Abstract
The optical output power of a laser diode is modulated by the self-mixing effect when the optical beam is back-reflected or back-scattered into the laser cavity by a target. The optical feedback factor C is the most important one that defines the feature of the self-mixing signals (SMSs). And the estimation of C is indispensable for the displacement reconstruction by the phase unwrapping method because it is impossible to reconstruct the displacement with sub-wavelength resolution, provided the exact value of C is unknown. Unfortunately, C is subject to constant change during the measurement and, what is worse; its estimation is usually very time-consuming. This paper studies the feature of a high and low fringe of SMSs in moderate and strong feedback regime and the effect of the feedback factor and the linewidth enhancement factor on the fringes and presents a simple approach to the estimation of C when C > 1.5 based on the behavioral model proposed by Plantier et al. In particular, the novel approach enables fast direct estimation of C because it is based on analytic relations between C and the amplitudes of the high and low peak in SMSs.
Highlights
The self-mixing effect occurred by optical feedback has been widely used during the last three decades for displacement, velocity, distance and flow measurements, for the setup is simple and compact and does not need difficult collimation and, it is very easy to use it
There have been proposed many methods of the estimation of C [1], [6]–[11]. These methods, are limited to a certain feedback level such as a weak or moderate regime and most of them except the method proposed in [6] need numerous samples for the estimation of C, which results in long time of calculation. Such a pity in these methods results mostly from not estimating C based on an analytic relationship between C and the so called interference function which expresses the shape of self-mixing signals (SMSs)
Because our estimation method is based on the analytic relation to C, it is exact enough and very simple, and it will be very useful to the real time and high-speed estimation of C for a low-cost embedded self-mixing sensor with sub-wavelength resolution
Summary
The self-mixing effect occurred by optical feedback has been widely used during the last three decades for displacement, velocity, distance and flow measurements, for the setup is simple and compact and does not need difficult collimation and, it is very easy to use it. These methods, are limited to a certain feedback level such as a weak or moderate regime and most of them except the method proposed in [6] need numerous samples for the estimation of C, which results in long time of calculation Such a pity in these methods results mostly from not estimating C based on an analytic relationship between C and the so called interference function which expresses the shape of SMSs. Many models which describe the self-mixing effect have been presented and the behavioral model in [5] can be applied to all kinds of feedback regimes. Because our estimation method is based on the analytic relation to C, it is exact enough and very simple, and it will be very useful to the real time and high-speed estimation of C for a low-cost embedded self-mixing sensor with sub-wavelength resolution
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