Internal Transverse Mode Selection in Folded-resonator Antimonide Broad Area Lasers

Abstract

Antimonide broad area lasers (BAL) have been prepared that include a Fourier-optical 4f spatial frequency filter set-up as a transverse mode selector (TMS). The resonator is folded about the Fourier-transform mirror with its focal length f equal to the resonator branch length d (i. e. half resonator length). The resonator length 2d is 1.65 mm and the whole resonator is gain section as well as part of the TMS. The approach to integrate BAL and TMS monolithically is verified; the experiments are typically performed around 85 K temperature. The concept can be employed for any edge emitting BAL, but we used an AlGaInAsSb-based laser design with mid-infrared emission wavelength around 2 μm, where lasers with higher output powers within the fundamental transverse mode are still needed for many applications. Above a certain operating temperature (≈140 K) a double-hysteresis emerges in the output-power versus pump-current characteristics. This as well as the free spectral range strongly suggest that both resonator branches act together as one entity.