Dual-period guided-mode resonance filters for SWIR multi-spectral image sensors.

Typical guided-mode resonance (GMR) transmission filter design, which is based on a single ridge per period, necessitates multiple etching/fabrication steps for implementing an array of filters (having different transmission bands) on the same substrate. To address this problem, we demonstrate dual-period narrow bandpass GMR filters that offer more degrees of freedom, two periods and two fill-factors, for tuning the filter characteristics and achieving wider stop bands without changing the grating height. A set of six transmission filters with well-separated passbands in the short-wave infrared region was designed using COMSOL Multiphysics simulations and produced on the same silicon-on-quartz wafer in a single fabrication run. The $90;{\unicode{x00B5}{\rm m}};{\times};90;{\unicode{x00B5}{\rm m}}$ size filters exhibited passbands as narrow as 15 nm with peak-wavelength tunability over 200 nm, flat stop bands as wide as ${\sim}{400};{\rm nm}$, and peak transmittance reaching 87%. The experimental transmission spectra were in good agreement with the corresponding simulations. These findings pave the way for the realization of pixel size filter arrays for multispectral image sensors.