Research On Frequency-shifted Laser Feedback Interference Displacement Sensor With All-fiber Structure

By comparison with traditional methods of the interference measurement,laser feedback interferometry has become one of the metrology methods for detecting weak signals due to its high sensitivity,compact structure,and no complicated alignment.However,the lowfrequency noise in the existing laser feedback interference system severely limits the application of the technology.Therefore,we propose an all-fiber laser feedback interference displacement sensor based on frequency-shift technology.The acousto-optic modulator effectively solves the interference of low-frequency noises to the signal,which in turn realizes the sensing of the small displacement of non-cooperative targets,the smallest measurable displacement is tens of picometers.Meanwhile,by establishing the related theoretical model of the detection sensitivity in the laser feedback frequency-shift interference displacement sensing system and the corresponding experimental research,the real-time and nondestructive measurement of the fluorescence lifetime of the gain media in different fiber lasers,which is an important parameter affecting the system detection sensitivity,was successfully realized.The innovations of this paper mainly include the following parts:1.Combining the three-mirror cavity theoretical model and the L-K rate equation,a tunable frequency-shift laser feedback interference displacement sensing model was established,and the influence of different parameters on the detection sensitivity of the system was explored through simulation.2.Based on the correlation between the fluorescence lifetime of the gain media in the laser and its relaxation oscillation characteristics,the real-time and non-destructive measurement of the fluorescence lifetime of the gain media in different fiber lasers were realized,and the error sources affecting the measurement accuracy of the system were analyzed.3.On the basis of the traditional laser self-mixing interferometer,by introducing the acousto-optic modulation technology,we propose a laser feedback interference displacement sensor based on the frequency-shift effect.The scheme effectively avoids the interference of the low-frequency signals,and realizes the measurement of small displacement of the target under weak feedback conditions.4.Most of the existing laser feedback interferometers combined with frequency shift technology have complex optical path,and the path cannot be bent,changed,and blocked.In this paper,the optical path of the all-fiber structure is adopted to improve the applicability of the sensing system in the complex,narrow and other harsh environments.