a first pulse amplitude modulation signal in a polarization state. Then, the vector shift unit performs vector shift processing on the first pulse amplitude modulation signal, and obtains a target pulse amplitude modulation signal in which the real parts of the constellation points on the constellation diagram are all positive. Thus, the quadrature phase shift keying signal is converted into the target pulse amplitude modulation signal.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology, and in particular to a signal conversion system and a signal conversion method. Background Technology

[0002] With the continuous development of modern communication technology, people's requirements and demands for communication systems are also constantly increasing. Currently, many modulation formats have been proposed, such as On-Off Keying (OOK), Binary Phase Shift Keying (BPSK), and Quadrature Amplitude Modulation (QAM). To improve the performance of communication systems, higher-order modulation formats have also been widely used.

[0003] All-optical signal processing (ASP) processes signals only in the optical domain, avoiding the Optical-Electrical-Optical (OEO) process and circumventing the problems caused by the "electronic bottleneck." Phase-sensitive amplification (PSA) technology can amplify or compress specific phases of a signal, thereby enabling functions such as all-optical signal regeneration and format conversion.

[0004] Currently, there are many all-optical format conversion schemes based on PSA, mainly targeting the conversion between different signals under single polarization states. Research on format conversion of polarization-multiplexed signals is still somewhat insufficient. Existing QAM (Quadrature Amplitude Modulation) to PAM (Pulse Amplitude Modulation) signal conversion methods can only perform format conversion for optical signals under one polarization state and cannot process polarization-multiplexed signals, thus limiting their application scope. Summary of the Invention

[0005] This invention provides a signal conversion system and a signal conversion method to overcome the technical deficiency in the prior art that it cannot perform format conversion on polarization multiplexed signals.

[0006] On one hand, the present invention provides a signal conversion system for converting quadrature phase shift keying signals into target pulse amplitude modulation signals, the signal conversion system comprising: a constellation compression unit and a vector shifting unit;

[0007] The constellation compression unit is used to receive the input quadrature phase shift keying signal, perform constellation compression processing on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal, compress the constellation points on the constellation diagram into a straight line, and obtain the first pulse amplitude modulation signal under polarization state;

[0008] The vector shifting unit is used to perform vector shifting processing on the first pulse amplitude modulation signal to obtain a target pulse amplitude modulation signal in which the real parts of all constellation points on the constellation diagram are positive.

[0009] According to a signal conversion system provided by the present invention, the constellation compression unit includes a first amplifier, a first polarization beam splitter, a second polarization beam splitter, a first polarization state controller, a second polarization state controller, a first coupler, and a second coupler;

[0010] The first amplifier is used to receive the input first pump light, the second pump light, and the quadrature phase shift keying signal, and to perform four-wave mixing processing on the first pump light, the second pump light, and the quadrature phase shift keying signal to obtain a first idler light with the same frequency as the quadrature phase shift keying signal;

[0011] The first polarization beam splitter is used to split the first idler light into a second idler light and a third idler light;

[0012] The second polarization beam splitter is used to split the quadrature phase shift keying signal to obtain a first quadrature phase shift keying sub-signal and a second quadrature phase shift keying sub-signal;

[0013] The first polarization state controller is used to adjust the polarization of the second idler light;

[0014] The second polarization state controller is used to adjust the polarization of the third idler light;

[0015] The first coupler is used to coherently superimpose the first orthogonal phase shift keying sub-signal and the polarization-adjusted second idler light to obtain a first pulse amplitude modulation signal;

[0016] The second coupler is used to coherently superimpose the second orthogonal phase shift keying sub-signal and the polarization-adjusted third idler light to obtain the second pulse amplitude modulation signal;

[0017] The first pulse amplitude modulation signal includes the first pulse amplitude modulation signal and the second pulse amplitude modulation signal.

[0018] According to a signal conversion system provided by the present invention, the vector shifting unit includes a second amplifier, a first filter, a second filter, a first polarizer, a second polarizer, and a third polarization beam splitter;

[0019] The second amplifier is used to perform four-wave mixing processing on the input third pump light, fourth pump light, fifth pump light, sixth pump light, first pulse amplitude modulation signal and second pulse amplitude modulation signal to obtain a first mixing signal and a second mixing signal.

[0020] The first filter is used to filter the first mixing signal to obtain the third pulse amplitude modulation signal and the fourth idler light;

[0021] The second filter is used to coherently superimpose the third pulse amplitude modulation signal and the fourth idler light to obtain the fourth pulse amplitude modulation signal and the fifth idler light;

[0022] The first polarizer is used to coherently superimpose the third pulse amplitude modulation signal and the fourth idler light to obtain the fifth pulse amplitude modulation signal;

[0023] The second polarizer is used to coherently superimpose the fourth pulse amplitude modulation signal and the fifth idler light to obtain the sixth pulse amplitude modulation signal;

[0024] The third polarization beam splitter is used to combine the fifth pulse amplitude modulation signal and the sixth pulse amplitude modulation signal to obtain the target pulse amplitude modulation signal.

[0025] According to a signal conversion system provided by the present invention, an interferometer, a modulator, and a third filter are also included.

