Plastic Objective Lens Ring Structure Temperature Correction
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Solution Overview
Problem
Conventional optical pickup devices with plastic objective lenses face challenges in maintaining good temperature characteristics and high light utilization efficiency, especially when used with short-wavelength light sources, due to poor spherical aberration correction and increased complexity from active correcting mechanisms.
Innovation Solution
A plastic objective lens with a ring-shaped structure featuring multiple zones that cause a predetermined optical path difference, where the direction of steps changes at least once within the effective aperture, enhancing temperature characteristics while maintaining high light utilization efficiency and sufficient back focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a diffractive structure with many ring-shaped zones is used to improve temperature characteristics, then temperature characteristics are improved, but light utilization efficiency is lowered due to errors in shapes caused by mold processing and defective transfer
Solution Approach 1:
The patent changes the key parameter from the number of ring-shaped zones to the depth variation of the ring-shaped structure. By controlling the depth to be 1/4 wavelength or less and creating continuous depth variation across zones, the design achieves temperature correction without the manufacturing errors that plague multi-zone diffractive structures.
2Temperature
If the back focus is reduced to improve temperature characteristics, then temperature characteristics are improved, but the objective lens easily interacts with the optical disc and optical pickup device applicability is restricted
Solution Approach 1:
The patent changes the approach from modifying back focus to modifying the ring-shaped structure depth profile. This allows temperature characteristic improvement while maintaining adequate back focus, preserving compatibility across different optical pickup device applications.
3Ease of manufacture
If a plastic objective lens is used to enable mass production and cost reduction, then ease of manufacture and cost are improved, but temperature characteristics are worsened
Solution Approach 1:
The patent applies local quality by creating a ring-shaped structure with specific depth characteristics (1/4 wavelength or less) at the optical surface of the plastic lens. This localized structural modification provides temperature correction exactly where needed while maintaining the overall plastic lens construction suitable for mass production.
Solution Approach 2:
The patent changes the depth parameter of the ring-shaped structure to be 1/4 wavelength or less, which fundamentally alters how the structure interacts with light. This parameter change enables temperature correction in plastic lenses without requiring complex active mechanisms, maintaining mass production suitability.
4Temperature
If an active correcting mechanism is added to correct spherical aberration from temperature changes, then temperature characteristics are improved, but device complexity and scale increase making it difficult to mount on actual apparatus
Solution Approach 1:
The patent implements self-service by embedding the temperature correction function directly into the objective lens structure itself. The ring-shaped structure with controlled depth automatically compensates for temperature-induced spherical aberration without requiring external sensors, processors, or active adjustment mechanisms.
Solution Approach 2:
The patent extracts the temperature correction function from a separate active correcting mechanism and integrates it directly into the objective lens. This eliminates the need for complex external correction systems while maintaining the temperature compensation 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
The solution allows for high-density recording and reproducing of information on optical discs with short-wavelength light fluxes, maintaining excellent temperature characteristics and high light utilization efficiency, while simplifying the optical pickup device design by reducing the need for complex active correcting mechanisms.
Implementation Method 1
ring-shaped zones which are three or more and thirty or less in number and which cause a predetermined optical path difference for incident light flux
Implementation Method 2
a light-converging optical system including an objective lens for converging the light flux emitted by the light source onto an information recording surface
Data Source
AI summary
There are provided an objective lens for an optical pickup device which can record and/or reproduce information on/from an optical disk with high density with the use of a light flux with a short wavelength while keeping a temperature characteristic to be satisfactory in spite of having a plastic objective lens, and the optical pickup device. The objective lens suppresses generation of a spherical aberration even if a temperature change arises, by sacrificing wavelength characteristics and by enhancing temperature characteristics. Such satisfactory temperature characteristics can be acquired by the ring-shaped structure formed as a turning structure on an optical surface of the objective lens, in which the ring-shaped structure includes ring-shaped zones whose number is 3 or more and 30 or less and the ring-shaped structure is formed such that adjoining ring-shaped zones cause a predetermined optical path difference for an incident light flux.