Sensitivity of Long-period Gratings Modified by their Bending

AbstractThe paper presents an effect of fiber bending on sensitivity of long-period gratings (LPGs) to temperature and to surrounding refractive index (RI). The LPGs were manufactured by UV-exposure of hydrogen-loaded Corning SMF28 fibers and their annealing was followed by wet etching in hydrofluoric acid up to dispersion turning point (DTP) where the LPG shows the highest sensitivity. The LPGs were subjected to curvatures in range 0.8 to 4.8 m-1 when their temperature (T=20-100°C) and refractive index (RI) responses (nD=1 to 1.47) were measured. Bending sensitivity reaching 54nm/m-1 has been obtained. It has been found that as a result of bending, coupling to asymmetrical cladding modes takes place. It results in the resonances increasing their depth and shifting towards longer wavelengths with bending. The bending effect also allows for post-fabrication tuning of the LPGs working at DTP. The LPGs with bending-modified temperature sensitivity up to 0.54nm/°C have been shown. The method can also be applied for tuning of RI sensitivity of the LPGs