Analysis of the Spectrum Distortions of Weak Fiber Bragg Gratings Fabricated In-Line on a Draw Tower by the Phase Mask Technique

Identical weak optical fiber Bragg grating (FBG) arrays can be fabricated in-line on a draw tower using the phase mask technique. On the FBG arrays, some grating spectrum distortions, for example, asymmetric side lobes or deformed side lobes, low extinction ratio of the main reflection peak and comb filter-type peaks, can be observed. We collected different distorted reflection spectra of the in-line-fabricated weak FBGs and compared them with the simulated spectra of weak FBGs. By comparing the experimental and theoretical weak FBG spectra, it is found that the different kinds of spectrum distortions are caused by phase shifting, asymmetric apodization and nonlinear chirp. This analysis is helpful to improve the FBG array fabricating process by phase mask in-line on a draw tower. And we got good FBG arrays which have good central wavelength consistency, good reflectivity consistency and minor spectral distortion.