CN101540468A - Method and devices for optically generating high-frequency microwave signals - Google Patents

Abstract

The invention relates to a method and device for optically generating high-frequency microwave signals. In the method of the present invention, the two ends of the high-gain polarization-maintaining fiber are respectively engraved with Bragg fiber gratings with matching wavelengths and the same period, and the polarization-state orthogonality is generated by utilizing the different refractive indices of the core layer of the high-gain polarization-maintaining fiber along the fast axis and the slow axis. The dual-wavelength laser, by adjusting the polarization controller so that it has the same polarization state after passing through the polarizer, obtains high-frequency microwave signals. The device for realizing the method includes a laser pump source with a wavelength of 980nm, a 980nm/1550nm optical wavelength division multiplexer, a polarization controller, a polarizer, a photodetector, a high-gain polarization-maintaining fiber, and the two ends of the high-gain polarization-maintaining fiber are respectively Fiber Bragg gratings engraved with matching wavelengths and the same period. The invention can generate high-quality and high-frequency microwave signals, has the advantages of simple structure, easy realization, low cost and the like, and is suitable for research and application in microwave communication, ROF and other fields.

Description

A method and device for optically generating high-frequency microwave signals

technical field

The invention belongs to the technical field of microwave photonics, and relates to a dual-wavelength single longitudinal mode distributed Bragg reflection (DBR) fiber laser based on a high-gain polarization-maintaining fiber and a method for generating high-frequency microwave signals realized by using the laser, as well as realizing the method The means of the method.

Background technique

At present, the operating frequencies of most wireless communication systems are concentrated below 5GHz, but with the rapid growth of the amount of information in human society, the existing communication frequencies are becoming more and more congested, so it will become inevitable to develop higher frequency communication bands. Traditional microwave signal generation and processing are based on electrical methods. However, due to the limitation of electronic bottlenecks, with the increase of microwave signal frequency, its generation and processing are facing severe challenges in terms of technology and cost. The emergence of microwave photonics technology provides a simple and low-cost new way for the generation and processing of high-frequency microwave signals. Microwave photonics is an emerging discipline integrating microwave technology and photonics. It mainly studies optical devices working at microwave frequencies and their applications in microwave and optical systems. The reason why microwave photonics has developed rapidly in recent years is precisely because the main task and value of this discipline is to use photon technology to realize some functions in microwave systems that are difficult to achieve with microwave technology, and to use microwave technology to improve the performance of optical communication network systems. performance. At present, the use of optical technology to realize microwave signal generation is one of the hot spots in the research of microwave photonics.

Dual-wavelength single-longitudinal-mode lasers are an important method for optically generating microwave signals, but most of the existing dual-wavelength single-longitudinal-mode lasers are based on specially designed fiber gratings with extremely narrow transmission bands (less than 1pm). Such a fiber grating is not only very complicated to design and manufacture, but generally can only be used to generate microwave signals below 40 GHz, and it is very difficult to generate microwave signals higher than 40 GHz. In addition, because the cavity length of such a fiber laser is generally long, it is easily disturbed by the external environment and the generated microwave signal is not stable enough.

Contents of the invention

The purpose of the present invention is exactly for the deficiencies in the prior art, provide a kind of method that utilizes the high-frequency microwave signal generation of the dual-wavelength single longitudinal mode distributed Bragg reflection (DBR) fiber laser based on high-gain polarization-maintaining optical fiber, provide and realize this method at the same time installation.

