Speaker: Saket Kaushal (Roll No.-EE12S069)
The CMOS fabrication compatibility of waveguide devices and the presence of strong thermo-optic effect makes silicon-on-insulator (SOI) an attractive platform for large scale integration of reconfigurable optical systems viz. routers, switches, filters, delay lines etc. Integrated optical micro-heaters are used for local reconfiguration/correction of phase-sensitive devices via thermo-optic effect. However, high thermal sensitivity of resonance devices (dλr /dT ~ 100 pm/K) leads to thermal crosstalk, especially for densely packed large-scale integrated optical circuits in SOI platform. It is therefore, important to investigate the temperature distribution and effective control of thermo-optic phase-shift by a micro-heater integrated with waveguide structures.
In this work, a linear piece-wise model is formulated to obtain temperature distribution along the waveguide. It is observed that the effective length of a thermo-optic phase-shifter (operating at a given temperature range) has a linear dependence on the slab height of SOI rib waveguides with microns to submicron cross- sectional dimensions. The model is used to extract exact thermal distribution of fabricated waveguides integrated with Ti micro-heaters in SOI substrate with 2-µm device layer thickness. Fabry-Perot modulation technique has been used to extract the effective thermo-optic phase-shifts. A typical thermo-optic phase tuning efficiency of ~ 0.9π rad/mW and a response time of ~ 7 µs have been recorded for a heater of length Lh = 50 µm and width Wh = 2 µm integrated with a waveguide of length ~20 mm (single-mode @ λ ~1550 nm). The separation between rib waveguide and metallic micro-heater was kept ~ 3 µm to avoid unwanted optical losses.