Fabry-Pérot resonator with nanostructures for multispectral visible filtering

We design, fabricate and characterise examples of a narrowband filter that is intended for post-processing onto complementary-metal oxide-semiconductor (CMOS) imaging sensors to make compact multispectral imaging instruments. The filter is based on a Fabry-Pérot cavity, with the centre frequency of the filter controlled by patterning subwavelength holes into the structure using electron beam lithography and dry etching. We show that even though the top mirror layer has holes, acceptable performance is obtained with full width half maximums in the range 46-60 nm and a full visible band free spectral range. We present simulations of a set of 16 filters spanning the visible range (400-750nm) requiring only 5 separate lithography cycles.