Fiber Optic Sensor Arrangement Using Pseudorandom Coding
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Solution Overview
Problem
The complexity and high power consumption of sensor systems increase with the number of fiber laser sensors, limiting their deployment due to the need for multiple photodetectors, data acquisition channels, and physical constraints on wavelength multiplexing, making it difficult to manage large-scale sensor systems effectively.
Innovation Solution
A fiber optic sensor system that uses phase modulation with pseudorandom binary sequences and an interferometer module to convert phase changes into optical intensity signals, allowing for decorrelation and demodulation of multiple frequency-separated optical carrier signals using a single photodetector and digital processing, reducing the need for individual channels and wavelength demultiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple individual fiber laser sensors are deployed with separate photodetectors and data acquisition channels, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple wavelength-separated optical signals from multiple fiber laser sensors into a single optical fiber and processes them through a single photodetector. The key innovation is using wavelength-division multiplexing to carry multiple sensor signals simultaneously on one fiber, and a single photodetector with spectral analysis capability to extract individual sensor wavelengths, thereby merging multiple detection channels into one physical channel while maintaining the ability to detect strain changes at each sensor location.
Solution Approach 2:
The single photodetector in the invention serves multiple functions: it detects all wavelength-separated optical signals from multiple sensors simultaneously, performs spectral decomposition to identify individual sensor wavelengths, and extracts strain information for each sensor location. This universal detector replaces multiple dedicated photodetectors, reducing system complexity while maintaining measurement precision across all sensors.
2Reliability
If multiple photodetectors and data acquisition channels are used for each sensor, then reliability is improved, but use of energy increases
Solution Approach 1:
The patent merges multiple independent detection channels into a single photodetector system. Instead of powering multiple photodetectors and data acquisition devices, the system uses one photodetector with wavelength-division multiplexing to handle all sensor signals. This consolidation dramatically reduces power consumption while maintaining system reliability through the ability to simultaneously monitor all sensor wavelengths through spectral analysis of the combined signal.
3Device complexity
If wavelength multiplexing is used to deploy multiple sensors on a single fiber, then device complexity is reduced, but the extent of automation decreases due to physical constraints on the number of multiplexed wavelengths
Solution Approach 1:
The patent extends the sensing capacity beyond the limited number of available wavelengths by introducing temporal dimension through pseudorandom coding. Each sensor's optical signal is modulated with a unique pseudorandom code sequence, allowing the system to distinguish between sensors not just by wavelength but also by their temporal coding patterns. This adds a time-based dimension to the multiplexing scheme, effectively increasing the number of distinguishable sensors beyond what wavelength multiplexing alone can provide.
Solution Approach 2:
The invention changes the discrimination parameter from purely wavelength-based to a combination of wavelength and temporal code-based identification. By modulating each sensor's optical carrier with a unique pseudorandom code, the system can distinguish sensors through their temporal signal characteristics in addition to their wavelength, thereby increasing the total number of sensors that can be multiplexed on a single fiber while maintaining manageable system complexity.
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 simplifies the system architecture, reduces power consumption, and enables efficient detection of small strain changes across multiple sensors without requiring separate channels for each wavelength, facilitating the use of a single interferometer and photodetector for large-scale sensor arrays.
Implementation Method 1
an interferometer module for receiving each of the phase modulated optical carrier signals, the interferometer module operable to convert a change in the phase modulated optical carrier signals to a change in optical intensity
Implementation Method 2
an optical intensity detector for measuring the combined modulated optical intensity signal and generating a time varying electrical detector signal
Data Source
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AI summary
A fiber optic sensor arrangement is disclosed that includes a plurality of optical fiber based sensor elements, the sensor elements configured to modify an associated optical carrier signal in accordance with changes in a sensed quantity at a location of the sensor element and a phase modulation arrangement for phase modulating each optical carrier signal in accordance with respective uncorrelated pseudorandom binary sequence signals. The sensor arrangement also includes an interferometer module for receiving each of the phase modulated optical carrier signals, the interferometer module operable to convert a change in the phase modulated optical carrier signals to a change in optical intensity of the corresponding optical carrier signal to generate a combined modulated optical intensity signal, an optical intensity detector for measuring the combined modulated optical intensity signal and generating a time varying electrical detector signal and an analog to digital convertor to convert the time varying electrical detector signal to a time varying digitized detector signal. Also included in the sensor arrangement is a decorrelator arrangement for decorrelating the time varying digitized detector signal against the respective uncorrelated pseudorandom binary sequence corresponding to each of the optical carrier signals to recover each of the modulated optical carrier signals and a demodulator for demodulating each of the modulated optical carrier signals to recover the respective optical carrier signal to determine the changes in the sensed quantity at the location of the sensor element.