Laser Doppler Velocimetry based on self-mixing effect in vertical-cavity surface-emitting lasers

In this paper, a laser Doppler velocimeter is developed base on self-mixing effect in a vertical-cavity surface-emitting laser (VCSEL). The monitor photodiode mounted on the back facet of the VCSEL acts as a transducer and it generates the self-mixing current signal. Measuring the power spectrum of Doppler frequency of this signal, the target velocity component projected along the optical axis of the laser beam is calculated. The experiment results show that the accuracy of velocity measurement is high with relative error of Doppler frequency lower than 2%, while for the velocity higher than 70 mm/s. The selection of one polarization state in the detection light beam by inserting a polarizer can enhance of several dB the responsivity of VCSEL to external optical injection.