Diffractive Aspherical Optical System Flare Suppression
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Solution Overview
Problem
Existing imaging optical systems using diffractive optical elements face challenges in effectively suppressing flare caused by high-order diffracted light and correcting various aberrations, as they primarily consider refractive power specified by low-order phase coefficients, leading to insufficient aberration correction and increased flare.
Innovation Solution
The optical system incorporates a diffractive surface with a phase function represented by high-order terms and an aspherical surface with corresponding aspherical coefficients, where the phase and aspherical functions increase with opposite signs, optimizing the refractive power distribution to suppress flare and correct aberrations effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the refractive power on the diffractive surface is increased to emphasize aberration correction, then the chromatic aberration correction is improved, but the flare caused by unnecessary diffracted light increases
Solution Approach 1:
The patent applies parameter changes by modifying the phase function coefficients (C2, C3, C4, C5) of the diffractive surface to optimize the balance between aberration correction and flare suppression. Specifically, the patent sets C2 within -0.003 to -0.0003, C3 within -0.0003 to -0.00003, C4 within -0.00003 to -0.000003, and C5 within -0.000003 to -0.0000003, thereby adjusting the refractive power distribution to achieve both chromatic aberration correction and flare reduction
Solution Approach 2:
The patent converts the harmful effect of high-order diffracted light causing flare into a beneficial effect by using aspherical surfaces to control and redirect these diffracted rays. The aspherical surfaces are designed to guide the unnecessary diffracted light away from the image plane, transforming the potential harm into a controlled optical path that does not degrade image quality
2Object-generated harmful factors
If the refractive power on the diffractive surface is decreased to suppress flare, then the flare is reduced, but the aberration correction effect is weakened
Solution Approach 1:
The patent segments the optical correction function by separating the diffractive surface (responsible for chromatic aberration correction) from the aspherical surfaces (responsible for controlling diffracted light paths). This segmentation allows each component to be optimized independently: the diffractive surface can maintain sufficient refractive power for aberration correction while the aspherical surfaces manage the flare suppression by directing unwanted diffracted light
Solution Approach 2:
The patent employs a composite optical system combining diffractive optical elements with aspherical refractive surfaces. This composite structure integrates the advantages of both diffractive elements (strong abnormal dispersion for chromatic correction) and aspherical surfaces (controlled light routing for flare suppression), achieving a synergistic effect that resolves the contradiction between aberration correction and flare reduction
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 approach results in a system that satisfactorily corrects various aberrations while suppressing flare, achieving a small and lightweight optical design with improved optical performance.
Implementation Method 1
a method of using a negative dispersion characteristic (νd=−3.453) or strong abnormal dispersion (θgF=0.296) of the diffractive optical element different from those of a common glass material to obtain a strong achromatic effect
Implementation Method 2
an aspherical function X(r) of the aspherical surface is represented by X(r)=(1/R)×r2/[1+√{1−(1+k)(r/R)2}]+A1×r4+A2×r6+A3×r8+A4×r10+ . . . +Aq×r2×(q+1)
Data Source
AI summary
An optical system includes a diffractive surface and at least one aspherical surface, an aspherical surface of at least one aspherical surface closest to the diffractive surface is referred to as a first aspherical surface, a phase function ψ(r) and an aspherical function X(r) of the first aspherical surface increase with different signs from each other in a height direction with increasing a distance from an optical axis, and a condition below is satisfied:-0.10≤∑i=1p(Ci⨯(f/Fno)2⨯i-1)/∑j=1q(Aj⨯(f/Fno)2⨯j+1)≤-0.01where f is a focal length of the optical system when focusing on an infinite object, and Fno is an F number of the optical system.