Reconfigurable flat-top narrow bandpass filter in prism pair coupled planar optical waveguide

A reconfigurable optical bandpass filter with flat-top transmission line shape and narrow bandwidth in nanometer scale is designed and theoretically analyzed. The filter is composed of two coupling prisms and a sandwiched planar optical waveguide (POW) which is comprised of 5 layers of uniform materials with an air gap in the center. Numerical simulations demonstrate that a single passband in the visible spectrum with flat top and completely null sideband can be obtained. The central wavelength of the passband can be tuned by about ±14 nm via a ±1.78° change of the incident angle while the high transmittance and flatness of the band top can always be maintained by almost linearly adjusting the thickness of the central air layer in the POW at the same time. During the adjustment process, the bandwidth changes from 0.92 to 2.43 nm. The simple structure and flexibility of the filter could facilitate its applications in various optical fields.