High-resolution microwave frequency measurement method and device based on tunable Brillouin fiber laser

Abstract

The invention relates to a microwave frequency testing technology, and aims to solve the problems that an existing microwave frequency measuring method based on Brillouin scattering is limited by the Brillouin gain spectrum width, and the frequency measuring resolution is difficult to improve; the invention discloses a high-resolution microwave frequency measurement technology based on a tunable Brillouin fiber laser, and the technology comprises the steps: outputting two narrow-linewidth optical carriers through a laser source, enabling an unknown signal of an upper branch to serve as pump light to excite Brillouin after intensity modulation, enabling a signal outputted by a vector network analyzer of a lower branch to serve as probe light after modulation, and enabling the probe light to serve as the probe light after intensity modulation. The probe light is selectively amplified after interacting with the Brillouin gain, an electric delay line is introduced into the Brillouin resonant cavity, and stepping tuning of the laser frequency is realized by changing the voltage applied to a medium on the electric delay line, so that a to-be-measured frequency signal is measured at high resolution; while the broadband frequency measurement range is maintained, the frequency resolution of 100 kHz is achieved, and the application potential in the fields of high-resolution radar signal detection and the like is shown.

Description

Technical Field

[0001] This invention relates to the field of microwave frequency measurement technology, and particularly to a high-resolution microwave frequency measurement method and apparatus based on a tunable Brillouin fiber laser. Background Technology

[0002] Stimulated Brillouin scattering is a nonlinear optical effect in optical fibers. Brillouin lasers have advantages such as narrow linewidth, low loss, high side-mode suppression ratio, wide tuning range, and resistance to electromagnetic interference. They have important application value in key areas such as signal monitoring of high-speed wireless communication links, high-resolution beamforming of phased array radar, and rapid identification and analysis of microwave signals in electronic warfare.

[0003] In the military field, Brillouin lasers, with their high-resolution frequency testing capabilities, significantly improve the accuracy of microwave signal identification, providing new technological support for target detection, identification, and tracking in complex electromagnetic environments. Phased array radars achieve rapid beam scanning and pointing by precisely controlling microwave frequencies; in electronic warfare, rapid and accurate identification of enemy microwave signal frequencies is a prerequisite for effective jamming and defense; the detection of cosmic microwave background radiation in radio astronomy and the detection of weak microwave signals in quantum communication all pose unprecedented challenges to high-resolution microwave frequency testing technology. Existing testing technologies have many shortcomings in terms of sensitivity, measurement range, and high-resolution capabilities, failing to meet the needs of cutting-edge research.

[0004] To address the aforementioned issues, researchers have proposed several microwave frequency measurement methods based on the stimulated Brillouin effect. In 2019, Jiao et al. detected the frequency information of the microwave signal under test by creating a mapping between the total output power of the system and the reference frequency. They used nonlinear fitting to alleviate the limitation of the Brillouin gain spectral linewidth, significantly improving the measurement resolution and achieving a minimum resolvable frequency interval of 18 MHz. In 2022, Wang et al. proposed a photon-assisted frequency measurement system based on stimulated Brillouin scattering. This system has high resolution and multi-frequency estimation capabilities. By superimposing the gain spectrum with two loss spectra to reduce the SBS gain bandwidth, the system can identify the frequency information of multiple unknown microwave signals with a high resolution of 14.5 MHz over a wide bandwidth. In 2023, Wang et al. established a frequency measurement system that can detect signals at fixed low-frequency points by introducing down-conversion technology combined with stimulated Brillouin scattering. When the beat frequency signal appears at a preset fixed frequency of 828 MHz, the unknown signal can be obtained by recording the frequency of the sweep frequency signal. Experimental results show that the measurement range reaches 1-9.5 GHz, and the resolution is improved to 15 MHz. Although the above-mentioned research has significantly improved the performance of microwave frequency measurement systems through innovative means such as nonlinear fitting of the mapping between power and frequency, photon-assisted frequency-time mapping technology, and the introduction of down-conversion technology, the Brillouin fiber laser, as the core light source, still faces fundamental technical bottlenecks in many aspects such as tuning accuracy, tuning range, stability, and response speed, which limits its further application in the field of high-resolution microwave frequency testing. Summary of the Invention

