Ultrawide dual contact strip fabricated quantum cascade lasers with reduced beam divergence angle

Abstract

Power scaling through the broadening of the laser core in Quantum Cascade Lasers can extract greater average power from devices at the cost of mode quality. To improve transverse mode quality for ultrawide (>100 µm) devices, a dual contact strip waveguide geometry is designed and demonstrated, utilizing a reduced top cladding thickness, and modifying the gold electrical epi-side contact to affect mode competition. A 200 µm wide Dual Contact Strip laser emitting at 4.6 µm wavelength is measured with far-field full-width half-maximum of 2.5° in a central single lobe. Relative an identical waveguide without the dual contact strips, peak power was 30% higher and far field was 32% narrower. This demonstrates the ability to achieve fundamental-like far field behavior in very broad quantum cascadel asers while potentially simplifying the fabrication method.