Multi-layer, Low-crosstalk Integrated Optical Switches

The rapid growth of cloud computing and data-intensive applications necessitates optical switching technologies with ultra-low crosstalk, high bandwidth, and nanosecond-scale reconfigurability. This work presents a comprehensive study of 3D Si-SiN-SiN tri-layer optical switches employing switch-and-select (S&S) architectures for strictly non-blocking connectivity. The 3D crossing-free waveguide shuffle eliminates in-plane intersections, significantly reducing crosstalk (as low as -51.9 dB) and insertion loss (as low as 2.1 dB) while enabling scalable, high-density photonic integration. Two distinct implementations: a thermo-optic microring resonator (MRR)-based 8×8 switch and an electro-optic microdisk switch are demonstrated, both leveraging the tri-layer platform to achieve >70 GHz bandwidth and sub-microsecond to nanosecond switching speeds. The thermo-optic device achieves crosstalk suppression of −33.2 to −50.8 dB and on-chip losses of 2.1–10.5 dB with micro-second scale switching time, while the electro-optic variant reduces switching times to 5.9 ns (rise) and 2.8 ns (fall) with crosstalk ratios as low as −51.9 dB. A dedicated control framework enables automated calibration and simultaneous multicasting/switching operations, validated through fronthaul experiments using 64-QAM LTE signals with >40 dB RF dynamic range and <1.8% error vector magnitude (EVM). Future work will focus on lossless optical switching systems through advanced material engineering (e.g., low-loss SiN waveguides with optimized adiabatic tapers) and hybrid modulation schemes combining electro-optic and thermo-optic tuning. Additionally, we aim to integrate fault-tolerant control algorithms and machine learning-driven optimization to further minimize insertion loss (<1 dB) and enable dynamic reconfiguration for terabit-scale data centre networks. By addressing scalability and energy efficiency challenges, this work paves the way for next-generation optical interconnects in cloud radio access networks (C-RAN) and ultra-low-latency computing architectures.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Sun, Bohao

Advisor dc:contributor.advisor

• Penty, Richard

• optical communication
• optical switches
• Photonic Integrated Circuits
• photonics

Licence

• https://www.repository.cam.ac.uk/bitstreams/c8162511-a969-40a4-9115-06e5dbd3ab20/download
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.122571

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/391434