Narrow band, large angular width resonant reflection from a periodic high index grid at terahertz frequency

The property of a thin silicon membrane with periodic air slits of definite depth and width to exhibit under normal incidence a close to 100% ultra-narrow band reflection peak is demonstrated experimentally in the terahertz frequency range on a single-crystal silicon grid fabricated by submillimeter microsystem technology. An analysis based on the true modes supported by the grid reveals the nature of such resonances and permits to sort out those exhibiting ultra-narrow band.