Method and apparatus for converting a DQPSK signal to a PAM4 signal

Abstract

The application discloses a method and device for converting a DQPSK signal into a PAM4 signal, and relates to the technical field of signal processing. The technical scheme points are as follows: a DQPSK signal is obtained, delay superposition processing is performed on the DQPSK signal to obtain two routes of star type 16QAM signals, a pump assisted nonlinear optical loop mirror (NOLM) is designed by utilizing the nonlinear effect of cross phase modulation (XPM), so that the process of phase matching is avoided, then symmetric processing is performed on the two routes of star type 16QAM signals to obtain two routes of OOK signals, which are respectively taken as a third signal and a fourth signal, the power ratio of the third signal and the relative phase shift of the fourth signal are adjusted, then vector superposition is performed on the third signal and the fourth signal to obtain a PAM4 signal, so that all-optical switching processing of the optical signal is more stable and simple, all-optical conversion of the phase modulation signal to the intensity modulation signal is realized, and the application can be applied to a gateway of a long distance power communication network to a short distance power access network, and the reliability of power grid service transmission is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of signal processing, more particularly, it relates to a method and device for converting DQPSK signal into PAM4 signal. BACKGROUND

[0002] With the development and construction of new power systems, power communication plays an increasingly important role in ensuring reliable transmission of services, etc. The traditional power communication gateway realizes the exchange of signals by adopting optical-electric-optical conversion. The reliability of service transmission and the accuracy of delay requirement of the power system make the time delay caused by optical-electric-optical conversion affect the reliability of large power grid service transmission under the new power system.

[0003] In the prior art, the format conversion of optical signals is realized by phase-sensitive amplification (PSA), but precise phase matching of signal light and pump light is required to realize the format conversion of signals. In actual application process, precise phase matching is extremely difficult and is prone to failure, thereby reducing the reliability of power grid service transmission. SUMMARY

[0004] In order to solve the problems of the prior art, the purpose of the present application is to provide a method and device for converting DQPSK signal into PAM4 signal. The present application first obtains the DQPSK signal of differential quadrature phase shift keying, performs delay superposition processing on the DQPSK signal to obtain two routes of star type 16QAM signals, designs a pump-assisted nonlinear optical loop mirror (NOLM) by utilizing the nonlinear effect of cross phase modulation (XPM), thereby avoiding the process of phase matching, then performs symmetric processing on the two routes of star type 16QAM signals to obtain two routes of OOK signals as the third signal and the fourth signal, respectively, adjusts the power ratio and relative phase shift between the third signal and the fourth signal, and then completes vector superposition of the third signal and the fourth signal to obtain the PAM4 signal, thereby realizing all-optical switching processing of optical signals more stably and simply, and improving the reliability of power grid service transmission.

[0005] The above technical purpose of the present application is realized by the following technical scheme:

[0006] In a first aspect, the present application provides a method for converting DQPSK signal into PAM4 signal, comprising:

[0007] obtaining the DQPSK signal of differential quadrature phase shift keying;

[0008] delay superposition is performed on the DQPSK signal to obtain two routes of star type 16QAM signals after delay superposition as the first signal and the second signal;

[0009] The first signal and the second signal are compressed and vector shifted at different power constellation points respectively to obtain two OOK signals corresponding to the first signal and the second signal respectively as a third signal and a fourth signal.

[0010] After adjusting the power ratio and the relative phase shift between the third signal and the fourth signal, vector superposition of the third signal and the fourth signal is completed to obtain a PAM4 signal.

[0011] In an embodiment, a DQPSK signal is subjected to delay superposition to obtain two delayed superposition star 16QAM signals as a first signal and a second signal, and the specific process is as follows:

[0012] A fixed phase shift of π / 4 is added to the DQPSK signal of the lower arm of the delay interferometer, and at the same time, a delay of one DQPSK signal symbol time is added, and then the DQPSK signal is superposed with the DQPSK signal of the upper arm of the delay interferometer to obtain a first signal, wherein the first signal is an I branch star 16QAM signal.

[0013] A fixed phase shift of-π / 4 is added to the DQPSK signal of the lower arm of the delay interferometer, and at the same time, a delay of one DQPSK signal symbol time is added, and then the DQPSK signal is superposed with the DQPSK signal of the upper arm of the delay interferometer to obtain a second signal, wherein the second signal is a Q branch star 16QAM signal.

