Quantum Cascade Surface Emitting Lasers

TL;DR

This paper introduces a novel quantum cascade surface emitting laser (QCSEL) designed for mid-infrared applications, demonstrating high efficiency, single mode operation, and surface emission for portable gas sensing.

Contribution

The paper presents the design, fabrication, and testing of a new QCSEL with high reflectivity mirrors and surface emission, achieving low threshold power and single mode operation.

Findings

Achieved mirror reflectivities > 0.9

Demonstrated pulsed threshold power of 237 mW near 7.5 μm

Realized single mode emission with >33 dB side-mode suppression

Abstract

A low-cost single frequency laser emitting in the mid-infrared spectral region and dissipating minimal electrical power is a key ingredient for the next generation of portable gas sensors for high-volume applications involving chemical sensing of important greenhouse and pollutant gases. We propose here a Quantum Cascade Surface Emitting Laser (QCSEL), which we implement as a short linear cavity with high reflectivity coated end-mirrors to suppress any edge emission and use a buried semiconductor diffraction grating to extract the light from the surface. By wafer-level testing we investigate the cavity length scaling, extract mirror reflectivities larger than 0.9, and achieve a pulsed threshold power dissipation of 237 mW for an emission wavelength near 7.5 $\mu$m. Finally, we demonstrate single mode emission with a side-mode suppression ratio larger than 33 dB of a 248 $\mu$m short cavity mounted with the epitaxial layer up and operated in continuous wave at 20 $^\circ$C.