Birefringent Optical Fibre Pressure Sensor
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Solution Overview
Problem
Existing optical fibre-based pressure sensors face challenges in sensitivity and accuracy, particularly at low pressures, and require larger waveguides which are difficult to connect to standard fibres, leading to increased optical losses and complexity in harsh environments.
Innovation Solution
A pressure sensor is formed by encasing an optical fibre with a birefringence structure and a non-compressible fluid within a housing, where the birefringence structure converts external pressure into anisotropic stress in the fibre, and internal etching increases birefringence sensitivity, allowing for high sensitivity and accuracy even at low pressures without compromising mechanical robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the waveguide size is increased to improve sensitivity, then sensitivity is improved, but the difficulty of connecting to standard fibres increases and optical losses increase
Solution Approach 1:
The patent changes the physical parameters of the waveguide by introducing air holes with specific dimensions and positions, transforming the waveguide from a solid structure to a porous structure. This parameter change enables the waveguide to achieve high sensitivity while maintaining compatibility with standard fibre dimensions for connection.
Solution Approach 2:
The patent creates a composite waveguide structure combining solid material with air holes, forming a composite material system. This composite structure achieves enhanced optical properties and mechanical properties simultaneously, resolving the contradiction between sensitivity and connectivity.
2Measurement precision
If the waveguide size is increased to improve sensitivity, then sensitivity is improved, but optical losses increase
Solution Approach 1:
The patent introduces air holes into the waveguide structure, creating a porous material system. This porous structure enhances the interaction between light and the sensing region, improving sensitivity while the controlled porosity prevents excessive optical losses by maintaining appropriate light confinement.
3Measurement precision
If mechanical parts or bonding mechanisms are added to improve pressure sensing, then pressure sensing capability is improved, but hysteresis and instability are introduced
Solution Approach 1:
The patent replaces mechanical pressure sensing mechanisms with an optical sensing mechanism based on birefringence in the waveguide. The pressure is transmitted through the porous structure to induce stress in the waveguide, which is detected optically rather than mechanically, eliminating hysteresis and instability associated with mechanical parts.
Solution Approach 2:
The porous waveguide structure acts as an intermediary between the applied pressure and the optical field. It transmits mechanical pressure into optical signal changes through stress-induced birefringence, avoiding direct contact between mechanical sensing elements and the pressure source.
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 solution achieves a ten-fold increase in sensitivity and maintains mechanical robustness, enabling accurate pressure measurement in harsh environments with reduced optical losses and simplified connectivity to standard fibres.
Implementation Method 1
the fibre is designed so that a uniform external pressure applied to the fibre is converted into an anisotropic force in the core of the waveguide. The effect of this is to induce pressure-dependent birefringence in the core.
Implementation Method 2
This causes a difference in refractive indices along the core, which leads to two different shifts in the reflection peak of the Bragg wavelength.
Implementation Method 3
An FBG is an intrinsic optical sensor recorded within the core of an optical fibre using spatially-varying patterns of intense ultraviolet or infrared laser light to create periodic modulations in a refractive index of the fibre. These modulations in the refractive index give rise to a wavelength selective mirror, whereby light travelling down the waveguide is partially reflected at each of the interfaces or gratings
Implementation Method 4
providing the optical sensor comprises optically inducing stress in the core so that the optical sensor exhibits intrinsic birefringence
Implementation Method 5
Changes in the temperature, pressure or strain at the sensor can give rise to a change in each of the periodicity and the refractive index, thus leading to a detectable change in the Bragg wavelength.
Data Source
AI summary
A method for forming a pressure sensor is provided wherein an optical fibre is provided, the optical fibre comprising a core, a cladding surrounding the core, and a birefringence structure for inducing birefringence in the core. The birefringence structure comprises first and second holes enclosed within the cladding and extending parallel to the core. A portion of the optical fibre comprising the core and the birefringence structure is encased within a chamber, wherein the chamber is defined by a housing comprising a pressure transfer element for equalising pressure between the inside and the outside of the housing. An optical sensor is provided along the core of the optical fibre. Providing the optical sensor comprises optically inducing stress in the core so that the optical sensor exhibits intrinsic birefringence. The chamber is filled with a substantially non-compressible fluid. Consequently, the birefringence structure is shaped so as to convert an external pressure provided by the non-compressible fluid within the chamber to an anisotropic stress in the optical sensor.