[0005] To overcome the problem of low resolution in microwave frequency testing of existing lasers, this invention provides a high-resolution microwave frequency measurement method and apparatus based on a tunable Brillouin fiber laser. The high-resolution measurement of microwave frequencies by the Brillouin fiber laser is achieved by adjusting the refractive index of the medium and the phase of the light wave by changing the voltage applied to the medium on the electric delay line.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A high-resolution microwave frequency measurement method based on a tunable Brillouin fiber laser is proposed. The method involves outputting two narrow-linewidth optical carriers from a laser source. The upper optical carrier, modulated by an unknown signal intensity, is used as pump light input to a Brillouin resonator containing an electro-delay line to excite the Brillouin. The lower optical carrier, modulated by a signal output from a vector network analyzer, serves as probe light. The probe light is selectively amplified after interacting with the Brillouin gain. Simultaneously, the voltage applied to the medium in the electro-delay line within the Brillouin resonator is changed to adjust the refractive index of the medium and the phase of the light wave. This phase change can be used to precisely delay the optical signal, achieving step-by-step tuning of the laser frequency, thereby enabling high-resolution microwave frequency measurement.

[0008] Furthermore, the high-resolution microwave frequency measurement is achieved by changing the delay Δt of the electric delay line to alter the free spectral range ΔFSR of the Brillouin resonator, thereby selectively amplifying the probe signal and realizing the measurement of the frequency signal under test.

[0009] A high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser includes a single-mode pump source, first-fourth fiber couplers, first and second polarization controllers, a first intensity modulator, a second intensity modulator, an optical isolator, first and second erbium-doped fiber amplifiers, an optical circulator, an electric delay line, a single-mode fiber, first and second voltage sources, a signal generator, a spectrometer, a photodetector, and a vector network analyzer.

[0010] The single-mode pump source is connected to the first input port a of the first fiber coupler. After being split by the first fiber coupler, the pump light, used to excite stimulated Brillouin scattering, is output from the first output port b of the first fiber coupler. This pump light is then connected to the a terminal of the second intensity modulator via a first erbium-doped fiber amplifier and a second polarization controller. The b terminal of the second intensity modulator is connected to a first voltage source. The signal generator receives a frequency f through the third input port c of the second intensity modulator. unk The unknown signal, the pump light output from the d end of the second intensity modulator is amplified by the second erbium-doped fiber amplifier and enters the first input end a of the optical circulator, and then enters the single-mode fiber through the first output end b of the optical circulator to excite stimulated Brillouin scattering; the optical circulator, single-mode fiber, second optical coupler, third optical coupler and electric delay line are connected in sequence to form a Brillouin resonant cavity.

[0011] The light output from the second output port c of the first fiber coupler is used as probe light. After passing through the first polarization controller, it enters the first input port a of the first intensity modulator. The second voltage source is connected to the second input port b of the first intensity modulator for carrier suppression. The vector network analyzer emits a frequency f. RFThe frequency sweep signal is frequency swept and modulated through the third input port c connected to the first intensity modulator. The detection signal is output through the first output port d of the first intensity modulator, passes through the optical isolator, and then enters the single-mode fiber through the first output port b of the second fiber coupler.

[0012] Furthermore, the single-mode pump light is split into two laser beams by the first fiber coupler, namely the pump light and the probe light. After the pump light excites the Brillouin, the Stokes light enters the second output port b of the optical circulator and is then output from the third output port c of the optical circulator. The Stokes light runs multiple times in the Brillouin resonant cavity, passes through the electric delay line, and enters the third optical coupler. The third fiber coupler splits the resonant signal into a first laser and a second laser. The first laser is injected into the Brillouin resonant cavity clockwise through the first output port b of the third fiber coupler for multiple resonances. The second laser enters the fourth fiber coupler through the second output port c of the third fiber coupler. The fourth fiber coupler splits the second laser into two lasers. One laser is connected to the spectrometer through the first output port b of the fourth fiber coupler, and the other laser is input to the photodetector through the second output port c of the fourth fiber coupler. The signal after photoelectric conversion by the photodetector is input to the vector network analyzer to measure the amplitude-frequency response, which is used to characterize the high-resolution microwave frequency measurement of the tunable Brillouin fiber laser.

[0013] Furthermore, the splitting ratios of the first, second, and fourth fiber couplers are all 50%:50%, and the splitting ratio of the third fiber coupler is 99%:1%. The first output end b of the third fiber coupler is a 99% port. The length of the single-mode fiber is 1 km, and the delay range of the motorized delay line is 0–1500 ps with a delay accuracy of 50 fs.

