Ultra-low threshold lasing through phase front engineering via a metallic circular aperture

TL;DR

This paper introduces a novel phase front engineering technique using a metallic aperture to significantly reduce laser thresholds and enhance transmission, enabling room-temperature operation of ultra-compact, efficient mid-infrared lasers for sensing applications.

Contribution

The study demonstrates that a carefully designed metallic aperture can simultaneously improve modal reflectivity and transmission, reducing mirror loss and enabling low-threshold, room-temperature laser operation.

Findings

Mirror loss reduced by up to 40%

Transmission increased by four orders of magnitude

Achieved room-temperature laser operation with 143 mW dissipation

Abstract

Semiconductor lasers with ultra-low thresholds and minimal footprints are a topic of active research. Such devices require a combination of high quality factor laser cavities with small active region volumes, which drives the quest for novel cavity geometries exploiting nano-optic concepts. For high-reflectivity coated ridge lasers, where light is tightly confined in the waveguide, a low threshold can only be achieved by strongly reducing the diffraction losses arising at the laser facet. We show here that, somewhat counter-intuitively, opening a carefully designed aperture in a metallic facet coating can simultaneously enhance both its transmission and modal reflectivity by correcting the phase front at the subwavelength scale. Numerical simulations and experimental results demonstrate a reduction of optical mirror loss by up to 40% while the transmission is increased by four orders of magnitude. Applying this approach to both facets of a short cavity quantum cascade laser, we achieve laser operation at room temperature with an electrical dissipation of only 143 mW. Such light sources are especially suitable for portable and battery-operated chemical agent sensing applications operating in the mid-infrared wavelength range, where multiple greenhouse and pollutant gases have their fundamental absorption lines. Our work suggests possibilities for further applications including frequency comb dispersion engineering, and can be implemented in a broad range of optoelectronic systems.