CN-224231082-U - Heterodyne Doppler laser vibration meter based on all-fiber

CN224231082UCN 224231082 UCN224231082 UCN 224231082UCN-224231082-U

Abstract

The utility model discloses a heterodyne Doppler laser vibration meter based on all optical fibers. The vibration meter adopts a double-light-path differential design, and the system divides laser into a measuring light beam and a reference light beam and respectively introduces the measuring light beam and the reference light beam into parallel. The measuring light path emits laser to the object to be measured, and the return signal contains the composite information of the vibration of the object and the systematic error after demodulation. Meanwhile, a closed loop is formed in the reference light path, and the demodulation signal of the reference light path can accurately extract the system error introduced by devices such as a frequency shifter and the like. The signal processing system real-time calculates two paths of demodulation signals, so that homologous errors are eliminated, and pure and real vibration data are obtained. The utility model replaces a complex phase-locked loop through the front-end light path difference, and remarkably improves the measurement precision, stability and environmental adaptability.

Inventors

Ge Yuanxun
ZHU XIN
ZHU WENJUAN

Assignees

南京牧镭激光科技股份有限公司

Dates

Publication Date: 20260512
Application Date: 20250702

Claims (8)

1. A heterodyne doppler laser vibrometer based on all-fiber, comprising: a light source for generating laser light; The beam splitting system is used for splitting the laser into a measuring beam entering a measuring light path and a reference beam entering a reference light path; A measuring light path, in which the measuring light beam is transmitted to the object to be measured via an optical probe and receives the reflected measuring signal light, and the measuring signal light and the local oscillation light beat frequency to generate a measuring beat frequency signal containing vibration information of the object to be measured and error information of a frequency shifter; a reference light path in which signal light and local oscillation light in the reference light beam are directly beat frequency without being reflected by the object to be measured to generate a reference beat frequency signal only containing error information of the frequency shifter; And a signal processing system configured to subtract the reference beat signal from the measured beat signal to cancel the common shifter error information to obtain accurate vibration information of the object under test.
2. The laser vibration measuring instrument according to claim 1, wherein the beam splitting system comprises a first beam splitter, a second beam splitter and a third beam splitter, the laser beam is split into local oscillation light and signal light by the first optical fiber beam splitter, the local oscillation light and the signal light respectively enter the second optical fiber beam splitter and the third optical fiber beam splitter, and after being split into two paths again, one path of the local oscillation light and the signal light enters the measuring light path as measuring light beams, and the other path of the local oscillation light and the signal light enters the reference light path as reference light beams.
3. The laser vibration meter according to claim 2, wherein the first fiber optic beam splitter has a split ratio of 1:99 to 20:80.
4. The laser vibration meter of claim 2, wherein the signal processing system is configured to set different delay compensation amounts to correct the reference beat signal when a distance between the optical probe and the object to be measured changes.
5. The laser vibrometer of claim 1 wherein the measurement optical path and the reference optical path each include a balance detector for receiving the beat signal.
6. The laser vibration meter according to claim 1, wherein the optical probe comprises an indication laser, and the beam of the indication laser and the beam of the measurement signal light are emitted from the optical probe after being combined by a wavelength division multiplexer.
7. The laser vibration meter according to claim 6, wherein a wave plate for changing a polarization state of light is integrated in the optical probe, and the wave plate and the polarization beam splitter together form a circulator structure for guiding a transmission and reception path of the measurement signal light.
8. The laser vibration meter according to claim 1, wherein an adjustable optical attenuator is provided on an optical path for transmitting the local oscillation light in the measuring optical path for adjusting an optical power ratio of the local oscillation light to the measuring signal light.

Description

Heterodyne Doppler laser vibration meter based on all-fiber Technical Field The utility model relates to the technical field of laser measurement, in particular to a heterodyne Doppler laser vibration meter based on all optical fibers. Background The laser Doppler vibration measurement technology is widely applied to a plurality of fields such as industrial detection, aerospace, biomedicine, civil engineering and the like due to the advantages of high measurement precision, wide dynamic range and non-contact measurement. At present, a main-stream laser Doppler vibration meter mostly adopts a coherent heterodyne optical path structure. In this configuration, the frequency accuracy of the frequency-shift modulator (typically an acousto-optic modulator) in the heterodyne optical path is one of the key factors limiting the overall accuracy of the vibration meter. The precision of a crystal oscillator signal source on which a frequency shifter is commonly used in the market depends can only reach the level of 10 to 10 ppb, and the error can be directly introduced into a measurement result, so that the vibration measurement precision is difficult to further improve. In addition, the frequency shift amount is also influenced by the ambient temperature, external vibration and inherent errors of the crystal oscillator, and irregular random fluctuation is shown. To solve this problem, the prior art generally employs a scheme of adding an analog or digital Phase Locked Loop (PLL) at a signal processing end, and tracking and compensating for the variation of the frequency shift amount through an algorithm. However, the effect of the phase-locked loop mechanism is limited by its loop filter design, and when the vibration frequency range of the measured object varies greatly, its locking and tracking performance is degraded, resulting in errors in the final measurement result. Therefore, how to fundamentally eliminate errors introduced by the frequency shifter and improve the accuracy and stability of vibration measurement is a technical problem to be solved in the field. Disclosure of utility model The utility model aims to provide a heterodyne Doppler laser vibration meter based on all optical fibers, which solves the problems in the background art, and comprises the following components: a light source for generating laser light; The beam splitting system is used for splitting the laser into a measuring beam entering a measuring light path and a reference beam entering a reference light path; A measuring light path, in which the measuring light beam is transmitted to the object to be measured via an optical probe and receives the reflected measuring signal light, and the measuring signal light and the local oscillation light beat frequency to generate a measuring beat frequency signal containing vibration information of the object to be measured and error information of a frequency shifter; a reference light path in which signal light and local oscillation light in the reference light beam are directly beat frequency without being reflected by the object to be measured to generate a reference beat frequency signal only containing error information of the frequency shifter; And a signal processing system configured to subtract the reference beat signal from the measured beat signal to cancel the common shifter error information to obtain accurate vibration information of the object under test. Further, the light splitting system comprises a first beam splitter, a second beam splitter and a third beam splitter, the laser is split into local oscillator light and signal light through the first optical fiber beam splitter, the local oscillator light and the signal light respectively enter the second optical fiber beam splitter and the third optical fiber beam splitter, and after being split into two paths again, one path of the laser is used as a measuring light beam to enter a measuring light path, and the other path of the laser is used as a reference light beam to enter a reference light path. Further, the first fiber optic beam splitter has a split ratio of 1:99 to 20:80. Further, the length of the optical fiber in the reference optical path is extended to compensate for the optical path difference between the reference optical path and the measurement optical path. Further, the signal processing system is configured to set different delay compensation amounts to correct the reference beat signal when the distance between the optical probe and the object to be measured is changed. Further, the measuring light path and the reference light path each comprise a balance detector for receiving beat signals. Further, the optical probe comprises an indication laser, and the beam of the indication laser and the beam of the measurement signal light are emitted by the optical probe after being combined by the wavelength division multiplexer. Further, a wave plate for changing the polarization state of light is integrated in the