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Quasi-distributed fiber bend and temperature measurement in femtosecond laser-structured POF

: Liehr, S.; Krebber, K.; Burgmeier, J.

Werneck, M.M. ; Laboratório de Instrumentação e Fotônica -LIF-, Rio de Janeiro:
POF 2013 Búzios, the 22nd International Conference on Plastic Optical Fibers. Proceedings : Rio De Janeiro, Brazil, Búzios, September 11 - 13, 2013
Búzios, 2013
International Conference on Plastic Optical Fibers (POF) <22, 2013, Armação dos Búzios>
Fraunhofer HHI ()

We proposed focusing femtosecond laser pulses into the core material of standard PMMA POF to create localized scattering damage for application in quasi-distributed sensing using optical time domain reflectometry. Fiber bend radius measurement and fiber bend direction measurement has been presented by evaluating backscatter changes at off-center-inscribed scattering damage in the fiber core. Quasi-distributed temperature sensing has been demonstrated by evaluating temperature-dependent Rayleigh scattering relative to the inscribed scattering points. The proposed fiber structuring and backscatter evaluation approach is very flexible and enables simultaneous and independent evaluation of multiple measurands along a single sensor fiber. Focused fs pulse inscription provides highly reproducible results and the fiber and cladding remain mechanically intact. The presence of liquid does not change the sensor signal and the small form factor of the sensor can be maintained since no additional protection of the fiber is required. In contrast to proposed transmission loss sensors, the presented technique allows accessing multiple sensor points from a single end but can only be used for static or low-dynamic measurement (> 1 Hz). The maximum measurement distance in standard PMMA POF is about 100 m whereas the measurement resolution is reduced with increasing fiber length due to the strong modal dispersion in the step-index POF. Self-referencing relative to the adjacent Rayleigh level compensates for possible disturbances inducing loss along the fiber.