Multifocal Diffractive Lens With Aspheric Base Surface
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Solution Overview
Problem
Current multifocal diffractive lenses lack intermediate vision capabilities and are sensitive to refractive errors, leading to reduced depth of focus and rapid image quality degradation with small deviations from the best focus position.
Innovation Solution
A multifocal diffractive lens design that includes multifocal grooves for near and distant foci, with an additional intermediate focus, and a multifocal surface that enhances depth of focus by varying the curvature between intermediate and far power levels, minimizing pupil diameter variations and maintaining constructive interference for high-quality near focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed single power lens is used, then good quality of vision is provided within a small range of viewing distances, but the range of viewing distances is significantly narrower than required from near to distant vision
Solution Approach 1:
The lens is divided into multiple functional zones: a central refractive zone for distance vision and an annular diffractive zone for near and intermediate vision. This segmentation allows different regions of the lens to serve different viewing distances, resolving the contradiction between providing good vision quality and covering a broad range of viewing distances.
Solution Approach 2:
The lens combines multiple functions in a single optical element: the refractive surface provides distance correction while the diffractive structure simultaneously provides near and intermediate vision capabilities. This multi-functionality eliminates the need for multiple separate lenses or adjustments, allowing one lens to serve the entire viewing distance range from near to distant vision.
2Device complexity
If a diffractive lens with spherical base surface is used, then the lens structure is simple, but the depth of focus is reduced and image quality degrades rapidly with small deviations from the best focus position
Solution Approach 1:
The base surface is designed as an aspheric surface rather than a simple spherical surface. This aspheric curvature profile is optimized to extend the depth of focus and maintain image quality over a broader range of object distances, thereby improving reliability without significantly increasing structural complexity.
Solution Approach 2:
The refractive index and curvature parameters of the lens are optimized to balance the diffractive and refractive powers. By adjusting these parameters, the lens achieves extended depth of focus and improved image quality stability while maintaining a relatively simple overall structure.
3Adaptability or versatility
If a multifocal diffractive lens with intermediate focus is added, then the range of vision is broadened from far to near, but the lens complexity increases
Solution Approach 1:
The diffractive near vision zones and the refractive intermediate vision zone are merged into a single integrated lens structure. The annular diffractive zone is positioned concentrically around the central refractive zone, creating a unified optical system that provides far, intermediate, and near vision without requiring separate lens components or complex mechanical adjustments.
4Reliability
If the base surface is made multifocal to enhance depth of focus, then tolerance to refraction errors is increased, but the calculation and design complexity increases
Solution Approach 1:
The aspheric base surface parameters are optimized to provide a power profile that extends depth of focus. By carefully selecting and adjusting the aspheric coefficients and curvature variations, the lens achieves increased tolerance to refraction errors while keeping the design methodology systematic and manageable.
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 design provides a broader range of vision from far to near, increases tolerance to refraction errors, and enhances image quality by maintaining high contrast and depth of focus, especially at distant vision.
Implementation Method 1
A diffractive lens generally consists of a number of annular surface zones of equal area, so called Fresnel type zones or grooves. The optical steps are provided between the adjacent zones that follow the specific rule hereinbelow described.
Implementation Method 2
A multifocal ophthalmic lens can provide refractive powers, diffractive powers or a combination of both. The multifocal diffractive lens includes multifocal diffractive surface to provide near focus and opposite refractive surface.
Data Source
AI summary
A multifocal ophthalmic lens includes a lens element having an anterior surface and a posterior surface, a refractive zone, or base surface having produced multifocal powers disposed on one of the anterior and posterior surfaces; and a near focus diffractive multifocal zone disposed on one of the anterior and posterior surfaces.