Single-stage 2 × 2 silicon thermo-optic switch with crosstalk < −35 dB over 40 nm and Pπ < 8 mW

The Mach–Zehnder interferometer (MZI) optical switch is a fundamental component in constructing photonic integrated circuits for broadband optical signal routing. Its performance is mainly determined by the 2 × 2 optical coupler and the phase shifter. We analyze the influence of the imbalances in power splitting and arm loss on the insertion loss and crosstalk of a single-stage 2 × 2 MZI switch. A 2 × 2 multimode interference (MMI) coupler with low excess loss (< 0.14 dB) and low imbalance (< 0.13 dB) over 40 nm is proposed. We show the robustness of the MMI to width variations up to ± 40 nm. Folded configurations are used for both the silicon waveguides and the metallic heaters to increase the power efficiency. The device is fabricated on a silicon-on-insulator substrate using e-beam lithography. It has an on-chip insertion loss of 0.7 dB and a crosstalk < –35 dB over 40 nm, and < –40 dB over 20 nm. The power required for a phase shift of π is 7.6 mW. The rise and fall times are both within 20 µs.