All-optical microwave oscillator under single-mode fiber torsion radial mode vernier effect

Abstract

The invention belongs to the technical field of microwave photons and optical communication, and particularly relates to an all-optical microwave oscillator under a single-mode fiber torsion radial mode vernier effect. The device comprises a self-excitation erbium-doped optical 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 light splitting coupler, a second light splitting coupler, a third light splitting coupler, a spectrograph, a photoelectric detector and a spectrum analyzer. Passive mode locking based on a torsion radial mode is realized by using a non-linear polarization rotation (NPR) technology, a line width is narrowed to a Hertz magnitude through a passive intrinsic resonant cavity, a side mode is effectively suppressed based on a double-ring vernier effect, the limitation that a high-performance torsion radial mode all-optical microwave oscillation signal cannot be generated conventionally is broken through, and the high-performance torsion radial mode all-optical microwave oscillation signal is generated. The torsion radial mode single longitudinal mode oscillation circuit has unique innovation advantages, and finally realizes torsion radial mode single longitudinal mode oscillation signal output with high side mode rejection ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave photons and optical communications, and in particular relates to an all-optical microwave oscillator, specifically an all-optical microwave oscillator under the single-mode optical fiber torsional radial mode vernier effect. Background Art

[0002] As a new type of microwave signal source, the all-optical microwave oscillator with narrow linewidth single longitudinal mode characteristics has the advantages of high precision, low noise, strong stability, etc. It can generate microwave signals with pure spectrum 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, navigation and positioning. Microwave oscillators with narrow linewidth can effectively suppress 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 with multi-mode oscillators, single longitudinal mode light sources avoid mode competition and can provide purer and more controllable output, which is particularly important for systems that require high synchronization and precise control (such as high-frequency synthesis and quantum information processing). In addition, all-optical microwave oscillators are based on optical devices and have strong anti-electromagnetic interference capabilities and environmental adaptability, and can maintain stable operation in harsh environments. This gives it unique advantages in environments with high temperature, high pressure or strong electromagnetic interference (such as military, aerospace, deep-sea exploration, etc.). All-optical microwave oscillators promote the integration of optical and microwave technologies and expand the application space of microwave signal processing. Optical fiber, optical modulation and optical transmission technology can be seamlessly connected with electronic microwave circuits, optimizing the system's integration and transmission efficiency. Especially in the field of optical fiber communication and wireless transmission, it can significantly improve transmission quality and system capacity.

[0003] The microwave photon generation methods based on the torsional radial mode of single-mode optical fiber include optoelectronic oscillators and passively mode-locked fiber oscillators. However, optoelectronic oscillators need to be feedback modulated by optoelectronic modulators and optoelectronic conversion needs to be performed by optoelectronic converters, which increases the complexity of microwave photon generation devices. In addition, conventional all-optical microwave oscillators have a wide line width and cannot generate high-performance torsional radial mode all-optical microwave oscillation signals. Summary of the invention

[0004] In order to overcome the technical defects that the existing optoelectronic oscillator has a relatively complex structure and the conventional all-optical microwave oscillator has a wide line width and cannot generate high-performance torsional radial mode all-optical microwave oscillation signals, the present invention provides an all-optical microwave oscillator under the single-mode optical fiber torsional radial mode vernier effect; compared with traditional electronic oscillators, it has the advantages of long transmission distance, large bandwidth, low noise, etc., and is suitable for communication, aerospace, military and other fields.

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

[0006] When the all-optical microwave oscillator under the single-mode optical fiber torsional radial mode vernier effect of the present invention is working, the 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) is used to select a suitable GAWBS (Guided Acoustic Wave Brillouin Scattering) pump wavelength. The isolator ensures the clockwise unidirectional propagation of light. The first polarization controller, the second polarization controller and the polarizer together constitute the NPR component to realize passive mode locking. The first single-mode optical fiber is used as a gain fiber of forward stimulated Brillouin scattering (FSBS) for selectively amplifying the longitudinal mode.

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

[0008] After passing through the polarizer in the main ring cavity R1, the linearly polarized light is converted into elliptically polarized light through the first polarization controller. Due to the nonlinear effect, the polarization state rotates. By fine-tuning the second polarization controller, when the optical signal passes through the polarizer again, the peak part of the pulse has a high transmittance, forming a similar saturable absorber. In a stable 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 is close to the FSBS sound frequency of the optical fiber, the refractive index modulation is enhanced and acts on the driving pulse in turn, realizing a passively mode-locked all-optical microwave oscillator.

[0009] The Stokes light generated by the main ring cavity R1 circulates back and forth in the secondary ring cavity R2 through the first splitter coupler. The secondary ring cavity using the second single-mode fiber and the third polarization controller realizes the effective free spectrum range alignment of the dual cavities, thereby realizing the single longitudinal mode operation of the FSBS Stokes light.

