All-optical microwave oscillator based on torsional-radial mode Vernier effect in a single-mode fiber

Abstract

The application belongs to the technical field of microwave photon and optical communication, and specifically relates to a full-optical microwave oscillator under single-mode optical fiber twist radial mode vernier effect, which comprises a self-excited erbium-doped fiber amplifier, a tunable optical filter, an isolator, a first polarization controller, a second polarization controller, a third polarization controller, a first single-mode optical fiber, a second single-mode optical fiber, a polarizer, a first optical coupler, a second optical coupler, a third optical coupler, a spectrometer, a photoelectric detector and a spectrum analyzer. The application realizes passive mode-locking based on twist radial mode by using nonlinear polarization rotation (NPR) technology, narrows the linewidth to the order of hertz by using a passive intrinsic resonant cavity, effectively suppresses the side mode based on double-ring vernier effect, breaks the limitation that a conventional twist radial mode full-optical microwave oscillator signal cannot generate high-performance twist radial mode full-optical microwave oscillator signal, has unique and innovative advantages, and finally realizes twist radial mode single-longitudinal-mode oscillator signal output with high side mode suppression ratio.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics and optical communication technology, and particularly relates to all-optical microwave oscillators, specifically all-optical microwave oscillators under the vernier effect of single-mode fiber torsion radial mode. Background Technology

[0002] All-optical microwave oscillators with narrow linewidth and single longitudinal mode characteristics, as a novel type of microwave signal source, offer advantages such as high precision, low noise, and strong stability. They can generate microwave signals with clean spectra and low phase noise, significantly improving the frequency stability and accuracy of microwave signals, which is crucial for applications such as high-precision measurement, radar systems, and navigation and positioning. The narrow linewidth of the microwave oscillator effectively suppresses frequency drift and noise interference. The single longitudinal mode characteristic means that the light source oscillates at only one frequency, which improves the frequency stability and coherence of the system. Compared to multimode oscillators, single longitudinal mode light sources avoid mode competition, providing a purer and more controllable output, which is particularly important for systems requiring high synchronization and precise control (such as high-frequency synthesis and quantum information processing). Furthermore, all-optical microwave oscillators, based on optical components, have strong resistance to electromagnetic interference and environmental adaptability, maintaining stable operation in harsh environments. This gives them a unique advantage in environments with high temperature, high pressure, or strong electromagnetic interference (such as military, aerospace, and deep-sea exploration). All-optical microwave oscillators promote the integration of optical and microwave technologies, expanding the application space of microwave signal processing. Optical fiber, optical modulation, and optical transmission technologies can be seamlessly integrated with electronic microwave circuits, optimizing system integration and transmission efficiency. In particular, they can significantly improve transmission quality and system capacity, especially in the fields of optical fiber communication and wireless transmission.

[0003] Microwave photon generation based on the torsional radial mode of single-mode fiber includes optoelectronic oscillators and passively mode-locked fiber oscillators. However, optoelectronic oscillators require feedback modulation via optoelectronic modulators and optoelectronic conversion via optoelectronic converters, which increases the complexity of microwave photon generation devices. Moreover, conventional all-optical microwave oscillators have a relatively wide linewidth and cannot generate high-performance torsional radial mode all-optical microwave oscillation signals. Summary of the Invention

[0004] To overcome the technical shortcomings of existing optoelectronic oscillators, which have relatively complex structures and conventional all-optical microwave oscillators with wide linewidths, making it impossible to generate high-performance torsional radial mode all-optical microwave oscillation signals, this invention provides an all-optical microwave oscillator based on the vernier effect of single-mode fiber torsional radial mode. Compared with traditional electronic oscillators, it has advantages such as long transmission distance, large bandwidth, and low noise, and is suitable for fields such as communications, aerospace, and military.

