Temperature and current dependence of doppler SNR in a VCSEL based self-mixing sensor

This paper proposes a method for maintaining the maximum signal-to-noise ratio (SNR) of the signal obtained from the self-mixing sensor based on a Vertical-Cavity Surface-Emitting Laser (VCSEL). The SNR of the Doppler self-mixing signal was investigated experimentally as a function of laser driving current and ambient temperature. It was found that the locus of the maximum SNR in the current-temperature space can be well approximated by the simple analytical model based on the temperature behaviour of the VCSELs threshold current. A self-mixing Doppler signal was acquired from the variation in VCSEL junction voltage rather than from a conventional variation in laser optical power to reduce the complexity of the system. It was found that the optimum sensor performance over a wide range of ambient temperatures can be achieved by tuning the laser current according to the proposed model. This enables the sensor to operate without temperature stabilisation making it attractive for mobile applications and applications with limited power supply.