[0014] In an embodiment, a DQPSK signal is subjected to delay superposition to obtain two delayed superposition star 16QAM signals as a first signal and a second signal, and the calculation formula is as follows:

[0015]

[0016] In the formula, E dqpsk (t) represents a differential quadrature phase shift keying DQPSK signal, t represents time, ΔT represents a delay of one DQPSK signal symbol time, A s represents the amplitude of the DQPSK signal; wherein when the fixed phase shift is π / 4, E 1，out (t) represents the first signal, and when the fixed phase shift is-π / 4, E 1，out (t) represents the second signal.

[0017] In an embodiment, the first signal and the second signal are compressed and vector shifted at different power constellation points respectively to obtain two OOK signals corresponding to the first signal and the second signal respectively as a third signal and a fourth signal, and the specific process is as follows:

[0018] The pump light assisted nonlinear optical loop mirror (NOLM) compresses and vector shifts different power constellation points of the first signal and the second signal respectively, and two OOK signals corresponding to the first signal and the second signal are obtained as the third signal and the fourth signal.

[0019] In an embodiment, the pump assisted nonlinear optical loop mirror (NOLM) compresses and vector shifts the first signal and the second signal to obtain the third signal and the fourth signal, and the formula is as follows:

[0020]

[0021] Wherein:

[0022]

[0023] P out P represents a power function of the OOK signal, L represents the length of the high nonlinear optical fiber, γ represents the nonlinear coefficient of the high nonlinear optical fiber, P 0，in P represents the power of the input pump light, P 1，in P represents the power of the inner layer and the outer layer signal constellation of the star 16QAM signal.

[0024] In an embodiment, after adjusting the power ratio of the third signal and the relative phase shift of the fourth signal, vector superposition of the third signal and the fourth signal is completed to obtain the PAM4 signal, and the specific process is as follows:

[0025] The power of the third signal is adjusted through a variable optical attenuator (VOA);

[0026] The phase shift of the fourth signal is adjusted through a variable phase shifter (VPS);

[0027] The third signal with adjusted power ratio and the fourth signal with adjusted phase shift are vector superimposed based on a 90° optical mixer, and the PAM4 signal is output from a first output port of the 90° optical mixer.

[0028] In a second aspect, the present application provides a device for converting a DQPSK signal into a PAM4 signal, comprising:

[0029] A DQPSK signal acquisition module is configured to acquire a differential quadrature phase shift keying (DQPSK) signal.

[0030] A star 16QAM signal acquisition module is configured to delay superimpose the DQPSK signal to obtain two delayed superimposed star 16QAM signals as the first signal and the second signal.

[0031] The OOK signal obtaining module is configured to compress and vector shift different power constellation points of the first signal and the second signal respectively to obtain two OOK signals corresponding to the first signal and the second signal as the third signal and the fourth signal respectively.

[0032] The PAM4 signal obtaining module is configured to complete vector superposition of the third signal and the fourth signal after adjusting the power ratio and the relative phase shift between the third signal and the fourth signal to obtain the PAM4 signal.

[0033] In an embodiment, the star 16QAM signal obtaining module comprises a first signal module and a second signal module.

[0034] The first signal module is configured to add a fixed phase shift of π / 4 and a delay of one DQPSK signal symbol time to the DQPSK signal of the lower arm of the delay interferometer, and superimpose the DQPSK signal of the upper arm of the delay interferometer to obtain the first signal, wherein the first signal is an I branch star 16QAM signal.

[0035] The second signal module is configured to add a fixed phase shift of-π / 4 and a delay of one DQPSK signal symbol time to the DQPSK signal of the lower arm of the delay interferometer, and superimpose the DQPSK signal of the upper arm of the delay interferometer to obtain the second signal, wherein the second signal is a Q branch star 16QAM signal.

[0036] In an embodiment, the OOK signal obtaining module specifically comprises:

[0037] The NOLM based on pump light assistance is configured to compress and vector shift different power constellation points of the first signal and the second signal respectively to obtain two OOK signals corresponding to the first signal and the second signal as the third signal and the fourth signal.

