Optical Power Sensor for HAMR Slider Mode Hopping
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Solution Overview
Problem
Conventional laser power monitoring in heat-assisted magnetic recording (HAMR) devices fails to detect mode hopping effectively, leading to power instability and errors due to standing waves formed by incident and back-reflected light, which are not adequately addressed by conventional wafer power monitors.
Innovation Solution
An optical power sensor is integrated in the HAMR slider with a tap waveguide optically coupled to the main waveguide, featuring a bolometer at one end to detect only the forward propagating mode and a light absorbing or anti-reflection feature at the other end to minimize back reflection, reducing the impact of mode hopping detection by at least a factor of 5.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional wafer power monitor is used to monitor laser power, then the monitoring function is provided, but mode hopping cannot be detected effectively due to standing waves formed by incident and back-reflected light
Solution Approach 1:
The waveguide structure is segmented into a main waveguide for light transmission and a separate tap waveguide for power monitoring. This segmentation allows the monitoring function to be separated from the main optical path, enabling independent optimization of each function and eliminating the interference that caused ineffective mode hopping detection in conventional monolithic designs.
Solution Approach 2:
The tap waveguide acts as an intermediary element that couples a portion of the light from the main waveguide to the bolometer. This intermediary structure allows the bolometer to measure power without being directly in the main optical path, thereby avoiding the standing wave formation that prevented effective mode hopping detection while maintaining accurate power monitoring.
2Measurement precision
If a bolometer is placed to detect light from the main waveguide, then power monitoring is achieved, but back reflection creates standing waves that reduce detection accuracy
Solution Approach 1:
The harmful back reflection is extracted and isolated from the detection path by using the tap waveguide configuration. The tap waveguide couples light laterally from the main waveguide, and the bolometer is positioned at the end of the tap waveguide where back reflection from the main waveguide does not interfere with the forward propagating mode detection, thereby removing the standing wave formation problem.
Solution Approach 2:
The back reflection that previously created harmful standing waves is converted into a beneficial configuration where the tap waveguide's geometry and positioning cause the back reflection to enter the bolometer only from a controlled reflection of the tap waveguide's end, not from the main waveguide. This transforms the harmful interference into a controlled measurement condition that improves detection accuracy.
3Measurement precision
If the bolometer detects both forward and backward propagating modes, then total power is measured, but mode hopping detection is obscured by standing waves
Solution Approach 1:
The detection system is designed with local quality differentiation: the bolometer is positioned and oriented to selectively detect only the forward propagating mode that carries mode hopping information, while the tap waveguide's geometry ensures that backward propagating modes are excluded from the detection region. This local selective detection preserves mode hopping information while maintaining power measurement capability.
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 configuration significantly reduces the impact of back reflection on mode hopping detection, enhancing the accuracy of laser power monitoring and mitigating power instability issues in HAMR devices.
Implementation Method 1
a bolometer optically coupled to the tap waveguide and configured to receive a portion of the light extracted from the main waveguide by the tap waveguide
Implementation Method 2
A light absorbing or anti-reflection feature is situated at or proximate the second end of the tap waveguide
Data Source
AI summary
An apparatus comprises a slider configured for heat-assisted magnetic recording comprising an air bearing surface (ABS). The slider comprises a write pole at or near the ABS, and a near-field transducer (NFT) at or near the ABS and proximate the write pole. A main waveguide is configured to receive light from a laser source and communicate the light to the NFT. An optical power sensor comprises a tap waveguide optically coupled to the main waveguide and comprising a first end and an opposing second end. The optical power sensor also comprises a bolometer optically coupled to the tap waveguide and configured to receive a portion of the light extracted from the main waveguide by the tap waveguide.