[0005] This invention provides an all-optical microwave oscillator under the vernier effect of a torsional radial mode in a single-mode fiber, comprising a self-excited erbium-doped fiber amplifier, a tunable optical filter, an isolator, a first polarization controller, a second polarization controller, a third polarization controller, a first single-mode fiber, a second single-mode fiber, a polarizer, a first optical splitter, a second optical splitter, a third optical splitter, a spectrometer, a photodetector, and a spectrum analyzer. The output of the self-excited erbium-doped fiber amplifier is connected to the input a of the first optical splitter in sequence via the tunable optical filter, the isolator, the first polarization controller, the first single-mode fiber, the second polarization controller, and the polarizer. The input c of the first optical splitter is connected to its output b via the first... The three-polarization controller is connected to the second single-mode fiber. The output terminal d of the first optical splitter is connected to the input terminal a of the second optical splitter. The output terminal b of the second optical splitter is connected to the input terminal a of the third optical splitter. The output terminal c of the second optical splitter is connected to the input terminal of the self-excited erbium-doped fiber amplifier. The output terminal b of the third optical splitter is connected to the spectrometer. The output terminal c of the third optical splitter is connected to the spectrum analyzer through a photodetector. The splitting ratio of the output terminals d and b of the first optical splitter is 50:50. The splitting ratio of the output terminals b and c of the second optical splitter is 10:90. The splitting ratio of the output terminals b and c of the third optical splitter is 90:10.

[0006] In the all-optical microwave oscillator of the single-mode fiber under torsional radial mode vernier effect described in this invention, a self-excited erbium-doped fiber amplifier (EDFA, EDFA-C-25-FA-B) provides pump light, and a tunable optical filter (TOF, XTM-50-SCL-SM) selects a suitable GAWBS (Guided Acoustic Wave Brillouin Scattering) pump wavelength. An isolator ensures unidirectional clockwise propagation of the light. A first polarization controller, a second polarization controller, and a polarizer together constitute an NPR component to achieve passive mode-locking. The first single-mode fiber serves as the gain fiber for forward stimulated Brillouin scattering (FSBS) to selectively amplify the longitudinal mode.

[0007] The self-excited erbium-doped fiber amplifier, tunable optical filter, isolator, first polarization controller, first single-mode fiber, second polarization controller, polarizer, input a and output d of the first optical splitter, and input a and output c of the second optical splitter form the main ring cavity R1. The circuit formed by input c and output b of the first optical splitter, the third polarization controller, and the second single-mode fiber forms the secondary ring cavity R2.

[0008] Linearly polarized light, after passing through the polarizer within the main ring cavity R1, is converted to elliptically polarized light by the first polarization controller. Due to nonlinear effects, a polarization state rotation occurs. By fine-tuning the second polarization controller, the peak portion of the pulse has high transmittance when the optical signal passes through the polarizer again, forming a similar saturable absorber. In a steady state, a pulse with a cavity round-trip frequency f is generated, which depends on the total cavity length L of the main ring cavity R1. When the harmonic frequency of the pulse train approaches the FSBS audio frequency of the optical fiber, refractive index modulation is enhanced and acts sequentially on the driving pulse, realizing a passively mode-locked all-optical microwave oscillator.

[0009] The Stokes light generated in the main ring cavity R1 circulates back and forth in the secondary ring cavity R2 through the first beam splitter. The secondary ring cavity, employing a second single-mode fiber and a third polarization controller, achieves effective free spectral range alignment between the two cavities, thereby enabling single-longitudinal-mode operation of the FSBS Stokes light.

[0010] The light output from 90% output terminal c of the second optical splitter returns to the self-excited erbium-doped fiber amplifier, while the light output from 10% output terminal b is split into two parts by the third optical splitter. The Stokes light from the 90% output terminal b of the third optical splitter is monitored by a spectrometer (OSA, AQ6370D-02EN). The Stokes light from the 10% output terminal c of the third optical splitter is converted into an electrical signal by a photodetector, and then the spectrum is monitored by a spectrum analyzer (ESA, FSV3030). Ultimately, the all-optical microwave oscillator effect under the vernier effect of the single-mode fiber torsional radial mode was detected.

[0011] Passive mode-locking technology has garnered widespread attention and research both domestically and internationally due to its advantages such as simple structure, low cost, and high pulse energy. The NPR (Non-Pulse Resonance) structure is widely used because of its low fabrication cost and ability to generate high peak power oscillation signals compared to other passive mode-locking methods. This invention achieves passive mode-locking through NPR technology and combines it with the double-ring vernier effect to realize a single-longitudinal-mode oscillation signal output in the torsional radial mode of a single-mode fiber. This breaks the limitation of conventional methods that cannot generate high-performance torsional radial mode all-optical microwave oscillation signals, possessing unique innovative advantages. Furthermore, the polarization sensitivity and complex tensor characteristics of the single-mode fiber torsional radial mode in this invention allow for its application in the field of fiber optic sensing. The resulting all-optical microwave oscillator under the vernier effect of the single-mode fiber torsional radial mode has significant research value and broad application prospects in fields such as wireless communication and radar detection.

