Rectangular Waveguide for Shingled TAR Disk Drives
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Solution Overview
Problem
Thermally-assisted recording (TAR) disk drives face challenges in minimizing temperature drop between the peak temperature and the trailing edge of the write pole while maintaining low laser power, especially in wide-area heating systems that can cause adjacent-track erasure (ATE) and inefficient heat transfer.
Innovation Solution
A TAR disk drive using shingled recording with a rectangular waveguide as a wide-area heat source, featuring a high aspect ratio core and asymmetrical cladding layers to generate an elliptically-shaped optical spot that heats multiple data tracks, reducing temperature drop and maintaining low laser power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a wide-area heater is used to heat a large volume of recording layer, then the temperature drop is reduced and thermal stability is improved, but adjacent-track erasure (ATE) occurs and laser power requirements increase
Solution Approach 1:
The patent applies local quality by creating an asymmetrical optical intensity distribution within the heated area. The optical intensity is concentrated closer to the trailing edge of the write pole tip where it is needed for writing, while the intensity decreases toward the leading edge. This non-uniform heating pattern allows the heated region to extend across multiple tracks (reducing ATE) while maintaining high temperature where required for successful writing.
Solution Approach 2:
The patent employs asymmetry in the waveguide structure, specifically using a rectangular waveguide core with different dimensions in the cross-track direction versus the along-track direction. This asymmetrical geometry produces the desired asymmetrical optical spot pattern that concentrates heat where needed while spreading it wider in other dimensions to prevent adjacent track erasure.
2Temperature
If laser power is increased to maintain peak temperature, then thermal stability is improved, but energy consumption increases and heat transfer efficiency decreases
Solution Approach 1:
The patent changes the geometric parameters of the waveguide core, specifically using a rectangular cross-section with optimized aspect ratio. This parameter change modifies the optical mode confinement and intensity distribution, allowing more efficient coupling of laser energy to the recording layer and reducing the total laser power required to achieve the necessary peak temperature.
3Stability of the object's composition
If the waveguide core aspect ratio is optimized to concentrate peak optical intensity near the trailing edge of the write pole tip, then temperature drop is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent addresses manufacturing precision challenges by optimizing the aspect ratio of the rectangular waveguide core. By carefully selecting the ratio of cross-track width to along-track thickness, the design achieves the desired optical intensity distribution and minimal temperature drop through a geometric parameter that can be controlled during fabrication, transforming a complex intensity distribution problem into a manageable dimensional optimization.
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 effectively reduces temperature drop and maintains peak temperature closer to the write pole tip, enhancing thermal stability and areal density without significant ATE, while optimizing laser power usage.
Implementation Method 1
The waveguide generates a generally elliptically-shaped optical spot that heats an area of the recording layer extending across multiple data tracks
Implementation Method 2
This moves the peak temperature point of the heated area closer to the write pole tip and reduces the temperature drop between the peak temperature and the temperature at the trailing edge of the write pole tip where writing occurs
Implementation Method 3
A TAR disk drive with a 'small-area' heater direct heat to just the area of the data track where data is to be written by the write head. The most common type of small-area TAR disk drive uses a laser source and an optical waveguide with a near-field transducer (NFT)
Implementation Method 4
In some proposed TAR systems, the magnetic recording material is heated to near or above its Curie temperature
Implementation Method 5
NFTs typically use a low-loss metal (e.g., Au, Ag, Al or Cu) shaped in such a way to concentrate surface charge motion at a surface feature shaped as a primary apex or tip. Oscillating tip charge creates an intense near-field pattern. The electromagnetic field of the oscillating tip charge gives rise to optical output in the near field, which is directed onto to the magnetic recording medium to heat just the area exposed to the write field from the write head
Implementation Method 6
Since it is known that the coercivity of the magnetic material of the recording layer is temperature dependent, one proposed solution to the thermal stability problem is thermally-assisted recording (TAR), also called heat-assisted magnetic recording (HAMR), wherein the magnetic recording material is heated locally during writing to lower the coercivity enough for writing to occur, but where the coercivity/anisotropy is high enough for thermal stability of the recorded bits at the ambient temperature of the disk drive
Implementation Method 7
The recorded data is then read back at ambient temperature by a conventional magnetoresistive (MR) read head
Implementation Method 8
one proposed solution to the thermal stability problem is thermally-assisted recording (TAR), also called heat-assisted magnetic recording (HAMR), wherein the magnetic recording material is heated locally during writing to lower the coercivity enough for writing to occur
Data Source
AI summary
A thermally-assisted recording (TAR) disk drive uses “shingled” recording and a rectangular waveguide as a “wide-area” heat source. The waveguide generates a generally elliptically-shaped optical spot that heats an area of the recording layer extending across multiple data tracks. The waveguide core has an aspect ratio (cross-track width to along-the track thickness) that achieves the desired size of the heated area while locating the peak optical intensity close to the trailing edge of the write pole tip where writing occurs. The large cross-track width of the waveguide core increases the volume of recording layer heated by the optical spot, which reduces the rate of cooling. This moves the peak temperature point of the heated area closer to the write pole tip and reduces the temperature drop between the peak temperature and the temperature at the trailing edge of the write pole tip where writing occurs.