Multiwavelength Objective Lens with Wavelength Selective Filter
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Solution Overview
Problem
Conventional optical disk apparatuses face challenges in efficiently focusing laser beams on different types of optical media, such as CDs, DVDs, and Blu-ray disks, due to variations in substrate thickness and wavelength, leading to issues like light loss and aberration, and existing solutions either require multiple lenses or coatings that are costly and difficult to manufacture.
Innovation Solution
A multiwavelength objective lens with a two-layer antireflection coating and a wavelength selective filter, designed to focus light with low wavefront aberration and high efficiency across multiple wavelengths, using a refractive index of 1.49 to 1.70 and a thermal deformation temperature of 300°C or below, and an antireflection coating composed of high and low refractive index layers to minimize reflectance in specific wavelength regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single objective lens is used for multiple optical disk types, then device complexity and cost are reduced, but focusing precision deteriorates due to substrate thickness variations
Solution Approach 1:
The objective lens is divided into multiple zones with different refractive powers. Specifically, the lens includes a first zone for focusing on thick substrates (CDs), a second zone for medium thickness substrates (DVDs), and a third zone for thin substrates (Blu-ray disks). This segmentation allows each zone to independently optimize focusing for its target substrate type, resolving the contradiction between using a single lens and achieving precise focusing across multiple disk types.
Solution Approach 2:
Different regions of the lens are assigned different optical properties (refractive powers) tailored to specific substrate thicknesses. The lens structure implements local quality by varying the refractive power across different radial zones, enabling each local region to handle a specific disk type optimally while the entire lens remains a single component.
2Loss of energy
If conventional antireflection coatings are applied, then light reflection is reduced, but manufacturing complexity and cost increase due to multiple coating layers
Solution Approach 1:
The patent extracts the wavelength-selective antireflection function from the conventional broadband coating approach and implements it through a wavelength selective filter integrated with the lens structure. This allows the coating to be optimized for specific wavelengths corresponding to different optical disk types, reducing the number of coating layers needed while maintaining low reflection losses.
Solution Approach 2:
The antireflection coating is designed to perform multiple functions simultaneously: it provides wavelength-selective reflection reduction for different optical disk types while being integrated into a single lens structure. This multi-functional coating reduces the need for separate coatings for different wavelengths, simplifying the manufacturing process.
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 efficient focusing of laser beams on various optical media with low wavefront aberration and high light use efficiency, reducing the need for multiple lenses and coatings, while being cost-effective and easy to manufacture.
Implementation Method 1
The objective lens has a positive power to focus each light beam on an information recording surface of a transparent substrate of each optical recording medium by refraction
Implementation Method 2
an antireflection coating composed of high and low refractive index layers to minimize reflectance in specific wavelength regions
Data Source
AI summary
An optical pickup system for reading information of three kinds of optical recording media. The optical pickup system has a wavelength selective filter that includes an outer area for shielding one light beam of light beams having three kinds of wavelengths and an inner area for allowing all the light beams to pass through. The optical pickup system also has an objective lens that focuses each light beam having passed through the wavelength selective filter on each light recording medium. An optical head and an optical disk apparatus have the optical pickup system.