Fiber Optic Temperature Sensor with Vernier Effect
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Solution Overview
Problem
Traditional temperature sensors fail to meet high-accuracy measurement requirements for temperature sensing, particularly in fields requiring precise temperature monitoring.
Innovation Solution
A fiber optic temperature sensor is developed, incorporating a Sagnac interferometer and a Fabry-Perot interferometer with a PDMS cavity, where the free spectral ranges of both interferometers are close but not equal, enhancing the vernier effect and sensitivity of temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional temperature sensors are used, then device complexity is low, but measurement precision is insufficient for high-accuracy requirements
Solution Approach 1:
The patent combines a Sagnac interferometer and a Fabry-Perot interferometer into a single integrated sensing head structure. The Sagnac interferometer provides temperature sensing through birefringence changes in polarization-maintaining fiber, while the Fabry-Perot interferometer provides temperature sensing through thermal expansion and refractive index changes of the PDMS cavity. By merging these two interferometers with close but unequal free spectral ranges, the system achieves enhanced vernier effect that amplifies temperature measurement precision beyond what either interferometer could achieve alone.
2Measurement precision
If a single interferometer is used, then device complexity is low, but temperature sensitivity is insufficient
Solution Approach 1:
The patent carefully designs the parameters of the two interferometers so that their free spectral ranges are close but not equal. The Sagnac interferometer uses polarization-maintaining fiber with specific birefringence characteristics, while the Fabry-Perot interferometer uses a PDMS cavity with specific thickness and refractive index. By adjusting these parameters to create nearly-matching but distinct free spectral ranges, the system maximizes the vernier effect, where the interference patterns of the two interferometers beat against each other to produce enhanced sensitivity for temperature detection.
3Measurement precision
If high-accuracy temperature measurement is required, then measurement precision improves, but traditional sensors cannot meet the requirements
Solution Approach 1:
The patent employs a detection system that analyzes the combined interference spectrum from both interferometers. By monitoring the beat frequency pattern produced by the vernier effect between the two close but unequal free spectral ranges, the system can accurately determine temperature changes. The dual-interferometer configuration provides redundant sensing mechanisms that enhance reliability, as the vernier effect amplifies the temperature signal while the broad spectrum light source ensures sufficient optical power reaches both interferometers for stable operation.
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 sensor achieves improved temperature sensitivity by utilizing two interferometers with opposite temperature responses, producing an enhanced vernier effect that surpasses conventional sensors, providing higher precision in temperature measurement.
Implementation Method 1
The incident light entering the Sagnac interferometer is divided in the polarizing optical fiber into two light beams having polarization directions perpendicular to each other, interference occurs between the two light beams after passing through the polarizing optical fiber
Implementation Method 2
the first sensing interferometer is a Sagnac interferometer including a second fiber optic coupler and a polarizing optical fiber
Implementation Method 3
A part of the incident light entering the F-P interferometer is reflected back to the single-mode optical fiber at an interface between the single-mode optical fiber and the PDMS cavity, and another part of the incident light is transmitted to enter the PDMS cavity and then partially reflected back
Implementation Method 4
the second sensing interferometer is an F-P interferometer formed by connecting a single-mode optical fiber and a polydimethylsiloxane (PDMS) cavity
Implementation Method 5
β is a thermal expansion coefficient of the PDMS
Implementation Method 6
α represents a thermo-optical coefficient of PDMS
Implementation Method 7
ΔB represents a change in refractive index of the polarizing optical fiber when the temperature increases by 1° C.
Implementation Method 8
A result of superimposing an interference spectrum returned by the Sagnac interferometer and an interference spectrum returned by the F-P interferometer is obtained by the spectrometer. A first terminal of the second fiber optic coupler is connected to the first fiber optic coupler
Data Source
AI summary
A fiber optic temperature sensor, a sensing head structure, and a manufacturing method are provided. The fiber optic temperature sensor includes a broad spectrum light source, a first fiber optic coupler, a spectrometer, a first sensing interferometer, and a second sensing interferometer. The first sensing interferometer and the second sensing interferometer have opposite temperature responses. A first free spectral range corresponding to the first sensing interferometer is close to but not equal to a second free spectral range corresponding to the second sensing interferometer. In the fiber optic temperature sensor, two sensing interferometers both sensitive to temperature are used, and the two sensing interferometers have opposite temperature responses, thereby achieving an enhanced vernier effect, and improving the sensitivity of temperature measurement.