Thermo-mechanically tunable Bragg grating filters on silicon-on-insulator rib waveguide bridges.

摘要

This thesis explores the integration of an optical device within a micromechanical structure to enhance its performance and enable behaviour it would otherwise be incapable of. Thermo-mechanically tunable Bragg grating filters on silicon-on-insulator rib waveguide bridges have been designed, fabricated and characterised to demonstrate what happens when an optical device, and the actuator used to tune its optical response, are physically the same structure. The process flow developed to fabricate the device was a five mask process that included a bridge waveguide, integrated filter, and integrated heater. A surface micromachining technique was developed to release up to 4000 mum long, 5 mum thick waveguide bridges.;The rib waveguide bridge was observed to possess a meta-stable regime between the pre- and post-buckle regimes. Before the critical buckle temperature could be attained, the bridge deflected 0.5 mum out-of-plane and remained static over a range of 7.5°C, whereupon it deflected to its full 15.1 mum buckling mode height. This metastable deflection caused a Bragg wavelength shift of 0.39 nm. The thermal sensitivity of the Bragg filter wavelength in this meta-stable regime was 62 pm/°C. Rectangular cross-section beams did not produce this behaviour.;Mechano-optical bi-stability was also observed. In this bi-stable regime there would be two possible Bragg wavelengths for a given temperature, depending on whether the device was in a forward or return path. The bi-stable regime occurred over a span of 15°C. The Bragg wavelength difference at the start of the post-buckle regime was 0.95 nm, while the Bragg wavelength difference at the return to the pre-buckle regime was 0.77nm.;The device has three distinct operating regimes: pre-buckle, buckle, and post-buckle. The pre-buckle experimental thermal sensitivity of the filter was 76 pm/°C and the theoretical sensitivity was 83 pm/°C. During the transient buckle regime, the Bragg filter wavelength was measured to shift 0.95 nm, and theorised to shift 0.55 nm. The post-buckle experimental thermal sensitivity of the filter was 88 pm/°C and the theoretical sensitivity was 99 pm/°C.