Tilted Fiber Grating Sensor for Refractive Index Detection
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Solution Overview
Problem
Current fiber Bragg grating (FBG) and Long Period Grating (LPG) sensors are highly sensitive to temperature, making it difficult to distinguish between temperature and refractive index changes, which limits their accuracy in sensing applications, especially in bio-chemical environments.
Innovation Solution
A tilted fiber grating (TFBG) sensor is used, which features a weakly tilted grating with a core mode resonance and multiple cladding mode resonances, allowing for temperature-independent measurements by monitoring the differential wavelength shifts between core and cladding modes, enabling sensitive detection of refractive index changes and physical strains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FBG or LPG sensors are used to detect refractive index changes, then sensitivity to physical manifestations is improved, but temperature sensitivity increases making it difficult to distinguish between temperature and refractive index changes
Solution Approach 1:
The patent segments the sensing function into two independent channels: one for temperature measurement (using FBG) and one for refractive index measurement (using TFBG). By dividing the sensing task into separate functional components, each sensor can be optimized for its specific parameter without interference from temperature effects on the other measurement channel.
Solution Approach 2:
The TFBG acts as an intermediary element that is selectively sensitive to refractive index changes while being relatively insensitive to temperature. This intermediary component transfers the refractive index information to the detection system without being significantly affected by temperature fluctuations, thereby isolating the measurement from harmful thermal interference.
2Measurement precision
If FBG or LPG sensors are used, then sensing capability is improved, but the spectral response becomes broad making high accuracy measurements difficult
Solution Approach 1:
The patent applies local quality by creating a tilted fiber grating structure where the tilt angle introduces directional coupling between core and cladding modes. This localized structural modification creates narrow, well-defined resonance peaks at specific wavelengths, concentrating the sensing response in a localized spectral region rather than distributing it broadly across the spectrum.
Solution Approach 2:
By changing the grating tilt angle parameter, the patent transforms the spectral response characteristics from broad (as in conventional FBG/LPG) to narrow and well-defined. This parameter change optimizes the spectral quality for high-precision wavelength measurements while maintaining the sensing functionality.
3Stability of the object's composition
If athermal packaging is used to reduce temperature sensitivity, then temperature stability is improved, but device complexity and bulk increase
Solution Approach 1:
The TFBG sensor performs self-service by inherently providing temperature compensation through its dual-mode operation. The sensor automatically separates temperature and refractive index effects through its physical principles, eliminating the need for external athermal packaging structures or complex compensation mechanisms.
Solution Approach 2:
The patent extracts the temperature sensitivity problem from the sensing system by using TFBG's selective coupling characteristics. The temperature dependency is effectively separated and can be independently characterized, allowing the refractive index measurement to proceed without requiring bulky athermal packaging.
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 TFBG sensor achieves high sensitivity and accuracy in measuring refractive index changes and physical strains while being insensitive to temperature variations, allowing for precise detection of biological and chemical elements, and physical manifestations like elongation and bending strains.
Implementation Method 1
a tilted grating in the optical pathway. The grating is responsive to electromagnetic radiation propagating in the optical pathway to generate a response
Implementation Method 2
The tilted grating is responsive to electromagnetic radiation propagating in the optical pathway to induce SPR adjacent the sensing surface
Implementation Method 3
The tilted grating is responsive to electromagnetic radiation propagating in the optical pathway to induce SPR adjacent the sensing surface
Data Source
AI summary
The present invention relates to a sensor using a tilted fiber grating to detect physical manifestations occurring in a medium. Such physical manifestations induce measurable changes in the optical property of the tilted fiber grating. The sensor comprises a sensing surface which is to be exposed to the medium, an optical pathway and a tilted grating in the optical pathway. The grating is responsive to electromagnetic radiation propagating in the optical pathway to generate a response conveying information on the physical manifestation.