Optical Pickup Diffraction Region for Multi-Layer Disc Crosstalk
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Solution Overview
Problem
In optical recording and reproduction devices, the tracking error signal deteriorates due to interference from adjacent layers in multi-layer optical discs, particularly in high-density discs with thin thicknesses, leading to fluctuations and crosstalk issues.
Innovation Solution
An optical pickup system is designed with a diffraction region, potentially a hologram, between the optical path changer and the objective lens or photodetector to diffract interference light from adjacent layers, preventing it from reaching the photodetectors and using a quarter wave plate and liquid crystal element to compensate for spherical aberration and thickness deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the NA of the objective lens is increased to improve recording density, then the light spot size is reduced and recording capacity increases, but the thickness of the optical disc must be reduced which causes performance deterioration due to tilt
Solution Approach 1:
The patent changes the physical parameters of the optical system by using a blue wavelength light source (405 nm) combined with a high NA objective lens (0.85), while simultaneously reducing the optical disc thickness to 0.1 mm. This parameter optimization resolves the contradiction by achieving high recording capacity through small spot size while maintaining tilt tolerance through the specific thickness reduction.
2Reliability
If the thickness of the optical disc is reduced to provide tilt tolerance for high NA, then tilt tolerance is improved, but spherical aberration increases due to thickness deviation
Solution Approach 1:
The patent optimizes the thickness parameter to 0.1 mm which provides sufficient tilt tolerance for high NA operation. The strict control of thickness deviation (±3 μm) compensates for the increased sensitivity to spherical aberration, resolving the contradiction between tilt tolerance and manufacturing precision.
3Productivity
If multi-layer recording is implemented to increase storage capacity, then recording density increases, but tracking error signal deteriorates due to interference from adjacent layers
Solution Approach 1:
The patent converts the harmful interference light from adjacent layers into a beneficial effect by using a diffraction grating to separate the light by wavelength. The tracking error signal is extracted from the diffracted light components, transforming the crosstalk problem into a useful signal separation mechanism that enables accurate tracking in multi-layer systems.
Solution Approach 2:
The diffraction grating acts as an intermediary element that separates the light from different layers by wavelength. This intermediary device enables the photodetector to distinguish between light reflected from the current layer and adjacent layers, resolving the tracking error signal deterioration caused by multi-layer interference.
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 effectively suppresses interference light, stabilizes the tracking error signal, and reduces crosstalk between layers, improving the accuracy of data recording and reproduction on multi-layer optical discs.
Implementation Method 1
a diffraction region, potentially a hologram, between the optical path changer and the objective lens or photodetector to diffract interference light from adjacent layers
Implementation Method 2
using a quarter wave plate and liquid crystal element to compensate for spherical aberration and thickness deviations
Implementation Method 3
an objective lens which focuses the light emitted from the light source into a spot on the optical information storage medium
Data Source
AI summary
An optical pickup including an optical member which inhibits interference light reflected from an adjacent layer from being received by a photodetector when an optical information storage medium includes a plurality of recording layers on at least one side thereof. The optical pickup suppresses a photodetector, especially first and second sub-photodetectors of the photodetector, from receiving the interference light reflected from the adjacent layer.