The present disclosure provides a few mode optical fiber. The few mode optical fiber includes a core region. A core region defined by a region around a central longitudinal axis of the few mode optical fiber. In addition, the core region has a first annular region extended from central longitudinal axis to radius r.sub.1, a second annular region extended from radius r.sub.1 to radius r.sub.2, a third annular region extended from radius r.sub.2 to radius r.sub.3, a fourth annular region extended from radius r.sub.3 to radius r.sub.4 and a fifth annular region extended from radius r.sub.4 to radius r.sub.5. Also, the few mode optical fiber has a cladding defined by the sixth annular region extended from radius r.sub.5 to radius r.sub.6.

An optical fiber with ultra-low attenuation and large effective-area includes a core layer and cladding layers. The cladding layers have 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 outer cladding layer. The core layer has a radius of 4.8-6.5 m, and a relative refractive index difference of 0.06% to 0.10%. The inner cladding layer has a radius of 9-15 m, and a relative refractive index difference of about 0.40% to 0.15%. The trench cladding layer has a radius of about 12-17 m, and a relative refractive index difference of about 0.8% to 0.3%. The auxiliary outer cladding layer has a radius of about 37-50 m, and a relative refractive index difference of about 0.6% to 0.25%. The outer cladding layer is a pure silicon-dioxide glass layer.

The core region of an optical fiber is doped with chlorine in a concentration that allows for the viscosity of the core region to be lowered, approaching the viscosity of the surrounding cladding. An annular interface region is disposed between the core and cladding and contains a concentration of fluorine dopant sufficient to match the viscosity of the core. By including this annular stress accommodation region, the cladding layer can be formed to include the relatively high concentration of fluorine required to provide the desired degree of optical signal confinement (i.e., forming a low loss optical fiber). The inclusion of the annular stress accommodation region allows for the formation of a large effective area optical fiber that exhibits low loss (i.e., <0.19 dB/km) in both the C-band and L-band transmission ranges.

A multi-clad optical fiber design is described in order to provide low optical loss, a high numerical aperture (NA), and high optical gain for the fundamental propagating mode, the linearly polarized (LP) 01 mode in the UV and visible portion of the optical spectrum. The optical fiber design may contain dopants in order to simultaneously increase the optical gain in the core region while avoiding additional losses during the fiber fabrication process. The optical fiber design may incorporate rare-earth dopants for efficient lasing. Additionally, the modal characteristics of the propagating modes in the optical core promote highly efficient nonlinear mixing, providing for a high beam quality (M.sup.2<1.5) output of the emitted light.

An optical fiber with ultra-low attenuation and bend insensitivity includes a core layer and cladding layers. The cladding layers have 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 outer cladding layer. The core layer has a radius of 3.0-3.9 m, and a relative refractive index difference of 0.04% to 0.12%. The inner cladding layer has a radius of 8-14 m, and a relative refractive index difference of about 0.35% to 0.10%. The trench cladding layer has a radius of about 14-20 m, and a relative refractive index difference of about 0.6% to 0.2%. The auxiliary outer cladding layer has a radius of about 35-50 m, and a relative refractive index difference of about 0.4% to 0.15%. The outer cladding layer is a pure silicon-dioxide glass layer.

A co-doped optical fiber is provided having an attenuation of less than about 0.17 dB/km at a wavelength of 1550 nm. The fiber includes a core region in the fiber having a graded refractive index profile with an alpha of greater than 5. The fiber also includes a first cladding region in the fiber that surrounds the core region. Further, the core region has a relative refractive index of about 0.10% to about +0.05% compared to pure silica. In addition, the core region includes silica that is co-doped with chlorine at about 1.2% or greater by weight and fluorine between about 0.1% and about 1% by weight.

The present invention provides a large-effective-mode-area low-loss optical fiber with optimized cladding components, which comprises a core layer and a cladding comprising, from the inside to the outside, a first sinking layer, a second sinking layer, an optional third sinking layer, and an outer cladding. In the present invention, phosphorus and aluminum are co-doped in the optical fiber cladding, to form a tetrahedron [AlPO.sub.4] in glass, thus optimizing the viscosity of the cladding while effectively reducing the refractive index of the cladding, without causing increased hydrogen loss. The process is simple, and highly repeatable.

A doping optimized single-mode optical fiber with ultra low attenuation includes a core layer and cladding layers. The cladding layers has 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 outer cladding layer. The content of fluorine in the core layer is 0.5 wt %, Ge0.12%, n.sub.10.12%. The content of fluorine in the inner cladding layer is 0.5-1.5 wt %, n.sub.20.14%. The content of fluorine in the trench cladding layer is 1-3 wt %, n.sub.30.25%. The content of fluorine in the auxiliary outer cladding layer is 0.5-2 wt %, n.sub.40.14%. The outer cladding layer is a pure silicon dioxide glass layer and/or a metal-doped silicon dioxide glass layer.

A bending-insensitive single-mode fiber with ultralow attenuation includes a core layer 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 core layer has a radius of 3.0 to 3.9 m and a relative refractive index of 0.04% to 0.12%. The inner cladding layer has a radius of 8 to 14 m and a relative refractive index 0.35% to 0.10%. The trench cladding layer has a radius of 14 to 20 m and a relative refractive index of 0.6% to 0.2%. The auxiliary outer cladding layer has a radius of 35 to 50 m and a relative refractive index of 0.4% to 0.15%. The outer cladding layer is a pure silica glass layer.

An optical fiber comprising: (i) a core region comprising an outer radius r.sub.1, and 3.0r.sub.17.0 microns and a relative refractive index .sub.1max and 0.32%.sub.1max0.5%; (b) a depressed index cladding region surrounding the core region comprising an outer radius r.sub.3 and a relative refractive index .sub.3 less than 0.2%, and trench volume V.sub.3 wherein 45% -micron.sup.2|V.sub.3|200% -micron.sup.2; (c) a first outer cladding region surrounding the depressed index cladding region and comprising a relative refractive index .sub.4 and an outer radius r.sub.4; and (d) a second outer cladding layer comprising 5 wt %-20 wt % titania, a relative refractive index .sub.5, and a thickness T.sub.M, wherein 3 micronT.sub.M30 microns, and outer radius r.sub.565 microns; the optical fiber has a mode field diameter MFD.sub.1550 and 8 micronsMFD.sub.155010.5 microns, a cutoff wavelength 1550 nm when bent 1 turn around a 2.5 mm radius mandrel, and a bending loss at 1550 nm when using a mandrel comprising a radius of 2.5 mm of 1.0 dB/turn.