Ultralow-Crosstalk Silicon Electro-Optic MZI Switch Based on Cascaded Phase Shifters with Arm Loss Equivalence

In silicon electro-optic (EO) Mach-Zehnder interferometer (MZI) switches, crosstalk is limited by the beam imbalance between the MZI arms, primarily caused by the free carrier absorption loss of the phase-shift arms, thereby hindering switch scalability. To address this issue, this study proposes 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, the PSLL in one arm and PSHS in the other arm are simultaneously forward-biased; the phase-shift difference between them is pi/2 to enable switching, while their losses are similar to minimize crosstalk. Simulations indicate that the proposed switch achieves crosstalk below -51 dB at a 1310 nm wavelength. The fabricated 2 x 2 silicon EO MZI switch exhibits crosstalk ranging from -33 to -44.2 dB at 1316 nm across all routing paths, and maintained crosstalk below -30 dB over an impressive optical bandwidth of 61 nm, with response times under 119 ns. Featuring single-pair electrode control, consistent two-state performance, and a compact footprint, this approach can enable high-radix switch fabrics in data centers and artificial intelligence compute clusters.