A method of drawing a material into sheet form includes forming a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is much greater than a second transverse dimension substantially perpendicular to the first transverse dimension. A furnace having substantially linearly opposed heating elements one spaced from the other is provided and the heating elements are energized to apply heat to the preform to create a negative thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a central plane of the preform. The preform is drawn in such a manner that the material substantially maintains its first transverse dimension and deforms across its second transverse dimension.

Optical waveguide cores having refractive index profiles that vary angularly about a propagation axis of the core can provide single-mode operation with larger core diameters than conventional waveguides. In one representative embodiment, an optical waveguide comprises a core that extends along a propagation axis and has a refractive index profile that varies angularly about the propagation axis. The optical waveguide can also comprise a cladding disposed about the core and extending along the propagation axis. The refractive index profile of the core can vary angularly along a length of the propagation axis.

A method of drawing different materials includes forming a first material into a preform body defining at least one channel extending therethrough having a first cross-sectional area. A first element formed of a second material is inserted into the channel and with the preform body creates a preform assembly. The first element has a cross-sectional area that is less than the cross-sectional area of the channel, and the second material has a higher melting temperature than the first material. The preform assembly is heated so that the first material softens and the preform assembly is drawn so that the preform body deforms at a first deformation rate to a smaller cross-sectional area and the first element substantially maintains a constant cross-sectional area throughout the drawing process. Upon completion of the drawing step, the cross-sectional area of the channel is equivalent to the cross-sectional area of the first element.

A quartz glass tube as a semi-finished product for an optical component that has an inner bore extending along a tube center axis for the acceptance of a core rod and a tube wall limited by an inner casing surface and an outer casing surface is already known; within said tube wall an inner region made of a first quartz glass and an outer region made of a second quartz glass with a different index of refraction surrounding the inner region contact one another at a contact surface which runs around the center axis. In order to provide a quartz glass on this basis that facilitates the production of optical components for special applications such as laser-activated optical components in wand or fiber form, the invention states that the contact surface has a non-round course in the radial cross-section and the inner casing surface has a circular course.

A method of drawing different materials includes forming a first material into a preform body defining at least one channel extending therethrough having a first cross-sectional area. A first element formed of a second material is inserted into the channel and with the preform body creates a preform assembly. The first element has a cross-sectional area that is less than the cross-sectional area of the channel, and the second material has a higher melting temperature than the first material. The preform assembly is heated so that the first material softens and the preform assembly is drawn so that the preform body deforms at a first deformation rate to a smaller cross-sectional area and the first element substantially maintains a constant cross-sectional area throughout the drawing process. Upon completion of the drawing step, the cross-sectional area of the channel is equivalent to the cross-sectional area of the first element.

A multicore fiber is provided. The multicore fiber includes a plurality of cores spaced apart from one another, and a cladding surrounding the plurality of cores and defining a substantially rectangular or cross-sectional shape having four corners. Each corner has a radius of curvature of less than 1000 microns. The multicore fiber may be drawn from a preform in a circular draw furnace in which a ratio of a maximum cross-sectional dimension of the preform to an inside diameter of the preform to an inside diameter of the draw furnace is greater than 0.60. The multicore fiber may have maxima reference surface.

A preform element, it production and fiber production methods from preform assemblies are disclosed. 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 comprises 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.

The invention relates to a method of manufacturing an active optical fiber having a cladding and a doped core, as well as the active optical fiber equipped with the cladding and the doped core. The active optical fiber according to the invention is adapted to conduct and generate radiation having a wavelength and is provided with a cladding and a core containing at least one active dopant, characterized in that the core comprises elongate elements made of a first type of glass having a first refractive index n.sub.1 and elongate elements of a second type of glass having a second refractive index n.sub.2, oriented along the optical fiber and forming a compact bundle, wherein transverse dimensions of the elongate core elements are smaller than of the wavelength . Such optical fibers are used in laser generation and in amplification techniques.

Preform for an optical waveguide containing a core with a non-circular geometry and at least one cladding layer, in which the dopand concentration of the cladding layer is increased compared to the dopand concentration of a preform with circular core geometry and identical NA. A method for the production of a preform for an optical fiber is provided. An optical waveguide with a nominal dopand concentration of c(eff)Fc(nom) in at least one cladding layer is also provided.

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.