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arXiv · 2609.22841

High-Q Magneto-Optical Microdisk Resonators Based on Monocrystalline Bismuth-substituted Yttrium Iron Garnets

Takeru Yambe·Kota Taniguchi·Tatsuya Kitai·Daisuke Sato·Syuan Gao·Hajime Kumazaki·Shun Fujii·Takasumi Tanabe·Satoshi Iwamoto·Yasutomo Ota
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Abstract

Microresonators based on diverse material platforms have driven the progress of integrated photonics by enhancing light-matter interactions in compact volumes. Extending this strategy to magneto-optical (MO) media is highly attractive for nonreciprocal photonics, magnonics, and quantum transduction, yet compact high-Q resonators based on single-crystalline yttrium iron garnet (YIG) have remained elusive because of the difficulty of its nanofabrication. Here we demonstrate high-Q, small-mode-volume MO microdisk resonators based on monocrystalline Bi-substituted YIG (Bi:YIG). Low-loss Bi:YIG thin films prepared by bonding and thinning, combined with optimized Ar-plasma etching, enable submicron-thick, air-suspended microdisks that support telecom-band whispering-gallery modes with $Q = 1.52\times 10^5$, a mode volume $V \approx 200$ cubic wavelengths, and $Q/V \approx 760$, representing an orders-of-magnitude improvement for integrated high-Q YIG MO cavities. The device exhibits clear magnetic-field-dependent spectral responses, including reciprocal resonance shifts and nonreciprocal frequency splitting of counter-propagating modes. A perturbative analytical model quantitatively reproduces these responses and indicates an effective MO coefficient about twice the bulk value, suggesting a possible miniaturization-induced enhancement. These results establish monocrystalline YIG microdisks as a compact high-Q MO platform for integrated isolators, optomechanics, microcombs, and photon-magnon quantum interfaces.

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Takeru Yambe, Kota Taniguchi, Tatsuya Kitai, Daisuke Sato, Syuan Gao, Hajime Kumazaki, Shun Fujii, Takasumi Tanabe, Satoshi Iwamoto, Yasutomo Ota. 2026-09-19. High-Q Magneto-Optical Microdisk Resonators Based on Monocrystalline Bismuth-substituted Yttrium Iron Garnets. https://arxiv.org/abs/2609.22841

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