Microwave photon self-interference cancellation and signal delay down-conversion device and method

Abstract

The application discloses a microwave photon self-interference elimination and signal delay down-conversion device and method, and belongs to the field of optical communication and microwave technology.The device comprises the following steps: introducing the differential delay of reference self-interference signals and received self-interference signals based on a ring modulation structure, simultaneously using polarization control to realize amplitude matching and reverse operation, and finally eliminating the self-interference signals in the optical domain; and loading a local oscillation signal, increasing a dispersion medium, adjusting laser wavelength, group dispersion coefficient and other parameters, and simultaneously realizing the down-conversion and delay functions of expected signals.The application realizes the elimination and delay down-conversion of self-interference signals, has simple structure and high practicability, and can be widely applied in phased array radars, electronic warfare and wireless communication electronic systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication and microwave technology, and more particularly to a microwave photon self-interference cancellation and signal delay down-conversion device and method. BACKGROUND

[0002] With the popularity of mobile devices, the amount of data that communication systems need to handle is increasing. At the same time, the In-Band Full-Duplex (IBFD) system can realize the same frequency transmission and reception, which can double the frequency utilization rate and transmission rate, and can alleviate the problem of spectrum resource shortage caused by excessive data in the current communication system. However, such a communication system always faces a serious self-interference problem, that is, part of the transmitted signal leaks into the receiver and cannot be directly filtered out using a filter, thereby affecting the correct demodulation of the received signal. Limited by the bandwidth and precision of electronic devices, the traditional electrical self-interference cancellation system is limited in terms of self-interference cancellation performance and application scenarios. Benefiting from the advantages of high frequency band, large bandwidth and anti-electromagnetic interference, the self-interference cancellation system based on photonics has improved in terms of working frequency band, cancellation bandwidth and cancellation depth, and has become a current research hotspot.

[0003] In order to reduce the requirements for the linearity of the radio frequency front end and the resolution of the subsequent analog-to-digital converter, while taking into account the self-interference cancellation depth index, the analog domain self-interference cancellation technology has become the key to microwave photon self-interference cancellation. Most current microwave photon-based analog domain self-interference cancellation schemes focus on improving the working frequency band, cancellation bandwidth and cancellation depth. Considering the sampling pressure of the analog-to-digital converter, researchers have combined self-interference cancellation with down-conversion technology. However, most of the schemes use electrical devices to reconstruct the reference interference signal to achieve self-interference cancellation, and the cancellation bandwidth and depth are still limited, and the full advantages of microwave photon technology have not been fully utilized. In addition, few schemes simultaneously achieve self-interference cancellation and down-conversion while performing delay processing on the expected signal, limiting the compatibility of the self-interference cancellation system with phased array radar, beam forming network and other systems. In summary, the microwave photon-based self-interference cancellation and signal delay down-conversion technology can provide solutions for the synchronization processing, calibration testing, delay storage and other aspects of the received signal in phased array radar. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide a microwave photon self-interference cancellation and signal delay down-conversion device and method, which realizes self-interference signal cancellation and delay down-conversion, has a simple structure and strong practicality, and can be widely applied in phased array radar, electronic warfare and wireless communication electronic systems.

[0005] The purpose of the present application is achieved by the following scheme:

[0006] The application discloses a microwave photon self-interference cancellation and signal delay down-conversion device, which comprises an adjustable laser, a phase modulator (PM), a double-drive Mach-Zehnder modulator (DDMZM), an optical tunable delay line (OTDL), an optical circulator (OC), a polarization beam splitter (PBS), a polarization controller (PC), a polarizer (Pol), a dispersion medium and a photoelectric detector (PD); the output port of the adjustable laser is connected with the input port 1 of the OC, and the output port 2 of the OC is connected with the common input port of the PBS; the port 1 of the PBS is connected with the light input port of the PM, the light output port of the PM is connected with the light output port of the DDMZM; the light output from the DDMZM in reverse direction is connected with the output port of the OTDL, and the input port of the OTDL is connected with the port 2 of the PBS; the output port 3 of the OC is connected with the input port of the PC, the output port of the PC is connected with the input port of the Pol, the output port of the Pol is connected with the input port of the dispersion medium, and the output port of the dispersion medium is connected with the light input port of the PD.

