Toward calibration-free Mach-Zehnder switches for next-generation silicon photonics

Silicon photonic Mach-Zehnder switches (MZSs) have been extensively investigated as a promising candidate for optical systems. However, conventional 2 x 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 developing next-generation N x N MZSs. Here we propose a novel design toward calibration-free 2 x 2 and N x 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 x 2 MZSs and one 4 x 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 x 2 MZSs exhibit significant reduction in the random phase imbalance. The measured extinction ratios of the present 2 x 2 and 4 x 4 MZSs operating in the all-cross state are 27-49 dB and similar to 20 dB across the wavelength range of similar to 60 nm, respectively, even without any calibrations. This work paves the way toward calibration-free large-scale N x N MZSs for next-generation silicon photonics. (C) 2022 Chinese Laser Press

Automated summary

This study proposes a novel design for calibration-free 2 x 2 and N x N MZSs, which reduces the random phase imbalance by optimizing the width of arm waveguides and incorporating mode filters. The fabricated MZSs show significant improvement in performance without the need for calibration, paving the way for large-scale N x N MZSs in next-generation silicon photonics.