Retroreflector Detector Polarization Filtering
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Solution Overview
Problem
Conventional retroreflector detection devices face limitations due to the return of light into the scene, which can compromise their utility, especially in applications requiring low observability, such as on the battlefield, where the detection device may be detected by emitting and reflecting light.
Innovation Solution
An optics arrangement featuring a polarized beam splitter, first and second quarter waveplates, and an illuminator, which limits the return of illumination by flipping polarization and directing it away from the scene, thereby reducing observability and enhancing contrast between scene reflections and internal optics reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional retroreflector detection devices emit light to detect retroreflectors, then detection capability is improved, but observability increases and the device may be detected
Solution Approach 1:
The patent converts the harmful effect of light reflection (which causes observability) into a beneficial polarization filtering mechanism. By using polarized light and quarter-wave plates, the system causes internally reflected light to return with orthogonal polarization that can be filtered out, while allowing detection of retroreflector returns. This transforms the harmful reflection into a distinguishable signal through polarization state manipulation.
Solution Approach 2:
The patent changes the polarization parameter of light throughout the optical path. The illuminator emits polarized light, quarter-wave plates convert linear polarization to circular and back, and the polarized beam splitter separates light based on polarization state. By manipulating polarization parameters, the system distinguishes between internally reflected light (which undergoes multiple polarization changes) and retroreflector returns (which maintain specific polarization characteristics), enabling detection while reducing observability.
2Measurement precision
If optical elements like lenses and windows are used in retroreflector detectors, then imaging capability is improved, but internal reflections occur that return light to the scene
Solution Approach 1:
The patent introduces polarization state as an intermediary property to distinguish between different light paths. The quarter-wave plates act as mediators that transform polarization states differently for internally reflected light versus retroreflector returns. This intermediary polarization manipulation allows the system to maintain necessary optical elements for imaging while selectively filtering out harmful internal reflections through polarization-based discrimination.
3Use of energy by moving object
If light is returned to the scene by the detection device, then optical path efficiency is improved, but contrast between scene reflections and internal optics reflections decreases
Solution Approach 1:
The patent applies different polarization transformations to different regions of the optical path. Light taking the direct path through the retroreflector undergoes specific polarization changes, while internally reflected light experiences different polarization transformations due to multiple reflections off optical surfaces. The polarized beam splitter and quarter-wave plates are positioned to create localized polarization differentiation, maintaining optical efficiency while enhancing contrast through selective polarization filtering.
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 effectively reduces the visibility of the retroreflector detector, allowing for covert detection of retroreflectors while maintaining image quality, thereby improving the device's survivability and effectiveness in low-observability environments.
Implementation Method 1
an optics arrangement including a polarized beam splitter arranged along a collection axis
Implementation Method 2
a first quarter waveplate arranged along the collection axis, and a second quarter waveplate arranged along the collection axis. The second quarter waveplate is optically coupled to the first quarter waveplate by the polarized beam splitter and is arranged to limit return of illumination reflected internally within a retroreflector imaging scene through the optics arrangement
Data Source
AI summary
An optics arrangement includes a polarized beam splitter arranged along an collection axis, a first quarter waveplate arranged along the collection axis, and a second quarter waveplate. The second quarter waveplate is arranged along the collection axis and is optically coupled to the first quarter waveplate by the polarized beam splitter to limit return of polarized illumination originating in a scene being illuminated for retroreflector detection. Retroreflector detectors and methods of imaging a scene are also described.