Ultralow-Crosstalk Silicon Electro-Optic Switch with Cascaded Phase Shifters for Loss Equivalence

TL;DR

This paper introduces a low-crosstalk silicon electro-optic switch using cascaded phase shifters to significantly reduce crosstalk and enhance scalability for data center and AI applications.

Contribution

It proposes a novel cascaded phase shifter design in silicon EO MZI switches that minimizes crosstalk through loss balancing, demonstrating improved performance over existing switches.

Findings

Crosstalk below -51 dB in simulations at 1310 nm.

Fabricated switch shows crosstalk between -33 and -44.2 dB at 1316 nm.

Maintains crosstalk below -30 dB over 61 nm bandwidth.

Abstract

In silicon electro-optic (EO) Mach-Zehnder interferometer (MZI) switches, crosstalk is typically limited by beam imbalance between the MZI arms, primarily caused by the free carrier absorption loss during routing, thus hindering switch scalability. To address this issue, we propose a low-crosstalk push-pull EO MZI switch by cascading a lightly doped, long phase shifter (PSLL) and a heavily doped, short phase shifter (PSHS) to construct phase-shift arms. In both BAR and CROSS states, PSLL in one arm and PSHS in the other arm are simultaneously forward-biased, with PSLL provides a pi/2 greater phase shift for switching, while PSHS balances loss of PSLL, effectively minimizing crosstalk. Simulations indicate that the proposed switch achieves a crosstalk below -51 dB at a 1310 nm wavelength. The fabricated 2 x 2 silicon EO MZI switch exhibited crosstalk between -33 and -44.2 dB at 1316 nm, and maintained crosstalk below -30 dB across an impressive 61 nm optical bandwidth, with response times under 119 ns. Featuring single-pair electrode control, consistent two-state performance, and a compact size, this approach could enable high-radix switch fabrics in data centers and artificial intelligence compute clusters.