Directional Waveguide Coupler for TAMR Light Intensity Control
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Solution Overview
Problem
Current magnetic recording technologies face challenges in accurately measuring light intensity at the air bearing surface (ABS) in thermally assisted magnetic recording (TAMR) systems, leading to variations in data storage density and recording quality due to inefficient light energy utilization and inaccurate intensity monitoring.
Innovation Solution
A waveguide structure with a main waveguide and detection waveguides is implemented, where back reflected light intensity is measured using photo detectors to adjust light source output, ensuring consistent light intensity at the ABS and media interface, even in the absence of a magnetic field, thereby maintaining optimal recording conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light intensity is measured using a photo detector behind the light source, then light intensity can be monitored, but the measurement accuracy deteriorates due to variations in light propagation percentage and lack of correlation with actual ABS intensity
Solution Approach 1:
The patent introduces a coupling waveguide as an intermediary component that couples to the main waveguide to extract and direct back-reflected light to the photo detector. This intermediary structure enables accurate measurement of light intensity at the ABS by measuring the back-reflected light that has interacted with the media, rather than attempting to measure the forward-propagating light directly behind the source. The coupling waveguide acts as a mediator that transfers the measurement function to a location where accurate measurement is possible.
Solution Approach 2:
Instead of measuring light intensity in the forward direction (from light source to ABS) which proved unreliable, the patent inverts the measurement approach by measuring the back-reflected light (from ABS back to light source). This inversion allows the system to indirectly measure the light intensity at the ABS by capturing the light that has already interacted with the media and returned through the waveguide structure.
2Device complexity
If no waveguide coupling structure is used, then the device structure remains simple, but light intensity control and monitoring capability are lost
Solution Approach 1:
The waveguide system is segmented into a main waveguide for light transmission and a separate coupling waveguide for light extraction and measurement. This segmentation allows the measurement function to be independently implemented without interfering with the primary light delivery function. The coupling waveguide is positioned to couple to the main waveguide at a specific location, creating a dedicated path for back-reflected light to reach the photo detector.
Solution Approach 2:
The coupling waveguide extends in a different spatial dimension relative to the main waveguide, allowing light extraction from the main waveguide without blocking the primary light path. The coupling waveguide is positioned adjacent to the main waveguide and extends in a direction that enables side-coupling of back-reflected light, effectively adding a measurement dimension separate from the primary transmission dimension.
3Measurement precision
If light source power is increased to compensate for measurement inaccuracies, then better monitoring can be achieved, but energy consumption increases and heating control precision deteriorates
Solution Approach 1:
The system implements feedback control by continuously measuring the back-reflected light intensity through the coupling waveguide and using this information to adjust the light source power. The photo detector monitors the back-reflected light and provides feedback signals that enable real-time control of the light source, allowing the system to maintain optimal heating conditions with precise energy management rather than relying on increased power margins.
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 provides a more accurate and efficient method for monitoring and controlling light intensity, enhancing data storage density and recording quality by maintaining a stable near-field at the ABS and media interface, allowing for real-time adjustments to ensure consistent energy absorption and improved write performance.
Implementation Method 1
A waveguide structure with a main waveguide and detection waveguides is implemented, where back reflected light intensity is measured
Implementation Method 2
back reflected light intensity is measured using photo detectors
Implementation Method 3
optical power from a light source is converted into localized heating
Implementation Method 4
optical power from a light source is converted into localized heating in a recording medium
Data Source
AI summary
A waveguide structure for a TAMR head is disclosed wherein at least one detection waveguide is formed parallel to a main waveguide and located a gap distance therefrom. A light source transmits light into the main waveguide and towards an ABS/medium interface. A plasmon generator converts light from the waveguide into plasmon waves that are directed onto a magnetic medium. Back reflected light is captured by the main waveguide, partially diverted into a detection waveguide, and transmitted to a photo detector that measures light intensity (IB) which correlates closely to the plasmon wave intensity at the ABS/medium interface. A controller linked to the photo detector is employed to calculate IB as a function of ABS/medium spacing in a non-write condition and this relationship can be used to control and maintain a constant plasmon wave intensity at the ABS during a series of TAMR write processes with a plurality of media.