[0026] The interferometer is used to receive the input first beam and perform interference processing on the first beam to obtain an optical comb;

[0027] The third filter is used to filter the optical comb to obtain the first pump light, the second pump light, the third pump light, the fourth pump light, the fifth pump light, and the sixth pump light.

[0028] The modulator is used to receive the input second beam and modulate the second beam to obtain the quadrature phase shift keying signal.

[0029] The signal conversion system provided by the present invention further includes a third amplifier;

[0030] The third amplifier is used to amplify the modulated second beam output by the modulator to obtain the quadrature phase shift keying signal.

[0031] According to a signal conversion system provided by the present invention, a fourth filter and a signal analysis unit are also included.

[0032] The fourth filter is used to filter the target pulse amplitude modulation signal;

[0033] The signal analysis unit is used to receive the filtered target pulse amplitude modulation signal and analyze the filtered target pulse amplitude modulation signal.

[0034] According to a signal conversion system provided by the present invention, it further includes a first circulator, a second circulator, a third circulator, and a fourth circulator;

[0035] The first circulator is used to perform frequency selection processing on the mixed signal after the first amplifier has undergone four-wave mixing processing to obtain the first idler light;

[0036] The second circulator is used to perform frequency selection processing on the mixed signal after the first amplifier has undergone four-wave mixing processing to obtain the quadrature phase shift keying signal;

[0037] The third circulator is used to perform frequency selection processing on the mixed signal after the second amplifier has undergone four-wave mixing processing to obtain the first mixed signal;

[0038] The fourth circulator is used to perform frequency selection processing on the mixed signal after the second amplifier has undergone four-wave mixing processing to obtain the second mixed signal.

[0039] On the other hand, the present invention provides a signal conversion method, comprising:

[0040] The input quadrature phase shift keying signal is received, and constellation compression processing is performed on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal to compress the constellation points on the constellation diagram into a straight line to obtain the first pulse amplitude modulation signal in the polarization state.

[0041] The first pulse amplitude modulation signal is vector shifted to obtain the target pulse amplitude modulation signal in which the real parts of all constellation points on the constellation diagram are positive.

[0042] According to a signal conversion method provided by the present invention, the step of performing constellation compression processing on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal, compressing the constellation points on the constellation diagram to a straight line, to obtain a first pulse amplitude modulation signal in a polarization state, includes:

[0043] The first pump light, the second pump light, and the quadrature phase shift keying signal are subjected to four-wave mixing processing to obtain a first idler light with the same frequency as the quadrature phase shift keying signal;

[0044] The first idler beam is split into a second idler beam and a third idler beam.

[0045] The quadrature phase shift keying signal is split to obtain a first quadrature phase shift keying sub-signal and a second quadrature phase shift keying signal;

[0046] The polarization of the second and third idler beams is adjusted;

[0047] The first orthogonal phase shift keying sub-signal and the polarization-adjusted second idler light are coherently superimposed to obtain the first pulse amplitude modulation signal;

[0048] The second orthogonal phase-shift keying sub-signal and the polarization-adjusted third idler light are coherently superimposed to obtain the second pulse amplitude modulation signal;

[0049] The first pulse amplitude modulation signal includes the first pulse amplitude modulation signal and the second pulse amplitude modulation signal.

[0050] According to a signal conversion method provided by the present invention, the step of performing vector shifting processing on the first pulse amplitude modulation signal to obtain a target pulse amplitude modulation signal in which all real parts of the constellation points on the constellation diagram are positive includes:

[0051] The third pump light, the fourth pump light, the fifth pump light, the sixth pump light, the first pulse amplitude modulation signal, and the second pulse amplitude modulation signal are subjected to four-wave mixing processing to obtain the first mixing signal and the second mixing signal.

[0052] The first mixing signal is filtered to obtain the third pulse amplitude modulation signal and the fourth idler light;

[0053] The third pulse amplitude modulation signal and the fourth idler light are coherently superimposed to obtain the fourth pulse amplitude modulation signal and the fifth idler light;

[0054] The third pulse amplitude modulation signal and the fourth idler light are coherently superimposed to obtain the fifth pulse amplitude modulation signal;

[0055] The fourth pulse amplitude modulation signal and the fifth idler light are coherently superimposed to obtain the sixth pulse amplitude modulation signal;

[0056] The fifth pulse amplitude modulation signal and the sixth pulse amplitude modulation signal are combined to obtain the target pulse amplitude modulation signal.