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

[0011] Passive mode locking technology has attracted extensive attention and research at home and abroad due to its advantages such as simple structure, low cost, and large pulse energy. The NPR structure has low production cost and is widely used because it is easier to obtain high peak power oscillation signals than other passive mode locking methods. The present invention realizes passive mode locking through NPR technology, and combines the double-ring cursor effect to realize the single longitudinal mode oscillation signal output of the single-mode optical fiber torsional radial mode, breaking the limitation that the conventional high-performance torsional radial mode all-optical microwave oscillation signal cannot be generated, and has unique innovative advantages. In addition, the single-mode optical fiber torsional radial mode in the present invention has the advantages of polarization sensitivity and complex tensor characteristics, which can be applied to the field of optical fiber sensing. The all-optical microwave oscillator under the cursor effect of the single-mode optical fiber torsional radial mode finally realized has important research value and broad application prospects in the fields of wireless communication and radar detection.

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

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

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

[0015] Preferably, the line width of the photodetector is 50 GHz, and the linear response of the optical input power reaches 10 dBm.

[0016] 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; and when the frequency range is 1MHz to 6GHz, the power range is -85dBm to 10dBm.

[0017] The technical solution provided by the present invention has the following beneficial effects compared with the prior art: the all-optical microwave oscillator under the vernier effect of the torsional radial mode of the single-mode optical fiber described in the present invention innovatively utilizes the nonlinear polarization rotation technology to realize passive mode locking based on the torsional radial mode, and narrows the line width to the Hertz level through the passive intrinsic resonant cavity, and effectively suppresses the side mode based on the double-ring vernier effect, breaking the conventional limitation that high-performance torsional radial mode all-optical microwave oscillation signals cannot be generated, and has unique innovative advantages, and finally realizes the output of torsional radial mode single longitudinal mode oscillation signals with high side mode suppression ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] 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.

[0020] Figure 1 It is a schematic structural diagram of an all-optical microwave oscillator under the single-mode optical fiber torsional radial mode vernier effect described in an 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 single-mode fiber torsional radial mode vernier effect in an embodiment of the present invention is 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 single-mode fiber torsional radial mode vernier effect in an embodiment of the present invention is 2,12 Mode single longitudinal mode oscillation output diagram;

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

[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 optical fiber; 5B. Second single-mode optical fiber; 6. Polarizer; 7A. First splitter coupler; 7B. Second splitter coupler; 7C. Third splitter coupler; 8. Spectrometer; 9. Photodetector; 10. Spectrum analyzer. DETAILED DESCRIPTION

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The following is combined with Figures 1 to 4 The specific embodiments of the present invention are described in detail.

[0029] In one embodiment, Figure 1As shown, an all-optical microwave oscillator under the single-mode fiber torsional radial mode vernier effect is disclosed, comprising 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 splitter coupler 7A, a second splitter coupler 7B, a third splitter coupler 7C, a spectrometer 8, a photodetector 9 and a spectrum analyzer 10; the output end of the self-excited erbium-doped fiber amplifier 1 is connected to the input end a of the first splitter coupler 7A 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 in sequence, and the input end c of the first splitter coupler 7A is connected to the output end b thereof. The optical fiber 10 is connected to the optical fiber 10 through the third polarization controller 4C and the second single-mode optical fiber 5B, the output end d of the first optical splitter coupler 7A is connected to the input end a of the second optical splitter coupler 7B, the output end b of the second optical splitter coupler 7B is connected to the input end a of the third optical splitter coupler 7C, the output end c of the second optical splitter coupler 7B is connected to the input end of the self-excited erbium-doped fiber amplifier 1, and the output end b of the third optical splitter coupler 7C is connected to the spectrometer 8; the output end c of the third optical splitter coupler 7C is connected to the spectrum analyzer 10 through the photodetector 9; the splitting ratio of the output end d and the output end b of the first optical splitter coupler 7A is 50:50; the splitting ratio of the output end b and the output end c of the second optical splitter coupler 7B is 10:90; the splitting ratio of the output end b and the output end c of the third optical splitter coupler 7C is 90:10.

[0030] When the all-optical microwave oscillator under the single-mode fiber torsional radial mode vernier effect of the present invention is working, the 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) is used to select a suitable GAWBS pump wavelength. The isolator 3 ensures the clockwise unidirectional propagation of light. The first polarization controller 4A, the second polarization controller 4B and the polarizer 6 together constitute the NPR component to achieve passive mode locking. The first single-mode optical fiber 5A is used as a gain fiber for forward stimulated Brillouin scattering to selectively amplify the longitudinal mode.

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

[0032] After passing through the polarizer 6 in the main ring cavity R1, the linearly polarized light is converted into elliptically polarized light through the first polarization controller 4A. Due to the nonlinear effect, the polarization state rotates. By fine-tuning the second polarization controller 4B, when the optical signal passes through the polarizer 6 again, the peak part of the pulse has a high transmittance, forming a similar saturable absorber. In a stable 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 is close to the FSBS acoustic frequency of the optical fiber, the refractive index modulation is enhanced and acts on the driving pulse in turn, realizing a passively mode-locked all-optical microwave oscillator.

[0033] The Stokes light generated by the main ring cavity R1 circulates back and forth in the secondary ring cavity R2 through the first splitter coupler 7A. The secondary ring cavity using the second single-mode fiber 5B and the third polarization controller 4C realizes the effective free spectrum range alignment of the dual cavities, thereby realizing the single longitudinal mode operation of the FSBS Stokes light.

