Anti reflection coatings in semiconductor lasers: effects on power emission and external cavity lasing

Abstract

Parameters controlling light generation and emission in semiconductor lasers were analyzed. Effects of facet reflectivity on laser emission and the overall power dissipation were studied. It is shown with typical values that, optimized conditions of facet coating can reduce the laser power dissipation by several hundred milliwatts for optical output levels on the order of 10 mw. A mathematical model was developed for external cavity lasing of semiconductor lasers. Effects of threshold shift and changes in slope efficiency for external cavity operation, as reported in the literature, are explained by our model. Our model also explains reported observations of residual Fabry-Pérot modes of oscillation in external cavity operation. It is shown that anti reflection coating plays the most significant role in decreasing the threshold current in external cavity mode compared to that of Fabry Pérot lasing. It is estimated that a coating reflectivity of 10 -5 with an external grating efficiency of 50% can result in a shift of threshold current by more than 50 mA. The effects of grating efficiency and facet reflectivity on increasing the window of feasible external cavity laser operation with reduced competition from residual modes were studied.

Mid-infrared external cavity lasing through suppression of Fabry-Perot oscillation

“…4 In a recent article, we presented a theoretical investigation on the effect of ECL system parameters on the quality of external cavity lasing. 9 In this paper, we describe a systematic analysis of a mid-infrared external cavity laser at 2.4 μm and give the range limiting factors for wavelength tuning. Our analysis shows the competitive nature of natural FP modes of emission with external cavity lasing, and also addresses the issue of achieving single mode emission through FP mode suppression.…”