Optical Disc Tracking Error Signal Segmentation
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Solution Overview
Problem
Existing optical disc devices face challenges in reducing crosstalk and tracking error signal offsets, particularly in high linear density recordings and land/groove recording methods, where radial tilt and aberrations lead to detracking issues, and existing techniques fail to effectively address these problems.
Innovation Solution
An optical disc device that splits the reflected light into multiple regions, using a specific weighting configuration for each region to generate a tracking error signal, allowing for improved symmetry and reduced influence of radial tilt, and employs a servo control system to adjust the objective lens for precise tracking on land or groove portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density is increased in the linear-density direction, then the recording capacity is improved, but inter-symbol interference is increased
Solution Approach 1:
The patent divides the detection process into multiple segments by separating reflected light into three regions (first, second, and third regions) corresponding to different track positions. This segmentation allows independent detection and weighting of signals from each region, enabling effective cancellation of crosstalk and inter-symbol interference through coordinated processing of segmented signals.
2Quantity of substance
If the track pitch is narrowed, then the recording density is improved, but adjacent track crosstalk is increased
Solution Approach 1:
The detection system is segmented into three spatial regions that correspond to different track positions. By assigning different weighting coefficients to signals from each region and combining them, the system can selectively enhance the desired track signal while suppressing crosstalk from adjacent tracks, even when track pitch is narrowed to increase density.
Solution Approach 2:
The patent dynamically adjusts the weighting coefficients applied to signals from different regions based on the detected track position and crosstalk conditions. This parameter change allows optimal signal combination under varying operating conditions, effectively reducing crosstalk impact when narrow track pitch is used to achieve high recording density.
3Device complexity
If a push-pull technique is used for tracking error detection, then the tracking servo is simplified, but offset of tracking error signal occurs at recording boundaries
Solution Approach 1:
The tracking error detection is segmented into three spatial regions with different weighting coefficients. This segmentation allows the system to detect tracking errors while compensating for boundary effects by appropriately weighting signals from regions that are less susceptible to boundary-induced offsets, thereby maintaining measurement precision without increasing overall system complexity.
Solution Approach 2:
The patent employs asymmetric weighting coefficients for the three detection regions, with the second region (center region) assigned a different weight than the first and third regions. This asymmetric weighting scheme compensates for the symmetric nature of boundary effects, reducing offset errors at recording boundaries while maintaining the simplicity of the push-pull tracking servo approach.
4Reliability
If radial tilt occurs, then the optical system becomes misaligned, but existing techniques fail to reduce the influence effectively
Solution Approach 1:
By dividing the detection into three spatial segments and applying different weighting coefficients, the system can detect and compensate for radial tilt effects. The segmented approach allows identification of asymmetric signal patterns caused by radial tilt and enables corrective weighting to maintain tracking stability despite the misalignment.
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
The solution effectively reduces crosstalk and tracking error signal offsets, enhancing the accuracy and reliability of high-density recordings by stabilizing the tracking servo even under conditions of defocus, spherical aberration, and radial tilt.
Implementation Method 1
an optical splitting element configured to split a luminous flux of a light beam reflected by the optical medium into a plurality of regions
Implementation Method 2
an objective lens configured to condense a light beam radiated from the light source onto the signal recording layer formed on the optical medium
Data Source
AI summary
A cross section of a luminous flux of returning light from a disc is split into a plurality of regions, and an operation is performed so that a weighting of a light amount of a region which has favorable symmetry in a radial direction and is formed on a circumference of an ellipse among the split regions is increased. Further, a lens shift detection signal is formed, and a lens shift detection signal is canceled from a push-pull signal.