An optical fiber includes a core that propagates a light that includes a wavelength equal to or larger than 1000 nm and equal to or smaller than 1100 nm. The light propagates in the core at least in an LP01 mode and an LP11 mode. A difference between a propagation constant of the light in the LP01 mode and a propagation constant of the light in the LP11 mode is 1735 rad/m or larger and 4000 rad/m or smaller.

Example embodiments include an optical interrogation system with a sensing fiber having a single core, the single core having multiple light propagating modes. Interferometric apparatus probes the single core multimode sensing fiber over a range of predetermined wavelengths and detects measurement interferometric data associated with the multiple light propagating modes of the single core for each predetermined wavelength in the range. Data processing circuitry processes the measurement interferometric data associated with the multiple light propagating modes of the single core to determine one or more shape-sensing parameters of the sensing fiber from which the shape of the fiber in three dimensions can be determined.

A polymer optical fibre (POF) (30) for transmitting light of wavelength, λi, between two separate elements of an active implantable medical device (AIMD), includes a core (31) which is cylindrical and made of a cyclic olefin polymer (COP) or copolymer (COC), having a core refractive index at the wavelength, λi, n_core, A cladding (32) which has a cladding refractive index at the wavelength, λi, n_clad<n_core, and which is made of a cladding copolymer including monomers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride. The cladding being itself enclosed in a coating (33) which is made of a coating polymer formed of one of the monomers of the cladding copolymer. The POF has a numerical aperture, NA, at the wavelength, λi, of at least 0.5.

Provided is an optical propagation device including an optical fiber having a core and a clad having a lower refractive index than a refractive index of the core, wherein the optical fiber is any of a step index multimode optical fiber or a few-mode optical fiber, an optical signal propagates in at least two or more multiple modes in the core of the optical fiber, the optical fiber is bent such that tensile force generated by bending is discontinuously applied to two or more locations of the optical fiber across a length direction of the optical fiber, and at each bent portion of the optical fiber, stress is non-uniformly generated across an outer peripheral direction of the optical fiber.

There is described an optical fiber coupler generally having: a first optical fiber having a longitudinally extending multimode guiding region and a first taper portion longitudinally extending between first and second locations of the first optical fiber, the first taper portion having a dimension progressively decreasing along a first taper direction from the first location to the second location; a second optical fiber having a longitudinally extending multimode guiding region and a second taper portion longitudinally extending between third and fourth locations of the second optical fiber, the second taper portion having a dimension progressively decreasing along a second taper direction from the third location to the fourth location; and a coupling region where at least a portion of the first taper portion is optically coupled to a portion of the second taper portion, with the first and second taper directions being opposite to one another.

An optical fiber for a fiber laser includes a core to which a rare-earth element is added, a first cladding formed around the core; and a second cladding formed around the first cladding, and excitation light is guided from at least one end of the first cladding to excite the rare-earth element to output a laser oscillation light. An addition concentration of the rare-earth element to the core is different in a longitudinal direction of the optical fiber for a fiber laser, and a core diameter and a numerical aperture of the optical fiber for a fiber laser are constant in the longitudinal direction of the optical fiber for a fiber laser.

A multicore fiber optic cable comprising of a dual core optical fiber having a dual core optical fiber geometry, the cores are spiraled parallel to one another along the longitudinal axis of the fiber to negate link path length difference, a coating that surrounds the fiber, a buffer tube that surrounds the coated fiber, a strength member that surrounds the buffer tube, and an outer jacket that surrounds the strength member.

An optical fiber, such as in some instances a high-power, diode-pumped, dual-clad, ytterbium-doped fiber amplifier (YDFAs), having a fundamental mode and at least one higher order mode, wherein the higher order mode or modes have mode areas that are substantially larger than a mode area of the fundamental mode.

Example embodiments include an optical interrogation system with a sensing fiber having a single core, the single core having multiple light propagating modes. Interferometric apparatus probes the single core multimode sensing fiber over a range of predetermined wavelengths and detects measurement interferometric data associated with the multiple light propagating modes of the single core for each predetermined wavelength in the range. Data processing circuitry processes the measurement interferometric data associated with the multiple light propagating modes of the single core to determine one or more shape-sensing parameters of the sensing fiber from which the shape of the fiber in three dimensions can be determined.

Example embodiments include an optical interrogation system with a sensing fiber having a single core, the single core having multiple light propagating modes. Interferometric apparatus probes the single core multimode sensing fiber over a range of predetermined wavelengths and detects measurement interferometric data associated with the multiple light propagating modes of the single core for each predetermined wavelength in the range. Data processing circuitry processes the measurement interferometric data associated with the multiple light propagating modes of the single core to determine one or more shape-sensing parameters of the sensing fiber from which the shape of the fiber in three dimensions can be determined.