An optical in-band self-interference cancellation and radio frequency signal delay control device and method

Abstract

Provided is an optical in-band self-interference cancellation and radio frequency signal delay regulation method, including the following steps: An optical carrier is injected into a PDM-DPMZM (2), modulated by a received signal and a reference signal to generate an optical carrier radio frequency signal; after the optical carrier radio frequency signal is output from the PDM-DPMZM (2), it enters a polarization controller (3) for polarization adjustment, and then is injected into an analyzer (4) to achieve optical domain self-interference cancellation; the signal after self-interference cancellation output by the analyzer (4) undergoes long-distance transmission, power amplification, and optoelectronic conversion through a single-mode optical fiber (5), an optical power amplifier (6), and a photodetector (7) to obtain a signal with adjustable linear delay. Also provided is an optical in-band self-interference cancellation and radio frequency signal delay regulation device based on this method. The present invention utilizes optical polarization regulation to achieve phase reversal and amplitude matching of self-interference and reference signals, enabling self-interference cancellation in the optical domain and avoiding the influence of subsequent optical fiber transmission on the self-interference cancellation performance; this device can also simultaneously compensate for dispersion-induced power fading in an in-band full-duplex optical carrier wireless system.

Description

Technical Field

[0001] The present invention relates to the field of microwave photon signal processing, and particularly to an in-band self-interference cancellation and radio frequency (RF) signal delay control device and method based on optical polarization modulation, which is used in an in-band full-duplex radio-over-fiber (RoF) transmission system and can achieve self-interference signal cancellation and delay processing of useful RF signals. Background Art

[0002] To solve the contradiction between limited spectrum resources and the increasing demand for higher data rates, full-duplex systems operating in the same frequency band simultaneously are adopted in multiple fields such as wireless communication, radar, Internet of Things (IoT), measurement and control, etc., so as to improve spectrum utilization by receiving and transmitting signals in the same frequency band simultaneously. However, this system faces a serious problem that the transmitted signal leaks to its own receiver and cannot be directly filtered, thus affecting the quality of the received signal, namely the self-interference problem. Self-interference cancellation schemes based on electrical principles are limited in self-interference cancellation performance and application due to the limited bandwidth of electrical devices, unsatisfactory response, large volume, and limited parameter tuning accuracy and tuning range. Therefore, domestic researchers have proposed a series of self-interference cancellation schemes based on photonics, which have significantly improved the frequency band range, working bandwidth, cancellation depth, and cost-effectiveness of self-interference cancellation schemes by leveraging the advantages of photonics.

[0003] Analog-domain self-interference cancellation, as a key link in self-interference cancellation, can effectively cancel high-power self-interference signals, thus avoiding receiver saturation. Currently, most photonics-based analog-domain self-interference cancellation schemes focus on how to achieve good cancellation of self-interference signals, that is, how to improve performance indicators such as cancellation depth, instantaneous bandwidth, and frequency coverage range, and rarely consider combining self-interference cancellation with delay processing of useful RF signals, which limits the compatibility between the self-interference cancellation system and the beamforming network. Therefore, a scheme that can achieve delay processing of useful RF signals after self-interference cancellation has the potential to be compatible with the beamforming network, and can provide a solution for deep cancellation of self-interference signals and efficient recovery of useful signals in multi-channel systems. Brief Description of the Drawings

[0004] Figure 1 It is a schematic structural diagram of the in-band self-interference cancellation and RF signal delay control device based on optical polarization modulation of the present invention. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides an optical in-band self-interference cancellation and RF signal delay control device, which includes a wavelength tunable laser 1, a polarization multiplexing - dual parallel - Mach - Zehnder modulator (PDM - DPMZM) 2, a polarization controller 3, a polarization analyzer 4, a single-mode fiber 5, an optical power amplifier 6, a photodetector 7, a first 90° electrical coupler 8, a second 90° electrical coupler 9, and an electrical delay line 10; wherein

[0006] A wavelength tunable laser 1, whose output laser with tunable wavelength serves as an optical carrier, and its output end is connected to the optical input end of a polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2;

[0007] The polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2, which receives the optical carrier output by the wavelength tunable laser 1 and outputs an optical carrier radio frequency signal after electro - optical modulation;

[0008] A polarization controller 3, which receives the optical carrier radio frequency signal output by the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2, performs polarization adjustment on the optical carrier radio frequency signal, and outputs the polarized - adjusted optical carrier radio frequency signal;

