Feasibility of tunable MEMS photonic crystal devices

Abstract

Periodic photonic crystal structures channel electromagnetic waves much as semiconductors/quantum wells channel electrons. Photonic bandgap crystals (PBC) are fabricated by arranging sub-wavelength alternating materials with high and low dielectric constants to produce a desired effective bandgap. Photons with energy within this bandgap cannot propagate through the structure. This property has made these structures useful for microwave applications such as frequency-selective surfaces, narrowband filters, and antenna substrates when the dimensions are on the order of millimeters. They are also potentially very useful, albeit much more difficult to fabricate, in the visible/near-infrared region for various applications when the smallest dimensions are at the edge of current micro-lithography fabrication tools. We micro-fabricated suspended free standing micro-structure bridge waveguides to serve as substrates for PBC features. These micro-bridges were fabricated onto commercial silicon-on-insulator wafers. Nanoscale periodic features were fabricated onto these micro-structure bridges to form a tunable system. When this combined structure is perturbed, such as mechanical deflection of the suspended composite structure at resonance, there can be a realtime shift in the material effective bandgap due to slight geometric alterations due to the induced mechanical stress. Extremely high resonance frequencies/device speeds are possible with these very small dimension MEMS.