Laser Diode Current Modulation for EAMR Noise Reduction
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Solution Overview
Problem
Energy Assisted Magnetic Recording (EAMR) and Heat Assisted Magnetic Recording (HAMR) technologies experience recording noise due to laser diode mode hopping caused by power magnitude changes, particularly when optical feedback occurs from elements more than 100 microns away from the laser diode facet, leading to phase shifts and power variations.
Innovation Solution
A laser diode with two contact sections for separate current modulations, where the currents are out of phase, stabilizes laser power during mode shifts by maintaining a constant total laser current through localized temperature changes across the p-n junction, reducing noise by averaging mode hops over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If laser diode power is increased for magnetic softening, then heating effect is improved, but mode hopping and power magnitude changes occur causing recording noise
Solution Approach 1:
The patent applies dynamic current modulation to compensate for mode hopping effects. A modulation current is applied to the laser diode that dynamically adjusts the operating point to counteract power magnitude changes during mode transitions, thereby stabilizing the average output power while maintaining the heating effect for magnetic softening
Solution Approach 2:
The system uses feedback from detecting longitudinal mode changes to adjust the laser diode operating current. When mode hopping is detected, the feedback mechanism modifies the current to compensate for power magnitude variations, reducing recording noise while preserving the necessary heating effect
2Device complexity
If optical feedback from distant elements is allowed, then system complexity is reduced, but phase shifts and power variations occur due to mode hopping
Solution Approach 1:
The patent converts the harmful optical feedback that causes mode hopping into a beneficial effect by using the feedback signal itself to detect mode changes and trigger compensation mechanisms. The feedback that would normally destabilize the laser is instead utilized to information about mode transitions, enabling active stabilization
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 maintains a constant average laser output power during multiple mode hops, reducing recording noise and ensuring stable magnetic softening for improved data writing on magnetic storage disks.
Implementation Method 1
The NFT focuses the optical energy to a small spot on the target recording area which heats the magnetic storage disk during a write operation
Implementation Method 2
A laser diode has a current modulation source for stabilizing laser power during mode shifts
Implementation Method 3
maintaining a constant total laser current through localized temperature changes across the p-n junction
Data Source
AI summary
An apparatus includes a laser diode, a near field transducer configured to direct light emitted from the laser diode to a magnetic recording medium, and a power source configured to provide modulated current to the laser diode.