NONLINEAR GAIN AND THE SPECTRAL OUTPUT OF SHORT-EXTERNAL-CAVITY 1.3 MU-M INGAASP SEMICONDUCTOR DIODE-LASERS

The effect of nonlinear gain on the steady-state spectral output of 1. 3 mum InGaAsP semiconductor diode lasers was investigated by measuring the spectral output of lasers that were operated in a short external cavity (SXC). For the SXC lasers, an increase in the powers in both th e long- and short-wavelength modes that are adjacent to the resonant m ode (i.e., the mode that is resonantly enhanced by the SXC and hence l ases strongly) was observed for output-power levels greater-than-or-eq ual-to 5 mW. These results suggest the presence of a symmetric-nonline ar-gain mechanism. Calculations that include a symmetric-nonlinear-gai n mechanism correctly predict the observed trends in the evolution of the power in the longitudinal modes of an SXC laser with increasing ou tput power. It is concluded therefore, that for strong single-mode osc illation and output powers above almost-equal-to 5 mW, such as found f or an SXC laser operated well-above threshold, that the effects of a s ymmetric-nonlinear-gain mechanism are observable in the spectral outpu t.