Online and Efficient Fabrication of Helical Long-Period Fiber Gratings

By taking the advantage of inherent core-cladding eccentricities in standard single-mode fibers, in this letter, we propose and demonstrate an efficient method to fabricate helical long-period fiber gratings (H-LPFGs) by directly twisting fibers. In the fabrication process, we use a double-beam CO₂ laser for heating the fiber stably and uniformly, together with an online scheme for monitoring the spectrum. Compared with other fabrication methods reported, the quality of H-LPFGs we fabricated is improved significantly, showing a high extinction ratio of over 30 dB and a low insertion loss of 1 dB. Based on the fact that H-LPFGs with different pitches for specific mode couplings can be fabricated efficiently and controllably, to the best of our knowledge, we actually achieve H-LPFGs with the highest quality up to now, which may find important applications, such as filtering, sensing, and optical vortex generation.