Aspherical Optical Pickup Lens for High Numerical Aperture
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Solution Overview
Problem
Optical pickup lenses with high numerical apertures face challenges in maintaining both on-axis and off-axis aberration characteristics, particularly with a working distance that becomes too short, leading to potential collisions with optical discs and compromised angle of view characteristics.
Innovation Solution
A single optical pickup lens design with a second surface having specific radii and sag differentials, ensuring a longer working distance and improved aberration characteristics, while maintaining a numerical aperture of 0.84 or higher and a refractive index between 1.51 and 1.64 for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the numerical aperture is increased to 0.80 or higher to improve recording capacity, then the recording density increases, but the working distance becomes too short causing collision risk with optical discs
Solution Approach 1:
The patent applies aspherical surfaces to both the object side and image side of the lens. The object side has aspherical surface (11) with curvature that varies radially, and the image side has aspherical surface (12) with similar characteristics. This curvature design enables high numerical aperture (0.80 or higher) while maintaining adequate working distance by optimizing the light path geometry, preventing collision with optical discs while achieving high recording density.
2Measurement precision
If the numerical aperture is increased to 0.80 or higher to improve recording capacity, then the recording density increases, but the angle of view characteristics deteriorate
Solution Approach 1:
The aspherical surfaces on both sides of the lens are designed with specific curvature profiles that correct off-axis aberrations. The object side aspherical surface (11) and image side aspherical surface (12) work together to maintain good angle of view characteristics even at high numerical aperture (0.80 or higher), enabling both high recording density and proper tracking performance.
Solution Approach 2:
The patent employs asymmetric aspherical designs where the object side and image side have different curvature profiles optimized for their respective functions. The object side (11) focuses on collecting light at high angles, while the image side (12) optimizes for wavefront quality and off-axis performance, creating an asymmetric configuration that balances high NA with good angle of view characteristics.
3Measurement precision
If the numerical aperture is increased to 0.80 or higher to improve recording capacity, then the recording density increases, but both on-axis and off-axis aberration characteristics become difficult to maintain
Solution Approach 1:
The patent uses aspherical surfaces on both the object side (11) and image side (12) to correct spherical aberration and other on-axis aberrations that become severe at high numerical aperture (0.80 or higher). The varying curvature of these aspherical surfaces enables precise control of light paths, maintaining focus quality and aberration correction across the entire aperture, thus achieving high recording density while preserving reliable on-axis characteristics.
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 design achieves a longer working distance and better on-axis and off-axis characteristics, facilitating the recording and playback of high-capacity optical discs with reduced risk of collision and enhanced angle of view.
Implementation Method 1
light from a light source of an optical disc apparatus, after passing through an optical path including transparent components such as a wave plate and a collimator lens, is focused by an optical pickup lens to form an optical spot on an optical disc
Data Source
AI summary
An optical pickup lens for focusing a light beam from a laser light source on an optical information recording medium is a single lens. The optical pickup lens has two surfaces, and a surface R2 opposite to a surface R1 closer to the laser light source has a continuous shape. When the surface R2 has radii h1, h2 and h3 (h1<h2<h3) from an optical axis to a lens periphery, and where sags in the radii h1, h2 and h3 are sag1, sag2 and sag3, and differentials in the sags are Δsag1, Δsag2 and Δsag3, respectively, 0>Δsag1>Δsag2 and Δsag2<Δsag3 are satisfied.