Tunable transmission filters based on double-subwavelength periodic membrane structures with an air gap

In this paper, a new design of a type of mechanically tunable transmission filter is theoretically presented by using double-subwavelength periodic membrane structures with an air gap. A strongly modulated periodic membrane provides a broad reflection band due to the guided mode resonance (GMR) effect. The interaction between the edges of the GMR and the broad reflection band creates the tunable transmission passbands. Stronger and weaker evanescent couplings between the two periodic membranes show a wide range of tunability. The overetching error should be avoided in both cases of symmetrical and unsymmetrical structures. An effective control of the tunability with good spectral properties can be obtained in the weaker evanescent coupling region due to the negligible lateral alignment condition. The localization of the electric field is mainly confined in the periodic membranes as the thickness of the air gap is smaller, while the energy of the electric field is mainly localized in the air cavity as the thickness of the air gap is larger. Thus the influence of the lateral shift of a periodic membrane on the spectral properties is different due to their different coupling mechanisms in both cases