Dispersive Element for Ambient Light Rejection in Optical Sensors
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Solution Overview
Problem
Computer vision systems face interference from ambient background radiation, which reduces image contrast and quality, particularly in systems using narrowband projected radiation for 3D mapping and laser scanning.
Innovation Solution
Incorporating a dispersive element with chromatic aberration in excess of one micrometer per nanometer of wavelength to spread broadband background radiation across the image sensor plane while maintaining sharp focus on narrowband features, effectively acting as a low-pass filter for ambient radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a bandpass filter is used to block ambient light, then ambient light rejection is improved, but the image sensor cannot capture broadband background radiation for applications requiring wide spectral coverage
Solution Approach 1:
The patent segments the optical spectrum by using a dispersive element to spatially separate different wavelengths. The image sensor is divided into multiple regions, each capturing a specific wavelength band. This allows the system to reject ambient light in certain spectral regions while maintaining sensitivity in others, resolving the contradiction between ambient light rejection and spectral coverage adaptability.
Solution Approach 2:
The patent introduces a spectral dimension by using a dispersive element (prism or grating) to separate light by wavelength before it reaches the image sensor. This transforms the problem from a single-channel intensity measurement to a multi-dimensional measurement including wavelength information, enabling selective rejection of ambient light while preserving broadband capture capability.
2Measurement precision
If the objective lens is optimized for narrowband radiation, then imaging performance at the target wavelength is improved, but the lens cannot effectively collect and focus broadband background radiation
Solution Approach 1:
The patent segments the optical path by placing a dispersive element in the path of the objective lens. This separates the narrowband target wavelength (which remains focused on the sensor) from broadband background radiation (which is dispersed spatially). The objective lens can thus be optimized for narrowband performance while the dispersive element handles the broadband separation, resolving the contradiction between imaging precision and broadband collection.
Solution Approach 2:
The dispersive element acts as an intermediary between the objective lens and the image sensor. It receives both narrowband and broadband radiation from the lens, processes them differently (focusing narrowband while dispersing broadband), and delivers the separated signals to the sensor. This intermediary resolves the contradiction by allowing the lens to maintain its narrowband optimization while still collecting broadband radiation.
3Loss of information
If the image sensor is exposed to both narrowband projected radiation and broadband ambient radiation, then the sensor captures complete spectral information, but image contrast is reduced due to ambient light interference
Solution Approach 1:
The patent segments the image sensor into multiple regions or uses spectral unmixing algorithms to separate narrowband projected radiation signals from broadband ambient radiation signals. By processing the spectral information from different wavelength bands separately, the system can preserve complete spectral information while enhancing the contrast of the narrowband features through selective extraction and ambient light subtraction.
Solution Approach 2:
The patent employs feedback mechanisms where the captured spectral information from multiple wavelength bands is processed to generate a model of the ambient light distribution. This model is then fed back into the image processing pipeline to subtract or suppress the ambient light contribution, thereby recovering the contrast of the narrowband projected radiation while preserving the complete spectral information.
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 enhances image quality by isolating narrowband features from broadband interference, allowing for clearer distinction and processing of images, even in the presence of ambient radiation, thereby improving the accuracy of 3D mapping and other computer vision applications.
Implementation Method 1
A dispersive element is positioned to spread the optical radiation collected by the objective optics so that different wavelengths in the range are focused along different, respective optical axes toward the plane
Implementation Method 2
The dispersive element is configured so that the optical radiation is focused with a chromatic aberration in excess of one micrometer per nanometer of wavelength at the plane of the image sensor
Implementation Method 3
an image sensor and objective optics, which are configured to collect and focus optical radiation over a range of wavelengths along a common optical axis toward a plane of the image sensor
Data Source
AI summary
Optical apparatus includes an image sensor and objective optics, which are configured to collect and focus optical radiation over a range of wavelengths along a common optical axis toward a plane of the image sensor. A dispersive element is positioned to spread the optical radiation collected by the objective optics so that different wavelengths in the range are focused along different, respective optical axes toward the plane.