Digital Bolometer with Interferometric Measurement for Uniform Temporal Response
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Solution Overview
Problem
Conventional imaging bolometers face limitations in dynamic response and signal-to-noise ratio due to fixed thermal time constants and mechanical integration processes, which restrict their adaptability to changing scene conditions and lead to frame cross-talk and reduced performance in computational imaging applications.
Innovation Solution
A digital bolometer architecture with interferometric temperature measurement and optical phase shifting, allowing dynamic control of integration time and reducing thermal time constants, enables uniform temporal response and sub-frame measurement, overcoming the limitations of conventional bolometers by integrating multiple samples with reduced thermal time constants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel is thermally isolated from the thermal sink to improve signal-to-noise ratio, then the thermal time constant increases, but the temporal response becomes slower
Solution Approach 1:
The patent implements dynamic control of the integration time through electronic switching mechanisms that allow the bolometer to adapt its thermal coupling to the sink. The integration time can be varied by controlling the switching frequency and duty cycle of the thermal coupling, enabling the system to optimize between signal-to-noise ratio and temporal response based on scene conditions.
Solution Approach 2:
The patent changes the thermal time constant parameter dynamically by modifying the thermal coupling strength between the pixel and the sink. This is achieved through controlled thermal switching mechanisms that adjust the effective thermal conductance, allowing the system to transition between different integration times and response characteristics as needed.
2Measurement precision
If the integration time is extended to improve signal-to-noise ratio, then more photons are integrated, but frame cross-talk increases and temporal smear occurs
Solution Approach 1:
The patent employs periodic switching of the thermal coupling between the pixel and the sink, creating discrete integration intervals. By controlling the period and duty cycle of this switching, the system achieves defined integration times that prevent excessive frame cross-talk while maintaining adequate signal-to-noise ratio. The periodic action creates distinct measurement windows that reduce temporal smear.
3Speed
If the thermal time constant is reduced to improve temporal response, then the response speed increases, but the signal-to-noise ratio decreases
Solution Approach 1:
The patent uses dynamic control mechanisms to adjust the thermal time constant in real-time based on the imaging requirements. By electronically controlling the thermal coupling strength, the system can switch between fast response mode (reduced time constant) and high sensitivity mode (increased time constant), optimizing performance for different scene conditions without being constrained by a fixed thermal design.
4Device complexity
If conventional resistive temperature sensing is used, then the device structure is simple, but the integration time cannot be adjusted dynamically
Solution Approach 1:
The patent replaces the conventional resistive temperature sensing mechanism with an optical interferometric measurement system. This substitution enables dynamic control of the integration time through electronic switching of the optical path and thermal coupling, providing adaptability while maintaining a relatively compact device structure. The optical measurement system allows for precise control of the integration interval without the limitations of purely mechanical or resistive approaches.
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 provides a more uniform temporal response, reduces frame-to-frame cross-talk, and allows dynamic trade-offs between signal-to-noise ratio and temporal smear, enabling adaptability to scene dynamics and improved performance in computational imaging.
Implementation Method 1
Each pixel comprises an absorptive element configured to absorb radiation (e.g., IR or LWIR) from the scene
Implementation Method 2
a thermally sensitive optical phase shifter configured to phase shift a coherent measurement beam based on the temperature of the absorptive element
Implementation Method 3
mix a coherent reference beam with the phase shifted coherent measurement beam from each pixel to detect a relative phase
Data Source
AI summary
A digital bolometer architecture provides dynamic control of a simultaneous integration time for all pixels, with a temporal response that is more uniform than conventional bolometers and lacks frame cross-talk from decay tails, and which supports sub-frame measurement for on readout computational imaging. This is accomplished by replacing resistive pixel temperature sensing with continuous optical interferometric measurement and subsequent signal accumulation. Balanced reference sensors allow rejection of temperature differences across the thermal sink. The thermal time constant of the pixels is substantially reduced and the lost SNR is recovered by integration of the measured signals, using a programmable integration time.