Silicon Electro-Optic Mach--Zehnder Switch Fabric With Ultralow-Crosstalk

The explosive growth of artificial intelligence (AI) workloads intensifies the demand for high-speed, wide-bandwidth, and energy-efficient optical switches. Silicon Mach-Zehnder interferometer- (MZI-) based switches, driven by the free-carrier dispersion (FCD) effect, are promising candidates for such applications, yet facing inherent challenges from free-carrier absorption (FCA), which limits their crosstalk and scalability. This paper presents a novel electro-optic (E-O) MZI cell that harnesses self-heating effect to mitigate FCA-induced power imbalance. The cell includes a conventional E-O phase shifter on one arm and a p-i-n-junction-based “amplitude-only” optical attenuator on the other, in which self-heating fully neutralizes the phase shift introduced by carrier injection, leaving only an adjustable loss to match the FCA in the phase shifter arm. A dual-MZI configuration additionally compensates coupling-ratio deviations from fabrication imperfections, enhancing extinction ratios. Monte Carlo simulations verify that this high-extinction-ratio cell can be adopted into various switch topologies, achieving crosstalk levels comparable to those in fully dilated structures, but with much fewer components. An 8 × 8 double-layer network (DLN) switch prototype is demonstrated with crosstalk of below −40 dB, on-chip loss of as low as 8.5 dB, and switching times of under 100 ns. Moreover, a compact curved tunable directional coupler (CTDC) is developed to further miniaturize the switch footprint. Overall, this work offers a promising solution for advancing scalable, high-performance optical switches in future AI-driven datacenter networks.