[0012] Preferably, the maximum output power of the self-excited erbium-doped fiber amplifier is 25dBm, and the operating wavelength of the self-excited erbium-doped fiber amplifier is 1550nm.

[0013] Preferably, the length of the first single-mode fiber is 20km and the length of the second single-mode fiber is 5km.

[0014] Preferably, the spectrometer has a wavelength range of 600–1700 nm, a wavelength resolution of 0.02–2 nm, and a measurement power range of -90–20 dBm.

[0015] Preferably, the photodetector has a linewidth of 50 GHz and a linear response of 10 dBm for optical input power.

[0016] Preferably, the frequency range of the spectrum analyzer is 300kHz to 20GHz, the frequency resolution is 1Hz, and the intermediate frequency linewidth is 10Hz to 1.5MHz; and when the frequency range is 1MHz to 6GHz, the power range is -85dBm to 10dBm.

[0017] Compared with the prior art, the technical solution provided by this invention has the following beneficial effects: The all-optical microwave oscillator under the vernier effect of the single-mode fiber torsional radial mode described in this invention innovatively utilizes nonlinear polarization rotation technology to achieve passive mode-locking based on the torsional radial mode, and narrows the linewidth to the Hertz level through a passive intrinsic resonant cavity. Based on the double-ring vernier effect, it effectively suppresses side modes, breaking the limitation that conventional methods cannot generate high-performance torsional radial mode all-optical microwave oscillation signals. It has unique innovative advantages and ultimately achieves the output of a torsional radial mode single longitudinal mode oscillation signal with a high side mode suppression ratio. Attached Figure Description

[0018] 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.

[0019] 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.

[0020] Figure 1 This is a schematic diagram of the structure of the all-optical microwave oscillator under the vernier effect of single-mode fiber torsion radial mode according to a certain embodiment of the present invention;

[0021] Figure 2 The TR of the single-ring and double-ring cavities of the all-optical microwave oscillator under the vernier effect of the torsional radial mode of single-mode fiber described in a certain embodiment of the present invention. 2,12 Mode-locked oscillation output diagram;

[0022] Figure 3 The TR of the single-ring and double-ring cavities of the all-optical microwave oscillator under the vernier effect of the torsional radial mode of single-mode fiber described in a certain embodiment of the present invention. 2,12 Output diagram of single longitudinal mode oscillation;

[0023] Figure 4 The TR of the single-ring and double-ring cavities of the all-optical microwave oscillator under the vernier effect of the torsional radial mode of single-mode fiber described in a certain embodiment of the present invention. 2,12 Pattern line width measurement diagram.

[0024] In the figure: 1. Self-excited erbium-doped fiber amplifier; 2. Tunable optical filter; 3. Isolator; 4A. First polarization controller; 4B. Second polarization controller; 4C. Third polarization controller; 5A. First single-mode fiber; 5B. Second single-mode fiber; 6. Polarizer; 7A. First optical splitter coupler; 7B. Second optical splitter coupler; 7C. Third optical splitter coupler; 8. Spectrometer; 9. Photodetector; 10. Spectrum analyzer. Detailed Implementation

[0025] 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.

[0026] 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.

[0027] Numerous 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, and not all, of the embodiments of the invention.

[0028] The following is in conjunction with the appendix Figures 1 to 4 Specific embodiments of the present invention will be described in detail below.

[0029] In one embodiment, such as Figure 1As shown, an all-optical microwave oscillator under the vernier effect of single-mode fiber torsion radial mode is disclosed, including a self-excited erbium-doped fiber amplifier 1, a tunable optical filter 2, an isolator 3, a first polarization controller 4A, a second polarization controller 4B, a third polarization controller 4C, a first single-mode fiber 5A, a second single-mode fiber 5B, a polarizer 6, a first optical splitter coupler 7A, a second optical splitter coupler 7B, a third optical splitter coupler 7C, a spectrometer 8, a photodetector 9, and a spectrum analyzer 10. The output of the self-excited erbium-doped fiber amplifier 1 is connected to the input a of the first optical splitter coupler 7A in sequence through the tunable optical filter 2, the isolator 3, the first polarization controller 4A, the first single-mode fiber 5A, the second polarization controller 4B, and the polarizer 6. The input c of the first optical splitter coupler 7A is connected to its output b. The first optical splitter 7A is connected to the second single-mode fiber 5B via a third polarization controller 4C. The output terminal d of the first optical splitter 7A is connected to the input terminal a of the second optical splitter 7B. The output terminal b of the second optical splitter 7B is connected to the input terminal a of the third optical splitter 7C. The output terminal c of the second optical splitter 7B is connected to the input terminal of the self-excited erbium-doped fiber amplifier 1. The output terminal b of the third optical splitter 7C is connected to the spectrometer 8. The output terminal c of the third optical splitter 7C is connected to the spectrum analyzer 10 via a photodetector 9. The splitting ratio of the output terminals d and b of the first optical splitter 7A is 50:50. The splitting ratio of the output terminals b and c of the second optical splitter 7B is 10:90. The splitting ratio of the output terminals b and c of the third optical splitter 7C is 90:10.

