Abstract: The specification describes methods for the manufacture of very large optical fiber preforms wherein the core material is produced by MCVD. Previous limitations on preform size inherent in having the MCVD starting tube as part of the preform process are eliminated by removing the MCVD starting tube material from the collapsed MCVD rod by etching or mechanical grinding. Doped overcladding tubes are used to provide the outer segments of the refractive index profile thus making most effective use of the MCVD produced glass and allowing the production of significantly larger MCVD preforms than previously possible.

Abstract: The specification describes methods for the manufacture of very large optical fiber preforms wherein the core material is produced by MCVD. Previous limitations on preform size inherent in having the MCVD starting tube as part of the preform process are eliminated by removing the MCVD starting tube material from the collapsed MCVD rod by etching or mechanical grinding. Doped overcladding tubes are used to provide the outer segments of the refractive index profile thus making most effective use of the MCVD produced glass and allowing the production of significantly larger MCVD preforms than previously possible.

Abstract: The specification describes methods for the manufacture of very large optical fiber preforms wherein the core material is produced by MCVD. Previous limitations on preform size inherent in having the MCVD starting tube as part of the preform process are eliminated by removing the MCVD starting tube material from the collapsed MCVD rod by etching or mechanical grinding. Doped overcladding tubes are used to provide the outer segments of the refractive index profile thus making most effective use of the MCVD produced glass and allowing the production of significantly larger MCVD preforms than previously possible.

Abstract: The present invention provides systems and methods for removing or decreasing the undesirable oscillations in MFD and dispersion in an OTDR trace of an optical fiber. In addition, the present invention removes the undesirable oscillations in core ovality of a preform fabricated by a vapor deposition technique. Briefly stated, the present invention comprises increasing the rotational rate of the substrate tube during the deposition process to between 50-65 rpm, preferably approximately 60 rpm.

Abstract: The inventive method of producing optical fiber comprises producing a rod-like silica-based body, overcladding the body with pre-existing silica-based glass, and drawing fiber from the thus produced preform. The rod-like body comprises a core and a first cladding that surrounds the core, both consisting of deposited glass, and further comprises a second cladding that surrounds the first cladding and that is derived from a substrate tube that has a refractive index n.sub.2 <n.sub.0, the refractive index of vitreous silica. The overcladding comprises pre-existing glass, and comprises a third cladding region that has a refractive index n.sub.3 .ltoreq.n.sub.0. Typically, the overcladding material is derived from one or more overcladding tubes. The inventive method can be used to produce preforms capable of yielding more fiber than prior art rod-in-tube preforms, potentially resulting in significant cost reduction without performance penalties.

Abstract: An optical fiber cable (20) includes a core (21) comprising plurality of units (22--22). Each unit is formed by a plurality of optical fibers (24--24) which are assembled together without intended stranding. Each of the optical fibers includes a core, and inner and outer claddings with the inner cladding characterized by an index of refraction depressed from that of the outer cladding. The ratio of the inner cladding diameter to the core diameter and the ratio of the difference in the indices of refraction of the inner and outer claddings to the difference in indices of refraction between the core and the inner cladding are such that each optical fiber is capable of operation in a single mode fashion at a predetermined wavelength. Also, the difference between the indices of refraction of the core and the inner cladding is sufficiently high to cause each fiber to be substantially insensitive to microbending.

Abstract: A single mode optical fiber comprises a core, a first cladding surrounding the core, and a second cladding surrounding the first cladding. It also comprises a third cladding region (or index "ring"). The core, has radius a and refractive index n.sub.c, the first, second, and third cladding regions have inner radii, R.sub.1i, R.sub.2i, and R.sub.3i, outer radii R.sub.1o, R.sub.2o, and R.sub.3o, and indices n.sub.1, n.sub.2, n.sub.3, respectively. The fiber has n.sub.1 <n.sub.3, R.sub.1o .ltoreq.R.sub.3i, R.sub.3o .ltoreq.R.sub.2i. In preferred embodiments, a=R.sub.1i, R.sub.1o =R.sub.3i, R.sub.3o =R.sub.2i. Appropriate choice of ring parameters can result in a lowering of the cut-off wavelength of the fiber, or in fiber that is less sensitive to macrobending than similar prior art fiber lacking an index ring, without substantial change in fiber parameters that depend primarily on the waveform in the core. An optical fiber communications system comprising the inventive fiber is also disclosed.