Phase compensation technique in diode-laser self-mixing interferometry

A novel phase compensation technique has been developed for diode laser self-mixing intereferometry. A reference reflector is added between the diode laser and the target. By refering to the phase corresponding to the reference reflector, the phase measurement error owing to the wavelength fluctuation of the laser diode can be reduced. Experimental results of measuring a piezoelectric controlled silicon wafer show that a diode-laser self-mixing interferometer can measure displacement with error less than 12 nanometers peak-to-peak, without temperiture control of the diode laser.