Diffractive Lens Segmented Grating for Flare Reduction
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Solution Overview
Problem
Conventional diffractive imaging lenses suffer from flare and decreased contrast when used as wide-angle lenses, leading to significant brightness differences between the center and peripheral parts of images due to unnecessary diffracted rays.
Innovation Solution
A diffractive lens design featuring a lens base with two groups of diffraction steps, where the first group is covered with a protective coating and the second group is not, with materials having different refractive indices and Abbe numbers, arranged concentrically around the optical axis, and the second group having a pitch of 30 μm or less, to enhance first-order diffraction efficiency and reduce unwanted diffracted light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffraction grating portion is formed on the surface of an aspheric lens to achieve high diffraction efficiency, then the image capturing performance is improved, but unnecessary diffracted rays are produced causing flare and decreased contrast
Solution Approach 1:
The diffraction grating is divided into two groups: a first group with larger pitch values that is covered by a protective coating to suppress unnecessary diffraction, and a second group with smaller pitch values that remains exposed to maintain high diffraction efficiency for the desired wavelength range. This segmentation allows different regions of the grating to serve different functional purposes.
Solution Approach 2:
Different regions of the diffraction grating are given different properties through selective coating application. The first group (peripheral region) has a protective coating to reduce harmful diffraction, while the second group (central region) remains uncovered to maximize useful diffraction efficiency. This local differentiation resolves the contradiction between reducing flare and maintaining image quality.
2Measurement precision
If a protective coating is applied to cover the entire diffraction grating to reduce wavelength dependence, then diffraction efficiency is improved, but the pitch of the diffraction steps increases causing loss of light
Solution Approach 1:
The protective coating is applied selectively only to the first group of diffraction steps with larger pitch values, while leaving the second group with smaller pitch values uncovered. This segmentation ensures that the coating's light-reducing effect is minimized while still achieving the goal of reducing wavelength dependence and improving diffraction efficiency where most needed.
Solution Approach 2:
The pitch values of the diffraction steps are optimized in two distinct ranges: the first group has larger pitch values suitable for being covered by the protective coating, while the second group has smaller pitch values that remain uncovered to minimize light loss. This parameter differentiation resolves the contradiction between improving diffraction efficiency and reducing light loss.
3Object-generated harmful factors
If the pitch of the diffraction steps is reduced to minimize flare, then unnecessary diffracted rays are reduced, but the diffraction efficiency decreases leading to dark peripheral parts in the image
Solution Approach 1:
The diffraction grating is segmented into two groups with different pitch characteristics: the first group has larger pitch values that are covered by a protective coating to suppress unnecessary diffraction and reduce flare, while the second group has smaller pitch values that remain uncovered to maintain high diffraction efficiency and ensure adequate brightness in the captured image.
Solution Approach 2:
Different regions of the diffraction grating are assigned different pitch characteristics and coating states: the peripheral first group has larger pitch and is covered to reduce harmful diffraction locally, while the central second group has smaller pitch and remains uncovered to maintain high efficiency and brightness. This local quality differentiation resolves the contradiction between reducing flare and maintaining image brightness.
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 minimizes flare and maintains high brightness in the peripheral parts of images, ensuring high resolution and contrast across a wide angle range by optimizing diffraction efficiency and reducing unnecessary diffracted light.
Implementation Method 1
a diffractive lens, which has a concentric diffraction grating portion on the surface of an aspheric lens, is known as a lens that would realize higher image capturing performance than an aspheric lens. By achieving not just the refraction effect of an aspheric lens but also diffraction effect
Implementation Method 2
the diffraction step d′ of the diffraction grating portion that makes 100% the first-order diffraction efficiency of a light ray striking the diffraction grating portion 112 perpendicularly is given by the following Equation (2): d′=mλ/|n1(λ)−n2(λ)| where n1(λ) is the refractive index of the base material, and n2(λ) is the refractive index of the protective coating material
Data Source
AI summary
A diffractive lens 11 that includes: a lens base 18, which has a second surface 13 with first and second groups of diffraction grating portions 20 and 21; and a protective coating 17, which is arranged on the first group of diffraction grating portions 20. The first group of diffraction grating portions 20 has a first group of diffraction steps and the second group of diffraction grating portions 21 has a second group of diffraction steps, which is lower in height than the first group of diffraction steps. One of the respective materials of the base 18 and the protective coating 17 has a higher refractive index and a greater Abbe number than the other material. And the second group of diffraction steps is not covered with the protective coating 17.