Single longitudinal mode all-optical microwave oscillator based on torsion radial mode space time symmetry

Abstract

The invention belongs to the technical field of microwave photons and optical communication, particularly relates to a single-longitudinal-mode all-optical microwave oscillator based on torsion radial mode space time symmetry, and solves the problems that an existing microwave photon generating device is complex in structure, and an all-optical microwave oscillator lacks research on a torsion radial acoustic mode. And more energy is wasted when a single longitudinal mode is generated. The device comprises a self-excitation erbium-doped fiber amplifier, a tunable optical filter, an isolator, a circulator, a space-time symmetric Sagnac ring, a first light splitting coupler, a second light splitting coupler, a first polarization controller, a second polarization controller, a single-mode fiber, a polarizer, a spectrometer, a photoelectric detector and a spectrum analyzer. And the space-time symmetric Sagnac ring comprises a third light splitting coupler, a third polarization controller, a fourth polarization controller and a polarization beam splitter. Passive mode locking based on a torsion radial mode is realized by using a nonlinear polarization rotation technology; and single longitudinal mode output with a high side mode rejection ratio is realized by using a space-time symmetric structure.

Description

Technical Field

[0001] The present invention relates to the field of microwave photon and optical communication technology, and in particular to an all-optical microwave oscillator, in particular to a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry. Background Art

[0002] An all-optical microwave oscillator is an advanced system that combines optical and microwave technologies, designed to overcome the limitations of traditional microwave oscillators in terms of frequency stability, low noise, and high precision. Traditional microwave oscillators, such as quartz oscillators based on electronic components, often face performance bottlenecks under the requirements of high frequency and low phase noise. Optical technology provides extremely high frequency accuracy and stability, becoming an important way to solve this problem. All-optical microwave oscillators usually rely on lasers, fiber frequency combs, and nonlinear optical effects. By converting optical signals into microwave frequency band signals, they can generate low-noise, high-stability microwave signals.

[0003] The generation of microwave oscillation signals includes optoelectronic oscillators and all-optical microwave oscillators. Y. London et al. proposed an optoelectronic oscillator based on forward Brillouin scattering of the acoustic mode of a standard single-mode optical fiber. The experiment produced an optoelectronic oscillator based on R 0,7 Y.Liu et al. proposed a dual-cavity optomechanical microwave oscillator (OM-MO) based on the radial acoustic mode of a single-mode fiber (SMF), which realizes the microwave oscillation signal based on R 0,7 Single-frequency output of microwave photons in acoustic mode. Since optoelectronic oscillators require electro-optical modulators (EOMs) for feedback modulation and optoelectronic converters for optoelectronic conversion, this increases the complexity of microwave photon generation devices. All-optical microwave oscillators are relatively simple in structure and low in cost, avoiding the complex circuit design in traditional optoelectronic oscillators, making single-longitudinal-mode forward Brillouin scattering all-optical microwave oscillators more compact and easy to integrate, suitable for high-frequency and high-stability requirements in modern communication systems. However, all-optical microwave oscillators previously studied have all focused on radial acoustic modes, with almost no research on polarization-sensitive torsional radial acoustic modes. In addition, the generation of a single longitudinal mode is achieved only by matching different comb teeth through the cursor effect to achieve the effect of suppressing the side mode, wasting more energy on the side mode, which cannot be reasonably converted into the main mode, and there are deficiencies. Summary of the invention

[0004] In order to overcome the technical defects of the existing microwave photon generating devices with complex structures, the lack of research on torsional radial acoustic modes in all-optical microwave oscillators, and the waste of a lot of energy in the generation of single longitudinal modes, the present invention provides a single longitudinal mode all-optical microwave oscillator based on the parity-time symmetry of torsional radial modes.

