An analytical coupling coefficient for MEMS tunable silicon nanowire waveguide coupler devices

Silicon nanowire waveguides are promising for future integration of photonic circuits with silicon electronics. Electromechanical control of waveguide is also favorable for variable silicon nanowire waveguide devices. In this study, we investigated analytically the characteristics of a silicon nanowire waveguide coupler for electromechanical waveguide devices. The electric field of the silicon nanowire waveguide was enhanced by the high-index contrast. The enhanced electric field increased the coupling coefficient by a factor of 2.7 for a silicon waveguide of 400 nm in width and 260 nm in thickness compared with the approximation on the basis of low-index-contract. The analytically derived coupling coefficient was evaluated experimentally by investigating a waveguide coupler switch with a micro-electromechanical actuator.