Displacement Measurements Using a Self-Mixing Laser Diode Under Moderate Feedback

Self-mixing sensor for real-time measurement of harmonic and arbitrary displacements

“…The Phase Unwrapping Method (PUM) has two principal steps [3]. The first one leads to the rough estimation of the phase x F (t).…”

“…In fact, if it weren't for the phase jumps occurring for every λ/2 target displacement, the SM signal would remain indicative of the target movement. This idea has thus been exploited to propose SM displacement measurement techniques with better precision, such as [3][4][5]. Note that these techniques thus follow the SM signal shape as opposed to the technique presented in [9] that uses local linearization of SM signal shape while compensating possible fringe-loss of the SM signal.…”

“…The variations in the optical output power of the laser diode P(t) caused by this optical feedback can be written as [3]:…”

“…So, by using simple fringe counting, a sensor would ensure λ/2 precision by detecting all fringes. However, various algorithms exist that allow even better measurement precision [3][4][5].…”

A new method for the acquisition of arterial pulse wave using self-mixing interferometry

“…The FCA typically recovers the signals in three steps Fig.5: first the transitions on the SMI signal are detected (typically applying a derivative process and comparing the result with a threshold value), then, a discrete step of λ/2 is set at every transition according to the positive or negative value of the transition and finally a smoothing process may be applied over the reconstructed signal. If higher resolution is required, other types of reconstruction processes may be applied such as the ones discussed in [24,25]. The FCA is highly efficient in the measurement of homogeneous surfaces.…”