Optical gain in laser diodes with null reflectivity

Optical gain measurement is extended to chips designed for external cavity lasers, where facet reflectivity is intentionally kept null, which prevents from any application of the Hakki-Paoli method. The new method is first shown to be consistent with the standard methods, by applying it to a chip with Fabry-Perot resonances and comparing the results of the new and the Hakki-Paoli method. The validated new method is then applied to the non-reflecting cavity of a tunable laser diode based on external cavity.