Single-longitudinal-mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry

Abstract

This invention belongs to the field of microwave photonics and optical communication technology, specifically a single-longitudinal-mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry. It solves the technical problems of existing microwave photonics generation devices having complex structures, all-optical microwave oscillators lacking research on torsional radial acoustic modes, and significant energy waste in single-longitudinal-mode generation. It includes a self-excited erbium-doped fiber amplifier, a tunable optical filter, an isolator, a circulator, a parity-time symmetric Sagnac ring, a first optical splitter coupler, a second optical splitter coupler, a first polarization controller, a second polarization controller, a single-mode fiber, a polarizer, a spectrometer, a photodetector, and a spectrum analyzer. 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. It utilizes nonlinear polarization rotation technology to achieve passive mode-locking based on the torsional radial mode; and utilizes a parity-time symmetric structure to achieve single-longitudinal-mode output with a high side-mode suppression ratio.

Description

Technical Field

[0001] This invention relates to the fields of microwave photonics and optical communication technology, and more particularly to all-optical microwave oscillators, specifically a single-longitudinal-mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry. Background Technology

[0002] All-optical microwave oscillators are advanced systems combining 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 when high frequencies and low phase noise are required. Optical technology, offering extremely high frequency accuracy and stability, has become a crucial approach to solving this problem. All-optical microwave oscillators typically rely on lasers, fiber frequency combs, and nonlinear optical effects to convert optical signals into microwave frequency signals, generating low-noise, highly stable microwave signals.

[0003] Microwave oscillation signals can be generated using photoelectric oscillators and all-optical microwave oscillators. Y. London et al. proposed a photoelectric oscillator based on forward Brillouin scattering of a standard single-mode fiber guided acoustic mode, and experimentally generated a signal based on R... 0,7 Microwave oscillation signals in acoustic modes. Y. Liu et al. proposed a dual-cavity optomechanical microwave oscillator (OM-MO) based on the radial acoustic mode of single-mode fiber (SMF), realizing R-mode... 0,7 Single-frequency output of microwave photons in acoustic mode. Since optoelectronic oscillators require an optoelectronic modulator (EOM) for feedback modulation and an optoelectronic converter for photoelectric 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 of traditional optoelectronic oscillators. This makes single-longitudinal-mode forward Brillouin scattering all-optical microwave oscillators more compact and easier to integrate, suitable for the high-frequency, high-stability requirements of modern communication systems. However, previous studies on all-optical microwave oscillators have focused on radial acoustic modes, with almost no research on polarization-sensitive torsional radial acoustic modes. Furthermore, the generation of single-longitudinal modes relies solely on the vernier effect to match different comb teeth to suppress side modes, wasting a significant amount of energy in the side modes. This energy cannot be effectively converted into the main mode, which is a drawback. Summary of the Invention

[0004] To overcome the technical shortcomings of existing microwave photon generation devices, such as complex structures, lack of research on torsional radial acoustic modes in all-optical microwave oscillators, and significant energy waste in the generation of single longitudinal modes, this invention provides a single longitudinal mode all-optical microwave oscillator based on parity-time symmetry of torsional radial modes.

[0005] This 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 optical splitter coupler, a second optical splitter coupler, a first polarization controller, a second polarization controller, a single-mode fiber, a polarizer, a spectrometer, a photodetector, and a spectrum analyzer. The output of the self-excited erbium-doped fiber amplifier is connected to port a of the circulator via the tunable optical filter and the isolator. Port b of the circulator is connected to the parity-time symmetric Sagnac ring. Port c of the circulator is connected to input a of the first optical splitter coupler. The output b of the first optical splitter coupler is connected to the input of the self-excited erbium-doped fiber amplifier via the first polarization controller, the single-mode fiber, the second polarization controller, and the polarizer. The output of the first optical splitter coupler... The first beam splitter is connected to the input terminal a of the second beam splitter, the output terminal b of the second beam splitter is connected to the spectrometer, and the output terminal c of the second beam splitter is connected to the spectrum analyzer through a photodetector. The parity-time symmetric Sagnac ring includes a third beam splitter, a third polarization controller, a fourth polarization controller, and a polarization beam splitter. The input terminal a of the third beam splitter is connected to the port b of the circulator. The output terminal b of the third beam splitter is connected to the port b of the polarization beam splitter through the third polarization controller. The output terminal c of the third beam splitter is connected to the port a of the polarization beam splitter through the fourth polarization controller. The splitting ratio between the output terminal b of the first beam splitter and the output terminal c of the second beam splitter is 90:10. The splitting ratio between the output terminal b of the second beam splitter and the output terminal c of the third beam splitter is 50:50.

