A single-mode fiber with an ultra-low attenuation and a large effective area includes a core layer having a radius of 4.8 to 6.5 and a relative refractive index difference n.sub.1 of 0.06% to 0.10%, and cladding layers. The cladding layers includes an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary cladding layer. The inner cladding layer has a radius of 9 to 15 m and a relative refractive index difference of 0.40% to 0.15%. The trench cladding layer has a radius of 12 to 17 m and a relative refractive index difference of 0.8% to 0.3%. The auxiliary outer cladding layer has a radius of 37 to 50 m and a relative refractive index difference of 0.6% to 0.25%. The outer cladding layer is a pure-silicon-dioxide glass layer.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

According to some embodiments an optical fiber comprising: (I) a silica based core having: an inner core region with maximum refractive index delta of the core, .sub.0 in % measured relative to pure SiO.sub.20.1%, and an outer core region with a minimum refractive index delta .sub.1, where .sub.1<.sub.0; such that the fiber has: (i) an effective area Aeff.sub.=1525 of LP.sub.01 mode at a wavelength =1525 nm such that 80 m.sup.2<Aeff.sub.=1525<250 m.sup.2; and (ii) an effective area Aeff.sub.=1475 of LP.sub.01 mode at wavelength =1450 nm such that 60 m.sup.2<Aeff.sub.=1475, wherein

Aeff.sub.=1525>Aeff.sub.=1475, and (Aeff.sub.=1525Aeff.sub.=1475)/Aeff.sub.=15250.07; and (II) an annular cladding surrounding the core, the cladding including: (i) a low index ring surrounding the core and having a minimum refractive index delta .sub.RMIN, where .sub.R,MIN.sub.1; and (ii) an outer cladding with a refractive index delta .sub.Outer-Clad relative to pure silica, such that .sub.Outer-Clad>.sub.R,MIN.

A single mode optical fiber having a core made from silica and less than or equal to about 6.5 weight % germania and having a maximum relative refractive index .sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index .sub.2MIN. A difference between a softening point of the core and a softening point of the inner cladding is less than or equal to about 20 C., and .sub.1MAX>.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The outer cladding has a maximum relative refractive index .sub.3MAX, and .sub.3MAX>.sub.2MIN. A method for manufacturing an optical fiber includes providing a preform to a first furnace, the preform, drawing the optical fiber from the preform, and cooling the drawn optical fiber in a second furnace.

Rare earth oxides doped multicomponent glass fibers for laser generation and amplification, including a core and a cladding, the core comprising at least 2 weight percent glass network modifier selected from BaO, CaO, MgO, ZnO, PbO, K.sub.2O, Na.sub.2O, Li.sub.2O, Y.sub.2O.sub.3, or combinations; wherein the mode of the core is guided with step index difference between the core and the cladding, a numerical aperture of the fiber is between 0.01 and 0.04; core diameter is from 25 to 120 micron, and a length of the gain fiber is shorter than 60 cm.

Rare earth oxides doped multicomponent glass fibers for laser generation and amplification, including a core and a cladding, the core comprising at least 2 weight percent glass network modifier selected from BaO, CaO, MgO, ZnO, PbO, K.sub.2O, Na.sub.2O, Li.sub.2O, Y.sub.2O.sub.3, or combinations; wherein the mode of the core is guided with step index difference between the core and the cladding, a numerical aperture of the fiber is between 0.01 and 0.04; core diameter is from 25 to 120 micron, and a length of the gain fiber is shorter than 60 cm.

Rare earth oxides doped multicomponent glass fibers for laser generation and amplification, including a core and a cladding, the core comprising at least 2 weight percent glass network modifier selected from BaO, CaO, MgO, ZnO, PbO, K.sub.2O, Na.sub.2O, Li.sub.2O, Y.sub.2O.sub.3, or combinations; wherein the mode of the core is guided with step index difference between the core and the cladding, a numerical aperture of the fiber is between 0.01 and 0.04; core diameter is from 25 to 120 micron, and a length of the gain fiber is shorter than 60 cm.

Rare earth oxides doped multicomponent glass fibers for laser generation and amplification, including a core and a cladding, the core comprising at least 2 weight percent glass network modifier selected from BaO, CaO, MgO, ZnO, PbO, K.sub.2O, Na.sub.2O, Li.sub.2O, Y.sub.2O.sub.3, or combinations; wherein the mode of the core is guided with step index difference between the core and the cladding, a numerical aperture of the fiber is between 0.01 and 0.04; core diameter is from 25 to 120 micron, and a length of the gain fiber is shorter than 60 cm.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

The present invention relates to an optical fiber which can improve OSNR in an optical transmission system in which Raman amplification and an EDFA are combined. With respect to the optical fiber, a predetermined conditional formula is satisfied by an effective area Aeff.sub.1450 [m.sup.2] at a wavelength of 1450 nm, a transmission loss .sub.1450 [/km] at a wavelength of 1450 nm, and a transmission loss .sub.1550.sub._.sub.dB [dB/km] at a wavelength of 1550 nm. Further, with respect to the optical fiber, another predetermined conditional formula is satisfied by an effective area Aeff.sub.1550 [m.sup.2] at a wavelength of 1550 nm, and a transmission loss .sub.1550 [/km] at a wavelength of 1550 nm.