Optical-feedback semiconductor laser Michelson interferometer for displacement measurements with directional discrimination

An optical-feedback semiconductor laser Michelson interferometer (OSMI) is presented for measuring microscopic linear displacements without ambiguity in the direction of motion. The two waves from the interferometer arms, one from the reference mirror and the other from the reflecting moving target, are fed back into the lasing medium (lambda = 830 nm), causing variations in the laser output power. We model the OSMI into an equivalent Fabry-Perot resonator and derive the dependence of the output power (and the junction voltage) on the path difference between the two interferometer arms. Numeri cal and experimental results consistently show that the laser output power varies periodically (period, lambda /2) with path difference. The output po wer variation exhibits an asymmetric behavior with the direction of motion, which is used to measure, at subwavelength resolution, the displacement ve ctor (both amplitude and direction) of the moving sample. Two samples are c onsidered in the experiments: (i) a piezoelectric transducer and (ii) an au dio speaker. (C) 2001 Optical Society of America.