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

Abstract

The invention discloses a microwave photon self-interference elimination and signal delay down-conversion device and method, and belongs to the technical field of optical communication and microwaves, the device is characterized in that differential delay introduction of a reference self-interference signal and a received self-interference signal is carried out based on an annular modulation structure, and meanwhile, amplitude matching and anti-phase operation are realized by utilizing polarization control; and finally, the self-interference signal is eliminated in the optical domain. By loading a local oscillator signal, adding a dispersive medium and adjusting parameters such as wavelength and group dispersion coefficient of a laser, down-conversion and delay functions of an expected signal are realized at the same time. According to the invention, elimination of self-interference signals and delay down-conversion are realized, the structure is simple, the practicability is very high, and the device can be widely applied to phased array radars, electronic warfare and wireless communication electronic systems.

Description

Technical Field

[0001] The present invention relates to the field of optical communication and microwave technology, and more specifically, to a microwave photon self-interference elimination and signal delay down-conversion device and method. Background Art

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

[0003] In order to reduce the requirements for the linearity of the RF front-end and the resolution of the subsequent analog-to-digital converter, while taking into account the self-interference elimination depth index, the analog domain self-interference elimination technology has become the key to microwave photon self-interference elimination. At present, most analog domain self-interference elimination solutions based on microwave photons focus on improving the working frequency band, elimination bandwidth and elimination depth. Considering the sampling pressure of the analog-to-digital converter, researchers also combine self-interference elimination with down-conversion technology. However, most solutions use electrical devices to reconstruct the reference interference signal to achieve self-interference elimination, and the elimination bandwidth and depth are still limited, and the full advantages of microwave photon technology have not been brought into play. In addition, few solutions delay the desired signal on the basis of realizing self-interference elimination and down-conversion at the same time, which limits the compatibility of the self-interference elimination system with phased array radars, beamforming networks and other systems. In summary, microwave photon-based self-interference elimination and signal delay down-conversion technology can provide solutions for the synchronous processing, calibration test, and delayed storage of received signals in phased array radars. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a microwave photon self-interference elimination and signal delay down-conversion device and method, which realizes the elimination of self-interference signals and delayed down-conversion. It has a simple structure and strong practicality and can be widely used in phased array radar, electronic warfare, and wireless communication electronic systems.

[0005] The object of the present invention is achieved through the following solutions:

[0006] A microwave photon self-interference elimination and signal delay down-conversion device comprises: an adjustable laser, a phase modulator PM, a dual-drive Mach-Zehnder modulator DDMZM, an optical adjustable 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 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; the 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 output port is connected to the output port of the OTDL after passing through the DDMZM in the reverse direction, and the input port of the OTDL is connected to the 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.

[0007] Furthermore, 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 for output through the Y-type optical combiner.

[0008] Furthermore, the device includes the following signal flow relationship: the initial reference interference signal is connected to the RF port of the PM, the receiving 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; the wavelength-adjustable laser signal is equally divided into two orthogonally polarized optical signals after passing through the PBS, and a clockwise optical CK output from port 1 enters the PM in the forward direction and is modulated by the initial reference interference signal; a counterclockwise optical CCK output from port 2 enters the DDMZM in the forward direction and is modulated by the interfered receiving signal and the local oscillator signal; when the clockwise signal in the loop is transmitted through the PM, DDMZM and OTDL in sequence for one cycle, and the counterclockwise signal in the loop is transmitted through the DDMZM, OTDL and PM in sequence for one cycle, the modulated CK optical signal and the CCK optical signal enter the reverse PBS to be synthesized into a polarization multiplexing optical signal.

[0009] Furthermore, the two orthogonally polarized optical signals are specifically a TE mode optical signal and a TM mode optical signal.

