According to embodiments, an optical fiber may include a core portion comprising an outer radius r.sub.C and a maximum relative refractive index .sub.Cmax. A cladding may surround the core portion and include a low-index trench and an outer cladding. The low index trench may surround the core portion and includes an outer radius r.sub.T and relative refractive index .sub.T. The outer cladding may surround and be in direct contact with the low-index trench. The outer cladding may be formed from silica-based glass comprising greater than 1.0 wt. % bromine and has a relative refractive index .sub.OC, wherein .sub.Cmax>.sub.OC>.sub.T. The optical fiber may have a cable cutoff of less than or equal to 1530 nm. An attenuation of the optical fiber may be less than or equal to 0.185 dB/km at a wavelength of 1550 nm.

An optical connector-equipped fiber (2A, 2B) has optical fibers (10a), a ferrule (11), guide holes, and a structure for regulating a space between end faces (11a) of the ferrules (11). A relative position between the end faces (11a) is fixed by guide pins being inserted into the guide holes. Normals with respect to leading end faces of the optical fibers are inclined with respect to optical axes of the optical fibers. MFDs of the optical fibers are gradually expanded toward the leading end faces and are maximized at the leading end faces. The optical axes of the pair of facing optical fibers that are optically coupled are not present on the same optical axis.

A system for providing electrical and optical interconnection using a 3D non-carbon-based topological insulator (TI) is disclosed. The system includes a length of the TI having a tube shape having wall thickness of about 10 nm to about 200 nm and a hollow interior portion surrounded by an interior surface of the TI. The length includes a first end and a second end, wherein the first end is configured to receive an optical signal, an electrical signal, or both. The optical signal propagates in the hollow interior portion along the length to the second end by total internal reflection due to a refractive index of the interior surface of the TI. The electrical signal propagates along an external surface of the TI to the second end.

An MCF of the present embodiment has eight or more cores. A diameter of a common cladding is not more than 126 m. Optical characteristics of each core are as follows: a TL at a predetermined wavelength of 1310 nm is not more than 0.4 dB/km; an MFD at the predetermined wavelength is from 8.0 m to 10.1 m; a BL in a BR of not less than 5 mm or in the BR of not less than 3 mm and, less than 5 mm is not more than 0.25 dB/turn at the predetermined wavelength; 0 is from 1300 nm to 1324 nm; cc is not more than 1260 nm; an XT or XTs at the predetermined wavelength is not more than 0.001/km.

An optical receptacle includes: a fiber stub including an optical fiber, a ferrule, and an elastic member; and a holder holding the fiber stub, the optical fiber including a cladding and a core for conducting light, the ferrule having a through-hole fixing the optical fiber, the elastic member fixing the optical fiber in the through-hole, the fiber stub having one end surface on the ferrule side, and another on an opposite side, the optical fiber including first and third portions on the opposite end surface sides and a second portion therebetween, a core diameter of the first portion being smaller than the third portion, and a core diameter of the second portion increasing from the first portion side toward the third portion side.

An optical fiber includes: a core portion made of glass; and a cladding portion made of glass, having a refractive index lower than the refractive index of the core portion, and positioned on an outer periphery of the core portion. Further, the cladding portion has an outer diameter smaller than 100 ?m, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.

A fiber includes a core and cladding, both of which may have temperature dependent indices of refraction. The materials and size of the core and cladding may be selected such that as the temperature of the core and/or cladding is heated above room temperature, the fiber transitions from supporting multimode optical waveguiding to supporting single mode waveguiding.

The optical fiber includes a glass fiber and a coating resin layer. The coating resin layer includes a primary resin layer and a secondary resin layer. The glass fiber has an outer diameter of from 79 ?m to 81 ?m. The secondary resin layer has an outer diameter of from 120 ?m to 170 ?m. The primary resin layer has an in situ elastic modulus of from 0.1 MPa to 0.4 MPa. The secondary resin layer has an in situ elastic modulus of from 1200 MPa to 2800 MPa. A maximum value of amplitude of an amount of eccentricity is 10 ?m or less in a spectrum obtained by measuring the amount of eccentricity of the glass fiber and by applying Fourier transform to a waveform representing the amount of eccentricity.

An MCF of the present embodiment has eight or more cores. A diameter of a common cladding is not more than 126 m. Optical characteristics of each core are as follows: a TL at a predetermined wavelength of 1310 nm is not more than 0.4 dB/km; an MFD at the predetermined wavelength is from 8.0 m to 10.1 m; a BL in a BR of not less than 5 mm or in the BR of not less than 3 mm and, less than 5 mm is not more than 0.25 dB/turn at the predetermined wavelength; 0 is from 1300 nm to 1324 nm; cc is not more than 1260 nm; an XT or XTs at the predetermined wavelength is not more than 0.001/km.

An optical fiber having both low macrobend loss and low microbend loss. The fiber has a central core region, a first (inner) cladding region surrounding the central core region and having an outer radius r.sub.2>16 microns and relative refractive index .sub.2, and a second (outer) cladding region surrounding the first cladding region having relative refractive index, .sub.3, wherein .sub.1>.sub.3>.sub.2. The difference between .sub.3 and .sub.2 is greater than 0.12 percent. The fiber exhibits a 22 m cable cutoff less than or equal to 1260 nm, and r.sub.1/r.sub.2 is greater or equal to 0.24 and bend loss at 1550 nm for a 15 mm diameter mandrel of less than 0.5 dB/turn.