Alternating Refractive Index Layers for Thin Optical Member Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical members in solid-state imaging devices, such as those using refracted type lenses, suffer from thickness issues leading to increased oblique incident light, color mixtures, and reduced sensitivity, while Fresnel lenses are limited in thickness reduction and require complex fabrication processes.
Innovation Solution
An optical member is configured with high refractive index and low refractive index layers alternately arrayed in the lateral direction, each width equal to or smaller than the wavelength of incident light, allowing for adjustment of equiphase wave surfaces to provide convex or concave lens functions and correct oblique incident light, resulting in a thinner, more efficient optical design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a refracted type lens configuration employing Snell's law is used, then light condensing function is achieved, but the lens becomes thick (around 1 μm or more) causing increased oblique incident light and color mixtures
Solution Approach 1:
The lens is divided into multiple thin layers with alternating high and low refractive indices. Each layer has a thickness of approximately one-quarter of the incident light wavelength. This segmentation allows the lens to achieve the required optical path difference for focusing while maintaining a total thickness much smaller than conventional lenses, thereby reducing oblique incident light and color mixtures.
Solution Approach 2:
The lens uses composite structure with alternating high refractive index layers (e.g., silicon nitride, TiO2) and low refractive index layers (e.g., silicon oxide, air gaps). This composite material approach enables precise control of light phase and amplitude, achieving effective light condensing in a thin profile while minimizing unwanted optical effects.
2Reliability
If existing fabrication processes including reflowing resist are used, then lens formation is achieved, but the process becomes complicated and costs increase
Solution Approach 1:
The patent replaces the mechanical reflow process with a lithography-based patterning approach. By using photolithography to directly form the alternating high and low refractive index layer structures, the complex thermal-mechanical reflow process is substituted with more controllable and simpler photochemical processes, reducing fabrication complexity and cost.
3Shape
If reflow process is used for lens fabrication, then spherical lens can be formed, but asymmetrical lens shapes cannot be fabricated
Solution Approach 1:
The lithography-based fabrication method allows different patterns to be applied to different regions of the lens. Each pixel region can have customized high and low refractive index layer arrangements, enabling asymmetrical shapes, deformed lateral directions, and region-specific optical characteristics that cannot be achieved with uniform reflow processes.
4Use of energy by moving object
If F value of external image formation system lens is reduced, then light gathering capability improves, but oblique incident light increases causing sensitivity deterioration
Solution Approach 1:
The patent changes the optical parameters by using alternating high and low refractive index layers with specific thicknesses (one-quarter wavelength each). This parameter optimization allows the thin lens to effectively focus oblique incident light from low F-value lenses, maintaining sensitivity by correcting the focal point position and reducing chromatic aberrations that would otherwise cause sensitivity deterioration.
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 configuration reduces color mixtures, improves sensitivity, and simplifies fabrication, enabling a thinner optical member that effectively corrects oblique incident light without the need for complex processing, thereby enhancing image quality and reducing noise.
Implementation Method 1
an optical member, and a solid-state imaging device employing this optical member, and a manufacturing method thereof... a member having a refracted type lens configuration employing Snell's law
Implementation Method 2
high refractive index layers and low refractive index layers which are each relatively thin as compared with an optical length (lens length) are disposed alternately in the lateral direction... the equiphase wave surfaces of the light passing through the optical member are formed in the same way as the equiphase wave surface of the medium at the incident side
Data Source
AI summary
A method of making an optical member including high refractive index layers and low refractive index layers, which are each relatively thin as compared with an optical length, and disposed alternately in the lateral direction with respect to an optical axis. Each width of the high refractive index layers and the low refractive index layers is equal to or smaller than the wavelength order of incident light.