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

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

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

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

[0014]

[0015] Among them, V S 、V I 、V R and V L Respectively represent the signal amplitudes of the received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal, ω S ,ω I and ω L They 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, and t0 represents the delay experienced by the self-interference signal from the transmitter to the receiver;

[0016] Based on the device structure described in claim 1, after the modulated signal output by the PM passes through OTDL, the optical carrier and the modulation sideband introduce delay at the same time; in the modulated signal output by the DDMZM, only the optical carrier introduces delay; in the entire signal modulation process, only the reference interference signal is delayed; at this time, the polarization multiplexed optical signal output by port 3 of the OC is expressed as:

[0017]

[0018] Among them, μ1 and μ2 are the losses of PM and DDMZM respectively; is the frequency-adjustable signal generated by the laser, E c is the amplitude of the laser output signal, ω TL =ω c +nω r is the laser angular frequency, ω c is the initial angular frequency, ω r is the frequency step interval, n is an integer; m R 、m S 、m I 、m L 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; τ represents the delay introduced by OTDL; represents the DC bias angle of DDMZM; J n (·) represents the nth-order Bessel function of the first kind; and Represent the unit vectors of the TE mode and TM mode of the light field respectively;

[0019] S2, the signal is input to PC and polarizer, and the output signal of PC is aligned with the main axis of polarizer, then the output signal of polarizer is expressed as:

[0020]

[0021] Wherein, 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 J0(m)≈1, when the following formula (4) conditions are simultaneously satisfied, the self-interference signal can be completely eliminated in the optical domain; at this time, the amplitude matching and phase inversion operations are both realized by polarization control;

[0022]

[0023] 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:

[0024]

[0025] Among them, α SMF and L are the attenuation coefficient and length of the optical fiber respectively; β0, β1 and β2 represent the medium at the center frequency ω c The propagation constant, the inverse of the group velocity and the group velocity dispersion under the condition; only β2 is considered in the subsequent derivation process, and the output of the single-mode fiber is expressed as:

[0026]

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

[0028] S4, after photodetection, the photocurrent recovered by PD is expressed as:

[0029]

[0030] Where η represents the responsivity of the photodetector. By using formula (7), we can obtain that the down-conversion of the desired signal can be achieved under the premise of eliminating the self-interference signal in the optical domain, and the interval nω can be adjusted by adjusting the group dispersion coefficient β2, the fiber length L and the laser frequency. r The delay control of the desired down-converted signal is achieved, thereby adjusting the phase; and φ compensation is performed by adjusting the DC bias angle of DDMZM to solve the problem of power fading caused by the dispersion introduced by the dispersive medium under double-sideband modulation.

[0031] Further, in step S1, for the IBFD system, ω S =ω I .

[0032] Further, in step S1, the first kind n-order Bessel function J n (·) Under small signal input, other high-order components are neglected.

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

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

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

[0036] The present invention constructs a new microwave photon self-interference elimination and signal delay down-conversion device. Based on the ring modulation structure, the differential delay introduction of the reference self-interference signal and the received self-interference signal is carried out, and the amplitude matching and inversion operation are realized by polarization control, and finally the self-interference signal is eliminated in the optical domain. In addition, by loading the local oscillator signal, adding the dispersion medium and adjusting the parameters such as the laser wavelength and the group dispersion coefficient, the down-conversion and delay functions of the desired signal can be realized at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 This is a diagram of a microwave photon self-interference elimination and signal delay down-conversion device of the present invention;

[0039] Figure 2 is the output signal spectrum under single-frequency interference; wherein (a) is the output signal spectrum when self-interference elimination is not performed, and (b) is the output signal spectrum when self-interference elimination is performed;

[0040] Figure 3 The output signal spectrum when the dispersion medium is introduced and self-interference is eliminated in the case of single-frequency interference;

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

[0042] Figure 5 Spectra of output signals under broadband interference, where (a) is the spectrum of output signals without self-interference elimination, and (b) is the spectrum of output signals with self-interference elimination. DETAILED DESCRIPTION

[0043] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or expanded or replaced in any manner.

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

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

[0046] 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 reverse, it 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 dispersive medium, and the output port of the dispersive medium is connected to the optical input port of the PD.

[0047] Among them, 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 for output through the Y-type optical combiner.

[0048] In the microwave photon self-interference elimination and signal delay down-conversion device, the initial reference interference signal is connected to the RF port of PM, the receiving signal of the mixed self-interference signal is connected to the RF port 1 of DDMZM, and the local oscillator signal is connected to the RF port 2 of DDMZM. ​​After passing through the PBS, the wavelength-adjustable laser signal is equally divided into two orthogonally polarized optical signals (TE mode and TM mode). The clockwise (CK) light (TE mode) output from port 1 enters the PM in the forward direction and is modulated by the initial reference interference signal; the counterclockwise (CCK) light (TM mode) output from port 2 enters the DDMZM in the forward direction and is modulated by the interfered receiving signal and the local oscillator signal. Since the rate of the optical signal entering the PM and DDMZM from the output end does not match the rate of the RF signal, the interfered receiving signal and the local oscillator signal will not modulate the PM, and the initial reference interference signal will not modulate the DDMZM. When the clockwise signal in the loop is transmitted through PM, DDMZM and OTDL in sequence, and the counterclockwise signal in the loop is transmitted through DDMZM, OTDL and PM in sequence, the modulated CK optical signal and CCK optical signal enter the reverse PBS to be synthesized into a polarization multiplexed optical signal.