[0005] The invention discloses a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry, comprising a self-excited erbium-doped fiber amplifier, a tunable optical filter, an isolator, a circulator, a parity-time symmetric Sagnac ring, a first splitter coupler, a second splitter coupler, a first polarization controller, a second polarization controller, a single-mode optical fiber, a polarizer, a spectrometer, a photodetector and a spectrum analyzer; the output end of the self-excited erbium-doped fiber amplifier is connected to the port a of the circulator through the tunable optical filter and the isolator in sequence, the port b of the circulator is connected to the parity-time symmetric Sagnac ring, the port c of the circulator is connected to the input end a of the first splitter coupler, the output end b of the first splitter coupler is connected to the input end of the self-excited erbium-doped fiber amplifier through the first polarization controller, the single-mode optical fiber, the second polarization controller and the polarizer in sequence, and the output end of the first splitter coupler is connected to the input end of the self-excited erbium-doped fiber amplifier through the first polarization controller, the single-mode optical fiber, the second polarization controller and the polarizer. c is connected to the input end a of the second optical splitter coupler, the output end b of the second optical splitter coupler is connected to the spectrometer, and the output end c of the second optical splitter coupler is connected to the spectrum analyzer through a photodetector; the parity-time symmetric Sagnac ring includes a third optical splitter coupler, a third polarization controller, a fourth polarization controller and a polarization beam splitter, the input end a of the third optical splitter coupler is connected to the port b of the circulator, the output end b of the third optical splitter coupler is connected to the port b of the polarization beam splitter through the third polarization controller, and the output end c of the third optical splitter coupler is connected to the port a of the polarization beam splitter through the fourth polarization controller; the splitting ratio of the output end b of the first optical splitter coupler and the output end c of the splitter is 90:10; the splitting ratio of the output end b of the second optical splitter coupler and the output end c of the splitter is 90:10; the splitting ratio of the output end b of the third optical splitter coupler and the output end c of the splitter is 50:50.

[0006] The pump light with a maximum pump power of 25dBm provided by the self-excited erbium-doped fiber amplifier is input into a tunable optical filter for selecting the forward spontaneous Brillouin scattering pump wavelength. The isolator ensures the clockwise unidirectional propagation of the light, and then it is input into the parity-time symmetric Sagnac ring through the port a of the circulator, so that it reaches the parity-time symmetry breaking state to realize single longitudinal mode output. The output end b of the first splitter coupler inputs 90% of the light into a nonlinear polarization rotation component composed of a polarizer and a first polarization controller and a second polarization controller to realize passive mode locking, and uses a single-mode optical fiber as a forward stimulated Brillouin scattering gain fiber for selective amplification of the longitudinal mode. The output end c of the first optical splitter coupler inputs 10% of the light to the second optical splitter coupler to achieve output, the output end b of the second optical splitter coupler directly inputs 90% of the light output signal into the spectrometer for observation, and the output end c of the second optical splitter coupler beats 10% of the light output signal through the photodetector, and then outputs the signal to the spectrum analyzer for testing, finally obtaining a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry.

[0007] When the parity-time symmetric Sagnac ring is working, stimulated Brillouin scattered light is input into the parity-time symmetric Sagnac ring through port a of the circulator, and the incident light is divided into two paths, moving in clockwise and counterclockwise directions to form two mutually coupled rings, one with gain and the other with loss. By adjusting the third polarization controller and the fourth polarization controller, the gain and loss can be precisely controlled to achieve a parity-time symmetry breaking state and realize single longitudinal mode output.

[0008] The single longitudinal mode all-optical microwave oscillator described in the present invention has unique advantages. Forward Brillouin scattering uses the interaction between light and sound waves to generate microwave signals. This process can provide very high frequency stability. At the same time, the single longitudinal mode oscillator avoids the mode noise introduced by the multi-longitudinal mode oscillator, and has important advantages in low phase noise and low-frequency drift. It has broad application prospects in quantum communication, high-precision clocks, 5G and higher-frequency wireless communication systems. In addition, the present invention is based on the torsional radial acoustic mode, adopts a parity-time symmetric loop structure, and uses the parity-time symmetry with its own loss component to achieve a single longitudinal mode signal output with a high side mode suppression ratio in the inherent multi-mode cavity. The remaining side mode energy can also be transferred to the main mode in the resonant system, solving the problem of incomplete energy utilization. And the research based on the torsional radial acoustic mode is of great significance in the application of optical fiber sensing because of its polarization sensitivity and complex tensor characteristics.

[0009] Preferably, the length of the single-mode optical fiber is 5000 m.

[0010] Preferably, the operating wavelength of the self-excited erbium-doped fiber amplifier is 1550 nm, and the maximum output power is 25 dBm.

