Self-mixing Interference in Fiber Ring Laser: Application for Displacement and Velocity Measurement

This paper investigates the self-mixing interference in erbium-doped fiber ring laser (FRL) and its application for displacement and velocity sensing. Self-mixing interference in FRL with a parallel dual-channel is proposed. The characteristics of the intensities of the laser in the dual channels with optical feedback are theoretically deduced. The experimental results show a good agreement with the theory, and indicate that self-mixing interference with a parallel dual-channel is an efficient approach for simultaneous multi-channel displacement measurement. Moreover, a new method for velocity detecting based on laser speckle optical feedback injected erbium-doped FRL is presented. Random speckle feedback causes changes in both intensity and frequency of the laser. A dynamic speckled-modulated laser output is observed and processed by FFT analysis. A linear dependant relationship between the velocity of an object and the mean speckle frequency defined as the ratio of the number of fluctuations is obtained, which indicates that speckle optical feedback injected erbium-doped FRL is an effective approach for velocity detecting.