A polarization-maintaining multi-core fiber includes a plurality of fiber core areas and a main outer cladding. The fiber core areas include one central fiber core area, and two or more than two outer fiber core areas equidistantly and uniformly arranged around the central fiber core area that is a polarization-maintaining fiber core area. Each outer fiber core area includes a fiber core and an inner cladding surrounding a core layer. A portion outside the fiber core areas is the main outer cladding. The fiber can greatly enhance spectral efficiency of an optical transmission system, and improve fiber communication capacity. The arrangement of the polarization-maintaining fiber core area provides a waveguide structure with a function of maintaining polarized light, which can be used for transmission of local light.

A communication system is provided. The communication system may include few mode fibers of at least two spans and a mode converter. The few mode fiber is configured to transmit M received mode groups, where group delays of the M mode groups during transmission in the few mode fiber are symmetrically distributed about a center. The mode converter is configured to: receive the M mode groups from the few mode fiber, perform mode group exchange between a first mode group and a second mode group in the M mode groups to obtain M exchanged mode groups, where a group delay of the first mode group and a group delay of the second mode group are symmetric about the center.

An optical fiber includes a glass fiber and a coating resin layer surrounding the outer periphery of the glass fiber. The coating resin layer has a primary resin layer that surrounds the outer periphery of the glass fiber, and a secondary resin layer that surrounds the outer periphery of the primary resin layer. The primary resin layer has a thickness of 7.5 μm or more and 17.5 μm or less. The primary resin layer has a Young's modulus of 0.10 MPa or greater and 0.50 MPa or less at 23° C. The secondary resin layer has a thickness of 5.0 μm or more and 17.5 μm or less. The secondary resin layer has an outer diameter of 165 μm or more and 175 μm or less. The secondary resin layer has a Young's modulus of 1200 MPa or greater and 2800 MPa or less at 23° C.

A fiber optic cable includes an optical fiber, a strength layer surrounding the optical fiber, and an outer jacket surrounding the strength layer. The strength layer includes a matrix material in which is integrated a plurality of reinforcing fibers. A fiber optic cable includes an optical fiber, a strength layer, a first electrical conductor affixed to an outer surface of the strength layer, a second electrical conductor affixed to the outer surface of the strength layer, and an outer jacket. The strength layer includes a polymeric material in which is embedded a plurality of reinforcing fibers. A method of manufacturing a fiber optic cable includes mixing a base material in an extruder. A strength layer is formed about an optical fiber. The strength layer includes a polymeric film with embedded reinforcing fibers disposed in the film. The base material is extruded through an extrusion die to form an outer jacket.

The optical fibers disclosed have single mode and few mode optical transmission for VCSEL-based optical fiber transmission systems. The optical fibers have a cable cutoff wavelength λ.sub.C of equal to or below 1260 nm thereby defining single mode operation at wavelengths greater than 1260 nm and few-mode operation at wavelengths in a wavelength range from 800 nm and 1100 nm. The mode-field diameter is in the range from 8.0 microns to 10.1 microns at 1310 nm. The optical fibers have an overfilled bandwidth OFL BW of at least 1 GHz.Math.km at at least one wavelength in the wavelength range. The optical fibers have a single-step or two-step core and can have a trench refractive index profile. VCSEL based optical transmission systems and methods are disclosed that utilize both single core and multicore versions of the optical fiber.

A multicore fiber includes: a plurality of first glass regions each including: a core portion; and a first cladding portion having a lower refractive index than a maximum refractive index of the core portion; and a cladding region formed on outer peripheries of the plurality of first glass regions, wherein compressive stress is applied to the plurality of first glass regions.

Disclosed is a multi-core optical fiber having a plurality of cores extending parallelly along a central axis of the multi-core optical fiber. Each core of the plurality of cores is up-doped with an up-dopant. The multi-core optical fiber further has a plurality of buffer layers such that each buffer layer of the plurality of buffer layers envelop a corresponding core of the plurality of cores. Each buffer layer of the plurality of buffer layers has a predefined buffer layer thickness. The multi-core optical fiber further has a plurality of trench layers such that each trench layer of the plurality of trench layers envelops a corresponding buffer layer of the plurality of buffer layers. Each trench layer of the plurality of trench layers is down-doped with a down-dopant. The multi-core optical fiber has an inter-core crosstalk of less than −30 decibel/kilometres (dB/km) at a wavelength of 1550 nanometres (nm).

The present embodiment relates to a method of directly measuring a leakage loss from a peripheral core in a MCF with a coating to the coating. In the measurement method, in a high refractive-index state in which the coating is present on an outer periphery of a common cladding, first transmission power of measurement light, which propagates through the peripheral core of the MCF, is measured. On the other hand, in a low refractive-index state in which a low-refractive-index layer with a lower refractive index than the common cladding is provided on the outer periphery of the common cladding, second transmission power of the measurement light, which propagates through the peripheral core of the MCF, is measured. The leakage loss LL from the peripheral core to the coating is calculated as a difference between the first transmission power and the second transmission power.

A multicore fiber is provided that includes a plurality of elliptical cores spaced apart from one another. Each of the plurality of elliptical cores has an elliptical shape. The multicore fiber also includes a cladding surrounding the plurality of elliptical cores.

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.