Improving Laser Feedback Interferometers Robustness Against Speckle Using Multiple Acquisition Schemes

This paper presents recent experimental developments in the field of interferometric sensing for displacement and/or velocity using Laser Feedback Interferometry (LFI). We demonstrate that the different acquisition schemes of LFI sensors (external photodiode and laser junction voltage) are subject to different speckle patterns and as a consequence the signal fading induced does not affect both signals simultaneously. We show that this effect largely depends on the laser to target distance. Since the speckle fading leads to incapacity to fringe detection or uncertainty in the computation of the Doppler frequency, the simultaneous acquisition of both laser voltage and in-package photodiode is a major advantage of LFI with regards to a large range of sensing applications.