Influence of ambient temperature on the performance of VCSEL based self-mixing sensors: Flow measurements

Contactless sensing that makes use of the self-mixing technique offers a compact, low cost solution that can be used for a range of measurement tasks. In this paper we demonstrate a method for maintaining the maximum signal-to-noise ratio (SNR) of the signal obtained from the self-mixing flow sensor based on a Vertical-Cavity Surface-Emitting Laser (VCSEL). It was found that the locus of maximum SNR in the current-temperature space can be well approximated by a simple analytical model related to the temperature behaviour of the VCSEL threshold current. The optimum sensor performance is achieved by tuning the laser current according to the proposed model thus enabling the sensor to operate without temperature stabilisation over a wide temperature range.