The inventive method comprises the following steps:

Step (1) The pump light output by the laser pump source with a wavelength of 980nm is input to the resonant cavity of the fiber laser through a 980nm/1550nm wavelength division multiplexer; Both ends of the fiber are engraved with fiber Bragg gratings with matching wavelengths and the same period; the absorption rate of the high-gain polarization-maintaining fiber for 980nm wavelength laser is 55-65dB/m, and the core layer of the polarization-maintaining fiber is along the fast axis direction The refractive index is n _x , and the refractive index along the slow axis is n _y , so the two fiber Bragg gratings inscribed on the core layers at both ends of the polarization-maintaining fiber show two reflection peaks with orthogonal polarization states, and the two Fiber Bragg gratings have the same period Λ, and therefore have the same peak reflection wavelength, and their peak reflection wavelengths along the fast and slow axes of the high-gain polarization-maintaining fiber are λ _x and λ _y , respectively

λ _x = 2n _x Λ

λ _y = 2n _y Λ,

Such a pair of wavelength-matched polarization-maintaining fiber gratings are used as the cavity mirror of the DBR fiber laser. After the pump source is turned on, the signals of the 980nm/1550nm wavelength division multiplexer will output the orthogonal polarization states with wavelengths of λ _x and λ _y respectively. Dual-wavelength laser with a wavelength interval of Δλ

Δλ=2BΛ

Where B is the refractive index difference between the fast axis and the slow axis of the polarization maintaining fiber, B=|n _{x -ny} |.

In order to ensure that each wavelength of the dual-wavelength laser is a single longitudinal mode output, it is necessary to design the parameters of the two fiber Bragg gratings as laser cavity mirrors. The fiber Bragg grating close to the 980nm/1550nm wavelength division multiplexer is a low-reflectivity fiber Bragg grating with a reflectivity of 50-70%, and the length is _L1 ; the other fiber Bragg grating is a high-reflectivity Bragg grating with a reflectivity greater than 99%. Fiber Bragg grating, the length is L ₂ ; the distance between two fiber Bragg gratings is L ₀ , the cavity length of this DBR laser is L, L=L ₀ +(L ₁ +L ₂ )/2, then the adjacent two of the output laser The interval Δv _k between longitudinal modes is

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="c"\; filenames="A20091009786800101.png"\; state="\{\{state\}\}">c</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; nL</span>}}$

Among them, c is the speed of light in vacuum, n is the effective refractive index in the resonator, and L is the length of the resonator (2nL is the optical path that the laser propagates in the resonator for one week). When the low-reflectivity fiber Bragg grating is used, the reflection wavelength bandwidth |λ _x | of the deceleration axis and the reflection wavelength bandwidth of the slow axis |λ _y | satisfy

$<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}$

$<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="y"\; filenames="A20091009786800101.png"\; state="\{\{state\}\}">y</figure-callout></span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}$

When , the laser output wavelengths of the two polarization states of the DBR fiber laser are in the working state of single longitudinal mode oscillation;

In step (2), the generated dual-wavelength laser passes through the polarization controller and the polarizer in turn, and the polarization controller is adjusted so that the two laser wavelengths with orthogonal polarization states have the same polarization state at the output end of the polarizer. The detector receives and obtains the high-frequency microwave signal generated by the double-wavelength laser beat frequency, and its frequency is f _RF

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c\&Delta;\&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; cB\&Lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Where λ is the average wavelength of the dual-wavelength laser output, $\mathrm{\&lambda;}=\frac{{\mathrm{\&lambda;}}_x+{\mathrm{\&lambda;}}_{\mathrm{the\; <figure-callout\; id="2"\; label="y"\; filenames="A20091009786800101.png"\; state="\{\{state\}\}">y</figure-callout>}}}{2}.$

The frequency of the generated microwave signal is mainly determined by the birefringence B of the fiber and the period Λ of the fiber Bragg grating (note that the laser wavelength λ here is determined by the reflection wavelength of the fiber Bragg grating, that is, the period Λ of the fiber Bragg grating). For the most common polarization-maintaining fiber, its birefringence is about 3.5×10 ^-4 . If a fiber grating (corresponding to a grating period of about 535nm) is fabricated to work in the communication wavelength window of 1550nm, the frequency of the generated microwave signal can reach 46.7GHz.

In step (3), high-frequency microwave signals of different frequencies can be obtained by selecting polarization-maintaining fibers with different birefringence, and the birefringence of polarization-maintaining fibers is related to the radial and axial stresses on the fibers. By applying radial or axial stress, the frequency of the generated microwave signal can be adjusted.

