Fresnel Lens Draft Angle Gradient for Stray Light Control
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Solution Overview
Problem
Normal Fresnel lenses suffer from deteriorated optical imaging quality due to lens flares and light spots caused by stray light from non-effective Fresnel surfaces, which are reflected at the same angle, resulting in high illuminance and reduced clarity.
Innovation Solution
The Fresnel lens design features a gradual increase in draft angles outward from the optical axis, expanding the irradiation area of stray light and reducing its illuminance, achieved by alternating effective and non-effective Fresnel surfaces with varying draft angles, ensuring each draft angle is less than 90 degrees.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the same draft angle is used for all non-effective Fresnel surfaces, then the manufacturing process is simplified, but the stray light is focused at the same angle forming high illuminance lens flares that deteriorate imaging quality
Solution Approach 1:
The patent applies local quality by assigning different draft angles to different regions of the non-effective Fresnel surfaces. Specifically, the first draft angle is used for non-effective surfaces in the first region, while the second draft angle (different from the first) is used for non-effective surfaces in the second region. This regional differentiation causes stray light to be reflected at different angles, preventing concentration at a single focal point and thereby reducing lens flares and light spots while maintaining manufacturing feasibility.
2Ease of manufacture
If larger draft angles are used for easier mold removal, then manufacturing ease is improved, but the stray light reflection angle increases causing more severe lens flares
Solution Approach 1:
The patent applies parameter changes by varying the draft angle parameter across different regions of the Fresnel lens. Instead of using a uniform large draft angle that would facilitate mold removal but increase stray light illuminance, the invention uses multiple draft angle values (first draft angle and second draft angle) in different regions. This parameter variation allows optimization of both mold removal ease and stray light control, as different regions can use draft angles suited to their specific requirements.
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 design effectively reduces the maximum illuminance of stray light while expanding its distribution area, improving overall optical imaging quality and clarity, particularly at the image center, while also facilitating easier processing and mold removal during injection molding.
Implementation Method 1
light rays incident on non-effective Fresnel surfaces are reflected at the same angle to form the stray light
Implementation Method 2
stray light generated by reflections of refractions by light rays incident on non-effective Fresnel surfaces
Data Source
AI summary
A Fresnel lens includes a Fresnel surface that includes effective Fresnel surfaces allowing imaging rays to pass through. Two adjacent effective Fresnel surfaces are connected through a non-effective Fresnel surface. On a cross-section including an optical axis of the Fresnel lens, a draft angle is between a reference line and a connecting straight line between one end of each non-effective Fresnel surface located at a tooth peak of the Fresnel lens and the other end of each non-effective Fresnel surface located at a tooth valley of the Fresnel lens. The optical axis coincides with the cross-section. The reference line is parallel to the optical axis and passes through the end of the effective Fresnel surface located at the tooth peak of the Fresnel lens. The draft angles each smaller than 90 degrees include first, second, third, fourth, and fifth draft angles which gradually increase radially outward from the optical axis.