CA1300943C - Multiple channel duct manifold system for fiber optic cables - Google Patents

Abstract

ABSTRACT OF DISCLOSURE
A multiple channel duct manifold system for optical fibers which includes a plurality of elongated, corrugated tubing sections extended in parallel, contiguous relation to each other, and retained in such contiguous relation by a surrounding overwrap of thin flexible, synthetic resin film.

Description

i300943 MVLTIPLE CHANNEL DUCT MANIFOLD S~STEM
FOR FIBER OPTIC CABLES
~ield of the Invention This invention relates to tubing or duct which is pro-viaed for containing long runs of optical fibers disposed in underground communications networks. More particularly, the invention relates to a multiple channel duct manifold system for optical fibers which includes a plurality of contiguous ducts or tubing sections adapted for the containment of lengthy runs of optical fibers, such as are typically employed in a long distance communication system.
Background of the Invention B ef Description of the Prior Art The use of light or optical conductors in place of, or in addition to, electrical conductors for the purpose of long distance transmission of information signals has rapidly increased in recent times. Glass fibers or fila-ments are preferably used as such light conductors, as are some other solid and liquid substances. Very long fiber-like conductors are frequently referred to as optical fiber cables, or as light conducting cables.
Optical fiber usage presents some problems due to the mechanical characteristics of these fibers, such as their low tensile strength and ultimate elongation. One effort made to reduce or solve these problems entails the encase-ment of the optical fibers in tubular elements or sheaths of various types (often termed innerducts) which both protects the optical fibers from mechanical damage, and also facili-tates their placement in underground systems extending over great distances. Among the sheathing materials which have been employed are thermoplastic synthetic resins such as polyethelene, polyester, polyamides and polyacrylates. It -1- ~

~3109A3 is still necessary, however, to attempt to minimize the magnitude o~ the stresses and deforming forces which act upon the optical fibers during the construction of cables, including the tubular protective elements, and during the laying of these cables in the earth.
In U.S. Patent 4,153,332 to Longoni, a sheathed optical fiber cable is disclosed and includes a surrounding external sheath of a plastic material which encloses a plurality of tubular elements. Each one of the tubular elements encloses an optical fiber. The tubular elements have smooth walls, both internally and externally. The Longoni patent explains that the optical fibers which are inserted in the tubular elements or sheaths can be bare, or each can be covered with a thin adhering protective layer of a plastic material.
Franke et al U. S. Patent 4,039,248 describes a fiber-like conductor which is housed within a tubular sheath. The sheath may be corrugated for the purpose of retaining the fiber-like conductor in a desired undulating configuration within the sheath.
Brief Description of the Present Invention The present invention is a multiple channel duct mani-fold system for containing optical fiber cables. The multiple channels are made up of a plurality of contiguous, codirectionally extending sections of elongated tubular ele-ments or conduits. The sections of tubing or conduit are corrugated and are highly flexible. The corrugations include contiguous alternating ridges and troughs or grooves extending along the length of the tubing or conduit section.
The several tubing sections are held in contiguous abutting relationship, with their longitudinal axes ~3~0943 extending substantially parallel, by a thin, encircling t-lexible sheath or overwrap of synthetic resin.
The length of the multiple channel duct manifold system can be extended by joining or splicing sections of the corrugated tubing or conduit in end-to-end relationship to each other b,,v the use of a suitable coupling or sleeve which functions to interlock the sections in end-to-end rela-tionship.
An important object o~ the invention is to provide a tubular system for encasing and carrying elongated runs of optical fibers as they are employed in an underground com-munication system.
Another object of the invention is to provide a multiple channel duct manifold system in which a plurality of corru-gated synthetic resin tubes or conduits are laid in abutting relationship to each other with their axes extending parallel, and are then overwrapped with a film of synthetic resin material which is capable of undergoing bending and flexing with the several corrugated tubing sections, as may be needed to negotiate curves and bends in an underground innerduct system.
A further object of the invention is to provide a mecha-nically strong, optical fiber tubing encasement system where a plurality of tubular sections are laid one upon the other and harnessed into a bundle by the use of a flexible overwrap element.
Additional objects and advantages will become apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings which illustrate a preferred embodiment of the invention.

