Speckle affected fringe detection based on three envelope extraction for self-mixing displacement measurement

Speckle is an especially relevant issue as far as self-mixing interferometry works onto diffusive targets and for large displacements sensing. This article proposed a new signal processing technique, based on three envelope extraction transition detection algorithm, to correctly extract and processes self-mixing signals corrupted by speckle. The algorithm also discriminates the direction of the target movement for different self-mixing regimes. The validity of the proposed method was demonstrated by means of simulated signals and confirmed by several experimental measurements with envelope variation of a decade in amplitude. The use of this technique effectively removes the need for optical/electro-mechanical component and strict sampling number determination.