Broadband Angular-selective Mid-infrared Photodetector

Abstract: Mid-infrared 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 signal-to-noise ratio of mid-infrared 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 mid-infrared photodetector. Our compact device leverages the conservation of etendue to attain high angular selectivity over a broad range of mid-infrared 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 mid-infrared photodetector holds great promise for wearable devices, medical diagnostics and space applications.