A quantum communication system that includes a multiphoton entanglement generator, a plurality of photon detector units, and a plurality of optical fiber links. The plurality of photon detector units include a first photon detector unit and a second photon detector unit. The multiphoton entanglement generator is structurally configured to output more than two entangled photons. The plurality of optical fiber links comprise a first optical fiber link optically coupled to the multiphoton entanglement generator and disposed between the multiphoton entanglement generator and the first photon detector unit. The plurality of optical fiber links comprise a second optical fiber link optically coupled to the multiphoton entanglement generator and disposed between the multiphoton entanglement generator and the second photon detector unit. Further, at least one of the plurality of optical fiber links has a core, a cladding, and a scattering region having a plurality of scattering structures.

An optical fiber distributed sensing system may include an optical fiber for distributed sensing. The optical fiber may include a core including glass and diamond particles with nitrogen-vacancy (NV) centers distributed within the glass. The optical fiber may also include at least one glass layer surrounding the core. An optical source may be coupled to the optical fiber and operable from an end thereof. An optical detector may be coupled to the optical fiber to detect fluorescence therefrom.

An optical fiber heating device includes a heat producing fiber wrapped around a cell which is filled with an atom vapor.

A low-crosstalk large-capacity few-mode optical fiber includes an optical fiber cladding. Few-mode units are arranged in the optical fiber cladding, each few-mode unit sequentially includes a few-mode fiber core, an inner cladding and a trench from inside to outside, and a high-refractive-index ring is arranged in the few-mode fiber core. The few-mode units include first few-mode subunits, second few-mode subunits and third few-mode subunits, where the first few-mode subunits, the second few-mode subunits and the third few-mode subunits are arranged at intervals. The first few-mode subunit includes a first few-mode fiber core, the second few-mode subunit includes a second few-mode fiber core, and the third few-mode subunit includes a third few-mode fiber core, the radii and refractive indexes of the first few-mode fiber cores, the second few-mode fiber cores and the third few-mode fiber cores being different, respectively.

A gain flattening filter includes a first optical fiber that has a core, a first cladding, and a second cladding and that has a uniform composition in a length direction; and a pair of second optical fibers fused to both ends of the first optical fiber. The first optical fiber has a first section in which a slanted refractive index grating is formed and a pair of second sections connecting both ends of the first section to the pair of second optical fibers. The first cladding contains a photosensitive material whose refractive index increases upon irradiation with light having a specific wavelength. In the core, a tensile stress remains in the first section. An average MFD of the second sections is larger than an average MFD of the second optical fibers and smaller than an average MFD of the first section.

An optical fiber containing alkali metal elements or the like in which Rayleigh scattering loss can be reduced is provided. An optical fiber includes a core composed of silica glass and a cladding which surrounds the core, has a refractive index lower than a refractive index of the core, and is composed of silica glass containing fluorine. The core contains a first group of dopants and a second group of dopants having a diffusion coefficient lower than a diffusion coefficient of the first group of dopants. The difference between the maximum value and the minimum value of residual stress in the optical fiber is 150 MPa or less.

The invention concerns 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 comprises a core extending along the length of said longitudinal axis and a cladding region surrounding the core. At least the cladding region comprises 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 comprises hydrogen and/or deuterium. In at least the degradation resistant length section the PCF further comprises a main coating surrounding the cladding region, which main coating is hermetic for the hydrogen and/or deuterium at a temperature below Th, wherein Th is at least about 50° C., preferably 50° C.<Th<250° C.

One of embodiments relates to an optical fiber in which an alkali metal element is efficiently doped to its core to suppress transmission loss from increasing. A mean concentration or a concentration distribution of the alkali metal element is adjusted such that 0.48 or less is obtained as an weighted value obtained by weighting a distribution of field intensity of guided light at a wavelength of 1550 nm, with respect to a radial direction distribution of a ratio I.sub.D2/I.sub.ω3 of an intensity I.sub.D2 of Raman scattering light by a silica three-membered ring structure and an intensity I.sub.ω3 of Raman scattering light by a Si—O stretching vibration, in a cross-sectional region having a diameter of 20 μm.

An optical fiber comprises a glass fiber, and a coating resin layer having a primary resin layer and a secondary resin layer, wherein the primary resin layer consists of a cured resin composition containing an oligomer, a monomer and a photopolymerization initiator, the oligomer is a reaction product of a specific polyol compound, a polyisocyanate compound, and a hydroxyl group-containing acrylate compound, the photopolymerization initiator includes 2,4,6-trimethylbenzoyldiphenyl phosphine and 1-hydroxycyclohexyl phenyl ketone at a mass ratio of 5:1 to 1:1, and a content of 2,4,6-trimethylbenzoyldiphenyl phosphine in the resin composition is 1.5 to 2.5% by mass.

Method and apparatus for producing metal-coated optical fiber involves providing a length of optical fiber having a glass fiber with or without a carbon layer surrounded by a liquid-soluble polymeric coating. The optical fiber is passed through a series of solution baths such that the fiber will contact the solution in each bath for a predetermined dwell time, the series of solution baths effecting removal of the polymer coating and subsequent electroless plating of metal on the glass fiber. The optical fiber is collected after metal plating so that a selected quantity of the metal-coated optical fiber is gathered, Preferably, the glass fiber passes through the series of solution baths without contacting anything except for the respective solution in each.