Building Large-Scale Active Devices in a Suspended GaAs PIC platform

: Engineering Centimeter-Scale Push-Pull Modulator Exploiting the GaAs r41 Pockels Asymmetry

Abstract

Electro-optic modulators (EOMs) underpin a wide range of critical applications in both classical and quantum information processing. While traditionally the focus has been on building these devices in materials with large Pockels coefficients (mainly ferroelectric insulators like lithium niobate), there is a need to engineer EOMs in a semiconductor platform with a view towards device stability (in radiation-hard en-vironments), manufacturability (wafer size and foundry compatibility), and integration (with active electronics and quantum confined structures). Gallium arsenide (GaAs) is thus a compelling choice towards monolithic integration with high integration density while preserving excellent electro-optic performance. In addition to its modulation functionality, GaAs exhibits advantages in manufacturability, thermal and radiation stability, and offers potential in seamless integration with high-speed electronics and quantum-confined struc-tures. These advantages make GaAs photonic integrated circuits competitive solutions for demands from modern communication systems, which show increasing demands on high data transmission rates and energy efficiency.

In this thesis, centimeter-scale electro-optic modulation is demonstrated on a suspended GaAs platform by integrating concepts from micro-electro-mechanical systems (MEMS) with photonic circuit design. By suspending optical structures on a GaAs membrane, optical modes are confined within micrometer scale and photonic routing is achieved with small footprints (<20 µm bending radii). We present the first demonstration of the scalable suspended GaAs EOM by demonstrating up to 2.5 cm-long suspended electro-optic modulator while exploiting the GaAs Pockels r41 asymmetry for push-pull operation. This work marks a major breakthrough in bringing the suspended GaAs photonic integrated circuit (PIC) to the active domain, providing great potential in developing large-scale, high-performance photonic systems for future applications.

Date of Award	30 Sept 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Krishna Coimbatore Balram (Supervisor) & Robert Thomas (Supervisor)