Few-Mode Optical Fiber Temperature Sensor Using Interference Pattern Analysis
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Solution Overview
Problem
Conventional fibre optic temperature monitoring is costly and inefficient for distributed temperature sensing in infrastructure, as it primarily measures temperature variation rather than absolute temperature, struggles to distinguish between heating and cooling phases, and often confuses temperature changes with vibration effects.
Innovation Solution
A method using a few-mode optical fibre with a coherent light source to determine temperature variation by analyzing the displacement of interference pattern lobes, which are filtered to suppress vibrations and cyclically heated/cool sections to determine temperature sign, allowing for absolute temperature measurement with reduced error drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fibre optic temperature monitoring based on Raman and Brillouin scatterings is used, then temperature sensing capability is achieved, but the cost is high and it is reserved for strategic infrastructure only
Solution Approach 1:
The patent uses inexpensive components including a standard laser diode, few-mode optical fibre, and CMOS camera sensor to replace expensive conventional temperature monitoring systems based on Raman and Brillouin scatterings. The system achieves distributed temperature sensing functionality at a fraction of the cost, making it suitable for widespread infrastructure monitoring applications.
Solution Approach 2:
The patent exploits changes in interference patterns caused by temperature-induced path length variations in few-mode optical fibres. By monitoring the displacement of intensity maxima in the interference pattern, the system converts temperature changes into measurable optical parameter changes, enabling cost-effective temperature sensing.
2Measurement precision
If usual methods are used to measure temperature, then temperature variation can be measured, but only relative temperature changes are obtained instead of absolute temperature
Solution Approach 1:
The patent performs a preliminary calibration step where the relationship between interference pattern characteristics and absolute temperature is established before actual measurements. By storing reference data from known temperature states, the system can later determine absolute temperature values from interference pattern analysis, rather than only measuring relative changes.
Solution Approach 2:
The patent replaces conventional temperature measurement approaches with optical interference-based measurement. By using few-mode fibres and analyzing the spatial interference pattern of coherent light, the system directly measures temperature-related path length changes, enabling absolute temperature determination through optical field analysis rather than mechanical or electrical sensing methods.
3Measurement precision
If integration operation is used to obtain temperature from temperature variation, then temperature can be calculated, but error drifts occur
Solution Approach 1:
The patent implements a feedback mechanism where the interference pattern analysis provides direct temperature information that can be used to correct and validate integrated temperature values. By continuously monitoring the interference pattern characteristics and comparing with calibration data, the system can detect and correct drift errors in real-time, improving the reliability of temperature measurements over extended periods.
Solution Approach 2:
The patent performs preliminary calibration to establish the relationship between interference pattern characteristics and absolute temperature before operation. This calibration data serves as a reference that prevents error accumulation by providing periodic validation points, eliminating the need for continuous integration operations that inherently accumulate errors over time.
4Measurement precision
If temperature sensing is performed using interference pattern disturbance, then temperature measurement is possible, but discrimination between heating and cooling phases is not straightforward
Solution Approach 1:
The patent exploits the asymmetric response of the interference pattern to heating versus cooling. By analyzing specific characteristics of the interference pattern displacement and using a cyclically heated reference fibre section, the system can distinguish the direction of temperature change (heating vs. cooling) from the pattern distortion, simplifying the discrimination process.
Solution Approach 2:
The patent introduces a cyclically heated and cooled fibre section as an intermediary element in the optical path. This reference section creates a known modulation pattern in the interference that serves as a marker, enabling the system to distinguish between heating and cooling phases by analyzing how the temperature-induced pattern changes interact with the reference modulation.
5Measurement precision
If interference pattern analysis is used for temperature sensing, then temperature detection is possible, but discrimination between temperature and vibration effects is difficult
Solution Approach 1:
The patent extracts and separates the temperature sensing function from vibration-sensitive measurements by using few-mode fibres and spatial filtering. The system analyzes specific spatial characteristics of the interference pattern that are primarily affected by temperature-induced path length changes, while being less sensitive to vibration-induced disturbances, effectively filtering out vibration effects from the temperature measurement.
Solution Approach 2:
The patent applies spatial filtering to select specific regions or characteristics of the interference pattern that are most sensitive to temperature changes and least sensitive to vibrations. By focusing analysis on localized pattern features with favorable temperature-to-vibration sensitivity ratios, the system achieves vibration-resistant temperature sensing.
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 method provides accurate, cost-effective distributed temperature sensing by directly measuring lobe displacement linked to temperature, reducing error drift and distinguishing between heating and cooling phases, suitable for infrastructure monitoring and extended applications like fire detection.
Implementation Method 1
determining the interference pattern of coherent light at a second end of the optical fibre
Implementation Method 2
based upon the determined path length of the trajectory of the selected maximum of intensity, determining the temperature variation of the few mode optical fibre
Data Source
AI summary
The present invention is related to a method for determining distributed temperature variation of a few mode optical fiber comprising the steps of:—providing a few mode optical fiber;—enlighting a first end of said few mode optical fiber by means of a coherent light source;—determining the interference pattern of coherent light at a second end of the optical fiber;—selecting one maximum of intensity at the second end of the optical fiber by spatially filtering the enlighting at the first end of the optical fiber;—determining the path length of the trajectory of the selected maximum of intensity;—based upon the determined path length of the trajectory of the selected maximum of intensity, determining the temperature variation of the few mode optical fiber.