Diffractive Lens Optical Path Difference for Thin Headlamp Design
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Solution Overview
Problem
Existing optical lenses, such as diffractive and Fresnel lenses, face challenges in maintaining optical performance and efficiency when used with white light sources due to wavelength deviations, leading to reduced diffraction efficiency and manufacturing difficulties, particularly in achieving high lens power and thinning of thick lenses while ensuring aberration performance.
Innovation Solution
A diffractive lens design that utilizes a phase function to create a meniscus lens with concentric annulus areas, where the optical path difference between adjacent areas is optimized to maintain diffraction efficiency across a wide wavelength range, allowing for the use of high-order diffracted light to increase annulus width and step depth, facilitating machining and reducing lens thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the optical path difference between adjacent annuli is reduced to one wavelength to maintain diffraction efficiency for first-order diffracted light, then diffraction efficiency is improved, but the pitch between annuli is reduced and machining becomes difficult
Solution Approach 1:
The patent changes the parameter of optical path difference from one wavelength to multiple wavelengths (n wavelengths). This allows the pitch between annuli to be increased by a factor of n while maintaining acceptable diffraction efficiency, thereby improving machinability without completely sacrificing optical performance
Solution Approach 2:
The patent accepts using higher-order diffracted light (n>1) which provides excessive lens power. This allows the annulus width to be increased for better machinability, while the system can tolerate the higher power in exchange for easier manufacturing
2Ease of manufacture
If the lens power of the diffractive lens is reduced to provide sufficient annulus width for machining, then machinability is improved, but the lens thickness cannot be reduced as expected
Solution Approach 1:
The patent increases the optical path difference to n wavelengths, which increases the lens power by a factor of n. This allows the use of higher-order diffracted light that provides sufficient annulus width for machining while achieving the desired thin lens effect through the increased power
3Ease of manufacture
If high-order diffracted light is used to increase the pitch between annuli, then machinability is improved, but diffraction efficiency decreases significantly
Solution Approach 1:
The patent systematically evaluates different values of n (optical path difference multiples) to find the optimal balance. By changing the parameter from n=1 to higher values, the patent achieves sufficient pitch for machining while controlling the decrease in diffraction efficiency through careful design
4Ease of manufacture
If a conventional Fresnel lens is used with a flat surface, then manufacturing is simplified, but aberration performance is degraded
Solution Approach 1:
The patent applies curvature to the diffractive lens surface, transitioning from a flat Fresnel lens design to a curved surface design. This curvature optimization maintains the manufacturing advantages of diffractive structures while significantly improving aberration performance and overall optical quality
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 enables a thin, high-performance lens that maintains optical properties, reduces weight and size in devices like cameras and projectors, and improves manufacturing productivity by suppressing diffraction efficiency decreases and optimizing aberration performance compared to conventional Fresnel lenses.
Implementation Method 1
A diffractive lens design that utilizes a phase function to create a meniscus lens with concentric annulus areas, where the optical path difference between adjacent areas is optimized to maintain diffraction efficiency across a wide wavelength range
Data Source
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AI summary
An object of the present application is to thin a thick lens used in an automobile headlamp optical system and a projector lighting optical system while maintaining the optical properties of the lens. A diffractive lens (101) includes, on at least one surface, an optical surface (103, 104) with a plurality of areas defined by a plurality of steps. A blaze wavelength of the diffractive lens (101) is within a wavelength spectral range of a light source (102) used. An optical path difference between adjacent areas at the blaze wavelength is larger than a coherence length of the light source (102). The diffractive lens (101) substantially acts as a Fresnel lens at a wavelength other than the blaze wavelength.