[0030] In the all-optical microwave oscillator of the single-mode fiber under torsional radial mode vernier effect described in this invention, a self-excited erbium-doped fiber amplifier 1 (EDFA, EDFA-C-25-FA-B) provides pump light, and a tunable optical filter (TOF, XTM-50-SCL-SM) selects a suitable GAWBS pump wavelength. Isolator 3 ensures unidirectional clockwise propagation of light. The first polarization controller 4A, the second polarization controller 4B, and polarizer 6 together constitute an NPR component to achieve passive mode locking. The first single-mode fiber 5A serves as the gain fiber for forward stimulated Brillouin scattering, used for selective amplification of longitudinal modes.

[0031] The main ring cavity R1 is formed by the self-excited erbium-doped fiber amplifier 1, tunable optical filter 2, isolator 3, first polarization controller 4A, first single-mode fiber 5A, second polarization controller 4B, polarizer 6, the input end a and output end d of the first optical splitter 7A, and the input end a and output end c of the second optical splitter 7B. The secondary ring cavity R2 is formed by the input end c and output end b of the first optical splitter 7A, the third polarization controller 4C, and the second single-mode fiber 5B.

[0032] Linearly polarized light, after passing through polarizer 6 within the main ring cavity R1, becomes elliptically polarized light via the first polarization controller 4A. Due to nonlinear effects, polarization state rotation occurs. By fine-tuning the second polarization controller 4B, the peak transmittance of the pulse is high when the optical signal passes through polarizer 6 again, forming a similar saturable absorber. In a steady state, a pulse with a cavity round-trip frequency f is generated, which depends on the total cavity length L of the main ring cavity R1. When the harmonic frequency of the pulse train approaches the FSBS audio frequency of the optical fiber, refractive index modulation is enhanced and acts sequentially on the driving pulse, realizing a passively mode-locked all-optical microwave oscillator.

[0033] The Stokes light generated in the main ring cavity R1 circulates back and forth in the secondary ring cavity R2 through the first beam splitter 7A. The secondary ring cavity, employing a second single-mode fiber 5B and a third polarization controller 4C, achieves effective free spectral range alignment between the two cavities, thereby enabling single-longitudinal-mode operation of the FSBS Stokes light.

[0034] The light output from the 90% output terminal c of the second optical splitter 7B returns to the self-excited erbium-doped fiber amplifier 1, and the light output from the 10% output terminal b is then split into two parts by the third optical splitter 7C. The Stokes light from the 90% output terminal b of the third optical splitter 7C is monitored by a spectrometer 8 (OSA, AQ6370D-02EN). The Stokes light from the 10% output terminal c of the third optical splitter 7C is converted into an electrical signal by a photodetector 9, and then the spectrum is monitored by a spectrum analyzer 10 (ESA, FSV3030). Finally, the all-optical microwave oscillator effect under the vernier effect of the single-mode fiber torsional radial mode was detected.

[0035] Passive mode-locking technology has garnered widespread attention and research both domestically and internationally due to its advantages such as simple structure, low cost, and high pulse energy. The NPR (Non-Pulse Resonance) structure is widely used because of its low fabrication cost and ability to generate high peak power oscillation signals compared to other passive mode-locking methods. This invention achieves passive mode-locking through NPR technology and combines it with the double-ring vernier effect to realize a single-longitudinal-mode oscillation signal output in the torsional radial mode of a single-mode fiber. This breaks the limitation of conventional methods that cannot generate high-performance torsional radial mode all-optical microwave oscillation signals, possessing unique innovative advantages. Furthermore, the polarization sensitivity and complex tensor characteristics of the single-mode fiber torsional radial mode in this invention allow for its application in the field of fiber optic sensing. The resulting all-optical microwave oscillator under the vernier effect of the single-mode fiber torsional radial mode has significant research value and broad application prospects in fields such as wireless communication and radar detection.

