The present disclosure provides an optical fibre. The optical fibre includes a core region, a primary trench region and a secondary trench region. The core region has a radius r.sub.1. In addition, the core region has a relative refractive index Δ.sub.1. Further, the primary trench region has a relative refractive index Δ.sub.3. Furthermore, the primary trench region has a curve parameter α.sub.trench-1. Moreover, the secondary trench region has a relative refractive index Δ.sub.4. Also, the secondary trench region has a curve parameter α.sub.trench-2.

An optical system comprising: an optical assembly having a first optical surface and a rear optical surface, said optical assembly comprising at least three optical elements; an optical fiber comprising a core portion with a mode field diameter (MFD) expanded region optically coupled to the rear optical surface of the optical assembly, the optical fiber comprising a core region doped with chlorine in a concentration greater than 0.5 wt %, wherein the MFD expanded region is less than 5 cm in length, and has MFD at the fiber end coupled to the optical assembly that is a least 20% greater than the MFD at other end of the optical fiber; an optical signal source coupled to first optical surface of the optical assembly, such that the optical signal provided by the optical signal source is routed along an optical path formed by the optical assembly to the mode field diameter expanded region of said optical fiber.

An optical fiber includes: a core portion made of glass; a cladding portion that is located on an outer periphery of the core portion and that is made of glass having a lower refractive index than a refractive index of the core portion; and a coating portion that covers an outer periphery of the cladding portion. Further, an average value of a relative refractive-index difference of a center core of the core portion is 0.1 to 0.5%, a fiber diameter including the coating portion is equal to or smaller than 220 μm, an effective cutoff wavelength is longer than 1260 nm and smaller than 1530 nm, and a mode field diameter of light at 1550 nm is equal to or larger than 9 μm.

The optical fiber according to the present invention includes, in a cross section of the optical fiber, one core region (11) and a cladding region (12) that is arranged on an outer periphery of the core region. The cladding region is a medium that has a lower refractive index than that of the core region and also has a smaller refractive index wavelength dispersion than that of the core region. The optical fiber has a solid core and therefore, allows more reduction in the Rayleigh scattering loss compared to an optical fiber having a hollow core. In addition, since the optical fiber adopts, for the cladding region, a medium that has a smaller refractive index wavelength dispersion than that of the core region, it allows a reduction in the wavelength dispersion of n.sub.eff.

This MCF ensures sufficient manufacturing tolerance, is excellent in mass productivity, and is also capable of suppressing degradation of splice loss. The MCF includes four cores and a common cladding. Each core has adjacent relationships with two cores of remaining cores, an adjacent core interval Λ is from Λ.sub.nominal−0.9 μm to Λ.sub.nominal+0.9 μm, a common cladding diameter is from 124 μm to 126 μm, an MFD, λ.sub.cc and d.sub.coat at a wavelength of 1310 nm satisfy a predetermined relationship, the MFD is from a MFD-reference-value−0.4 μm to the MFD-reference-value+0.4 μm with the MFD-reference-value of from 8.6 μm to 9.2 μm, a zero-dispersion wavelength is from a wavelength-reference-value−12 nm to the wavelength-reference-value+12 nm with the wavelength-reference-value of from 1312 nm to 1340 nm, a dispersion slope at a zero-dispersion wavelength is 0.092 ps/(nm.sup.2.Math.km) or less, λ.sub.cc is 1260 nm or less, and a predetermined structural condition and an optical condition are satisfied.

An MCF or the like according to the present disclosure ensures sufficient manufacturing tolerance, is excellent in mass productivity, and is also capable of suppressing degradation of splice loss. The MCF includes four cores that extend along a central axis, and a common cladding. On a cross-section, the common cladding has a circular outer periphery, the four cores are arranged at positions to be line symmetric with respect to a straight line that intersects with a central axis and that intersects with none of the four cores, and a core arrangement defined by the four cores has rotational symmetry once with central axis being a center of rotation.

An optical fiber comprising: (a) a core having an outer radius r.sub.1; (b) a cladding having an outer radius r.sub.4<32.5 microns; (c) a primary coating surrounding the cladding having an outer radius r.sub.5, a thickness t.sub.P>8 microns, in situ modulus E.sub.P≤0.35 MPa and a spring constant χ.sub.P<2.0 MPa, where χ.sub.P=2E.sub.P r.sub.4/t.sub.P; and (d) a secondary coating surrounding said primary coating, the secondary coating having an outer radius r.sub.6 and a thickness t.sub.S=r.sub.6−r.sub.5, and in situ modulus E.sub.S of 1200 MPa or greater; t.sub.S>8 microns, r.sub.6≤56 microns. The fiber has a mode field diameter MFD greater than 8.2 microns at 1310 nm; a fiber cutoff wavelength of less than 1310 nm; and a bend loss at a wavelength of 1550 nm, when wrapped around a mandrel having a diameter of 10 mm, of less than 1.0 dB/turn.

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.

An optical fiber is provided that includes a core region, a cladding region having a radius less than about 62.5 microns; a polymer coating comprising a high-modulus layer and a low-modulus layer, wherein a thickness of the low-modulus inner coating layer is in a range of 4 microns to 20 microns, the modulus of the low-modulus inner coating layer is less than or equal to about 0.35 MPa, a thickness of the high-modulus coating layer is in a range of 4 microns to 20 microns, the modulus of the high-modulus inner coating layer is greater than or equal to about 1.6 GPa, and wherein a puncture resistance of the optical fiber is greater than 20 g, and wherein a microbend attenuation penalty of the optical fiber is less than 0.03 dB/km, and wherein an outer diameter of the coated optical fiber is less than or equal to 175 microns

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.