RESUMO
A guided-mode resonance (GMR) filter with wide angular tolerances is experimentally demonstrated as an authentication label illuminated with unpolarized white light. The proposed filter, based on a free-standing silicon nitride membrane suspended on a silicon substrate, is fabricated by using anisotropic wet etching to remove the substrate beneath the silicon nitride layer. Both grating and waveguide structures without a lower cladding layer, i.e., a substrate, are fabricated simultaneously on a silicon nitride membrane. Since the silicon nitride is transparent within the spectra of visible and infrared light, such suspended-membrane-type GMR filters are well suited for applications within the visible spectrum. Moreover, the high refractive index of silicon nitride allows the proposed filters to have strongly modulated gratings and an immunity to high angular deviation. The measured reflection resonance has an angular tolerance up to +/-5 degrees under normal incidence for the wavelength of 629.5 nm.
RESUMO
The miniature spectrometer has many applications in integrated optics and photonics. The blazed grating with the Rowland circle structure has the advantage of self-focusing and is chosen as the major component in the spectrometer chip. In the simulations for the blaze angle design in the visible spectrum, we discover the phenomenon of the double reflection diffraction. Its cause and parameter space are discussed. The spectrometer utilizing the phenomenon has similar performance to the standard blazed grating and is easier to manufacture in microelectromechanical systems (MEMS) technology. The discovery will greatly ease the design of the spectrometer chip.
