An optical fiber includes (i) a chlorine doped silica based core having a core alpha (Core.sub.)4, a radius r.sub.1, and a maximum refractive index delta .sub.1 max% and (ii) a cladding surrounding the core. The cladding surrounding the core includes a) a first inner cladding region adjacent to and in contact with the core and having a refractive index delta .sub.2, a radius r.sub.2, and a minimum refractive index delta .sub.2 min such that .sub.2 min<.sub.1 max, b) a second inner cladding adjacent to and in contact with the first inner cladding having a refractive index .sub.3, a radius r.sub.3, and a minimum refractive index delta .sub.3 min such that .sub.3 min<.sub.2, and c) an outer cladding region surrounding the second inner cladding region and having a refractive index .sub.5, a radius r.sub.max, and a minimum refractive index delta .sub.3 min such that .sub.3 min<.sub.2. The optical fiber has a mode field diameter MFD at 1310 of 9 microns, a cable cutoff of 1260 nm, a zero dispersion wavelength of 1300 nmzero dispersion wavelength 1324 nm, and a macrobending loss at 1550 nm for a 20 mm mandrel of less than 0.75 dB/turn.

A 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 3.9-4.8 m and a relative refractive index difference of 0.08% to 0.10%. The inner cladding layer has a radius of 9-14 m and a relative refractive index difference of 0.40% to 0.15%. The trench cladding layer has a radius of 13-25 m and a refractive index difference of 0.7% to 0.3%. The auxiliary outer cladding layer has a radius of 30-50 m and a relative refractive index difference of 0.4% to 0.15%. The outer cladding layer is a pure silicon dioxide glass layer.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

A single mode optical fiber, comprising: A single mode optical fiber, comprising: (i) a silica based core having a refractive index profile with an alpha () between 1.8 and 200, a relative refractive index .sub.1max %, and an outer radius r.sub.1, wherein 7 microns >r.sub.14.5 microns, the core further comprising silica doped with chlorine, wherein the maximum chlorine concentration in the core is greater than 0.5 wt %; and wherein

1.40<X<1.7 where X=[(2n.sub.1(2.sub.1max %r.sub.1.sup.2).sup.1/2/V.sub.c)+(0.0028*V.sub.m)],

n.sub.1 is maximum refractive index of the core, V.sub.m is moat volume, and V.sub.c is a function of core alpha () and (ii) an outer cladding region surrounding the first cladding region, the outer cladding region having a relative refractive index .sub.4 % such that .sub.1max>.sub.4 %.

A single mode optical fiber including a germania doped silica central core region having outer radius r.sub.1 and refractive index .sub.1, a maximum refractive index .sub.1max, and 0.32%.sub.1max0.45%, and a core alpha profile (Core.sub.). In various embodiments, the optical fiber also contains a cladding region including: (i) a second inner cladding region or ring region surrounding the first inner cladding region; or (ii) an inner cladding region or pedestal region surrounding the germania doped silica central core region. The corresponding resultant optical fibers exhibit a 22 m cable cutoff less than or equal to 1260 nm, a macrobending loss at 1550 nm of 0.75 dB/turn on a 20 mm diameter mandrel, a zero dispersion wavelength, .sub.0, of 1300 nm.sub.01324 nm, and a mode field diameter at 1310 nm of 8.2 micronsMDF.sub.1310 nm9.6 microns.

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.

An optical fiber includes (i) a chlorine doped silica based core having a core alpha (Core.sub.)4, a radius r.sub.1, and a maximum refractive index delta .sub.1 max% and (ii) a cladding surrounding the core. The cladding surrounding the core includes a) a first inner cladding region adjacent to and in contact with the core and having a refractive index delta .sub.2, a radius r.sub.2, and a minimum refractive index delta .sub.2 min such that .sub.2 min<.sub.1 max, b) a second inner cladding adjacent to and in contact with the first inner cladding having a refractive index .sub.3, a radius r.sub.3, and a minimum refractive index delta .sub.3 min such that .sub.3 min<.sub.2, and c) an outer cladding region surrounding the second inner cladding region and having a refractive index .sub.5, a radius r.sub.max, and a minimum refractive index delta .sub.3 min such that .sub.3 min<.sub.2. The optical fiber has a mode field diameter MFD at 1310 of 9 microns, a cable cutoff of 1260 nm, a zero dispersion wavelength of 1300 nmzero dispersion wavelength1324 nm, and a macrobending loss at 1550 nm for a 20 mm mandrel of less than 0.75 dB/turn.

A single mode optical fiber including a germania doped silica central core region having outer radius r.sub.1 and refractive index .sub.1, a maximum refractive index .sub.1max, and 0.32%.sub.1max0.45%, and a core alpha profile (Core.sub.). In various embodiments, the optical fiber also contains a cladding region including: (i) a second inner cladding region or ring region surrounding the first inner cladding region; or (ii) an inner cladding region or pedestal region surrounding the germania doped silica central core region. The corresponding resultant optical fibers exhibit a 22 m cable cutoff less than or equal to 1260 nm, a macrobending loss at 1550 nm of 0.75 dB/turn on a 20 mm diameter mandrel, a zero dispersion wavelength, .sub.0, of 1300 nm.sub.01324 nm, and a mode field diameter at 1310 nm of 8.2 micronsMDF.sub.1310nm9.6 microns.

A present embodiment relates to a MDL measurement method and the like including a structure for enabling MDL measurement without increasing a processing load. The present embodiment sequentially executes, for N (2) spatial modes, light-input operation of inputting light of a predetermined intensity to an arbitrary spatial mode, and intensity measurement operation of measuring an output light intensity of each of the N spatial modes including the arbitrary spatial mode, to generate a transfer matrix relating to transmission loss in an optical fiber as a measurement target, and determine at least a linear value of MDL per unit fiber length by using each component value of the generated transfer matrix.

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.