Compact non-volatile multilevel Sb2Se3 electro-optical switching in the mid-infrared group-IV-photonics platform

This theoretical modeling and simulation paper presents designs and projected performances of two non-volatile, broadband, on-chip 2 × 2 electro-optical switches based upon the germanium-on-insulator (GeOI) photonic-electronic platform operating at the 2.5 µm mid-infrared wavelength. These compact devices facilitate large-scale integration on a “monolithic wafer” where all components are made of group-IV semiconductors. The switches are the two-waveguide directional coupler (DC) and the Mach-Zehnder interferometer (MZI). A thin-film graphene Joule-effect micro-heater is assumed on the planarized GeOI device to change the phase (reversably) of DC-slot-embedded Sb2Se3 phase-change material (PCM) from crystalline to amorphous. The MZI has this PCM within its slotted-arm waveguides. Simulations show high-performance bistable or multi-stable cross-bar switching in both devices. The 2 × 2 DC has an active coupling length of 17 µm, 130 nm gap, and a footprint of 5 µm x 31 µm. The device bandwidth is 30 nm over a wavelength range where cross and bar insertion losses IL are less than 0.3 dB, and where optical crosstalk is less than −15 dB. Results for the 2 × 2 MZI show crossbar switching attained with a 7.8 µm-length Sb2Se3 slot and a 5 µm x 51 µm switch footprint. Stable, multi-level switching in both devices is attained via partial amorphization. Thermal modeling shows that careful control of the voltage-pulse amplitude V applied to graphene (rectangular pulse duration of 500 ns) can give 32 levels, for example, using V in the range from 6.18 to 7.75 Volts. Multi-level switching is shown also in PCM-based ring resonators.