Asymmetric Optical Filter for Ghost Reduction in Surveillance Cameras
Solution Overview
Problem
Conventional half mirrors used in imaging and surveillance applications suffer from high reflectance for light incident from both sides, leading to ghost and flare issues due to reflected light entering the camera and being reflected back.
Innovation Solution
An optical filter with different reflectances depending on the incident light direction is designed, comprising a substrate with an antireflection layer, an absorption layer, and an enhanced reflection layer, ensuring |R1−R2|≥10%, where R1 and R2 are the reflectances for light incident from opposite sides, effectively serving as an antireflection film for one side and a reflection film for the other.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional half mirror is used with high reflectance for light incident from the object side, then the surveillance camera can hide its existence and orientation, but light reflected by the inside of the camera and then reflected by the half mirror enters the camera again, causing ghost and flare
Solution Approach 1:
The patent applies asymmetry by creating an optical filter with different reflectance characteristics for light incident from opposite sides. The filter has high reflectance for light from the object side (R1 ≥ 80%) to maintain surveillance camera concealment, while having low reflectance for light from the camera side (R2 ≤ 20%) to prevent ghost and flare. This asymmetric optical property is achieved through specific layer结构设计 with an absorption layer and reflection layer having different optical constants.
Solution Approach 2:
The patent applies local quality by assigning different optical functions to different sides of the same optical filter. The front surface (object side) is designed with high reflectance characteristics for concealment, while the back surface (camera side) is designed with low reflectance characteristics to minimize internal reflections. This is achieved through the layered structure where the absorption layer and reflection layer create direction-dependent optical properties.
2Ease of operation
If a half mirror has substantially the same reflectance for light incident from front surface side and back surface side, then the structure is simple, but light entering the camera from the object side, reflected by the inside of the camera and then reflected by the half mirror cover enters the camera again
Solution Approach 1:
The patent applies composite materials by combining multiple layers with different optical properties to create the optical filter. The structure includes a substrate, an absorption layer with specific extinction coefficients, and a reflection layer with specific refractive indices. These composite layers work together to produce the asymmetric reflectance characteristics, where the absorption layer absorbs light differently depending on incident direction and the reflection layer provides direction-dependent reflection.
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 ghost and flare by minimizing unwanted reflections, allowing for clearer images and improved visibility while maintaining the functionality of half mirrors.
Implementation Method 1
an absorption layer; and a second layer... an absorption layer having an extinction coefficient k550 at a wavelength of 550 nm
Implementation Method 2
an optical filter that reflects part of incident light and transmits the other part thereof
Data Source
AI summary
The disclosed optical filter is provided on a substrate. The optical filter includes a first layer, an absorption layer, and a second layer in order from a substrate side. The condition of |R1−R2|≥10 is satisfied where R1 [%] represents a reflectance of the optical filter for light whose wavelength is 550 nm and that makes incident on the optical filter from a side opposite to the substrate, and R2 [%] represents a reflectance of the optical filter for light whose wavelength is 550 nm and that makes incident on the optical filter from the substrate side.