Tapered Waveguide Near-Field Transducer for TAR Head
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Solution Overview
Problem
Conventional thermally-assisted recording (TAR) systems require high laser power to efficiently heat the magnetic recording material, which can lead to thermal instabilities and data loss due to the high magneto-crystalline anisotropy of the recording media.
Innovation Solution
A TAR head design featuring a near-field transducer (NFT) with a tapered optical waveguide that concentrates light energy at the air-bearing surface, generating an evanescent wave that couples efficiently to surface plasmons, reducing the required laser power by focusing energy at the center of the waveguide and directing it to the NFT output end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high laser power is used to heat the magnetic recording material, then the thermal stability of recorded data is improved, but thermal instabilities and data loss occur due to high magneto-crystalline anisotropy
Solution Approach 1:
The waveguide structure is designed with different cross-sectional widths at different positions (wider at input, narrower at output) to create localized optical field concentration. This local structural variation enables the optical energy to be focused precisely at the NFT output end where heating is needed, rather than distributing energy uniformly throughout the waveguide.
Solution Approach 2:
The invention transitions from a uniform cross-section waveguide to a tapered waveguide with varying cross-sectional dimensions. This dimensional change along the waveguide length creates a gradient in optical field intensity, concentrating energy at the narrower output end where the NFT is located, thereby achieving localized heating with reduced overall power requirements.
2Stability of the object's composition
If high magneto-crystalline anisotropy (Ku) is used in recording media, then thermal stability of recorded data is improved, but coercivity increases beyond the write field capability of the write head
Solution Approach 1:
The invention changes the temperature parameter of the magnetic recording material dynamically during the writing process. By heating the material to elevated temperatures using the tapered waveguide-NFT system, the coercivity of the high-Ku magnetic material is temporarily reduced to levels that can be overcome by the write head's magnetic field, enabling successful data writing while maintaining high thermal stability at ambient temperatures.
3Device complexity
If conventional waveguide structure is used, then device complexity is reduced, but laser power requirements increase
Solution Approach 1:
The waveguide is designed with non-uniform cross-sectional dimensions, being wider at the input end and narrower at the output end. This local variation in geometry creates a gradient in the optical mode confinement, causing the optical field to become increasingly concentrated as it propagates along the waveguide. The result is enhanced light energy density at the NFT output end, improving coupling efficiency and reducing the total laser power needed.
Solution Approach 2:
The tapered waveguide introduces a gradual geometric transition rather than an abrupt change. This curved/tapered profile allows for adiabatic mode transformation, where the optical mode smoothly adapts to the changing waveguide dimensions, minimizing reflection losses and maximizing energy transfer to the NFT with reduced power requirements.
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
This design reduces laser power requirements while maintaining thermal stability and data integrity by concentrating light energy and increasing the intensity of the evanescent wave, enhancing the coupling efficiency between the waveguide and surface plasmons.
Implementation Method 1
an evanescent wave is generated at the waveguide's tapered surface and couples to a surface plasmon excited on the surface of the NFT
Implementation Method 2
The evanescent wave generated at a surface of the waveguide couples to surface plasmons excited on the surface of the NFT and a strong optical near-field is generated
Implementation Method 3
The surface of the waveguide facing the NFT back edge is tapered, with a width W1 in the cross-track axis direction at a region recessed from the ABS and a width W2 less than W1 in the cross-track axis direction at an end near the ABS
Implementation Method 4
a near-field transducer (NFT) for heating the recording material on the disk... At the apex of the NFT output an optical near-field spot is generated in the space at the ABS between the apex and the write pole
Implementation Method 5
The write pole applies a magnetic field at the optical spot
Data Source
AI summary
A thermally-assisted recording (TAR) head for recording data in data tracks of a TAR disk has an air-bearing slider that supports a near-field transducer (NFT) and an optical waveguide that directs laser light to the NFT. The NFT has an output end at the slider's air-bearing surface (ABS) located between the write pole and the optical waveguide in the along-the-track direction. The NFT output end is generally triangularly shaped with an apex facing the write pole and a back edge wider than the apex in the cross-track axis direction facing the waveguide. The surface of the waveguide facing the NFT back edge is tapered, with a width in the cross-track axis direction at a region recessed from the ABS and a smaller width in the cross-track axis direction at an end near the ABS.