[0036] Based on the above embodiments, in a preferred embodiment, the maximum output power of the self-excited erbium-doped fiber amplifier 1 is 25dBm, and the operating wavelength of the self-excited erbium-doped fiber amplifier 1 is 1550nm.

[0037] Based on the above embodiments, in a preferred embodiment, the length of the first single-mode fiber 5A is 20km and the length of the second single-mode fiber 5B is 5km.

[0038] Based on the above embodiments, in a preferred embodiment, the wavelength range of the spectrometer 8 is 600–1700 nm, the wavelength resolution is 0.02–2 nm, and the measurement power range is -90–20 dBm.

[0039] Based on the above embodiments, in a preferred embodiment, the photodetector 9 has a linewidth of 50 GHz and a linear response of 10 dBm for optical input power.

[0040] Based on the above embodiments, in a preferred embodiment, the frequency range of the spectrum analyzer 10 is 300kHz to 20GHz, the frequency resolution is 1Hz, and the intermediate frequency linewidth is 10Hz to 1.5MHz; and when the frequency range is 1MHz to 6GHz, the power range is -85dBm to 10dBm.

[0041] The working principle of the all-optical microwave oscillator under the vernier effect of single-mode fiber torsion radial mode described in this invention is as follows:

[0042] The all-optical microwave oscillator should meet the condition of 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 the single-mode fiber, c is the speed of light in vacuum, and L is the laser cavity length. Given the TR of the single-mode fiber... 2,12 The MHz frequency is approximately 260 MHz, and the laser cavity length is designed to be L = 20 km, resulting in f = 0.0103 MHz and f N (N=25242)≤260MHz to meet the matching conditions.

[0043] 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. The sound wave can be represented as:

[0044]

[0045] 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 mode, where q is its propagation constant along the axis of the single-mode fiber, A is the mode area of ​​the fundamental mode in the single-mode fiber, ρ0 is the density of silica, and Γ B It is the Brillouin line width. It is the relative phase shift between the sound wave and its driving pulse train, and is given by the following equation:

[0046]

[0047] According to the phase matching condition, when Within the range (0, π), acoustic gain appears, when At that time, the amplitude of the sound wave reaches its maximum value.

[0048] With TR 2,12 For example, in other TR modes 2,m All modes can be achieved by adjusting the PC and TOF. Due to its high forward stimulated Brillouin scattering gain coefficient, its output has high harmonic frequencies and high side-mode rejection ratio. TR is achieved by adjusting the PC to match the phase-matching condition. 2,12 Forward stimulated Brillouin scattering enhances the mode-locked oscillation effect.

[0049] According to the vernier effect, the effective FSR of the dual-ring cavity structure is the least common multiple of the main ring cavity R1 and the secondary ring cavity R2, that is:

[0050] FSR=n1FSR1=n2FSR2(3),

[0051] FSR1 and FSR2 correspond to the main annular cavity R1 and the secondary annular cavity R2, respectively;

[0052] FSR m =c / nL m (m=1,2)(4),

[0053] Among them, L m (m=1,2) are the lengths of the main annular cavity R1 and the secondary annular cavity R2, and n=1.4682 is the effective refractive index of the SMF. FSR1 is approximately 10kHz, and FSR2 is approximately 41kHz.

[0054] When the frequency is v p When the pump light is injected into the SMF, the FSBS is excited. When the FSR of the dual-ring cavity exceeds the FSBS gain bandwidth and the gain is greater than the loss, the FSBS can only oscillate at the frequency that simultaneously satisfies the resonance conditions of the main ring cavity and the secondary ring cavity, thereby realizing the output of a torsional radial mode single longitudinal mode oscillation signal.

[0055] Narrow-linewidth torsional radial mode microwave photons generated by an all-optical microwave oscillator are achieved by reducing the intrinsic linewidth of the passive resonant cavity. The formula for calculating the linewidth of an all-optical microwave oscillator is as follows:

[0056]

[0057] in, It is the intrinsic linewidth of the passive resonant cavity, Δυ B is the torsional radial 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.

[0058] from Figure 2 It can be concluded that the present invention achieves TR-based [technology / mechanism] in both single-ring and double-ring cavities. 2,12 The mode locks the oscillation output.

