Fundamental Transverse Mode Selection (TMS#0) of Broad Area Semiconductor Lasers with Integrated Twice-Retracted 4f Set-Up and Film-Waveguide Lens

Figure 1

Former concept (4f set-up “retracted once”): sketch of a BAL laser with integrated 4f set-up in the configuration with two orthogonal branches. The spatial filter to support the fundamental mode is made up of a nontilted and several tilted/oblique flanks/segments, the latter intended to refract and reflect unwanted rays out of the resonator and to reflect the supported rays back into the resonator. Fresnel reflectivity of ≈31% at the semiconductor-air interface is used. In the bottom part of the figure there is an SEM (scanning electron microscope) image of the facet with filter of an actual TMS#0-BAL sample.