
Proceedings Paper
Multi-objective inverse design of sub-wavelength optical focusing structures for heat assisted magnetic recordingFormat | Member Price | Non-Member Price |
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Paper Abstract
We report using Inverse Electromagnetic Design to computationally optimize the geometric shapes of metallic
optical antennas or near-field transducers (NFTs) and dielectric waveguide structures that comprise a sub-wavelength
optical focusing system for practical use in Heat Assisted Magnetic Recording (HAMR). This magnetic data-recording
scheme relies on focusing optical energy to locally heat the area of a single bit, several hundred square nanometers on a
hard disk, to the Curie temperature of the magnetic storage layer. There are three specifications of the optical system that
must be met to enable HAMR as a commercial technology. First, to heat the media at scan rates upward of 10 m/s,
~1mW of light (<1% of typical laser diode output power) must be focused to a 30nm×30nm spot on the media. Second,
the required lifetime of many years necessitates that the nano-scale NFT must not over-heat from optical absorption.
Third, to avoid undesired erasing or interference of adjacent tracks on the media, there must be minimal stray optical
radiation away from the hotspot on the hard disk. One cannot design the light delivery system by tackling each of these
challenges independently, because they are governed by coupled electromagnetic phenomena. Instead, we propose multiobjective
optimization using Inverse Electromagnetic Design in conjunction with a commercial 3D FDTD Maxwell’s
equations solver. We computationally generated designs of a metallic NFT and a high-index waveguide grating that meet
the HAMR specifications simultaneously. Compared to a mock industry design, our proposed design has a similar
optical coupling efficiency, ~3x improved suppression of stray optical radiation, and a 60% (280°C) reduction in NFT
temperature rise. We also distributed the Inverse Electromagnetic Design software online so that industry partners can
use it as a repeatable design process.
Paper Details
Date Published: 5 September 2014
PDF: 13 pages
Proc. SPIE 9201, Optical Data Storage 2014, 92010M (5 September 2014); doi: 10.1117/12.2062531
Published in SPIE Proceedings Vol. 9201:
Optical Data Storage 2014
Ryuichi Katayama; Thomas D. Milster, Editor(s)
PDF: 13 pages
Proc. SPIE 9201, Optical Data Storage 2014, 92010M (5 September 2014); doi: 10.1117/12.2062531
Show Author Affiliations
Samarth Bhargava, Univ. of California, Berkeley (United States)
Eli Yablonovitch, Univ. of California, Berkeley (United States)
Published in SPIE Proceedings Vol. 9201:
Optical Data Storage 2014
Ryuichi Katayama; Thomas D. Milster, Editor(s)
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