The device for realizing the above method includes a laser pump source with a wavelength of 980nm, a 980nm/1550nm optical wavelength division multiplexer, a polarization controller, a polarizer, a photodetector, a high-gain polarization-maintaining fiber, and the two ends of the high-gain polarization-maintaining fiber are respectively Fiber Bragg gratings engraved with matching wavelengths and the same period, among which the fiber Bragg grating close to the 980nm/1550nm wavelength division multiplexer is a low reflectivity fiber Bragg grating with a reflectivity of 50-70%, and the other fiber Bragg grating is a reflectivity More than 99% high reflectivity fiber Bragg grating. The pump end of the 980nm/1550nm optical wavelength division multiplexer is connected to the laser pump source with a wavelength of 980nm, the common end is connected to the low-reflectivity fiber Bragg grating optically, the signal end is connected to the input end of the polarization controller, and the output of the polarization controller The terminal is connected with the input terminal of the polarizer, and the output terminal of the polarizer is connected with the photodetector. The signal end of the 980nm/1550nm optical wavelength division multiplexer is used as the output port of the fiber laser.

The invention can generate microwave signals with high quality and high frequency (up to 40 GHz or more), has the advantages of simple structure, easy realization, low cost, etc., and is suitable for research and application in microwave communication, ROF and other fields.

Description of drawings

Fig. 1 is a structural representation of the present invention

specific implementation plan

As shown in Figure 1, a device for optically generating high-frequency microwave signals includes a laser pump source 1 with a wavelength of 980nm, a 980nm/1550nm optical wavelength division multiplexer 2, a polarization controller 6, a polarizer 7, and a photodetector 8 1. High-gain polarization-maintaining fiber 4, the two ends of the high-gain polarization-maintaining fiber 4 are respectively engraved with fiber Bragg gratings 3 and 5 with matching wavelengths and the same period, wherein the fiber Bragg grating 3 close to the 980nm/1550nm wavelength division multiplexer 2 is A fiber Bragg grating with a low reflectivity of 50-70% reflectivity, and another fiber Bragg grating 5 is a fiber Bragg grating with a high reflectivity greater than 99% reflectivity. The pump end of the 980nm/1550nm optical wavelength division multiplexer 2 is connected to the laser pump source 1 with a wavelength of 980nm, the common end is optically connected to the low-reflectivity fiber Bragg grating 3, the signal end is connected to the input end of the polarization controller 6, and the polarization The output terminal of the controller 6 is connected with the input terminal of the polarizer 7 , and the output terminal of the polarizer 7 is connected with the photodetector 8 . The signal end of the 980nm/1550nm optical wavelength division multiplexer 2 is used as the output port of the fiber laser.

The specific high-frequency microwave signal generation method includes the following steps:

Step (1) The pump light output by the laser pump source with a wavelength of 980nm is input to the resonant cavity of the fiber laser through a 980nm/1550nm wavelength division multiplexer; Both ends of the fiber are engraved with fiber Bragg gratings with matching wavelengths and the same period; the absorption rate of the high-gain polarization-maintaining fiber for 980nm wavelength laser is 55-65dB/m, and the core layer of the polarization-maintaining fiber is along the fast axis direction The refractive index is n _x , and the refractive index along the slow axis is n _y , so the two fiber Bragg gratings inscribed on the core layers at both ends of the polarization-maintaining fiber show two reflection peaks with orthogonal polarization states, and the two Fiber Bragg gratings have the same period Λ, and therefore have the same peak reflection wavelength, and their peak reflection wavelengths along the fast and slow axes of the high-gain polarization-maintaining fiber are λ _x and λ _y , respectively

λ _x = 2n _x Λ

λ _y = 2n _y Λ,

Such a pair of wavelength-matched polarization-maintaining fiber gratings are used as the cavity mirror of the DBR fiber laser. After the pump source is turned on, the polarization states with output wavelengths of λ _x and λ _y are orthogonal to each other at the signal end of the 980nm/1550nm wavelength division multiplexer. The dual-wavelength laser with a wavelength interval of Δλ

Δλ=2BΛ

Where B is the refractive index difference between the fast axis and the slow axis of the polarization maintaining fiber, B=|n _{x -ny} |.

