Objective Lens Diffractive Structure for Multi-Wavelength Focus

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Solution Overview

Problem

Existing optical pickups for high-density-recording optical discs require multiple objective lenses to accommodate different wavelengths, leading to suboptimal angles, increased complexity, and reduced sensitivity due to unwanted diffracted light caused by temperature and wavelength variations, affecting focus servo stability.

Innovation Solution

A single objective lens with a diffraction section featuring a staircase-like structure on its entry-side surface, which selectively diffracts light beams for three wavelengths, ensuring optimal focusing and minimizing unwanted diffracted light by adjusting aperture diameters and diffraction orders to maintain stable focus servo control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If two types of objective lenses are used for different wavelengths, then compatibility with multiple optical disc formats is achieved, but device complexity and production cost increase

Engineering Contradiction:

Improvecompatibility with multiple optical disc formatsVSAvoidnumber of objective lenses and optical components

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent employs a single objective lens that serves multiple functions by diffracting different wavelengths of light into different focal directions. This universal lens replaces what would traditionally require multiple specialized lenses, thereby reducing device complexity while maintaining compatibility with CD, DVD, and Blu-ray formats

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The objective lens is segmented into multiple diffraction regions, each optimized for specific wavelength ranges. This segmentation allows the single lens to handle multiple wavelengths effectively by directing each wavelength to its appropriate focal point, achieving multi-format compatibility without requiring multiple separate lenses

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If two objective lenses are mounted on the actuator, then multi-format support is enabled, but weight of the actuator increases

Engineering Contradiction:

Improvemulti-format supportVSAvoidweight of the actuator

Core Design Contradiction:

Adaptability or versatilityVSWeight of moving object

Solution Approach 1:

The patent merges the functions of multiple objective lenses into a single integrated lens structure with diffractive elements. This consolidation reduces the total weight of the actuator assembly while maintaining the capability to support multiple optical disc formats through wavelength-selective diffraction

Inventive Principle:

Principle #5Merging (Combining)

3Manufacturing precision

If a diffractive structure is added to correct spherical aberration, then focus quality is improved, but unwanted diffracted light increases due to temperature and wavelength variations

Engineering Contradiction:

Improvefocus qualityVSAvoidunwanted diffracted light

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by creating distinct diffraction regions with different structural characteristics within the single objective lens. Each region is optimized to produce desired diffraction patterns for specific wavelengths while minimizing unwanted diffraction, thereby maintaining focus quality and reducing harmful diffracted light through localized structural optimization

Inventive Principle:

Principle #3Local quality

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 excellent recording and reproduction characteristics across varying temperatures and wavelengths, simplifying the optical components and reducing production costs while maintaining high sensitivity and stability.

Implementation Method 1

diffract light with the diffraction section in a divergent direction or in a convergent direction, so as to correct spherical aberration generated in accordance with a combination of a wavelength and a medium

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS8139463B2Objective lens, optical pickup, and optical disc apparatus

Publication Date: 2012.03.20 SONY GROUP CORP

AI summary

Provided is an objective lens for selectively focusing each of light beams having three wavelengths λ1, λ2, and λ3 on a signal recording surface of a corresponding optical disc, the wavelengths λ1, λ2, and λ3 satisfying at least a relationship λ1<λ2<λ3, the objective lens including a diffraction section disposed on an entry-side surface thereof, the diffraction section including a first region disposed in an innermost radius portion, a second region disposed outside the first region, and a third region disposed outside the second region, the first to third regions being formed so that an aperture of the light beams are appropriately limited, the first region including a staircase-like diffractive structure having a certain number of levels configured so that diffracted light of a predetermined order has the highest diffraction efficiency and optical-path-difference phase amounts for the levels of the diffractive structure has a certain relationship.