Efficient Dielectric Metasurface Collimating Lenses for Mid-Infrared Quantum Cascade Lasers

TL;DR

This paper introduces low-cost, efficient dielectric metasurface flat lenses for collimating mid-infrared quantum cascade laser beams, achieving high numerical aperture and beam quality with simple fabrication methods.

Contribution

It presents a novel dielectric metasurface lens design for mid-infrared lasers that is easy to fabricate and offers high performance, reducing reliance on costly traditional lenses.

Findings

Achieved 0.86 numerical aperture with 79% transmission efficiency.

Collimated beam with 0.36° divergence angle and M^2=1.02.

Fabrication using single-step UV binary lithography.

Abstract

Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. Here we report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lenses are composed of amorphous silicon posts on a flat sapphire substrate and can be fabricated at low cost using a single step conventional UV binary lithography. Mid-infrared radiation from a 4.8 $\mu$m distributed-feedback quantum cascade laser is collimated using a polarization insensitive metasurface lens with 0.86 numerical aperture and 79% transmission efficiency. The collimated beam has a half divergence angle of 0.36$^\circ$ and beam quality factor of $M^2$=1.02.