HAMR Laser Power Prediction Using Thermal Sensor Feedback
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Solution Overview
Problem
Existing HAMR disk drives face challenges in accurately monitoring laser power during writing due to the slow response time of electrically conductive thermal sensors, making it difficult to maintain the output power within a predetermined range, which can result in either under-magnetization of data bits or adjacent bits being magnetized.
Innovation Solution
A thermal sensor is used to measure laser power, and a processor computes a prediction based on a history of laser power settings, comparing it to the measured value to generate an error signal for adjusting the laser power setting and initiating a re-write if necessary, with the thermal sensor located either adjacent to the waveguide recessed from the air-bearing surface or near the air-bearing surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an electrically conductive thermal sensor is used to monitor laser power, then the cost is reduced compared to using a photo-detector, but the response time is too slow for accurate laser power monitoring at each data sector
Solution Approach 1:
The system performs preliminary calibration to establish a relationship between thermal sensor readings and actual laser power. Historical laser power settings are stored and used to predict expected power levels, allowing the slow thermal sensor to provide useful information through pattern recognition and prediction algorithms.
Solution Approach 2:
The system implements feedback by comparing predicted laser power (based on historical settings and thermal sensor data) with actual thermal sensor measurements. When discrepancies are detected, the system adjusts laser power settings and initiates re-write operations, creating a closed-loop control system that compensates for the sensor's slow response time.
2Reliability
If laser power setting is increased to ensure proper magnetization of data bits, then the desired data bit will be magnetized, but adjacent bits will also be magnetized
Solution Approach 1:
The system uses feedback control to continuously monitor laser power through the thermal sensor and adjust settings in real-time. By comparing predicted power levels with actual measurements and making dynamic adjustments, the system maintains laser power within the optimal range, ensuring reliable magnetization of target bits while preventing interference with adjacent bits.
Solution Approach 2:
The system dynamically changes laser power parameters based on thermal sensor feedback and predicted power levels. By adjusting power settings in real-time rather than using fixed high power, the system achieves reliable magnetization while minimizing the risk of affecting adjacent bits through excessive power application.
3Object-affected harmful factors
If laser power setting is decreased to avoid magnetizing adjacent bits, then adjacent bits will not be magnetized, but the desired data bit will not be magnetized
Solution Approach 1:
The feedback mechanism continuously monitors thermal sensor readings and compares them with predicted power levels based on historical data. This allows the system to detect when laser power is insufficient and automatically adjust settings upward, ensuring reliable magnetization of target bits while maintaining control to prevent adjacent bit interference.
Solution Approach 2:
The system performs preliminary calibration and stores historical laser power settings to establish baseline expectations. This preliminary work enables the feedback system to make accurate real-time adjustments, ensuring that laser power is optimized for each writing operation to achieve reliable magnetization without affecting adjacent bits.
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 solution allows for accurate monitoring and adjustment of laser power, ensuring that data bits are properly magnetized without affecting adjacent bits, improving the accuracy and reliability of the HAMR disk drive.
Implementation Method 1
an electrically conductive thermal sensor has been proposed
Implementation Method 2
an optical waveguide with a near-field transducer (NFT) directs heat from a radiation source, such as a laser, to heat localized regions of the magnetic recording layer on the disk
Implementation Method 3
The radiation heats the magnetic material locally to near or above its Curie temperature to lower the coercivity enough for writing to occur by the write head
Data Source
AI summary
A thermally-assisted magnetic recording (HAMR) disk drive uses a thermal sensor to accurately monitor laser power during writing. The disk drive controller, or a separate processor, computes a prediction of the laser power from a history of laser power settings. This predicted value is compared with the measured value from the thermal sensor. If the difference is too large or too small, indicating that the laser power is too high or too low, an error signal is sent to the disk drive controller. The disk drive controller may adjust the laser power setting and initiate a re-write of the data. The predicted laser power is calculated from a convolution of a sequence of current and prior laser power settings with a sequence of coefficients. A calibration process generates the sequence of coefficients when the disk drive is idle or just after it is powered on.