[0009] A polarization analyzer 4, which receives the optical carrier radio frequency signal output by the polarization controller 3, combines the signals in two orthogonally polarized directions of the two optical carrier radio frequency signals into the same direction, and outputs the polarized - analyzed optical carrier radio frequency signal;

[0010] A single - mode optical fiber 5, which receives the polarized - analyzed optical carrier radio frequency signal output by the polarization analyzer 4 and performs long - distance transmission on it;

[0011] An optical power amplifier 6, which receives the optical carrier radio frequency signal transmitted by the single - mode optical fiber 5, amplifies the optical power of the optical carrier radio frequency signal, and outputs the optically - power - amplified optical carrier radio frequency signal;

[0012] A photodetector 7, which receives the optically - power - amplified optical carrier radio frequency signal output by the optical power amplifier 6, performs optoelectronic conversion on the optical carrier radio frequency signal, and outputs an electrical signal;

[0013] A first 90° electrical coupler 8, which receives a mixed received signal containing a self - interference signal and a useful signal received from the outside, performs beam splitting on the received signal, outputs two signals with equal power and orthogonal phases, and outputs the two beam - split signals to the two radio frequency input ports on the upper path of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM;

[0014] A second 90° electrical coupler 9, which receives the delay - adjusted reference signal output by the electrical delay line 10, performs beam splitting on the received signal, outputs two signals with equal power and orthogonal phases, and outputs the two beam - split signals to the two radio frequency input ports on the lower path of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM;

[0015] The electrical delay line 10 receives the reference signal required by the device of the present invention, performs delay adjustment on it and outputs it to the second 90° electrical coupler 9.

[0016] The present invention also provides an optical in-band self-interference cancellation and radio frequency signal delay regulation method, which is based on the above-mentioned optical in-band self-interference cancellation and radio frequency signal delay regulation device, and specifically includes the following steps:

[0017] Step 1: Inject an optical carrier into PDM-DPMZM 2, which is modulated by the received signal and the reference signal to generate an optical carrier radio frequency signal;

[0018] Inject the optical carrier generated by the wavelength tunable laser 1 into PDM-DPMZM 2, and the optical carrier is expressed as E c (t) = E c expj(ω c +nω r )t, where E c , ω c and ω r respectively represent the amplitude, zero-dispersion reference center frequency, and optical carrier frequency tuning step of this optical carrier, n is an integer, and j represents the imaginary unit; the mixed received signal V RF (t) containing the self-interference signal and the useful signal received from the outside is expressed as V RF (t) = V SOI expjω SOI (t + τ SOI ) + V SI expjω SI (t + τ SI ), where V SOI , ω SOI , τ SOI are the amplitude, angular frequency, and initial delay of the useful signal in the mixed received signal, and V SI , ω SI , τ SI are the amplitude, angular frequency, and initial delay of the self-interference signal in the mixed received signal;

[0019] The mixed received signal first passes through the first 90° electrical coupler 8 and is divided into two paths with equal power and orthogonal phases, serving as the radio frequency drive signals on the upper path of PDM-DPMZM 2; the reference signal V REF (t) is expressed as V REF (t) = V REF expjω REF (t + τ REF ), where V REF , ω REF , τ REFare the amplitude, angular frequency, and initial time delay of the reference signal, respectively. The reference signal first passes through the electrical delay line 10 to adjust its delay, obtaining a reference signal with adjustable delay and transmitting it to the second 90° electrical coupler 9, where it is divided into two paths with equal power and orthogonal phases as the radio frequency drive signals for the lower path of the PDM-DPMZM 2;

[0020] Adjust the DC bias voltage input to the upper path of the PDM-DPMZM 2 so that the sub-modulator in the upper path of the PDM-DPMZM 2 operates at the minimum bias point and the main modulator operates at the quadrature bias point, thereby generating a carrier-suppressed single-sideband modulation signal of the useful signal and the self-interference signal; adjust the DC bias voltage input to the lower path of the PDM-DPMZM 2 so that both the sub-modulator and the main modulator in the lower path of the PDM-DPMZM 2 operate at the quadrature bias point, thereby generating a single-sideband modulation signal of the reference signal; therefore, the output signal of the PDM-DPMZM 2 is expressed as

[0021]

