CN-121995393-A - Doppler velocity measurement system based on whispering gallery microcavity Brillouin laser

CN121995393ACN 121995393 ACN121995393 ACN 121995393ACN-121995393-A

Abstract

The invention discloses a Doppler velocity measurement system based on whispering gallery microcavity Brillouin laser, and belongs to the technical field of laser detection. The system comprises a whispering gallery microcavity Brillouin laser realization unit, a light selection and amplification unit and a Doppler velocity measurement unit. The method comprises the steps of inputting pumping light into a high-quality factor whispering gallery microcavity through evanescent coupling, exciting a cascade stimulated Brillouin scattering process to generate narrow linewidth cascade Brillouin laser, screening out laser of a specific order by using a tunable filter, amplifying the laser by an erbium-doped fiber amplifier to serve as a detection light source, re-injecting feedback light carrying Doppler frequency shift after the detection light is reflected by a moving target into the microcavity, generating self-mixing interference beat frequency signals with the laser in the cavity, and finally demodulating the target speed through photoelectric detection and spectrum analysis. The invention utilizes the microcavity enhancement effect and the cascade Brillouin process to compress the narrow linewidth and combines the self-mixing interference structure to realize the laser Doppler velocity measurement with high resolution, high signal-to-noise ratio, compact structure and strong robustness.

Inventors

YU QI
ZHANG JIAN
BAI YONGTAO
XU ZHENXIANG
LV LIANG

Assignees

安徽大学

Dates

Publication Date: 20260508
Application Date: 20260209

Claims (10)

1. Doppler velocity measurement system based on whispering gallery microcavity Brillouin laser, which is characterized by comprising: The whispering gallery microcavity Brillouin laser implementation unit is used for inputting pumping light into the whispering gallery microcavity through evanescent coupling to excite stimulated Brillouin scattering so as to generate cascade Brillouin laser; The optical selection and amplification unit is connected to the whispering gallery microcavity Brillouin laser realization unit and is used for screening out Brillouin laser with a specific order from cascade Brillouin laser and amplifying power so as to obtain a detection light source; The Doppler speed measuring unit is connected to the light selecting and amplifying unit and is used for transmitting the detection light source to the moving target and receiving Doppler frequency shift-carrying feedback light reflected by the moving target, re-injecting the feedback light into the whispering gallery microcavity to enable the feedback light and Brillouin laser oscillated in the cavity to generate beat frequency signals, and detecting and demodulating the beat frequency signals to acquire speed information of the moving target.
2. The Doppler velocity measurement system based on the whispering gallery microcavity Brillouin laser according to claim 1, wherein the whispering gallery microcavity Brillouin laser realizing unit comprises a pumping light source, an evanescent coupling device, an isolator, a polarization controller and a first circulator; the pump light source is used for emitting pump light; the isolator is arranged in the light-emitting light path of the pumping light source and is used for isolating back scattered light; The polarization controller is arranged behind the isolator and used for adjusting the polarization state of the pump light; the first circulator is arranged behind the polarization controller and is used for transmitting the pumping light to the evanescent coupling device and receiving the Brillouin laser which is generated by the acoustic wall microcavity and is transmitted back; the evanescent coupling device is used for coupling pump light from the circulator to the whispering gallery microcavity through an evanescent field.
3. The whispering gallery microcavity brillouin laser-based Doppler velocity measurement system according to claim 2, wherein the evanescent coupling device comprises a micro-nano optical fiber and a whispering gallery microsphere cavity; the micro-nano optical fiber is formed by drawing a single mode fiber and is used for carrying out evanescent coupling with the whispering gallery microsphere cavity; the whispering gallery microsphere cavity is formed by firing the tail end of a heated single-mode fiber.
4. The whispering gallery microcavity brillouin laser-based Doppler velocimetry system according to claim 1, wherein the optical selection and amplification unit comprises a tunable filter and an erbium-doped fiber amplifier; The tunable filter is connected to the whispering gallery microcavity Brillouin laser realization unit and is used for receiving the cascade Brillouin laser and filtering out the Brillouin laser with a specific order from the cascade Brillouin laser by adjusting the central wavelength and bandwidth of the cascade Brillouin laser; The erbium-doped fiber amplifier is connected to the tunable filter for power amplifying the filtered brillouin laser of a specific order.
5. The whispering gallery microcavity brillouin laser based doppler velocimetry system according to claim 4, wherein the transmission wavelength of the tunable filter is controlled by a tuning mechanism, the center wavelength of which is aligned with the wavelength of the third-order brillouin laser in the cascade brillouin laser, and the filtering bandwidth of which is smaller than the wavelength interval of the adjacent-order brillouin laser.
6. The whispering gallery microcavity brillouin laser-based doppler velocimetry system according to claim 1, wherein the doppler velocimetry unit comprises a coupler, a collimating lens, a second circulator, a photodetector and a spectrum analyzer; The input end of the coupler is connected to the light selection and amplification unit and is used for receiving amplified Brillouin laser and feedback light; the collimating lens is used for collimating and emitting the laser from the coupler to the moving target; the second circulator is arranged between the whispering gallery microcavity and the collimating lens and is used for conducting detection light to enter the collimating lens and guiding feedback light from the moving target to the whispering gallery microcavity; The photoelectric detector is used for converting the received optical signal into an electric signal; the spectrum analyzer is connected to the photoelectric detector and is used for performing spectrum analysis on the electric signal to obtain a beat frequency signal.
7. The whispering gallery microcavity brillouin laser-based Doppler velocity measurement system according to claim 6, wherein the feedback light is re-injected into the whispering gallery microcavity, self-mixing interference occurs between the feedback light and the brillouin laser oscillating in the cavity, and the frequency of the beat signal detected by the photodetector corresponds to the Doppler frequency shift.
8. The whispering gallery microcavity brillouin laser-based Doppler velocimetry system according to claim 7, wherein the working principle of generating cascade brillouin laser by the whispering gallery microcavity includes: When the pump light coupled into the whispering gallery microcavity resonates with the microcavity optical mode, the enhanced optical field in the cavity generates Stokes photons through the electrostriction effect, and the resonance enhancement of the microcavity enables the Stokes photons to find the optical mode matched with the phase, so that coherent Brillouin laser output is formed; As the pump power increases, the first order stokes light acts as a new pump light source, exciting the second order stimulated brillouin process, and so on; And if resonance modes resonate in each step of stimulated gain region, cascading Brillouin laser output is formed, and each high-order Stokes light is generated by taking the previous step of Brillouin laser as a pump in the cascading process.
9. The whispering gallery microcavity brillouin laser-based doppler velocimetry system according to claim 8, wherein the continuous narrowing of the microcavity laser linewidth in step-by-step excitation is achieved based on the high quality factor inherent to the whispering gallery microcavity: Wherein, the For the linewidth of the brillouin laser, And Is stokes damping of the acoustic and optical modes, And The heat sub-numbers of the mechanical and optical fields, For pumping the laser linewidth, qtot represents the total quality factor of the microcavity, qext represents the external cavity quality factor of the microcavity, pout represents the laser power, Which represents the planck's constant and, Indicating the laser angular frequency.
10. The whispering gallery microcavity brillouin laser based doppler velocimetry system according to claim 8, wherein the velocity information is demodulated by the following relationship: where n is the refractive index of the medium, v is the velocity of the laser at the spot of the moving object, For the angle between the velocity and the direction of propagation of the brillouin laser, Is the brillouin laser wavelength.

