Interleaved Laser Current Calibration for HAMR Heads
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Solution Overview
Problem
Conventional laser calibration techniques for heat-assisted magnetic recording (HAMR) heads are time-consuming and cannot be used during normal service due to time and customer constraints, as they involve writing individual tracks with single operational currents and analyzing bit error rate (BER) for each, which is impractical for field use.
Innovation Solution
The method involves interleaving the laser current throughout a revolution of the magnetic recording medium to average out variations in write performance metrics, reducing the time required for calibration by writing sectors using different operational currents and calculating the best average write performance metric.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional laser calibration techniques are used (writing individual tracks with single operational currents and analyzing BER for each), then measurement precision is improved, but loss of time increases significantly
Solution Approach 1:
The calibration process is segmented by dividing the magnetic recording medium into multiple sector groups distributed around the circumference, with each sector group containing multiple sectors. Different operational currents are applied to different sectors within each sector group, allowing parallel calibration measurements across multiple sectors simultaneously rather than sequentially writing individual tracks.
Solution Approach 2:
Multiple calibration measurements using different operational currents are merged into a single calibration pass by interleaving the currents across different sectors. The controller combines the BER measurements from all sectors into a single average write performance metric, enabling comprehensive calibration data collection in one operation rather than requiring separate track writings for each current level.
2Manufacturing precision
If multiple different operational currents are tested to find the optimal current, then manufacturing precision is improved, but productivity decreases due to time constraints
Solution Approach 1:
The calibration process maintains continuous useful action by interleaving multiple operational currents across different sectors within the same rotation of the magnetic recording medium. This allows the calibration to proceed continuously in a single pass without stopping to rewrite tracks or perform separate measurements for each current level, thereby maintaining high productivity while still testing multiple current values.
Solution Approach 2:
The system performs preliminary action by pre-configuring the sector groups and interleaving pattern before the calibration run. The controller is pre-programmed with the sector group assignments and current interleaving sequence, allowing the calibration to execute efficiently without real-time decision-making delays, thus improving both precision and productivity.
3Reliability
If calibration is performed during normal service to improve reliability, then reliability is improved, but loss of time increases due to service interruptions
Solution Approach 1:
The calibration process uses periodic action by implementing a repeating interleaved current pattern across sector groups that completes within a single or few rotations of the magnetic recording medium. This periodic structure allows calibration to be performed rapidly during normal service operations without causing significant interruptions, as the calibration cycle repeats efficiently and can be completed between customer-access intervals.
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 approach significantly reduces the time needed for laser calibration, achieving a tighter distribution of bit error rate (BER) around the medium, improving calibration efficiency and accuracy, and allowing for faster identification of the optimal operational current.
Implementation Method 1
heat-assisted magnetic recording head... laser diode of the head... different operational currents supplied to the laser diode
Data Source
AI summary
A heat-assisted magnetic recording head is moved relative to a magnetic recording medium. The medium comprises a plurality of sectors. The sectors define a plurality of sector groups distributed around a circumference of the medium. The sectors of each sector group are written using different operational currents supplied to a laser diode of the head such that at least one sector from each sector group is written using one of the different operational currents. For each of the different operational currents, an average write performance metric is calculated for all sectors written at each of the different operational currents. A particular operational current of the different operational currents is determined that results in a best average write performance metric.