Active Illumination Receiver Offset for Retro-Reflection Suppression
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Solution Overview
Problem
Active illumination systems face issues with dynamic range limitations, leading to overexposure or underexposure due to specular reflections from retro-reflectors, which overwhelm the receiver components, causing adverse effects like blooming or reduced signal-to-noise contrast.
Innovation Solution
The system physically separates the illuminator and optical receiver by an offset distance to prevent retro-reflections from reaching the receiver, and employs techniques such as crossed polarizers and ambient light reduction to mitigate these effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the illuminator and optical receiver are co-located in active illumination systems, then the system can effectively illuminate and detect diffuse scatterers (Lambertian targets), but retro-reflections from retroreflectors in the scene overwhelm the receiver components causing sensor saturation and blooming effects
Solution Approach 1:
The system segments the illumination and detection functions by using multiple transmit (Tx) components and multiple receive (Rx) components arranged in a distributed configuration. This spatial segmentation allows the system to separate the illumination source from the detection path, preventing retro-reflected light from directly entering the receiver while maintaining the ability to detect scattered light from diffuse targets.
Solution Approach 2:
The patent introduces optical elements such as beam splitters, dichroic mirrors, and polarizing beamsplitters as intermediaries between the illuminator and optical receiver. These intermediary components redirect light paths to separate retro-reflection paths from detection paths, allowing the system to maintain co-location benefits while blocking harmful retro-reflections from reaching the sensor.
2Adaptability or versatility
If the dynamic range of the imaging system is increased to cover both bright specular reflections and less bright scatter reflections, then the system can handle high contrast scenes, but the system complexity and cost increase
Solution Approach 1:
Instead of trying to capture both bright retro-reflections and dim scattered light simultaneously by increasing dynamic range, the system inverts the approach by actively blocking retro-reflections from reaching the receiver. This allows the system to use a standard dynamic range sensor while achieving the effect of handling high contrast scenes by preventing the brightest elements from overwhelming the detector.
Solution Approach 2:
The system extracts and separates the problematic retro-reflection component from the detection path using optical beam splitters and polarizing elements. By taking out the harmful retro-reflected light and directing it away from the receiver, the system can focus the receiver's full dynamic range on detecting the scattered light from diffuse targets without being overwhelmed by specular reflections.
3Use of energy by moving object
If the illuminator emits high intensity light to improve signal return from distant targets, then the detection range is extended, but the retro-reflections become even more intense causing severe sensor saturation
Solution Approach 1:
The system converts the harmful retro-reflections into a beneficial spatial separation opportunity. By using the high intensity illumination to create strong retro-reflections, the system can then use beam splitters and polarizing elements to redirect these intense reflections away from the receiver path. The same high intensity light that would cause saturation is thus used to improve distant target detection while the retro-reflection path is separately managed.
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 effectively reduces the impact of retro-reflections, enhancing the dynamic range and signal-to-noise ratio, allowing for improved imaging quality in the presence of bright specular reflections and ambient light.
Implementation Method 1
Retroreflectors typically reflect light back directly at the illuminating light source within a narrow cone angle
Implementation Method 2
The optical receiver may be configured to receive returned portions of the illumination signal scattered or reflected from the scene
Implementation Method 3
employs techniques such as crossed polarizers and ambient light reduction to mitigate these effects
Data Source
AI summary
Systems and methods for reducing or eliminating undesired effects of retro-reflections in imaging are disclosed. A system for reducing the undesired effects of retro-reflections may include an illuminator and an optical receiver. The illuminator is configured to emit an illumination signal for illuminating a scene. The optical receiver is configured to receive returned portions of the illumination signal scattered or reflected from the scene. Return signals from retroreflectors present in the scene may oversaturate or otherwise negatively affect sensors in the optical receiver. To limit return signals from retroreflectors that may be present in the scene, the illuminator and optical receiver are physically separated from each other by an offset distance that limits or prevents retro-reflections from the retroreflectors from being received by the optical receiver.