Phase Shift Element for Spherical Aberration Correction in Optical Pickups
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Solution Overview
Problem
Existing optical pickup devices face challenges in ensuring downward compatibility between high-density Blu-ray Discs and lower-density DVDs, with fluctuations in spherical aberrations during wavelength changes, and require complex designs that are difficult to manufacture and increase the number of components.
Innovation Solution
An optical pickup device is designed with an objective lens having a numerical aperture of 0.75 or above, a chromatic aberration correction element, and a phase shift element with a tiered phase difference pattern to correct spherical aberrations due to substrate thickness differences between Blu-ray and DVD discs, using a single objective lens for both formats.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single objective lens with NA≥0.75 is used for both Blu-ray Disc and DVD, then device complexity is reduced, but spherical aberration fluctuations occur during wavelength changes
Solution Approach 1:
A phase shift element is introduced as an intermediary component between the objective lens and the optical recording medium. This element compensates for spherical aberration fluctuations caused by wavelength changes when switching between Blu-ray Disc and DVD formats, enabling stable performance with a single objective lens.
2Manufacturing precision
If the objective lens is designed for Blu-ray Disc with NA≥0.75, then recording density is improved, but compatibility with DVD deteriorates due to substrate thickness differences
Solution Approach 1:
The phase shift element introduces controlled phase changes to the laser beam based on the detected format. By adjusting the phase shift amount, the system adapts the beam characteristics to match the substrate thickness requirements of either Blu-ray Disc (0.1mm) or DVD (0.6mm), enabling a single lens to serve both formats.
Solution Approach 2:
The system dynamically adjusts the phase shift element's characteristics based on the detected optical recording medium format. When switching between Blu-ray Disc and DVD, the phase shift amount is modified in real-time to compensate for substrate thickness differences, maintaining optimal focusing performance.
3Reliability
If chromatic aberration correction is applied, then optical performance is improved, but device complexity increases
Solution Approach 1:
The phase shift element combines multiple functions: it corrects spherical aberration, compensates for substrate thickness differences, and enables format switching. By merging these functions into a single component rather than using separate correction elements, the system achieves excellent optical performance without significantly increasing device complexity.
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 solution provides excellent performance for both Blu-ray and DVD recording and reproduction, simplifies manufacturing by reducing the number of components, and stabilizes spherical aberrations across wavelength changes, ensuring reliable compatibility and data integrity.
Implementation Method 1
a phase shift element which corrects a spherical aberration generated due to a difference in substrate thickness between first and second optical recording mediums
Implementation Method 2
the phase shift element has a tiered phase difference pattern portion formed in annular shapes on one surface thereof, the tiered phase difference pattern portion being obtained by continuously connecting an inner circular side tiered phase difference pattern portion with an outer circular side tiered phase difference pattern portion based on a phase function curve
Implementation Method 3
an objective lens which has a numerical aperture (NA) set to 0.75 or above for the first optical recording medium, in which at least one of respective surfaces thereof backing onto each other is formed into an aspherical surface, and which converges the first and second laser lights on the respective signal surfaces
Implementation Method 4
at least one of respective surfaces thereof backing onto each other is formed into an aspherical surface
Data Source
AI summary
A phase shift element has a tiered phase difference pattern portion, in which an inner circular side tiered phase difference pattern portion is continuously connected with an outer circular side tiered phase difference pattern portion based on a phase function curve obtained by a single phase-function with a wavelength having the same value as a reference wavelength λ1 of a first laser light being determined as a designed wavelength λ, formed in annular shapes on one surface thereof. A tier pitch of tiers of the inner circular side tiered phase difference pattern portion is set to a height corresponding to a phase difference of substantially 1λ and, on the other hand, a tier pitch of tiers of the outer circular side tiered phase difference pattern portion is set to a height corresponding to a phase difference of substantially mλ (where m is a natural number which does not include 0) or a height corresponding to the phase difference of substantially mλ by changing a value of m for each step.