Diffractive Optical Element for Aberration Correction

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Solution Overview

Problem

Existing optical pickup devices face challenges in ensuring downward compatibility between high-density Blu-ray Discs and lower-density DVDs, with fluctuations in spherical aberrations during wavelength changes, and difficulties in manufacturing chromatic aberration correction elements that are both effective and easy to produce.

Innovation Solution

An optical pickup device is designed with a diffractive optical element featuring an inner circular side irregular or tiered diffraction pattern and an outer circular side tiered diffraction pattern, correcting spherical aberrations for the second laser light and chromatic aberrations for the first laser light, respectively, using a single objective lens with a numerical aperture of 0.75 or above, facilitating manufacturing and maintaining compatibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a single objective lens with NA≥0.75 is used for both Blu-ray Disc and DVD, then downward compatibility is achieved, but spherical aberration fluctuations occur during wavelength changes

Engineering Contradiction:

Improvedownward compatibilityVSAvoidspherical aberration stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The diffractive optical element introduces local optical path differences in specific regions of the wavefront to correct spherical aberration. By applying localized phase corrections rather than uniform adjustments, the system maintains stable focusing for both 405nm Blu-ray and 650nm DVD wavelengths while using a single high-NA objective lens.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The chromatic aberration correction element modifies optical parameters (refractive index, optical path length) as a function of wavelength. This allows the optical system to adapt its correction characteristics dynamically based on the laser wavelength being used, stabilizing spherical aberration across wavelength transitions between Blu-ray and DVD modes.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If chromatic aberration correction elements are designed for effective correction, then optical performance is improved, but manufacturing complexity increases

Engineering Contradiction:

Improveaberration correction effectivenessVSAvoidmanufacturing simplicity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent combines the chromatic aberration correction element with the diffractive optical element into a single integrated component. This merging reduces the total number of separate optical elements that need to be manufactured and assembled, while still providing effective chromatic aberration correction through the combined optical path.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The diffractive optical element is designed to serve multiple functions simultaneously: correcting spherical aberration for both wavelengths and providing chromatic aberration correction. This multi-functionality eliminates the need for separate dedicated correction elements for each type of aberration, simplifying the overall manufacturing process.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 effectively corrects spherical and chromatic aberrations for both Blu-ray Discs and DVDs, ensuring excellent recording and reproduction performance while simplifying the design and manufacturing of chromatic aberration correction elements.

Implementation Method 1

a diffractive optical element which corrects a spherical aberration generated due to a difference in substrate thickness between first and second optical recording mediums

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

a chromatic aberration correction element which corrects a chromatic aberration with respect to a first laser light

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS7301882B2Optical pickup device and diffractive optical element

Publication Date: 2007.11.27 JVC KENWOOD CORP

AI summary

When a wavelength having the same value as a reference wavelength λ1 of a first laser light is set to a designed wavelength λ, a diffractive optical element has: an inner circular side irregular diffraction pattern portion, in which a plurality of irregular portions in which a height of a convex portion is set to approximately 1λ-fold of the designed wavelength λ with respect to a concave portion are repeated, being formed in an annular shape in an inner circular area having a predetermined diameter for the correction of a spherical aberration generated due to a difference in substrate thickness between first and second optical recording mediums centering on a central point through which an optical axis runs while gradually changing a pitch of the irregular portions in a radial direction toward the outer circular side; and an outer circular side tiered diffraction pattern portion which is intended to improve a chromatic aberration with respect to the first laser light by forming in an annular shape in an outer circular area outside the inner circular side irregular diffraction pattern portion a plurality of tiers by setting a height of each tier to approximately mλ-fold (where m is a natural number which does not include 0) of the designed wavelength λ or by setting the same while changing a value of m for each tier.