Thermo-optic phase modulators in SIMOX material

An investigation of a series of low-power thermo-optic phase-modulating devices fabricated in SIMOX material suitable for use in distributed sensing or as optical variable attenuators is presented. These devices are integrated in a balanced Mach-Zehnder Interferometer (MZI) utilising multi-micron vertical sidewall rib waveguides and exhibit low polarisation dependence. The investigation highlights the power consumption (<100mW) of various lengths (100-500 mu m) of devices with low-lateral heat diffusion operated by ohmic heating and quantifies the attainable modulation depths under quasi-static operation. Non-linear device behaviour is demonstrated and explained with a proposal for these characteristics giving rise to devices which would operate with further pow er reductions. AC characteristics are also investigated, showing the modulators to have 3dB bandwidths of approximately 40kHz. A second device geometry is presented which was fabricated utilising an under-etching technique to suspend the arms of the Mach-Zehnder. Results indicate lower power operation (<10mW) with a corresponding reduction in bandwidth to approximately 1kHz. An improvement in overall device geometry provides modulation depths in excess of 99%, independent of bath bandwidth and power.