Brillouin Scattering Measurement Using Golay Code Pulse Train
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Solution Overview
Problem
The fluctuations in Brillouin Optical Time-Domain Reflectometry (BOTDR) signals due to the Rayleigh distribution cause significant noise, requiring multiple measurements to achieve a high Signal-to-Noise (SN) ratio, which increases measurement time and reduces space resolution.
Innovation Solution
An interpulse code-modulated Brillouin scattering measurement method using a composite pulse train with an interval longer than the phonon lifetime, combined with Golay code sequences for phase modulation and optical heterodyne reception, to improve the SN ratio and reduce signal fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the pulse duration is shortened to increase space resolution, then space resolution is improved, but the spectrum broadens and Brillouin frequency shift measurement accuracy deteriorates
Solution Approach 1:
The patent applies periodic action by using a composite pulse train with multiple pulses having different durations and intervals. The pulse train includes short pulses for high space resolution and long pulses for narrow spectrum, arranged periodically with intervals longer than the phonon lifetime. This periodic structure allows the system to achieve both high space resolution and high Brillouin frequency shift measurement accuracy simultaneously by combining the advantages of different pulse durations through coherent accumulation.
2Measurement precision
If multiple measurements are repeated to improve SN ratio, then measurement accuracy is improved, but measurement time increases and productivity decreases
Solution Approach 1:
The patent applies preliminary action by pre-arranging a composite pulse train with multiple pulses of different durations and intervals before measurement. The pulse train is designed in advance with intervals longer than the phonon lifetime, allowing coherent accumulation of Brillouin scattered light signals from multiple pulses. This preliminary structuring enables high SN ratio to be achieved in a single measurement or fewer repetitions, significantly reducing measurement time while maintaining high accuracy.
3Reliability
If composite pulse train with interval longer than phonon lifetime is used, then SN ratio is improved, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by systematically varying key parameters of the pulse train: pulse durations (short and long), pulse intervals (longer than phonon lifetime), and phase relationships. By optimizing these parameters, the system achieves high SN ratio through coherent accumulation of Brillouin scattered light. The parameter optimization allows the use of relatively simple hardware while achieving high reliability and SN ratio.
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 enables high-accuracy, high-space-resolution Brillouin scattering measurements with improved SN ratio, reducing the need for repeated measurements and enhancing measurement efficiency.
Implementation Method 1
a laser light source (1)
Implementation Method 2
Brillouin backscattered light generated by the composite pulse train in the optical fiber
Implementation Method 3
optically heterodyne-receiving the Brillouin backscattered light from each composite pulse with a reference light from the laser light source
Data Source
AI summary
In a measurement requiring a high space resolution using S-BOTDR, a pulse train composed of a plurality of pulses having the interval between the pulses longer than the phonon lifetime is interpulse-code-modulated. A Golay code is used for the interpulse code modulation to eliminate the sidelobes of the correlation in using a technique of correlation. In a technique without using correlation, an Hadamard matrix is used for the interpulse code modulation and the resultant matrix is inverted in the signal processing.