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

[0050] First, let the expressions of the expected received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal be:

[0051]

[0052] Among them, V S 、V I 、V R and V L represents the amplitude of the above signal, ω S ,ω I and ω L They 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. For the IBFD system, ω S =ω I t0 represents the delay experienced by the self-interference signal from the transmitter to the receiver.

[0053] according to Figure 1 In the structure shown, after the modulated signal output by PM passes through OTDL, both the optical carrier and the modulation sideband are delayed; while in the modulated signal output by DDMZM, only the optical carrier is delayed. Therefore, in the entire signal modulation process, only the reference interference signal is delayed.

[0054] At this time, the polarization multiplexed optical signal output by port 3 of the OC can be expressed as:

[0055]

[0056] Among them, μ1 and μ2 are the losses of PM and DDMZM respectively; is the frequency-adjustable signal generated by the laser, E c is the amplitude of the laser output signal, ω TL =ω c +nω r is the laser angular frequency, ω c is the initial angular frequency, ω r is the frequency step interval, n is an integer; m R 、m S 、m I 、m L 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; τ represents the delay introduced by OTDL; represents the DC bias angle of DDMZM; J n (·) represents the first-kind n-order Bessel function. Under small signal input, other high-order components are ignored; and represent the unit vectors of the TE mode and TM mode of the light field respectively.

[0057] Next, the above signal is input into the PC and the polarizer, and the output signal of the PC is aligned with the main axis of the polarizer. Then the output signal of the polarizer can be written as:

[0058]

[0059] Where α is the polarization control angle of the PC; δ is the phase difference between the two polarization multiplexed lights. According to formula (3), under the small signal approximation J0(m)≈1, when the following conditions are met 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.

[0060]

[0061] Then, the optical signal after eliminating the self-interference signal is input into the dispersive medium. In practice, there are many devices that can act as dispersive media, such as gratings, chirped mirrors, high-dispersion optical fibers, single-mode optical fibers, etc. Here, single-mode optical fibers are used as an example for functional demonstration.

[0062] When only loss and dispersion are considered, the transmission function of the optical fiber can be expressed as:

[0063]

[0064] Among them, α SMF and L are the attenuation coefficient and length of the optical fiber respectively. β0, β1 and β2 represent the medium at the center frequency ω c The propagation constant, the inverse of the group velocity, and the group velocity dispersion under β0 and β1 are given in Figure 1. Since β0 and β1 only introduce fixed phase shifts, only β2 is considered in the subsequent derivation process. The output of a single-mode fiber can be expressed as:

[0065]

[0066] in, It represents the phase shift introduced by group velocity dispersion to the desired signal and the local oscillator sideband.

[0067] Finally, after photodetection, the photocurrent recovered by PD can be expressed as:

[0068]

[0069] Where η represents the responsivity of the photodetector. By observing formula (7), it can be found that under the premise of eliminating the self-interference signal in the optical domain, the present invention also realizes the down-conversion of the desired signal, and adjusts the group dispersion coefficient β2, the fiber length L and the laser frequency to adjust the interval nω. r In addition, under double-sideband modulation, the dispersion introduced by the dispersive medium will cause power fading problems, especially in the case of high and medium frequencies, where this fading is very serious. At this time, the DC bias angle of DDMZM can be adjusted to achieve the desired delay control of the down-converted signal and thus adjust the phase. compensate.

[0070] In other embodiments, a microwave photon self-interference elimination and signal delay down-conversion device is provided, which specifically includes: an adjustable 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 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; the 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 the input port 2 of the PBS; the output of the PBS is connected to the input port of the PC after passing through the output port 3 of the OC, 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 PD output electrical signal is connected to the spectrum analyzer.