[0057] The signal conversion system provided by this invention includes a constellation compression unit and a vector shifting unit. First, the constellation compression unit receives the input quadrature phase shift keying (QPSK) signal and performs constellation compression processing on the constellation points on the constellation diagram corresponding to the QPSK signal, compressing the constellation points on the constellation diagram into a straight line to obtain a first pulse amplitude modulation signal in a polarization state. Then, the vector shifting unit performs vector shifting processing on the first pulse amplitude modulation signal to obtain a target pulse amplitude modulation signal where all real parts of the constellation points on the constellation diagram are positive. This achieves the conversion of the QPSK signal into a target pulse amplitude modulation signal. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0059] Figure 1 This is a schematic diagram of the signal conversion process provided by the present invention;

[0060] Figure 2 This is one of the structural schematic diagrams of a signal conversion system provided in an embodiment of the present invention;

[0061] Figure 3 This is a schematic diagram of the constellation compression unit provided in an embodiment of the present invention;

[0062] Figure 4 A schematic diagram illustrating the spectral relationship between pump light and quadrature phase shift keying signal provided in an embodiment of the present invention;

[0063] Figure 5 This is a schematic diagram of the structure of the vector transfer unit provided in an embodiment of the present invention;

[0064] Figure 6 A schematic diagram of the spectral relationship of a vector non-degenerate PSA provided for an embodiment of the present invention;

[0065] Figure 7 This is a schematic diagram of the signal conversion system structure provided in an embodiment of the present invention;

[0066] Figure 8 This is a flowchart of a signal conversion method provided in an embodiment of the present invention. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0068] The following explains the technical terms and their abbreviations involved in this invention.

[0069] Binary Phase Shift Keying (BPSK);

[0070] Quadrature Amplitude Modulation (QAM);

[0071] Pulse Amplitude Modulation (PAM);

[0072] All-optical signal processing (ASP);

[0073] Phase-sensitive amplification (PSA);

[0074] PDM (Polarization Division Multiplexing);

[0075] QPSK (Quadrature Phase Shift Keying);

[0076] Polarization beam splitter (PBS);

[0077] Polarization beam splitter (PBS);

[0078] Quadrature Phase Shift Keying (QPSK);

[0079] Four-level pulse amplitude modulation (PAM4);

[0080] Unnatural PAM (u-PAM).

[0081] To improve the performance of communication systems, higher-order modulation formats have been widely used, with QAM now evolving to 64QAM, 256QAM, and even 512QAM. To meet the increasing demands of communication networks, multiplexing techniques have been proposed in the development of optical communication networks. The application of technologies such as wavelength division multiplexing (WDM), space division multiplexing (SDM), frequency division multiplexing (FDM), and partial division multiplexing (PDM) has significantly improved the performance of communication networks. Among these, PDM uses two mutually orthogonal polarization states to transmit signals, doubling the spectral efficiency of the communication network without increasing the complexity of the communication system, making it one of the most important technologies in optical communication networks. Therefore, combining polarization multiplexing with higher-order modulation has become a widely used technique.

[0082] While higher-order modulation formats improve spectral efficiency, they also present drawbacks such as increased technical difficulty, higher modulator costs, and more demanding requirements on the receiver. Therefore, downscaling higher-order signals to lower-order signals through format conversion significantly reduces the demands on modulators and demodulators. In current communication networks, different signal formats are chosen based on the transmission distance. In short-distance transmission networks, Pulse Amplitude Modulation (PAM) signals are commonly used due to their simplicity and lower cost. However, in long-distance transmission networks, QAM is more widely used to meet the demands for transmission capacity and speed. Therefore, interconnecting different networks requires signal modulation format conversion. How to convert between different formats is a key technology for flexible optical networks.

[0083] Existing PSA-based all-optical format conversion schemes mainly convert between different signals under single polarization, and cannot achieve format conversion for polarization-multiplexed signals. Another technical solution uses vector PSA to achieve orthogonal decomposition of PDM-QPSK signals, converting the original signal into two PDM-BPSK signals. This adds extra workload to subsequent signal processing, resulting in higher signal conversion costs.

[0084] To overcome the technical deficiencies in existing technologies, this application provides a signal conversion method, primarily targeting the conversion of PDM-QPSK (Quadrature Phase Shift Keying) signals to PDM-PAM4 (4Pulse Amplitude Modulation) signals. First, constellation diagram compression technology is used to compress the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal, compressing them into a straight line to obtain the first pulse amplitude modulation signal in the polarization state. Then, based on vector shifting technology, the first pulse amplitude modulation signal is vector-shifted to obtain the target pulse amplitude modulation signal where all real parts of the constellation points on the constellation diagram are positive. This achieves the conversion of a PDM-QPSK signal into a single PDM-PAM4 signal, which can be used for interconnection between different transmission networks.

[0085] Figure 1 Please refer to the schematic diagram of the signal conversion process provided by this invention. Figure 1 As shown, the first step is constellation diagram compression based on vector degenerate PSA. This process compresses the points on the constellation diagram of the quadrature phase shift keying (QPSK) signal in both polarization states onto a single straight line. In this case, each polarization state of the QPSK signal has only two phases, resulting in an anomalous PAM signal (i.e., u-PAM, unnatural-PAM). Next, the u-PAM signal undergoes vector shifting. Vector shifting is based on vector non-degenerate PSA. The purpose of vector shifting is to add a constant rightward vector to the u-PAM signal as a whole, converting the u-PAM signal in each polarization state into a standard PAM signal with all positive real parts. This achieves the conversion from PDM-QAM to PDM-PAM signals.

[0086] The following is combined Figures 1-8 The technical solution of the present invention is described.

[0087] Figure 2 This is one of the structural schematic diagrams of the signal conversion system provided in the embodiments of the present invention. Please refer to... Figure 2 As shown, the signal conversion system 1 includes a constellation compression unit 20 and a vector transfer unit 21.

