New fiber-optic devices for sensing applications

Faculty of Science
STEM Complex.
Professor Xiaoyi Bao’s research has many tangible applications in the area of infrastructure monitoring.

With postdoctoral fellow Huibo Fan and collaborator Liang Chen, Prof. Bao recently completed an important study in which she overcame the detection limitations of fiber-optic sensors. This major advance will allow the monitoring of oil and gas pipelines, preventing ruptures.

Professor Xiaoyi Bao and postdoctoral fellow Huibo Fan
Professor Xiaoyi Bao and postdoctoral fellow Huibo Fan

Fiber optic sensors used in infrastructure monitoring typically use telecom fibers. As they are made of glass, telecom fibers are not ideal for measuring compressible strain. Glass is stiff, which means that bare telecom fiber has a very limited range of elongation, less than 1 cm/m. In order to increase the sensing range of fiber optics sensors for tension or compression measurements in infrastructure such as pipelines, Prof. Bao discovered that it was necessary to make the fiber behave like a material with low stiffness, which can deform easily.

Seeing that springs have a broad tension and compression range due to the free space between rings, as well as impressive elastic properties and resistance to deformation, Prof. Bao and her team designed and developed a spring-like optical fiber structure known as  off-core fibre sections, which are then fused by a fusion splicer. In this type of fiber structure, the effective stiffness is significantly reduced, enabling +/- 20 millimetre strain measurements with an incredible 1 µm/m strain accuracy. The number of off-core fusion sections can be optimized for various strain measurement applications. In the field of optical sensing, identical fiber section lengths can limit the free-spectrum range and thus limit strain measurement range. To overcome this and keep the sensor ultra-compact and cost effective, Prof. Bao and her team designed a non-uniform, multiple-core-offset fiber, which provides tremendous flexibility in the range of strain measurements.

Through this innovative research, Prof. Bao achieved a combined compression-tension strain sensor with wide strain range and high sensitivity. The new multiple core-offset fibre has great potential for sensing applications, such as in the monitoring of pipeline buckling for rupture prevention.

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