[0014] Furthermore, after the modulation signal is emitted from the second output terminal c of the first optical fiber coupler, it passes sequentially through the first polarization controller, the first intensity modulator, and the optical isolator, and then enters the optical annular cavity from the first output terminal b of the second optical coupler to form a tunable Brillouin fiber laser. The Brillouin laser is output from the second output terminal c of the third optical coupler.

[0015] Furthermore, the free spectral range (FSR) of the Brillouin resonator is expressed by the following formula:

[0016]

[0017] Where c = 3.0 × 10 8 m / s represents the speed of light in a vacuum; L represents the cavity length of the optical ring resonator; n = 1.468 is the effective refractive index of the optical fiber.

[0018] Furthermore, the position of the Brillouin gain can be adjusted by changing the voltage applied to the medium in the electric delay line to regulate the refractive index of the medium and the phase of the light wave, as expressed by the following formula:

[0019] Depend on have to

[0020] Will Substituting the above From

[0021] right By integrating both sides simultaneously, we can obtain...

[0022] When L = 1 km, substituting the above... Therefore, t = 4.8 × 10 -6 s;

[0023] Let t = 4.8 × 10 -6 Substituting s into the above Therefore, ΔFSR = -4.3 × 10 10 Δt.

[0024] Where V represents the speed of light in the medium, t represents the time it takes for light to travel one revolution in the medium, ΔFSR represents the change in the free spectral range, and Δt represents the delay of the electro-delay line; when L = 1 km and the delay of the electro-delay line Δt = 1 ps, the change in the free spectral range ΔFSR = -4.3 × 10⁻⁶ ps. -2 Hz.

[0025] In summary, the invention has the following effects:

[0026] This invention discloses a high-resolution microwave frequency measurement method and apparatus based on a tunable Brillouin fiber laser. It proposes to change the propagation time of the optical signal in the cavity by using an electric delay line, thereby changing the refractive index of the medium and the phase of the light wave, and thus changing the frequency response of the resonant cavity. Experimental studies show that the laser frequency can be controlled to shift in 100kHz increments, achieving high-resolution microwave frequency measurement. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate examples consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0028] Figure 1 This is a schematic diagram illustrating the structure of a high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser, as provided in this invention.

[0029] Figure 2This is a schematic diagram of the structure of a high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser connected to a spectrometer, as provided in this invention example.

[0030] Figure 3 This diagram illustrates the high-resolution characteristics of the output laser center frequency of a high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser, as provided in this invention.

[0031] Figure 1 In the middle: 1-Single-mode pump light source, 2A-First fiber coupler, 2B-Second fiber coupler, 2C-Third fiber coupler, 2D-Fourth fiber coupler, 3A-First polarization controller, 3B-Second polarization controller, 4-First intensity modulator, 5-Second intensity modulator, 6-Optical isolator, 7A-First erbium-doped fiber amplifier, 7B-Second erbium-doped fiber amplifier, 8-Optical circulator, 9-Electrically operated delay line, 10-Single-mode fiber, 11A-First voltage source, 11B-Second voltage source, 12-Signal generator, 13-Spectrometer, 14-Photodetector, 15-Vector network analyzer. Detailed Implementation

[0032] To more intuitively demonstrate the objectives, features, and advantages of this invention, the technical solution of this invention will now be described in detail with reference to specific embodiments.

[0033] The following is in conjunction with the appendix Figures 1 to 3 Specific examples of the present invention will be described in detail below.

[0034] In one embodiment, such as Figure 1 As shown, the single-mode pump light source 1 is connected to the first input port a of the first fiber coupler 2A. After being split by the first fiber coupler 2A, the pump light used to excite stimulated Brillouin scattering is output from the first output port b of the first fiber coupler 2A. This pump light is then connected to the a end of the second intensity modulator 5 via the first erbium-doped fiber amplifier 7A and the second polarization controller 3B. The b end of the second intensity modulator 5 is connected to the first voltage source 11A. The signal generator 12 receives a frequency f through the third input port c of the second intensity modulator 5. unk The unknown signal, the pump light output from the d end of the second intensity modulator 5 is amplified by the second erbium-doped fiber amplifier 7B and enters the first input end a of the optical circulator 8, and then enters the single-mode fiber 10 through the first output end b of the optical circulator 8 to excite stimulated Brillouin scattering.

