Nonlinear virtual lens for programmable and multispectral infrared upconversion imaging

TL;DR

This paper introduces a nonlinear virtual lens system for programmable, multispectral infrared upconversion imaging that enables tunable focus and bandwidth, allowing direct visible imaging of IR signals with a standard camera.

Contribution

It presents a novel adaptive IR-to-visible imaging platform using sum-frequency generation and a spatial light modulator to achieve tunable bandwidth and focus in IR imaging.

Findings

Demonstrated tunable focal length via wavelength variation

Achieved programmable multispectral focusing

Enabled direct IR image visualization with visible cameras

Abstract

Conventional infrared (IR) imaging techniques depend on IR cameras based on narrow-bandgap semiconductors, which offer limited spectral bandwidth, coupled with a separate lens. Recently, advances in nonlinear flat optics have opened a novel pathway for converting IR signals into the visible through nonlinear generations, enabling the direct visualisation of IR images using standard visible cameras. However, the narrow spectral bandwidth and the requirement for an additional lens remain the key challenges. Here, we address both issues via a novel adaptive and multifunctional IR-to-visible imaging platform offering tunable bandwidth and focusing simultaneously. We utilise sum-frequency generation (SFG) to convert IR light into the visible, by introducing a pump beam modulated by a spatial light modulator (SLM) to construct a virtual metalens enabling precisely controlled focusing of the generated nonlinear optical field. As a result, we demonstrate both theoretically and experimentally an optical focusing mechanism with a tunable focal length, achieved by varying the pump and signal wavelengths and modulating the phase distribution. Furthermore, since the focal length depends on the input signal wavelength, the imaging plane position varies accordingly, indicating a promising potential for the multispectral IR imaging applications. Our upconversion platform delivers SLM-controlled, programmable multispectral focusing for next-generation IR imaging, opening new avenues in the fields of computational and multispectral imaging techniques.