Optical Disc Focus and Spherical Aberration Control
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Solution Overview
Problem
Existing optical disc technologies face challenges in maintaining stable tracking control while adjusting the focus position and spherical aberration amount to optimize reproduced signal quality, as increasing the numerical aperture and decreasing the wavelength of the light beam lead to increased spherical aberration, causing instability in tracking control.
Innovation Solution
An optical disc apparatus with a focus position changing section, spherical aberration amount changing section, tracking error detecting section, tracking control section, and control section that performs a two-dimensional first search while tracking control is off and a two-dimensional second search while tracking control is on, to determine optimal focus positions and spherical aberration amounts for improved signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the numerical aperture of the light beam is increased and the wavelength is decreased to reduce spot size and increase recording density, then the recording density is improved, but the spherical aberration amount generated due to protection layer thickness errors is increased rapidly, causing instability in tracking control
Solution Approach 1:
The system performs preliminary adjustment of the spherical aberration correction amount before tracking control is activated. By pre-adjusting the spherical aberration correction in advance (before the critical tracking phase), the system ensures that when tracking control begins, the spherical aberration is already compensated, thereby maintaining tracking stability while achieving high recording density with increased numerical aperture
Solution Approach 2:
The system dynamically changes the spherical aberration correction amount as a controllable parameter to compensate for spherical aberration effects. By adjusting this parameter based on detection signals, the system maintains optimal focus and tracking performance even when using high numerical aperture optics that inherently produce more spherical aberration, thus enabling high recording density without sacrificing tracking stability
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 allows for optimal adjustment of focus position and spherical aberration amount, ensuring stable tracking control and improved reproduced signal quality, effectively addressing the instability issues associated with spherical aberration.
Implementation Method 1
A light beam emitted from a laser source is refracted by a protection layer 14 of the optical disc 13 in a state where the focus control is operated.
Data Source
AI summary
An optical disc apparatus includes a control section. The control section performs a first search while the tracking control is in the off state. The first search is for searching for a plurality of sets of the focus positions of the light beam and the spherical aberration amounts such that an amplitude of the tracking error signal is greater than a predetermined value. The control section performs a second search while the tracking control is in the on state. The second search is for determining a set of the focus position of the light beam and the spherical aberration amount such that the reproduced signal quality index is substantially optimal, among the plurality of sets of the focus positions of the light beam and the spherical aberration amounts obtained in the first search.