Quantum Dot Laser Diode for Thermally Stable Magnetic Recording
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Solution Overview
Problem
Conventional thermally assisted magnetic heads experience unstable recording quality due to temperature-sensitive laser diodes, which lead to mode hopping and fluctuations in light emission intensity, wavelength, and phase, resulting in errors and reduced recording quality.
Innovation Solution
A light source-unit with a laser diode featuring an active layer that includes a quantum dot layer with varying density and composition, designed to confine carrier movements in three-dimensional directions, making the laser diode insensitive to temperature changes and enhancing light emission intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional laser diode is used in the thermally assisted magnetic head, then the device can operate at room temperature, but the laser diode exhibits mode hopping and fluctuations in light emission intensity, wavelength, and phase due to temperature sensitivity, resulting in unstable recording quality
Solution Approach 1:
The patent changes the physical parameters of the laser diode by incorporating quantum dots with specific size distributions (5-15 nm diameter) into the active layer. This quantum dot structure modifies the density of states and carrier confinement, making the laser emission characteristics insensitive to temperature variations. The quantum dots provide discrete energy levels that stabilize the lasing wavelength and reduce mode hopping across a wide temperature range from 200K to 400K.
Solution Approach 2:
The patent creates a composite laser diode structure by integrating quantum dots (semiconductor nanocrystals) into the active layer of the laser diode. This composite material approach combines the light-emitting properties of conventional semiconductor materials with the quantum confinement effects of quantum dots, resulting in a laser diode that maintains stable optical properties across temperature variations while enabling thermally assisted magnetic recording.
2Productivity
If the magnetic fine particles are made smaller to increase recording density, then the recording density increases, but the magnetization becomes unstable with respect to heat, increasing the possibility that recorded data is lost
Solution Approach 1:
The patent utilizes phase transition of the magnetic recording medium by heating it above its Curie temperature using near-field light from the laser diode. When heated above the Curie temperature, the magnetic medium transitions from a magnetized state to a paramagnetic state with reduced coercive force, allowing easy magnetization reversal for data recording. After cooling below the Curie temperature, the coercive force increases again, stabilizing the recorded data against thermal decay.
Solution Approach 2:
The patent converts the harmful effect of heat on magnetization stability into a beneficial recording mechanism. By using the laser diode to locally heat the magnetic medium above the Curie temperature, the patent temporarily reduces the coercive force to enable data writing, then allows the medium to cool and regain high coercive force for stable data retention. This transforms thermal instability into a controlled recording process.
3Reliability
If the magnetic energy of the magnetic fine particles is increased to enhance magnetization stability, then the magnetization stability improves, but the coercive force increases, deteriorating the data recording performance
Solution Approach 1:
The patent employs phase transition at the Curie temperature to temporarily reduce the coercive force of high-stability magnetic particles during the recording process. By heating the medium above the Curie temperature, the magnetic particles transition to a paramagnetic state where coercive force is dramatically reduced, enabling easy magnetization reversal even for particles with high magnetic energy and stable magnetization at room temperature.
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 stabilizes the recording quality of thermally assisted magnetic heads by reducing temperature-induced fluctuations, improving light emission efficiency, and extending the lifetime of the laser diode while maintaining high data integrity.
Implementation Method 1
an active layer which emits laser-light and includes a quantum dot layer including a plurality of quantum dots, which respectively confine movements of carriers in the three-dimensional directions
Implementation Method 2
When light enters an opening smaller than the wavelength of light, the light slightly seeps from the opening and locally exists near the opening. The light locally existing near the opening is called near-field light. The near-field light is confined in a region much smaller than that of a spot light obtained by collecting light using a lens
Implementation Method 3
a laser diode including an optical generating layer including an active layer which emits laser-light
Data Source
AI summary
A light source-unit includes a laser diode, a sub-mount which the laser diode is joined. The laser diode includes an optical generating layer including an active layer which emits laser-light and cladding layers being formed so as to sandwich the active layer. The active layer includes a quantum dot layer including a plurality of quantum dots, which respectively confine movements of carriers in the three-dimensional directions.