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

[0035] Passive mode locking technology has attracted extensive attention and research at home and abroad due to its advantages such as simple structure, low cost, and large pulse energy. The NPR structure has low production cost and is widely used because it is easier to obtain high peak power oscillation signals than other passive mode locking methods. The present invention realizes passive mode locking through NPR technology, and combines the double-ring cursor effect to realize the single longitudinal mode oscillation signal output of the single-mode optical fiber torsional radial mode, breaking the limitation that the conventional high-performance torsional radial mode all-optical microwave oscillation signal cannot be generated, and has unique innovative advantages. In addition, the single-mode optical fiber torsional radial mode in the present invention has the advantages of polarization sensitivity and complex tensor characteristics, which can be applied to the field of optical fiber sensing. The all-optical microwave oscillator under the cursor effect of the single-mode optical fiber torsional radial mode finally realized has important research value and broad application prospects in the fields of wireless communication and radar detection.

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

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

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

[0039] On the basis of the above embodiments, in a preferred embodiment, the line width of the photodetector 9 is 50 GHz, and the linear response of the optical input power reaches 10 dBm.

[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, the intermediate frequency line width 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 single-mode optical fiber torsional radial mode vernier effect of the present invention is as follows:

[0042] The condition that the all-optical microwave oscillator 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 fiber, c is the speed of light in a vacuum, and L is the length of the laser cavity. 2,12 is about 260MHz, and the laser cavity length is designed to be L = 20km, so that f = 0.0103MHz and f N (N=25242)≤260MHz to meet the matching conditions.

[0043] 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 light pulse is suppressed and other frequencies are suppressed. The sound wave can be expressed 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 a (r, θ) is TR 2,mThe dimensionless acoustic profile of the forward stimulated Brillouin scattered acoustic mode, 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, Γ B is the Brillouin linewidth, is the relative phase offset between the acoustic wave and its driving pulse train and is given by:

[0046]

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

[0048] TR 2,12 mode as an example, (other TR 2,m The TR mode can be achieved by adjusting PC and TOF. Due to its high forward stimulated Brillouin scattering gain coefficient, its output has high harmonic frequency and high side mode suppression ratio. TR is achieved by adjusting PC to match the phase matching condition. 2,12 The forward stimulated Brillouin scattering of the mode 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 ring cavity R1 and the secondary ring cavity R2 respectively;

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

[0053] Among them, L m (m=1,2) is the length of the main ring cavity R1 and the secondary ring cavity R2, n=1.4682 is the effective refractive index of the SMF. FSR1 is about 10kHz, and FSR2 is about 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 a frequency that satisfies the resonance conditions of the main ring cavity and the secondary ring cavity, thereby achieving the output of a single longitudinal mode oscillation signal in the torsional radial mode.

[0055] The narrow linewidth torsional radial mode microwave photons generated by the all-optical microwave oscillator are achieved by reducing the intrinsic linewidth of the passive resonant cavity. The calculation formula of the linewidth of the all-optical microwave oscillator is:

[0056]

[0057] in, 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, n is the refractive index of the single-mode fiber, is the intensity coupling coefficient, and γ0 is the coupler insertion loss.

[0058] from Figure 2 It can be concluded that the present invention realizes TR-based 2,12 mode-locked oscillator output.

[0059] from Figure 3 It can be concluded that Figure 3 a and c are the spectrum detection results with a span of 2MHz and 100kHz in a single ring cavity, respectively. Figure 3 Figures b and d are the spectrum detection results with a span of 2MHz and 100kHz in the dual ring cavity, respectively. Figure 3 From a and b, we can see that the addition of the secondary ring cavity R2 can effectively suppress the longitudinal mode generated by the main ring cavity R1. Figure 3 c and d show that TR in a single ring cavity 2,12 The frequency interval of the mode microwave photons is 10kHz, which basically corresponds to the FSR of a single ring cavity, and the side mode suppression ratio is 21dB. 2,12 The adjacent longitudinal modes of the mode microwave photons are suppressed at a frequency interval of 40.8kHz, which almost corresponds to the FSR of the dual-ring cavity. The side mode suppression ratio is as high as 51dB, which is 30dB 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 the present invention realizes the TR 2,12 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. The experimental results of the single-ring cavity and the double-ring cavity are basically consistent. The final actual 3dB linewidth in the double-ring cavity is 2√99 times its 20dB linewidth, that is, 6.27Hz, achieving Hz-level linewidth narrowing.

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

10.

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

3. The all-optical microwave oscillator under the single-mode optical fiber torsional radial mode vernier effect according to claim 1, characterized in that: The length of the first single-mode optical fiber (5A) is 20 km, and the length of the second single-mode optical fiber (5B) is 5 km.

4. The all-optical microwave oscillator under the single-mode optical fiber torsional radial mode vernier effect according to any one of claims 1 to 3, 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.

5. The all-optical microwave oscillator under the single-mode optical fiber torsional radial mode vernier effect according to claim 4, characterized in that: The line width of the photodetector (9) is 50 GHz, and the linear response of the optical input power reaches 10 dBm.

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

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