Optical Head Device with Variable Aperture for Multi-Disc Focus
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Solution Overview
Problem
Existing optical head devices struggle to provide a wide dynamic range for lower density optical discs while maintaining high sensitivity for higher density discs, and they are not cost-effective for compatibility with multiple light sources, especially for three different wavelengths.
Innovation Solution
An optical head device with multiple switchable light sources, including a first and second light source with different wavelengths, and an objective lens with specific zones for converging light to achieve a wide dynamic range and high sensitivity focusing error signals, using astigmatism and spherical aberration to optimize focusing error signals for various disc types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single objective lens is used for multiple optical disc types, then device complexity is reduced, but the ability to provide wide dynamic range for lower density discs and high sensitivity for higher density discs deteriorates
Solution Approach 1:
The patent applies dynamics by making the objective lens adjustable through a variable aperture mechanism. The aperture can be dynamically changed to provide different numerical apertures (NA) depending on the optical disc type being read. This allows the single lens to adapt its focusing characteristics to match the requirements of different disc densities, thereby maintaining both wide dynamic range for low-density discs and high sensitivity for high-density discs without requiring multiple fixed lenses.
Solution Approach 2:
The patent changes the parameter of numerical aperture (NA) by adjusting the aperture size of the objective lens. By varying the aperture diameter, the system can optimize the focusing error signal characteristics for different optical disc types. This parameter change enables the same lens to provide appropriate focusing performance across a wide range of disc densities, resolving the contradiction between device simplicity and measurement precision.
2Adaptability or versatility
If multiple light sources with different wavelengths are used for compatibility, then adaptability improves, but device complexity and cost increase
Solution Approach 1:
The patent applies universality by designing a single optical head device that can read multiple types of optical discs (CD, DVD, Blu-ray) using different light sources. The device incorporates a light source selection mechanism that can switch between red (650nm), green (532nm), and blue (405nm) lasers, allowing one device to perform multiple functions across different disc formats. This multi-functional design improves adaptability while managing device complexity through integrated control.
3Adaptability or versatility
If variable aperture is used to change numerical aperture, then adaptability to different disc types improves, but device complexity increases
Solution Approach 1:
The patent merges the variable aperture mechanism directly into the objective lens structure, combining the lens and aperture control into a single integrated component. This integration allows the numerical aperture to be changed without requiring separate mechanical assemblies or additional optical elements, thereby improving adaptability to different disc types while minimizing the increase in device complexity through consolidation.
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 optical head device achieves stable and precise focus servo for both high and low density discs with a single device, ensuring compatibility and low cost, enabling efficient recording and reproduction across different optical disc types.
Implementation Method 1
an objective lens for converging light emitted from one of the plurality of light sources to an information recording layer of an optical disc
Implementation Method 2
a light detector for receiving the light reflected by the information recording layer and outputting an electric signal based on the amount of the received light
Implementation Method 3
using astigmatism and spherical aberration to optimize focusing error signals for various disc types
Implementation Method 4
using astigmatism and spherical aberration to optimize focusing error signals for various disc types
Data Source
AI summary
An optical head device compatible to different types of optical discs and capable of guaranteeing a sufficiently wide dynamic range for a low density optical disc, and the like are provided.The optical head device includes a plurality of light sources switchably usable; an objective lens for converging light emitted from one of the plurality of light sources to an information recording layer of an optical disc; and a light detector for receiving the light reflected by the information recording layer and outputting an electric signal based on the amount of the received light. The plurality of light sources include a first light source for emitting light having a first wavelength and a second light source for emitting light having a second wavelength shorter than the first wavelength. In the optical head device, a defocus detection range of a focusing error signal obtained based on the light having the first wavelength is set to be wider than a defocus detection range of a focusing error signal obtained based on the light having the second wavelength.