SPECTRAL LINEWIDTH REDUCTION IN PARTLY GAIN-COUPLED 1.55-MU-M STRAINED MULTIPLE-QUANTUM-WELL DISTRIBUTED-FEEDBACK LASER

The effective linewidth enhancement factor alpha(eff) and the spectral linewidth DELTAupsilon are reported for the first time for a partly gain-coupled distributed feedback laser with a gain corrugation in a strained multiple quantum-well active region emitting at 1.55 mum wavelength. The alpha(eff) value is estimated to be as low as 1 and is independent of the laser cavity length L, while a decrease in the linewidth-power product DELTAupsilonP(o) with L has been observed, with a measured linewidth of 2 MHz at 10 mW optical output power for 300-mum-long devices. The experimental results demonstrate that a small alpha(eff) is obtained due to the strain and the gain coupling effects, while further reduction of the spectral linewidth with L is the result of longitudinal index coupling effects.