Optical Head Aberration Correction via Segmented Collimator and Deformable Mirror
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Solution Overview
Problem
Conventional optical head devices face significant challenges in correcting spherical aberrations, particularly third-order and fifth-order aberrations, when dealing with optical information recording media having multiple information recording surfaces, leading to residual wavefront aberrations that affect information recording and reproducing quality.
Innovation Solution
The optical head device incorporates an aberration corrector, such as a collimator lens, which adjusts the light beam to equalize the variation of wavefront aberrations across different information recording surfaces, ensuring that the optimal substrate thickness of the objective lens minimizes both third-order and fifth-order spherical aberrations, thereby correcting the aberrations and enhancing recording and reproducing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a collimator lens is moved to correct third-order spherical aberration resulting from light transmissive layer thickness errors, then third-order spherical aberration is corrected, but fifth-order spherical aberration is generated
Solution Approach 1:
The aberration correction function is divided into two independent components: a first aberration corrector (collimator lens) that corrects third-order spherical aberration by adjusting light convergence/divergence, and a second aberration corrector (deformable mirror) that specifically corrects fifth-order spherical aberration by deforming its reflective surface. This segmentation allows each component to address its specific aberration order without interfering with the other, resolving the contradiction where third-order correction previously generated fifth-order aberration.
Solution Approach 2:
A deformable mirror is introduced as an intermediary component between the collimator lens and the objective lens. This deformable mirror acts as a mediator that receives the light beam after third-order aberration correction and applies additional fifth-order aberration correction through surface deformation controlled by actuators, thereby eliminating the harmful fifth-order spherical aberration generated during the third-order correction process.
2Adaptability or versatility
If the moving range of the collimator lens is increased to correct spherical aberration across multiple information recording surfaces, then aberration correction range is extended, but device complexity and fifth-order spherical aberration increase
Solution Approach 1:
The aberration correction system is segmented into two independent correctors: the first aberration corrector (collimator lens) handles third-order spherical aberration correction with limited movement, while the second aberration corrector (deformable mirror) handles fifth-order spherical aberration correction through surface deformation. This segmentation enables the system to accommodate multiple information recording surfaces with different light transmissive layer thicknesses without requiring excessive collimator lens movement range, thereby reducing device complexity while maintaining broad adaptability.
Solution Approach 2:
Instead of relying solely on large collimator lens movement to correct aberrations for multiple recording surfaces, the system changes the correction mechanism by introducing a deformable mirror that adjusts its surface shape (parameter change) to correct fifth-order spherical aberration. This allows the collimator lens to maintain a more limited, practical moving range while still achieving comprehensive aberration correction across multiple surfaces with different thicknesses.
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 effectively suppresses the influence of wavefront aberrations, allowing for satisfactory information recording and reproducing by equally distributing the variation of fifth-order spherical aberration between information recording surfaces, thereby improving the optical head device's performance and reducing the need for re-learning optimal positions.
Implementation Method 1
a spherical aberration of about 10 mλ is generated with respect to a change in light transmissive layer thickness of 10 μm... a spherical aberration of about 100 mλ is generated... a measure for correcting spherical aberration is necessary
Implementation Method 2
an objective lens for collecting the light beam emitted from the light source on the optical information recording medium
Data Source
AI summary
An object of the invention is to suppress an influence of a wavefront aberration which is generated at the time of correcting a third-order spherical aberration, and realize satisfactory information recording and/or reproducing. A collimator lens 4 corrects a third-order spherical aberration which is generated depending on the thickness of a light transmissive layer from a surface of a first optical information recording medium 30, corresponding to an optimal substrate thickness of a first objective lens 6, to an intended information recording surface, assuming that the light transmissive layer thickness of the first optical information recording medium 30 which minimizes a residual third-order spherical aberration at the time of incidence of parallel light into the first objective lens 6 is defined as the optimal substrate thickness of the first objective lens 6. The optimal substrate thickness of the first objective lens 6 is defined in such a manner that a variation of a wavefront aberration which is generated on the information recording surface of the first optical information recording medium 30 farthest from the first objective lens 6 at the time of correcting the third-order spherical aberration, and a variation of a wavefront aberration which is generated on the information recording surface of the first optical information recording medium 30 closest to the first objective lens 6 at the time of correcting the third-order spherical aberration are set equal to each other.