Objective Optical Element with Diffractive Structures for Multi-Disk Tracking
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Solution Overview
Problem
Existing optical pickup apparatuses face challenges in recording and reproducing information for high-density optical disks, DVDs, and CDs with a single objective optical element, often resulting in insufficient light for recording, interference with tracking sensors, and inaccurate tracking due to the design of the optical system, particularly when using an infinite optical system.
Innovation Solution
The optical pickup apparatus employs a single objective optical element with a central and peripheral area, each having a specific optical path difference structure, allowing it to converge light fluxes of different wavelengths onto various optical disks, maintaining accurate tracking and temperature stability, and using a plastic lens for cost-effectiveness and simplicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single objective optical element is used for high-density optical disks, DVDs, and CDs, then the device complexity is reduced, but the manufacturing precision becomes insufficient due to the need to accommodate different wavelengths and protective substrate thicknesses
Solution Approach 1:
The objective optical element incorporates an optical path difference providing structure with different step heights in different regions. The first region has a first step height optimized for high-density optical disks, while the second region has a second step height optimized for DVDs and CDs. This local differentiation allows a single optical element to precisely accommodate multiple disk types with different protective substrate thicknesses and wavelengths.
Solution Approach 2:
The patent designs a universal objective optical element that can focus light for three different types of optical disks (high-density optical disks, DVDs, and CDs) simultaneously. By integrating multiple optical path difference providing structures with different step heights into one element, the system achieves multi-functionality without requiring separate objective lenses for each disk type, thereby reducing device complexity while maintaining precision.
2Reliability
If the optical path difference providing structure has large step heights for high-density optical disks, then the spherical aberration is reduced, but the light flux for tracking becomes insufficient and interferes with tracking sensors
Solution Approach 1:
The optical path difference providing structure is divided into multiple regions with different step heights. The first region (central area) has a larger step height optimized for correcting spherical aberration in high-density optical disks, while the second region (peripheral area) has a smaller step height that allows sufficient light flux to pass through for tracking operations. This spatial differentiation resolves the contradiction between aberration correction and tracking light availability.
Solution Approach 2:
The optical path difference providing structure is segmented into multiple discrete regions, each with independently optimized step heights. This segmentation allows the system to provide different optical path differences for different functional requirements (recording/focusing vs. tracking) without compromising either function. The first region handles high-density disk focusing while the second region ensures adequate tracking light flux.
3Measurement precision
If multiple optical systems are used for different optical disks, then the recording and reproducing accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The patent creates a single universal objective optical element that replaces multiple separate optical systems. By integrating optical path difference providing structures with different step heights into one element, the system maintains the recording and reproducing accuracy for high-density optical disks, DVDs, and CDs while eliminating the need for multiple objective lenses and associated switching mechanisms, thereby reducing device complexity and cost.
Solution Approach 2:
The patent merges the functions of multiple objective optical elements (designed for different disk types) into a single integrated objective optical element. The optical path difference providing structure combines multiple step height configurations in one component, allowing the system to achieve the accuracy of multiple separate systems while physically consolidating them into one element, thus reducing overall 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
This configuration enables the optical pickup apparatus to efficiently record and reproduce information on high-density optical disks, DVDs, and CDs with improved tracking accuracy and temperature stability, while reducing the complexity and cost of the optical system.
Implementation Method 1
an optical path difference providing structure having a wavelength dependency for the spherical aberration, which is formed thereon
Implementation Method 2
European patent application EP-A 1304689 discloses an objective optical system which has the diffractive structure as an optical path difference providing structure
Data Source
AI summary
An optical pickup apparatus according to the present invention includes: a first light source for emitting a first light flux; a second light source for emitting a second light flux; a third light source for emitting a third light flux; and an objective optical element. The objective optical element has an optical surface including at least two areas provided with optical path difference providing structures. The objective optical element converges the first to third light fluxes each passing through the predetermined areas on the objective optical element onto respective information recording surfaces of the first to third optical disks. The optical pickup apparatus provides a wavelength dependency of a spherical aberration so as to correct a change in a spherical aberration due to a refractive index change with a temperature change of the objective optical element.