[0071] In other implementations, the above device is verified for technical effects according to the following steps:

[0072] Step 1: The tunable laser generates an optical carrier with an operating frequency of 193.1THz and an optical power of 16dBm; the RF signal source 1 generates an initial reference self-interference signal and a receiving self-interference signal with a frequency of 12GHz and powers of 10dBm and -10dBm respectively; the RF signal source 2 generates a desired receiving signal with a frequency of 12.5GHz and a power of -10dBm; the local oscillator signal source generates a local oscillator signal with a frequency of 10GHz and a power of 10dBm; the half-wave voltages of PM and DDMZM are both 3.5V, the extinction ratio of DDMZM is 35dB; the responsivity of PD is 0.75A / W.

[0073] Step 2: Remove PM and keep only the tunable laser, DDMZM and PD as the control group. Without adding the expected signal and the initial reference interference signal, input the received self-interference signal and the local oscillator signal into the upper and lower arms of the DDMZM respectively, set the initial DC bias angle of the DDMZM to π, and observe the spectrum when the self-interference elimination is not performed. 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, and the power is -70.6dBm. Figure 2 (a) Compared with the single-frequency self-interference cancellation depth, it is 66.8dB.

[0074] Step 3: According to Figure 1 The complete system architecture shown in the figure is experimentally tested, using a single-mode optical fiber with a length of 1 km as the dispersion medium, a loss coefficient of 0.2 dB / km, and a dispersion coefficient of 16 ps / km.nm. In order to more intuitively observe the effect of self-interference elimination, the self-interference signal and the useful signal are set to have a frequency difference of 0.5 GHz (in fact, the two are equal). It can be found that the present invention successfully achieves signal down-conversion. Figure 3 In the case of single-frequency interference, the output signal spectrum when the dispersive medium is introduced and self-interference elimination 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 elimination depth is 57.9dB.

[0075] Step 4: When the frequency variation interval of the adjustable laser is set to 50 GHz and the values ​​of n are 1, 5, 10, 15 and 20 respectively, use an oscilloscope to observe the time domain waveform of the desired intermediate frequency signal at 2.5 GHz, as shown in the figure below: Figure 4 It can be found that, under fixed dispersion coefficient and fiber length, the delay control of the desired down-converted signal can be achieved by changing the output frequency of the laser.

[0076] Step 5: Use the same control group settings as step 3, and let the RF signal source 1 generate 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. The desired signal and the local oscillator signal remain unchanged. Figure 5 (a) is the output signal spectrum without self-interference elimination in the case of broadband interference, and the self-interference signal power is -11.5dBm; then, the same experimental group settings as step 3 are used. Figure 5 (b) is the output signal spectrum when self-interference is eliminated in the case of broadband interference, and the self-interference signal power is -53.2dBm. Figure 5 (a) Compared with the previous example, the broadband self-interference cancellation depth is 41.7dB.

[0077] In summary, the scheme of the present invention constructs a microwave photon self-interference elimination and signal delay down-conversion device, performs amplitude matching and phase inversion operations between the reference interference signal and the received signal through polarization control technology, and realizes the self-interference elimination function based on down-conversion based on the optical domain elimination method. In addition, it is also possible to delay the desired received signal by adjusting the laser output frequency or wavelength, and adjust the bias control angle of the modulator to compensate for the power attenuation introduced by the dispersive medium. The scheme has a simple structure and flexible operation, and has potential application value in electronic systems such as phased array radars and beamforming networks.

[0078] In conclusion, the above-mentioned embodiments are only examples of the present invention, and are not intended to limit the protection scope of the present invention. It should be pointed out that, for those skilled in the art, several equivalent deformations and substitutions can be made based on the content disclosed in the present invention, and the modulator type, laser type, desired signal frequency, self-interference signal frequency, local oscillator signal frequency, optical carrier wavelength, optical carrier power, desired signal power, reference interference signal power, modulator DC bias angle, polarization control angle, adjustable phase difference, dispersion medium type, etc. can all be changed. These equivalent deformations and substitutions and the adjustment of the frequency range should also be regarded as the protection scope of the present invention.

Claims

1. A microwave photon self-interference elimination and signal delay down-conversion device, characterized in that: include: Tunable laser, a phase modulator PM, a dual-drive Mach-Zehnder modulator DDMZM, an optically adjustable 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 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; the 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 reverse, it is connected to the output port of the OTDL, and the input port of the OTDL is connected to the 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.

