Multi-Wavelength Objective Lens Diffractive Structure
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Solution Overview
Problem
Existing optical pickups face challenges in achieving compatibility with multiple optical disc formats, such as CDs, DVDs, and high-density recording optical discs, due to issues like suboptimal objective lens attachment angles, increased component complexity, cost, and sensitivity deterioration, particularly with unwanted diffracted light affecting focus servo stability across varying temperatures and wavelengths.
Innovation Solution
A single objective lens with a diffractive portion having specific diffraction structures for three wavelengths (405 nm, 655 nm, and 785 nm) is designed, featuring a periodic orbicular zone diffraction structure with a blazed and multi-step configuration to manage light beams effectively across different disc formats, reducing spherical aberration and unwanted diffracted light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two types of objective lenses are used for different optical disc formats, then compatibility with multiple disc formats is achieved, but the attachment angle of the actuator becomes unsuitable and the quality of reproduced signals deteriorates
Solution Approach 1:
The patent applies universality by designing a single objective lens that can focus three different wavelength light beams (405nm, 655nm, and 785nm) onto the signal recording surfaces of different optical disc formats. This eliminates the need for switching between multiple objective lenses, thereby maintaining both multi-format compatibility and optimal attachment angle for high-quality signal reproduction.
2Adaptability or versatility
If two types of objective lenses and two types of optical systems are provided, then recording and reproducing on three types of optical discs is enabled, but the number of components increases leading to increased cost and size
Solution Approach 1:
The patent merges multiple optical systems into a single integrated system. By providing a single objective lens with diffractive structures that can handle all three wavelengths, the patent combines what would otherwise require separate optical paths and components, thereby reducing the total number of components, lowering cost, and decreasing the size of the optical pickup while maintaining full functionality.
Solution Approach 2:
The single objective lens is designed to perform multiple functions by incorporating diffractive structures that enable it to focus different wavelengths (405nm for BD, 655nm for DVD, 785nm for CD) onto their respective signal recording surfaces, eliminating the need for multiple specialized lenses and optical systems.
3Adaptability or versatility
If two objective lenses are mounted on the actuator, then multi-format support is achieved, but the weight of the actuator increases and sensitivity deteriorates
Solution Approach 1:
The patent combines the function of two separate objective lenses into a single objective lens with integrated diffractive structures. This merging reduces the weight of the actuator by eliminating the need to mount and switch between multiple heavy lens assemblies, while maintaining the capability to support multiple optical disc formats through wavelength-selective focusing.
4Device complexity
If a diffractive portion is provided to enable three-wavelength compatibility with a single objective lens, then component complexity is reduced, but unwanted diffracted light increases and focus servo stability deteriorates
Solution Approach 1:
The patent applies local quality by designing the diffractive portion with non-equidistant multi-step structures where the step widths vary across different radial positions. This local variation in structure allows different regions of the diffractive portion to selectively diffract different wavelengths while suppressing unwanted diffracted light, thereby maintaining focus servo stability despite the presence of the diffractive structure.
Solution Approach 2:
The patent changes the geometric parameters of the diffractive structure by using non-equidistant multi-step structures instead of uniform patterns. By varying the step widths and depths according to specific design parameters, the diffractive structure achieves wavelength-selective diffraction while minimizing the generation of unwanted diffracted light that would interfere with focus servo operation.
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 and efficient recording and reproducing of information signals on multiple optical disc formats without compromising quality, maintaining performance across temperature and wavelength changes, and simplifying the optical pickup configuration.
Implementation Method 1
A basic principle for providing an objective lens for three-wavelength light beams is to provide a diffractive portion in the optical path and thereby diffract the light beams in a divergent direction or in a convergent direction, thereby correcting spherical aberration caused by the combination of the used wavelengths and the media.
Data Source
AI summary
Provided is an objective lens used in an optical pickup that performs recording and/or reproducing of information signals on three different types of optical discs using different wavelengths. The objective lens is configured to collect light beams with the at least three wavelengths λ1, λ2, and λ3, which satisfy a relationship of λ1<λ2<λ3, on signal recording surfaces of compatible optical discs corresponding to the respective wavelengths. The objective lens includes: a diffractive portion that has a predetermined diffraction structure formed on an incident side surface. The diffractive portion has a first region that is provided in an innermost peripheral portion so as to diffract the light beams, a second region that is provided outside the first region so as to diffract the light beams, and a third region that is provided outside the second region.