Research On Laser Heat-Assisted Magnetic Recording Based On Ring Resonator And Nano-Antenna System

Heat assisted magnetic recording（HAMR）is a promising technique with high recording density.Its high recording density lies in the fact that the size of each recording bit is reduced to the order of nanometer,which is achieved by using laser heating the recording medium to break through the size limits of magnetic recording.Due to the diffraction limit,it is difficult for the far-field optical focusing method to make the heated spot size reach the required recording bit size,so a near-field transducer is usually used to apply with the method of near-field optics,so as to reduce the spot size and improve the laser energy density.The authors’team proposes a new HAMR device in which the near-field transducer is a metal nano-antenna connected to a semiconductor ring resonator that acts as a light source,acting as a nano-heater.For this device,local surface plasmon resonance at the tip of the nano-antenna excites near-field light to form extremely small recording bits of the nanometer order to increase the recording density.And because the light source is integrated,the energy loss of light transmission process is small,and the equipment is small to be easily to be integrated in the magnetic recording head.In order to improve the performance of the device,the effects of the nano-antenna shape,length and bottom diameter on the spot size and energy density of the near-field light were calculated by numerical simulation.A new dielectric-core-metal-shell nano-antenna was also discussed to improve the energy density of the antenna.The simulation results show that the minimum spot size of near-field light can reach 18×18 nm²,which means the magnetic recording density can reach 2.1Tb/inch²,and the theoretical maximum normalized energy density of the tip of the nano-antenna can reach 5.28×10²⁰m^-3.In addition,the oscillation of the ring resonator as an integrated light source should be stable to produce a stable near-field light with appropriate energy density to heat the recording medium.The resonant frequency,the distribution of electric field intensity and the normalized energy density of the tip of the nano-antenna are calculated by numerical simulation.The results show that the wider the ring width,the more stable and maneuverable the resonant frequency and normalized energy density are,and the wider the manufacturing tolerance is.Although some higher order radial modal solutions are unnecessary in this case,they are easy to control.When the ring size becomes smaller,the frequency interval between adjacent modes becomes wider,thus improving the stability of laser oscillation.A non-axisymmetric ring resonator is proposed to improve the oscillation stability and energy density.The results show that only one eigenmode can be selected when the inner centrifugal value of the non-axisymmetric ring resonator reaches a certain value,thus realizing the single-mode oscillation.And the energy density can be increased to 21～27 times of the axisymmetric ring.The research of this paper provide a theoretical basis for the application of ring-resonator-nano-antenna device in heat assisted magnetic recording,and have done optimization of each part of the device.