[0007] Further, the DDMZM comprises a Y-type optical splitter, two parallel sub-modulators PM1 and PM2 and a Y-type optical combiner, the input light is equally divided into two paths after passing through the Y-type optical splitter and enters the PM1 and PM2 respectively, and the light signals output by the two sub-modulators are combined into one output beam after passing through the Y-type optical combiner.

[0008] Further, the device comprises the following signal flow relationships: the initial reference interference signal is connected with the radio frequency port of the PM, the received signal of the mixed self-interference signal is connected with the radio frequency port 1 of the DDMZM, and the local oscillator signal is connected with the radio frequency port 2 of the DDMZM; the wavelength-adjustable laser signal is equally divided into two orthogonal polarization light signals after passing through the PBS, one of the two light signals is output from the port 1 and enters the PM in a clockwise direction to be modulated by the initial reference interference signal, and the other light signal is output from the port 2 and enters the DDMZM in a counterclockwise direction to be modulated by the received signal and the local oscillator signal; after the clockwise signal in the loop sequentially passes through the PM, the DDMZM and the OTDL for one cycle and the counterclockwise signal in the loop sequentially passes through the DDMZM, the OTDL and the PM for one cycle, the modulated CK light signal and the CCK light signal enter the reverse PBS to be combined into one polarization multiplexing light signal.

[0009] Further, the two orthogonal polarization light signals are TE mode light signals and TM mode light signals.

[0010] Further, the one clockwise light CK output from the port 1 is a TE mode light.

[0011] Further, the one counterclockwise light CCK output from the port 2 is a TM mode light.

[0012] A microwave photon self-interference cancellation and signal delay down-conversion method based on the above-mentioned device, comprising the following steps:

[0013] S1, the expressions of the desired received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal are respectively:

[0014] (1)

[0015] , , and represent the signal amplitudes of the received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal respectively, , and represent the angular frequencies of the desired signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal respectively, represents the delay experienced by the self-interference signal from the transmitting end to the receiving end;

[0016] Based on the device structure, the modulation signal output by the PM is introduced into the OTDL, and the optical carrier and the modulation sideband are introduced into the delay at the same time; in the modulation signal output by the DDMZM, only the optical carrier is introduced into the delay; only the reference interference signal is introduced into the delay in the whole signal modulation process; at this time, the polarization multiplexing optical signal output by port 3 of the OC is represented as:

[0017] (2)

[0018] wherein, and are the losses of the PM and the DDMZM respectively; is the frequency-adjustable signal generated by the laser, is the amplitude of the laser output signal, is the laser angular frequency, is the initial angular frequency, is the frequency step interval, n is an integer; , , , are the modulation indexes of the initial reference self-interference signal, the desired received signal, the received self-interference signal and the local oscillator signal respectively; represents the delay amount introduced by the OTDL; represents the DC bias angle of the DDMZM; represents the first-order Bessel function; n and ​​unit vectors representing the unit vectors of the optical field TE mode and TM mode, respectively;

[0019] S2, the signal input PC and polarizer, the output signal of PC and the polarizer axis alignment, the output signal of the polarizer is represented as:

[0020] (3)

[0021] wherein, α is the polarization control angle of PC; δ is the phase difference between the two polarization multiplexing light; according to formula (3), in the small signal approximation When the following formula (4) conditions are met simultaneously, the self-interference signal can be completely eliminated in the optical domain; at this time, the amplitude matching and the reverse operation are realized by the polarization control;

[0022] (4)

[0023] S3, the optical signal after eliminating the self-interference signal is input into the dispersion medium; the dispersion medium includes a single-mode optical fiber, and when only considering the loss and dispersion, the transmission function of the optical fiber is represented as:

[0024] (5)

[0025] wherein, and L are the attenuation coefficient and length of the optical fiber, respectively; , and represent the propagation constant, the inverse of the group velocity and the group velocity dispersion of the medium at the center frequency , respectively; only is considered in the subsequent derivation process, and the output of the single-mode optical fiber is represented as:

[0026] (6)

[0027] wherein, represents the phase shift introduced by the group velocity dispersion to the expected signal and the local oscillator sideband;

[0028] S4, after photoelectric detection, the optical current recovered by the PD is represented as:

[0029] (7)

[0030] wherein, represents the responsivity of the photoelectric detector; through formula (7), under the premise of eliminating the self-interference signal in the optical domain, the down-conversion of the expected signal is realized, and the group dispersion coefficient , the fiber length L and the laser frequency adjustment interval The delay control of the expected down-converted signal is realized, and then the phase is adjusted; and the DC bias angle of the DDMZM is adjusted to compensate The power fading problem caused by the dispersion introduced by a dispersion medium under double-sideband modulation is solved.

