Objective Lens Diffractive Structure for Multi-Wavelength Aberration Control
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Solution Overview
Problem
Existing optical pickup apparatuses struggle to maintain compatibility and performance across different types of optical discs, such as Blu-ray Discs (BDs), Digital Versatile Discs (DVDs), and Compact Discs (CDs), due to variations in wavelength and temperature, leading to issues with spherical aberration and diffraction efficiency.
Innovation Solution
A single plastic objective lens with a specific diffractive structure is designed to accommodate multiple wavelengths, featuring a central region with a first optical path difference providing structure and an intermediate region with a second optical path difference providing structure, which corrects spherical aberration and maintains diffraction efficiency across BDs, DVDs, and CDs, even with temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single common objective lens is used for BDs, DVDs, and CDs, then device complexity and cost are reduced, but spherical aberration and diffraction efficiency deteriorate due to wavelength and temperature variations
Solution Approach 1:
The patent applies dynamics by making the objective lens adjustable through a drive mechanism that moves the lens along the optical axis. This allows the lens position to be dynamically changed based on the disc type (BD, DVD, or CD) to optimize focus and aberration correction for each specific wavelength and disc configuration, thereby maintaining reliable performance across different media while using a single lens design.
Solution Approach 2:
The patent changes the parameter of lens position along the optical axis to adapt to different disc types and wavelengths. By adjusting this positional parameter, the system compensates for spherical aberration and maintains proper focus for BDs, DVDs, and CDs, resolving the contradiction between using a single lens and maintaining optical performance across different media.
2Productivity
If the numerical aperture is increased to 0.85 for BD compatibility, then recording capacity is improved, but spherical aberration increases due to wavelength and temperature variations
Solution Approach 1:
The patent incorporates feedback through detection means that monitor the optical characteristics and disc type, then feed this information back to control the lens position adjustment. This feedback loop enables the system to automatically compensate for spherical aberration by adjusting the lens position in response to detected variations in wavelength and temperature, maintaining high recording capacity while minimizing harmful aberration effects.
Solution Approach 2:
The system dynamically adjusts the lens position along the optical axis based on real-time detection of disc type and environmental conditions. This dynamic adjustment allows the high NA 0.85 lens to maintain optimal performance across different wavelengths and temperatures, preventing spherical aberration from degrading recording capacity while preserving the high productivity benefits of increased NA.
3Reliability
If multiple optical systems are used for different disc types, then recording and reproducing performance is improved for each disc type, but device complexity and cost increase
Solution Approach 1:
The patent implements universality by designing a single objective lens that can serve multiple functions for BDs, DVDs, and CDs. Through the addition of a drive mechanism for positional adjustment, this single lens achieves the versatility of multiple specialized lenses, maintaining reliable recording and reproducing performance for each disc type while significantly reducing device complexity and cost.
Solution Approach 2:
The patent merges the functions of multiple optical systems into a single adjustable objective lens. By combining the lens with a drive mechanism that enables position adjustment, the system integrates what would otherwise require separate dedicated lenses for different disc types into one multi-functional component, thereby improving reliability across disc types while reducing overall device complexity.
4Object-affected harmful factors
If the protective substrate thickness is reduced for BDs, then spherical aberration from skew is reduced, but mechanical strength and durability deteriorate
Solution Approach 1:
The patent introduces the adjustable objective lens as an intermediary that compensates for the reduced substrate thickness. By adjusting the lens position along the optical axis, the system compensates for the shorter optical path caused by the thinner protective substrate, thereby maintaining proper focus and reducing aberration effects without requiring the substrate to be thicker for mechanical strength.
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 enables stable performance and high light utilization efficiency for all three types of optical discs, allowing for effective recording and reproducing while minimizing the number of optical components and reducing costs.
Implementation Method 1
an objective lens which has a structure in which two basic structures with respective diffractive structures are superimposed on each other
Implementation Method 2
it is required to form a diffractive structure having wavelength dependency for a spherical aberration on an objective lens
Implementation Method 3
a diffractive structure having wavelength dependency for a spherical aberration on an objective lens
Data Source
AI summary
An optical pickup apparatus including an objective lens capable of enhancing temperature characteristics and wavelength characteristics, and which enables compatibility for three types of optical discs of BDs, DVDs, and CDs by using the objective lens in common, an optical information recording and reproducing apparatus, and an objective lens suitable for it. In a first optical path difference providing structure in which at least a first basic structure and a second basic structure are superimposed on each other, an amount of a level difference in an optical axis direction can be reduced, whereby it becomes possible to suppress the lowering of a diffraction efficiency when wavelength changes. Further, in the first basic structure and the second basic structure deterioration of the spherical aberration due to the change of the refractive index of the objective lens can be corrected by utilizing a phenomenon that the wavelength of the light source rises similarly due to a rise in the environmental temperature.