The present disclosure provides a pitch reducing optical fiber array or a multicore fiber including at least one chiral fiber grating incorporated therein that is operable to couple the modes in different fiber cores within a spectral range determined in some instances by the helical pitch of the corresponding chiral fiber grating.

The disclosed embodiments provide systems and methods for mitigating lensing and scattering as an optical fiber is being inscribed with a grating. The disclosed systems and methods mitigate the lensing phenomenon by surrounding an optical fiber with an index-matching material that is held in a vessel with an integrated interferometer (e.g., phase mask, etc.). The index-matching material has a refractive index that is sufficient to reduce intensity variations of the actinic radiation within the optical fiber. Some embodiments of the system include different vessels for holding the index-matching material, with the vessel having an interferometer integrated into the vessel. These vessels permit the optical fiber to be surrounded by the index-matching material while the gratings are written to the optical fiber.

An object of the present disclosure is to enable LPG applied over the entire length of an optical fiber without inhibiting an operation of taking out the optical fiber.

The present disclosure relates to an optical fiber cable in which at least one or more optical fibers for transmission in at least two or more modes are gathered, the optical fiber cable including: a linear material abutting on at least one of the optical fibers, in which a thickness of the linear material periodically varies in a longitudinal direction of the linear material.