Fly Height Sensor Detects Laser Threshold via Disk Protrusion

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Solution Overview

Problem

Existing data storage devices face challenges in accurately detecting the lasing threshold power of a laser used for writing data to a disk without increasing manufacturing cost and complexity, as conventional methods like integrating a photodiode are costly and complex.

Innovation Solution

The lasing threshold power is detected by measuring the fly height of the head over the disk at different laser powers, using techniques such as fly height sensors, read signal amplitude, noise level, or harmonic ratio, eliminating the need for a photodiode and reducing complexity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a photodiode is integrated into the head to detect lasing threshold power, then measurement precision is improved, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improvelasing threshold detection accuracyVSAvoidhead structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts the lasing threshold detection function from the head assembly by using a separate fly height sensor positioned away from the head. This allows the head to remain simple while still achieving accurate lasing threshold detection through the protrusion effect measurement method.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The fly height sensor serves multiple functions: it measures fly height for normal operation and simultaneously detects lasing threshold power through the protrusion effect. This multi-functionality eliminates the need for a dedicated photodiode in the head, reducing complexity while maintaining detection capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If a photodiode is integrated into the head to detect lasing threshold power, then measurement precision is improved, but manufacturing cost increases

Engineering Contradiction:

Improvelasing threshold detection accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The detection function is extracted from the head assembly and performed by a separate fly height sensor, eliminating the need for expensive photodiode integration in the head and reducing manufacturing costs.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The fly height sensor uses the laser-induced protrusion effect on the disk surface to detect lasing threshold, allowing the system to self-detect the threshold without requiring additional expensive components like photodiodes.

Inventive Principle:

Principle #25Self-service

3Productivity

If laser power is increased to ensure proper writing, then productivity is improved, but harmful factors increase due to potential damage to servo data

Engineering Contradiction:

Improvedata writing efficiencyVSAvoiddamage to servo data

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary detection of the lasing threshold power before actual data writing operations. By identifying the exact threshold power in advance, the system can set optimal writing power levels that ensure efficient data writing while preventing excessive power that could damage servo data.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses feedback from fly height measurements at different laser power levels to determine the lasing threshold. This feedback mechanism enables dynamic adjustment of writing power to maintain optimal levels for productivity while avoiding harmful effects on the disk surface and servo data.

Inventive Principle:

Principle #23Feedback

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 method allows for accurate detection of the lasing threshold power without increasing manufacturing costs, enabling efficient data writing operations while maintaining the integrity of servo data on the disk.

Implementation Method 1

a laser power is applied to a laser (20), and while applying the laser power, a fly height of the head (16) is measured

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

at least four fly height measurements are taken at different laser powers (28), and based on the measured fly heights, a lasing threshold power of the laser (20) is detected (30)

Methodology Applied

Scientific EffectThermal protrusion detection: Thermal Expansion

Data Source

PatentUS9786310B1Data storage device detecting lasing threshold of laser by measuring protrusion effect

Publication Date: 2017.10.10 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A data storage device is disclosed comprising a head actuated over a disk, wherein the head comprises a laser configured to heat the disk while writing data to the disk. At least four different laser powers are applied to the laser and a fly height of the head over the disk is measured at each laser power. A lasing threshold power for the laser is detected based on the measured fly heights.