[0022] where β SOI = πV SOI / V π , β SI = πV SI / V π , β REF = πV REF / V π are the modulation coefficients of the useful signal, the self-interference signal, and the reference signal, respectively, V π is the half-wave voltage of the PDM-DPMZM 2, J0(β REF ) is the zero-order Bessel function of the first kind of the reference signal, J1(β SOI ) and J1(β SI ) are the first-order Bessel functions of the first kind of the useful signal and the self-interference signal, τ is the adjustable delay introduced by the electrical delay line 10 on the reference signal, and are unit vectors in two orthogonal directions;

[0023] Step 2: After the optically loaded radio frequency signal is output from the PDM-DPMZM 2, it enters the polarization controller 3 for polarization adjustment, and then is injected into the polarization analyzer 4 to achieve optical domain self-interference cancellation;

[0024] The two polarization-orthogonal optically loaded radio frequency modulation signals output from the PDM-DPMZM 2 enter the polarization controller 3, and the polarization controller 3 adjusts their polarization states. The optically loaded radio frequency signal after polarization adjustment output by the polarization controller 3 enters the polarization analyzer 4, and the polarization analyzer 4 combines the signals in the two polarization directions at 45° and outputs them. The signal output by the polarization analyzer 4 is expressed as:

[0025]

[0026] Wherein, α is the angle between the polarization direction of the polarization controller 3 and the main axis of the PDM-DPMZM; it can be seen from Equation (2) that adjusting the polarization direction of the electrical delay line 10 and the polarization controller 3 can simultaneously satisfy the conditions that the modulation sidebands of the self-interference signal and the reference signal satisfy equal amplitude, delay matching, and opposite phase, that is, satisfy:

[0027]

[0028] In the formula, m is an arbitrary integer; therefore, self-interference cancellation is achieved in the optical domain. At this time, the output signal of the polarization analyzer 4 is:

[0029]

[0030] Step 3: The self-interference-cancelled signal output by the polarization analyzer 4 is transmitted over a long distance, amplified in power, and photoelectrically converted through a single-mode optical fiber 5, an optical power amplifier 6, and a photodetector 7 to obtain a signal with an adjustable linear delay;

[0031] The self-interference-cancelled signal output by the polarization analyzer 4 is first input into the single-mode optical fiber 5 to introduce a dispersion phase. Then, the optical carrier microwave signal with the dispersion phase output by the single-mode optical fiber 5 is injected into the optical power amplifier 6 for power amplification. Subsequently, the optical carrier microwave signal output from the optical power amplifier 6 is injected into the photodetector 7 for photoelectric conversion. The electrical signal output by the photodetector 7 is expressed as:

[0032] i = A cos[ω SOI (t + τ SOI + β1L + β2Lnω r ) + β ２ Lω SOI 2 / 2] (5)

[0033] Wherein, i represents the electrical signal output by the photodetector 7; A represents the amplitude coefficient of the radio frequency signal output by the photodetector 7, α, L, β1, and β2 are respectively the attenuation coefficient, length, first-order dispersion coefficient, and second-order dispersion coefficient of the single-mode optical fiber 5, R is the responsivity of the photodetector 7, and G is the gain of the optical power amplifier 6;

[0034] It can be seen from Equation (5) that a useful signal with a linearly adjustable delay is obtained after photoelectric detection, and its adjustable delay amount is β1L + β2Lnω r , and by changing the length or dispersion coefficient of the single-mode optical fiber 5 and changing the optical carrier frequency output by the wavelength tunable laser 1, its delay can be changed.

[0035] The device of the present invention is based on a coherent optical system and a single optical path, with a compact system structure and high cost-effectiveness. It uses optical polarization modulation to achieve phase inversion and amplitude matching of the self-interference and reference signals, enabling self-interference cancellation in the optical domain and avoiding the impact of subsequent fiber optic transmission on the self-interference cancellation performance. The device can also simultaneously compensate for dispersion-induced power fading in an in-band full-duplex radio-over-fiber system, regulate the delay of the useful signal by changing the frequency of the tunable laser, and combine with beamforming functions to improve the signal transmission quality of the system, achieve effective signal recovery, and provide a solution for the efficient recovery of useful signals in subsequent multi-channel systems. Specific implementation method

[0036] The following further describes the present invention with reference to the accompanying drawings:

[0037] Figure 1 FIG. is a schematic structural diagram of the optical in-band self-interference cancellation and radio frequency signal delay regulation device of the present invention, including a wavelength tunable laser 1, a polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2, a polarization controller 3, a polarization analyzer 4, a single-mode fiber 5, an optical power amplifier 6, a photodetector 7, a first 90° electrical coupler 8, a second 90° electrical coupler 9, and an electrical delay line 10.

