We review principles and applications of nanophotonic devices based on electromagnetic resonance effects in thin periodic films. We discuss the fundamental resonance dynamics that are based on lateral Bloch modes excited by evanescent diffraction orders in these subwavelength devices. Theoretical and experimental results for selected example devices are furnished. Ultra-sparse nanogrids with duty cycle less than 10% are shown to provide substantially wide reflection bands and operate as effective polarizers. Narrow-passband resonant filters with extensive low sidebands are presented with focus on the zero-contrast grating architecture. This study is extended to long-wave operation in the THz region. Examples of fabricated guided-mode resonance devices with outstanding performance are given. This includes an unpolarized wideband reflector using serial single-layer reflectors, an ultra-sparse silicon nanowire grid as wideband reflector and polarizer, resonant bandpass filter with wide low sidebands, and a spatial/spectral filter permitting compact nonfocusing spatial filtering. The guided-mode resonance concept applies in all spectral regions, from the visible band to the microwave domain, with available low-loss materials.
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