2. The microwave photon self-interference elimination and signal delay down-conversion device 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 device according to claim 1 is 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; The wavelength-tunable laser signal is equally divided into two orthogonally polarized optical signals after passing through the PBS. The clockwise optical CK output from port 1 enters the PM forward and is modulated by the initial reference interference signal; the counterclockwise optical CCK output from port 2 enters the DDMZM forward and is modulated by the interfered receiving signal and the local oscillator signal; when the clockwise signal in the loop is transmitted through the PM, DDMZM and OTDL in sequence, and the counterclockwise signal in the loop is transmitted through the DDMZM, OTDL and PM in sequence, the modulated CK optical signal and CCK optical signal enter the reverse PBS to be synthesized into a polarization multiplexed optical signal.

4. The microwave photon self-interference elimination and signal delay down-conversion device according to claim 1, characterized in that: The two orthogonally polarized optical signals are specifically a TE mode optical signal and a TM mode optical signal.

5. The microwave photon self-interference elimination and signal delay down-conversion device according to claim 1, characterized in that: The clockwise light CK output from port 1 is TE mode light.

6. The microwave photon self-interference elimination and signal delay down-conversion device according to claim 1, characterized in that: The counterclockwise light CCK output from port 2 is TM mode light.

7. A method for eliminating microwave photon self-interference and signal delay down-conversion, characterized in that: The device according to claim 1 comprises the following steps: S1, assuming that the expressions of the expected received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal are: Among them, V S 、V I 、V R and V L Respectively represent the signal amplitudes of the received signal, the received self-interference signal, the initial reference self-interference signal and the local oscillator signal, ω S ,ω I and ω L They 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, and t0 represents the delay experienced by the self-interference signal from the transmitter to the receiver; Based on the device structure described in claim 1, after the modulated signal output by the PM passes through OTDL, the optical carrier and the modulation sideband introduce delay at the same time; in the modulated signal output by the DDMZM, only the optical carrier introduces delay; in the entire signal modulation process, only the reference interference signal is delayed; at this time, the polarization multiplexed optical signal output by port 3 of the OC is expressed as: Among them, μ1 and μ2 are the losses of PM and DDMZM respectively; is the frequency-adjustable signal generated by the laser, E c is the amplitude of the laser output signal, ω TL =ω c +nω r is the laser angular frequency, ω c is the initial angular frequency, ω r is the frequency step interval, n is an integer; m R 、m S 、m I 、m L 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; τ represents the delay introduced by OTDL; represents the DC bias angle of DDMZM; J n (·) represents the nth-order Bessel function of the first kind; and Represent the unit vectors of the TE mode and TM mode of the light field respectively; S2, the signal is input to PC and polarizer, and the output signal of PC is aligned with the main axis of polarizer, then the output signal of polarizer is expressed as: Wherein, 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 J0(m)≈1, when the following formula (4) conditions are simultaneously satisfied, the self-interference signal can be completely eliminated in the optical domain; at this time, the amplitude matching and phase inversion operations are both realized by polarization control; 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: Among them, α SMF and L are the attenuation coefficient and length of the optical fiber respectively; β0, β1 and β2 represent the medium at the center frequency ω c The propagation constant, the inverse of the group velocity and the group velocity dispersion under the condition; only β2 is considered in the subsequent derivation process, and the output of the single-mode fiber is expressed as: 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: Where η represents the responsivity of the photodetector. By using formula (7), we can obtain that the down-conversion of the desired signal can be achieved under the premise of eliminating the self-interference signal in the optical domain, and the interval nω can be adjusted by adjusting the group dispersion coefficient β2, the fiber length L and the laser frequency. r To achieve the desired down-conversion signal delay control, thereby adjusting the phase; and, by adjusting the DC bias angle of DDMZM Compensation is used to solve the problem of power attenuation caused by dispersion introduced by dispersive media under double-sideband modulation.

8. The microwave photon self-interference elimination and signal delay down-conversion device according to claim 7, characterized in that:In step S1, for the IBFD system, ω S =ω I .

9. The microwave photon self-interference elimination and signal delay down-conversion device according to claim 7, characterized in that: In step S1, the first kind n-order Bessel function J n (·) Under small signal input, other high-order components are neglected.

10. The microwave photon self-interference elimination and signal delay down-conversion device according to claim 7, 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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