[0031] Further, in step S1, for the IBFD system .

[0032] Further, in step S1, the first type n Bessel function Under small signal input, other high-order components are ignored.

[0033] Further, in step S3, the dispersion medium includes a grating, a chirped mirror and a highly dispersive optical fiber.

[0034] The beneficial effects of the present application include:

[0035] The present application realizes the elimination of self-interference signals and the delay down-conversion on the basis of the ring modulation structure by reasonably adjusting the polarization parameters of the polarization multiplexed optical signal, the delay of the OTDL and the wavelength of the laser, and has the advantages of simple structure and strong practicability, can provide a solution for the synchronous processing, calibration test, delay storage and the like of the received signals in the phased array radar, and can be widely applied to the phased array radar, electronic warfare, wireless communication and the like electronic systems.

[0036] The present application constructs a new microwave photon self-interference elimination and signal delay down-conversion device. Based on the ring modulation structure, the differential delay of the reference self-interference signal and the received self-interference signal is introduced, and the amplitude matching and the reverse operation are realized by using the polarization control, and finally the self-interference signal is eliminated in the optical domain. In addition, by loading the local oscillator signal, increasing the dispersion medium and adjusting the laser wavelength, group dispersion coefficient and the like parameters, the down-conversion and delay functions of the expected signal can also be realized. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0038] Figure 1 A microwave photon self-interference elimination and signal delay down-conversion device of the present application;

[0039] Figure 2is the output signal spectrum under single frequency interference, (a) is the output signal spectrum without self-interference cancellation, and (b) is the output signal spectrum with self-interference cancellation;

[0040] Figure 3 is the output signal spectrum under single frequency interference, (a) is the output signal spectrum without self-interference cancellation, and (b) is the output signal spectrum with self-interference cancellation;

[0041] Figure 4 is n is the output time-domain waveform of the expected down-converted signal after self-interference cancellation when the values of n are 1, 5, 10, 15 and 20 respectively;

[0042] Figure 5 is the output signal spectrum under wideband interference, (a) is the output signal spectrum without self-interference cancellation, and (b) is the output signal spectrum with self-interference cancellation. DETAILED DESCRIPTION

[0043] All features disclosed in the specification or all steps of any method or process disclosed in the specification can be combined and / or extended or replaced by other features or steps, except for mutually exclusive features and / or steps, in any way.

[0044] The specific implementation process of the present application is as follows:

[0045] As a first aspect of the present application, a microwave photon self-interference cancellation and signal delay down-conversion device is provided, which comprises an adjustable laser, a PM, a DDMZM, an OTDL, an OC, a PBS, a PC, a Pol, a dispersion medium and a PD.

[0046] The output port of the adjustable laser is connected to the input port 1 of the OC, and the output port 2 of the OC is connected to the common input port of the PBS; port 1 of the PBS is connected to the optical input port of the PM, and the optical output port of the PM is connected to the optical output port of the DDMZM; the light passes through the DDMZM in reverse and is connected to the output port of the OTDL, and the input port of the OTDL is connected to port 2 of the PBS; the output port 3 of the OC is connected to the input port of the PC, the output port of the PC is connected to the input port of the Pol, the output port of the Pol is connected to the input port of the dispersion medium, and the output port of the dispersion medium is connected to the optical input port of the PD.

[0047] The DDMZM comprises a Y-type optical splitter, two parallel sub-modulators (PM1 and PM2), and a Y-type optical combiner, the input light is equally divided into two paths after passing through the Y-type optical splitter, and enters PM1 and PM2 respectively, and the optical signals output by the two sub-modulators are combined into one output beam through the Y-type optical combiner.

