Drawing-tower inscription of apodized fiber Bragg grating arrays using a rotated focusing cylindrical lens

Abstract

Large-scale, densely distributed fiber Bragg grating (FBG) arrays have a wide range of applications in industrial safety surveillance. Due to the limitation of inscription pulse-width, most grating interrogators have difficulties distinguishing each grating when the spacing between adjacent gratings reduces to specific small values. Multiple gratings within a fiber section are generally deemed as a single sensing element, and their superposed reflection spectra are acquired for necessary sensing information. The challenge is that serious crosstalk exists in multiple gratings caused by the accumulation of sidelobes from numerous reflections. Such crosstalk, indeed, can be eliminated when the sidelobe suppression ratio (SLSR) is kept high, which has been a long-term difficulty in such systems. In this work, we propose and experimentally demonstrate a novel and simple online fabrication technique for writing apodized fiber Bragg grating (AFBG) arrays during fiber drawing by simply rotating a focusing cylindrical lens for modified pulse intensities. At four degrees rotation angle, the fabricated AFBG has good performance and consistency with full width at half maximum (FWFH) of 0.088 nm, and the SLSR on the long-wavelength side is maintained as high as 20.8 dB. Experimental results further prove that using this fiber-based system, a hot spot of 10 cm size can be well perceptive over one-km fiber length, and the minimum measurable temperature change is 6 ℃. This work clearly addresses a reliable and potential method for the online fabrication of AFBG arrays with suppressed sidelobe-induced crosstalk.