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

An up-taper is applied by a mode adapter to increase a signal mode area prior to tapering and combining.

A quasi-single-mode optical fiber with a large effective area is disclosed. The quasi-single-mode fiber has a core with a radius greater than 5 μm, and a cladding section configured to support a fundamental mode and a higher-order mode. The fundamental mode has an effective area greater than 170 μm.sup.2 and an attenuation of no greater than 0.17 dB/km at a wavelength of 1530 nm. The higher-order mode has an attenuation of at least 1.0 dB/km at the wavelength of 1530 nm. The quasi-single-mode optical fiber has a bending loss of less than 0.02 dB/turn for a bend diameter of 60 mm for a wavelength of 1625 nm.

In one embodiment, an optical fiber includes an inner core having a core refractive index delta and profile shape parameter α in the range of 1.8 to 2.6, including endpoints, and a cladding layer surrounding the inner core. The cladding layer includes an inner cladding segment having an inner refractive index delta, a trench segment having a trench refractive index delta, and an outer cladding segment having an outer refractive index delta. The optical fiber further includes a coating layer surrounding the cladding layer and having a thickness of less than 30 .Math.m and a modulus greater than or equal to 0.5 GPa.

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.

An optical fiber assembly is provided including an optical fiber and a beam shaping component affixed to an extremity of the optical fiber. The optical fiber supports a guided mode having a spatial profile defining a first shape. The beam shaping component defines a light path and has a transversal refractive index profile including an outer refractive index value greater than an inner refractive index value. The beam shaping component transforms the spatial profile of a light beam propagating along the light path between the first shape and a second shape different from the first shape. The optical assembly may for example transform a Gaussian light beam into a flat-top or donut shape.

Disclosed herein are configurations for few-mode fiber optical endoscope systems employing distal optics and few-mode, double-clad or other optical fiber wherein the systems directing an optical beam to a sample via the optical fiber; collecting light backscattered from the sample; direct the backscattered light to a detector via the optical fiber; and detect the backscattered light; wherein the directed optical beam is single mode and the collected light is one or more higher order modes.

An optical fiber includes: a first core portion capable of transmitting first light; a second core portion formed on an outer periphery of the first core portion in a structure different from that of the first core portion and capable of transmitting second light different from the first light. The second core portion is formed around the outer periphery of the first core portion, and a center of the second core portion is positioned in a region of the first core portion.

In an optical fiber, a plurality of individual cores extend through a common cladding. Each individual core supports at least one local transverse spatial mode. The individual cores and surrounding cladding are structured to support propagation of plurality of desired signal-carrying modes, while suppressing undesired modes, thereby supporting the propagation of one or more spatially multiplexed signals. The core-to-core spacing of the fiber is configured to maintain an acceptably low level of mode-coupling between cores.

A graded index multimode fiber and method of producing the graded index multimode fiber utilize a technique of reducing an index profile of the core of the multimode fiber below a standard parabolic index profile. This can be done by changing dopant concentrations in the fiber core over the radius of the fiber core. The result is a multimode fiber having differential mode delay characteristics that are intentionally not minimized. The index profile can be reduced below the standard parabolic index profile over the entire radius of the core, or only for radii above a specified radius.