Integration of subwavelength metal gratings with MEMS actuators

Metal films perforated with periodically-spaced subwavelength diameter holes have been shown to transmit light with greater efficiency than predicted by classical models for evanescent propagation. This transmission mechanism is caused either by the coupling of light to surface plasmon polariton modes on the surfaces of the metal film or by diffraction patterns in the lateral evanescent modes of electromagnetic field. Regardless of the root cause, this characteristic performance leads to electric field enhancement at the apertures in the metal, an effect that holds promise for nanoscale optical sensors. In particular, the propagation of these modes is very sensitive to changes in the index of refraction on either surface of the metal. This paper will describe our work on patterned metal films which are interrogated using infrared (IR) radiation. These metal gratings are fabricated using a surface micromachining process, allowing MEMS actuators to be integrated alongside the optically-active surface. The integration of MEMS structures with subwavelength optical structures can be used to create structures whose optical properties are modulated by changes in the position of a MEMS element, resulting in mechanical sensors and tunable optical filters. We will describe structures in which small changes in the separation between the metal film and a dielectric substrate result in large changes in the optical transmission and reflection spectra.