Simulation on double-ring-resonator-type device considering gain for heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is a promising technology for improving the recording density of hard disk drives. A near-field transducer (NFT), which forms a small light spot on a recording medium, is necessary in HAMR. The authors’ group previously proposed a device, in which a metal nano-antenna acting as an NFT is attached to a semiconductor ring resonator acting as a laser. There are TE- and TM-like modes in the ring resonator. Because a near-field light is generated at the tip of nano-antenna only in TE-like mode, how to excite TE-like mode selectively is an important issue. In this study, a numerical simulation considering gain was conducted to investigate whether a double-ring-resonator-type device is effective for improving the mode selectivity between TE- and TM-like modes. The size of the ring resonators was determined so that the resonance frequency of each ring resonator was almost the same for TE-like mode and slightly different for TM-like mode. The double-ring-resonator-type device was found to be effective for making the laser oscillation with TE-like mode more dominant than with TM-like mode. The size of the smaller ring resonator should not be too small to secure practical manufacturing tolerance. Moreover, both ring resonators should have gain to obtain adequate gain for each mode and energy density at the tip of nano-antenna simultaneously.