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

摘要

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