2D Material Based Nonlinear Optical Mirror for Widefield Up‐Conversion Imaging from Near Infrared to Visible Wavelengths

Abstract

Infrared up‐conversion imaging is used for frequency conversion of near and mid‐infrared photons to the visible or shorter near‐infrared wavelength range where high‐performance silicon sensors can be used for imaging in‐lieu of the cumbersome infrared counterparts. Nonlinear optical crystals are used for up‐conversion imaging, however, this typically requires long lengths, high pump power, and careful phase matching between interacting waves. To miniaturize the up‐conversion imaging device and eliminate stringent phase‐matching requirements, sub‐wavelength size optical metasurfaces are being explored as the nonlinear optical medium supporting resonances in the near‐infrared, albeit being prone to higher‐order diffraction at the up‐converted wavelengths. Here, a novel two‐dimensional (2D) layered material‐based nonlinear optical mirror (NLOM) based wide‐field up‐conversion imaging device is demonstrated with only 45 nm thick Gallium Selenide (GaSe) layer on a gold reflector with a suitable dielectric spacer. Near‐infrared input at 1550 nm is up‐converted to 622 nm visible output in the presence of a pump beam at 1040 nm through a sum frequency generation (SFG) process. The NLOM stack is optimized using particle swarm optimization algorithm for maximizing the detected SFG signal. Image up‐conversion experiments are performed demonstrating real, Fourier‐plane imaging, and real‐time Fourier‐domain processing with good imaging fidelity and efficiency.