HAMR Laser Write Power Calibration via Error Function Coefficient
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Solution Overview
Problem
Current data storage devices face challenges in accurately calibrating the write power of lasers during heat-assisted magnetic recording (HAMR) to prevent undersaturation and inter-track interference, which affects data reliability and quality.
Innovation Solution
The calibration of the operating write power for the laser is achieved by estimating a coefficient of an error function using track width metrics and peak amplitudes generated from test patterns written at different power levels, ensuring optimal recording conditions without damaging the laser or causing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser write power is increased to improve data recording quality, then recording reliability is improved, but inter-track interference increases
Solution Approach 1:
The patent applies parameter changes by systematically varying the laser write power level to establish a calibration curve that relates write power to track width. This enables selection of an optimal write power parameter that achieves sufficient data recording reliability while maintaining track width within limits that prevent inter-track interference.
Solution Approach 2:
The patent replaces direct mechanical measurement of track width with an optical measurement system using a read element to detect magnetic transitions. This substitution enables precise, non-contact measurement of track width through read signal analysis, allowing accurate calibration of write power without mechanical intervention.
2Object-generated harmful factors
If laser write power is decreased to prevent inter-track interference, then inter-track interference is reduced, but undersaturation occurs
Solution Approach 1:
The patent implements feedback by using the read element to measure the actual track width written by the laser, then using this measurement to calibrate and adjust the write power. This closed-loop feedback system ensures that the write power is optimized to prevent both undersaturation and inter-track interference based on actual recorded track characteristics.
Solution Approach 2:
The patent applies preliminary action by performing calibration operations before normal data recording. Test patterns are written and measured in advance to establish the relationship between write power and track width, allowing optimal write power to be determined before actual data recording begins.
3Manufacturing precision
If calibration operations are performed to optimize write power, then data recording quality is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by enabling the system to perform its own calibration using built-in test pattern generation and readback capabilities. The calibration process uses the device's own read element and control logic to measure track width and determine optimal write power, eliminating the need for external calibration equipment or complex additional components.
Solution Approach 2:
The patent applies universality by using the same read element and control circuitry for both normal data readback and calibration measurements. The test pattern generation utilizes existing write capabilities, and the calibration data is processed by the existing control logic, allowing one system to serve multiple functions without adding significant complexity.
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 method ensures reliable data recording by selecting the appropriate write power, preventing undersaturation and inter-track interference, thereby enhancing the quality and reliability of the recorded data.
Implementation Method 1
heating the disk surface with a laser during write operations in order to decrease the coercivity of the magnetic medium
Implementation Method 2
Data is typically written to the disk by modulating a write current in an inductive coil to record magnetic transitions onto the disk surface
Implementation Method 3
the magnetic transitions are sensed by a read element (e.g., a magnetoresistive element) and the resulting read signal demodulated
Data Source
AI summary
A data storage device is disclosed comprising a head actuated over a disk, wherein the head comprises a laser configured to heat the disk during write operations. A first test pattern written at a first laser power is read to generate a first track width metric and a first peak amplitude. A second test pattern written at second laser power is read to generate a second track width metric and a second peak amplitude. The first track width metric, the first peak amplitude, the second track width metric, and the second peak amplitude are processed to estimate a coefficient C of an error function. An operating write power for the laser is calibrated based on the estimated coefficient C of the error function.