Two cavities mirror model of laser diodes (LDs) based on spatial dependent rate equations

Dynamical behaviors of laser diodes with Fabry-Perot cavity including internal cavity and strong external cavity feedback are studied. Usually, the reflectivity of front cavity or external cavity is only designed; the accurate values are not known. The spatial dependent rate equations are analyzed by method of feature lines; the invariant quantities are found. The original differential equations are reduced to a set of nonlinear algebraic equation systems employed by the approach of Newton iteration. A full parameter adjustable model is established; results are obtained in condition of different reflectivity of cavity mirrors not only symmetric reflectivity. Through measurement of power and slope efficiency of LD chips based on GaN, the gain distribution can be derived from the tests. And the reflectivity of front cavity can be characterized by experimental measurements of slope efficiency. Through power measurement, the reflectivity of output mirror is about 6.6% while the design value is 6.5%. The measurement results agree well with the simulations demonstrating the correctness of the established model. And this indirect method provides a novel measurement of reflectivity of front cavity or external cavity in condition of strong feedback.