[0048] In the microwave photon self-interference cancellation and signal delay down-conversion device, the initial reference interference signal is connected to the RF port of the PM, the received signal mixed with the self-interference signal is connected to the RF port 1 of the DDMZM, and the local oscillation signal is connected to the RF port 2 of the DDMZM. The wavelength-tunable laser signal is divided into two orthogonal polarization light signals (TE mode and TM mode) after passing through the PBS, one of which is output from the port 1 and enters the PM in the clockwise (CK) direction (TE mode) to be modulated by the initial reference interference signal; the other is output from the port 2 and enters the DDMZM in the counterclockwise (CCK) direction (TM mode) to be modulated by the received interference signal and the local oscillation signal. Since the speed of the light signal entering the PM and the DDMZM from the output end does not match the speed of the RF signal, the received interference signal and the local oscillation signal will not modulate the PM, and the initial reference interference signal will not modulate the DDMZM. When the clockwise signal in the loop sequentially passes through the PM, the DDMZM and the OTDL for one cycle, and the counterclockwise signal in the loop sequentially passes through the DDMZM, the OTDL and the PM for one cycle, the modulated CK light signal and the CCK light signal enter the reverse PBS to be combined into a polarization multiplexing light signal.

[0049] As a second aspect of the present application, a microwave photon self-interference cancellation and signal delay down-conversion method is provided, comprising the following steps:

[0050] First, the expressions of the desired received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillation signal are respectively:

[0051] (1)

[0052] wherein, , , and represent the amplitudes of the above signals, , and represent the angular frequencies of the desired signal, the received self-interference signal, the initial reference self-interference signal and the local oscillation signal respectively, and for the IBFD system . represents the delay experienced by the self-interference signal from the transmitting end to the receiving end.

[0053] According to the structure shown in Figure 1 , the modulated signal output by the PM introduces delay to both the optical carrier and the modulation sideband after passing through the OTDL; while in the modulated signal output by the DDMZM, only the optical carrier introduces delay. Therefore, only the reference interference signal is delayed in the entire signal modulation process. At this time, the polarization multiplexing light signal output from the port 3 of the OC can be represented as:

[0054] (2)

[0055] where, and are the losses of PM and DDMZM, respectively; is the frequency-tunable signal generated by the laser, is the amplitude of the laser output signal, is the angular frequency of the laser, is the initial angular frequency, is the frequency step interval, n is an integer; , , , are the modulation indices of the initial reference self-interference signal, the desired received signal, the received self-interference signal and the local oscillator signal, respectively; denotes the amount of delay introduced by the OTDL; denotes the DC bias angle of the DDMZM; denotes the first-order n Bessel function, and other high-order components are neglected under small-signal input; and denote the unit vectors of the optical field TE mode and TM mode, respectively.

[0056] Next, the above signal input PC and polarizer, the output signal of PC and the polarizer axis alignment, the output signal of the polarizer can be written as:

[0057] (3)

[0058] where, α is the polarization control angle of PC; δ is the phase difference between the two polarization multiplexed lights. According to formula (3), under the small-signal approximation , when the following conditions are met simultaneously, the self-interference signal can be completely eliminated in the optical domain. At this time, the amplitude matching and the reverse operation are realized by polarization control.

[0059] (4)

[0060] Then, the optical signal after eliminating the self-interference signal is input into the dispersion medium. There are many devices that can act as dispersion media in practice, such as gratings, chirped mirrors, highly dispersive optical fibers, single-mode optical fibers, etc. Here, a single-mode optical fiber is taken as an example to demonstrate the function.

[0061] Only considering the loss and dispersion, the transmission function of the optical fiber can be expressed as:

[0062] (5)

[0063] where, and L are the attenuation coefficient and length of the fiber, respectively. , and denote the propagation constant, the inverse of the group velocity and the group velocity dispersion of the medium at the center frequency of the signal, respectively. Since and only introduce a fixed phase shift, we only consider in the following derivation. The output of the single-mode fiber can be expressed as:

[0064] (6)

[0065] where, denotes the phase shift introduced by the group velocity dispersion to the desired signal and the local oscillator sideband.

