The development of a novel micro-bridge actuator for optical switching applications is presented in this book. It covers the design, simulation, micro-fabrication, and testing of the actuator including its integration with a vertical micro-mirror. Detail studies on the buckled shape multi-layered micro-bridge actuator, its bi-stability and two-way actuation, and thermo-mechanical behaviour have been carried out during the design phase. The studies lead to formulations of a new bi-stability design methodology, buckled shape and thermo-mechanical models. Finite element analysis using ANSYS and micro-fabricated structures are used to validate the methodology and models. Micro-fabrication techniques have been developed to form the actuator, and incorporate a vertical micro-mirror with the actuator to realize a monolithically integrated optical cross-switch. The fabricated device is packaged and actuated electro-thermally to characterise its mechanical and optical switching performances. The novelty of the actuator lies in enabling intial out-of-plane deflection, which facilitates future integration of planar silica waveguides with the switch on the same substrate relatively easily.