Calibration-Free Silicon Photonic Non-Blocking 6 x 6 Mach-Zehnder Switch

Moderate-scale silicon photonic Mach-Zehnder switches (MZSs) are important for small-scale optical telecom network nodes and photonic/optical network-on-chip (NoC) for multicore processor architectures. However, conventional elementary MZS designs are prone to size variations in the fabrication processes, resulting in considerable random phase imbalance between the two arms. Based on our previous work, we have further demonstrated a new calibration-free elementary 2 x 2 MZS design with widened multimode arm waveguides, which features improved tapered Euler S-bends (TES-bends) with bent asymmetric directional couplers (ADCs) to suppress the random phase imbalance and higher-order modes within an ultra-compact footprint. With 12 of such elementary MZSs cascaded in 5 stages, we have demonstrated a calibration-free non-blocking 6 x 6 MZS with optimized Spanke-Benes topology. Fabricated with standard 180-nm silicon photonic foundry processes, the 6 x 6 MZS features low excess loss of 1-3.5 dB and low crosstalk of <-20 dB across the C-band in the all-OFF state without calibration. Meanwhile, the excess loss and the crosstalk further reduce to 1-3.2 dB and <-22 dB, respectively, in the calibrated all-OFF and all-ON states, as well as 36 selected global switching states for all the routing configurations with a single input and a single output. This work enables high-performance and robust moderate-scale MZSs and paves the way to further scaling-up calibration-free MZSs for a broad spectrum of applications in photonic/optical telecom and interconnects.