We have demonstrated that fiber Bragg gratings can be written through the carbon layer of carbon-coated optical fibers having different coating thicknesses. Specifically, grating index modulation amplitudes of ~2.5x10-5 and 0.52x10-5 were obtained in optical fibers having carbon layers 29 nm and 56 nm thick, respectively, without any extra photosensitization of the fibers. Subsequent experimental results showed that the carbon coatings in the grating areas didn’t change their hermetic properties. Finally, we describe the advantages of these gratings and their potential applications in fiber optic sensing.
We present for the first time a cascaded Raman fiber laser where the Yb-doped fiber laser and Raman fiber are combined
into a single fiber. We achieve 42.6 % slope efficiency at 1236 nm with respect to launched pump power.
We demonstrated a novel twin-core fiber grating sensor system for accurate and simultaneous measurements of
temperature and strain. Specifically, we designed two cores with custom index and dopant profiles such that the gratings
in these two cores have different temperature coefficients, but almost same strain coefficients. Our data also showed that
both gratings had almost the same wavelength shift at the same deuterium concentration level in the fiber. This, together
with the strain characteristics of the gratings, enables us to isolate the temperature measurement when strain, temperature
and gaseous diffusion all apply to the sensor simultaneously. It makes our grating sensor extremely useful for
hydrothermal down-hole temperature mapping applications.
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