[0088] The constellation compression unit 20 receives the input quadrature phase shift keying (QPSK) signal and performs constellation compression processing on the constellation points on the constellation diagram corresponding to the QPSK signal, compressing the constellation points on the constellation diagram into a straight line to obtain the first pulse amplitude modulation (PAM) signal in the polarization state. The vector shifting unit 21 performs vector shifting processing on the first PAM signal to obtain the target PAM signal where all real parts of the constellation points on the constellation diagram are positive. This achieves the conversion of PDM-QAM to PDM-PAM signals, which can be used for interconnection between different transmission networks.

[0089] Figure 3 Please refer to the schematic diagram of the constellation compression unit provided in the embodiment of the present invention. Figure 3 As shown, the constellation compression unit 20 includes a first amplifier 201, a first polarization beam splitter 202, a second polarization beam splitter 203, a first polarization state controller 204, a second polarization state controller 205, a first coupler 206, and a second coupler 207.

[0090] The first amplifier 201 is used to receive the input first pump light pump1, second pump light pump2 and quadrature phase shift keying signal signal, and to perform four-wave mixing processing on the first pump light pump1, second pump light pump2 and quadrature phase shift keying signal signal to obtain a first idler light with the same frequency as the quadrature phase shift keying signal.

[0091] The first polarization beam splitter 202 is used to split the first idler light into a second idler light and a third idler light. The second polarization beam splitter 203 is used to split the quadrature phase shift keying (QPSK) signal into a first QPSK sub-signal and a second QPSK sub-signal.

[0092] The first polarization state controller 204 is used to adjust the polarization of the second idler frequency light; the second polarization state controller 205 is used to adjust the polarization of the third idler frequency light.

[0093] The first coupler 206 is used to coherently superimpose the first quadrature phase shift keying sub-signal and the polarization-adjusted second idler light to obtain the first pulse amplitude modulation signal.

[0094] The second coupler 207 is used to coherently superimpose the second quadrature phase shift keying sub-signal and the polarization-adjusted third idler light to obtain the second pulse amplitude modulation signal.

[0095] The first pulse amplitude modulation signal includes a first pulse amplitude modulation signal and a second pulse amplitude modulation signal.

[0096] In one embodiment, the first amplifier 201 of this embodiment is a semiconductor optical amplifier (SOA), which injects two pump lights (i.e., pump1, pump2) with orthogonal polarization states and an orthogonal phase shift keying signal signal into the semiconductor optical amplifier (SOA) after passing through a 3dB coupler.

[0097] In one embodiment, the signal conversion system of this embodiment further includes a first circulator 208 and a second circulator 209. The first circulator 208 is used to perform frequency selection processing on the mixed signal after the first amplifier 201 has undergone four-wave mixing processing to obtain a first idler light. The second circulator 209 is used to perform frequency selection processing on the mixed signal after the first amplifier 201 has undergone four-wave mixing processing to obtain a quadrature phase shift keying signal.

[0098] Figure 4 This is a schematic diagram illustrating the spectral relationship between the pump light and the quadrature phase shift keying signal provided in an embodiment of the present invention. The spectral relationships between the first pump light pump1, the second pump light pump2, and the quadrature phase shift keying signal are as follows: Figure 4 As shown, pump1, pump2, and signal undergo a four-wave mixing effect in the first amplifier 201, generating a first idler light with the same wavelength as the signal. Then, a first polarization beam splitter (PBS), a second polarization beam splitter 203, a first polarization controller (PC), and a second polarization controller 205 are used to change the polarization states of the second and third idler lights. Then, the two orthogonal phase-shift keying sub-signals are coherently superimposed with the two idler lights via a first coupler 206 and a second coupler 207, completing the constellation diagram compression process of the signals. This yields a first pulse amplitude modulated signal and a second pulse amplitude modulated signal.

[0099] For example, the first and second pump lights of the two input orthogonal polarization states are respectively The expression for the input quadrature phase shift keying signal is: in That is, the phase term of the quadrature phase shift keying (QPSK) signal can be decomposed into the sum of the information phase and the carrier phase. After a four-wave mixing effect in the first amplifier 201, a first idler light with the same frequency as the QPSK signal is generated, expressed as: The amplitude of the first idler light is proportional to the power ratio of the first pump light and the quadrature phase-shift keying signal, as well as the nonlinear coefficient of the nonlinear medium. Its phase relationship satisfies... The phase of the idler light generated in the x-polarization state (i.e., the second idler light) is coherent with the phase of the signal light in the y-polarization state (i.e., the first quadrature phase shift keying sub-signal), and the phase of the idler light generated in the y-polarization state (the third idler light) is coherent with the phase of the signal light in the x-polarization state (the second quadrature phase shift keying sub-signal).