[0038] In an embodiment, the PAM4 signal obtaining module comprises:

[0039] The signal power ratio adjusting module is configured to adjust the power of the third signal through a VOA.

[0040] The signal phase shift adjusting module is configured to adjust the phase shift of the fourth signal through a VPS.

[0041] The signal superposition module is configured to perform vector superposition on the third signal with adjusted power ratio and the fourth signal with adjusted phase shift based on a 90° optical mixer, and output the PAM4 signal from a first output port of the 90° optical mixer.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] The application firstly obtains a DQPSK signal, performs delay superposition processing on the DQPSK signal to obtain two star-type 16QAM signals, designs a pump-assisted nonlinear optical loop mirror (NOLM) by using the nonlinear effect of cross-phase modulation (XPM), thereby avoiding the process of phase matching, then performs symmetric processing on the two star-type 16QAM signals to obtain two OOK signals as a third signal and a fourth signal respectively, adjusts the power ratio and relative phase shift between the third signal and the fourth signal, and then completes vector superposition of the third signal and the fourth signal to obtain a PAM4 signal, so that the all-optical switching processing of the optical signal is more stable and simple, and the reliability of the power grid service transmission is improved. BRIEF DESCRIPTION OF DRAWINGS

[0044] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0045] Figure 1 A method flow diagram for converting a DQPSK signal into a PAM4 signal is provided for the embodiments of the application;

[0046] Figure 2 A scheme overall concept diagram for converting a DQPSK signal into a PAM4 signal is provided for the embodiments of the application;

[0047] Figure 3 A constellation point diagram of each intermediate signal for converting a DQPSK signal into a PAM4 signal is provided for the embodiments of the application;

[0048] Figure 4 A structure block diagram of a device for converting a DQPSK signal into a PAM4 signal is provided for the embodiments of the application. DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application with reference to the embodiments and drawings, and the illustrative embodiments of the present application and the description thereof are only used to explain the present application and cannot be used as limitations to the present application.

[0050] It should be understood that the terms "first", "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0051] As Figure 1As shown, the present application provides a method for converting a DQPSK signal into a PAM4 signal, comprising:

[0052] Step S110, obtaining a DQPSK signal of differential quadrature phase shift keying;

[0053] Step S120, performing delay superposition on the DQPSK signal to obtain two paths of delayed superimposed star 16QAM signals as a first signal and a second signal respectively;

[0054] Step S130, performing compression and vector shift of different power constellation points on the first signal and the second signal respectively to obtain two paths of OOK signals corresponding to the first signal and the second signal as a third signal and a fourth signal respectively;

[0055] Step S140, after adjusting the power ratio and relative phase shift between the third signal and the fourth signal, performing vector superposition on the third signal and the fourth signal to obtain a PAM4 signal.

[0056] Specifically, based on the existing differential quadrature phase shift keying generating transmitting device, the DQPSK signal is transmitted, and the transmitting device is mainly composed of a laser, a pre-coding unit, a control unit, a delay adjustable unit and a double parallel modulator and other existing instruments and equipment. The specific working principle of generating DQPSK signal is a relatively mature way in the prior art. In step S110, the differential quadrature phase shift keying DQPSK signal is mainly received by a receiving device composed of a splitter, a control unit, two interferometers and two balanced receivers.

[0057] In step S120, since the differential processed DQPSK signal obtained in step S110, the DQPSK signal is subjected to delay processing and superposition processing, and is subjected to two path processing. As a person skilled in the art should understand, the two path signals correspond to the I branch and Q branch signals of the IQ demodulator. The DQPSK signal is subjected to delay processing and superposition processing on the I branch and Q branch respectively, so that the first signal is output at the output port of the I branch, and the second signal is output at the output port of the Q branch. It should be noted that the delay processing and superposition processing can be realized by the existing mature signal processing device delay interferometer. The specific model of the delay interferometer is not described here.

[0058] In step S130, the first and second signals obtained in step S120 are input into a nonlinear optical loop mirror (NOLM). The pump-assisted nonlinear optical loop mirror (NOLM) compresses and vector-shifts the first and second signals at different power constellation points, resulting in two OOK signals. Correspondingly, there are also a third and a fourth signal, namely the third signal of the I branch and the fourth signal of the Q branch. It is important to understand that the first signal corresponds to one nonlinear optical loop mirror (NOLM), and the second signal also corresponds to one nonlinear optical loop mirror (NOLM). However, regarding the pump light, the nonlinear optical loop mirror (NOLM) only injects one pump light signal at a time.

