Self-mixing Interferometry Based on Quadrature Demodulation Technique for Displacement Measurement

A new, to the best of our knowledge, method for the measurement of the micro-displacement of a remote target based on the laser diode self-mixing interferometry(LDSMI) is presented. Quadrature demodulation technique is introduced to improve the measurement accuracy. Phase modulation of the laser beam is obtained by an electro-optic modulator (EOM) in the external cavity. Detection of the target's displacement can be easily achieved by sampling the interference signal at those times which satisfied certain conditions. The major advantage of the technique is that it does not involve any complicated calculation and insensitive to the sampling error. Experimental results show that the proposed method can effectively improve the displacement measurement accuracy of the LDSMI system to a few nanometers.