[0100] After the second passage through the 3dB coupler, the quadrature phase shift keying (QPSK) signal and the generated first idler light are separated into two transmission paths. Then, the first polarization beamsplitter 202 separates the two polarization states of the first idler light, and the second polarization beamsplitter 203 separates the two polarization states of the QPSK signal. The polarization states of the second and third idler lights are modified by the first polarization state controller 204 and the second polarization state controller 205. Finally, the two QPSK sub-signals and the two idler lights are coherently superimposed. The output signal obtained from this process can be expressed as:

[0101]

[0102] in m represents the amplitude gain of the quadrature phase shift keying signal during the four-wave mixing process. j (j=x,y) is derived from A i With A s The ratio is determined by the angle of the first polarization beam splitter 202 or the second polarization beam splitter 203, which is defined here. θ is the angle between the straight line containing the constellation points after constellation compression and the real axis of the coordinate system. The value of θ can be adjusted by changing the relative phase of the quadrature phase-shift keying (QPSK) signal and either the first or second pump light. Simultaneously, the power ratio between the first pump light and the QPSK signal can be adjusted to maintain a suitable power ratio, ensuring that all points in the compressed constellation diagram are on a straight line and equidistant from each other. This allows control over the shape of the converted u-PAM4 constellation diagram, thereby converting the QPSK signal into a first pulse amplitude modulation (PAM) signal.

[0103] Figure 5 This is a schematic diagram of the structure of the vector transfer unit provided in an embodiment of the present invention, as shown below. Figure 5 As shown, the vector shifting unit 21 includes a second amplifier 211, a first filter 212, a second filter 213, a first polarizer 214, a second polarizer 215, and a third polarization beam splitter 216.

[0104] The second amplifier 211 is used to perform four-wave mixing processing on the input third pump light signal3, fourth pump light signal4, fifth pump light signal5, sixth pump light signal6, first pulse amplitude modulation signal and second pulse amplitude modulation signal to obtain the first mixing signal and the second mixing signal.

[0105] The first filter 212 is used to filter the first mixing signal to obtain the third pulse amplitude modulation signal and the fourth idler light.

[0106] The second filter 213 is used to coherently superimpose the third pulse amplitude modulation signal and the fourth idler light to obtain the fourth pulse amplitude modulation signal and the fifth idler light.

[0107] The first polarizer 214 is used to coherently superimpose the third pulse amplitude modulation signal and the fourth idler light to obtain the fifth pulse amplitude modulation signal.

[0108] The second polarizer 215 is used to coherently superimpose the fourth pulse amplitude modulation signal and the fifth idler light to obtain the sixth pulse amplitude modulation signal.

[0109] The third polarization beam splitter 216 is used to combine the fifth pulse amplitude modulation signal and the sixth pulse amplitude modulation signal to obtain the target pulse amplitude modulation signal, that is, to obtain the PDM-PAM signal.

[0110] In one embodiment, the first filter 212 and the second filter 213 may be bandpass filters (Berkeley Packet Filters).

[0111] In one embodiment, the signal conversion system further includes a third circulator 217 and a fourth circulator 218. The third circulator 217 is used to perform frequency selection processing on the mixed signal after the second amplifier 211 has undergone four-wave mixing processing to obtain a first mixed signal. The fourth circulator 218 is used to perform frequency selection processing on the mixed signal after the second amplifier 211 has undergone four-wave mixing processing to obtain a second mixed signal.

[0112] Specifically, after constellation diagram compression, the two u-PAM4 signals need to undergo a vector shifting process to be converted into standard PDM-PAM signals. Figure 6 This is a schematic diagram of the spectral relationship of a vector non-degenerate PSA provided in an embodiment of the present invention, as shown below. Figure 5 and Figure 6 As shown, the signal after constellation diagram compression is split into two transmission paths, which are then input into the second amplifier 211 along with multiple pump lights. The X-polarization state expression of the quadrature phase-shift keying signal is: Along with it, the second amplifier 211 is fed with the third pump light and the second pump light in the Y-polarized state, with the following expressions: The expression for the quadrature phase shift keying signal in the Y-polarization state is: Along with it, the fifth and sixth pump lights in the X-polarized state are input to the second amplifier 211, with the following expressions: The phase of the quadrature phase shift keying signal can also be expressed as This refers to the sum of the information phase and the carrier phase. After four-wave mixing, a fourth and fifth idler light, orthogonal to the polarization states of the first and second pulse amplitude modulation signals, are generated. Then, the third pulse amplitude modulation signal and the fourth idler light are coherently superimposed using a first polarizer 214, and the fourth pulse amplitude modulation signal and the fifth idler light are coherently superimposed using a second polarizer 215. This achieves vector shifting by coherently superimposing the pulse amplitude modulation signal and the idler light, and the third polarization beam splitter 216 combines them into a PDM-PAM4 signal. The final system output is:

[0113]

[0114] Where C s This is the final signal output after vector shifting. Let this be the amplitude gain of the pulse amplitude modulation signal input to the second amplifier 211 during the four-wave mixing process. Here, we define... The relative phase between the pump light and the pulse amplitude modulation signal is determined. By setting δ to a controllable constant, this process is equivalent to adding a fixed vector to the input, achieving a complete rightward shift of the constellation diagram. The magnitude of the shift is determined by n. j The values ​​(j=1,2) can be determined by the power ratio of the pulse amplitude modulation signal and the pump light, as well as the angles of the first polarizer 214 and the second polarizer 215. When the power of the pulse amplitude modulation signal and the pump light is fixed, adjusting the angles of the first polarizer 214 and the second polarizer 215 allows the power of the pulse amplitude modulation signal and the idler light to be superimposed in an appropriate ratio, converting the constellation-compressed u-PAM signal into a normal PAM signal, thus achieving vector shifting based on vector PSA.