[0059] In step S140, since the ultimate goal of this application is to obtain a PAM4 signal, after adjusting the power ratio and relative phase shift between the third and fourth signals, the two OOK signals after adjusting the power ratio and phase shift are vector-superimposed based on the mixer, so that a signal in PAM4 format can be output from the first output port of the mixer.

[0060] In summary, the four steps described above first acquire the differential quadrature phase shift keying (DQPSK) signal. The DQPSK signal is then delayed and superimposed to obtain two star-shaped 16QAM signals. By utilizing the nonlinear effect of cross-phase modulation (XPM), a pump-assisted nonlinear optical loop mirror (NOLM) is designed to avoid phase matching. The two star-shaped 16QAM signals are then symmetrically processed to obtain two OOK signals, which serve as the third and fourth signals, respectively. After adjusting the power ratio and relative phase shift between the third and fourth signals, the vector superposition of the third and fourth signals is completed to obtain the PAM4 signal. This allows for a more stable and simpler all-optical switching process for optical signals, achieving all-optical conversion from phase-modulated signals to intensity-modulated signals. This technology can be applied at gateways connecting long-distance power communication networks to short-distance power access networks, improving the reliability of power grid service transmission.

[0061] In one implementation, such as Figure 2 As shown, the DQPSK signals are delayed and superimposed to obtain two delayed and superimposed star-shaped 16QAM signals, which are used as the first signal and the second signal, respectively. The specific process is as follows:

[0062] By adding a fixed phase shift of π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of 1 DQPSK signal symbol time, and then superimposing it with the DQPSK signal of the upper arm of the delay interferometer, a first signal is obtained, wherein the first signal is the star-shaped 16QAM signal of the I branch.

[0063] The second signal is a star 16QAM signal of the Q branch, which is obtained by adding a fixed phase shift of -π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of 1 DQPSK signal symbol time, and then superimposing the DQPSK signal of the upper arm of the delay interferometer.

[0064] Specifically, as shown in Figure 2 , the obtained DQPSK signals are input into the delay interferometer. Since the DQPSK signal has only four constellation points, the phase between adjacent constellation points is 90 degrees. For details, please refer to Figure 3 , which is well known to those skilled in the art, and therefore will not be explained in detail. As shown in Figure 2 , the first signal is obtained by adding a fixed phase shift of π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of 1 DQPSK signal symbol time, i.e. ΔT, and then superimposing the DQPSK signal of the upper arm of the delay interferometer. Figure 2 , which is the star-16QAM-I signal in Figure 2 . Similarly, the star-16QAM-Q signal in Figure 2 is obtained. It should be noted that Part A in

[0065] is the part for generating the first signal and the second signal.

[0066] In the formula, E dqpsk (t) represents the DQPSK signal of differential quadrature phase shift keying, t represents time, ΔT represents a delay of 1 DQPSK signal symbol time, A s represents the amplitude of the DQPSK signal; wherein when the fixed phase shift is π / 4, E 1，out (t) represents the first signal, and when the fixed phase shift is -π / 4, E 1，out (t) represents the second signal.

[0067] In an embodiment, the first signal and the second signal are compressed and vector shifted at different power constellation points, respectively, to obtain two OOK signals corresponding to the first signal and the second signal, respectively, as the third signal and the fourth signal. Specifically,

[0068] The first signal and the second signal are compressed and vector shifted at different power constellation points, respectively, based on a nonlinear optical loop mirror (NOLM) assisted by pump light, to obtain two OOK signals corresponding to the first signal and the second signal, respectively, as the third signal and the fourth signal.

[0069] In the present embodiment, as shown in Figure 2As shown in FIG. 2, a bundle of pump light (Pump) and star-16QAM-I signal are simultaneously injected into a nonlinear optical loop mirror (NOLM) composed of a high nonlinear fiber and a 3dB optical coupler, and the nonlinear effects of cross-phase modulation (XPM) in the high nonlinear fiber are used to compress and vector shift different power constellation points in the first signal and the second signal respectively, so as to obtain two OOK signals, namely OOK-I signal and OOK-Q signal as shown in FIG. 2. It should be noted that, Figure 2 Part B in FIG. 1 is the part for generating the third signal and the fourth signal.

