Tunable optical reflectance using a monolithic encapsulated grating

Tunable optical reflectance using a monolithic encapsulated grating in fused silica is presented based on the guided-mode resonance (GMR) effect. The resonance location can be altered by slightly varying the thickness of the top layer. For small thickness of the grating layer, the variation of the grating thickness can be tailored to create variable optical reflectance at the same operating wavelength with the filter linewidth and the reflection sidebands kept almost the same. By proper choosing the grating thickness, the novel dual functional device that combines functions of narrowband filtering and three-port beam splitting in the resonance domain can be obtained using the monolithic encapsulated grating. Multiline reflection filters can be obtained by increasing the thickness of the top layer, and tunable reflectivity for multiple operating wavelengths can be obtained by changing the grating thickness.