[0115] Figure 7 This is a schematic diagram of the signal conversion system structure provided in an embodiment of the present invention, such as... Figure 7 As shown, the signal conversion system also includes an interferometer 301, a modulator 303, and a third filter 302.

[0116] Among them, the interferometer 301 is used to receive the input first beam and perform interference processing on the first beam to obtain an optical comb.

[0117] The third filter 302 is used to filter the optical comb to obtain the first pump light, the second pump light, the third pump light, the fourth pump light, the fifth pump light, and the sixth pump light; wherein the first pump light, the second pump light, and the third pump light have the same frequency and amplitude as the fourth pump light, the fifth pump light, and the sixth pump light, respectively.

[0118] Modulator 303 is used to receive the input second beam and modulate the second beam to obtain a quadrature phase shift keying signal.

[0119] Specifically, in this embodiment, the interferometer 301 can be a Mach-Zehnder modulator (MZM), and the third filter 302 can be a band-pass filter (BPF). The modulator 303 can be an IQ modulator commonly used in the industry.

[0120] Please refer to Figure 7 The continuous wave (CW) is split into two parts. The first beam is input into interferometer 301 to generate an optical comb, and then passes through a third filter 302 to select three pump beams with the required center frequency and phase coherence as the pump beams needed by the conversion system. The second beam serves as the carrier signal and is used by an IQ modulator to generate a QAM signal. The IQ modulator is driven by pseudo random bit sequences (PRBSs). A third amplifier 304 can be added before the QAM signal is input into the system. The third amplifier 304 amplifies the modulated second beam output from modulator 303 to obtain a quadrature phase shift keying (QPSK) signal.

[0121] For example, the third amplifier 304 may employ an amplified spontaneous emission (ASE) amplifier to amplify and radiate noise to control the signal-to-noise ratio of the quadrature phase shift keying signal.

[0122] In one embodiment, the signal conversion system further includes a third polarization state controller 401, a fourth polarization state controller 402, a fifth polarization state controller 403, a sixth polarization state controller 404, and a seventh polarization state controller 405. The third polarization state controller 401, the fourth polarization state controller 402, the fifth polarization state controller 403, the sixth polarization state controller 404, and the seventh polarization state controller 405 are respectively used to filter and modulate the output second pump light, third pump light, fourth pump light, fifth pump light, and sixth pump light.

[0123] In one embodiment, the signal conversion system further includes a fourth filter 305 and a signal analysis unit 306.

[0124] The fourth filter 305 is used to filter the target pulse amplitude modulation signal; the signal analysis unit 306 is used to receive the filtered target pulse amplitude modulation signal and to detect and analyze the filtered target pulse amplitude modulation signal.

[0125] It can be seen that the signal conversion system provided in this embodiment has the following advantages compared with the prior art:

[0126] 1. Based on constellation diagram compression and vector shifting, QAM to PAM signal conversion is achieved. This process, based on scalar PSA, requires adjusting the power ratio between the quadrature phase-shift keying (QPSK) signal and the pump light to achieve the desired effect. This embodiment uses vector PSA processing, superimposing the QPSK signal with idler light, and adjusting the angle of the polarization beam splitter changes the power ratio without needing to adjust the QPSK signal or pump power.

[0127] 2. The signal conversion system of this embodiment can be used for format conversion of polarization multiplexed signals, such as realizing the conversion of PDM-QAM to PDM-PAM signals, making the application scenarios of the signal conversion system of this embodiment more extensive.

[0128] The signal conversion method provided by the present invention is described below. The signal conversion method described below can be referred to in correspondence with the signal conversion system described above.

[0129] Figure 8 This is a flowchart of the signal conversion method provided in an embodiment of the present invention, such as... Figure 8 As shown, the signal conversion method includes:

[0130] S801: Receive the input quadrature phase shift keying signal, perform constellation compression processing on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal, compress the constellation points on the constellation diagram into a straight line, and obtain the first pulse amplitude modulation signal in the polarization state.

[0131] S802. Perform vector shifting processing on the first pulse amplitude modulation signal to obtain the target pulse amplitude modulation signal in which the real parts of all constellation points on the constellation diagram are positive.

[0132] In one embodiment, constellation compression processing is performed on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal, compressing the constellation points on the constellation diagram into a straight line to obtain the first pulse amplitude modulation signal in the polarization state, including:

[0133] The first pump light, the second pump light, and the quadrature phase shift keying signal are subjected to four-wave mixing processing to obtain a first idler light with the same frequency as the quadrature phase shift keying signal;

[0134] The first idler beam is split into two beams to obtain the second and third idler beams.

