Single-core multi-channel moiré fiber grating and multi-wavelength LMA fiber grating fabricated based on two-dimensional spatially encoded phase mask

A two-dimensional optical fiber grating with multi sub-gratings based on a 2D spatially encoded phase mask is designed in this study. The 2D fiber Bragg grating (FBG) is composed of two non-overlapping sub-FBGs, which are laterally separated along the radial direction of the fiber core. Unlike traditional FBGs, the refractive index of the 2D FBG is modulated both on the axial and radial directions of the fiber core, which are realized by spatially encoded diffraction based on a 2D spatially encoded phase mask. Compared with the overlapping grating, the 2D FBG can be fabricated at one time to achieve multi-wavelength output, and its compact structure provides a new idea for multi-wavelength multiplexing. As examples, a single-core multi-channel moiré fiber grating and 2D FBG with three subgratings are designed and fabricated on a single-mode fiber and LMA fiber, respectively. Using a 2D spatially encoded mask can improve the optical fiber refractive index modulation from one- to two- or even three-dimensions, which is helpful for precise manipulation of the complex optical field of optical fiber.