Influence of the UV irradiation on mechanical properties

FBG sensors produced on-line during the process using an excimer laser pulse suffer no measurable loss of strength relative to unirradiated fibre. This emphasizes the fact that it is favourable to use draw-tower FBGs as sensor elements to overcome the problem related to fibre stripping and high fluence UV irradiation. 

Feced et al. has studied the influence of different wavelength UV irradiation on the strength of optical fibres with a single pulse radiation. The single mode 

It has previously been reported that the processes induced in the fibre by 248 nm radiation are different from those induced by 193 nm radiation. In addition, it is thought that the exposure of optical fibre to UV increases the stress in the core. The results reinforce these concepts they suggest that the 248 nm mechanism increases the internal core stress of the fibre significantly more than the 193 nm mechanism, such that 248 nm radiation causes a larger degradation of the fibre strength. 

7 SEM of the cross-section of the broken grating. The start of the break is at the lower side. The UV laser is radiated from bottom to top. 

FBG sensor degraded drastically with the increase in UV irradiation, and after a certain dose the mechanical strength will not degrade with the growth 

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