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

Semiconductor lasers with extremely low threshold power require a combination of small volume active region with high-quality-factor cavities. For ridge lasers with highly reflective coatings, an ultra-low threshold demands significantly suppressing the diffraction loss at the facets of the laser. Here, we demonstrate that introducing a subwavelength aperture in the metallic highly reflective coating of a laser can correct the phase front, thereby counter-intuitively enhancing both its modal reflectivity and transmissivity at the same time. Theoretical and experimental results manifest a decreasing in the mirror loss by over 40% and an increasing in the transmissivity by 10(4). Implementing this method on a small-cavity quantum cascade laser, room-temperature continuous-wave lasing operation at 4.5 mu m wavelength with an electrical consumption power of only 143 mW is achieved. Our work suggests possibilities for future portable applications and can be implemented in a broad range of optoelectronic systems. Low threshold lasing is widely required, especially for portable systems. Here the authors design a circular subwavelength metallic aperture in a QCL to shape its phase front and control diffraction losses, which in turn allows a lower threshold dissipation power, enabling the fabrication of shorter cavities.

Automated summary

In this study, the authors designed a circular subwavelength metallic aperture in a quantum cascade laser to adjust its phase front, control diffraction losses, and achieve lower threshold power dissipation, enabling the fabrication of shorter cavities.