Objective Lens Optical Path Difference Structure for Multi-Format Disc Compatibility
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Solution Overview
Problem
Existing optical pickup apparatuses struggle to record and reproduce information compatibly for Blu-ray Discs (BDs), Digital Versatile Discs (DVDs), and Compact Discs (CDs) using a common objective lens, particularly due to issues with working distance and optical system compatibility, especially for CDs with thicker substrates.
Innovation Solution
The development of an objective lens with a specific optical path difference providing structure, comprising overlapping basic structures that diffract light with odd and even orders, ensuring compatibility for BDs, DVDs, and CDs, while maintaining a sufficient working distance and balanced light utilization efficiency, and controlling aberrations and manufacturing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common objective lens is used for BDs, DVDs, and CDs, then device complexity and cost are reduced, but working distance becomes insufficient especially for CDs with thicker substrates
Solution Approach 1:
The objective lens is divided into multiple regions (first region, second region, third region) with different optical path difference providing structures optimized for different disc types. Each region handles specific wavelength ranges and disc thicknesses, allowing a single lens to serve multiple disc formats (BDs, DVDs, CDs) while maintaining appropriate working distances for each.
Solution Approach 2:
Different portions of the objective lens have locally optimized properties: the first region has structures for BD wavelengths with specific optical path differences, the second region handles DVD wavelengths with different optical path differences, and the third region addresses CD wavelengths with yet another optical path difference profile. This local optimization enables each region to properly focus light for its intended disc type while maintaining overall lens compatibility across all formats.
2Device complexity
If a common objective lens is used for all disc types, then the number of optical parts is reduced, but light utilization efficiency becomes unbalanced across different disc types
Solution Approach 1:
The optical path difference providing structure is segmented into multiple regions with different diffraction order optimizations. The first region optimizes for odd-order diffraction at BD wavelengths, the second region for even-order diffraction at DVD wavelengths, and the third region for odd-order diffraction at CD wavelengths. This segmentation ensures that each disc type receives optimized light distribution, maintaining high light utilization efficiency across all formats while using a single objective lens.
3Device complexity
If a common objective lens is used for BDs, DVDs, and CDs, then cost is reduced, but manufacturing precision requirements increase to control aberrations
Solution Approach 1:
The objective lens incorporates segmented optical path difference providing structures in different regions, each with specific manufacturing tolerances and design optimizations. By dividing the lens into regions with distinct functional requirements, the patent enables targeted manufacturing approaches where each region can be optimized for its specific wavelength and disc type, making it feasible to manufacture a single lens that meets the diverse precision requirements of BDs, DVDs, and CDs.
Solution Approach 2:
Different regions of the objective lens have locally optimized optical path difference profiles and structural characteristics. The first region is optimized for BD wavelengths with specific optical path differences, the second region for DVD wavelengths with different optical path differences, and the third region for CD wavelengths with yet another profile. This local quality approach allows each region to be manufactured with precision tailored to its specific function, reducing overall manufacturing difficulty while maintaining high performance across all disc types.
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
Enables the recording and reproduction of information for all three types of discs with a common objective lens, ensuring stable performance under temperature changes and maintaining high light utilization efficiency, while securing a sufficient working distance for CDs and controlling aberrations.
Implementation Method 1
it is required that a diffractive structure having a wavelength dependency for the spherical aberration, is formed in the objective optical system
Data Source
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AI summary
Disclosed are an optical pick-up device, an optical information recording/reproducing device, and an objective preferable therefor enabling achievement of compatibility among three types of optical discs, i.e., BDs, DVDs, and CDs by means of a common objective and enabling the working distance of the CDs to be adequately ensured. The objective is provided with a first optical path difference imparting structure wherein the fundamental structures are superimposed in such a way that the step in the fundamental structure in which the order of diffraction of the blue-violet laser beam is an odd order is directed in the opposite direction from the optical axis, and the direction of the step in the fundamental structure in which the order of diffraction of the blue-violet laser beam is an even order is directed toward the optical axis.