Diffraction Grating Lens Design for Fringe Flare Suppression
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Solution Overview
Problem
Conventional methods for designing diffraction grating lenses struggle with suppressing fringe flare light, which occurs when diffraction zone widths are increased, leading to decreased image quality, especially under high optical intensity conditions, and make machining difficult due to narrow zone widths.
Innovation Solution
A method for designing diffraction grating lenses that involves determining the widths of diffraction zones and fixing them to prevent narrow widths, allowing for non-uniform zone widths to minimize fringe flare light, while maintaining ease of machining by optimizing the aspherical coefficient of the diffraction surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffraction zone widths are increased to facilitate machining, then ease of manufacture is improved, but fringe flare light increases and image quality deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the step height of the diffraction grating to control the phase difference. By setting the step height to satisfy specific conditions (Exp. 2 and Exp. 3), the patent achieves a phase difference of 2π between base and tip of the diffraction step portion, which suppresses unnecessary-order diffraction light while maintaining manufacturable zone widths. This resolves the contradiction by changing the height parameter rather than the width parameter.
Solution Approach 2:
The patent applies local quality by creating a blazed diffraction grating structure where the slope angle varies locally to direct diffraction light preferentially in the first order. The blazed structure with specific slope angles (greater than 45 degrees) locally modifies the diffraction pattern to suppress higher-order diffraction and reduce fringe flare, while maintaining adequate zone widths for machining.
2Object-affected harmful factors
If diffraction zone widths are decreased to reduce fringe flare light, then image quality is improved, but machining difficulty increases
Solution Approach 1:
The patent changes the step height parameter to compensate for wider diffraction zones. By increasing the step height to achieve a 2π phase difference, the patent suppresses unnecessary-order diffraction light even with wider zones, thereby maintaining image quality while improving ease of machining.
Solution Approach 2:
The patent employs an aspherical base shape combined with the diffraction grating structure. The aspherical surface provides aberration correction while the superimposed diffraction grating with blazed structure suppresses fringe flare, allowing wider diffraction zones without significant image quality degradation.
3Use of energy by moving object
If step height is increased to achieve 100% first-order diffraction efficiency at a specific wavelength, then diffraction efficiency is improved, but unnecessary-order diffraction light occurs at other wavelengths
Solution Approach 1:
The patent uses parameter changes by optimizing the step height to satisfy Exp. 3, which balances the phase difference across a broader wavelength range. This reduces the occurrence of unnecessary-order diffraction light at wavelengths other than the design wavelength, while maintaining high first-order diffraction efficiency at the design wavelength.
Solution Approach 2:
The blazed structure with curved slope surfaces directs diffraction light preferentially in the first order across multiple wavelengths. The specific slope angle configuration reduces higher-order diffraction effects, suppressing fringe flare across the operational wavelength range.
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 effectively reduces fringe flare light and facilitates easy machining of diffraction grating lenses by setting zone widths within a range that minimizes fringe flare, thereby improving image quality and manufacturing feasibility.
Implementation Method 1
a diffraction grating lens whose surface has a pattern of diffraction zones is superior in correcting lens aberrations... because a diffraction grating has peculiar characteristics, such as inverse dispersiveness and abnormal dispersiveness, providing a significant chromatic aberration correcting capability
Data Source
AI summary
A method for designing a diffraction grating lens of the present invention is a method for designing a diffraction grating lens having a diffraction grating composed of a plurality of diffraction zones, the method including the steps of: (a) determining widths of the plurality of diffraction zones; and (b) determining an aspherical coefficient of a diffraction surface on which the diffraction grating is provided while the determined widths of the plurality of diffraction zones are fixed, after the step (a).