A Broadband Angular-Selective Midinfrared Photodetector

Abstract

Midinfrared photodetectors are susceptible to background noise since every object in the surroundings emits thermal radiation from different directions. To reduce this background noise and enhance the signal-to-noise ratio of midinfrared sensing, different strategies to achieve angular-selective filtering have been proposed. However, these methods are either wavelength- and polarization-dependent or require bulky lens or mirror systems. The former compromises the photodetector sensitivity, and the latter makes it difficult to integrate with wearable or on-chip devices. In this study, we present a novel angular-selective microstructure array that can seamlessly integrate onto a midinfrared photodetector. Our compact device leverages the conservation of etendue to attain high angular selectivity over a broad range of midinfrared wavelengths. Radiation from unwanted angles is substantially filtered, which leads to a markedly enhanced photodetection signal-to-noise ratio. Furthermore, the device’s photoresponse is shown to be polarization- and wavelength-insensitive, avoiding signal losses associated with narrow spectral ranges or polarization dependence and therefore circumventing degradation in photodetector sensitivity. Our broadband angular-selective midinfrared photodetector holds great promise for wearable devices, medical diagnostics, and space applications.