Investigation on how to excite a desired eigenmode selectively in the ring-resonator-type device for heat-assisted magnetic recording

Abstract

Heat-assisted magnetic recording (HAMR) is a promising technology for achieving more than 10 Tb/inch² recording density. A near-field transducer (NFT), which forms a small light spot on a recording medium, is necessary in HAMR. The authors’ group has proposed a novel device, in which a metal nano-antenna as an NFT is attached to a semiconductor ring resonator as a light source. There are multiple eigenmodes in this device. If they are excited simultaneously, the device becomes unstable because of the mode competition. Moreover, a near-field light is generated at the tip of nano-antenna for some eigenmodes but not generated for other eigenmodes. Therefore, in this study, how to excite a desired eigenmode selectively among the multiple eigenmodes was investigated through a numerical simulation. The eigenmodes were classified into four types: modes in the radial direction (characterized by the order of mode <i>l</i>), modes in the tangential direction (characterized by the order of mode <i>m</i>), even and odd modes, and TE and TM modes. The mode with <i>l</i> = 1 could be excited by increasing the inner diameter of the ring resonator. The mode with specific <i>m</i> and the even mode could be excited by forming the slits in the ring resonator and using the frequency dependence of gain. The TE mode could be excited automatically because of its strong light confinement in the active layer. By combining these methods, the device could be made stable and the near-field light could be generated at the tip of nanoantenna.