Description

Doppler velocity measurement system based on whispering gallery microcavity Brillouin laser Technical Field The invention belongs to the technical field of laser detection, and particularly relates to a Doppler velocity measurement system based on whispering gallery microcavity Brillouin laser. Background The laser Doppler velocity measurement technology is used as a high-precision non-contact motion sensing means and has important application value in the fields of fluid mechanics, aerospace, industrial automation, biomedical imaging and the like. The technology realizes speed calculation by detecting a coherent beat signal between reflected or scattered light of a moving target and reference light, and the measurement accuracy and detection limit of the technology are mainly limited by the coherence of a laser light source and the detection sensitivity of a system. Specifically, the minimum speed variation which can be resolved by the system is directly related to the line width of the light source, the narrower the line width is, the better the speed resolution capability is, and the effective detection distance of the system is limited by the coherence length of laser. The traditional laser Doppler velocimetry system mainly relies on a space optical element to construct an interference light path. Although the system can realize high-precision measurement, the system has inherent limitations of complex structure, huge volume, difficult optical alignment debugging, sensitivity to environmental vibration and temperature change and the like, and is difficult to meet the requirements of modern industry on portability, robustness and long-term stability. In recent years, an all-fiber speed measurement scheme becomes a research hot spot due to the advantages of compact structure, strong anti-interference capability and the like. The scheme adopts an optical fiber device to construct a sensing link, and a distributed feedback laser or a distributed Bragg reflection laser is commonly used as a light source. However, typical linewidths of such lasers are on the order of megahertz, and the limited coherence length limits the effective detection distance of the system, and the broad spectral linewidth also limits the speed resolution of the system. In addition, the existing scheme still depends on an external reference light path and a balance detector, and the improvement of the system integration level and the sensitivity faces the bottleneck. Disclosure of Invention In order to solve the defects of the laser Doppler velocity measurement system in the prior art in the aspects of integration level, sensitivity and functional integrity, the invention provides a Doppler velocity measurement system based on whispering gallery microcavity Brillouin laser. The speed measuring system aims at solving the problems of complex structure, poor robustness and low resolution of the existing speed measuring system. In order to achieve the above object, the present invention provides a doppler velocity measurement system based on whispering gallery microcavity brillouin laser, comprising: The whispering gallery microcavity Brillouin laser implementation unit is used for inputting pumping light into the whispering gallery microcavity through evanescent coupling to excite stimulated Brillouin scattering so as to generate cascade Brillouin laser; The optical selection and amplification unit is connected to the whispering gallery microcavity Brillouin laser realization unit and is used for screening out Brillouin laser with a specific order from cascade Brillouin laser and amplifying power so as to obtain a detection light source; The Doppler speed measuring unit is connected to the light selecting and amplifying unit and is used for transmitting the detection light source to the moving target and receiving Doppler frequency shift-carrying feedback light reflected by the moving target, re-injecting the feedback light into the whispering gallery microcavity to enable the feedback light and Brillouin laser oscillated in the cavity to generate beat frequency signals, and detecting and demodulating the beat frequency signals to acquire speed information of the moving target. Preferably, the whispering gallery microcavity Brillouin laser realization unit comprises a pumping light source, an evanescent coupling device, an isolator, a polarization controller and a first circulator; the pump light source is used for emitting pump light; the isolator is arranged in the light-emitting light path of the pumping light source and is used for isolating back scattered light; The polarization controller is arranged behind the isolator and used for adjusting the polarization state of the pump light; the first circulator is arranged behind the polarization controller and is used for transmitting the pumping light to the evanescent coupling device and receiving the Brillouin laser which is generated by the acoustic wall microcavity and is transmitted