Fabry-Perot Interferometer Salinity Sensor
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Solution Overview
Problem
Existing salinity and temperature sensors based on fiber Bragg gratings suffer from low sensitivity due to dependence on a weak evanescent field and physical fragility when the cladding is removed for exposure.
Innovation Solution
The use of Fabry-Perot interferometers with a sensing cavity formed by fusion splicing a single-mode optical fiber to a graded-index optical fiber, where a small cavity is created by etching and expanded during splicing, enhancing sensitivity and robustness through a larger cavity and radial access channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fiber Bragg gratings with etched fibers are used for salinity and temperature measurement, then the sensors can provide simultaneous temperature and salinity information, but the sensitivity is low due to dependence on the weak evanescent field
Solution Approach 1:
The invention extracts the sensing function from the evanescent field interaction and relocates it to a Fabry-Perot interferometer cavity. By removing the cladding and exposing the core to form a cavity with radial access channels, the sensor utilizes refractive index changes in the cavity rather than relying on the weak evanescent field, thereby improving sensitivity while maintaining structural integrity.
Solution Approach 2:
The invention changes the fundamental measurement parameter from evanescent field interaction to Fabry-Perot interferometer resonance. By transforming the sensing mechanism from surface-based evanescent field to cavity-based interference, the sensor achieves enhanced sensitivity to refractive index changes while the solid-state cavity structure provides mechanical robustness.
2Adaptability or versatility
If the cladding is removed to expose the sensing element, then the sensor can interact with the surrounding environment, but the physical fragility increases
Solution Approach 1:
The invention uses a thin film or coating on the fiber surface to define the cavity boundary while maintaining structural strength. The cavity is formed by controlled etching and deposition processes that create a robust structure capable of environmental exposure without the fragility associated with complete cladding removal.
Solution Approach 2:
The sensor structure employs composite construction with the optical fiber core, cladding layers, and cavity-forming materials working together. This composite structure provides both the necessary environmental exposure for sensing and the mechanical strength to prevent fragility, allowing the sensor to interact with the surrounding medium while maintaining structural integrity.
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 provides improved sensitivity and durability, enabling more accurate and reliable salinity and temperature measurements compared to traditional fiber-Bragg grating sensors.
Implementation Method 1
a first Fabry-Perot interferometer that includes a reference cell formed between a first single-mode optical fiber and a coaxially aligned first graded-index fiber; a second Fabry-Perot interferometer that includes a measurement cell formed between a second single-mode optical fiber and a coaxially aligned second graded-index fiber
Data Source
AI summary
A fiber-optic salinity and temperature measurement includes a first Fabry-Perot interferometer and a second Fabry-Perot interferometer. Each of the Fabry-Perot interferometers includes a first optical fiber fusion spliced to a second optical fiber such that a relatively large cavity is formed between the fibers. The relatively large cavity forms the measurement chamber for each Fabry-Perot interferometer. The input port on each of the Fabry-Perot interferometers is coupled to an optical splitter such that a single optical signal input is provided to each Fabry-Perot interferometer. The output port on each of the Fabry-Perot interferometers is coupled to an optical combiner that combines the interference signal received from each of the Fabry-Perot interferometers. An optical signal analyzer coupled to an output port of the optical combiner determines the salinity and temperature of a sample material in the large cavity of the second Fabry-Perot interferometer.