Lucent Technologies Inc.

At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Ofs Fitel, LLC

Fitel USA Corporation

Paul Francis Glodis

Kenneth L Walker

Man Fei Yan

James William Fleming

David Kalish

Parbhubhai D Patel

Robert M Atkins

Thomas John Miller

Siu-Ping Hong

Katherine Theresa Nelson

Zhi Zhou

Kim Willard Womack

Donald Paul Jablonowski

Shunhe Xiong

Charles H Gartside, Iii

Charles Francis Gridley

Terrence A Lenhan

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.

MCVD optical fiber method with partial removal of substrate tube

Methods for modifying preform core ovality during and subsequent to the formation of an optical fiber preform. After MCVD deposition forms the core rod, but prior to overcladding of the core rod, the code rod may be etched to change its ovality. In order to etch the core rod, the core rod may be mounted to lathe, rotated by at least two rotors, and subjected to a heat source. Additionally, one of the at least two rotors may be phase-shifted from another one of the at least two rotors after the core rod is mounted on the lathe.

Methods for modifying ovality of optical fiber preforms

Bubble-free core glass can be deposited at relatively high rate (e.g., &gt;0.3 gm SiO.sub.2 /minute, preferably 0.6 gm SiO.sub.2 /minute or more) by MCVD if the deposition conditions are appropriately selected. For instance, a relatively high torch traverse speed, a relatively low sintering temperature, and/or relatively low gas flow rates can facilitate high rate deposition of bubble-free glass. By way of example, conditions are disclosed that yielded essentially bubble-free core glass (.DELTA.=0.35%) at a rate of 1 gm SiO.sub.2 /minute.

High rate MCVD method of making an optical fiber preform

A large optical preform 303 is made by a modified chemical vapor deposition (MCVD) process by depositing successive layers of core and cladding materials onto the inside surface of a rotating glass tube 33 having a hydroxyl ion (OH.sup.-) level that is less than 0.5 parts per million (ppm) by weight. The tube is then collapsed inwardly to form a core rod 301 in which the deposited core material 31 has a diameter that is greater than about 5 millimeters and the deposited cladding material 32 has an outside diameter that is less than about 15 millimeters. A machine-vision system 140, 150, 160 monitors and controls the diameter of the glass tube by regulating the pressure within the tube. Moreover, the machine-vision system monitors and controls the straightness of the tube by varying its rotational speed according to angular position. After the core rod 301 is formed, it is plasma etched to remove contaminants, and then overclad with two glass jackets 34, 35 having a hydroxyl ion (OH.sup.-) level that is less than 1.0 ppm by weight to create a large preform 303 from which about 400 kilometers of singlemode optical fiber can be drawn per meter of length.

Method of making a large MCVD single mode fiber preform by varying

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 &lt;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. A variety of advantageous embodiments of the inventive methods, as well as of fiber produced by the method, are disclosed.

Method of producing optical fiber, and fiber produced by the method

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. The plurality of units are enclosed in a common tube (34) which provides a predetermined packing density. In one embodiment, a waterblocking material (46) is disposed within the tube to fill the interstices between the optical fibers and between the units. The waterblocking material is such that its critical yield stress does not exceed about 70 Pa at 20.degree. C. and such that it has a shear modulus of less than about 13 KPa at 20.degree. C. The common tube is enclosed with a sheath system. This arrangement is such that the optical performance of the cable is not degraded at temperatures as low as -40.degree. F.

Depressed cladding optical fiber cable

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 &lt;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.

Single mode optical fiber

Growing community of inventors

Atlanta, GA, United States of America

Paul Francis Glodis