[0059] from Figure 3 It can be concluded that Figure 3 a and c represent the spectral detection results with spans of 2MHz and 100kHz in a single-ring cavity, respectively. Figure 3 b and d represent the spectral detection results with spans of 2MHz and 100kHz in the dual-ring cavity, respectively. (Comparison) Figure 3 From a and b, it can be seen that the addition of the secondary ring cavity R2 can effectively suppress the longitudinal mode generated by the main ring cavity R1. (Comparison) Figure 3 From c and d, we can see that TR in a single-ring cavity 2,12 The mode microwave photon frequency spacing is 10kHz, which basically corresponds to the FSR of a single-ring cavity, and the side-mode suppression ratio is 21dB. The TR in a dual-ring cavity... 2,12 Adjacent longitudinal modes of the mode microwave photon are suppressed at a frequency interval of 40.8 kHz, which almost corresponds to the FSR of the dual-ring cavity. The side-mode suppression ratio is as high as 51 dB, which is 30 dB higher than that of the single-ring cavity, realizing single longitudinal mode all-optical microwave oscillation output.

[0060] from Figure 4 It can be concluded that this invention achieves TR-based 2,12 The narrow linewidth oscillation signal output of the mode is significantly affected by noise due to the large influence of its 3dB linewidth, which alters the line shape. Fitting with the Lorentz curve introduces errors and makes it difficult to 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. The experimental results in single-ring and dual-ring cavities are basically consistent. In the dual-ring cavity, the final actual 3dB linewidth is 2√99 times its 20dB linewidth, which is 6.27Hz, achieving linewidth narrowing at the Hz level.

[0061] 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. An all-optical microwave oscillator under the vernier effect of a single-mode fiber torsion radial mode, characterized in that, It includes a self-excited erbium-doped fiber amplifier (1), a tunable optical filter (2), an isolator (3), a first polarization controller (4A), a second polarization controller (4B), a third polarization controller (4C), a first single-mode fiber (5A), a second single-mode fiber (5B), a polarizer (6), a first optical splitter (7A), a second optical splitter (7B), a third optical splitter (7C), a spectrometer (8), a photodetector (9), and a spectrum analyzer (10). The output of the self-excited erbium-doped fiber amplifier (1) is connected in sequence to the input a of the first optical splitter (7A) via a tunable optical filter (2), an isolator (3), a first polarization controller (4A), a first single-mode fiber (5A), a second polarization controller (4B), and a polarizer (6). The input c of the first optical splitter (7A) and its output b are connected via a third polarization controller (4C) and a second single-mode fiber (5B). The output d of the first optical splitter (7A) is connected to the input a of the second optical splitter (7B). The output b of the second optical splitter (7B) is connected to the input a of the third optical splitter (7C). The output c of the second optical splitter (7B) is connected to the input of the self-excited erbium-doped fiber amplifier (1). The output b of the third optical splitter (7C) is connected to the spectrometer (8). The output c of the third optical splitter (7C) is connected to the spectrum analyzer (10) via a photodetector (9). The splitting ratio between the output terminals d and b of the first optical splitter (7A) is 50:50; the splitting ratio between the output terminals b and c of the second optical splitter (7B) is 10:90; and the splitting ratio between the output terminals b and c of the third optical splitter (7C) is 90:

10. The first single-mode fiber (5A) is 20km long, and the second single-mode fiber (5B) is 5km long.

2. The all-optical microwave oscillator under the vernier effect of single-mode fiber torsion radial mode according to claim 1, characterized in that, The maximum output power of the self-excited erbium-doped fiber amplifier (1) is 25dBm, and the operating wavelength of the self-excited erbium-doped fiber amplifier (1) is 1550nm.

3. The all-optical microwave oscillator under the vernier effect of single-mode fiber torsion radial mode according to claim 1 or 2, characterized in that, The wavelength range of the spectrometer (8) is 600~1700nm, the wavelength resolution is 0.02~2nm, and the measurement power range is -90~20dBm.

4. The all-optical microwave oscillator under the vernier effect of single-mode fiber torsion radial mode according to claim 3, characterized in that, The photodetector (9) has a linewidth of 50 GHz and a linear response of 10 dBm for optical input power.

5. The all-optical microwave oscillator under the vernier effect of single-mode fiber torsion radial mode according to claim 4, characterized in that, The frequency range of the spectrum analyzer (10) is 300kHz to 20GHz, the frequency resolution is 1Hz, the intermediate frequency linewidth is 10Hz to 1.5MHz, and the power range is -85dBm to 10dBm when the frequency range is 1MHz to 6GHz.

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