INVESTIGATIONS OF 1 × 1 AND 1 × 2 TERAHERTZ PHOTONIC SWITCHES

Abstract

I have designed and numerically studied single-mode rib waveguide using high resistivity float zone silicon as the core material on silica substrate in the ter ahertz frequencies from 0.5 Terahertz to 1 Terahertz. I have investigated the loss due to bending in the above-designed waveguide to optimise directional coupler and microring resonator devising. The switches were contrived by em bedding GST (Ge2Sb2Te5), a phase change material, into the waveguide, for a one-in-one (1 × 1) switch and directional coupler for a one-in and two-out (1×2) switch. The reversible change between the on and off states of the switch can be achieved by applying voltage pulses that cause the material to change from a crystalline to an amorphous (ON) state and vice versa (OFF) by reach ing certain temperatures. Varying voltage signals in amplitude or time period achieve re-configurable multilevel switching by capturing the material’s inter mediate phase states. Ge2Sb2Te5 was positioned on top, partially etched and fully embedded into the waveguide. The extinction ratios for these three con figurations for the optimised geometry, considered after achieving the highest Figure of Merit, are 22.884 dB, 24.574 dB and 54.790 dB, with an insertion loss of 1.714dB, 1.784dB and 2.33dB, respectively, for the 1×1 switch. Ge2Sb2Te5 was introduced on top of the waveguide for 1×2 directional coupler switch with the Extinction ratio for bar state, and cross-state is observed to be 11.87dB and 8.938dB. Special joule heaters were designed at a distance from the exist ing switches to achieve the necessary temperatures required for operation. The phase transition from amorphous to crystalline and the intermediary phases are confirmed to occur uniformly throughout the Ge2Sb2Te5 area in both types of switches by electro-thermal simulations.