Rolling Shutter Laser Detection Beyond Nyquist Ambiguity
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Solution Overview
Problem
Existing detectors for short pulse lasers face challenges in accurately determining pulse repetition frequencies due to ambiguities in beat signal frequencies and peak-to-trough ratios, particularly when operating above the Nyquist limit, which limits their frequency coverage and can lead to detector damage.
Innovation Solution
A computer-implemented method using a sensor array with a rolling shutter operation to extract a beat signal, calculate beat frequency, peak-to-trough ratio, and pulse shape parameter, and apply a pulse repetition frequency function to resolve the ambiguity, enabling detection of short pulse lasers beyond the Nyquist limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a rolling shutter operation with predetermined integration period is used to detect pulsed radiation, then the detection cost is reduced, but the frequency coverage is limited by the Nyquist Theorem
Solution Approach 1:
The patent applies dynamics by making the integration period variable rather than fixed. The integration period is dynamically adjusted based on the detected pulse repetition frequency and the beating effect observed in the radiation image. This allows the system to adapt to different frequency ranges beyond the static Nyquist limit, resolving the contradiction between using a simple rolling shutter (low cost) and achieving wide frequency coverage.
2Adaptability or versatility
If expensive detectors are used to achieve wide frequency coverage, then the frequency coverage is improved, but the detector becomes vulnerable to damage from high pulse powers
Solution Approach 1:
The patent employs a low-cost rolling shutter camera as the detector, which is inherently more robust and less vulnerable to damage from high pulse powers compared to expensive specialized detectors. By combining this durable, inexpensive detector with signal processing techniques (beating effect analysis and variable integration periods), the system achieves wide frequency coverage without exposing expensive sensitive components to damaging high power pulses.
3Speed
If the integration period is reduced to detect higher frequency pulses, then the maximum detectable frequency is improved, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The system dynamically adjusts the integration period based on the detected pulse repetition frequency. When high-frequency pulses are detected, the integration period is reduced to capture the rapid oscillations, and when lower frequencies are detected, the integration period is increased to improve signal-to-noise ratio. This dynamic adaptation resolves the contradiction between detecting high frequencies and maintaining signal quality.
Solution Approach 2:
The patent implements feedback by using the beating effect observed in the radiation image to inform subsequent detection parameters. The system analyzes the beat frequency and uses this information to adjust the integration period for optimal signal capture, creating a feedback loop that maintains high signal-to-noise ratio across varying frequency conditions.
4Device complexity
If a fixed integration period is used in rolling shutter operation, then the device complexity is reduced, but the pulse repetition frequency detection accuracy is limited due to ambiguities
Solution Approach 1:
The patent resolves the contradiction by making the integration period dynamic rather than fixed. The system starts with an initial integration period, detects the beating effect, calculates the beat frequency, and then adjusts the integration period based on the detected pulse repetition frequency. This dynamic adjustment eliminates detection ambiguities while maintaining relatively simple device architecture.
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 method unambiguously determines pulse repetition frequencies of short pulse lasers by utilizing a combination of beat frequency, peak-to-trough ratio, and pulse shape parameter, enhancing detection capabilities of low-cost rolling shutter devices and protecting against potential damage.
Implementation Method 1
irradiating a portion of an array of sensor elements with pulsed radiation and addressing the array using a rolling shutter operation to obtain a radiation image
Implementation Method 2
for high pulse repetition frequency lasers a further beating effect becomes apparent within pixel values of a radiation image. This beating effect can be utilised in a pulse detection operation to extract the unambiguous pulse repetition frequency
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
The present application relates to the field of detecting pulsed radiation, in particular to methods and apparatus suitable for use in detecting short pulse lasers and extracting their pulse repetition frequencies, and especially an improved computer implemented method for detecting a pulse repetition frequency of pulsed radiation using a sensor array of sensor elements arranged in element lines.