Diffractive Optical Element Asymmetric Grating Flare Reduction
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Solution Overview
Problem
Existing diffractive optical elements struggle to effectively reduce flare and facilitate manufacturing while maintaining positive optical power and diffraction efficiency, particularly in optical systems like digital cameras, due to interference issues with mold release and refractive index mismatches.
Innovation Solution
A diffractive optical element design featuring a first lens with a convex surface and a second lens with a concave surface, where the diffraction grating section includes a first diffraction grating and a second diffraction grating with a larger refractive index, inclined such that the inner diameter of the grating wall surface decreases towards the second lens, satisfying the condition θH × θM < 0, which reduces flare and improves manufacturing ease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the grating wall surface is made parallel with incident light to reduce flare, then flare is reduced, but manufacturing becomes difficult due to mold release interference
Solution Approach 1:
The patent introduces asymmetric inclination angles for the grating wall surfaces. The first grating has an inclination angle θ1 and the second grating has an inclination angle θ2, where θ1 ≠ θ2. This asymmetric design allows the grating wall surfaces to be non-parallel with incident light, resolving the conflict between flare reduction and manufacturing ease by finding an optimal asymmetric configuration that balances both requirements.
Solution Approach 2:
The patent optimizes specific parameter ranges for the inclination angles θ1 and θ2, and for the refractive index difference between the two gratings. By changing these parameters within defined ranges, the patent achieves a balance where flare is sufficiently reduced while maintaining manufacturability through appropriate mold design and release conditions.
2Device complexity
If a single diffraction grating is used, then the structure is simple, but chromatic aberration correction is insufficient
Solution Approach 1:
The patent divides the diffraction grating into two separate gratings with different refractive indices and different inclination angles. This segmentation allows each grating to contribute differently to chromatic aberration correction, achieving superior correction performance while maintaining a relatively simple overall structure that can be manufactured as an integrated component.
Solution Approach 2:
The patent uses two gratings made of materials with different refractive indices. This composite structure leverages the different optical properties of each material to achieve broad-spectrum chromatic aberration correction across multiple wavelengths, improving correction precision without significantly increasing structural complexity.
3Ease of manufacture
If the inner diameter of grating wall surface is constant, then manufacturing is easier, but flare reduction effectiveness is diminished
Solution Approach 1:
The patent introduces a dynamic variation in the inner diameter of the grating wall surface along the optical axis. The inner diameter changes according to a specific function that depends on the position along the optical axis, creating a tapered or curved profile. This dynamic design improves flare reduction by optimizing the angle of incidence for different regions, while the mathematical definition of the variation function allows for controlled manufacturing within specified tolerances.
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 effectively reduces flare generation and enhances manufacturing simplicity by optimizing the refractive index difference and inclination of the grating surfaces, thereby improving diffraction efficiency and correcting chromatic aberrations in optical systems.
Implementation Method 1
a diffractive optical element having a saw-tooth diffraction grating is known as an optical element used to reduce the chromatic aberration of an optical system
Implementation Method 2
it is important to reduce flare arising when light is reflected or refracted by a wall surface of the diffraction grating
Implementation Method 3
flare arising when light is reflected or refracted by a wall surface of the diffraction grating
Data Source
AI summary
A diffractive optical element includes a first lens having a convex surface, a second lens having a concave surface, disposed in such a manner that the concave surface of the second lens faces the convex surface of the first lens, and a diffraction grating section formed between the first and the second lenses and having positive optical power through diffraction. The diffraction grating section includes a first diffraction grating and a second diffraction grating disposed in this order from a side closer to the first lens; the second diffraction grating has a refractive index larger than that of the first diffraction grating, and an inner diameter of a grating wall surface of the diffraction grating section decreases as approaching to the second lens from the first lens.