Optimal Mode Matching Study Of Optomagnonic Whispering-gallery Mode Microdisk Cavities

Hybrid quantum systems,such as optomechanic systems,optomagnonic systems and cavity quantum electrodynamical systems are important platforms in nanophotonics and quantum information science.Among these hybrid systems,optomagnonic system can support the interaction between light(photons)and spin waves(magnons)which is the key platforms for the realization of magnon-mediated microwave to optical transducers in various applications of quantum computing.In the optomagnonics structure,many physical phenomena and applications are realized on the basis of the strong coupling between photons and magnons.The coupling strength is an important parameter to characterize the performance of the optical magnetic system.Recently,the coupling between the photons and the magnons is mainly concentrated on the Kittle mode.Its advantage is that the mode is evenly distributed in the whole cavity,which is convenient for detection and external tuning.However,the Kittle mode is a bulk mode and has a small overlap with whisperinggallery-mode(WGM)optical field,resulting in the low coupling efficiency.It has been found that its coupling intensity is limited to about 10 Hz.Recently,the theory of coupling photons with higher-order magnon modes in microcavity through selection rules has been proposed,which effectively improves the efficiency of optomagnonical coupling.In order to improve the coupling strength of photons and magnons in the optomagnonic system,this paper establishes the coupling model between microdisk resonator and fiber cone in whispering-gallery mode,studies the mode matching between photons and magnons,and obtains the following results:1.We use Lagrange multiplier method to calculate the theoretical upper bound of photon magnon coupling constant in kittle mode and higher-order magnon mode.we find the coupling constant can approach 87.6×2π Hz in Kittle mode,and 459×2π Hz in high-order magnon mode for a yttrium iron garne(YIG)microdisk cavity with a radius of 300 microns and a thickness of 10 microns.2.Through the magnetization dynamic equation,we study the distribution of the magnetic amplitude in the YIG microdisk cavity and analyze the overlap between the magnetic amplitude and the WGM optical field.We find that there is a strong coupling between the magnon mode and the optical mode near the edge of the cavity.Next,we discuss the influence of different microcavity size parameters on the coupling strength.We believe these results may provide an efficient way for enhancing the magneto-optical interaction in the optical devices,which will facilitate the development of magneto-optical control,optical-microwave interaction,and optical nonlinearity.