Thermo-optic phase shifters for integrated photonics at low temperatures

Abstract

Quantum information processing can provide tools to tackle problems beyond the capacity of classical computers, sensors and communication systems. Quantum photonics is one of the most promising quantum technologies that aim to implement systems that harness the quantum mechanical properties of nature.

Such technologies can be implemented using photonic integrated circuits, a scalable solution compatible with the long-established CMOS fabrication technologies that benefit from developing telecommunication applications.

The maturity level of silicon photonic technology offers vast libraries of standard components that can be used to design integrated quantum photonic devices. Single-photon detectors (SPD) are the only critical component essential for any quantum photonic device that is not readily available yet. SPDs based on superconducting nanowires offer the best performance currently and can be integrated into photonic devices but require operation temperatures below 4K. This conflicts with another essential building block, optical phase-shifters, used for routing single photons in the circuits that introduce local temperature shifts of several hundred degrees Kelvin.

This thesis studies the viability of the operation of thermo-optic phase shifters in cryogenic environments. It analyses the optical and electrical properties of matter in a range of temperatures and the combined effect of the specific heat with the thermo-optic coefficient. It presents simulation results on integrated photonic devices' electrical and optical properties. It also presents measurement protocols for low-temperature characterisation using different cryogenic systems. Finally, it shows that standard thermo-optic phase-shifters can be used at low temperatures with a slight increase (<10%) in power consumption. This validates the route towards the scalability of integrated quantum photonic systems.

Date of Award	23 Jan 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Mark G Thompson (Supervisor)