Programmable photonic matrices using hybrid silicon - phase change devices

Abstract

This thesis aims to develop and characterise hybrid silicon-on-insulator integrated photonic devices clad with low-loss optical phase change materials. Thin films of such materials can be optically addressed using direct writing with short pulses of above-bandgap laser light, thereby enabling reversible, non-volatile programming capabilities to be incorporated into a range of integrated devices without the need for any external regulatory electronics or equipment. These devices have far-reaching applications, particularly in the fields of optical and neuromorphic computing, as well as quantum simulation and the creation of optical analogue systems

In this work, I introduce a platform based on multi-mode interferometers and arrays of coupled silicon waveguides clad with thin films of the ultra-low-loss chalcogenide phase change material antimony tri-selenide. Devices are experimentally programmed and characterised using a contact-free prism coupler to address multiple output ports simultaneously. The systems under study showcase the ability of our platform to realise a wide variety of transmission matrices using a single device geometry, achieved by inscribing nanoscale refractive index perturbation patterns into the phase change film.

A crucial step in advancing this technology is the creation of an inverse design protocol capable of predicting the required refractive index pixel pattern for a given target transmission matrix. In the later stages of this work I present a machine-learning-based inverse design approach, built around neural network surrogate models, designed for near real-time prediction of pixel patterns to implement any arbitrary unitary transformation. We demonstrate full control over both the phase and amplitude of all matrix elements, matching the performance of several commercially available alternative technologies, before examining some of the challenges and constraints associated with the scaling of such an approach.

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Identifiers

ORCID for Otto Muskens: orcid.org/0000-0003-0693-5504

ORCID for Alberto Politi: orcid.org/0000-0002-3668-9474

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