Multi-ridged Subwavelength Aperture for Elongated Hot Spot
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Solution Overview
Problem
Conventional subwavelength apertures have poor transmittance efficiency for heating small areas in magnetic media, requiring high power lasers and producing circular hot spots that do not match the elongated shape of magnetic data bits, limiting data recording density.
Innovation Solution
A multi-ridged subwavelength aperture with closely spaced ridges is integrated into a magnetic head, coupled with an optical resonant cavity to produce an elongated hot spot with a predetermined aspect ratio, enhancing near-field optical heating efficiency and conforming to the shape of magnetic data bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a conventional circular subwavelength aperture is used for near-field heating, then a circular hot spot is produced, but the transmittance efficiency is very poor and the hot spot shape does not match the elongated shape of magnetic data bits
Solution Approach 1:
The aperture is divided into multiple ridges (typically three ridges forming a Y-shaped or multi-lobed pattern) instead of a single circular opening. Each ridge acts as an independent optical antenna that generates its own hot spot, and the combination of these segmented hot spots creates an elongated overall heating pattern that matches the aspect ratio of magnetic data bits while maintaining higher transmittance efficiency through each individual ridge structure
Solution Approach 2:
The aperture transitions from a symmetric circular shape to an asymmetric multi-ridged configuration. The ridges are positioned at specific angles and distances from the center, creating an asymmetric field distribution that produces an elongated hot spot pattern. This asymmetric geometry allows the aperture to generate a heating pattern with the desired aspect ratio (typically 2:1 or 3:1) while maintaining efficient optical transmission through the ridged structure
2Area of moving object
If the aperture size is reduced to heat smaller areas for higher data density, then the heated area is reduced, but the transmittance efficiency decreases as (r/λ)4 requiring high power lasers
Solution Approach 1:
By segmenting the aperture into multiple ridges, each ridge acts as an efficient optical antenna with its own transmission channel. This segmentation allows the total heated area to be reduced while each individual ridge maintains high transmittance efficiency, avoiding the (r/λ)4 efficiency loss that would occur with a single small circular aperture of equivalent total area
Solution Approach 2:
The ridged aperture creates localized high-intensity hot spots at specific positions corresponding to each ridge, rather than distributing energy uniformly across a circular area. This local concentration of energy maintains high transmittance efficiency at each ridge location while the overall heated footprint is reduced and shaped to match the data bit dimensions
3Quantity of substance
If higher data areal storage densities are pursued with smaller bit cells, then the volume of recording material is decreased, but the superparamagnetic limit is approached requiring thermally assisted recording
Solution Approach 1:
The ridged aperture is positioned to create hot spots that precede the magnetic write pole tip in the down-track direction. This preliminary heating action softens the magnetic media coercivity before the write pole arrives, enabling reliable writing of smaller bit cells that would otherwise be affected by the superparamagnetic limit. The heating pattern is pre-configured to match the anticipated bit cell geometry
Solution Approach 2:
The aperture geometry (ridge number, spacing, and dimensions) is optimized to produce hot spots with specific temperature profiles and spatial distributions. By controlling the physical parameters of the ridges (width, separation, distance from substrate), the heating characteristics are tuned to achieve the precise temperature elevation needed to temporarily reduce coercivity in the smallest viable bit cell dimensions while maintaining magnetic stability after cooling
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves higher data areal storage densities and improved coercivity in magnetic media, enabling scalable data recording beyond 1 Tbits/in2 with a heated spot that approximates the aspect ratio of magnetic data bits, thus overcoming the limitations of conventional technologies.
Implementation Method 1
Subwavelength apertures are known for the transmission of optical energy... optical energy that passes through it creates a single, approximately round hot spot in the near field away from the aperture
Implementation Method 2
A multi-ridged subwavelength aperture for optical transmission... The ridges may be closely spaced such that the hot spots associated with the ridges are likewise closely spaced and create an elongated hot spot
Implementation Method 3
coupled with an optical resonant cavity to produce an elongated hot spot with a predetermined aspect ratio, enhancing near-field optical heating efficiency
Implementation Method 4
Heat from the heating device temporarily reduces the localized coercivity of the magnetic media, such that the magnetic head is able to record data bits within the media
Data Source
AI summary
A subwavelength aperture includes a plurality of ridges that project from an aperture sidewall into the aperture opening. The ridges may be closely spaced such that the hot spots associated with the ridges are likewise closely spaced and create an elongated hot spot. The subwavelength aperture of the present invention may be adapted for use in a magnetic head of a hard disk drive for improved thermally assisted recording (TAR) of magnetic data bits. Such a magnetic head may include an optical resonant cavity that is fabricated within the magnetic head structure.