An apparatus includes a multi-mode optical fiber having a selected plurality of optical propagating modes. The selected plurality may include only a proper subset of or may include all of the optical propagating modes of the multi-mode optical fiber. Each optical propagating mode of the selected plurality has a group velocity that varies over a corresponding range for light in, at least, one of the optical telecommunications C-band, the optical telecommunications L-band, and the optical telecommunications S-band. The ranges corresponding to different ones of the modes of the selected plurality are non-overlapping. The ranges of a group velocity-adjacent pair of the ranges are separated by a nonzero gap of less than about 10,000 meters per second.

A quantum communications system includes a quantum key generation system having a photonic quantum bit generator, a low loss dispersion limiting fiber having a length L, for example greater than 200 km, and a photon detector unit and a communications network having a signal generator, a signal channel, and a signal receiver. The low loss dispersion limiting fiber extends between and optically couples the photonic quantum bit generator and the photon detector unit. Further, the low loss dispersion limiting fiber is structurally configured to limit dispersion at an absolute dispersion rate of about 9 ps/(nm)km or less, and preferably 0.5 ps/(nm)km or less, and induce attenuation at an attenuation rate of about 0.175 dB/km or less such that the quantum key bit information of a plurality of photons output by the one or more photonic quantum bit generators is receivable at the photon detector unit at a bit rate of at least 10 Gbit/sec.

A microstructured optical fiber having a length and a longitudinal axis along its length, the finer including a core region capable of guiding light along the longitudinal axis and a cladding region which surrounds the core region, the cladding region comprising a cladding background material and a plurality of cladding features within the cladding background material, the cladding features being arranged around the core region, wherein the cladding region comprises an inner cladding region comprising an innermost ring of cladding features and an outer cladding region comprises outer cladding rings of outer cladding features, the innermost ring consisting of those cladding features being closest to the core region, wherein the rings of cladding features each comprise bridges of cladding background material separating adjacent features of the ring, wherein the bridges of the innermost ring have an average minimum width (w1), the minimum width of a bridge of a ring being the shortest distance between two adjacent features of the ring; and wherein at least one outer cladding ring has an average minimum width (w2) of bridges that is larger than the average minimum width (w1) of the bridges of the innermost ring. Also described are a cascade optical fiber with at least one fiber as described, as well as a source of supercontinuum radiation.

A hollow-core photonic crystal fiber (HC-PCF) assembly for converting input radiation to broadband radiation, the hollow core fiber assembly including: a micro-structured fiber with a hollow core extending along a length of the fiber from an input end configured to receive input radiation to an output end configured to output broadband radiation, wherein the hollow core of the fiber is configured to include a medium; and a density control system configured to control a density profile of the medium along at least a part of the length of the fiber to establish a desired zero dispersion wavelength profile along at least a part of the length of the fiber.

Optical pulse sources. In one example, the pulse source includes an optical fiber ring resonator with at least one normal dispersion fiber segment characterized by a positive group velocity dispersion (GVD) per unit length and at least one anomalous dispersion fiber segment characterized by a negative GVD per unit length. In another example, the pulse source includes an optical fiber ring resonator with one or more fiber segments having a positive net group velocity dispersion (GVD); and an intracavity spectral filter optically coupled to the one or more fiber segments. The pulse source is configured to generate one or more optical solitons in the optical fiber ring resonator.

Embodiments of the current disclosure include low moat volume single mode ultra-low loss optical fibers. In some embodiments, a single mode optical fiber includes a first core region; a second core region surrounding and directly adjacent to the first core region, wherein a volume V of the second core region is less than or equal to 14% Δμm.sup.2; a cladding region surrounding the core region; and wherein the optical fiber has a cable cutoff of less than 1260 nm, a mode field diameter at 1310 nm of 8.6 microns to 9.7 microns, a mode field diameter at 1550 nm of 9.9 microns to 11 microns, and an attenuation at 1550 nm of less than or equal to 0.17 dB/km.

An optical fiber includes: a core made of silica based glass; a cladding made of silica based glass, the cladding having a refractive index that is lower than a maximum refractive index of the core; and a coating including a primary coating layer, and a secondary coating layer. An outer diameter of the cladding is less than 100 μm. A thickness of the primary coating layer is larger than or equal to 15 μm. A mode field diameter at a wavelength of 1310 nm is larger than or equal to 8.6 μm and smaller than or equal to 9.2 μm. An effective cutoff wavelength is smaller than or equal to 1260 μm. A bending loss at a wavelength of 1550 nm when bending is made at a diameter of 60 mm is smaller than or equal to 0.1 dB/100 turn.

Disclosed herein is a method comprising injecting light of a first wavelength λ.sub.1 into a wavelength division multiplexer; injecting light of a second wavelength λ.sub.2 into the wavelength division multiplexer; combining the light of the first wavelength λ.sub.1 and the light of the second wavelength λ.sub.2 in the wavelength division multiplexer to produce light of a third wavelength λ.sub.3; and reflecting the light of the third wavelength λ.sub.3 in a dual-Brillouin peak optical fiber that is in communication with the wavelength divisional multiplexer; wherein the dual-Brillouin peak optical fiber has at least two Brillouin peaks, such that an amplitude A.sub.1 of at least one of said Brillouin peaks is within 50% to 150% of an amplitude A.sub.2 of another Brillouin peak 0.5A2≤A.sub.1≤1.5A.sub.2; wherein the dual-Brillouin peak optical fiber generates a Brillouin dynamic grating that reflects an improved back-reflected Brillouin signal of the combined light.

A optical fiber comprising a central core region having an outer radius r.sub.1 of 3 μm to 7 μm, and a maximum refractive index Δ.sub.1 of 0.25% to 0.5% and an alpha (a) profile of 1 to 20; a cladding region comprising (i) a first inner cladding region surrounding the core, having a refractive index Δ.sub.2 of −0.25% to 0.05% and a radius r.sub.2 of 6 μm to 15 μm, (ii) a second inner cladding region, surrounding the first inner cladding region, having a refractive index Δ.sub.3 of −0.1% to 0.2% and a radius r.sub.3 of 7 μm to 15 μm, and (iii) an outer cladding region, surrounding the second inner cladding region, having a refractive index Δ.sub.4 between −0.05% to 0.1%; wherein the optical fiber exhibits a cable cutoff of less than 1260 nm, a mode field diameter at 1310 nm of greater than 8.2 microns.

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 μm, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.