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Recently, self-mixing interferometry (SMI) is a reliable method that has been applied to measuring displacements, absolute distances, and velocities of remote targets. Evaluating the optical feedback factor C and the linewidth enhancement factor α is a vital step in calculating laser diode(LD) parameters and in processing SMI signals using phase unwrapping.
In order to measure an external target, it is necessary to determine more accurate C and α, and the studies associated with SMI has been widely developed. But the methods proposed in the preceding studies need some kinds of complicated experiments or more and more calculating time. These methods depend either on relatively high sampling frequencies or on complex data processing in order to achieve higher resolution and so need a great cost. In addition, some of these methods also depend on target waveforms.
We study a novel evaluation method for both the optical feedback factor and the linewidth enhancement factor using a simple investigation on the slopes of phase discontinuity distribution. First of all, we evaluate the optical feedback factor and the linewidth enhancement factor based on the effects that the slope of phase discontinuity distribution has on the prediction of them. Next, we improve measurement accuracy using the cumulative effect of discontinuity distribution in selecting the discontinuities.
The proposed method can be implemented as a straightforward algorithm both in evaluating target vibration by phase unwrapping and in calculating LD parameters. And it is valid for any waveforms in the C>1 regime. A series of simulations and experiments with a low-cost semiconductor laser are performed for verify the proposed method.
The detail discussion has been published with the title of "Evaluation method for the optical feedback factor and linewidth enhancement factor using phase discontinuities in self-mixing interferometry"(https://doi.org/10.1364/AO.59.000687) in "Applied Optics"(Vol 59,2020,687-693).
