Design of ultracompact broadband focusing spectrometers based on diffractive optical networks

We propose the inverse design of ultracompact, broadband focusing spectrometers based on adaptive diffractive optical networks (a-DONs). Specifically, we introduce and charac-terize two-layer diffractive devices with engineered angular dispersion that focus and steer broadband incident radi-ation along predefined focal trajectories with the desired bandwidth and nanometer spectral resolution. Moreover, we systematically study the focusing efficiency of two -layer devices with side length L = 100 mu m and focal length f = 300 mu m across the visible spectrum and demonstrate accurate reconstruction of the emission spectrum from a commercial superluminescent diode. The proposed a-DONs design method extends the capabilities of efficient multi-focal diffractive optical devices to include single-shot focusing spectrometers with customized focal trajectories for appli-cations to ultracompact spectroscopic imaging and lensless microscopy. (c) 2022 Optica Publishing Group