Self-mixing Speckle And Orthogonal Polarization Speckle Sensing Research Based On Erbium-doped Fiber Laser

Laser self-mixing speckle interference combines the traditional speckle with the self-mixing interference, refers to light emitted from a laser reflected or scattered by the external roughness object surface and coupled into the laser cavity, mixed with the light in the cavity, forming the effect of optical feedback. Analyzing the self-mixing speckle signal produced in the cavity of the laser, one can determine the state of the object. In addition, reference and signal beams are introduced in the process of orthogonal polarization speckle interference research. The outside information detected by signal beam is taken back to the laser and mixed with the reference beam. Then direction information about object can be obtained by analyzing the mixed orthogonally polarized signals. Fiber laser sensor is a new speckle measurement technology developed in recent years, whose optical structure is simpler, more compact, and easier to adjust, comparing with the traditional speckle interference. It is expected to develop to be a new generation of active sensing technology, and gear to the developing era of internet of things.First of all, this paper focuses on erbium-doped fiber laser for study, analysis ring erbium-doped fiber laser self-mixing speckle sensor system applied to liquid surface speed sensing. Expression of self-mixing speckle modulation laser output is deduced.Secondly, for the rough object direction sensor, an orthogonally polarized speckle sensor model is constructed. Orthogonal speckle signal in this system is theoretically studied and numerically simulated using MATLAB. Relationship between orthogonal polarization speckle phase and object direction is proposed. Ring erbium-doped fiber laser orthogonal polarization speckle sensor model is constituted by being introduced to all-fiber system.Finally, set up two experiment systems. One is about liquid speed sensor. The self-mixing speckle signals in different speed levels are collected, and linear relationship between the liquid velocity and processing result is obtained by three signals processing methods. The reliability and accuracy of different methods are compared. Required polarization degree signal beam and reference beam can be obtained in another system by adding polarization control components on first system. Signal and reference beams are mixed and return to the laser cavity, then laser sequential amplify. Orthogonal polarization speckle signal is detected by polarization components detector. Orthogonal polarization speckle signal phase and object moving direction is analyzed.