We describe te production and characterization of FC/PC connectorised fibre Bragg grating sensors in polymer fibre. Sensors were recorded in few-moded and single mode microstructured fibre composed of poly (methyl methacrylate).
With regard to polymer fibre Bragg gratings, we investigate one of the consequences of the visco-elastic nature of the
constituent polymer: hysteresis in the response of wavelength shift vs sensor elongation. We show that when a grating
sensor is directly bonded to a substrate, the hysteresis is reduced by a factor of 10 from the case where the sensor is
freely suspended between two supports.
The authors fabricated a demountable Ferrule connector/Physical contact connection between silica fiber and a polymer optical fiber (POF) containing a fiber Bragg grating. The use of a connector for POF grating sensors eliminates the limitations of ultraviolet glued connections and increases the ease with which the devices can be applied to real-world measurement tasks.
The inscription of Bragg gratings has been demonstrated in PMMA-based polymer optical fibre. The water affinity of
PMMA can introduce significant wavelength change in a polymer optical fibre Bragg grating (POFBG). In polymer
optical fibre losses are much higher than with silica fibre. Very strong absorption bands related to higher harmonics of
vibrations of the C-H bond dominate throughout the visible and near infrared. Molecular vibration in substances
generates heat, which is referred to as the thermal effect of molecular vibration. This means that a large part of the
absorption of optical energy in those spectral bands will convert into thermal energy, which eventually drives water
content out of the polymer fibre and reduces the wavelength of POFBG. In this work we have investigated the
wavelength stability of POFBGs in different circumstances. The experiment has shown that the characteristic wavelength
of a POFBG starts decreasing after a light source is applied to it. This decrease continues until equilibrium inside the
fibre is established, depending on the initial water content inside the fibre, the surrounding humidity, the optical power
applied, and the fibre size. Our investigation has shown that POFBGs operating at around 850 nm show much smaller
wavelength reduction than those operating at around 1550 nm in the same fibre; POFBGs with different diameters show
different changes; POFBGs powered by a low level light source, or operating in a very dry environment are least affected
by this thermal effect.