Single-mode lasing in ring-cavity surface-emitting lasers

Subject of study. Distributed-feedback ring-cavity surface-emitting quantum-cascade lasers are studied. Aim of study. The aim is to realize stable single-mode emission in ring-cavity surface-emitting quantum-cascade lasers through a Bragg grating formed by direct-write ion beam lithography. Method. The selection of longitudinal whispering gallery modes owing to the fabrication of a second-order Bragg grating in the top waveguide cladding layers based on InP was implemented using direct-write ion beam lithography. Main results. The possibility of implementing stable single-mode emission in distributed-feedback ring-cavity surface-emitting quantum-cascade lasers with a Bragg grating formed by direct-write ion beam lithography was demonstrated. An increase in the etching depth of the grooves of the Bragg grating to 2.8 µm facilitated the implementation of stable single-mode emission at a temperature of 83 K. Single-mode emission was observed at a wavelength of 7.45 µm with a threshold current density of approximately 2kA/cm2. The maximum side mode suppression ratio was 25 dB. Practical significance. Single-mode distributed-feedback ring-cavity surface-emitting quantum-cascade lasers are promising for the creation of compact gas sensors, wherein a laser and a photodetector of the mid-infrared spectral range are monolithically integrated on one chip.