Low-thermal-budget monolithic integration of optical isolators for silicon photonics

Integrated optical isolators are crucial components of Photonic Integrated Circuits (PICs) and have garnered significant attention. Monolithic integration using magneto-optical materials is ideal for optical isolator fabrication due to its compact footprint, broadband, polarization-diverse operation, and scalability. However, current monolithic optical isolators face a major challenge: a high thermal budget required for the deposition and crystallization of magneto-optical materials, hindering their integration into foundry-processed PICs. This study introduces a novel approach for monolithic integration of on-chip optical isolators with a low thermal budget, compatible with standard CMOS Back-End-of-Line (BEOL) processes. The proposed optical isolators employ Bismuth Yttrium Iron garnet with a lower crystallization temperature and integrated micro-doped silicon heaters for local heat treatment, presenting a new method for incorporating non-reciprocity into various integrated photonic devices.