Directional Emission and Universal Far-Field Behavior from Semiconductor Lasers with Limacon-Shaped Microcavity

Abstract

We report experimental demonstration of directional light emission from limaçon-shaped microcavity semiconductor lasers. Quantum cascade lasers (QCLs) emitting at (\lambda \approx 10 \mu m) are used as a model system. Both ray optics and wave simulations show that for deformations in the range (0.37< \epsilon <0.43), these microcavities support high quality-factor whispering gallerylike modes while having a directional far-field profile with a beam divergence (\theta \approx 30°) in the plane of the cavity. The measured far-field profiles are in good agreement with simulations. While the measured spectra show a transition from whispering gallerylike modes to a more complex mode structure at higher pumping currents, the far field is insensitive to the pumping current demonstrating the predicted “universal far-field behavior” of this class of chaotic resonators. Due to their relatively high quality factor, our microcavity lasers display reduced threshold current densities compared to conventional ridge lasers with millimeter-long cavities. The performance of the limaçon-shaped QCLs is robust with respect to variations of the deformation near its optimum value of ( \epsilon = 0.40).