A single mode optical fiber having a core made from silica and less than or equal to about 11 weight % germania and having a maximum relative refractive index Δ.sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index Δ.sub.2MIN, a first outer cladding surrounding the inner cladding and a second outer cladding surrounding the first outer cladding. The viscosity at 1650° C. of the second outer cladding minus the viscosity at 1650° C. of the first outer cladding is greater than 0.1e.sup.7 Poise, and Δ.sub.1MAX>Δ.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The first outer cladding has a maximum relative refractive index Δ.sub.3MAX, and Δ.sub.3MAX>Δ.sub.2MIN.

An optical fiber manufacturing method includes setting a first holding member and a rod inside a glass pipe, the first holding member made of glass and having plural holes formed, so that the rod is supported by the first holding member; filling glass particles between the rod and a glass pipe inner wall; holding the rod such that the rod and the filled glass particles are enclosed by the glass pipe inner wall and the first and second holding members, and sealing one end of the glass pipe and manufacturing an intermediate; and manufacturing an optical fiber from the intermediate, wherein a bulk density of the first and second holding members is set with reference to a bulk density of a filling portion made from the glass particles, and the predetermined range is determined according to a core diameter permissible variation range in its longitudinal direction.

In some implementations, a waveguide may comprise an inner core to receive a first beam and an outer core surrounding the inner core to receive a second beam that is displaced from the first beam by an offset. The outer core may comprise a beam guiding region that rotationally expands over a length of the waveguide into an annulus that concentrically surrounds the inner core or a partial annulus that partially surrounds the inner core. For example, the beam guiding region may be defined by one or more low refractive index features that have a varied orientation and/or a varied shape over the length of the waveguide such that the second beam enters the waveguide as an offset beam and exits from the waveguide as a ring-shaped beam or a partial ring-shaped beam.

Methods and systems for generating a laser beam with different beam profile characteristics are provided. In one aspect, a method includes coupling an input laser beam into one fiber end of a multi-clad fiber, in particular a double-clad fiber and emitting an output laser beam from the other fiber end of the multi-clad fiber. To generate different beam profile characteristics of the output laser beam, the input laser beam is electively coupled either at least into the inner fiber core of the multi-clad fiber or at least into at least one outer ring core of the multi-clad fiber, or a first sub-beam of the input laser beam is coupled into at least into the inner fiber core of the multi-clad fiber and a second, different sub-beam of the input laser beam is coupled at least into the at least one outer ring core of the multi-clad fiber.

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.

Methods and systems for generating a laser beam with different beam profile characteristics are provided. In one aspect, a method includes coupling an input laser beam into one fiber end of a multi-clad fiber, in particular a double-clad fiber and emitting an output laser beam from the other fiber end of the multi-clad fiber. To generate different beam profile characteristics of the output laser beam, the input laser beam is electively coupled either at least into the inner fiber core of the multi-clad fiber or at least into at least one outer ring core of the multi-clad fiber, or a first sub-beam of the input laser beam is coupled into at least into the inner fiber core of the multi-clad fiber and a second, different sub-beam of the input laser beam is coupled at least into the at least one outer ring core of the multi-clad fiber.

A quantum communications system includes a quantum key generation system having a photonic quantum bit generator, a dispersion compensating optical fiber link, and a photon detector unit and a communications network having a signal generator, a signal channel, and a signal receiver. The dispersion compensating optical fiber link extends between and optically couples the photonic quantum bit generator and the photon detector unit. Further, the dispersion compensating optical fiber link is structurally configured to induce dispersion at an absolute dispersion rate of about 9 ps/(nm)km or less and induce attenuation at an attenuation rate of about 0.18 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 about 10 Gbit/sec.

A combined optical coherent tomography (OCT) pressure sensor system includes an optical cable comprising a single-mode core and a multi-mode core. An OCT optical imaging sensor near a distal end of the optical cable can be inserted into a lumen of a living being. First light exiting a distal end of the single-mode core illuminates an interior of the lumen. The OCT optical imaging sensor acquires image information about the interior of the lumen and transmits an optical signal carrying the image information into the distal end of the single-mode core, toward a proximal end of the single-mode core. An optical pressure sensor attached near the OCT optical imaging sensor receives second light from the distal end of the optical cable, senses ambient pressure within the lumen and transmits an optical signal indicative of the ambient pressure into a distal end of the multi-mode core, toward a proximal end of the multi-mode core.

A low-dispersion single-mode fiber includes a core and claddings covering the core. The core layer has a radius in a range of 3-5 μm and a relative refractive index difference in a range of 0.15% to 0.45%. The claddings comprise a first depressed cladding, a raised cladding, a second depressed cladding, and an outer cladding arranged sequentially from inside to outside. The first depressed cladding has a unilateral width in a range of 2-7 μm and a relative refractive index difference in a range of −0.4% to 0.03%. The raised cladding has a unilateral width in a range of 2-7 μm and a relative refractive index difference in a range of 0.05% to 0.20%. The second depressed cladding has a unilateral width in a range of 0-8 μm and a relative refractive index difference in a range of 0% to −0.2%. The outer cladding is formed of pure silicon dioxide glass.

Methods and systems for generating a laser beam with different beam profile characteristics are provided. In one aspect, a method includes coupling an input laser beam into one fiber end of a multi-clad fiber, in particular a double-clad fiber and emitting an output laser beam from the other fiber end of the multi-clad fiber. To generate different beam profile characteristics of the output laser beam, the input laser beam is electively coupled either at least into the inner fiber core of the multi-clad fiber or at least into at least one outer ring core of the multi-clad fiber, or a first sub-beam of the input laser beam is coupled into at least into the inner fiber core of the multi-clad fiber and a second, different sub-beam of the input laser beam is coupled at least into the at least one outer ring core of the multi-clad fiber.