Electrically Tunable Liquid Crystal–Metasurface Devices for Phase Modulation in Telecom Band

Phase modulation of light is essential for reconfigurable photonic applications like display and optical communication. In liquid crystal on silicon (LCoS) devices, it is achieved by tuning the effective refractive index of the liquid crystal (LC) material. However, realising a full 2π shift requires a thick LC layer, which slows the response and limits device performance. Metasurfaces introduce phase shifts with ultrathin structures, and when integrated with LC, they enable dynamic 2π modulation with reduced LC thickness, thereby improving response speed while maintaining a large phase modulation depth. Building on this concept, this thesis presents the design, fabrication, and characterisation of electrically tunable LC–metasurface devices capable of high-speed phase modulation in the telecom band. Two device architectures were investigated. The first, fabricated directly on a reflective backplane, exploited constructive resonance interference to achieve full 2π modulation across 1545–1565 nm with reflectance above 60% and maintained angular tolerance up to ±2.5°. The second, fabricated on an ITO-coated coverplate to ensure LCoS compatibility, incorporated a silicon dioxide (SiO₂) spacer to suppress ITO-induced damping, and the LC director reorientation was simulated using the Oseen–Frank model with anchoring effects to capture realistic alignment. This device achieved 2π modulation across 1590–1615 nm with reflectance above 60%, establishing a pathway toward LCoS-compatible LC–metasurfaces. The results showed that LC-metasurfaces operated with a reduced LC thickness of 2.5 μm and achieved 3.5 ms switching speeds, about 10 times faster than conventional LC-based phase modulators. Overall, this research demonstrated that integrating metasurfaces with LC enables full 2π phase modulation with high reflectance and fast response in the telecom band, and it established a framework of design, fabrication, modelling, and characterisation for LCoS-compatible, high-speed phase modulators in optical networks.

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

• Zhang, Wenhan

Advisor dc:contributor.advisor

• Pivnenko, Mike

• nanophotonics
• metasurfaces

Licence

• https://www.repository.cam.ac.uk/bitstreams/65002f29-d471-4171-af37-ecc8ab249f4e/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.127614

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/398870