[0038] The wavelength tunable laser 1 outputs a laser with a tunable wavelength as an optical carrier, and its output end is connected to the optical input end of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2;

[0039] The polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2 receives the optical carrier output by the wavelength tunable laser 1 and outputs an optical radio frequency signal after electro-optic modulation;

[0040] The polarization controller 3 receives the optical radio frequency signal output by the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2, adjusts the polarization of the optical radio frequency signal, and outputs the polarization-adjusted optical radio frequency signal;

[0041] The polarization analyzer 4 receives the optical radio frequency signal output by the polarization controller 3, combines the signals in two polarization orthogonal directions of the two optical radio frequency signals into the same direction, and outputs the polarization-analyzed optical radio frequency signal;

[0042] The single-mode fiber 5 receives the polarization-analyzed optical radio frequency signal output by the polarization analyzer 4 and performs long-distance transmission on it;

[0043] The optical power amplifier 6 receives the optical radio frequency signal transmitted by the single-mode fiber 5, amplifies the optical power of the optical radio frequency signal, and outputs the optical radio frequency signal with amplified power;

[0044] An optoelectronic detector 7, which receives the optically amplified radio frequency signal output by the optical power amplifier 6, performs optoelectronic conversion on the optically amplified radio frequency signal, and outputs an electrical signal;

[0045] A first 90° electrical coupler 8, which receives the mixed received signal containing the self-interference signal and the useful signal received by the device of the present invention from the outside, performs beam splitting on the received signal, outputs two signals with equal power and orthogonal phases, and outputs the two split signals to the two radio frequency input ports on the upper path of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2;

[0046] A second 90° electrical coupler 9, which receives the delay - adjusted reference signal output by the electrical delay line 10, performs beam splitting on the received signal, outputs two signals with equal power and orthogonal phases, and outputs the two split signals to the two radio frequency input ports on the lower path of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM 2;

[0047] The electrical delay line 10 receives the reference signal required in the device of the present invention, adjusts its delay and outputs it to the second 90° electrical coupler 9. The reference signal is provided by a signal source (not shown in the figure).

[0048] Using Figure 1 The structure shown, the method for achieving in - band optical self - interference cancellation and radio frequency signal delay control based on polarization control is as follows:

[0049] Step 1: The optical carrier is injected into the PDM - DPMZM 2 and modulated by the received signal and the reference signal to generate an optically amplified radio frequency signal;

[0050] Inject the optical carrier generated by the wavelength - tunable laser 1 into the PDM - DPMZM 2. The optical carrier is expressed as E c (t)=E c expj(ω c +nω r )t, where E c , ω c and ω r respectively represent the amplitude, zero - dispersion reference center frequency, and optical carrier frequency tuning step of this optical carrier. n is an integer, and j represents the imaginary unit. The mixed received signal V RF (t) received by the device of the present invention from the outside can be expressed as V RF (t)=V SOI expjω SOI (t + τ SOI )+V SI expjω SI (t + τ SI), where V SOI , ω SOI , τ SOI are the amplitude, angular frequency, and initial time delay of the useful signal in the mixed received signal, and V SI , ω SI , τ SI are the amplitude, angular frequency, and initial time delay of the self-interference signal in the mixed received signal.

[0051] The mixed received signal first passes through the first 90° electrical coupler 8 and is divided into two paths with equal power and orthogonal phases, serving as the radio frequency drive signals for the upper path of the PDM-DPMZM 2. The reference signal V REF (t) can be expressed as V REF (t) = V REF exp(jω REF (t + τ REF ), where V REF , ω REF , τ REF are respectively the amplitude, angular frequency, and initial time delay of this reference signal. The reference signal first passes through the electrical delay line 10 to adjust its delay, obtaining a delay-adjustable reference signal and transmitting it to the second 90° electrical coupler 9, where it is divided into two paths with equal power and orthogonal phases as the radio frequency drive signals for the lower path of the PDM-DPMZM 2.

