Optical Element Anisotropy for Uniform Low-Pass Filtering
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Solution Overview
Problem
Optical low-pass filters using anisotropic media face challenges in achieving uniform light separation effects across varying incident angles, leading to non-uniform optical low-pass filter effects in image-pickup apparatuses, particularly in digital cameras and video camcorders, due to material processing difficulties and reduced mechanical strength from excessive anisotropy.
Innovation Solution
An optical element with specific conditions for refractive index difference, optic axis orientation, and thickness is designed to separate light into perpendicular polarization directions, ensuring a consistent light separation width across different incident angles, using lithium niobate or quartz with carefully controlled optic axis angles between 50° and 60° for lithium niobate, and 51° to 61° for quartz, to maintain a uniform optical low-pass filter effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If an anisotropic medium with strong anisotropy (e.g., lithium niobate) is used to reduce optical element thickness, then the light separation width per unit thickness increases, but the material processing difficulty increases and mechanical strength decreases
Solution Approach 1:
The patent changes the optical parameter (anisotropy strength) by selecting lithium niobate with higher anisotropy than quartz, which increases the light separation width per unit thickness. This allows achieving the desired light separation effect with a thinner optical element while managing the trade-off through careful parameter selection and control.
2Length of moving object
If the optic axis angle is optimized for maximum light separation, then the light separation width increases, but the uniformity of light separation across different incident angles deteriorates
Solution Approach 1:
The patent optimizes the optic axis angle parameter within a specific range (45° to 60° from the normal direction) rather than at a single maximum value. This parameter optimization balances two competing requirements: achieving sufficient light separation width while maintaining relatively uniform optical low-pass filter effects across different incident angles of light.
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 solution provides a consistent optical low-pass filter effect across the entire image, reducing aliasing noise and false-color noise, while maintaining mechanical strength and ease of material processing by optimizing the optic axis angle and thickness of the optical element.
Implementation Method 1
optical element having optical anisotropy, the optical element separating entering light into light rays having polarization directions perpendicular to each other
Implementation Method 2
a plane-parallel plate with birefringence, such as quartz, is used to separate light into ordinary and extraordinary rays
Data Source
AI summary
An optical element is disclosed which has an excellent optical low-pass filter effect. The optical element has optical anisotropy and separates entering light into light rays having polarization directions perpendicular to each other. The optical element satisfies the following conditions: 0.1<|ne−no|, and θmax<θ. no and ne represent refractive indices for ordinary and extraordinary rays at a wavelength of 530 nm, θ represents an angle between the direction of an optic axis of the optical element and a normal to an incident surface of the optical element, and θmax represents an angle between the direction of the optic axis and the normal to the incident surface at which the angle of separation is maximized when the light that enters the incident surface of the optical element at the normal angle is separated into the light rays.