Wavelength tuning of through-coating-written fiber bragg gratings

This paper reports on the inscription of fiber Bragg gratings (FBGs) into fibers under tension. In order to avoid mechanical weakening of the fiber the coating is not removed and the FBG is directly inscribed through the coating. Releasing the fiber after the inscription leads to a lower period and thus to a lower Bragg wavelength. For the experiments we used a fiber coated with Ormocer or acrylate and a diameter of 80 mm. The fiber core with a diameter of 8 mm was made of pure silica. The inscription process took less than one minute. The fibers with FBGs showed a breaking strength of (4795+498) MPa, similar to the pristine fiber ((5212 + 478) MPa). The FBGs were calibrated as strain and temperature sensors to prove this functionality. For the strain calibration the FBGs show the expected linear behavior with a slope of (1.213 + 0.004) pm/mstrain. The results of the temperature calibration exhibit a slope of (11.07 + 0.31) pm/K. We have demonstrated the inscription of high strain resistant FBGs through the coating of fibers with a diameter of 80 mm. Inscription under tension of the fiber allowed to tune the Bragg wavelength by 5 nm without compromising the mechanical strength.