[0135] The quadrature phase shift keying (QPSK) signal is split to obtain the first QPSK sub-signal and the second QPSK signal;

[0136] The polarization of the second and third idler beams is adjusted;

[0137] The first orthogonal phase-shift keying sub-signal and the polarization-adjusted second idler light are coherently superimposed to obtain the first pulse amplitude modulation signal;

[0138] The second orthogonal phase-shift keying sub-signal and the polarization-adjusted third idler light are coherently superimposed to obtain the second pulse amplitude modulation signal.

[0139] The first pulse amplitude modulation signal includes a first pulse amplitude modulation signal and a second pulse amplitude modulation signal.

[0140] In one embodiment, the first pulse amplitude modulation signal is subjected to vector shifting processing to obtain a target pulse amplitude modulation signal in which all real parts of constellation points on the constellation diagram are positive, specifically including:

[0141] The third pump light, the fourth pump light, the fifth pump light, the sixth pump light, the first pulse amplitude modulation signal, and the second pulse amplitude modulation signal are subjected to four-wave mixing processing to obtain the first mixing signal and the second mixing signal.

[0142] The first mixing signal is filtered to obtain the third pulse amplitude modulation signal and the fourth idler light;

[0143] The third pulse amplitude modulation signal and the fourth idler light are coherently superimposed to obtain the fourth pulse amplitude modulation signal and the fifth idler light;

[0144] The third pulse amplitude modulation signal and the fourth idler light are coherently superimposed to obtain the fifth pulse amplitude modulation signal.

[0145] The fourth pulse amplitude modulation signal and the fifth idler light are coherently superimposed to obtain the sixth pulse amplitude modulation signal.

[0146] The fifth pulse amplitude modulation signal and the sixth pulse amplitude modulation signal are combined to obtain the target pulse amplitude modulation signal.

[0147] In one embodiment, the signal conversion method further includes:

[0148] The first input beam is received and subjected to interference processing to obtain an optical comb;

[0149] The optical comb is filtered to obtain a first pump light, a second pump light, a third pump light, a fourth pump light, a fifth pump light, and a sixth pump light;

[0150] The second beam is received and modulated to obtain a quadrature phase shift keying signal.

[0151] In one embodiment, the signal conversion method further includes:

[0152] The modulated second beam is amplified to obtain the quadrature phase shift keying signal.

[0153] In one embodiment, the signal conversion method further includes:

[0154] Filter the target pulse amplitude modulation signal;

[0155] The filtered target pulse amplitude modulation signal is received and analyzed.

[0156] In one embodiment, the signal conversion method further includes:

[0157] The mixed signal after four-wave mixing is subjected to frequency selection processing to obtain the first idler light;

[0158] Frequency selection processing is performed on the mixed signal after four-wave mixing to obtain the quadrature phase shift keying signal;

[0159] The mixed signal after four-wave mixing is subjected to frequency selection processing to obtain the first mixed signal;

[0160] The mixed signal after four-wave mixing is frequency-selected to obtain the second mixed signal.

[0161] The signal conversion method according to this embodiment can be used for format conversion of polarization multiplexed signals, such as realizing the conversion of PDM-QAM to PDM-PAM signals, making the application scenarios of the signal conversion system of this embodiment more extensive.

[0162] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0163] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A signal conversion system for converting quadrature phase shift keying signals into target pulse amplitude modulation signals, characterized in that, The signal conversion system includes: a constellation compression unit and a vector shifting unit; The constellation compression unit is used to receive the input quadrature phase shift keying signal, perform constellation compression processing on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal, compress the constellation points on the constellation diagram into a straight line, and obtain the first pulse amplitude modulation signal under polarization state; The vector shifting unit is used to perform vector shifting processing on the first pulse amplitude modulation signal to obtain a target pulse amplitude modulation signal in which the real parts of all constellation points on the constellation diagram are positive. The constellation compression unit includes a first amplifier, a first polarization beam splitter, a second polarization beam splitter, a first polarization state controller, a second polarization state controller, a first coupler, and a second coupler. The first amplifier is used to receive the input first pump light, the second pump light, and the quadrature phase shift keying signal, and to perform four-wave mixing processing on the first pump light, the second pump light, and the quadrature phase shift keying signal to obtain a first idler light with the same frequency as the quadrature phase shift keying signal; The first polarization beam splitter is used to split the first idler light into a second idler light and a third idler light; The second polarization beam splitter is used to split the quadrature phase shift keying signal to obtain a first quadrature phase shift keying sub-signal and a second quadrature phase shift keying sub-signal; The first polarization state controller is used to adjust the polarization of the second idler light; the second polarization state controller is used to adjust the polarization of the third idler light. The first coupler is used to coherently superimpose the first orthogonal phase shift keying sub-signal and the polarization-adjusted second idler light to obtain a first pulse amplitude modulation signal; The second coupler is used to coherently superimpose the second orthogonal phase shift keying sub-signal and the polarization-adjusted third idler light to obtain the second pulse amplitude modulation signal; The first pulse amplitude modulation signal includes the first pulse amplitude modulation signal and the second pulse amplitude modulation signal; The vector shifting unit includes a second amplifier, a first filter, a second filter, a first polarizer, a second polarizer, and a third polarization beam splitter; The second amplifier is used to perform four-wave mixing processing on the input third pump light, fourth pump light, fifth pump light, sixth pump light, first pulse amplitude modulation signal and second pulse amplitude modulation signal to obtain a first mixing signal and a second mixing signal. The first filter is used to filter the first mixing signal to obtain the third pulse amplitude modulation signal and the fourth idler light; The second filter is used to coherently superimpose the third pulse amplitude modulation signal and the fourth idler light to obtain the fourth pulse amplitude modulation signal and the fifth idler light; The first polarizer is used to coherently superimpose the third pulse amplitude modulation signal and the fourth idler light to obtain the fifth pulse amplitude modulation signal; The second polarizer is used to coherently superimpose the fourth pulse amplitude modulation signal and the fifth idler light to obtain the sixth pulse amplitude modulation signal; The third polarization beam splitter is used to combine the fifth pulse amplitude modulation signal and the sixth pulse amplitude modulation signal to obtain the target pulse amplitude modulation signal.

