Manufacturing optical fibre Bragg grating strain sensors with an excimer laser for high-strain, multiplexed embedded applications

Fibre optic Bragg grading sensors are ideally suited for applications where embedding the sensor directly within the structural material will enable useful measurements to be taken. The particular application envisioned is to embed the sensors within a pultruded tendon produced for the prestressed concrete industry. The sensors within a composite pultruded tendon will experience long-term high strains. Bragg gratings are written into the core of an optical fibre by ultra-violet radiation produced by an excimer laser. This process however, compromises the strength of the optical fibre and therefore severely limits the strain range and long term viability of this type of sensor in this type of application. Presented herein is the assessment of the UV-induced strength degradation and its effect on free and embedded strain gauges. A presentation of alternative methods of creating Bragg gratings without compromising the strength is also presented.