[0035] The light output from the second output port c of the first fiber coupler 2A is used as probe light. After passing through the first polarization controller 3A, it enters the first input port a of the first intensity modulator 4. The second voltage source 11B is connected to the second input port b of the first intensity modulator 4 for carrier suppression. The vector network analyzer 15 emits a frequency of f. RF The frequency sweep signal is frequency swept and modulated through the third input port c connected to the first intensity modulator 4. The detection signal is output through the first output port d of the first intensity modulator 4, passes through the optical isolator 6, and then enters the single-mode fiber 10 through the first output port b of the second fiber coupler 2B.

[0036] The Brillouin resonator is composed of an optical circulator 8, a single-mode fiber 10, a second fiber coupler 2B, a third fiber coupler 2C, and an electro-optic delay line 9 connected sequentially. The single-mode pump light is split into two laser beams by the first fiber coupler 2A: the pump light and the probe light. After the pump light excites the Brillouin, the Stokes beam enters the second output port b of the optical circulator 8 and is then output from the third output port c. The Stokes beam travels multiple times within the Brillouin resonator, passes through the electro-optic delay line 9, and enters the third fiber coupler 2C. The third fiber coupler 2C splits the resonant signal into a first laser beam and a second laser beam. The first laser beam is injected clockwise into the Brillouin resonator through the first output port b of the third fiber coupler 2C for multiple resonances. The second laser beam enters the fourth fiber coupler 2D through the second output terminal c of the third fiber coupler 2C. The fourth fiber coupler 2D splits the second laser beam into two laser beams. One laser beam is connected to the spectrometer through the first output terminal b of the fourth fiber coupler 2D, and the other laser beam is input to the photodetector 14 through the second output terminal c of the fourth fiber coupler 2D. The signal after photoelectric conversion by the photodetector 14 is input to the vector network analyzer 15. The amplitude-frequency response is measured to characterize the high-resolution microwave frequency measurement of the tunable narrow-linewidth Brillouin fiber laser.

[0037] Based on the above examples, in a preferred embodiment, the splitting ratio of the first fiber coupler 2A, the second fiber coupler 2B, and the fourth fiber coupler 2D is 50%:50%, the splitting ratio of the third fiber coupler 2C is 99%:1%, wherein the first output end b of the third fiber coupler 2C is the 99% port, the length of the single-mode fiber 10 is 1km, and the delay range of the motorized delay line 9 is 0 to 1500ps with a delay accuracy of 50fs.

[0038] Furthermore, after the modulation signal is emitted from the second output terminal c of the first fiber coupler 2A, it passes sequentially through the first polarization controller 3A, the first intensity modulator 4, and the optical isolator 6, and then enters the optical circulator 8 from the first output terminal b of the second fiber coupler 2B to form a tunable Brillouin fiber laser. The Brillouin laser is output from the second output terminal c of the third fiber coupler 2C.

[0039] Furthermore, the free spectral range (FSR) of the Brillouin resonator is expressed by the following formula:

[0040]

[0041] Where c = 3.0 × 10 8 m / s represents the speed of light in a vacuum; L represents the cavity length of the Brillouin resonator; n = 1.468 is the effective refractive index of the optical fiber.

[0042] In a specific example, the b-end of the fourth fiber coupler 2D described in this invention can be connected to a spectrometer 13. The spectrometer 13 can then be used to measure the wavelength and power of the output laser. Figure 2 It can be seen that the maximum output power of the Brillouin fine-tuned fiber laser based on the electro-optic effect provided in this embodiment of the invention is as follows. In this example, the gain of the first erbium-doped fiber amplifier 7A is adjusted to 16 dBm, and the high gain is used as the energy to suppress the second intensity modulator 5. At the same time, the gain of the second erbium-doped fiber amplifier 7B, which is used to excite the stimulated Brillouin effect, is adjusted to 20 dBm. In this example, the first voltage source 11A is adjusted to 7.1V. Figure 2 It can be seen that the pump light under the Brillouin effect is effectively suppressed, and it is clear that the output Brillouin laser has a significant frequency shift compared to the pump light, i.e., a Brillouin frequency shift, with a shift amount f. B Defined as f B =(v A / c)v P , where v A where c is the speed of sound in the medium, and v is the speed of light in a vacuum. P f is the frequency of the pump light. B At a wavelength of 1550 nm, the frequency is approximately 10.737 GHz. The double-peak spacing in the figure is twice the frequency of the signal generator 12 receiving the second intensity modulator 5, a typical characteristic of the Brillouin effect. The figure shows that the output Brillouin laser has a signal-to-noise ratio of 74 dB, indicating that the high-resolution microwave frequency measurement system based on a tunable Brillouin fiber laser has high signal quality and stronger anti-interference capability.

