Described and claimed herein are radiation curable compositions for coating an optical fiber, particularly primary coating compositions, wherein the composition possesses specified liquid glass transition temperatures, and/or viscosity ratios between, e.g., 25 C. and 85 C. Such compositions possess preferably high amounts of a reactive oligomer component with a backbone not derived from polypropylene glycol, preferably reactive oligomers with select diisocyanate constituents, one or more reactive diluent monomers, a photoinitiator, and optionally, one or more additives. Such compositions also are preferably sufficiently viscous at room temperature to ensure optimum optical fiber coating processability. Also described are methods of coating the radiation curable compositions elsewhere described, and the fiber optic coatings resulting therefrom.

An optical receptacle includes a fiber stub, a block, and a first elastic member. The fiber stub includes an optical fiber, and a ferrule provided on one end side of the optical fiber. The block is separated from the ferrule and has one end surface, an other end surface, and a through-hole extending from the one end surface to the other end surface. A portion of the optical fiber protrudes from the ferrule and is inserted into the through-hole. The first elastic member fixes the optical fiber in the through-hole. The portion of the optical fiber includes first to third portions. The second portion is provided between the first portion and the third portion. A core diameter at the first portion is smaller than a core diameter at the third portion. A core diameter at the second portion increases from the first portion toward the third portion.

An optical system comprising an optical conduit (e.g., gain fiber or rare-earth-doped fiber) with a bend having a bend radius (R). The bend induces a tension and a compression in the fiber core, which results in a corresponding strain (). The corresponding bend-induced strain impacts the signal properties in the core of the fiber.

An optical fiber includes: a core made of silica-based glass; a cladding configured to cover an outer circumference of the core and made of silica-based glass having a refractive index smaller than a maximum refractive index of the core; and a coating configured to cover an outer circumference of the cladding. The cladding has an outer diameter of 120 m or smaller, a mode field diameter at a wavelength of 1310 nm is 8.6 m to 9.2 m, an effective cut-off wavelength is 1260 m or smaller, and a bending loss at a wavelength of 1550 nm in a case of bending at a diameter of 20 mm is 0.75 dB/turn or smaller.

As described herein, a mode field adapter (MFA) comprises a first fiber including a core associated with a fundamental mode field diameter and a cladding with a diameter that decreases toward a waist. The MFA comprises a second fiber including a core associated with a fundamental mode field diameter that matches the fundamental mode field of the first fiber at the waist and a cladding with a diameter that matches the diameter of the cladding of the first fiber at the waist and increases from the waist of the second fiber. The cladding of the first fiber may be adiabatically etched such that a core-to-cladding ratio of the first fiber changes over a length of the first fiber, and the core and the cladding of the second fiber may be adiabatically tapered such that a core-to-cladding ratio of the second fiber is constant over a length of the second fiber.

A method of processing by controlling one or more beam characteristics of an optical beam may include: launching the optical beam into a first length of fiber having a first refractive-index profile (RIP); coupling the optical beam from the first length of fiber into a second length of fiber having a second RIP and one or more confinement regions; modifying the one or more beam characteristics of the optical beam in the first length of fiber, in the second length of fiber, or in the first and second lengths of fiber; confining the modified one or more beam characteristics of the optical beam within the one or more confinement regions of the second length of fiber; and/or generating an output beam, having the modified one or more beam characteristics of the optical beam, from the second length of fiber. The first RIP may differ from the second RIP.

An optical fiber includes: a core portion made of glass; and a cladding portion made of glass, having a refractive index lower than the refractive index of the core portion, and positioned on an outer periphery of the core portion. Further, the cladding portion has an outer diameter smaller than 100 m, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.

An optical fiber according to an embodiment includes: a core; an inner cladding surrounding the core and having a refractive index smaller than a refractive index of the core; an outer cladding surrounding the inner cladding and having a smaller refractive index than the refractive index of the core and having a refractive index greater than the refractive index of the inner cladding, in which a ratio of a caustic radius to a MAC-value (caustic radius/MAC-value) at a bending radius of 10 mm at a wavelength of 1625 nm is 2.70 m or more.

Disclosed herein are methods, apparatus, and systems for providing an optical beam delivery system, comprising an optical fiber including a first length of fiber comprising a first RIP formed to enable, at least in part, modification of one or more beam characteristics of an optical beam by a perturbation assembly arranged to modify the one or more beam characteristics, the perturbation assembly coupled to the first length of fiber or integral with the first length of fiber, or a combination thereof and a second length of fiber coupled to the first length of fiber and having a second RIP formed to preserve at least a portion of the one or more beam characteristics of the optical beam modified by the perturbation assembly within one or more first confinement regions. The optical beam delivery system may include an optical system coupled to the second length of fiber including one or more free-space optics configured to receive and transmit an optical beam comprising the modified one or more beam characteristics.

An optical fiber includes: a core; a depressed layer surrounding the core; and a cladding surrounding the depressed layer. A refractive index profile of the core is an -th power distribution having an index of 1.0 or more and 2.9 or less. A relative refractive index difference .sup. of the depressed layer with respect to the cladding has an absolute value |.sup.| that is 0.05% or more and 0.15% or less. A ratio r1/r2 of a radius r1 of the core to an outer radius r2 of the depressed layer is 0.35 or more and 0.60 or less. A cable cutoff wavelength cc of 22 m is less than 1.26 m. A mode field diameter at a wavelength of 1.31 inn is larger than 8.6 inn and smaller than 9.5 m.