Effect of Linewidth Enhancement Factor on Fringe in a Self Mixing Signal and Improved Estimation of Feedback Factor in Laser Diode
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 <inline formula> <tex math notation="LaTeX"$C$ /tex math>/inline formula> is the most important one that defines the feature of the self mixing signals (SMSs) And the estimation of <inline formula> <tex math notation="LaTeX"$C$ /tex math>/inline formula> 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 <inline formula> <tex math notation="LaTeX"$C$ /tex math>/inline formula> is unknown. Unfortunately, <inline formula> <tex math notation="LaTeX"$C$ /tex math>/inline formula> 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 <inline formula> <tex math notation="LaTeX"$C$ /tex math>/inline formula> when <inline formula> <tex math notation="LaTeX"$C>1.5$ /tex math>/inline formula> based on the behavioral model proposed by Plantier <italic>et al./italic> In particular, the novel approach enables fast direct estimation of <inline formula> <tex math notation="LaTeX"$C$ /tex math>/inline formula> because it is based on analytic relations between <inline formula> <tex math notation="LaTeX"$C$ /tex math>/inline formula> and the amplitudes of the high and low peak in SMSs.
IEEE Access