Single-Photon Imager Dynamic Range via Segmented Integration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing single-photon imaging systems face limitations in dynamic range due to after-pulsing effects, which restrict the ability to detect photons over a wide range of optical intensities and require significant dead time between detection events.
Innovation Solution
A focal plane array of single-photon photodetectors that utilize both the number and timing of photon arrivals to determine light intensity, employing a gating signal with detection and reset periods to minimize after-pulsing and enhance dynamic range, particularly using Geiger-mode avalanche photodiodes with timing circuitry for precise photon arrival data analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large electrical gain is applied to detect single photons with high fidelity, then signal-to-noise ratio is improved, but saturation effects occur limiting dynamic range
Solution Approach 1:
The patent divides the dynamic range measurement into multiple segments by using multiple integration capacitors with different capacitance values. Each capacitor handles a specific range of photon flux levels, allowing the system to maintain high sensitivity for low light levels while avoiding saturation for higher light levels. The system selectively activates appropriate capacitors based on the detected signal strength.
Solution Approach 2:
The patent adds a temporal dimension to the detection process by implementing time-resolved measurement capabilities. By measuring photon arrivals over multiple time bins within an integration period, the system can distinguish between different intensity levels even when using high gain, effectively extending the dynamic range through time-based differentiation of signal levels.
2Measurement precision
If integration time is extended to detect low light levels, then sensitivity is improved, but thermal noise from integration capacitors increases
Solution Approach 1:
The patent applies different integration strategies to different spatial regions or signal levels. By using multiple integration capacitors with optimized capacitance values tailored to specific signal ranges, each capacitor is locally optimized to minimize thermal noise for its intended operating range while maintaining the required sensitivity.
Solution Approach 2:
The system dynamically changes integration parameters (capacitor selection, integration time) based on the detected signal level. For low light levels, longer integration times with appropriate capacitors are used to maximize sensitivity, while for higher levels, shorter integration times prevent thermal noise accumulation, thus adapting the noise characteristics to the signal conditions.
3Measurement precision
If Geiger-mode APD is used to achieve single-photon sensitivity, then detection sensitivity is improved, but dead time increases due to after-pulsing
Solution Approach 1:
The patent introduces quenching circuits as intermediary elements between the Geiger-mode APD and the readout electronics. These circuits actively manage the discharge process, providing controlled quenching that reduces after-pulsing effects and minimizes the dead time between detection events, thereby maintaining single-photon sensitivity while improving the time response.
Solution Approach 2:
The system implements periodic gating of the Geiger-mode APD, activating detection only during specific time windows when the detector is ready. This periodic operation allows the detector to recover from previous events and reduces the impact of dead time by concentrating measurements into active periods, effectively managing the time loss due to after-pulsing.
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 significantly increases the dynamic range of single-photon imaging systems, enabling accurate intensity determination over a wide range of light conditions while maintaining single-photon sensitivity, effectively mitigating the limitations imposed by after-pulsing and dead time constraints.
Implementation Method 1
In essentially all semiconductor photodetectors of visible and infrared light, each incident photon creates a single photo-excited electron via the photoelectric effect
Implementation Method 2
When an injected charge reaches a sufficiently high kinetic energy, it can generate an electron-hole pair through an inelastic collision with lattice atoms in a process referred to as 'impact ionization.' These newly liberated carriers are then also accelerated, and the process continues to create an 'avalanche' of charge
Implementation Method 3
At sufficiently large electric-field intensity, known as the 'avalanche breakdown field,' there is a finite probability that the avalanche multiplication process can lead to a self-sustaining avalanche
Implementation Method 4
Thermal fluctuations give rise to noise associated with electrons that are randomly moving on to and off of integration capacitors
Data Source
AI summary
A method for computing the intensity of light incident on a photodiode capable detecting single photons comprises using arrival-time statistics for a plurality of detected single photons. The statistics are based on the determination of the arrival time for each detected photon relative to the beginning of a detection period within an image frame in which the photon is detected. In some embodiments, Poisson statistics are applied to the computation of the intensity. By computing the intensity of light in this manner for each of plurality of single-photon photodetectors that compose a focal plane array, a high-contrast image of a scene can be developed.