[0066] Finally, after photo-detection, the photo-current recovered by the PD can be expressed as:

[0067] (7)

[0068] where, denotes the responsivity of the photo-detector. It can be observed from equation (7) that, under the premise of eliminating the self-interference signal in the optical domain, the present application also realizes the down-conversion of the desired signal, and the delay control of the desired down-converted signal is realized by adjusting the group dispersion coefficient , the fiber length L and the laser frequency adjustment interval , so as to adjust the phase. In addition, under the double sideband modulation, the dispersion introduced by the dispersion medium will cause the power fading problem, especially in the high frequency case, the fading is very serious, at this time the direct current bias angle of the DDMZM can be adjusted to compensate.

[0069] In other embodiments, a microwave photon self-interference elimination and signal delay down-conversion device is provided, specifically comprising: a tunable laser, a radio frequency signal source, a local oscillator signal source, an oscilloscope, a PM, a DDMZM, an OTDL, an OC, a PBS, a PC, a Pol, a dispersive medium, and a PD. The output end of the tunable laser is connected to input port 1 of the OC, and output port 2 of the OC is connected to the common input port of the PBS; output port 1 of the PBS is connected to the input port of the PM, and the output end of the PM is connected to the output port of the DDMZM; the input port of the DDMZM is connected to the output port of the OTDL, and the input port of the OTDL is connected to input port 2 of the PBS; the output of the PBS passes through output port 3 of the OC and is connected to the input port of the PC, and the output port of the PC is connected to the input port of the Pol; the output port of the Pol is connected to the input port of the dispersive medium, and the output port of the dispersive medium is connected to the input port of the PD, and the output electrical signal of the PD is connected to a spectrum analyzer.

[0070] In other embodiments, the above device is verified for its technical effect according to the following steps:

[0071] Step 1: The tunable laser generates an optical carrier with an operating frequency of 193.1 THz and an optical power of 16 dBm. RF signal source 1 generates an initial reference self-interference signal and a received self-interference signal with a frequency of 12 GHz and powers of 10 dBm and -10 dBm respectively. RF signal source 2 generates a desired received signal with a frequency of 12.5 GHz and a power of -10 dBm. The local oscillator signal source generates a local oscillator signal with a frequency of 10 GHz and a power of 10 dBm. The half-wave voltages of PM and DDMZM are both 3.5 V, the extinction ratio of DDMZM is 35 dB, and the responsivity of the PD is 0.75 A / W.

[0072] Step 2: Remove PM and retain only the tunable laser, DDMZM, and PD as a control group. Without applying the desired signal or initial reference interference signal, the received self-interference signal and local oscillator signal are fed into the upper and lower arms of the DDMZM, respectively. The initial DC bias angle of the DDMZM is set to π, and the spectrum is observed without self-interference cancellation. Figure 2 (a) is the output signal spectrum without self-interference elimination in the case of single-frequency interference, and the self-interference signal power is -3.8dBm; then the reference interference signal is added, and according to the attached Figure 1 The complete system architecture shown is experimentally tested. Figure 2 (b) is the output signal spectrum when self-interference elimination is performed under single-frequency interference. The self-interference signal has been completely submerged by the noise, with a power of -70.6dBm, which is the same as Figure 2 (a) Compared with the single-frequency self-interference cancellation depth, it is 66.8dB.

[0073] Step 3: According to Figure 1The complete system architecture shown is tested, using a single-mode optical fiber with a length of 1km as a dispersion medium, a loss coefficient of 0.2dB / km, and a dispersion coefficient of 16ps / km.nm. In order to more intuitively observe the effect of self-interference cancellation, the self-interference signal and the useful signal are made to have a frequency difference of 0.5GHz (in fact, the two are equal). It can be found that the present application successfully realizes signal down-conversion, Figure 3 For the single-frequency interference case, the output signal spectrum when the dispersion medium is introduced and self-interference cancellation is performed, the power of the expected signal is -11.8dBm, and the power of the self-interference signal is -69.7dBm. At this time, the single-frequency self-interference cancellation depth is 57.9dB.

[0074] Step four: When the frequency variation interval of the adjustable laser is set to 50GHz, and the value of n is 1, 5, 10, 15 and 20 respectively, the time-domain waveform of the expected intermediate frequency signal at 2.5GHz is observed using an oscilloscope, as shown in Figure 4 It can be found that, under the condition of fixed dispersion coefficient and fiber length, the delay control of the expected down-converted signal can be realized by changing the output frequency of the laser.