[0052] Adjust the DC bias voltage input to the upper path of the PDM-DPMZM 2 so that the sub-modulator in the upper path of the PDM-DPMZM 2 operates at the minimum bias point and the main modulator operates at the quadrature bias point, thereby generating a carrier-suppressed single-sideband modulation signal of the useful signal and the self-interference signal; adjust the DC bias voltage input to the lower path of the PDM-DPMZM 2 so that both the sub-modulator and the main modulator in the lower path of the PDM-DPMZM 2 operate at the quadrature bias point, thereby generating a single-sideband modulation signal of the reference signal. Therefore, the output signal of the PDM-DPMZM 2 can be expressed as

[0053]

[0054] where β SOI = πV SOI / V π , β SI = πV SI / V π , β REF = πV REF / V π are respectively the modulation coefficients of the useful signal, the self-interference signal, and the reference signal, V π is the half-wave voltage of the PDM-DPMZM 2, J0(β REF) is the zero-order Bessel function of the first kind of the reference signal, J1(β SOI ) and J1(β SI ) are the first-order Bessel functions of the first kind of the useful signal and the self-interference signal. τ is the adjustable delay introduced by the electrical delay line 10 on the reference signal. and are unit vectors in two orthogonal directions.

[0055] Step 2: After the optical carrier radio frequency signal is output from the PDM-DPMZM 2, it enters the polarization controller 3 for polarization adjustment, and then is injected into the polarization analyzer 4 to achieve optical domain self-interference cancellation;

[0056] The two polarization-orthogonal optical carrier radio frequency modulation signals output from the PDM-DPMZM 2 enter the polarization controller 3, and the polarization controller 3 adjusts their polarization states. The polarization-adjusted optical carrier radio frequency signal output from the polarization controller 3 enters the polarization analyzer 4, and the signals in the two polarization directions are combined at 45° by the polarization analyzer 4 and then output. The signal output by the polarization analyzer 4 can be expressed as:

[0057]

[0058] where α is the angle between the polarization direction of the polarization controller 3 and the main axis of the PDM-DPMZM. It can be seen from Equation (2) that adjusting the electrical delay line 10 and the polarization direction of the polarization controller 3 can simultaneously satisfy the conditions that the modulation sidebands of the self-interference signal and the reference signal satisfy equal amplitude, delay matching, and opposite phase, that is, satisfy:

[0059]

[0060] In the formula, m is any integer. Therefore, self-interference cancellation is achieved in the optical domain. At this time, the output signal of the polarization analyzer 4 is:

[0061]

[0062] Step 3: The signal after self-interference cancellation output by the polarization analyzer 4 undergoes long-distance transmission, power amplification, and optoelectronic conversion through the single-mode fiber 5, the optical power amplifier 6, and the photodetector 7 to obtain a signal with adjustable linear delay;

[0063] The signal after self-interference cancellation output by the polarization analyzer 4 is first input into the single-mode fiber 5 to introduce the dispersion phase. Then, the optical carrier microwave signal with the dispersion phase output by the single-mode fiber 5 is injected into the optical power amplifier 6 for power amplification. Subsequently, the optical carrier microwave signal output from the optical power amplifier 6 is injected into the photodetector 7 for optoelectronic conversion. The electrical signal output by the photodetector 7 is expressed as:

[0064] i = A cos[ω SOI (t + τSOI +β1L + β2Llnω r ) + β2Lω SOI 2 / 2] (5)

[0065] Wherein, i represents the electrical signal output by the photodetector 7; A represents the amplitude coefficient of the radio frequency signal output by the photodetector 7, α, L, β1, and β2 are respectively the attenuation coefficient, length, first-order dispersion coefficient, and second-order dispersion coefficient of the single-mode optical fiber 5, R is the responsivity of the photodetector 7, and G is the gain of the optical power amplifier 6.

[0066] It can be seen from Equation (5) that a useful signal with linearly adjustable delay is obtained after photodetection, and its adjustable delay amount is β1L + β2Llnω r , and by changing the length or dispersion coefficient of the single-mode optical fiber 5 and changing the optical carrier frequency output by the wavelength tunable laser 1, its delay can be changed. In addition, single-sideband modulation eliminates the periodic fading phenomenon of the radio frequency signal power induced by fiber dispersion, which is beneficial to realizing long-distance signal transmission and ensuring signal quality.

