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 mode equalization filter for reducing a difference in optical power between modes of signal light propagating inside FMFs of an MDM optical transmission scheme includes an FMF on the input side, a collimating lens, an ND filter, a condensing lens, and an FMF on the output side. The ND filter includes partial ND filters combined each other and having main surfaces placed in parallel to each other, a ring portion having a low transmittance is provided in a part of the partial ND filter, and a ring portion having a low transmittance is also provided in a part of the partial ND filter. When the ring portions have different aspects, and the partial ND filters are adjusted and set to be slidable in directions of axes, respectively, the partial ND filters have a property that the transmittance of each mode of the signal light differs and can obtain a function of a variable mode equalization filter.

There is provided an optical waveguide that performs propagation only in a reference mode at a first wavelength. Communication is performed using light of a second wavelength that enables the optical waveguide to perform propagation in at least a first order mode in addition to the reference mode. When light entering the optical waveguide deviates with respect to an optical axis or deviates angularly, propagation is performed in at least the first order mode in addition to the reference mode, the first order mode being generated due to the deviation with respect to the optical axis or the angular deviation. This results in a reduction in a loss of coupling of optical power. This makes it possible to relax the accuracy with respect to a deviation with respect to an optical axis or an angular deviation, and thus to reduce costs.

A method of making a multi-mode optical fiber that includes: depositing a porous germania-doped silica soot to form a germania-doped porous soot preform; depositing a porous silica layer over the porous soot preform; doping the porous soot preform and the porous silica layer with a fluorine dopant to form a co-doped soot preform having a core region and a fluorine-doped trench region; consolidating the co-doped soot preform to form a sintered glass, co-doped core preform having a refractive index alpha profile between 1.9 and 2.2 measured at 850 nm; depositing a cladding comprising silica over the sintered glass, co-doped preform to form a multi-mode optical fiber preform; drawing the optical fiber preform into a multi-mode optical fiber. Further, the step of doping the germania-doped soot preform and the porous silica layer is conducted according to a doping parameter (Φ) that is set between 20 and 300, and given by:

[00001]$\Phi =\frac{1\times {10}^{14}.Math.R_{\mathrm{prc}}^2.Math.\exp \left(-E/{\mathrm{RT}}_{\mathrm{dop}}\right).Math.T_{\mathrm{dop}}^{1/2}}{x^{3/4}}.$

Optical transmission systems and methods are disclosed that utilize a QSM optical fiber with a large effective area and that supports only two modes, namely the fundamental mode and one higher-order mode. The optical transmission system includes a transmitter and a receiver optically coupled by an optical fiber link that includes at least one section of the QSM optical fiber. Transmission over optical fiber link gives rise to MPI, which is mitigated using a digital signal processor. The QSM optical fiber is designed to have an amount of DMA that allows for the digital signal processor to have reduced complexity as reflected by a reduced number of filter taps as compared to if the DMA were zero.

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 multi-mode HIC (high index contrast) waveguide (102, 104, 201, 301) for transporting electromagnetic radiation in the optical waveband, the waveguide comprising a guiding core portion (204) with higher refractive index, and cladding portion (206) with substantially lower refractive index configured to at least partially surround the light guiding core in the transverse direction to facilitate confining the propagating radiation within the core, the waveguide being configured to support multiple optical modes of the propagating radiation, wherein the waveguide incorporates a bent waveguide section (202) having bend curvature that is configured to at least gradually, preferably substantially continuously, increase towards a maximum curvature of said section from a section end.

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.

To relax the accuracy with respect to a deviation with respect to an optical axis or an angular deviation, and thus to reduce costs.

An optical waveguide is included that performs propagation only in a reference mode at a first wavelength. Communication is performed using light of a second wavelength that enables the optical waveguide to perform propagation in at least a first order mode in addition to the reference mode. When light entering the optical waveguide deviates with respect to an optical axis or deviates angularly, propagation is performed in at least the first order mode in addition to the reference mode, the first order mode being generated due to the deviation with respect to the optical axis or the angular deviation. This results in a reduction in a loss of coupling of optical power. This makes it possible to relax the accuracy with respect to a deviation with respect to an optical axis or an angular deviation, and thus to reduce costs.

A method of categorizing single mode optical fibers, the method including determining one or more fiber properties of an optical fiber, the optical fiber being a single mode optical fiber at an operating wavelength of about 1310 nm. The method further including calculating a peak bandwidth wavelength of the optical fiber based on the one or more fiber properties, comparing the calculated peak bandwidth wavelength with a target peak bandwidth wavelength and based on the comparison, determining if the optical fiber meets a target modal bandwidth.