A lens assembly for an optical fiber includes an optical gap structure and a multi-mode optical fiber. The optical gap structure has first and second ends and a length measured therebetween. The first end of the optical gap structure is configured to attach to an end of a single-mode optical fiber. The multi-mode optical fiber has first and second ends and a length measured therebetween. The first end of the multi-mode optical fiber is attached to the second end of the optical gap structure. The length of the optical gap structure and the length of the multi-mode optical fiber are set to provide a prescribed working distance and a prescribed light beam waist diameter. The prescribed working distance is a distance measured from the second end of the multi-mode optical fiber to a location of the prescribed light beam waist diameter.

A hollow-core photonic crystal fiber (HC-PCF)(10) for guiding at least one mode of a light field(1) along a mode guiding section(11) of the HC-PCF(10), comprises an outer jacket(12), an inner cladding(13) and a hollow core(14), which extend along the HC-PCF(10), wherein the inner clad-ding(13) is arranged on an interior surface of the outer jacket(12) and comprises anti-resonant structures(15) surrounding the hollow core(14), and the hollow core(14) has a mode guiding core diameter(d) provided along the mode guiding section of the HC-PCF(10), and wherein at least one fiber end (16) of the HC-PCF(10) has a light field coupling section(17) in which the hollow core(14) is tapered over an axial coupling section length from a fiber end core diameter(D) at the at least one fiber end (16) to the mode guiding core diameter(d). Furthermore, methods of using the HC-PCF and manufacturing the HC-PCF are described.

A system for positioning an optical preform in a furnace is provided that includes an upper muffle and a downfeed handle assembly with a tube defining a first end and a second end, the second end extending into the upper muffle. A handle is disposed within the tube. A second end of the handle extends into the upper muffle and a seal assembly is positioned around both the tube and the handle. The first end of the handle extends through the seal assembly and a drive assembly is coupled with the downfeed handle.

Provided is an optical fiber coupler capable of suppressing variation of polarization state of light passing through a coupler portion. The optical fiber coupler includes: a substrate having a groove; a coupler portion which is inserted into the groove and to which a middle portion of each of optical fibers is joined; and an adhesive for bonding the coupler portion to the substrate. Shore D hardness of the adhesive is 10 to 35. By setting the Shore D hardness of the adhesive to 10 to 35, it is possible to suppress the variation of the polarization state of the light passing through the coupler portion.

A fused-biconical-taper bend-insensitive single mode optical fiber includes a core and a cladding. The core is a fluorine-germanium co-doped silicon-dioxide quartz glass layer, a diameter D.sub.core thereof is 7-10 m, and a relative refractive index difference 1 thereof is 0.20% to 0.40%. A range of Ge is 0.30% to 0.60%, and a range of F is 0.05% to 0.15%. The cladding includes three layers. A first layer is a fluorine-germanium co-doped silicon-dioxide quartz glass layer, a relative refractive index difference 31 thereof is 0.02% to 0.10%, and a diameter D31 thereof is 15-30 m. A second layer is a fluorine-doped silicon-dioxide quartz glass layer, a relative refractive index difference 32 thereof is 0.01% to 0.05%, and a diameter D32 thereof is 30-50 m. A third layer is a pure silicon-dioxide quartz glass layer, and a diameter D33 thereof is 124-126 m.

An optical fibre (10) which has a first refractive index profile (61) that can be changed by heating to a second refractive index profile (62), at least one first dopant (7) for providing the first refractive index profile, at least one concealed dopant (8), and at least one mobile dopant (9), wherein the mobile dopant has a molar refractivity and is present in a concentration (19) such as to balance a change (146) in the first refractive index profile induced by the concealed dopant, and has a diffusion constant (16) greater than a diffusion constant (15) of the concealed dopant, so that heating of the optical fibre causes the mobile dopant to diffuse more quickly than the concealed dopant, thereby allowing the concealed dopant and the mobile dopant to change the first refractive index profile to the second refractive index profile.

Provided is a method of manufacturing an optical device that includes a multicore fiber including a plurality of cores and a fan-in/fan-out device including single-core fibers that are respectively connected to the cores based on a plurality of connection combinations when the multicore fiber is rotated. The method includes: a first step of determining an optical loss for each of the cores while changing the connection combinations between the single-core fibers and the cores; and a second step of selecting one of the connection combinations according to a result of the first step and connecting an end portion of the multicore fiber and an end portion of the fan-in/fan-out device to connect the single-core fibers with the cores based on the one of the connection combinations.

A multicore optical connector includes: a ferrule in which a plurality of optical fibers with lenses are arranged and held, the optical fibers with lenses having GRIN lenses fused to tips of optical fibers; and a coupling member which couples a pair of the ferrules so that the ferrules oppose each other in a non-contact state and end faces of the ferrules are parallel to each other, wherein the ferrules each have an end face inclined by a set angle .sub.0 relative to a central axis Of, the GRIN lenses are arranged and held parallel to the central axis Of so that a center of arrangement Op is at a position eccentric by t relative to the central axis Of, and the optical fibers with lenses held by the pair of the ferrules have end faces of the GRIN lenses inclined along the end faces of the ferrules.

Provided is a system for and a method of processing an optical fiber, such as tapering an optical fiber. The method includes receiving fiber parameters defining characteristics of an optical fiber, modeling an idealized fiber based on the fiber parameters to establish modeled data, and establishing processing parameters. A processing operation is performed on the optical fiber according to the processing parameters to produce a resultant fiber. Aspects of the resultant fiber are measured to establish measured data. The measured data and the modeled data are normalized to a common axis and a difference between the two is determined. The processing parameters are adjusted based on the differences.

A system for positioning an optical preform in a furnace is provided that includes an upper muffle and a downfeed handle assembly with a tube defining a first end and a second end, the second end extending into the upper muffle. A handle is disposed within the tube. A second end of the handle extends into the upper muffle and a seal assembly is positioned around both the tube and the handle. The first end of the handle extends through the seal assembly and a drive assembly is coupled with the downfeed handle.