Practical optical gain by an extended Hakki-Paoli method

The revision of the classic Hakki-Paoli method shows that the a priori knowledge of facet reflectivity and confinement factor is not required for measuring optical gain in semiconductor laser and LED emitters. Moreover, a recently proposed new formula for gain as a function of the applied voltage, combined with that method, allows for calculating the relevant parameters of the gain function by the sole sub-threshold spectral data. This avoids the known critical problems issued by instrument resolution on spectral data from the above-threshold domain. Moreover, this last chance allows for complete gain measurement also in degraded devices, when they do no more display any laser threshold, and then for including optical gain among the relevant parameters for monitoring device degradation.