A preform element, its production, and fiber production methods from preform assemblies. The preform element has a length and a center axis along its length, a first and second end defined by its length and an outer preform element surface. The preform element includes a plurality of longitudinal structures disposed to form longitudinal hole(s) in a background material. At least one slot extending from its outer preform element surface and intersecting at least one of the longitudinal holes, wherein the at least one slot does not fully intersect the preform element. The preform element may be a preform center element or a preform ring element and may be assembled to a form part of a preform assembly for an optical fiber.

A hollow core fiber has a cladding comprising a matrix of cells, wherein each cell comprises a hole and a wall surrounding the hole. The fiber further has a hollow core region comprising a core gap in the matrix of cells, wherein the core gap spans a plurality of cells and has a boundary defined by the interface of the core gap. The matrix of cells comprises a plurality of lattice cells, and a plurality of defect cells characterised by at least one difference in at least one property from that of the lattice cells. The cells at the core region boundary include lattice cells and defect cells that are arranged in a pattern so as to produce birefringence in a light propagating through the hollow core fiber. Further described is a technique for making the fiber.

A hollow core fiber has a cladding comprising a matrix of cells, wherein each cell comprises a hole and a wall surrounding the hole. The fiber further has a hollow core region comprising a core gap in the matrix of cells, wherein the core gap spans a plurality of cells and has a boundary defined by the interface of the core gap. The matrix of cells comprises a plurality of lattice cells, and a plurality of defect cells characterised by at least one difference in at least one property from that of the lattice cells. The cells at the core region boundary include lattice cells and defect cells that are arranged in a pattern so as to produce birefringence in a light propagating through the hollow core fiber. Further described is a technique for making the fiber.

The invention relates to a method for producing a polarization-maintaining optical fiber, consisting of a core region and stress-generating elements embedded in the fiber body, having the following method steps: producing a core preform for the core region using internal deposition on a substrate tube, the internally coated substrate tube subsequently being collapsed, generating recesses on the core preform by virtue of the material on the outer surface of the core preform being removed parallel to the longitudinal axis of the core preform at diametrically opposed positions, filling the recesses with stress-generating rods, with the tightest possible rod packing, in a freely selectable first filling geometry, possibly filling the recesses in addition with non-stress-generating rods in a second filling geometry, sheathing the filled core preform with a jacketing tube, preparing the sheathed core preform for a fiber-drawing process, and drawing the sheathed arrangement to form the optical fiber. A preform for producing a polarization-maintaining optical fiber contains a core preform, having a core region and a lateral region, and also contains a jacketing tube, which encloses the core preform, as well as stress-generating elements contained in the lateral region, wherein the stress-generating elements are provided in the form of recesses in the lateral region, wherein the recesses are filled with doped rods and/or undoped rods, and wherein the rod filling forms a first and/or a second arrangement geometry.

A hollow core fiber has a cladding comprising a matrix of cells, wherein each cell comprises a hole and a wall surrounding the hole. The fiber further has a hollow core region comprising a core gap in the matrix of cells, wherein the core gap spans a plurality of cells and has a boundary defined by the interface of the core gap. The matrix of cells comprises a plurality of lattice cells, and a plurality of defect cells characterized by at least one difference in at least one property from that of the lattice cells. The cells at the core region boundary include lattice cells and defect cells that are arranged in a pattern that define two orthogonal axes of reflection symmetry, so as to produce birefringence in a light propagating through the hollow core fiber.

The invention relates to a method for producing a polarization-maintaining optical fibre, consisting of a core region and stress-generating elements embedded in the fibre body, having the following method steps: producing a core preform for the core region using internal deposition on a substrate tube, the internally coated substrate tube subsequently being collapsed, generating recesses on the core preform by virtue of the material on the outer surface of the core preform being removed parallel to the longitudinal axis of the core preform at diametrically opposed positions, filling the recesses with stress-generating rods, with the tightest possible rod packing, in a freely selectable first filling geometry, possibly filling the recesses in addition with non-stress-generating rods in a second filling geometry, sheathing the filled core preform with a jacketing tube, preparing the sheathed core preform for a fibre-drawing process, and drawing the sheathed arrangement to form in the optical fibre. A preform for producing a polarization-maintaining optical fibre contains a core preform, having a core region and a lateral region, and also contains a jacketing tube, which encloses the core preform, as well as stress-generating elements contained in the lateral region, wherein the stress-generating elements are provided in the form of recesses in the lateral region, wherein the recesses are filled with doped rods and/or undoped rods, and wherein the rod filling forms a first and/or a second arrangement geometry.

Embodiments disclosed herein include an optical fiber. In an embodiment, the optical fiber comprises a core and a cladding around the core. In an embodiment, a first rod is within the cladding and adjacent to the core. In an embodiment, the first rod comprises a magnetic material. In an embodiment, the optical fiber further comprises a second rod within the cladding and adjacent to the core, where the first rod and the second rod are on opposite sides of the core.