Towards calibration-free Mach-Zehnder switches on silicon

TL;DR

This paper introduces a novel design for silicon photonic Mach-Zehnder switches that are calibration-free, scalable, and exhibit significantly reduced phase imbalance, enabling more reliable and large-scale optical interconnects.

Contribution

The paper presents a new design employing widened waveguides and mode filters to achieve calibration-free 2x2 and N×N Mach-Zehnder switches on silicon photonics.

Findings

Over 370-fold reduction in phase imbalance for 2x2 switches.

Extinction ratios of ~30 dB for 2x2 and ~20 dB for 4x4 switches.

Successful fabrication and characterization using standard CMOS processes.

Abstract

Silicon photonic Mach-Zehnder switches (MZSs) have been extensively investigated as a promising candidate for practical optical interconnects. However, conventional 2{\times}2 MZSs are usually prone to the size variations of the arm waveguides due to imperfect fabrication, resulting in considerable random phase imbalance between the two arms, thereby imposing significant challenges for further scaling up NN MZSs. Here we propose a novel design towards calibration-free 2{\times}2 and N{\times}N MZSs, employing optimally widened arm waveguides, enabled by novel compact tapered Euler S-bends with incorporated mode filters. With standard 180-nm CMOS foundry processes, more than thirty 2{\times}2 MZSs and one 4{\times}4 Benes MZS with the new design are fabricated and characterized. Compared with their conventional counterparts with 0.45-{\mu}m-wide arm waveguides, the present 2{\times}2 MZSs exhibit ~370-fold reduction in the random phase imbalance. The measured extinction ratios of the present 2{\times}2 and 4{\times}4 MZSs operating in the all-cross state are ~30 dB and ~20 dB across the wavelength range of ~60 nm, respectively, even without any calibrations. This work paves the way towards calibration-free large-scale N{\times}N silicon photonic MZSs.