Multichannel Long-Period Fiber Grating Realized by Using the Helical Sampling Approach

A simple and efficient sampling approach enabling fabrication of a multichannel long-period fiber grating (LPG) was proposed and demonstrated for the first time both theoretically and experimentally. Unlike the previous sampling methods in which a sampling function is employed to modulate only the amplitude of the seed grating, i.e., the ac part of the grating's index-modulation, in this study, a helical-type sampling is used to modulate only the dc part of the grating's index-modulation. The proposed method enables a significant enhancement in the utilization efficiency of the fiber, and it will greatly facilitate the fabrication of multichannel LPG by using the CO
₂
laser technique. As one typical example, a helically sampled three-channel LPG was successfully demonstrated both numerically and experimentally, and it was found that the experimental results agree well with the theoretical predictions.