Monolithic optical isolators that provide modal (transverse electric, TE) and dimensional (500 nm core) matching to on-chip lasers have been realized with "one step" seedlayer-free garnets. To date, seedlayer-free garnet claddings have required thinner (<340 nm) silicon-on-insulator (SOI) cores because mode-cladding interactions were too weak for laser-matched cores. However, laser matching is important because tapers and mode converters between the laser and the isolator can cause detrimental reflections prior to isolation. This paper reports the use of cerium-doped terbium iron garnet (Ce:TbIG) in a quasi-phase matched nonreciprocal mode conversion (NRMC) isolator that operates on both TE and TM modes without an external field. A key innovation presented here is a repeatable process for foundry-friendly sputter deposition of Ce:TbIG, which enables this high Faraday rotation material (-3200°/cm) to be synthesized in any isolator design that would benefit from one-step lithographical manufacturing. A proof-of-feasibility 500 nm SOI NRMC device is demonstrated with seedlayer-free Ce:TbIG that achieves an isolation ratio of 11 dB. With an optimal length, this NRMC design can provide greater than 30 dB isolation.
Bibliographical noteFunding Information:
This research was sponsored as a World Materials Network project by the U.S. National Science Foundation (DMR-1210818) and the U.K. Engineering and Physical Sciences Research Council (EP/J018708/1) and also supported by the China Scholarship Council. Parts of this work were carried out in the Characterization Facility and the Minnesota Nano Center, University of Minnesota, which receives partial support from the NSF through the MRSEC and the National Nano Coordinated Infrastructure Network (NNCI Award Number 1542202) programs, respectively. The authors acknowledge the valuable support of waveguide patterning by the technical staff of the James Watt Nanofabrication Centre. Useful discussions with Dr. Barry Holmes are acknowledged by the authors.
© 2019 American Chemical Society.
- Faraday rotation
- cerium-doped terbium iron garnet
- magnet-free isolators
- magneto-optical garnets
- non-reciprocal mode conversion
- silicon photonics