Diffractive Trifocal Lens With Alternating Step Heights
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Solution Overview
Problem
Existing multifocal intraocular and contact lenses fail to effectively direct sufficient light into intermediate focal distances, leading to reduced visual quality and difficulty in predicting lens power due to excess light being directed into higher diffractive orders.
Innovation Solution
A diffractive multifocal lens design with alternating step heights in concentric annular zones to optimize diffraction order efficiencies, specifically tailoring the step heights to enhance intermediate vision by directing light power into designated diffraction orders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional diffractive lenses use equal step heights in all zones, then the lens structure is simple and manufacturing is easier, but insufficient light is directed into intermediate focal distances and higher diffractive orders receive excess light
Solution Approach 1:
The patent applies local quality by varying the step height values at different radial zones of the lens. Specifically, the step height is made smaller in zones corresponding to intermediate focal distances and larger in zones for distance and near vision. This localized variation optimizes light distribution to enhance intermediate vision while maintaining adequate distance and near vision, thereby improving overall visual quality without requiring complete redesign of the entire lens structure.
Solution Approach 2:
The patent changes the parameter of step height values across different zones to control diffraction order efficiencies. By making step heights non-uniform (smaller for intermediate, larger for distance and near), the lens achieves optimized light distribution. This parameter change allows the lens to direct sufficient light into intermediate focal distances while reducing excess light in higher diffractive orders, resolving the contradiction between manufacturing simplicity and visual quality.
2Adaptability or versatility
If the lens directs light into multiple diffractive orders, then multifocal vision is achieved, but excess light is directed into higher diffractive orders reducing visual quality
Solution Approach 1:
The patent applies local quality by assigning different step height values to different radial zones corresponding to different focal distances. Zones for intermediate vision have smaller step heights, while zones for distance and near vision have larger step heights. This localized differentiation optimizes light distribution across multiple diffractive orders, ensuring sufficient light reaches intermediate focal distances while preventing excessive light in higher orders, thus maintaining high visual quality across all focal planes.
3Reliability
If step heights are made smaller in intermediate zones, then intermediate vision is enhanced, but the complexity of the lens structure increases
Solution Approach 1:
The patent implements local quality by introducing variation in step height values specifically in the radial zones corresponding to intermediate focal distances. These zones have smaller step heights compared to distance and near vision zones. This localized modification enhances intermediate vision without requiring complete redesign of the entire lens, thereby limiting the increase in structural complexity to only the necessary regions.
Solution Approach 2:
The patent applies segmentation by dividing the lens into multiple radial zones with different step height characteristics. Each zone is optimized for its specific focal distance function: intermediate zones have smaller step heights, while distance and near zones have larger step heights. This segmentation allows independent optimization of each focal plane without requiring complete redesign of the entire lens structure, thus managing complexity effectively.
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 lens design achieves improved visual performance across the full focal range by equally enhancing distance, intermediate, and near vision, optimizing light distribution for each focal distance.
Implementation Method 1
The resulting surface structure acts as a circularly symmetric diffraction grating that disperses light into multiple diffraction orders, each diffraction order having a consecutive number, zero, one, two, and so forth.
Implementation Method 2
Diffraction efficiency refers to the percentage of incident light power transmitted into each of the various diffractive orders comprising the diffraction pattern at the focal plane.
Implementation Method 3
Conventional corrective optics are typically refractive lenses, meaning that they bend and focus light rays reflected from an object to form a focused image of the object on the retina. The bending of the light rays is dictated by Snell's law which describes the degree of bending that occurs as light rays cross the boundary of two materials with distinct indices of refraction.
Data Source
AI summary
A diffractive multifocal lens is disclosed, comprising an optical element having at least one diffractive surface, the surface profile comprising a plurality of annular concentric zones. The optical thickness of the surface profile changes monotonically with radius within each zone, while a distinct step in optical thickness at the junction between adjacent zones defines a step height. The step heights for respective zones may differ from one zone to another periodically so as to tailor diffraction order efficiencies of the optical element. In one example of a trifocal lens, step heights alternate between two values, the even-numbered step heights being lower than the odd-numbered step heights. By plotting a topographical representation of the diffraction efficiencies resulting from such a surface profile, step heights may be optimized to direct a desired level of light power into the diffraction orders corresponding to near, intermediate, and distance vision, thereby optimizing the lens performance.