A few-mode optical fiber including a core's refractive-index profile n(r) of trapezoid-like shape. The optical core having a center part of radius R1 and a transition part ranges from the radius R1 to a radius R2, such that R2>R1 with R2 between 6.8 and 11.5 m, said refractive-index profile being defined by a surface integral of the core index profile of between 18010.sup.3 and 27010.sup.3 m; a transition slope S of between 1.710.sup.3 and 1210.sup.3 m.sup.1; with n1 and n2 the refractive-index difference respectively of the center part of the optical core and of the cladding part adjacent to the optical core, with respect to the outer optical cladding.

An optical fiber device may include a unitary core including a primary section and a secondary section, wherein at least a portion of the secondary section is offset from a center of the unitary core, wherein the unitary core twists about an optical axis of the optical fiber device along a length of the optical fiber device, and wherein a refractive index of the primary section is greater than a refractive index of the secondary section; and a cladding surrounding the unitary core.

A method includes generating a multimode laser beam having an initial beam parameter product (bpp) and directing the multimode laser beam to an input end of a fiber so as to produce an output beam at an output of the fiber with a final bpp that is greater than the initial bpp. Another method includes measuring a base bpp associated with a multimode laser beam generated from a laser source and emitted from an output fiber output end, determining a bpp increase for the multimode laser beam, and selecting a bpp increasing optical fiber having an input end and an output end so that the multimode laser beam with the base bpp coupled to the input end has an output bpp at the output end of the bpp increasing optical fiber corresponding to the determined bpp increase.

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.

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 invention concerns an apparatus and its use for laser processing. The invention also concerns a method and an optical component. According to the invention, at a first laser device, providing a first optical feed fiber and a second laser device providing a second optical feed fiber is provided. A beam combining means connected to the first and second feed fibers and to a multi-core optical fiber is adapted to form a composite laser beam by having the first optical feed fiber aligned with a first core of the multi-core optical fiber and the second optical feed fiber aligned with at least one second core of the multi-core optical fiber. The first and second cores outputs a composite laser beam to a workpiece to be processed. A control unit controls power density of at least one of first and second laser beams of the composite laser beam in at least one of: in response to approaching a change point in direction of cutting progression and to cause change in relation between the power density of the first output laser beam and power density of the second output laser beam in accordance with thickness of the workpiece being cut.

An optical fiber according to an embodiment comprises, as a structure suitable for large capacity transmission over a long haul, a core, a cladding having an outer diameter of 80 m or more and 130 m or less, a primary coating, and a secondary coating having elasticity higher than that of the primary coating and an outer diameter of 210 m or less. The optical fiber having the structure as described above has an MFD of 10 m or more at a wavelength of 1550 nm, a cable cutoff wavelength longer than 1260 nm, and a microbending loss of 0.6 dB/km or less at a wavelength of 1550 nm.

Disclosed is an annular-beam coupling system enabling reduction of noise generated from a core of a double-clad fiber. The disclosed annular-beam coupling system comprises: a fiber for transmitting light of a light source; a collimator for receiving the light outputted from the fiber and forming a parallel beam of a circular shape; an annular-beam generation unit for converting the parallel beam into an annular beam; and a double-clad fiber having the annular beam coupled to a cladding region thereof.

The present embodiment relates to an optical device or the like that is high in non-linearity and resistance to UV light and includes a structure allowing stable wavelength conversion. The optical device is comprised of glass containing SiO.sub.2 and comprises a repetitive structure including first sections being crystallized regions in which a radial polarization-ordered structure is formed and second sections being non-crystallized regions alternately arranged along a center axis extending from a center of a light-incidence end face toward a center of a light-emission end face.

An optical fiber device may include a unitary core including a primary section and a secondary section, wherein at least a portion of the secondary section is offset from a center of the unitary core, wherein the unitary core twists about an optical axis of the optical fiber device along a length of the optical fiber device, and wherein a refractive index of the primary section is greater than a refractive index of the secondary section; and a cladding surrounding the unitary core.