High Resolution Laser Self-Mixing Displacement Sensor Under Large Variation in Optical Feedback and Speckle

Self-Mixing interferometry (SMI) signal characteristics are highly dependent on both the operating optical regime and target surface. In this paper, a method is proposed to overcome some identified limitations of the even power scalable algorithm (EPSA), such as the required operating regime to be weak feedback. In addition, by using the up-sampling techniques, the number of stages involved in the even-power scalable algorithm can be drastically increased without any data acquisition bandwidth modification. Here, 10 successive stages have been successfully implemented to achieve a theoretical resolution of {\lambda } _{\sf 0}/ {\sf 2}^{\sf 13} . It is further shown that the proposed method can handle and process weak, moderate and strong feedback regime as well as speckle affected SMI signals more efficiently. Lastly, FPGA based hardware emulation of EPSA is also done for later embedded implementation of this high-resolution algorithm. FPGA synthesis results show that the designed system can measure maximum target velocity up to 1.18 m/s while consuming total power of 1.4W.