In order to ensure that each wavelength of the dual-wavelength laser is a single longitudinal mode output, it is necessary to design the parameters of the two fiber Bragg gratings as laser cavity mirrors. The fiber Bragg grating close to the 980nm/1550nm wavelength division multiplexer is a low-reflectivity fiber Bragg grating with a reflectivity of 50-70%, and the length is _L1 ; the other fiber Bragg grating is a high-reflectivity Bragg grating with a reflectivity greater than 99%. Fiber Bragg grating, the length is L ₂ ; the distance between two fiber Bragg gratings is L ₀ , the cavity length of this DBR laser is L, L=L ₀ +(L ₁ +L ₂ )/2, then the adjacent two of the output laser The interval Δv _k between longitudinal modes is

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="c"\; filenames="A20091009786800101.png"\; state="\{\{state\}\}">c</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; nL</span>}}$

Among them, c is the speed of light in vacuum, n is the effective refractive index in the resonator, and L is the length of the resonator (2nL is the optical path that the laser propagates in the resonator for one week). When the low-reflectivity fiber Bragg grating is used, the reflection wavelength bandwidth |λ _x | of the deceleration axis and the reflection wavelength bandwidth of the slow axis |λ _y | satisfy

$<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}$

$<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="y"\; filenames="A20091009786800101.png"\; state="\{\{state\}\}">y</figure-callout></span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}$

When , the laser output wavelengths of the two polarization states of the DBR fiber laser are in the working state of single longitudinal mode oscillation;

In step (2), the generated dual-wavelength laser passes through the polarization controller and the polarizer in turn, and the polarization controller is adjusted so that the two laser wavelengths with orthogonal polarization states have the same polarization state at the output end of the polarizer. The detector receives and obtains the high-frequency microwave signal generated by the double-wavelength laser beat frequency, and its frequency is f _RF

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c\&Delta;\&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; cB\&Lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Where λ is the average wavelength of the dual-wavelength laser output, $\mathrm{\&lambda;}=\frac{{\mathrm{\&lambda;}}_x+{\mathrm{\&lambda;}}_{\mathrm{the\; <figure-callout\; id="2"\; label="y"\; filenames="A20091009786800101.png"\; state="\{\{state\}\}">y</figure-callout>}}}{2}.$

The frequency of the generated microwave signal is mainly determined by the birefringence B of the fiber and the period Λ of the fiber Bragg grating (note that the laser wavelength λ here is determined by the reflection wavelength of the fiber Bragg grating, that is, the period Λ of the fiber Bragg grating). For the most common polarization-maintaining fiber, its birefringence is about 3.5×10 ^-4 . If a fiber grating (corresponding to a grating period of about 535nm) is fabricated to work in the communication wavelength window of 1550nm, the frequency of the generated microwave signal can reach 46.7GHz.

In step (3), high-frequency microwave signals of different frequencies can be obtained by selecting polarization-maintaining fibers with different birefringence, and the birefringence of polarization-maintaining fibers is related to the radial and axial stresses on the fibers. By applying radial or axial stress, the frequency of the generated microwave signal can be adjusted.

