A multicore optical fiber comprises a common cladding and a plurality of core portions disposed in the common cladding. Each of the core portions includes a central axis, a core region extending from the central axis to a radius r.sub.1, the core region comprising a relative refractive index Δ.sub.1, an inner cladding region extending from the radius r.sub.1 to a radius r.sub.2, the inner cladding region comprising a relative refractive index Δ.sub.2, and a depressed cladding extending from the radius r.sub.2 to a radius r.sub.3, the depressed cladding region comprising a relative refractive index Δ.sub.3 and a minimum relative refractive index Δ.sub.3 min. The relative refractive indexes may satisfy Δ.sub.1>Δ.sub.2>Δ.sub.3 min. The mode field diameter of each core portion may greater than or equal to 8.2 μm and less than or equal to 9.5 μm.

A multi-core optical amplifying fiber includes: core portions doped with a rare-earth element; an inner cladding portion; and an outer cladding portion. A mode field diameter of each core portion at a wavelength at which the rare-earth element performs optical amplification is 5 μm to 11 μm, a relative refractive-index difference of the maximum refractive index of each core portion with respect to the inner cladding portion is 0.35% to 2%, a core-to-core distance is set such that total inter-core crosstalk is −40 dB/100 m or lower in an optical amplification wavelength band subjected to the optical amplification, a cladding thickness is smaller than a value obtained by adding the mode field diameter to a minimum value of the core-to-core distance, and a ratio of a total sectional area of the core portions to a sectional area of the inner cladding portion is 1.9% or more.

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.

The disclosed embodiments generally relate to extruding multiple layers of micro- to nano-polymer layers in a tubular shape. In particular, the aspects of the disclosed embodiments are directed to a method for producing a Bragg reflector comprising co-extrusion of micro- to nano-polymer layers in a tubular shape.

An optical fiber can include a core comprising silica co-doped with nitrogen and chlorine and an outer cladding surrounding the core. In some aspects, the core can be characterized by an annealing temperature of less than or equal to about 1150° C. and/or the core can include a relative refractive index Δ.sub.core in a range of from about 0.15% to about 0.45%.

The disclosed embodiments generally relate to extruding multiple layers of micro- to nanopolymer layers in a tubular shape. In particular, the aspects of the disclosed embodiments are directed to a method for producing a Bragg reflector comprising co-extrusion of micro- to nanopolymer layers in a tubular shape.

The present embodiment relates to an MCF having a low transmission loss and having a structure for reducing a transmission loss and effectively suppressing an inter-core XT. The uncoupled MCF includes alkali metal having a predetermined concentration in which each of a plurality of cores contributes to reduction in the transmission loss, and a core pitch is set so that a sum h_.sub.total of power coupling coefficients of a specific core and the remaining all cores of the plurality of cores is 2.3×10.sup.−4/km or less.

Embodiments of the invention are directed a waveguide having a first waveguide segment that includes a set of first waveguide segment confinement parameters; a second waveguide segment having routing bends and a set of second waveguide segment confinement parameters; and a third waveguide segment having a set of third waveguide segment confinement parameters. The waveguide is configured to guide optical data according to an asymmetric optical-loss performance curve that is a plot of the sets of first, second, and third waveguide segment confinement parameters on a first axis; and a level of optical-loss performance that results from the sets of first, second, and third waveguide segment confinement parameters on a second axis. The sets of first, second, and third waveguide segment confinement parameters are configured to, collectively, maximize a predetermined worst-case optical-loss performance level of the asymmetric optical-loss performance curve within a range of waveguide fabrication tolerances.

Large mode area optical fibers include cores that are selected to be smaller than a core size associated with a minimum mode field diameter of a lowest order mode. Cross-sectional shape of such cores can be circular or annular, and a plurality of such cores can be used. Gain regions can be provided in cores or claddings, and selected to produce a selected state of polarization.

A bandpass filter may include a set of layers. The set of layers may include a first subset of layers. The first subset of layers may include hydrogenated germanium (Ge:H) with a first refractive index. The set of layers may include a second subset of layers. The second subset of layers may include a material with a second refractive index. The second refractive index may be less than the first refractive index.