Self-mixing Speckle Active Sensing Theory And Experiment Research Based On Erbium-doped Fiber Ring Laser

Self-mixing speckle theoretical model derived from the laser self-mixing interference, which refers to a portion of light emitted from a laser is reflected or scattered by the external moving roughness object and coupled into the laser cavity. The reentered light mixes with the original light in the laser cavity and changes the output power and spectra of the laser, forming the effect of optical feedback. It can measure the state of moving object by analyzing self-mixing speckle signal. According to coupled into the laser cavity, the light signal mixes with the original light and amplifies cycle by cycle, so the Laser is not only the coherent light but also the sense organ sensing external physical measurements. It is called active sensing. Compared to passive sensing, active sensing has a advantage in signal stability, signal to noise ratio as well as system architecture, testing, etc. Compared to traditional optical speckle detection, self-mixing speckle combines the traditional speckle with the self-mixing interference, only having one optical axis. Self-mixing speckle detection which is simple, compact and easy to adjust is a new developed speckle measurement technique. It is expected to be used in variety of new lasers and to be developed a new generation active sensing technique.This paper focuses on the output wavelength of 1550nm fiber laser for study, referring to ring erbium-doped fiber laser self-mixing speckle model of the active sensing system. First of all, self-mixing speckle signal is numerically simulated on the theory. The self-mixing speckle signals produced by simulation representing different velocities are analyzed by fast Fourier transform (FFT), and the result shows that the mean speckle frequency is linear related with the velocity; Secondly, the experimental model of self-mixing speckle based on an erbium-doped fiber ring (EDFR) laser is presented and the signals of deferent velocities and detecting distances of the dynamic object are obtained. The result shows that the mean speckle frequency is linear related with the velocity by using the spectral analysis, which is agreed with that of the numerical simulation study, also the linear relationship is obtained between spectrum energy density of the self-mixing signal and the detecting distance of the dynamic object; Lastly, based on the model of active sensing system of self-mixing speckle. The system that obtains and processes the self-mixing speckle signal on the real time is founded by using Matlab and LabView mixed programming.