Evanescent Wave Multimode Optical Waveguide for Linear Absorbance
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Solution Overview
Problem
Conventional evanescent wave optical waveguide sensors face challenges in accurately quantifying chemical concentrations due to non-proportional absorbance between waveguide and cladding, especially in colored and turbid solutions, as high-order modes are depleted rapidly, violating the Beer-Lambert law.
Innovation Solution
An evanescent wave multimode optical waveguide with high mode coupling and a cladding having variable optical absorption, where the evanescent wave interacts with a chemical indicator, redistributes unabsorbed light power among modes, ensuring linear absorbance dependence on cladding concentration and stability against light injection conditions and environmental disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional multimode optical waveguide is used for evanescent wave sensing, then the waveguide can propagate light through the sample solution, but the absorbance measurement becomes non-proportional to cladding concentration due to rapid depletion of high-order modes
Solution Approach 1:
The patent changes the mode coupling parameter by introducing a periodic structure in the waveguide core that induces continuous mode coupling along the waveguide length. This parameter change transforms the optical power distribution from a static configuration (where high-order modes are rapidly depleted) to a dynamic equilibrium state where modes continuously exchange energy, thereby maintaining proportional absorbance measurement consistent with Beer-Lambert law.
Solution Approach 2:
The patent implements continuous mode coupling along the entire waveguide length through periodic refractive index modulation. This continuous action ensures that optical power is constantly redistributed among modes, preventing the rapid depletion that occurs in conventional waveguides. The continuous energy exchange between modes maintains a stable absorbance-concentration relationship throughout the waveguide.
2Quantity of substance
If high-order modes are allowed to propagate in the waveguide, then more light interacts with the cladding, but these modes are rapidly depleted by evanescent wave absorption
Solution Approach 1:
The periodic structure in the waveguide core creates a feedback mechanism where modes that are depleted by cladding absorption receive continuous energy input from other modes through mode coupling. This feedback loop maintains a balanced energy distribution among modes, ensuring sustained light-cladding interaction without net energy loss.
Solution Approach 2:
The patent transforms the static optical power distribution into a dynamic equilibrium state through continuous mode coupling. The optical energy is constantly redistributed among different modes along the waveguide length, creating a dynamic balance between modes that are being depleted and modes that are being generated, thereby maintaining sustained interaction with the cladding.
3Stability of the object's composition
If the waveguide is designed for low mode coupling, then optical power distribution remains stable, but absorbance is not proportional to cladding concentration
Solution Approach 1:
The patent introduces a periodic refractive index modulation parameter that induces continuous mode coupling. This parameter change creates a dynamic optical power distribution that adapts along the waveguide length, transforming the system from a static low-coupling state to a dynamic high-coupling state that maintains absorbance proportionality while preserving measurement stability.
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 approach allows reliable absorbance-based chemical analysis in various solutions, including colorless, transparent, colored, and turbid ones, by maintaining a linear relationship between absorbance and concentration, enhancing the accuracy and stability of chemical sensing.
Implementation Method 1
Light is guided in the waveguide by internal reflection at the waveguide-solution interface. The refractive index of the waveguide is higher than that of the solution so that the solution acts as a cladding for the optical waveguide. Light is mostly propagated in the waveguide but part of the light, namely the evanescent wave, propagates in the solution
Implementation Method 2
The cladding has an optical absorption varying with a chemical or a physical parameter to be sensed and interrogated by means of the evanescent wave
Implementation Method 3
Light is guided in the waveguide by internal reflection at the waveguide-solution interface
Implementation Method 4
A chemical indicator is provided in the cladding for causing a variation of the optical absorption of the cladding as a function of the chemical species or the physical parameter
Data Source
AI summary
There is provided an evanescent wave multimode optical waveguide sensitive to a chemical species or to a physical parameter. The optical waveguide comprises a core and a cladding having a cladding refractive index lower than that of the core for guiding light to be propagated in the optical waveguide. The cladding defines with the core an optical waveguide providing mode coupling. A chemical indicator is provided in the cladding for causing a variation of the optical absorption of the cladding as a function of the chemical species or the physical parameter. The cladding is interrogated by the evanescent wave of the propagated light. The mode coupling causes unabsorbed light power to be redistributed among the multiple modes while light propagates along the optical waveguide.