[0006] The self-excited erbium-doped fiber amplifier provides pump light with a maximum pump power of 25 dBm, which is input into a tunable optical filter for selecting the forward-stimulated Brillouin scattering pump wavelength. An isolator ensures unidirectional clockwise propagation of the light, which is then input through port a of the circulator into a parity-time symmetric Sagnac ring, achieving parity-time symmetry breaking and realizing single-mode output. Output b of the first beam splitter inputs 90% of the light into a nonlinear polarization rotation component consisting of a polarizer, a first polarization controller, and a second polarization controller to achieve passive mode-locking. This is achieved by using a single-mode fiber as the forward-stimulated Brillouin scattering gain fiber for selective amplification of the longitudinal mode. The output terminal c of the first beam splitter inputs 10% of the light to the second beam splitter for output. The output terminal b of the second beam splitter directly inputs 90% of the light output signal into the spectrometer for observation. The output terminal c of the second beam splitter passes 10% of the light output signal through a photodetector for beat frequency and then outputs the signal to the spectrum analyzer for testing. Finally, a single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry is obtained.

[0007] When the parity-time symmetric Sagnac ring is in operation, stimulated Brillouin scattering light is input into the parity-time symmetric Sagnac ring through port a of the circulator. The incident light is split into two paths, moving in clockwise and counterclockwise directions, forming two coupled rings, one with gain and the other with loss. By adjusting the third and fourth polarization controllers, the gain and loss can be precisely controlled to achieve a parity-time symmetry broken state, realizing single-mode output.

[0008] The single-longitudinal-mode all-optical microwave oscillator described in this invention possesses unique advantages. Forward Brillouin scattering utilizes the interaction between light and sound waves to generate microwave signals, a process that provides high frequency stability. Simultaneously, the single-longitudinal-mode oscillator avoids the mode noise introduced by multi-longitudinal-mode oscillators, exhibiting significant 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. Furthermore, this invention is based on a torsional radial acoustic mode and employs a parity-time symmetric loop structure. Utilizing the inherent loss component of parity-time symmetry, it achieves a high side-mode suppression ratio single-longitudinal-mode signal output within a pre-existing multi-mode cavity. The energy of other side modes can also be transferred to the dominant mode in the resonant system, solving the problem of incomplete energy utilization. Moreover, research based on torsional radial acoustic modes, due to its polarization sensitivity and complex tensor characteristics, holds significant importance for fiber optic sensing applications.

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

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

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

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

[0013] Preferably, the frequency range of the spectrum analyzer is 300kHz to 20GHz, its frequency resolution is 1Hz, and its intermediate frequency linewidth 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 this invention has the following technical advantages: The single-longitudinal-mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry described in this invention has a simple structure. Firstly, it utilizes nonlinear polarization rotation technology to achieve passive mode-locking based on torsional radial mode, narrowing the linewidth to the Hertz level. Secondly, it utilizes a parity-time symmetric structure to achieve a single-longitudinal-mode output with high side-mode rejection ratio, which can be applied to the design of high-resolution signal recognition systems in fields such as communication, sensing, and military. By adopting a parity-time symmetric loop structure, and utilizing the inherent loss component of parity-time symmetry, a single-longitudinal-mode signal output with high side-mode rejection ratio is achieved in the inherent multimode cavity. The energy of other side modes can also be transferred to the main mode in the resonant system, thus improving energy utilization. Attached Figure Description

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

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[0018] Figure 2 This is a schematic diagram of the parity-time symmetric Sagnac ring described in a certain embodiment of the present invention;

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

[0020] Figure 4 The TR of the single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry described in a certain embodiment of the present invention 2,7 Pattern linewidth measurement diagram;

[0021] Figure 5 The TR of the single longitudinal mode all-optical microwave oscillator based on torsional radial mode parity-time symmetry described in a certain embodiment of the present invention 2,7 Output diagram of single longitudinal mode oscillation.

[0022] In the diagram: 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 fiber; 9. Polarizer; 10. Spectrometer; 11. Photodetector; 12. Spectrum analyzer; 13. Polarization beam splitter. Detailed Implementation

[0023] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0024] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0026] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

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

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

[0029] When the parity-time symmetric Sagnac ring 5 is in operation, stimulated Brillouin scattering light is input into the parity-time symmetric Sagnac ring 5 through port a of the circulator 4. The incident light is split into two paths, moving in clockwise and counterclockwise directions, forming 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 broken state, realizing single-mode output.

[0030] The single-longitudinal-mode all-optical microwave oscillator described in this invention possesses unique advantages. Forward Brillouin scattering utilizes the interaction between light and sound waves to generate microwave signals, a process that provides high frequency stability. Simultaneously, the single-longitudinal-mode oscillator avoids the mode noise introduced by multi-longitudinal-mode oscillators, exhibiting significant 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. Furthermore, this invention is based on a torsional radial acoustic mode and employs a parity-time symmetric loop structure. Utilizing the inherent loss component of parity-time symmetry, it achieves a high side-mode suppression ratio single-longitudinal-mode signal output within a pre-existing multi-mode cavity. The energy of other side modes can also be transferred to the dominant mode in the resonant system, solving the problem of incomplete energy utilization. Moreover, research based on torsional radial acoustic modes, due to its polarization sensitivity and complex tensor characteristics, holds significant importance for fiber optic sensing applications.

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

[0032] Based on the above embodiments, in a preferred embodiment, the self-excited erbium-doped fiber amplifier 1 operates at a wavelength of 1550 nm and has a maximum output power of 25 dBm.

