Self-mixing laser sensor for large displacements: signal recovery in the presence of speckle

Usman Zabit (1) , Olivier Bernal (2) , Thierry Bosch (1)

1 LAAS-OSE - Équipe Optoélectronique pour les Systèmes Embarqués
2 LAAS - Laboratoire d'analyse et d'architecture des systèmes

Laser self-mixing (SM) sensors have been successfully used to measure displacement in the absence of speckle. However, speckle deforms the SM signal rendering it unusable for standard displacement extraction techniques. This article proposes a new signal processing technique, based on tracking the signal envelope, to remedy this problem. Algorithm was successfully employed to measure long-range displacements (25 mm), in the presence of speckle and the lateral movement of the target, both causing severe corruption of the SM signal. It therefore enabled the use of the sensor on non-cooperative targets without the need for sensor positioning and/or alignment. The results have been obtained for SM signals where the envelope amplitude has varied by a factor 28, without a loss of interferometric fringes. The use of this technique effectively removes the need for opto/electro-mechanical components traditionally used to measure long-range displacement in the presence of speckle.

Mots clés: Speckle; displacement measurement; envelope extraction; self-mixing interferometry

Domaines: Optique / photonique

Usman Zabit, Olivier Bernal, Thierry Bosch. Self-mixing laser sensor for large displacements: signal recovery in the presence of speckle. IEEE Sensors Journal, 2013, 13 (2), pp.824-831. ⟨10.1109/JSEN.2012.2227718⟩. ⟨hal-00762287⟩