Effect of waveguide thickness layer on spectral resonance of a Guided Mode Resonance Filter

We demonstrated cost-effective Guided Mode Resonance Filters (GMRFs) that are diffraction gratings with spectrally narrow reflectance peaks due to resonance anomalies and couple incident light into a semi-guided mode in a corrugated waveguide. The GMRF consists of a single high index dielectric layer on a periodically corrugated transparent substrate to couple light. The GMRFs are designed by Fourier Modal Method (FMM), a numerical tool based on rigorous calculations of electromagnetic diffraction theory. In FMM the field is expanded in different regimes with the application of boundary conditions at each interface. GMRFs in polymer materials (polycarbonate) are fabricated by Nano-Imprint Lithography (NIL) from a master silicon-stamp. The master Si-stamp is fabricated by the exposure of Electron Beam Lithography (EBL) on a negative & binary tone resist, Hydrogen silsesquioxane (HSQ) to make sub-wavelength grating structures. The fabricated gratings are coated by a high refractive index TiO₂ amorphous thin layer using Atomic Layer Deposition (ALD). GMRFs are demonstrated both theoretically and experimentally to shift spectral resonance towards longer wavelengths with the increase in TiO₂ thickness.