2. The signal conversion system according to claim 1, characterized in that, It also includes an interferometer, a modulator, and a third filter; The interferometer is used to receive the input first beam and perform interference processing on the first beam to obtain an optical comb; The third filter is used to filter the optical comb to obtain the first pump light, the second pump light, the third pump light, the fourth pump light, the fifth pump light, and the sixth pump light. The modulator is used to receive the input second beam and modulate the second beam to obtain the quadrature phase shift keying signal.

3. The signal conversion system according to claim 2, characterized in that, It also includes a third amplifier; The third amplifier is used to amplify the modulated second beam output by the modulator to obtain the quadrature phase shift keying signal.

4. The signal conversion system according to claim 3, characterized in that, It also includes a fourth filter and a signal analysis unit; The fourth filter is used to filter the target pulse amplitude modulation signal; The signal analysis unit is used to receive the filtered target pulse amplitude modulation signal and analyze the filtered target pulse amplitude modulation signal.

5. The signal conversion system according to claim 2, characterized in that, It also includes a first circulator, a second circulator, a third circulator, and a fourth circulator; The first circulator is used to perform frequency selection processing on the mixed signal after the first amplifier has undergone four-wave mixing processing to obtain the first idler light; The second circulator is used to perform frequency selection processing on the mixed signal after the first amplifier has undergone four-wave mixing processing to obtain the quadrature phase shift keying signal; The third circulator is used to perform frequency selection processing on the mixed signal after the second amplifier has undergone four-wave mixing processing to obtain the first mixed signal; The fourth circulator is used to perform frequency selection processing on the mixed signal after the second amplifier has undergone four-wave mixing processing to obtain the second mixed signal.

6. A signal conversion method, characterized in that, include: The input quadrature phase shift keying signal is received, and constellation compression processing is performed on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal to compress the constellation points on the constellation diagram into a straight line to obtain the first pulse amplitude modulation signal in the polarization state. The first pulse amplitude modulation signal is subjected to vector shifting processing to obtain a target pulse amplitude modulation signal in which the real parts of all constellation points on the constellation diagram are positive. The step of performing constellation compression processing on the constellation points on the constellation diagram corresponding to the quadrature phase shift keying signal, compressing the constellation points on the constellation diagram to a straight line to obtain the first pulse amplitude modulation signal in the polarization state, includes: The first pump light, the second pump light, and the quadrature phase shift keying signal are subjected to four-wave mixing processing to obtain a first idler light with the same frequency as the quadrature phase shift keying signal; The first idler beam is split into a second idler beam and a third idler beam. The quadrature phase shift keying signal is split to obtain a first quadrature phase shift keying sub-signal and a second quadrature phase shift keying signal; The polarization of the second and third idler beams is adjusted; The first orthogonal phase shift keying sub-signal and the polarization-adjusted second idler light are coherently superimposed to obtain the first pulse amplitude modulation signal; The second orthogonal phase-shift keying sub-signal and the polarization-adjusted third idler light are coherently superimposed to obtain the second pulse amplitude modulation signal; The first pulse amplitude modulation signal includes the first pulse amplitude modulation signal and the second pulse amplitude modulation signal; The step of performing vector shifting processing on the first pulse amplitude modulation signal to obtain a target pulse amplitude modulation signal in which all real parts of the constellation points on the constellation diagram are positive includes: The third pump light, the fourth pump light, the fifth pump light, the sixth pump light, the first pulse amplitude modulation signal, and the second pulse amplitude modulation signal are subjected to four-wave mixing processing to obtain the first mixing signal and the second mixing signal. The first mixing signal is filtered to obtain the third pulse amplitude modulation signal and the fourth idler light; The third pulse amplitude modulation signal and the fourth idler light are coherently superimposed to obtain the fourth pulse amplitude modulation signal and the fifth idler light; The third pulse amplitude modulation signal and the fourth idler light are coherently superimposed to obtain the fifth pulse amplitude modulation signal; The fourth pulse amplitude modulation signal and the fifth idler light are coherently superimposed to obtain the sixth pulse amplitude modulation signal; The fifth pulse amplitude modulation signal and the sixth pulse amplitude modulation signal are combined to obtain the target pulse amplitude modulation signal.

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