A multicore optical fiber comprises a common cladding and a plurality of core portions disposed in the common cladding. Each of the core portions includes a central axis, a core region extending from the central axis to a radius r.sub.1, the core region comprising a relative refractive index Δ.sub.1, an inner cladding region extending from the radius r.sub.1 to a radius r.sub.2, the inner cladding region comprising a relative refractive index Δ.sub.2, and a depressed cladding extending from the radius r.sub.2 to a radius r.sub.3, the depressed cladding region comprising a relative refractive index Δ.sub.3 and a minimum relative refractive index Δ.sub.3 min. The relative refractive indexes may satisfy Δ.sub.1>Δ.sub.2>Δ.sub.3 min. The mode field diameter of each core portion may greater than or equal to 8.2 μm and less than or equal to 9.5 μm.

Optical waveguide cores having refractive index profiles that vary angularly about a propagation axis of the core can provide single-mode operation with larger core diameters than conventional waveguides. In one representative embodiment, an optical waveguide comprises a core that extends along a propagation axis and has a refractive index profile that varies angularly about the propagation axis. The optical waveguide can also comprise a cladding disposed about the core and extending along the propagation axis. The refractive index profile of the core can vary angularly along a length of the propagation axis.

The present disclosure provides an optical fibre. The optical fibre includes a core extended from a central longitudinal axis to a first radius r1. Further, the optical fibre includes a first trench region extended from a second radius r2 to a third radius r3, a second trench region extended from the third radius r3 to a fourth radius r4 and a cladding region extended from the fourth radius r4 to a fifth radius r5.

The present invention satisfies at least one of the condition of the degree of freedom of a primary layer 11 shown in the equation (I) and the condition of the rigidity of a secondary layer 12 shown in the equation (II). Thus, a coated optical fiber 1 capable of suppressing transmission loss in a low temperature environment is provided, in which, even when an optical fiber 10 having a large effective core cross-sectional area A.sub.eff of the optical fiber 10 at a wavelength of 1550 nm and having high microbend sensitivity is used, transmission loss in a low temperature environment can be suppressed.

[Math. 1]

β.sub.P×P.sub.ISM<600  (I)

(S/P)×(S.sub.ISM/P.sub.ISM)≤1000  (II)

The present disclosure provides optical fibers that exhibit low macrobend loss at 1550 nm at bend diameters greater than 40 mm. The relative refractive index profile of the fibers includes a trench cladding region having a trench volume configured to minimize macrobend loss at large bend diameters. The thickness and/or depth of the trench cladding region are controlled to reduce trench volume to a degree consistent with reducing macrobend loss at bend diameters greater than 40 mm. The optical fiber includes an outer cladding region that surrounds and is directly adjacent to the trench cladding region and an optional offset cladding region between the trench cladding region and the core region. In some embodiments, the core region is a segmented core region that includes inner and outer core regions. The low macrobend loss available from the optical fibers makes them particularly suitable for applications in submarine telecommunications systems.

A single mode optical fiber is provided that includes a core region having an outer radius r.sub.1 and a maximum relative refractive index Δ1.sub.max. The single mode optical fiber has a bend loss at 1550 nm for a 15 mm diameter mandrel of less than about 0.75 dB/turn, has a bend loss at 1550 nm for a 20 mm diameter mandrel of less than about 0.2 dB/turn, and a bend loss at 1550 nm for a 30 mm diameter mandrel of less than 0.002 dB/turn. Additionally, the single mode optical fiber has a mode field diameter of 9.0 microns or greater at 1310 nm wavelength and a cable cutoff of less than or equal to about 1260 nm.

An optical fiber includes a core and a cladding. An effective area A.sub.eff of light of a fundamental mode, having a wavelength of 1070 nm and propagating through the core, is 500 μm.sup.2 or more. A numerical aperture NA of the core satisfies the following formula:

NA≥(1.3×10.sup.−11×a.sup.4/b.sup.6).sup.1/6

where a (m) is a radius of the core and b (m) is a radius of the cladding. A V value, that is a waveguide parameter of the optical fiber, satisfies the following formula:

V≤1.3583×b.sup.−0.2555.

An MCF having a structure excellent in mass productivity and suppressing increases in splicing cost and loss are provided. The MCF includes 12 or 16 cores, a cladding, and a coating. The cores are arranged at positions of line symmetry while no adjacent relationship is established between the cores having an adjacent relationship with any core. A coating diameter is 235-265 .Math.m, a cladding diameter CD is from CD.sub.nominal -1 .Math.m to CD.sub.nominal +1 .Math.m with a nominal value CD.sub.nominal of 195 .Math.m or less, an MFD at 1310 nm is from MFD-reference-value -0.4 .Math.m to the MCF-reference-value+0.4 .Math.m with the MFD-reference-value of 8.2-9.2 .Math.m, and a 22m-cable-cutoff wavelength λ.sub.cc is 1260-1360 nm. A core’s zero-dispersion wavelength is a wavelength-reference-value - 12 nm to the wavelength-reference-value+12 nm with the wavelength-reference-value of 1312-1340 nm, and a dispersion slope at the wavelength is 0.092 ps/(nm.sup.2.Math.km) or less. A shortest distance from a cover-cladding interface to each core center, a structure, and optical characteristics satisfy predetermined conditions.

The glass-based THz optical waveguides (10) disclosed herein are used to guide optical signals having a THz frequency in the range from 0.1 THz to (10) THz and include a core (20) surrounded by a cladding (30). The core has a diameter D1 in the range from (30) μm to 10 mm and is made of fused silica glass having a refractive index n.sub.1. The cladding is made of either a polymer or a glass or glass soot and has a refractive index n.sub.2<n.sub.1 and an outer diameter D2 in the range from 100 μm to 12 mm. The THz optical waveguides can be formed using processes that are extensions of either fiber, ceramic and soot-based technologies. In an example, the THz waveguides have a dielectric loss D.sub.f<0.005 at 100 GHz.

An object is to obtain an optical fiber having a small diameter and suppressing the increase of a microbending loss of the optical fiber. The optical fiber includes: a core portion made of silica glass; a cladding portion made of silica glass, the cladding portion covering the outer periphery of the core portion and having a refractive index smaller than a maximum refractive index of the core portion; and a coating portion covering the outer periphery of the cladding portion. The outer diameter of the cladding portion is 100 μm or smaller, the relative refractive-index difference Δ1 of the core portion is 0.5% or smaller, and the thickness of the coating portion is 10 μm or larger.