[0070] As a specific embodiment, the third signal and the fourth signal are calculated as follows:

[0071]

[0072] Wherein:

[0073]

[0074] P out represents the power function of the OOK signal, represents the phase function of the OOK signal, L represents the length of the high nonlinear fiber, γ is the nonlinear coefficient of the high nonlinear fiber, P 0，in represents the power of the input pump light, P 1，in represents the power of the inner layer and outer layer signal constellation of the star-16QAM signal.

[0075] It should be noted that M and N have no actual meaning and only play a representation role, and similarly, and only play a representation role and have no actual meaning.

[0076] In an embodiment, as shown in FIG. 3, after adjusting the power ratio and the relative phase shift between the third signal and the fourth signal, vector superposition of the third signal and the fourth signal is completed to obtain the PAM4 signal, which is specifically: Figure 2 The power of the third signal is adjusted through a variable optical attenuator (VOA);

[0077] The phase shift of the fourth signal is adjusted through a variable phase shifter (VPS);

[0078] The third signal with adjusted power ratio and the fourth signal with adjusted phase shift are vector superimposed based on a 90° optical mixer, and the PAM4 signal is output from the first output port of the 90° optical mixer.

[0079]

[0080] ​Specifically, since the nonlinear optical environment mirror can complete the compression and vector shift processing of the star-shaped 16QAM signal, in order to finally output the PAM4 signal from the first output port of the frequency mixer, it is necessary to adjust the power ratio and the relative phase shift between the third signal and the fourth signal, so that the final two OOK signals can be vector superimposed through the 90° optical frequency mixer to obtain the PAM4 signal. For example, the power ratio between the third signal and the fourth signal is adjusted by placing a variable optical attenuator (VOA) after the third signal; and the relative phase shift between the third signal and the fourth signal is adjusted by placing a variable phase shifter (VPS) after the fourth signal. As shown in Figure 3 , the PAM4 signal in the first quadrant is finally obtained, and based on the corresponding adjustment, the PAM4 signals in the second quadrant, the third quadrant and the fourth quadrant can also be obtained. Specifically, as long as the parameters of the variable optical attenuator (VOA) and the variable phase shifter (VPS) are changed based on the symmetry principle, detailed description is not made. It should be noted that, Figure 2 Part C in the figure is the part of generating the PAM4 signal.

[0081] Based on the same technical concept, the embodiment provides a device for converting a DQPSK signal into a PAM4 signal. Since the principle of the device for solving the problem is similar to the method shown in Figure 1 , the implementation of the device can refer to the embodiments of the method shown in Figure 1 , and the repeated parts will not be described in detail. As shown in Figure 4 , the embodiment of the present application provides a device for converting a DQPSK signal into a PAM4 signal, which comprises:

[0082] The DQPSK signal acquisition module 210 is configured to acquire a differential quadrature phase shift keying (DQPSK) signal.

[0083] The star-shaped 16QAM signal acquisition module 220 is configured to delay and superimpose the DQPSK signal to obtain two delayed and superimposed star-shaped 16QAM signals as a first signal and a second signal.

[0084] The OOK signal acquisition module 230 is configured to compress and vector shift the first signal and the second signal to obtain two OOK signals corresponding to the first signal and the second signal as a third signal and a fourth signal.

[0085] The PAM4 signal acquisition module 240 is configured to adjust the power ratio and the relative phase shift between the third signal and the fourth signal, and then complete vector superposition of the third signal and the fourth signal to obtain a PAM4 signal.

[0086] In an embodiment, the star 16QAM signal obtaining module 220 comprises a first signal module and a second signal module.

[0087] The first signal module is configured to superimpose the DQPSK signal of the lower arm of the delay interferometer with the DQPSK signal of the upper arm of the delay interferometer by adding a fixed phase shift of π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of 1 DQPSK signal symbol time, to obtain a first signal, wherein the first signal is an I branch star 16QAM signal.

