DC-Sampled Helical Fiber Grating and its Application to Multi-Channel OAM Generator

A novel DC-sampling method allowing generation of a multichannel helical long-period fiber grating (HLPG) has been proposed. Unlike the previous phase-only sampling method where phases of the continuous sampling function must be discretely adopted and inserted into the local pitches of the grating (thus high precision setups for controlling all the individual pitches of the grating are essential), the proposed method can greatly facilitate the fabrication of the multichannel HLPG by using the CO
₂
laser writing technique. As one typical example, the DC-sampled 3-channel HLPG has been demonstrated both theoretically and experimentally. The orbital angular momentum (OAM) modes inherently existed in this kind of HLPGs have also been verified. This is the first report for generation of a multi-channel (wavelength) OAM mode by using only one HLPG.