[0075] Step five: The same control group setting as in step three is adopted, and the radio frequency signal source 1 generates an initial reference self-interference signal and a received self-interference signal with a modulation format of 16QAM, a carrier frequency of 12GHz, a bandwidth of 300MHz, and powers of 10dBm and -10dBm respectively, and the expected signal and the local oscillator signal remain unchanged. Figure 5 (a) is the output signal spectrum under the condition of wideband interference without self-interference cancellation, and the power of the self-interference signal is -11.5dBm; then, the same experimental group setting as in step three is adopted, Figure 5 (b) is the output signal spectrum under the condition of wideband interference with self-interference cancellation, and the power of the self-interference signal is -53.2dBm. Compared with Figure 5 The wideband self-interference cancellation depth is 41.7dB compared with (a).

[0076] In summary, the present application scheme constructs a microwave photon self-interference cancellation and signal delay down-conversion device, amplitude matching and inverse operation between the reference interference signal and the received signal are performed through polarization control technology, and the self-interference cancellation function is realized on the basis of down-conversion based on the optical domain elimination method. In addition, the expected received signal can be delayed by adjusting the output frequency or wavelength of the laser, and the power fading introduced by the dispersion medium can be compensated by adjusting the bias control angle of the modulator. The scheme has simple structure and flexible operation, and has potential application value in phased array radar, beam forming network and other electronic systems.

[0077] In summary, the above described embodiments are only examples of the present application and are not intended to limit the scope of the present application. It should be noted that those skilled in the art can make several equivalent modifications and substitutions on the basis of the disclosure of the present application. The modulator type, the laser type, the desired signal frequency, the self-interference signal frequency, the local oscillator signal frequency, the optical carrier wavelength, the optical carrier power, the desired signal power, the reference interference signal power, the direct current bias angle of the modulator, the polarization control angle, the adjustable phase difference, the dispersion medium type, etc. can be changed. These equivalent modifications and substitutions and the adjustment of the frequency range should also be considered as the scope of protection of the present application.

Claims

1. A method for eliminating microwave photon self-interference and signal delay down-conversion, characterized in that: A microwave photon self-interference elimination and signal delay down-conversion device is provided, comprising: a tunable laser, a phase modulator (PM), a dual-drive Mach-Zehnder modulator (DDMZM), an optical tunable delay line (OTDL), an optical circulator (OC), a polarization beam splitter (PBS), a polarization controller (PC), a polarizer (Pol), a dispersive medium, and a photodetector (PD); the output port of the tunable laser is connected to the input port 1 of the OC, and the output port 2 of the OC is connected to the common input port of the PBS; port 1 of the PBS is connected to the optical input port of the PM, and the optical output port of the PM is connected to the optical output port of the DDMZM; after passing through the DDMZM in the reverse direction, the optical output port of the OTDL is connected to the input port of the OTDL, and the input port of the OTDL is connected to port 2 of the PBS; the output port 3 of the OC is connected to the input port of the PC, the output port of the PC is connected to the input port of the Pol, the output port of the Pol is connected to the input port of the dispersive medium, and the output port of the dispersive medium is connected to the optical input port of the PD; and the device comprises the following steps: S1, suppose the expressions of the expected received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal are: （1） in, 、 、 and Represent the signal amplitudes of the received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal, respectively. 、 and denote the angular frequencies of the desired signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal, respectively. It represents the delay experienced by the self-interference signal from the transmitter to the receiver; After the modulated signal output by PM passes through OTDL, both the optical carrier and the modulation sideband are delayed. In the modulated signal output by DDMZM, only the optical carrier is delayed. During the entire signal modulation process, only the reference interference signal is delayed. In this case, the polarization-multiplexed optical signal output from port 3 of the OC is expressed as: （2） in, and are the losses of PM and DDMZM respectively; The frequency-adjustable signal generated by the laser, is the amplitude of the laser output signal, is the laser angular frequency, is the initial angular frequency, is the frequency step interval, n is an integer; 、 、 、 are the modulation indexes of the initial reference self-interference signal, the expected received signal, the received self-interference signal and the local oscillator signal respectively; Indicates the delay introduced by OTDL; Indicates the DC bias angle of DDMZM; Indicates the first category n order Bessel functions; and Represent the unit vectors of the TE mode and TM mode of the light field respectively; S2, signal input PC and polarizer, make the output signal of PC aligned with the main axis of polarizer, then the output signal of polarizer is expressed as: （3） in, α is the polarization control angle of PC; δ is the phase difference between the two polarization multiplexed lights; According to formula (3), in the small signal approximation Under this condition, when the following formula (4) is satisfied at the same time, the self-interference signal can be completely eliminated in the optical domain; at this time, the amplitude matching and phase inversion operations are both achieved by polarization control; （4） S3, inputting the optical signal after eliminating the self-interference signal into a dispersive medium; the dispersive medium includes a single-mode optical fiber. When only loss and dispersion are considered, the transmission function of the optical fiber is expressed as: （5） in, and L are the attenuation coefficient and length of the optical fiber, respectively; 、 and Represents the medium at the center frequency The propagation constant, the inverse of the group velocity and the group velocity dispersion under the condition of , the output of a single-mode fiber is expressed as: （6） in, It represents the phase shift introduced by group velocity dispersion to the desired signal and the local oscillator sideband; S4, after photodetection, the photocurrent recovered by PD is expressed as: （7） in, Represents the responsivity of the photodetector; through formula (7), it can be obtained that the down-conversion of the desired signal is achieved under the premise of eliminating the self-interference signal in the optical domain, and by adjusting the group dispersion coefficient , fiber length L and laser frequency adjustment interval Realize the delay control of the desired down-converted signal and adjust the phase; and adjust the DC bias angle of DDMZM to achieve Compensation is used to solve the problem of power attenuation caused by dispersion introduced by dispersive media under double-sideband modulation.

