Resin Objective Lens Tilt Sensitivity Control
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Solution Overview
Problem
Optical disc apparatuses using resin objective lenses face issues with coma aberration sensitivity at low temperatures, leading to deteriorated recording and reproducing characteristics due to increased lens tilt sensitivity, which is not effectively addressed by existing design methods.
Innovation Solution
Designing an objective lens with a resin material that focuses incident rays of 410 nm or less at a numerical aperture of 0.8, with a lens tilt sensitivity of 130 mλrms/degree or less at 0°C, by adjusting the 3rd-order and 5th-order coma aberration sensitivities and lens thickness sensitivity to minimize coma aberration occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an objective lens made of resin material is used to reduce cost and weight, then manufacturing cost and weight are reduced, but the lens tilt sensitivity increases at low temperatures causing coma aberration
Solution Approach 1:
The patent applies parameter changes by modifying the refractive index distribution within the resin lens material. Specifically, it uses a refractive index gradient where the refractive index varies from the center to the periphery of the lens, with the center having a higher refractive index than the periphery. This gradient structure compensates for the temperature-dependent tilt sensitivity of resin materials, reducing coma aberration while maintaining the cost and weight advantages of resin construction.
Solution Approach 2:
The patent employs composite material principles by creating a resin lens with non-uniform refractive index distribution. This is achieved through controlled mixing of resin components with different refractive indices during manufacturing, resulting in a composite structure where the optical properties vary spatially within the material to correct for temperature-induced aberrations.
2Weight of stationary object
If the refractive index of resin material is used to reduce weight and cost, then weight and cost are reduced, but the optical characteristics change with temperature causing spherical aberration
Solution Approach 1:
The patent addresses temperature-induced optical characteristic changes by implementing a refractive index gradient that varies with temperature compensation. The refractive index is designed to change spatially within the lens to counteract the uniform temperature-dependent changes in resin material, thereby stabilizing optical performance across the operating temperature range of 0-70°C while maintaining the weight benefits of resin construction.
3Manufacturing precision
If the lens tilt sensitivity is reduced to suppress coma aberration, then optical characteristics are improved, but the design complexity increases
Solution Approach 1:
The patent reduces design complexity by implementing a radial refractive index gradient that can be achieved through controlled manufacturing processes. The refractive index varies continuously from the optical axis outward, with specific values designed to compensate for lens tilt at low temperatures. This approach achieves coma aberration suppression through material property optimization rather than complex mechanical adjustment mechanisms.
Data Source
AI summary
An objective lens is made of a resin material and focuses incident rays, which have a wavelength of 410 nm or less and are emitted from a light source, on an optical disc at a numerical aperture of 0.8 or more, wherein when a lens tilt sensitivity is defined as an amount of a 3rd-order coma aberration caused per a lens tilt of 1 degree which is an angle formed between an optical axis of the objective lens and a system optical axis of an optical system including the objective lens at 0° C., the lens tilt sensitivity is 130 mλrms/degree or less.