Objective Lens Aberration Correction via Parameter Optimization
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Solution Overview
Problem
In optical recording systems with a numerical aperture of 0.85 or higher, fifth-order spherical aberration caused by temperature changes is significant and difficult to correct, leading to focus issues and performance deterioration when using plastic objective lenses.
Innovation Solution
The objective lens is designed such that the ratios of fifth-order spherical aberration to third-order aberration, caused by cover layer thickness, incident magnification, and temperature changes, are within specific ranges, allowing for effective correction of these aberrations using an optical pickup apparatus and recording/reproduction system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a plastic objective lens is used to improve productivity and reduce cost, then manufacturing ease and productivity are improved, but temperature-induced aberrations (third- and fifth-order) increase significantly
Solution Approach 1:
The patent applies parameter changes by carefully selecting the refractive index and Abbe number of the plastic lens material, and by optimizing the lens curvature radii and thickness parameters. These parameter adjustments compensate for the temperature-induced aberrations inherent in plastic materials, allowing the lens to maintain optical performance across temperature variations while retaining the manufacturing advantages of plastic materials.
Solution Approach 2:
The patent employs composite material principles by combining plastic lens material with specific aspheric surface designs and by integrating the lens into a composite optical system that includes other optical elements. This composite approach allows the plastic lens to achieve temperature stability that would be difficult to obtain with plastic alone, while maintaining the cost and manufacturing benefits of using plastic rather than glass.
2Productivity
If the numerical aperture is increased to 0.85 or higher to improve recording capacity, then information density and productivity are improved, but fifth-order spherical aberration becomes significant and difficult to correct
Solution Approach 1:
The patent applies spheroidality principles by designing aspheric surfaces on the objective lens instead of simple spherical surfaces. The aspheric profiles are specifically optimized to correct fifth-order spherical aberration that becomes significant at high numerical apertures of 0.85 or higher. This curvature optimization allows the lens to maintain high recording capacity while achieving the necessary aberration control precision.
3Quantity of substance
If the cover layer thickness varies in multilayer recording media to enable multi-layer storage, then information capacity is improved, but disc spherical aberration increases due to thickness variations
Solution Approach 1:
The patent applies local quality principles by designing the objective lens with different zone-specific optical properties. The lens is divided into different radial zones with locally optimized surface profiles and refractive index distributions. This allows the lens to compensate for disc spherical aberration caused by cover layer thickness variations in multilayer recording media, while maintaining high information capacity through multi-layer storage capability.
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 design enables the favorable correction of fifth-order spherical aberrations due to temperature changes, improving the recording and reproduction performance by maintaining a focused light spot and stable signal pattern, even with plastic lenses.
Implementation Method 1
information is recorded on and/or reproduced from a BD by using light at a wavelength of 405 nm
Implementation Method 2
an objective lens having a numerical aperture equal to or greater than 0.80
Implementation Method 3
spherical aberration becomes sensitive to variations in the thickness of the cover layer of an optical recording medium
Implementation Method 4
aberration is cancelled by adjusting the movement of the collimating lens appropriately so that spherical aberration caused by a change in the incident magnification of the objective lens may have a polarity opposite that of spherical aberration caused by a change in the thickness of the cover layer
Implementation Method 5
Temperature spherical aberration is generated by such factors as expansion and contraction of the lens, a change in the refractive index of the material of the lens, and a change in the wavelength of incident light
Implementation Method 6
the coefficient of linear expansion of plastic is large, as compared with glass. Thus, the index of refraction and the shape of a plastic lens vary more significantly than those of a glass lens when temperature changes
Data Source
AI summary
Provided is an objective lens for which expressions 0.83<(pM/pL)<1.17 and 0.83<(pM/pT)<1.17 or expressions 0.80<(pM/pL)<1.20 and 0.86<(pM/pT)<1.14 are satisfied, where pL is the ratio of fifth-order spherical aberration to third-order spherical aberration, the spherical aberrations being caused by a difference in the thickness of a cover layer of an optical recording medium, pT is the ratio of fifth-order spherical aberration to third-order spherical aberration, the spherical aberrations being caused by a change in the temperature of an environment of the objective lens, and pM is the ratio of fifth-order spherical aberration to third-order spherical aberration, the spherical aberrations being caused by a change in incident magnification.