2. The microwave photon self-interference elimination and signal delay down-conversion method according to claim 1 is characterized in that: The DDMZM includes a Y-type optical splitter, two parallel sub-modulators PM1 and PM2, and a Y-type optical combiner. The input light is divided into two equal paths after passing through the Y-type optical splitter and enters PM1 and PM2 respectively. The optical signals output by the two sub-modulators are combined into one beam and output through the Y-type optical combiner.

3. The microwave photon self-interference elimination and signal delay down-conversion method according to claim 1, characterized in that: The device includes the following signal flow relationship: the initial reference interference signal is connected to the RF port of the PM, the received signal of the mixed self-interference signal is connected to the RF port 1 of the DDMZM, and the local oscillator signal is connected to the RF port 2 of the DDMZM; After passing through the PBS, the wavelength-tunable laser signal is equally split into two orthogonally polarized optical signals. The clockwise optical CK signal output from port 1 enters the PM in the forward direction and is modulated by the initial reference interference signal. The counterclockwise optical CCK signal output from port 2 enters the DDMZM in the forward direction and is modulated by the interfered receive signal and the local oscillator signal. After the clockwise signal in the loop passes through the PM, DDMZM, and OTDL in sequence, and the counterclockwise signal in the loop passes through the DDMZM, OTDL, and PM in sequence, the modulated CK and CCK optical signals enter the PBS in the opposite directions and are combined into a polarization-multiplexed optical signal.

4. The method for eliminating microwave photon self-interference and signal delay down-conversion according to claim 3, characterized in that: The two orthogonally polarized optical signals are specifically a TE mode optical signal and a TM mode optical signal.

5. The method for eliminating microwave photon self-interference and signal delay down-conversion according to claim 3, characterized in that: The clockwise light CK output from port 1 of the polarization beam splitter PBS is TE mode light.

6. The microwave photon self-interference elimination and signal delay down-conversion method according to claim 3, characterized in that: The counterclockwise light CCK output from port 2 of the polarization beam splitter PBS is TM mode light.

7. The microwave photon self-interference elimination and signal delay down-conversion method according to claim 1, characterized in that: In step S1, for the IBFD system .

8. The microwave photon self-interference elimination and signal delay down-conversion method according to claim 1, characterized in that: In step S1, the first category n Bessel function Under small signal input, other high-order components are neglected.

9. The method for eliminating microwave photon self-interference and signal delay down-conversion according to claim 1, characterized in that: In step S3, the dispersive medium includes a grating, a chirped mirror and a high-dispersion optical fiber.

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