Claims (2)

1. A method for optically generating high-frequency microwave signals, characterized in that the method comprises the following steps: Step (1) The pump light output by the laser pump source with a wavelength of 980nm is input to the resonant cavity of the fiber laser through a 980nm/1550nm wavelength division multiplexer; Both ends of the fiber are engraved with fiber Bragg gratings with matching wavelengths and the same period. The high-gain polarization-maintaining fiber has an absorption rate of 55-65dB/m for 980nm wavelength laser light, which is close to that of the 980nm/1550nm wavelength division multiplexer. The Fiber Bragg Grating is a low-reflectivity Fiber Bragg Grating with a reflectivity of 50-70%, and the length is L ₁ . The other Fiber Bragg Grating is a high-reflectivity Fiber Bragg Grating with a reflectivity greater than 99%, and the length is L ₂ . The distance between the fiber Bragg gratings is L ₀ , and the two fiber Bragg gratings exhibit the same two reflection peaks with orthogonal polarization states. The peak reflection wavelengths along the fast axis of the high-gain polarization-maintaining fiber are λ _x , and The peak reflection wavelengths of the slow axis of polarization-maintaining fibers are λ _y , λ _x =2n _x Λ, n _x is the refractive index of the core layer of the polarization-maintaining fiber along the fast axis direction, λ _y =2ny _Λ , _ny is the refractive index of the core layer of the polarization-maintaining fiber along the slow axis direction, Λ is the period of two fiber Bragg gratings; Turn on the pump source, and output dual-wavelength lasers with orthogonal polarization states at wavelengths λ _x and λ _y at the signal end of the 980nm/1550nm wavelength division multiplexer, and the wavelength interval is Δλ Δλ=2BΛ Where B is the refractive index difference between the fast axis and the slow axis of the polarization-maintaining fiber core, B=|n _{x -ny} |, The interval Δv _k between two adjacent longitudinal modes of the output laser is $\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; nL</span>}}$ Where c is the speed of light in vacuum, n is the effective refractive index in the resonant cavity, L is the length of the resonant cavity, L=L ₀ +(L ₁ +L ₂ )/2; The bandwidth of the reflection wavelength |λ _x | and the bandwidth of the reflection wavelength of the slow axis |λ _y | satisfy $<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}$ $<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}$ When , the two laser output wavelengths with orthogonal polarization states are in the working state of single longitudinal mode oscillation; In step (2), the generated dual-wavelength laser passes through the polarization controller and the polarizer in turn, and the polarization controller is adjusted so that the two laser wavelengths with orthogonal polarization states have the same polarization state at the output end of the polarizer. The detector receives and obtains the high-frequency microwave signal generated by the double-wavelength laser beat frequency, and its frequency is f _RF ${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c\&Delta;\&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; cB\&Lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$ Where λ is the average wavelength of the dual-wavelength laser output, $\mathrm{\&lambda;}=\frac{{\mathrm{\&lambda;}}_x+{\mathrm{\&lambda;}}_{\mathrm{the\; y}}}{2};$ Step (3) By selecting polarization-maintaining fibers with different birefringence, high-frequency microwave signals of different frequencies can be obtained, and radial or axial stress is applied to the resonator cavity of the fiber laser, that is, the frequency of the generated microwave signals can be adjusted. 2. The device for generating high-frequency microwave signals that realizes the method as claimed in claim 1, comprising a laser pump source with a wavelength of 980nm, a 980nm/1550nm optical wavelength division multiplexer, a polarization controller, a polarizer, a photodetector, a high The gain polarization maintaining fiber is characterized in that: the two ends of the high gain polarization maintaining fiber are respectively engraved with fiber Bragg gratings with matching wavelength and the same period, and the fiber Bragg grating close to the 980nm/1550nm wavelength division multiplexer has a reflectivity of 50 ~70% low-reflectivity fiber Bragg grating, another fiber Bragg grating is a high-reflectivity fiber Bragg grating with a reflectivity greater than 99%, two fiber Bragg gratings and a high-gain polarization-maintaining fiber in between constitute the resonant cavity of the fiber laser ; The pump end of the 980nm/1550nm optical wavelength division multiplexer is connected to the laser pump source with a wavelength of 980nm, the common end is connected to the optical fiber Bragg grating with low reflectivity, the signal end is connected to the input end of the polarization controller, and the polarization controller's The output end is connected with the input end of the polarizer, and the output end of the polarizer is connected with the photodetector.

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