Measurement Of The Absolute Distance Inside A Tunable All-fiber Laser By Self-mixing Technique

Self-mixing distance measurement technology has been widely concerned by researchers in recent years by virtue of its compact structure,simple optical path,no external optical beam splitting device and many other advantages.Existing conventional semiconductor laser self-mixing distance measurement technology is subject to the linear tuning range of the laser output wavelength and power fluctuations,greatly restricting the measurement resolution,accuracy,and limit the use of occasions.This paper presents an all-fiber laser self-mixing distance measurement system with optical fiber technology.It has the advantages of flexible optical path arrangement,high spatial resolution,anti-electromagnetic interference and interconnection with communication network,which can avoid the above drawbacks of the traditional laser self-mixing distance measurement.Theoretical study,we combined the three mirror cavity theory,optical amplification equation and boundary condition equation,established a fiber laser self-mixing distance measurement system theory model.The principle of self-mixing distance measurement of DBR fiber laser and fiber ring laser is studied in detail,and the correspondence between laser cavity distance and self-mixing signal fluctuation frequency is deduced.In the experimental study,the all-fiber self-mixing distance measurement system with different tuning mechanisms and different cavity structure are designed and built.The characteristics of all-fiber self-mixing distance measurement system under different cavity structure are studied emphatically.At the same time,the overall performance of the laser self-mixing absolute distance sensing system is further optimized and improved by optimizing the system environment,detecting circuit noise,fiber characteristic parameters,exit beam parameters and optical feedback intensity depth.The innovation of this paper mainly includes:1.The theoretical model of laser self-mixing absolute distance sensing based on tunable DBR fiber laser and fiber ring laser is established.The theoretical model of laser self-mixing sensor with different cavity structure is discussed and analyzed in depth.2.Based on the fiber grating wavelength tuning mechanism,a set of all-fiber DBR fiber laser self-mixing distance measurement system is built,the absolute distance of the external cavity is measured,and the experimental results are analyzed.3.Combining the tunable FFP filter,a self-mixing distance measurement system of all-fiber ring laser is designed,and the distance measurement experiment of different target is carried out.Also,the measurement accuracy and range of the all-fiber ring laser self-mixing distance measurement system are studied and analyzed.