Infrared Detector Calibration Source Assembly
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Solution Overview
Problem
Infrared detector assemblies face challenges in calibration due to the need for large mechanical systems and thermal loads when using external illumination sources, which can shadow the focal plane and degrade performance, especially in space-based applications where size, weight, and complexity are critical.
Innovation Solution
A filter injected calibration flood source using a rotatable spectral filter wheel with a light redirector and light source optically coupled to the focal plane, allowing for calibration without introducing additional thermal loads and maintaining existing mechanical systems, enabling calibration at any orientation and reducing the need for complex external mechanics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a large illumination source is used to calibrate the entire focal plane, then uniform illumination can be achieved, but the system size and mechanical complexity increase significantly
Solution Approach 1:
The illumination source is segmented into multiple smaller LED elements arranged in an array, where each LED illuminates a specific portion of the focal plane. This segmentation allows the system to achieve complete focal plane coverage without requiring a single large, complex mechanical illumination source, thereby reducing overall system complexity while maintaining illumination uniformity.
2Volume of moving object
If the illumination source is placed within the cold cavity assembly, then the system size is reduced, but thermal load on the detector increases
Solution Approach 1:
The illumination source (LED array) is extracted from the cold cavity assembly and placed in the ambient temperature environment outside the vacuum seal. This extraction eliminates the thermal load that would be introduced by placing the illumination source within the cold cavity, while the optical coupling mechanism ensures that the focal plane still receives adequate calibration light without requiring the source to be physically inside the cold cavity.
3Object-affected harmful factors
If the illumination source is moved out of the way to avoid shadowing the focal plane, then shadowing is eliminated, but additional mechanical actuation components are required
Solution Approach 1:
The illumination source is positioned in a different spatial dimension (outside the cold cavity assembly and in the ambient environment) rather than attempting to move it within the cold cavity to avoid shadowing. This dimensional relocation eliminates shadowing effects without requiring complex mechanical actuation mechanisms to move the source within the constrained cold cavity space.
4Measurement precision
If regular re-calibration is performed after deployment, then pixel performance uniformity is maintained, but system complexity and operational time increase
Solution Approach 1:
The calibration system is designed to be self-contained and self-activating, with the LED array and control circuitry integrated into the detector assembly. The system can perform self-calibration without requiring external equipment or complex operational procedures, enabling rapid re-calibration events that maintain pixel response uniformity while minimizing time loss and operational complexity.
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 solution provides reliable and efficient calibration by redirecting light uniformly across the focal plane, minimizing thermal impact and allowing for rapid calibration without compromising existing systems, thus ensuring accurate and consistent measurements.
Implementation Method 1
the light redirector structured and arranged to receive light from the edge and to redirect the light out the first side
Implementation Method 2
a rotatable spectral filter wheel optically coupled to an IR focal plane of the detector
Data Source
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AI summary
An IR detector with a calibration source assembly (104) includes a cold cavity assembly tube (106) providing an internal vacuum (108), the tube (106) having a first end (110) providing a cold stop (112) and a second end (114) providing an IR focal plane (116) oriented towards the first end (110). The IR detector with a calibration source assembly (104) also includes a rotatable spectral filter wheel (118) optically coupled to an IR focal plane (116) of the detector, the filter wheel (118) having a plurality of areas (120) each of at least a minimum size, at least one area being a calibration area (120A). The calibration area includes: a substrate (122) having a first side (124) facing the IR focal plane (116) and a second side (126) opposite from the first side (124); a light transmitting edge section (128) disposed between the first side (124) and the second side (126); and, at least one light redirector (130) disposed at least partially within the substrate (122), the light redirector (130) structured and arranged to receive light from the edge (128) and to redirect the light out the first side (124). The IR detector with a calibration source assembly (104) also includes a light source (132) optically coupled to the edge section (128).