Miniaturization of a-Si guided mode resonance filter arrays for near-IR multi-spectral filtering

Sub-wavelength periodic arrays exhibit narrow near-unity reflection bands that arise from guided mode resonances. These resonances have extremely high quality factor (i.e., narrow band features) and are ideal for filtering applications. A high quality factor requires many periods, causing large lateral footprints that limit an imaging system's spatial resolution. We present a 1D ultra-thin (<100 nm) compact finite design of seven periods of amorphous Si slabs with subwavelength periodicity surrounded by Al mirrors, which allow the finite array to approximate an infinite array and enabling a small footprint (∼5 μm), for near-infrared applications (λ = 800–2000 nm). We demonstrate spectral tunability (amplitude, bandwidth, and peak location) via geometric parameter variation and demonstrate the performance of these filters both in experiment and in simulation. This work miniaturizes guided-mode resonance filters, previously limited by extremely large footprints, while being relatively cheap and simple to fabricate compared to many existing designs.