[0067] The present invention proposes a device and method for in-band self-interference cancellation and radio frequency signal delay control based on optical polarization control. The device is based on a coherent optical system and a single optical path, has a compact system structure and high cost-effectiveness, uses optical polarization control to achieve phase inversion and amplitude matching of self-interference and reference signals, and can achieve self-interference cancellation in the optical domain, avoiding the influence of subsequent fiber transmission on the self-interference cancellation performance; the device can also simultaneously compensate for the dispersion-induced power fading in an in-band full-duplex radio-over-fiber system, can achieve delay control of useful signals by changing the frequency of the tunable laser, and can be combined with the beamforming function, thereby improving the signal transmission quality of the system, realizing effective signal recovery, and providing a solution for the efficient recovery of useful signals in subsequent multi-channel systems.

Claims

1. An optical in-band self-interference cancellation and RF signal delay control method, which is based on an optical in-band self-interference cancellation and RF signal delay control device. The device includes a wavelength tunable laser (1), a polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM (2), a polarization controller (3), a polarization analyzer (4), a single-mode optical fiber (5), an optical power amplifier (6), a photodetector (7), a first 90° electrical coupler (8), a second 90° electrical coupler (9), and an electrical delay line (10); where The wavelength tunable laser (1) outputs a laser with a tunable wavelength as an optical carrier, and its output end is connected to the optical input end of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM (2); The polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM (2) receives the optical carrier output by the wavelength tunable laser (1), and outputs an optical carrier RF signal after electro-optic modulation; The polarization controller (3) receives the optical carrier RF signal output by the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM (2), performs polarization adjustment on the optical carrier RF signal, and outputs the polarized adjusted optical carrier RF signal; The polarization analyzer (4) receives the optical carrier RF signal output by the polarization controller (3), combines the signals in two polarization orthogonal directions in the two optical carrier RF signals into the same direction, and outputs the polarization analyzed optical carrier RF signal; The single-mode optical fiber (5) receives the polarization analyzed optical carrier RF signal output by the polarization analyzer (4) and performs long-distance transmission on it; The optical power amplifier (6) receives the optical carrier RF signal transmitted by the single-mode optical fiber (5), amplifies the optical power of the optical carrier RF signal, and outputs the optical carrier RF signal with amplified power; The photodetector (7) receives the optical carrier RF signal with amplified power output by the optical power amplifier (6), performs optoelectronic conversion on the optical carrier RF signal, and outputs an electrical signal; The first 90° electrical coupler (8) receives the mixed received signal containing self-interference signal and useful signal received from the outside, performs beam splitting on the received signal, outputs two signals with equal power and orthogonal phases, and outputs the two split signals to the two RF input ports on the upper path of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM (2); The second 90° electrical coupler (9) receives the delay adjusted reference signal output by the electrical delay line (10), performs beam splitting on the received signal, outputs two signals with equal power and orthogonal phases, and outputs the two split signals to the two RF input ports on the lower path of the polarization multiplexing - dual parallel - Mach - Zehnder modulator PDM - DPMZM (2); The electrical delay line (10) receives the reference signal required in the device, performs delay adjustment on it and outputs it to the second 90° electrical coupler (9); The method specifically includes the following steps: Step 1: The optical carrier is injected into the PDM - DPMZM (2), modulated by the received signal and the reference signal, and an optical carrier RF signal is generated; Inject the optical carrier generated by the wavelength-tunable laser (1) into the PDM-DPMZM (2). The optical carrier is expressed as E c (t) = E c exp[j(ω c + nω r )t], where E c , ω c and ω r represent the amplitude, zero-dispersion reference center frequency, and optical carrier frequency tuning step of this optical carrier respectively, n is an integer, and j represents the imaginary unit; the mixed received signal V RF (t) containing the self-interference signal and the useful signal received from the outside is expressed as V RF (t) = V SOI exp[jω SOI (t + τ SOI ) + V SI exp[jω SI (t + τ SI ), where V SOI , ω SOI , τ SOI are the amplitude, angular frequency, and initial time delay of the useful signal in the mixed received signal, and V S1 , ω SI , τ SI are the amplitude, angular frequency, and initial time delay of the self-interference signal in the mixed received signal; The mixed received signal first passes through the first 