Tunable guided-mode resonances in coupled gratings.

We present a rigorous numerical analysis on tunable characteristics of guided-mode resonances (GMRs) in coupled gratings. Two schemes of strong and negligible evanescent coupling of guided modes are treated. Both show wide range tunability. In the case of strong evanescent coupling, independent control of the center wavelength and the linwidth of the resonance is obtained via variations of a gap size between the gratings and lateral alignment conditions. We believe that this characteristic will provide a useful means to realize a tunable filter in conjunction with micro/nano-electromechanical system technologies. We also present a generalized theoretical analysis on the tunable characteristics of the GMRs in coupled gratings, which is qualitatively in good agreement with the numerical analysis.