[0011] Preferably, the wavelength range of the spectrometer is 600 to 1700 nm, the wavelength resolution is 0.02 to 2 nm, the wavelength linearity is 0.01 to 0.02, and the measurement power range is -90 to 20 dBm.

[0012] Preferably, the bandwidth of the photodetector is 50 GHz, and the linear response of the optical input power is 10 dBm.

[0013] Preferably, the frequency range of the spectrum analyzer is 300kHz to 20GHz, the frequency resolution is 1Hz, and the intermediate frequency line width is 10Hz to 1.5MHz; when the frequency range is 1MHz to 6GHz, the power range is -85dBm to 10dBm.

[0014] Compared with the prior art, the technical solution provided by the present invention has the following technical effects: the single longitudinal mode all-optical microwave oscillator based on the parity-time symmetry of the torsional radial mode described in the present invention has a simple structure. On the one hand, the nonlinear polarization rotation technology is used to realize the passive mode locking based on the torsional radial mode, and the line width is narrowed to the Hertz level; on the other hand, the parity-time symmetric structure is used to realize the single longitudinal mode output with a high side mode suppression ratio, which can be applied to the design of high-resolution signal recognition systems in the fields of communication, sensing and military; the parity-time symmetric loop structure is adopted, and the loss component of the parity-time symmetry is used to realize the single longitudinal mode signal output with a high side mode suppression ratio in the inherent multi-mode cavity, and the remaining side mode energy can also be transferred to the main mode in the resonant system, thereby improving the energy utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0016] 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 It is a structural schematic diagram of a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of the structure of a parity-time symmetric Sagnac ring according to an embodiment of the present invention;

[0019] Figure 3 TR of a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to an embodiment of the present invention 2,7 Mode-locked oscillation output diagram;

[0020] Figure 4 TR of a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to an embodiment of the present invention 2,7 Pattern line width measurement graph;

[0021] Figure 5 TR of a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to an embodiment of the present invention 2,7 Mode single longitudinal mode oscillation output diagram.

[0022] In the figure: 1. Self-excited erbium-doped fiber amplifier; 2. Tunable optical filter; 3. Isolator; 4. Circulator; 5. Parity-time symmetric Sagnac ring; 6A. First optical splitter coupler; 6B. Second optical splitter coupler; 6C. Third optical splitter coupler; 7A. First polarization controller; 7B. Second polarization controller; 7C. Third polarization controller; 7D. Fourth polarization controller; 8. Single-mode optical fiber; 9. Polarizer; 10. Spectrometer; 11. Photodetector; 12. Spectrum analyzer; 13. Polarization beam splitter. DETAILED DESCRIPTION

[0023] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0024] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. It should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two components. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0025] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0026] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0027] In one embodiment, Figure 1As shown, a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry is disclosed, comprising a self-excited erbium-doped fiber amplifier 1, a tunable optical filter 2, an isolator 3, a circulator 4, a parity-time symmetric Sagnac ring 5, a first splitter coupler 6A, a second splitter coupler 6B, a first polarization controller 7A, a second polarization controller 7B, a single-mode optical fiber 8, a polarizer 9, a spectrometer 10, a photodetector 11 and a spectrum analyzer 12; the output end of the self-excited erbium-doped fiber amplifier 1 is connected to the port a of the circulator 4 through the tunable optical filter 2 and the isolator 3 in sequence, the port b of the circulator 4 is connected to the parity-time symmetric Sagnac ring 5, the port c of the circulator 4 is connected to the input end a of the first splitter coupler 6A, the output end b of the first splitter coupler 6A is connected to the input end of the self-excited erbium-doped fiber amplifier 1 through the first polarization controller 7A, the single-mode optical fiber 8, the second polarization controller 7B and the polarizer 9 in sequence, and the output end of the first splitter coupler 6A is connected to the input end of the self-excited erbium-doped fiber amplifier 1 through the first polarization controller 7A, the single-mode optical fiber 8, the second polarization controller 7B and the polarizer 9 in sequence. c is connected to the input end a of the second optical splitter coupler 6B, the output end b of the second optical splitter coupler 6B is connected to the spectrometer 10, and the output end c of the second optical splitter coupler 6B is connected to the spectrum analyzer 12 through the photodetector 11; the parity-time symmetric Sagnac ring 5 includes a third optical splitter coupler 6C, a third polarization controller 7C, a fourth polarization controller 7D and a polarization beam splitter 13, the input end a of the third optical splitter coupler 6C is connected to the port b of the circulator 4, the output end b of the third optical splitter coupler 6C is connected to the port b of the polarization beam splitter 13 through the third polarization controller 7C, and the output end c of the third optical splitter coupler 6C is connected to the port a of the polarization beam splitter 13 through the fourth polarization controller 7D; the splitting ratio of the output end b of the first optical splitter coupler 6A to the output end c of the splitter is 90:10; the splitting ratio of the output end b of the second optical splitter coupler 6B to the output end c of the splitter is 90:10; the splitting ratio of the output end b of the third optical splitter coupler 6C to the output end c of the splitter is 50:50.

