Gain measurements on semiconductor lasers by optical feedback from an external grating cavity

We report on new methods to determine the curvature around maximum of the mode gain curve of homogeneously line-broadened semiconductor lasers, either by measuring the wavelength dependence of threshold current of the laser coupled to an external grating cavity or by measuring the tuning range of the laser versus the amount of optical feedback. We experimentally found the mode gain width and the current-induced peak-gain wavelength shift of a GaAlAs CSP laser to 175 Å and 2.1 Å/ mA, respectively.