Disclosed is an ultralow loss hollow-core antiresonant fiber, which includes an outer layer structure, a hollow-core area and a plurality of closed cavities. The radial section of the inner surface of the outer layer structure is a circle with a first radius. In the circumferential direction of the inner surface of the outer layer structure, the plurality of the closed cavities are spaced from one another and are distributed uniformly and circumferentially. Each closed cavity includes: an outermost wall serving as a first thin wall, and the radial section of the outermost wall is a fan shape or a circle with a second radius. Each closed cavity further includes: second thin walls located in the inner space surrounded by the inner surface of the outermost wall, and the end surfaces of the second thin walls are annular thin-walled structures with thin-walled spacers arranged in the centers.

A preform (10) for an antiresonant hollow core optical fibre comprises an outer jacket tube (12) having an inner surface and a central longitudinal axis (24); a plurality of antiresonant cladding tubes (14) spaced apart at predefined peripheral locations around the inner surface of the outer jacket tube (12), each antiresonant cladding tube (14) in contact with the inner surface such that a central longitudinal axis (26) of each antiresonant cladding tube (14) is at a first radial distance from the central longitudinal axis (24) of the outer jacket tube (12); and a plurality of spacing elements (22) disposed alternately with the antiresonant cladding tubes (14) and each in contact with an outer surface of each of two adjacent antiresonant cladding tubes (14) at one or more contact points (28), the contact points (28) at a second radial distance from the central longitudinal axis (24) of the outer jacket tube (12), the second radial distance being greater than the first radial distance.

According to embodiments of the present invention, a fiber preform or an optical fiber is provided. The fiber preform or the optical fiber includes a core region having a plurality of cores, wherein two cores of the plurality of cores are bridged by an air gap, and a cladding arrangement including a first cladding region having a plurality of structures surrounding the core region, and a second cladding region in between the core region and the first cladding region, the second cladding region having a plurality of tubes, wherein at least one split is defined in the second cladding region. According to further embodiments of the present invention, a method for forming the fiber preform, a method for forming the optical fiber, an optical coupler having the optical fiber, an optical combiner having the optical fiber, and an optical apparatus having the optical fiber are also provided.

A method of processing an out-coupling end of a hollow core fiber including a plurality of anti-resonance elements surrounding a hollow core, and a hollow core fiber having been so processed. The method may include performing a tapering step to form a taper in the anti-resonance elements; performing a cleaving step at the taper to form at least one tapered out-coupling end of the hollow core fiber; and performing an end processing step including further heating the out-coupling end in a controlled manner to smoothen the out-coupling end.

A hollow core photonic crystal fiber (PCF) including an outer cladding region and seven hollow tubes surrounded by the outer cladding region. Each of the hollow tubes is fused to the outer cladding to form a ring defining an inner cladding region and a hollow core region surrounded by the inner cladding region. The hollow tubes are not touching each other, but are arranged with distance to adjacent hollow tubes. The hollow tubes each have an average outer diameter d2 and an average inner diameter d1, wherein d1/d2 is equal to or larger than about 0.8, such as equal to or larger than about 0.85, such as equal to or larger than about 0.9. Also, a laser system.

An optical fiber may comprise a core doped with one or more active ions to guide signal light from an input end of the optical fiber to an output end of the optical fiber, a cladding surrounding the core to guide pump light from the input end of the optical fiber to the output end of the optical fiber, and one or more inserts formed in the cladding surrounding the core. The core may have a geometry (e.g., a cross-sectional size, a helical pitch, and/or the like) that varies along a longitudinal length of the optical fiber, which may cause an absorption of the pump light to be modulated along the longitudinal length of the optical fiber.

The invention generally relates to optical fibers, and, more particularly, to hollow-core optical fibers and cables for use in high-speed data transmission, including transmission of telecommunications data, and methods of manufacturing such hollow-core optical fibers and cables.

A Photonic Crystal Fiber (PCF) a method of its production and a supercontinuum light source comprising such PCF. The PCF has a longitudinal axis and includes a core extending along the length of said longitudinal axis and a cladding region surrounding the core. At least the cladding region includes a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the PCF in at least a microstructured length section. In at least a degradation resistant length section of the microstructured length section the PCF includes hydrogen and/or deuterium. In at least the degradation resistant length section the PCF further includes a main coating surrounding the cladding region, which main coating is hermetic for the hydrogen and/or deuterium at a temperature below T.sub.h, wherein Th is at least about 50° C., preferably 50° C.<Th.sub.h<250° C.

A hollow core photonic crystal fiber (PCF) including an outer cladding region and seven hollow tubes surrounded by the outer cladding region. Each of the hollow tubes is fused to the outer cladding to form a ring defining an inner cladding region and a hollow core region surrounded by the inner cladding region. The hollow tubes are not touching each other, but are arranged with distance to adjacent hollow tubes. The hollow tubes each have an average outer diameter d2 and an average inner diameter d1, wherein d1/d2 is equal to or larger than about 0.8, such as equal to or larger than about 0.85, such as equal to or larger than about 0.9. Also, a laser system.

Methods are known for producing an anti-resonant hollow-core fiber which has a hollow core extending along a fiber longitudinal axis and an inner jacket region that surrounds the hollow core, said jacket region comprising multiple anti-resonant elements. The known methods have the steps of: providing a cladding tube that has a cladding tube inner bore and a cladding tube longitudinal axis along which a cladding tube wall extends that is delimited by an interior and an exterior; providing a number of tubular anti-resonant element preforms; arranging the anti-resonant element preforms at target positions of the interior of the cladding tube wall, thereby forming a primary preform which has a hollow core region and an inner jacket region; and elongating the primary preform in order to form the hollow-core fiber or further processing the primary preform in order to form a secondary preform. The aim of the invention is to achieve a high degree of precision and an exact positioning of the anti-resonant elements in a sufficiently stable and reproducible manner on the basis of the aforementioned methods. This is achieved in that while further processing the primary preform according to step (c), an external layer cylinder is used which has a radial viscosity profile such that the viscosity increases towards the interior of the external layer cylinder.