[0088] The second signal module is configured to superimpose the DQPSK signal of the lower arm of the delay interferometer with the DQPSK signal of the upper arm of the delay interferometer by adding a fixed phase shift of -π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of 1 DQPSK signal symbol time, to obtain a second signal, wherein the second signal is a Q branch star 16QAM signal.

[0089] In an embodiment, the OOK signal obtaining module 230 comprises:

[0090] The first signal and the second signal are compressed and vector shifted at different power constellation points based on a pump light assisted nonlinear optical loop mirror (NOLM), to obtain two paths of OOK signals corresponding to the first signal and the second signal, as a third signal and a fourth signal respectively.

[0091] In an embodiment, the PAM4 signal obtaining module 240 comprises:

[0092] The signal power ratio adjusting module is configured to adjust the power of the third signal by a variable optical attenuator (VOA);

[0093] The signal phase shift adjusting module is configured to adjust the phase shift of the fourth signal by a variable phase shifter (VPS);

[0094] The signal superimposition module is configured to perform vector superimposition on the third signal with adjusted power ratio and the fourth signal with adjusted phase shift based on a 90° optical mixer, and output a PAM4 signal from a first path output port of the 90° optical mixer.

[0095] The device for converting a DQPSK signal into a PAM4 signal provided in the embodiment has the following beneficial effects: first, the DQPSK signal is obtained, and two routes of star-type 16QAM signals are obtained by performing delay superposition processing on the DQPSK signal; by using the nonlinear effect of cross-phase modulation (XPM), a pump-assisted nonlinear optical loop mirror (NOLM) is designed, so that the process of phase matching is avoided; then, two routes of OOK signals are obtained by performing symmetric processing on the two routes of star-type 16QAM signals, and the two routes of OOK signals are respectively taken as a third signal and a fourth signal; after adjusting the power ratio of the third signal and the relative phase shift of the fourth signal, vector superposition of the third signal and the fourth signal is completed to obtain a PAM4 signal, so that all-optical switching processing of the optical signal is more stable and simple, the reliability of power grid service transmission is improved, all-optical conversion of a phase modulation signal to an intensity modulation signal is realized, and the device can be applied at a gateway of a long-distance power communication network to a short-distance power access network.

[0096] The above detailed description further explains the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of converting a DQPSK signal into a PAM4 signal, characterized by, The method comprises the following steps: obtaining a DQPSK signal; delaying and superimposing the DQPSK signal to obtain two delayed and superimposed star 16QAM signals as a first signal and a second signal; The constellation points of different power sizes in the first signal and the second signal are compressed and vector shifted respectively to obtain two OOK signals corresponding to the first signal and the second signal as the third signal and the fourth signal; the generation process of the two OOK signals is specifically as follows: a pump light (Pump) and a star-16QAM-I signal are simultaneously injected into a nonlinear optical loop mirror (NOLM) composed of a high nonlinear optical fiber and a 3dB optical coupler, and the nonlinear effects of cross phase modulation (XPM) in the high nonlinear optical fiber are used to compress and vector shift the constellation points of different power sizes in the first signal and the second signal respectively to obtain the two OOK signals; the expressions of the two OOK signals are: ; wherein: wherein, denotes a power function of the OOK signal, denotes a phase function of the OOK signal, L denotes a length of the high nonlinear fiber, and γ is a nonlinear coefficient of the high nonlinear fiber, denotes a power of the input pump light, denotes a signal power of the inner and outer constellation points of the star-shaped 16QAM signal; adjusting the power ratio and the relative phase shift between the third signal and the fourth signal, and then completing vector superposition of the third signal and the fourth signal to obtain a PAM4 signal.

2. The method of claim 1, wherein, The method comprises the following steps: delaying and superimposing the DQPSK signal to obtain two delayed and superimposed star 16QAM signals as a first signal and a second signal, and the specific process is as follows: adding a fixed phase shift of π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of one DQPSK signal symbol time, and then superimposing the DQPSK signal of the upper arm of the delay interferometer to obtain the first signal, wherein the first signal is an I branch star 16QAM signal; 3. The method of claim 2, wherein, adding a fixed phase shift of -π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of one DQPSK signal symbol time, and then superimposing the DQPSK signal of the upper arm of the delay interferometer to obtain the second signal, wherein the second signal is a Q branch star 16QAM signal. wherein, DQPSK denotes a differential quadrature phase shift keying signal, t denotes time, denotes a delay of one DQPSK signal symbol time, denotes an amplitude of the DQPSK signal; wherein, at a fixed phase shift of π / 4, denotes a first signal, at a fixed phase shift of -π / 4, denotes a second signal.