[0043] Furthermore, the position of the Brillouin gain is adjusted by changing the voltage applied to the medium in the electric delay line 9 to regulate the refractive index of the medium and the phase of the light wave, as expressed by the following formula:

[0044] Depend on have to

[0045] Will Substituting the above From

[0046] right By integrating both sides simultaneously, we can obtain...

[0047] When L = 1 km, substituting the above... Therefore, t = 4.8 × 10 -6 s;

[0048] Let t = 4.8 × 10 -6 Substituting s into the above Therefore, ΔFSR = -4.3 × 10 10 Δt.

[0049] Where V represents the speed of light in the medium, t represents the time it takes for light to travel one revolution in the medium, ΔFSR represents the change in the free spectral range, and Δt represents the delay of the electro-delay line 9; when L = 1 km and the delay of the electro-delay line 9 Δt = 1 ps, the change in the free spectral range ΔFSR = -4.3 × 10⁻⁶ -2 Hz.

[0050] Therefore, when the center frequency is 10 GHz, and the delay Δt = 1 ps for the electro-delay line 9, the change in the free spectral range ΔFSR = -2.2 kHz. In this example, the theoretical values ​​for a 1 ps delay of the electro-delay line at center frequencies of 10 GHz, 12.5 GHz, 15 GHz, 17.5 GHz, and 20 GHz are approximately 2.2 kHz, 2.7 kHz, 3.3 kHz, 4.0 kHz, and 4.3 kHz, respectively. Figure 3 To perform 100kHz resolution tests on five different center frequencies (10GHz, 12.5GHz, 15GHz, 17.5GHz, and 20GHz), the motor delay line 9 was adjusted to introduce a precise phase delay, thereby adjusting its output frequency to match the frequency of the signal under test. This achieved selective amplification of the frequency signal under test, ultimately achieving a resolution of approximately 100kHz while maintaining a wide frequency measurement range.

Claims

1. A high-resolution microwave frequency measurement method based on a tunable Brillouin fiber laser, characterized in that, The laser source outputs two narrow-linewidth optical carriers, one upper and one lower. The upper optical carrier is modulated by an unknown signal intensity and used as pump light to excite the Brillouin in the Brillouin resonator containing the electric delay line (9). The lower optical carrier is modulated by the signal output by the vector network analyzer (15) and used as probe light. The probe light is selectively amplified after interacting with the Brillouin gain. At the same time, the voltage applied to the medium in the electric delay line (9) in the Brillouin resonator is changed to adjust the refractive index of the medium and the phase of the light wave. This phase change can be used to accurately delay the optical signal and achieve step-by-step tuning of the laser frequency, thereby performing high-resolution microwave frequency measurement.

2. The high-resolution microwave frequency measurement method based on a tunable Brillouin fiber laser according to claim 1, characterized in that, The high-resolution microwave frequency measurement is achieved by changing the delay Δt of the electric delay line (9) to change the free spectral range ΔFSR of the Brillouin resonator, thereby selectively amplifying the detection signal and realizing the measurement of the frequency signal to be measured.

