Optical Pickup Light Scattering for Multilayer Disc Tracking
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Solution Overview
Problem
Optical pickup apparatuses face challenges in preventing degradation of tracking error signals due to overlapping light from adjacent layers during data reproduction from multilayer optical discs, particularly with high-density discs like Blu-ray and HD DVDs, where the increased numerical aperture of the objective lens leads to coma aberration and reduced depth, and existing solutions like polarization holograms either block desired signals or require costly adjustments.
Innovation Solution
Incorporating a light scattering portion, such as a plate or surface with a light scattering area, between the photodetector and objective lens to scatter light from non-target layers, thereby reducing the impact of overlapping light from adjacent layers on the photodetector without blocking the desired signal, thus maintaining signal quality and avoiding the need for complex adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the numerical aperture of the objective lens is increased to increase recording capacity, then the light spot size is reduced and recording density is improved, but coma aberration is increased and depth of focus is reduced
Solution Approach 1:
A light scattering portion is introduced as an intermediary element between the objective lens and the optical disc. This scattering portion selectively scatters the main light component from the adjacent layer while allowing the differential light components (carrying tracking error signal information) to pass through to the photodetector, thereby resolving the coma aberration issue without sacrificing recording capacity
2Reliability
If a polarization hologram is used to block the main light component from the adjacent layer, then the tracking error signal degradation is reduced, but the desired signal is blocked and complex adjustments are required
Solution Approach 1:
The patent replaces the complex polarization hologram with a simple light scattering portion that can be implemented as a basic optical element. This scattering portion effectively blocks the harmful main light component from the adjacent layer without requiring precise alignment or complex polarization control mechanisms, thereby simplifying the device structure while maintaining tracking signal quality
3Quantity of substance
If the light spot size is reduced to increase recording density, then more data can be stored, but the depth of focus is reduced and coma aberration is increased
Solution Approach 1:
The light scattering portion is designed to selectively scatter light based on its origin. It locally affects only the main light component from the adjacent layer while leaving the differential light components from the target layer undisturbed. This localized selective scattering allows reduced light spot size for high density recording without compromising depth of focus
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 approach effectively minimizes the degradation of tracking error signals by increasing the size of the light spot from adjacent layers on the photodetector, reducing signal loss, and simplifying the optical pickup design by eliminating the need for precise alignment of polarization holograms, while maintaining signal integrity.
Implementation Method 1
a light scattering portion to reduce an amount of light reflected from one or more non-target layers of the recording layers and incident on the photodetector by scattering part of the light reflected from the optical disc
Data Source
AI summary
An optical pickup apparatus includes a light source to emit light of a predetermined wavelength, an objective lens to focus the light emitted from the light source to form a light spot on an optical disc having a plurality of recording layers, a photodetector to detect a signal and an error signal by detecting the light reflected from the optical disc, and a light scattering portion to reduce an amount of the light reflected from a non-target layer of the recording layers and incident on the photodetector by scattering part of the light reflected from the optical disc during a reproduction of data from the optical disc.