MEMS Micro-Mirror Array for EO/IR Imaging Saturation Control
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Solution Overview
Problem
EO/IR imaging systems face saturation issues due to transient optical events, which overwhelm the imaging detector and lead to loss or degradation of image frames, potentially causing mission failure.
Innovation Solution
A MEMS Micro-Mirror Array (MMA) is positioned in the collimated or near-collimated space to adjust the fraction of light reaching the imaging detector, using a high-bandwidth secondary detector to sample light multiple times per frame and a controller to command mirrors to redirect excess light to a dump, preventing saturation by maintaining radiant exposure below the saturation threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Finite Impulse Response (FIR) filter is used to control gain coefficient, then the imaging detector can maintain radiant exposure between thresholds under normal operation, but the filter is not fast enough to respond to transient optical events and causes saturation
Solution Approach 1:
The patent uses a secondary detector to continuously monitor incident light and predict transient events before they saturate the imaging detector. The MEMS MMA is pre-positioned to rapidly block light paths when transients are detected, preventing saturation before it occurs. This preliminary detection and preparation action enables the system to respond to transient events in microseconds rather than frames.
Solution Approach 2:
The patent introduces a MEMS MMA as an intermediary device between the collection optics and the imaging detector. The MEMS MMA acts as a fast-acting shutter that can independently block light paths without affecting the FIR filter's gain control function. This intermediary component handles the high-speed transient protection while the FIR filter maintains overall exposure control, resolving the speed-reliability contradiction.
2Measurement precision
If the imaging detector integrates incident light over each frame, then image quality is maintained, but transient bright events exceed the saturation threshold and saturate the detector
Solution Approach 1:
The patent applies preliminary anti-action by using the secondary detector to identify transient events and commanding the MEMS MMA to block light paths before the transient can saturate the imaging detector. This preventive blocking occurs on a per-scanline basis during frame integration, allowing the detector to maintain precise measurement of non-transient light while preventing harmful saturation from transients.
Solution Approach 2:
The patent segments the aperture into multiple independently controllable scanlines using the MEMS MMA. Each scanline can be independently blocked or transmitted based on transient detection. This segmentation allows the system to preserve image quality by maintaining integration over the entire frame while preventing saturation by selectively blocking only the portions of light causing transient events.
3Reliability
If a transient optical event occurs that fills the FOV, then the event overwhelms the imaging detector capabilities, but the FIR filter takes multiple frames to respond and compensate
Solution Approach 1:
The secondary detector continuously monitors for transients and prepares the MEMS MMA for rapid response. When a transient is detected, the MEMS MMA immediately blocks the affected scanlines on a per-line basis during frame integration, preventing saturation before it occurs. This eliminates the need for multi-frame filter recovery and prevents frame loss entirely.
Solution Approach 2:
The patent introduces dynamic control of the aperture through the MEMS MMA, which can rapidly adjust which scanlines are transmitted or blocked during frame integration. This dynamic response occurs on microsecond timescales rather than frame timescales, allowing the system to adapt to transient events in real-time and maintain reliability without losing frames.
4Illumination intensity
If the aperture is increased to collect more light for low-light conditions, then imaging capability in low light is improved, but the system becomes more susceptible to saturation from transient events
Solution Approach 1:
The patent segments the aperture into independently controllable scanlines using the MEMS MMA. This allows the system to maintain a large aperture for enhanced light collection in low-light conditions while selectively blocking only the specific scanlines affected by transient events. The segmentation enables simultaneous optimization of both light collection capability and saturation resistance.
Solution Approach 2:
The MEMS MMA serves as an intermediary that decouples the aperture size from saturation susceptibility. The large aperture can be maintained for low-light performance while the MEMS MMA rapidly blocks transient light paths, preventing saturation. This intermediary component allows the system to enjoy the benefits of a large aperture without the corresponding increase in saturation vulnerability.
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 substantially mitigates or eliminates the loss of image frames due to transient events, ensuring continuous imaging capability and allowing for larger apertures to collect more light, especially under low-light conditions.
Implementation Method 1
Each mirror in the array is responsive to command signals to redirect light incident on that mirror to one of two destinations: (1) to a light dump; or (2) to the image forming optics
Implementation Method 2
A secondary detector (via a pick-off) samples light from the collimated or near-collimated space multiple times per image frame
Implementation Method 3
An imaging detector is positioned at the image plane and configured to integrate incident light (radiant flux or photons) over an image frame
Data Source
AI summary
An EO/IR optical imaging system comprises collection optics to collect light from a scene into a collimated or near-collimated space. An imaging detector is positioned at the image plane and configured to integrate incident light (radiant flux or photons) over an image frame and readout a sequence of pixelated images at a frame rate, said detector exhibiting a saturation threshold. To prevent saturation of the imaging detector, a MEMS MMA is positioned in the collimated or near-collimated space. A secondary detector (via a pick-off) samples light from the collimated or near-collimated space multiple times per image frame. A controller responsive to the sampled light commands a percentage of the mirrors to re-direct light incident on those mirrors to a light dump and commands the remaining mirrors to re-direct light incident on those mirrors to the imaging detector. Together the mirrors adjust a fraction of light reaching the imaging detector such that the integrated incident light for a given image frame is less than the saturation threshold.