Optical Fiber Sensor Reference Reflector Reliability
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Solution Overview
Problem
Existing optical fiber sensor systems face challenges such as contamination susceptibility, limited reflectivity, and dead-space issues due to cleaved reference reflectors, which affect signal quality and sensor compactness.
Innovation Solution
The optical fiber sensor system incorporates a reference reflector disposed between the proximal and distal ends of the fiber, at least 1 mm spaced apart from the distal end, and uses a fiber Bragg grating as the reference reflector to enhance robustness and reduce contamination risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cleaved reference reflector is used at the distal end of the fiber, then the sensor system can be implemented, but the reference reflector is susceptible to contamination and mechanical damage
Solution Approach 1:
The reference reflector is extracted from the distal end location and repositioned to the proximal end of the optical fiber, removing it from the harmful environment at the distal end where it was previously susceptible to contamination and mechanical damage
Solution Approach 2:
The optical fiber itself acts as an intermediary, allowing the reference reflector to be positioned at the proximal end while still enabling measurement of physical parameters in the distal region through the fiber's optical path
2Measurement precision
If the reference reflector is placed at the distal end of the fiber, then the sensor can measure physical parameters, but dead-space is created affecting sensor compactness
Solution Approach 1:
The measurement function is shifted from the spatial dimension at the distal end to the optical path dimension through the fiber, allowing the reference reflector to be positioned at the proximal end while maintaining measurement capability through the optical fiber's transmission properties
3Measurement precision
If Fiber Bragg Grating is used with high reflectivity to achieve narrow bandwidth, then wavelength resolution is improved, but signal to noise ratio is reduced
Solution Approach 1:
The system changes the measurement parameter from wavelength domain (FBG) to optical path length domain (FSI), allowing the use of high reflectivity gratings for narrow bandwidth without the same signal-to-noise tradeoff, as the measurement is based on interferometric path length changes rather than wavelength filtering
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 configuration enhances the robustness and reliability of the optical fiber sensor system by reducing contamination and mechanical damage risks, allowing for more compact designs and improved signal quality.
Implementation Method 1
The light source is configured to emit light with a coherence length longer than a maximum distance between any of the sensing reflectors and the closest of the at least one reference reflectors
Implementation Method 2
The sensing reflectors together with the reference reflectors form a series of Fabry-Pérot optical cavities, also known as Fabry-Pérot (F-P) or resonators. The distance from the reference reflector to each individual sensing reflector is unique, resulting in each resonator exhibiting different resonant wavelengths
Implementation Method 3
FSI is a Range Resolved Interferometry technique originally developed by Cranfield University in the UK
Implementation Method 4
When reflected light is resonant with the grating structure, the reflected waves reinforce (constructive interference). The reflected wavelength λB, also known as Bragg wavelength, is defined as λB=2ne Λ
Data Source
AI summary
A sensor system includes an optical fiber, a modulable light source, and a photodetector. The optical fiber includes two sensing reflectors and a reference reflector. The optical fiber defines a distal end and a proximal end. A measuring segment is defined between the two sensing reflectors and disposed between the distal end and the proximal end. The light source is disposed at the proximal end and configured to emit light with a coherence length longer than the maximum distance between the sensing reflectors and the reference reflector.