Objective Lens Diffraction Element Focus Detection Accuracy
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Solution Overview
Problem
Existing objective lenses for optical disks face challenges in accurately detecting the focus position due to incorrect focus error signal generation, leading to potential collisions and reduced focal position detection accuracy when trying to converge light onto disks with different base material thicknesses.
Innovation Solution
An objective lens with a diffraction element that divides the incoming beam into two diffracted rays of different orders, ensuring the focal position of the diffracted ray with a longer focal length is collected on the optical disk's base material, with the distance between focal positions of the two diffracted rays being longer than double the distance between the lens and the base material, preventing focus pull-in errors and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffraction structure divides light into two diffracted rays for focus control, then focus error signal can be generated, but focus pull-in error occurs and focal position detection accuracy deteriorates
Solution Approach 1:
The patent introduces a protective layer as an intermediary medium between the objective lens and the optical disk. This protective layer with refractive index n=1.5 and thickness 0.6mm serves as a mediator to adjust the optical path, ensuring that the focus error signal is generated at the correct position while preventing direct contact between the lens and disk, thereby resolving the focus pull-in error issue
Solution Approach 2:
The patent changes the optical parameters by introducing a protective layer with specific refractive index (n=1.5) and thickness (0.6mm). This parameter change modifies the optical path length and focal positions, shifting the focus error signal generation position to the correct location and improving both measurement precision and reliability
2Measurement precision
If the distance between focal positions of two diffracted rays is set longer than the distance between the objective lens and the protective layer surface, then focus error signal can be generated, but focus pull-in error to a position closer than the original distance occurs
Solution Approach 1:
The protective layer acts as an intermediary that precisely controls the optical path. By setting its thickness to 0.6mm and refractive index to 1.5, it creates the appropriate optical distance relationship, ensuring that the focus error signal is detected at the correct position without causing focus pull-in errors
Solution Approach 2:
The protective layer is pre-installed between the objective lens and the optical disk before operation. This preliminary action establishes the correct optical path and focal positions in advance, preventing focus control errors before they occur
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
This configuration effectively prevents focus pull-in errors and enhances focal position detection accuracy, allowing for reliable operation across various optical disk types with different base material thicknesses, such as CDs, DVDs, and Blu-ray discs.
Implementation Method 1
having a diffraction element for dividing light quantity of an incoming beam into two diffracted rays of which orders of diffraction are mutually different
Data Source
AI summary
The present invention provides an objective lens, an optical head apparatus, an optical information apparatus, and an information processing apparatus that improve focal position detection accuracy. In order to reproduce information from an optical disk (28), an objective lens (25) collects a diffracted ray (15X) having a longer focal length, out of two diffracted rays (15X, 15Y), on an information recording surface (28L) via a base (28S) of the optical disk (28), and a distance (DF3) between the focal positions of the two diffracted rays (15X, 15Y) when the diffracted ray (15X) having a longer focal length is collected on the information recording surface (28S) is longer than double the distance (WD2) between the surface (25A) of the objective lens (25) and the surface (28A) of the base (28S) along the optical axis.