Laser Diode Fingerprinting for Stable HAMR Optical Power
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Solution Overview
Problem
Laser diodes in heat-assisted magnetic recording (HAMR) drives experience temperature-induced mode hopping, leading to abrupt changes in optical output power, which affects disk drive performance by causing non-uniformities in recording and degrading HAMR recording performance.
Innovation Solution
A technique for measuring the steady-state laser diode fingerprint by setting the laser diode to various temperatures, measuring optical power output, and determining a power output profile to adjust the laser current and maintain constant optical power across temperature changes, using methods such as preheating with reverse bias and applying forward bias to stabilize the laser diode operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the laser diode operates at different temperatures, then the optical output power changes, but this causes mode hopping and non-uniform recording
Solution Approach 1:
The patent applies preliminary action by pre-heating the laser diode to its operating temperature before actual data recording begins. This preliminary heating step allows the laser diode to reach thermal equilibrium and stabilize its optical output, preventing mode hopping during subsequent recording operations. The laser diode is heated to a target temperature and held there for a predetermined time period before writing data.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the laser diode temperature to a specific target temperature range optimized for HAMR operations. By controlling the temperature parameter within a narrow range (e.g., 50-150°C above ambient), the system maintains stable optical output characteristics and prevents mode hopping while enabling effective heat-assisted magnetic recording.
2Stability of the object's composition
If the laser diode temperature is stabilized, then mode hopping is reduced, but this requires additional heating control mechanisms
Solution Approach 1:
The patent merges the laser diode heating function with the existing thermal fly-height control (TFC) heater that is already present in the slider. By utilizing the same heater element for both TFC and laser diode pre-heating purposes, the system avoids adding separate heating control mechanisms. The heater is controlled to maintain the laser diode at a target temperature during idle periods before recording operations.
Solution Approach 2:
The patent applies universality by making the thermal fly-height control heater serve multiple functions: maintaining proper slider fly height and pre-heating the laser diode to operational temperature. This multi-functional use of the existing heater eliminates the need for dedicated laser heating components, reducing overall system complexity while achieving stable laser operation.
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 helps maintain a stable optical output power from the laser diode across a range of temperatures, reducing mode hopping and enhancing disk drive performance by minimizing variations in laser power output.
Implementation Method 1
the output of a laser diode, such as those used in heat assisted magnetic recording (HAMR) drivers, is dependent on a multitude of factors including the mode in which the laser diode operates in a steady state condition
Implementation Method 2
the laser diode temperature can change significantly during operation. For instance, the laser diode temperature can be affected by self-heating induced in the laser diode
Implementation Method 3
Laser diodes in heat-assisted magnetic recording (HAMR) drives experience temperature-induced mode hopping, leading to abrupt changes in optical output power
Data Source
AI summary
A data storage device may include one or more disks, an actuator arm assembly comprising one or more magnetic recording heads, at least one laser diode, and one or more processing devices configured to: set the at least one laser diode to a first temperature; apply a first forward bias and supply a first current to the at least one laser diode such that it is in a lasing state; measure, for the at least one laser diode, a first output corresponding to the first temperature and current; set the at least one laser diode to a second temperature; measure, for the at least one laser diode, a second output corresponding to the second temperature and the first current; and determine an output profile for the at least one laser diode, based at least in part on the respective output at the first temperature and the second temperature.