[0028] The pump light with a maximum pump power of 25 dBm provided by the self-excited erbium-doped fiber amplifier 1 (EDFA, EDFA-C-25-FA-B) is input into a tunable optical filter 2 (TOF, XTM-50-SCL-SM) for selecting the forward spontaneous Brillouin scattering pump wavelength. The isolator 3 ensures the clockwise unidirectional propagation of the light, and then inputs it into the parity-time symmetric Sagnac ring 5 through the port a of the circulator 4, so that it reaches the parity-time symmetry breaking state to realize single longitudinal mode output. The output end b of the first optical splitter coupler 6A inputs 90% of the light into a nonlinear polarization rotation component composed of a polarizer 9 and a first polarization controller 7A and a second polarization controller 7B to realize passive mode locking, and uses a single-mode optical fiber 8 as a forward stimulated Brillouin scattering gain fiber for selective amplification of the longitudinal mode. The output end c of the first optical splitter coupler 6A inputs 10% of the light to the second optical splitter coupler 6B for output, and the output end b of the second optical splitter coupler 6B directly inputs 90% of the light output signal into the spectrometer 10 for observation. The output end c of the second optical splitter coupler 6B passes 10% of the light output signal through the photodetector 11 for frequency beat, and then outputs the signal to the spectrum analyzer 12 for testing, and finally a single longitudinal mode all-optical microwave oscillator based on the parity-time symmetry of the torsional radial mode is obtained.

[0029] When the parity-time symmetric Sagnac ring 5 is working, the stimulated Brillouin scattered light is input into the parity-time symmetric Sagnac ring 5 through the port a of the circulator 4, and the incident light is divided into two paths, moving in the clockwise and counterclockwise directions to form two mutually coupled rings, one with gain and the other with loss. By adjusting the third polarization controller 7C and the fourth polarization controller 7D, the gain and loss can be precisely controlled to achieve a parity-time symmetry breaking state and realize single longitudinal mode output.

[0030] The single longitudinal mode all-optical microwave oscillator described in the present invention has unique advantages. Forward Brillouin scattering uses the interaction between light and sound waves to generate microwave signals. This process can provide very high frequency stability. At the same time, the single longitudinal mode oscillator avoids the mode noise introduced by the multi-longitudinal mode oscillator, and has important advantages in low phase noise and low-frequency drift. It has broad application prospects in quantum communication, high-precision clocks, 5G and higher-frequency wireless communication systems. In addition, the present invention is based on the torsional radial acoustic mode, adopts a parity-time symmetric loop structure, and uses the parity-time symmetry with its own loss component to achieve a single longitudinal mode signal output with a high side mode suppression ratio in the inherent multi-mode cavity. The remaining side mode energy can also be transferred to the main mode in the resonant system, solving the problem of incomplete energy utilization. And the research based on the torsional radial acoustic mode is of great significance in the application of optical fiber sensing because of its polarization sensitivity and complex tensor characteristics.

[0031] Based on the above embodiments, in a preferred embodiment, the length of the single-mode optical fiber 8 is 5000 m.

[0032] On the basis of the above embodiments, in a preferred embodiment, the operating wavelength of the self-excited erbium-doped fiber amplifier 1 is 1550 nm, and the maximum output power is 25 dBm.

[0033] On the basis of the above embodiments, in a preferred embodiment, the wavelength range of the spectrometer 10 is 600-1700 nm, the wavelength resolution is 0.02-2 nm, the wavelength linearity is 0.01-0.02, and the measurement power range is -90-20 dBm.

