Optical Delay Measurement via Interference Fringe Scanning
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Solution Overview
Problem
Current methods for synchronizing a large number of laser pulses in coherent amplifier networks are not robust, reliable, or cost-effective, especially when dynamic delays occur due to heating and mechanical fluctuations, making it challenging to achieve precise phase locking and synchronization across multiple channels.
Innovation Solution
A method using collective architectures for optical phase measurement by interference with an external reference, where a variable delay line on the reference channel is scanned to analyze interference fringes, allowing for the determination of delays and synchronization of pulses across multiple channels, utilizing spatial or temporal interference fringes depending on pulse characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual adjustment of optical delay is used for each pulse pair, then synchronization precision is improved (to nearest femtosecond), but device complexity and measurement time increase exponentially with number of channels
Solution Approach 1:
The patent combines all N pulse channels with a single reference pulse in one interferometric measurement setup, rather than measuring each pulse pair separately. This merging approach allows simultaneous measurement of all relative delays through a single interference pattern analysis, reducing device complexity from exponential to linear scaling with number of channels.
Solution Approach 2:
The reference pulse serves multiple functions simultaneously: it provides the interference reference for all N channels, enables collective delay measurement, and establishes the synchronization baseline. This universal reference approach eliminates the need for separate adjustment mechanisms for each channel.
2Measurement precision
If FROG device is used for delay measurement, then synchronization accuracy is improved, but it cannot be implemented collectively for large number of pulses
Solution Approach 1:
The patent merges the measurement of all N pulses into a single interferometric experiment using one reference pulse and one detector, achieving collective delay characterization. This approach maintains high measurement accuracy while enabling simultaneous measurement of all channels, thus improving productivity.
3Adaptability or versatility
If optical lengths of channels are not precisely controlled, then system adaptability is improved, but delay variation increases (few cms variation equivalent to tens-hundreds of picoseconds)
Solution Approach 1:
The patent implements a feedback mechanism where the interferometric measurement provides real-time delay information for each channel, which is then used to adjust the optical path lengths. This closed-loop feedback compensates for thermal and mechanical fluctuations, maintaining delay stability despite environmental variations.
Solution Approach 2:
The system uses its own interference pattern as the measurement signal, allowing it to self-diagnose and self-correct delay variations without external reference equipment. The interferometric setup automatically provides the necessary feedback information for delay compensation.
4Loss of information
If variable delay line is added to reference channel for scanning, then complete delay map can be obtained, but device complexity increases
Solution Approach 1:
The variable delay line on the reference channel acts as an intermediary that systematically varies the reference pulse timing to probe all relative delays. This single delay line mediates the measurement of all N channels, providing complete delay information without requiring individual delay lines for each channel.
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
Enables robust and cost-effective synchronization of multiple laser pulses, allowing for coherent recombination and phase locking, resulting in a high-power, high-luminance laser source with improved beam quality and synchronization accuracy.
Implementation Method 1
emission of a reference pulse of the same repetition frequency capable of producing interference fringes with each of the N pulses
Data Source
Figure 1~3
Figure 2
Figure 4~5a
AI summary
The invention relates to a method for measuring the delay between N pulses (1) having a duration of less than 100 picoseconds, which comprises the following steps: collimated emission of pulses (1k) having the same repetition frequency; emission of a reference pulse (2) having the same repetition frequency capable of producing interference fringes with each of the pulses; for each of the pulses, detection by a detector (3) of the coherent sum of said pulse and the reference pulse, said sum producing said interference fringes, it being possible to differentiate the fringes coming from each of the pulses from one another. The reference pulse is emitted with an adjustable delay, and the method also comprises: for each delay, simultaneously measuring N interference fringe contrasts for the pulses; and, for each of the pulses, determining a delay value between said pulse and the reference pulse using the delay corresponding to the maximum contrast.