Single-Step Deposition of Cerium-Substituted Yttrium Iron Garnet for Monolithic On-Chip Optical Isolation

Abstract

Photonic integrated circuits require magneto-optical (MO) materials for making nonreciprocal devices such as isolators and circulators. The most successful MO materials are rare-earth-substituted iron garnets, but these can be challenging to grow on silicon without a seed layer, which introduces spacing loss between the waveguide and the MO cladding. A pulsed-laser deposition (PLD) method is used for making MO Ce:YIG (Ce[superscript 1]Y[superscript 2]Fe[superscript 5]O[superscript 12])/YIG (Y[superscript 3]Fe[superscript 5]O[superscript 12]) bilayer or trilayer films on different substrates, including silicon, quartz, and Gd[superscript 3]Ga[superscript 5]O[superscript 12] (GGG), in which a multilayer film is deposited in one run and then annealed. A YIG seed layer grown above the MO Ce:YIG facilitates recrystallization during ex situ rapid thermal annealing, which results in a reduced thermal budget and simplified deposition process. A monolithically integrated optical isolator was demonstrated by direct deposition of a bilayer Ce:YIG/YIG capping layer onto a silicon-on-insulator resonator. The device exhibited an insertion loss of 7.4 ± 1.8 dB and an isolation ratio of 13.0 ± 2.2 dB within the telecommunication window (λ = 1564.4 nm), which outperforms previously reported monolithic isolators.