Coiled Evanescent Optical Sensor for Compact High Sensitivity
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Solution Overview
Problem
Existing optical sensors face challenges in achieving high sensitivity while maintaining a compact size, as longer sensor lengths increase spatial delocalization and are not suitable for miniature applications, and folded or spirally bent photonic wire sensors experience high losses and inadequate sensitivity.
Innovation Solution
An evanescent optical sensor is formed as a coil of optical fiber or microfiber, which reduces size while maintaining sensitivity through the creation of whispering gallery modes that propagate along the curved fiber, allowing for increased optical path length within a compact area, and optimizing couplers for reduced losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the interferometer arm length is increased to enhance sensor sensitivity, then sensitivity is improved, but the overall physical size of the sensor increases and spatial delocalization occurs
Solution Approach 1:
The patent transitions from a linear interferometer arm configuration to a coiled fiber configuration, utilizing three-dimensional spatial arrangement to achieve the required optical path length within a compact footprint. The coil geometry allows the optical path to extend in multiple dimensions while maintaining a small overall sensor volume.
Solution Approach 2:
The patent employs a coiled fiber configuration where the optical path is curved rather than straight. This curvature allows the optical path length to be extended within a compact area, as the coil can be tightly wound while still providing the necessary path length for high sensitivity measurements.
2Length of stationary object
If folded or spirally bent photonic wire sensors are used to reduce size, then sensor size is reduced, but optical losses increase and sensitivity decreases
Solution Approach 1:
The patent uses optical fiber, which has a flexible structure that can be coiled without causing significant optical losses. The fiber's flexibility allows it to be formed into compact coils while maintaining low insertion losses and high sensitivity, overcoming the limitations of rigid photonic wire structures.
Solution Approach 2:
The patent employs a coiled fiber configuration where the optical path is curved rather than straight. This curvature allows the optical path length to be extended within a compact area, as the coil can be tightly wound while still providing the necessary path length for high sensitivity measurements.
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 coiled sensor achieves enhanced sensitivity and reduced spatial delocalization, with sensitivity improvements demonstrated by significant shifts in transmission spectra in response to ambient changes, such as refractive index variations, and reduced insertion losses.
Implementation Method 1
The use of a coil configuration results in creating a plurality of whispering gallery modes (WGMs) that will propagate along the coil by reflecting from the surface of the curved fiber/microfiber forming the coil
Implementation Method 2
the overlap of an incoming beam and the internally reflected beam leads to a field that penetrates into the medium adjacent to the core region of the fiber. This electromagnetic field, which tails into the adjacent medium, is defined as the 'evanescent field'
Implementation Method 3
evanescent wave absorption is an effective technique for performing various types of environmental sensing
Data Source
AI summary
An evanescent optical sensor is formed as a coil of either optical fiber or microfiber. By coiling the fiber/microfiber, the overall size of the sensor is significantly reduced when compared to “straight path” fiber sensors, yet exhibits a similar degree of sensitivity. An optical signal is coupled into a fiber coil that has been immersed in an ambient to be analyzed. The use of a coil configuration results in creating a plurality of whispering gallery modes (WGMs) that will propagate along the coil by reflecting from the surface of the curved fiber/microfiber forming the coil. The interference between these modes will be modified as a function of the properties of the ambient environment. Environmental changes cause variations in the optical length of the coil as “seen” by the various modes, and the interference of the modes is analyzed by studying the transmission spectrum at the output of the coil.