90° electrical coupler (8) and is divided into two paths with equal power and quadrature phases, serving as the RF drive signals for the upper path of the PDM-DPMZM (2); the reference signal V REF (t) is expressed as V REF (t) = V REF expjω REF (t + τ REF ), where V REF , ω REF , τ REF are respectively the amplitude, angular frequency, and initial time delay of the reference signal; the reference signal first passes through the electrical delay line (10) to adjust its delay, obtaining a reference signal with adjustable delay and transmitting it to the second 90° electrical coupler (9), where it is divided into two paths with equal power and quadrature phases as the RF drive signals for the lower path of the PDM-DPMZM (2); Adjust the DC bias voltage on the upper path of the input PDM-DPMZM(2) so that the sub-modulator on the upper path in the PDM-DPMZM(2) operates at the minimum bias point and the main modulator operates at the quadrature bias point, thereby generating a carrier-suppressed single-sideband modulation signal of the useful signal and the self-interference signal; Adjust the DC bias voltage on the lower path of the input PDM-DPMZM(2) so that both the sub-modulator and the main modulator on the lower path in the PDM-DPMZM(2) operate at the quadrature bias point, thereby generating a single-sideband modulation signal of the reference signal; Therefore, the output signal of the PDM-DPMZM(2) is expressed as where β SOI = πV SOI / V π , β SI = πV SI / V π , β REF = πV REF / V π are the modulation coefficients of the useful signal, the self-interference signal, and the reference signal respectively, V π is the half-wave voltage of the PDM-DPMZM(2), J0(β REF ) is the zero-order Bessel function of the first kind of the reference signal, J1(β SOI ) and J1(β SI ) are the first-order Bessel functions of the first kind of the useful signal and the self-interference signal respectively, τ is the adjustable delay introduced by the electrical delay line (10) on the reference signal, and are unit vectors in two orthogonal directions; Step 2: The optical carrier radio frequency signal enters the polarization controller (3) for polarization adjustment after being output from the PDM-DPMZM(2), and then is injected into the polarization analyzer (4) to achieve optical domain self-interference cancellation; The two polarization-orthogonal optical carrier radio frequency modulation signals output from the PDM-DPMZM(2) enter the polarization controller (3), and the polarization controller (3) adjusts their polarization states. The polarization-adjusted optical carrier radio frequency signal output from the polarization controller (3) enters the polarization analyzer (4), and the signals in the two polarization directions are combined at 45° by the polarization analyzer (4) and then output. The signal output from the polarization analyzer (4) is expressed as: where α is the angle between the polarization direction of the polarization controller (3) and the main axis of the PDM-DPMZM; It can be seen from Equation (2) that adjusting the electrical delay line (10) and the polarization direction of the polarization controller (3) can simultaneously satisfy the conditions that the modulation sidebands of the self-interference signal and the reference signal satisfy equal amplitude, delay matching, and opposite phase, that is, satisfy: In the formula, m is an arbitrary integer; Therefore, self-interference cancellation is achieved in the optical domain. At this time, the output signal of the polarization analyzer (4) is: Step 3: The self-interference-cancelled signal output from the polarization analyzer (4) undergoes long-distance transmission, power amplification, and optoelectronic conversion through the single-mode fiber (5), the optical power amplifier (6), and the photodetector (7) to obtain a signal with adjustable linear delay; The self-interference-cancelled signal output from the polarization analyzer (4) is first input into the single-mode fiber (5) to introduce a dispersion phase. Then, the optical carrier microwave signal with the dispersion phase output from the single-mode fiber (5) is injected into the optical power amplifier (6) for power amplification. Subsequently, the optical carrier microwave signal output from the optical power amplifier (6) is injected into the photodetector (7) for optoelectronic conversion. The electrical signal output from the photodetector (7) is expressed as: i = A cos[ω SOI (t + τ SOI + β1L + β2Lnω r ) + β2Lω SOI 2 / 2] (5) where, i represents the electrical signal output by the photodetector (7); A represents the amplitude coefficient of the radio frequency signal output by the photodetector (7), and A = 4RGE c 2 e -αL J1(β SOI )J0(β SI )J0(β REF )(cosα 2 -sinα 2 ); α, L, β1, and β2 are respectively the attenuation coefficient, length, first-order dispersion coefficient, and second-order dispersion coefficient of the single-mode optical fiber (5), R is the responsivity of the photodetector (7), and G is the gain of the optical power amplifier (6); It can be seen from Equation (5) that a useful signal with linearly adjustable delay is obtained after optoelectronic detection, and the adjustable delay amount is β1L + β2Lnω r , and its delay can be changed by changing the length or dispersion coefficient of the single-mode optical fiber (5) and changing the optical carrier frequency output by the wavelength tunable laser (1).

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