[0033] Based on 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] Based on the above embodiments, in a preferred embodiment, the photodetector 11 has a bandwidth of 50 GHz and a linear response of 10 dBm for the optical input power.

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

[0036] The condition that an all-optical microwave oscillator based on the torsional radial mode should satisfy is a 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), where n is the effective refractive index of single-mode fiber 8, c is the speed of light in vacuum, and L is the laser cavity length. Given the TR of single-mode fiber 8... 2,7 The MHz frequency is approximately 140 MHz, and the laser cavity length is designed to be L = 5 km, resulting in f = 0.0414 MHz and f N (N=3381)≤140MHz to meet the matching conditions.

[0037] When the pulse energy Ep reaches a threshold, the light pulse modulates the refractive index through the electrostriction effect, which amplifies the amplitude of the sound wave. Conversely, the forward stimulated Brillouin scattering process enhances the frequency f. N The light pulse suppresses other frequencies. Sound waves 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 is the electrostriction coefficient. 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 within 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: [[ID=Twenty-six]]

[0044] <The Eighteen]]

[0045] where ω n is the nth-order 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] [[ID=4 twenty-two]]

[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-order mode, under the condition of κ0 < g0, and for all other modes κ n > g nUnder the condition of (n≠0), a fully optical microwave oscillator is proposed by breaking the 0th-order symmetric mode selection oscillation, while other complete modes are suppressed. A single-mode oscillation fully optical microwave oscillator can also be realized when only one mode has an amplification, and the gain contrast ratio does not exceed g. max g max for:

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

[0051] Where 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 gain difference of forward stimulated Brillouin scattering is significantly enhanced, ensuring the stable single-longitudinal-mode oscillation signal of the main mode.

[0053] Narrow linewidth TR generated by all-optical microwave oscillator 2,7 Mode microwave photonics is achieved by reducing the intrinsic linewidth of the passive resonator. The formula for calculating the linewidth of an all-optical microwave oscillator is:

[0054]

[0055] in, It 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, and n is the refractive index of the single-mode fiber. γ is the strength coupling coefficient, and γ0 is the coupler insertion loss.

[0056] from Figure 3 It can be concluded that this invention achieves TR-based 2,7 The mode locks the oscillation output.

[0057] from Figure 4 It can be concluded that this invention achieves TR-based 2,7 The narrow linewidth oscillation signal output of the mode is significantly affected by noise due to its 3dB linewidth, which alters the line shape. Lorentz curve fitting has errors and cannot accurately reflect its linewidth level. However, its 20dB linewidth is less affected by noise. Therefore, the linewidth of this all-optical microwave oscillator is calculated based on the 20dB linewidth, and the final actual 3dB linewidth is 6.18Hz.

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

[0059] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within 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 includes 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 optical splitter (6A), a second optical splitter (6B), a first polarization controller (7A), a second polarization controller (7B), a single-mode fiber (8), a polarizer (9), a spectrometer (10), a photodetector (11), and a spectrum analyzer (12); The output of the self-excited erbium-doped fiber amplifier (1) is connected to port a of the circulator (4) in sequence through a tunable optical filter (2) and an isolator (3). Port b of the circulator (4) is connected to a parity-time symmetric Sagnac ring (5). Port c of the circulator (4) is connected to input a of the first optical splitter (6A). Output b of the first optical splitter (6A) is connected to input a of the self-excited erbium-doped fiber amplifier (1) in sequence through a first polarization controller (7A), a single-mode fiber (8), a second polarization controller (7B), and a polarizer (9). Output c of the first optical splitter (6A) is connected to input a of the second optical splitter (6B). Output b of the second optical splitter (6B) is connected to a spectrometer (10). Output c of the second optical splitter (6B) is connected to a spectrum analyzer (12) through a photodetector (11). The parity-time symmetric Sagnac ring (5) includes a third beam splitter (6C), a third polarization controller (7C), a fourth polarization controller (7D), and a polarization beam splitter (13). The input terminal a of the third beam splitter (6C) is connected to the port b of the circulator (4). The output terminal b of the third beam splitter (6C) is connected to the port b of the polarization beam splitter (13) through the third polarization controller (7C). The output terminal c of the third beam splitter (6C) is connected to the port a of the polarization beam splitter (13) through the fourth polarization controller (7D). The splitting ratio between the output terminal b and the output terminal c of the first optical splitter (6A) is 90:

10. The splitting ratio between the output terminal b and the output terminal c of the second optical splitter (6B) is 90:

10. The splitting ratio between the output terminal b and the output terminal c of the third optical 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 5000m.

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 self-excited erbium-doped fiber amplifier (1) operates at a wavelength of 1550 nm and has a maximum output power of 25 dBm.

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 600~1700nm, the wavelength resolution is 0.02~2nm, the wavelength linearity is 0.01~0.02, and the measurement power range is -90~20dBm.

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 photodetector (11) has a bandwidth of 50 GHz and a linear response of 10 dBm for the optical input power.

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, its frequency resolution is 1Hz, and its intermediate frequency linewidth is 10Hz to 1.5MHz; when the frequency range is 1MHz to 6GHz, the power range is -85dBm to 10dBm.

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