Key words:  Fiber optics, fiber optics components, helical long-period fiber grating, optical vortices.

As is known that, in a single-helix helical long-period fiber grating (SHLPG), due to the inherent one-fold azimuthal symmetric structure of the fiber core (i.e., in general, the high-order Fourier expansion coefficients of the core boundary profile is extremely small), it is very hard to efficiently obtain the high-order azimuthal mode couplings. In this study, we have proposed and demonstrated a phase-sampling approach to overcome this obstacle, which is realized by periodically inserting phase shifts in the transverse direction of the SHLPG. As results of the proposed method, high-efficient couplings between the fundamental mode and the second- and third-order azimuthal modes in a SHLPG have been successfully demonstrated. The proposed method can be applied to generate and convert high-order orbital angular momentum (OAM) modes even with the SHLPG.

References

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