[0034] On the basis of the above embodiments, in a preferred embodiment, the bandwidth of the photodetector 11 is 50 GHz, and the linear response of the optical input power is 10 dBm.

[0035] On the basis of the above embodiments, in a preferred embodiment, the frequency range of the spectrum analyzer 12 is 300kHz to 20GHz, the frequency resolution is 1Hz, and the intermediate frequency line width is 10Hz to 1.5MHz; when the frequency range is 1MHz to 6GHz, the power range is -85dBm to 10dBm.

[0036] The condition that an all-optical microwave oscillator based on torsional radial mode should satisfy is the repetition rate f N (integer multiples of f) and TR 2,m (m=1, 2, 3...) The acoustic resonance frequencies are equal or the difference is close to zero, where f N =Nc / nL (N=1, 2, 3), n is the effective refractive index of the single-mode optical fiber 8, c is the speed of light in a vacuum, and L is the length of the laser cavity. 2,7 is about 140MHz, and the laser cavity length is designed to be L = 5km, so that f = 0.0414MHz and f N (N=3381)≤140MHz to meet the matching condition.

[0037] When the pulse energy Ep reaches a threshold, the optical pulse modulates the refractive index through the electrostrictive effect, which amplifies the acoustic wave amplitude. In turn, the forward stimulated Brillouin scattering process enhances the frequency f N The sound wave can be represented as

[0038]

[0039] where γe is the electrostriction coefficient, Q is the overlap integral between the fundamental optical mode and the acoustic mode, and ρ a (r, θ) is TR 2,mThe dimensionless acoustic profile of the forward stimulated Brillouin scattering acoustic mode, where q is the propagation constant along the axis of the single-mode fiber 8, A is the mode area of the fundamental optical mode in the single-mode fiber 8, ρ0 is the density of silica, and Γ B is the Brillouin linewidth, is the relative phase shift between the acoustic wave and its driving pulse train, and is given by:

[0040]

[0041] According to the phase matching condition, when is in the range (0, π), acoustic gain appears, and when the acoustic wave amplitude reaches its maximum value.

[0042] Select the TR 2,7 mode. Due to its highest forward stimulated Brillouin scattering gain coefficient, the output has a higher harmonic frequency and a higher side mode suppression ratio. The enhanced mode-locked oscillation effect of forward stimulated Brillouin scattering of the TR 2,7 mode is achieved by adjusting the PC to match the phase matching condition.

[0043] In a parity-time symmetric system, the characteristic frequency is:

[0044]

[0045] where ω n is the nth characteristic frequency of the two loops, and represent the gain coefficients of the two loops of the nth mode, and κ n represents the coupling coefficient between the two loops of the nth mode. Under the parity-time symmetric condition, that is, the gain of one loop is equal to the loss of the other loop;

[0046]

[0047] then Equation (3) can be rewritten as:

[0048]

[0049] Under the condition of κ n > g n the all-optical microwave oscillator experiences bounded neutral oscillation, indicating that the parity-time symmetry is invariant. In contrast, under the condition of κ n < g n it experiences conjugate oscillation modes and decaying modes, which means that the parity-time symmetry is broken. Obviously, when only the mode with the maximum gain is considered, we assume it is the 0th mode, under the condition of κ0 < g0, and for all other modes κ n > g nUnder the condition of (n≠0), the 0th-order symmetric mode selective oscillation is broken and the other complete modes are suppressed. When only one mode has an amplification, a single-mode oscillation all-optical microwave oscillator can also be realized, and the gain contrast g is not exceeded. max , g max for:

[0050] g max =g0-g1 (6),

[0051] Among them, g0 is the gain of the oscillation mode with the largest gain, and g1 is the gain of the mode with the second largest gain.

[0052] Since g0>g1, the forward stimulated Brillouin scattering gain difference is significantly enhanced, ensuring a stable single longitudinal mode oscillation signal of the main mode.

[0053] Narrow Linewidth TR Generated by All-Optical Microwave Oscillator 2,7 Mode microwave photons are realized by reducing the intrinsic linewidth of the passive resonator. The calculation formula of the linewidth of the all-optical microwave oscillator is:

[0054]

[0055] in, is the intrinsic linewidth of the passive resonant cavity, Δυ B It is TR 2,7 mode gain bandwidth, R is the optical amplitude feedback coefficient of the ring cavity, c is the speed of light in vacuum, L is the length of the fiber ring cavity, n is the refractive index of the single-mode fiber 8, is the intensity coupling coefficient, and γ0 is the coupler insertion loss.

