Low cost velocity sensor based on the self-mixing effect in a laser diode

In this paper, a low cost velocity sensor based on the self-mixing effect in a laser diode is described. Theory of self-mixing effect in the laser diode is shortly presented. Experimental velocity measurements are presented in order to evaluate the operation of the velocity sensor. In the design, the attention is focused to develop a budget sensor, which frequency response of the detection electronics is up to 85 MHz. This limits the maximum measurable velocity to 27.5 m/s. The total material costs of the velocity sensor were 234 euros. The experimental measurements conducted so far show that the linearity of the developed velocity sensor is at least as good of a mirror moved by a translation stage with velocities ranging from 1.0 to 48.5 mm/s. The velocity of the translation stage was controlled by a computer. When the mirror velocity is lower than 20 mm/s, the maximum relative presision with the mirror velocity is less than 3.5%. When the mirror velocity is higher than 20 mm/s the relative precision with the mirror velocity is below 0.5%. In an additional experiment with a vibrating loudspeaker's membrane, it is also demonstrated that a maximum Doppler frequency is clearly detectable over the noise level at 12.5 MHz.