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

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 (Ce1Y2Fe5O12)/YIG (Y3Fe5O12) bilayer or trilayer films on different substrates, including silicon, quartz, and Gd3Ga5O12 (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 siliconon-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 (lambda = 1564.4 nm), which outperforms previously reported monolithic isolators.