Thin-film optical filters with diffractive elements and waveguides

The chief principles and properties of optical reflection and transmission guided-mode resonance (GMR) filters are presented. These devices are based on GMR effects in dielectric structures comprising gratings and homogeneous thin films. Detailed characteristics are calculated using rigorous coupled-wave analysis for bandpass filters operating in reflection and transmission for TE- and TM-polarized incident waves. High resonance efficiency with narrow or wide linewidths is achievable with near-zero reflectance or transmittance sidebands over extended wavelength ranges. To illustrate the potential of this technology, example GMR reflection and transmission characteristics are presented for filters operating in the visible spectral region. Excellent reflection-filter features are found when antireflection conditions prevail away from the resonance wavelength. Furthermore, long-range, low sidebands are found to be obtainable for a single-layer GMR reflection filter with a TM-polarized plane wave incident at the Brewster angle. The transmission filter is optimized when the structure is highly reflective off resonance. GMR filter fabrication tolerances are discussed with examples illustrating the sensitivity of the filter center wavelength to variations in layer thickness, grating shape, and incident angle. GMR filters are found to exhibit loss-dependent wavelength shifts such that the reflection peak occurs at a different wavelength than the corresponding transmission notch. However, under antireflection conditions, the resonance location becomes insensitive to loss. Finally, reflective GMR thin-film structures that support multiple waveguide modes are studied. These devices exhibit unique characteristic angular and spectral signatures. (C) 1998 Society of Photo-Optical Instrumentation Engineers.