An MCF cable according to an embodiment contains a plurality of MCFs each including at least one coupled core group and a common cladding. Λ is set such that κ at a wavelength of 1550 nm is falls within a range of from 1×10.sup.−1 [m.sup.−1] to 1×10.sup.3 [m.sup.−1], and (βΛC.sub.avg)/(2κ) or (βΛC.sub.f)/(2κ) is set in a specific range in a wavelength band of from 1530 nm to 1625 nm, where C.sub.avg [m.sup.−1], C.sub.f [m.sup.−1], and f.sub.twist [turn/m] represent the average curvature, the pseudo-curvature, and the average torsion, respectively, for each MCF, and κ [m.sup.−1], β [m.sup.−1], and Λ [m] represent the coefficient of mode coupling between adjacent cores, the average of propagation constants, and the core center-to-center distance, respectively.

In various embodiments, the beam parameter product and/or numerical aperture of a laser beam is adjusted utilizing a step-clad optical fiber having a central core, a first cladding, an annular core, and a second cladding.

An apparatus for providing multicore fiber (OCF) optical switching is disclosed. The apparatus may include an input fiber to receive an optical signal from an optical source. The apparatus may also include an output fiber to receive the optical signal from the input fiber. The apparatus may further include an optical switch element to provide optical switching between the input fiber and the output fiber. In some examples, at least one of the input fiber and the output fiber may be a multicore fiber (MCF), and the optical switching may be performed between at least one core of the input fiber and the output fiber. In some examples, the optical switch element may provide optical switching using a multicore fiber (MCF) optical switching technique, such as a lens offset technique, a rotation-based technique, a tip-tilt technique, or an orientable optical element technique.

In this multi-core fiber, a plurality of cores are arranged at a prescribed interval, and the peripheries thereof are covered by a cladding having a lower refractive index than the plurality of cores. A resin coating is formed on the outer periphery of the cladding. A colored section is formed on a section of the outer surface of the resin coating in the peripheral direction. The colored section is formed continuously along the length direction of the multi-core fiber. In a multi-core fiber cross section orthogonal to the length direction, the position of a specific core and the peripheral position where the colored section is formed are substantially constant along the length direction of the multi-core fiber. In other words, in the multi-core fiber cross section orthogonal to the length direction, the position of the specific core and the position where the colored section is formed are substantially constant along the length direction of the multi-core fiber.

The present invention relates to an optical fiber sensor for shape sensing, comprising an optical fiber having embedded therein a number of at least four fiber cores (1 to 6) arranged at a distance from a longitudinal center axis (0) of the optical fiber, the number of fiber cores (1 to 6) including a first subset of at least two fiber cores (1, 3, 5) and a second subset of at least two fiber cores (2, 4, 6), the fiber cores (2, 4, 6) of the second subset being arranged to provide a redundancy in a shape sensing measurement of the fiber sensor (12′). The fiber cores (1, 3, 5) of the first subset are distributed in azimuthal direction around the center axis (0) with respect to one another, and each fiber core (2) of the second subset is arranged in non-equidistantly fashion in azimuthal direction around the center axis (0) with respect to two neighboring fiber cores (1, 3) of the first subset.

A connector system includes: a first ferrule configured to hold end parts of multi-core fibers; a second ferrule configured to hold end parts of single-core fibers; and an optical connection member. The optical connection member is arranged between the first and the second ferrule, and includes an optical system configured to optically connect respective cores included in the multi-core fibers and the single-core fibers. A guide pin is formed on one of the first and the second ferrule, and a guide hole is formed in another of the first and the second ferrule. A through hole is formed in the optical connection member, and the first ferrule, the optical connection member, and the second ferrule can be aligned by fitting the guide pin in the guide hole through the through hole.

The inventive configurable optical fiber polarization mode coupler is capable of providing a low-loss, high-coupling coefficient interface with high accuracy and easy alignment between a plurality of optical fibers (or other optical devices) with a first channel-to-channel spacing, and an optical device having a plurality of closely-spaced waveguide interfaces with a second channel-to-channel spacing, where each end of the optical fiber coupler array is configurable to have different channel-to-channel spacing, each matched to a corresponding one of the first and second channel-to-channel spacing, and that are preferably optimized for use with photonic integrated circuits, such as coupling to dense optical input/output interfaces, wafer-level testing, etc. The novel optical coupler array includes a plurality of waveguides (at least one of which may optionally be polarization maintaining), that comprises at least one gradually reduced vanishing core fiber, at least in part embedded within a common housing structure. Advantageously, in at least one embodiment of the present invention, the configurable optical fiber polarization mode coupler addresses various polarization-related applications.

The invention relates to an optical assembly for producing such. The invention also relates to the use of the optical assembly. Laser radiation received via a bundle of individual optical feed fibers is guided to a fiber laser fiber. Each feed fiber has a cladding layer surrounding the core of the fiber to provide total internal reflection in said core, and the cladding layers of the fibers are fused at least partially together to form a zone containing the cores of the feed fibers arranged in a cylindrical configuration inside said zone This configuration provides the shaping of an annular laser beam that can be fed into a fiber laser fiber having an annular light guiding zone and to present the annular laser beam e.g. to a workpiece.

A multichannel optical coupler array can include a coupler housing structure and longitudinal waveguides. At least one of the longitudinal waveguides can be a vanishing core waveguide having an inner vanishing core having a first refractive index (N-1), an outer core having a second refractive index (N-2), and an outer cladding having a third refractive index (N-3). A refractive index transition between N-1 and N-2 can have a function form N(r), where r is a transverse distance from the inner vanishing core center. The function N(r) can be a smooth function having a positive average of the second derivative or function N(r) can be a step function with at least one step approximating the smooth function. The coupler housing structure may have non-circular holes formed by convex-shaped housing structure elements.

A multicore fiber includes: a center core that propagates four LP mode light beams including an LP.sub.02 mode light beam; and a first to a fifth cores disposed on a first line to a fifth line segments extend from the center of the center core in the radial direction at predetermined angles. The multicore fiber includes a different mode interaction section in which the propagation constants of each mode light beam propagated through the center core are matched with the propagation constants of LP.sub.01 mode light beams propagated through the first to fifth cores.