CHARACTERISTICS OF A GRATING-EXTERNAL-CAVITY SEMICONDUCTOR-LASER CONTAINING INTRACAVITY PRISM BEAM EXPANDERS

A grating tuned external cavity semiconductor laser incorporating a gradient-index rod lens and a pair of intracavity silicon prism beam expanders was constructed using a configuration aimed at simultaneously achieving the following objectives: the ability to operate at any external cavity longitudinal mode without tuning gaps caused by residual resonances of the laser diode cavity, stable feedback coupling between the diode and external cavities, narrow optical linewidth, and a high degree of external cavity longitudinal sidemode suppression. The results are summarized as follows. Complete wavelength coverage was achieved from 1255 to 1335 nm. The tolerance of the feedback coupling to angular grating misalignment was increased by about sixfold in comparison with a conventional microscope-objective cavity. A linewidth of 100 kHz or less was observed. Single longitudinal mode operation was repeatably achieved across a 60-nm wavelength range with a sidemode suppression ratio of 70 dB using grafting rotation as the sole adjustment.