4. The method of claim 1, wherein, The method comprises the following steps: delaying and superimposing the DQPSK signal to obtain two delayed and superimposed star 16QAM signals as a first signal and a second signal, and the specific process is as follows: adjusting the power ratio of the third signal and the fourth signal through a variable optical attenuator (VOA); adjusting the phase shift of the fourth signal through a variable phase shifter (VPS); 5. An apparatus for converting a DQPSK signal into a PAM4 signal, the apparatus comprising: vector superimposing the third signal with the adjusted power ratio and the fourth signal with the adjusted phase shift based on a 90° optical mixer, and outputting a PAM4 signal from a first output port of the 90° optical mixer. The method comprises the following steps: obtaining a DQPSK signal; The OOK signal obtaining module is configured to compress and vector shift different power constellation points in the first signal and the second signal respectively to obtain two OOK signals corresponding to the first signal and the second signal as the third signal and the fourth signal respectively; compress and vector shift constellation points with different power in the first signal and the second signal respectively to obtain two OOK signals corresponding to the first signal and the second signal as the third signal and the fourth signal respectively; the generation process of the two OOK signals is as follows: a pump light (Pump) and a star-16QAM-I signal are simultaneously injected into a nonlinear optical loop mirror (NOLM) composed of a high nonlinear optical fiber and a 3dB optical coupler, and the nonlinear effect of cross phase modulation (XPM) in the high nonlinear optical fiber is used to compress and vector shift different power constellation points in the first signal and the second signal respectively to obtain two OOK signals; the expression of the two OOK signals is as follows: ; wherein: , P (t) represents a power function of the OOK signal, φ (t) represents a phase function of the OOK signal, L represents a length of the high nonlinear fiber, and γ represents a nonlinear coefficient of the high nonlinear fiber, Pp represents a power of the input pump light, P (t) represents a signal power of inner and outer constellation points of the star type 16QAM signal delaying and superimposing the DQPSK signal to obtain two delayed and superimposed star 16QAM signals as a first signal and a second signal; 6. The apparatus for converting a DQPSK signal into a PAM4 signal according to claim 5, wherein, adjusting the power ratio and the relative phase shift between the third signal and the fourth signal, and then completing vector superposition of the third signal and the fourth signal to obtain a PAM4 signal. The method comprises the following steps: delaying and superimposing the DQPSK signal to obtain two delayed and superimposed star 16QAM signals as a first signal and a second signal, and the specific process is as follows: adding a fixed phase shift of π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of one DQPSK signal symbol time, and then superimposing the DQPSK signal of the upper arm of the delay interferometer to obtain the first signal, wherein the first signal is an I branch star 16QAM signal; adding a fixed phase shift of -π / 4 to the DQPSK signal of the lower arm of the delay interferometer and simultaneously adding a delay of one DQPSK signal symbol time, and then superimposing the DQPSK signal of the upper arm of the delay interferometer to obtain the second signal, wherein the second signal is a Q branch star 16QAM signal. The second signal module is configured to superimpose the DQPSK signal of the lower arm of the delay interferometer with a fixed phase shift of -π / 4 and a delay of one DQPSK signal symbol time, and simultaneously superimpose the DQPSK signal of the upper arm of the delay interferometer to obtain a second signal, wherein the second signal is a Q branch star 16QAM signal.

7. The apparatus for converting a DQPSK signal into a PAM4 signal according to claim 5, wherein, The PAM4 signal obtaining module comprises: The signal power ratio adjusting module is configured to adjust the power of the third signal through a variable optical attenuator (VOA); The signal phase shift adjusting module is configured to adjust the phase shift of the fourth signal through a variable phase shifter (VPS); The signal superimposition module is configured to perform vector superimposition on the third signal with the adjusted power ratio and the fourth signal with the adjusted phase shift based on a 90° optical mixer, and output a PAM4 signal from a first output port of the 90° optical mixer.

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