An optical fiber includes a glass portion, a primary coating layer, and a secondary coating layer. In the optical fiber, a value of microbend loss characteristic factor F.sub.μBL_GO is 2.6 ([GPa.sup.−1.Math.μm.sup.−10.5.Math.dB/turn].Math.10.sup.−27) or less, when represented by

F.sub.μBL_GO=F.sub.μBL_G×F.sub.μBL_O

by using geometry microbend loss characteristic F.sub.μBL_G and optical microbend loss characteristic F.sub.μBL_O.

A method of forming an optical fiber, including: exposing a soot core preform to a dopant gas at a pressure of from 1.5 atm to 40 atm, the soot core preform comprising silica, the dopant gas comprising a first halogen doping precursor and a second halogen doping precursor, the first halogen doping precursor doping the soot core preform with a first halogen dopant and the second halogen precursor doping the soot core preform with a second halogen dopant; and sintering the soot core preform to form a halogen-doped closed-pore body, the halogen-doped closed-pore body having a combined concentration of the first halogen dopant and the second halogen dopant of at least 2.0 wt %.

An optical fiber can include a core comprising silica co-doped with nitrogen and chlorine and an outer cladding surrounding the core. In some aspects, the core can be characterized by an annealing temperature of less than or equal to about 1150° C. and/or the core can include a relative refractive index Δ.sub.core in a range of from about 0.15% to about 0.45%.

An optical fiber includes a glass portion, a primary coating layer, and a secondary coating layer. In the optical fiber, a value of microbend loss characteristic factor F.sub.μBL_GO is 2.6 ([GPa.sup.−1.Math.μm.sup.−10.5.Math.dB/turn].Math.10.sup.−27) or less, when represented by
F.sub.μBL_GO=F.sub.μBL_G×F.sub.μBL_O
by using geometry microbend loss characteristic F.sub.μBL_G and optical microbend loss characteristic F.sub.μBL_O.

An optical fiber has a core to which chlorine is added and a clad to which fluorine is added, chlorine of 9000 to 13000 ppm is added to the core, a relative refractive index difference Δ1 of the core to a pure silica glass is 0.09 to 0.13%, a relative refractive index difference Δ2 of the clad to a pure silica glass is −0.36 to −0.17%, a difference (Δ1-Δ2) between the relative refractive index difference Δ1 of the core and the relative refractive index difference Δ2 of the clad is larger than or equal to 0.30%, a mode field diameter at wavelength 1.31 μm is 8.8 to 9.6 μm, and a stress difference occurring at an interface between the core and the clad is lower than or equal to 60 MPa.

An optical fiber includes a core, and a cladding. When a refractive index of silica glass is set as no, a refractive index of the core is set as n.sub.1, and a refractive index of the cladding is set as n.sub.2, a relative refractive index difference Δ defined by Expression (1):

Δ[%]=100×(n.sub.1.sup.2−n.sub.2.sup.2)/2n.sub.0.sup.2  (1)

is 0.2% or higher. A ratio of a maximum value of a concentration of the dopant composed of the alkali metal element or the alkaline-earth metal element in the cladding to a maximum value of a concentration of the dopant composed of the alkali metal element or the alkaline-earth metal element in the core is 0.06 or higher and 0.25 or lower.

In order to reduce the degree of relaxation after an optical substrate has been compacted, in particular after a longer period, substrates (51) or reflective optical elements (50), in particular for EUV lithography, with substrates (51) of this type, are proposed. These substrates (51), which have a surface region (511) with a reflective coating (54), are characterised in that, at least near to the surface region (511), the titanium-doped quartz glass has a proportion of Si—O—O—Si bonds of at least 1*10.sup.16/cm.sup.3 and/or a proportion of Si—Si bonds of at least 1*10.sup.16/cm.sup.3 or, along a notional line (513) perpendicular to the surface region (511), over a length (517) of 500 nm or more, a hydrogen content of more than 5×10.sup.18 molecules/cm.sup.3.

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.

The invention relates to a method and device for fiber optic temperature measurement. The invention also relates to a multimode quartz glass fiber with nanocomposite (NK) containing a polymer and quantum dots (QDs) and its manufacture. These are based on temperature-dependent emission of quantum dots on the surface of optical fibers.

Bromine doping of silica glass is demonstrated. Bromine doping can be achieved with SiBr.sub.4 as a precursor. Bromine doping can occur during heating, consolidation or sintering of a porous silica glass body. Doping concentrations of bromine increase with increasing pressure of the doping precursor and can be modeled with a power law equation in which doping concentration is proportional to the square root of the pressure of the doping precursor. Bromine is an updopant in silica and the relative refractive index of silica increases approximately linearly with doping concentration. Bromine can be used as a dopant for optical fibers and can be incorporated in the core and/or cladding regions. Core doping concentrations of bromine are sufficient to permit use of undoped silica as an inner cladding material in fibers having a trench in the refractive index profile. Co-doping of silica glass with bromine and chlorine is also demonstrated.