[0056] from Figure 3 It can be concluded that the present invention realizes the TR 2,7 mode-locked oscillator output.

[0057] from Figure 4 It can be concluded that the present invention realizes the TR 2,7 The narrow linewidth oscillation signal output of the mode is greatly affected by noise, and the line shape changes. There are errors in fitting with the Lorentz curve, and it is difficult to accurately reflect its linewidth level. However, its 20dB linewidth is less affected by noise, so the 20dB linewidth is used to calculate the linewidth of this all-optical microwave oscillator, and the actual 3dB linewidth is 6.18Hz.

[0058] from Figure 5 It can be concluded that the present invention realizes the TR 2,7 The single longitudinal mode oscillation output of the mode, the side mode is well suppressed under the parity-time symmetry breaking state, and the side mode suppression ratio is relatively improved by 30.3dB.

[0059] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry, characterized in that: It comprises a self-excited erbium-doped fiber amplifier (1), a tunable optical filter (2), an isolator (3), a circulator (4), a parity-time symmetric Sagnac ring (5), a first splitter coupler (6A), a second splitter coupler (6B), a first polarization controller (7A), a second polarization controller (7B), a single-mode optical fiber (8), a polarizer (9), a spectrometer (10), a photodetector (11) and a spectrum analyzer (12); The output end of the self-excited erbium-doped fiber amplifier (1) is connected to the port a of the circulator (4) through a tunable optical filter (2) and an isolator (3) in sequence; the port b of the circulator (4) is connected to the parity-time symmetric Sagnac ring (5); the port c of the circulator (4) is connected to the input end a of the first splitter coupler (6A); the output end b of the first splitter coupler (6A) is connected to the input end of the self-excited erbium-doped fiber amplifier (1) through a first polarization controller (7A), a single-mode optical fiber (8), a second polarization controller (7B), and a polarizer (9) in sequence; the output end c of the first splitter coupler (6A) is connected to the input end a of the second splitter coupler (6B); the output end b of the second splitter coupler (6B) is connected to a spectrometer (10); and the output end c of the second splitter coupler (6B) is connected to a spectrum analyzer (12) through a photodetector (11); The parity-time symmetric Sagnac ring (5) comprises a third optical splitter coupler (6C), a third polarization controller (7C), a fourth polarization controller (7D) and a polarization beam splitter (13), wherein an input end a of the third optical splitter coupler (6C) is connected to a port b of the circulator (4), an output end b of the third optical splitter coupler (6C) is connected to a port b of the polarization beam splitter (13) via a third polarization controller (7C), and an output end c of the third optical splitter coupler (6C) is connected to a port a of the polarization beam splitter (13) via a fourth polarization controller (7D); The splitting ratio between the output end b of the first splitting coupler (6A) and the output end c is 90:10; The splitting ratio between the output end b of the second optical splitting coupler (6B) and the output end c is 90:10; The splitting ratio between the output end b and the output end c of the third optical splitting coupler (6C) is 50:

50.

2. The single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to claim 1, characterized in that: The length of the single-mode optical fiber (8) is 5000 m.

3. The single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to claim 1, characterized in that: The operating wavelength of the self-excited erbium-doped fiber amplifier (1) is 1550nm, and the maximum output power is 25dBm.

4. The single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to claim 1, characterized in that: The wavelength range of the spectrometer (10) is 600-1700 nm, the wavelength resolution is 0.02-2 nm, the wavelength linearity is 0.01-0.02, and the measurement power range is -90-20 dBm.

5. The single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to claim 1, characterized in that: The bandwidth of the photodetector (11) is 50 GHz, and the linear response of the optical input power is 10 dBm.

6. The single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry according to claim 1, characterized in that: The frequency range of the spectrum analyzer (12) is 300kHz to 20GHz, the frequency resolution is 1Hz, and the intermediate frequency line width is 10Hz to 1.5MHz; when the frequency range is 1MHz to 6GHz, the power range is -85dBm to 10dBm.

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