Frank Schreier, Martin Schmitz, and OIof Bryngdahl, Physics Dept., Univ. of Essen, Essen, Germany.
Resonant diffraction gratings are frequently used as convenient and flexible wavelength filters since they offer a reflectance >99% for their central wavelength, whereas far off the central wavelength the reflectance can fall below 1%. The central wavelength can be adjusted by the choice of the angle of incidence, and the FWHM of the filter can be fixed over a wide range during the design process. Resonance effects occur due to the coupling of the incident wave to guided modes supported by a waveguide layer of the structure. Numerical considerations concerning resonant gratings are usually carried out under the assumption of an incident plane wave.
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