Heat-assisted magnetic recording (HAMR) is a promising technology to increase the recording density of hard disk drives to more than 10 Tb/inch2. In HAMR, a near-field transducer (NFT) is necessary to form a light spot with the order of 10 nm to heat the recording medium locally to reduce its coercivity during recording. The authors’ group has proposed a device for HAMR, in which a metal nano-antenna acting as an NFT is attached to a semiconductor ring resonator acting as a light source. Because the characteristics of near-field light are influenced by the material and structure of nano-antenna, we investigated a metal-dielectric hybrid nano-antenna in this study. Especially, a core-shell-type nano-antenna, in which a dielectric sphere as a core was embedded in a gold tip as a shell, was taken as an example, and how the core refractive index and core radius influence the energy density and spot size of near-field light was numerically simulated. The tip radius of nano-antenna was 25 nm. As a result, when the core radius was 20 nm, maximum energy density of about 25 times and minimum spot size of about 91% compared with conventional gold-only nano-antenna were obtained at the core refractive index of 4.4 and 4.8, respectively. As the core refractive index became higher, the optimum core radius became smaller. Moreover, the behavior of energy density could be understood by one-sphere model and that of spot size could be understood by two-sphere model, both of which are determined by the localized surface plasmons.
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 l), modes in the tangential direction (characterized by the order of mode m), even and odd modes, and TE and TM modes. The mode with l = 1 could be excited by increasing the inner diameter of the ring resonator. The mode with specific m 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.
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