ECE EDS Seminar: Bethanie Stadler: Magneto-Optical Garnets for Integrated Photonics Isolators



Cornell Electron Devices Society (EDS) presents:

Bethanie Stadler
University of Minnesota

Magneto-Optical Garnets for Integrated Photonics Isolators

Photonic isolators are essentially diodes for optical signals, and as such they prevent backward propagation of light as needed, most frequently in front of lasers as protection from reflected power. After introducing the phenomenon of non-reciprocity, the operation of commercial (bulk) isolators will be discussed including magneto-optical Faraday rotation which is prevalent in iron garnets. Although commercial isolators have their own markets, future hyperscale data needs are moving ever closer to integrated photonics as pluggable transceivers are replaced by on-board optics and co-packaged optics. The laser is the most sensitive element in integrated photonics, and passive (zero power) isolators require magneto-optical garnet films in one of two configurations. The first configuration involves the use of permanent magnets to achieve a transverse magnetization in the garnet, which in turn achieves a non-reciprocal phase shift (NRPS) in the propagating signal. Isolation is then achieved by either a Mach Zhender Interferometer or a Ring Resonator. However, these devices only work in TM-mode operation unless bulky polarization converters or difficult sidewall coating are employed. The second configuration involves longitudinal magnetization for non-reciprocal mode conversion (NRMC). This magnetization is the remnant state of the garnet, so no magnet is needed. In addition, cerium-doped terbium iron garnets (Ce:TbIG) with high Faraday rotation but low saturation magnetization can be designed to reduce dipole fields for zero device cross talk. In NRMC devices, quasi-phase matching can be used to offset any waveguide bi-refringence. The resulting devices are one-dimensional and polarization diverse (TM- and TE-mode operation), which benefits all current on-chip lasers (TE mode). The only downside to integrated garnets is their high crystallization temperatures. Monolithic integration is possible if the garnet is incorporated before temperature sensitive materials. Alternatively, large scale transfer lithography has been recently demonstrated where a simple anneal induced strain-mediated diffusion of vacancies to create an exfoliation gap between Ce:TbIG films and their growth wafers. Commercial grade devices are currently being produced and tested for fully integrated Si-photonic isolators.

Bethanie Stadler is a Professor and Associate Head of Electrical & Computer Engineering at the University of Minnesota, where she also holds the CS&E Distinguished Professorship and is on the Graduate Faculty of both Chemical Engineering & Materials Science and Mechanical Engineering. She earned her PhD from MIT and a BS from Case Western Reserve University. She is a Fellow of the Materials Research Society (MRS). Stadler works on magnetic nanowires for applications in RF design and biomedicine, including contact-free barcoded bandaids for deep labeling that is detected using novel magnetic readout. She also works on magneto-optical garnets for integrated photonics, including one-dimensional magnet-free isolators. Stadler has been a visiting professor at IMEC and KU Leuven in Belgium and also at Wright Patterson Air Force Base in Dayton Ohio. In 2015, Stadler was an IEEE Magnetics Society Distinguished Lecturer. She has taught at the IEEE Magnetic Summer School in India and Italy, and hosted the school in Minnesota in 2015. In serving MRS, Stadler has been a meeting chair (Fall 2004), director on the board, secretary and chair of the program development subcommittee. She has also served as chair the program committee and in many other roles for the IEEE Magnetics Society, and she will be the General Co-Chair of Intermag 2023 in Sendai, Japan.

Sponsored by

School of ECE, Cornell University
Partially funded by GPSAFC