3. A high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser, used to implement the method described in claim 1 or 2, characterized in that, Includes a single-mode pump light source (1), first-fourth fiber couplers, first and second polarization controllers, first intensity modulator (4), second intensity modulator (5), optical isolator (6), first and second erbium-doped fiber amplifiers, optical circulator (8), electric delay line (9), single-mode fiber (10), first and second voltage sources, signal generator (12), spectrometer (13), photodetector (14), and vector network analyzer (15); The single-mode pump light source (1) is connected to the first input port a of the first fiber coupler (2A). After being split by the first fiber coupler (2A), the pump light is output from the first output port b of the first fiber coupler (2A) as the excitation of stimulated Brillouin scattering. It is then connected to the a end of the second intensity modulator (5) through the first erbium-doped fiber amplifier (7A) and the second polarization controller (3B). The b end of the second intensity modulator (5) is connected to the first voltage source (11A). The signal generator (12) inputs a frequency f through the third input port c of the second intensity modulator (5). unk The unknown signal, the dual-tone pump light output from the d end of the second intensity modulator (5) is amplified by the second erbium-doped fiber amplifier (7B) and then enters the first input end a of the optical circulator (8), and then enters the single-mode fiber (10) through the first output end b of the optical circulator (8) to excite stimulated Brillouin scattering; the optical circulator (8), the single-mode fiber (10), the second optical coupler (2B), the third optical coupler (2C) and the electric delay line (9) are connected in sequence to form a Brillouin resonant cavity; The light output from the second output port c of the first fiber coupler (2A) is used as probe light. After passing through the first polarization controller (3A), it enters the first input port a of the first intensity modulator (4). The second voltage source (11B) is connected to the second input port b of the first intensity modulator (4) for carrier suppression. The vector network analyzer (15) emits a frequency of f. RF The frequency sweep signal is frequency swept and modulated through the third input port c connected to the first intensity modulator (4). The detection signal is output through the first output port d of the first intensity modulator (4), passes through the optical isolator (6), and then enters the single-mode fiber (10) through the first output port b of the second fiber coupler (2B).

4. The high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser according to claim 3, characterized in that, The single-mode pump light (1) is split into two laser beams by the first optical coupler (2A), namely the pump light and the probe light. After the pump light excites the Brillouin, the Stokes light enters the second output port b of the optical circulator (8) and is then output from the third output port c of the optical circulator (8). The Stokes light circulates multiple times in the Brillouin resonator and enters the third fiber coupler (2C) through the electro-delay line (9). The third fiber coupler (2C) splits the resonant signal into the first laser and the second laser. The first laser is injected into the Brillouin resonator clockwise through the first output port b of the third fiber coupler (2C) for multiple resonances. The second laser beam enters the fourth fiber coupler (2D) through the second output terminal c of the third fiber coupler (2C). The fourth fiber coupler (2D) splits the second laser beam into two laser beams. One laser beam is connected to the spectrometer (13) through the first output terminal b of the fourth fiber coupler (2D), and the other laser beam is input to the photodetector (14) through the second output terminal c of the fourth fiber coupler (2D). The signal after photoelectric conversion by the photodetector (14) is input to the vector network analyzer (15). The amplitude-frequency response is measured to characterize the high-resolution microwave frequency measurement of the tunable Brillouin fiber laser.

5. A high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser according to claim 4, characterized in that, The splitting ratios of the first fiber coupler (2A), the second fiber coupler (2B), and the fourth fiber coupler (2D) are all 50%:50%, and the splitting ratio of the third fiber coupler (2C) is 99%:1%. The first output end b of the third fiber coupler (2C) is the 99% port. The length of the single-mode fiber (10) is 1 km, and the delay range of the motorized delay line (9) is 0 to 1500 ps, ​​with a delay accuracy of 50 fs.

6. A high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser according to any one of claims 3-5, characterized in that, The free spectral range (FSR) of the Brillouin resonator is expressed by the following formula: Where c = 3.0 × 10 8 m / s represents the speed of light in a vacuum; L represents the cavity length of the optical ring resonator; n = 1.468 is the effective refractive index of the optical fiber.

7. A high-resolution microwave frequency measurement device based on a tunable Brillouin fiber laser according to claim 6, characterized in that, The adjustment of the refractive index of the medium and the phase of the light wave by changing the voltage applied to the medium in the electric delay line (9), thereby adjusting the position of the Brillouin gain, is expressed by the following formula: Depend on have to Will Substituting the above From right By integrating both sides simultaneously, we can obtain... When L = 1 km, substituting the above... Therefore, t = 4.8 × 10 -6 s; Let t = 4.8 × 10 -6 Substituting s into the above Therefore, ΔFSR = -4.3 × 10 10 Δt; Where V represents the speed of light in the medium, t represents the time it takes for light to travel one revolution in the medium, ΔFSR represents the change in the free spectral range, and Δt represents the delay of the electro-delay line (9); when L = 1 km and the delay of the electro-delay line (9) Δt = 1 ps, the change in the free spectral range ΔFSR = -4.3 × 10⁻⁶ -2 Hz.

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