Multimode VCSELs for self-mixing velocity measurements

In this paper, we present the feasibility of a laser Doppler velocimeter using self-mixing effect in low-cost strongly multimode VCSELs (AlGaAs). The prototype of velocity sensor demonstrates a 20dB signal-to-noise ratio over an amplification bandwidth of 10MHz allowing velocity measurements up to 8.5m.s(-1). The VCSEL-based self-mixing sensor has been characterized at various distances from the target, and with cooperative and non-cooperative surfaces. A characterization of the temperature sensitivity of the VCSEL-based velocimeter results is presented which demonstrates the great stability of the device over an important temperature range. A comparison between results obtained with strongly multimode VCSELs and Fabry-Perot laser diodes in velocimetry applications is achieved. We finally discuss the intrinsic advantages of VCSELs in self-mixing applications as in particular for on-board sensors.