Fibre optic remote sensing based on long period gratings with In Situ optical source
D. Viegas, J. P. Carvalho, University of Porto (Portugal); L. Coelho, INESC Porto - Institute for Systems and Computers Engineering of Porto (Portugal); J. L. Santos, University of Porto (Portugal); L. A. Ferreira, F. M. Araújo, O. Frazão, INESC Porto - Institute for Systems and Computers Engineering of Porto (Portugal)
In this work the concept of long period based optical fibre sensors with the broadband light illumination generated just after the sensing structure is presented. This new approach allows the interrogation in transmission of the sensing head while integrated in a reflective configuration, which means the LPG sensor is seen in transmission by the optical source but in reflection by the measurement system. Also, it is shown that with this illumination layout the optical power balance is more favorable when compared with the standard configurations, allowing better sensor performances particularly when the sensing head is located far away from the photodetection and processing unit. This is demonstrated for the case of the LPG structure applied to measure strain and using ratiometric interrogation based on the readout of the optical power reflected by two fibre Bragg gratings spectrally located in each side of the LPG resonance.
