Magnon–photon coupling in the YIG-based disk and ring microcavities

Optomagnonic dielectric resonators offer a promising platform for the bidirectional conversion of microwave and optical photons at the single quantum level. Current implementation of such a conversion suffers from low magneto-optical interaction strength, limiting its practical utilization in quantum technologies. The main bottleneck is the small spatial overlap between optical and magnon modes. Here, we show that the utilization of a disk and ring geometries notably increases the mode overlap. We analyze the interaction volume of optical whispering gallery and magnon Kittel modes inside yttrium iron garnet disk and ring microcavities of various sizes and found a significant improvement in mode coupling up to ∼4.5 kHz. Maximal theoretical optomagnonic conversion efficiency for small disks with a radius of 40–50 μm can reach unity for an optimal optical power of ∼100mW. Strategies for further improvements of interactions are discussed.