i~O0943 General Description of the Drawings Figure 1 is a front elevational view of the optical fiber duct manifold system of the invention depicting a typical system containing three optical fiber ducts which are contained within an external synthetic resin sheath. A
portion of the external synthetic resin sheath has been bro-ken away to show two of the optical fiber ducts which are here made up of serially or end-to-end coupled duct sec-tions.
Figure 2 is a sectional view taken along the line 2-2 of Figure 1.
Figure 3 is a view in elevation illustrating the manner in which manifolded optical fiber ducts constructed in accordance with the invention are reeled upon a storage reel ready to be paid out for typical installation in an underground location.
Detailed Description of a Preferred Embodiment of the Invention Referring to Figure 1, the fiber optic multiple channel duct manifold system of the invention includes a plurality of elongated conduit or tubing sections which are manifolded into contiguous relationship to each other. In the illustrated embodiment of the invention, three sections of corrugated conduit, denominated by reference numerals 10, 12 and 14, are utilized. In some applications, many more than three co-extending conduits or tubular elements may be uti-lized, and are positioned contiguously to each other.
As will be perceived in referring to Figure 1, each of - the corrugated conduit sections 10, 12 and 14 is charac-terized in having contiguous, circumferentially extending corrugations formed over the entire length of the conduit section. The corrugations are made up of a series of ridges 16 and valleys or troughs 18, and these provide the charac-teristic internal wall geometry of each of the conduit sec-tions, as well as the external wall configuration. Although regular, precisely circular corrugations constitute the pre-ferred corrugation configuration, helical corrugations can also be utilized.
The material of whicb each corrugated conduit section 10, 12 and 14 is constructed can be any of various synthetic resins incl~ding, but not limited to, polyvinylchloride, polyethylene, polypropylene and various polyamides. It is important that the materials selected have relatively good flexibility since, as will be hereinafter explained, an important and advantageous characteristic of the fiber optic multiple channel manifold system of the invention is its ability to be coiled or bent through a relatively small radius without fracture or damage.
A typical utilization of conduits for the purpose of containing optical fibers is for burial in subterranean tun-nels or large diameter ducts, or direct burial in the earth as a part of communications systems. In any case, each con-duit section extends over substantial distances, and encases or encloses the optical fibers which are to constitute the communication medium. Typically, a section of the corru-gated conduit and duct can have a length of from about 20 feet to about 2,000 feet, and a number of sections of the conduit are usually spliced or connected together in end-to-end relation so that the overall length of the newly con-nected conduit sections may be many miles in length.
For the purpose of retaining the manifolded corrugated conduit or duct sections in contiguous and abutting rela-i3~1094~3 tionship to each other, a thin flexible film or sheath 20 of synthetic resin is wrapped tightly around the sections of conduit as illustrated in Figure 1. The sheath or film 20 of overwrapped material is preferably from about 5 mils to about 15 mils in thickness, and has sufficient flexibility and strength that the manifolded optical fiber ducts can be bent through a relatively small radius without fracture or mechanical failure of the film overwrap. The sheath 20 is preferably constructed of rigid polyvinylchloride, but other synthetic resin materials can also be utilized.
~t those locations along the manifolded sections of corrugated conduit or duct where the sections terminate, and it is necessary, for tubular continuity and extension of length, to connect sections of the duct or conduit in an end-to-end relation, sleeves or couplings 24 of the type depicted in Figure 1 are utilized. Various types of such couplings 24 can be employed, including the types used for coupling standard Schedule 40 plastic conduit sections to each other. The coupling or interlock can be achieved mechanically, by glue or adhesion or by thermal fusion. The type of coupling currently marketed under the name "ENDOCLIP" by ~ndot Industries of Denville, New Jersey can also be employed. Preferably, the sleeves or couplings 24 are relatively thin so that no significant enlargement in the overall outside diameter of the conduit section is caused as a result of connection of the coupling or sleeve thereto. Generally, the coupling or sleeve utilized will be an internally ribbed element which can mechanically interengage the corrugation on the conduit sections, and thus form a positive interlock between adjacent end portions of the duct or conduit sections.

1~0094~

I have found that the duct manifold system of the type described is surprisingly flexible and can be easily coiled around relatively large reels of the type illustrated in Figure 3 of the drawings, and there denominated by referencP
numeral 26. A great length of the duct manifold system 28 can be coiled on the reel 26 for lay out into an underground communications pipe, or can be reeled into a trench for direct burial.
An important advantage of the present invention is that the multiple sections of duct or corrugated conduit can be retained in the same relationship to each other at one end of the manifold system as at the other. Thus, it will be possible to know which of the ducts contain certain specific optical fibers connected to certain signal inputs at one end thereof, so that no misconnections occur as a result of con-fusing the optical fibers in one of the ducts with those in another duct as a result of twisting or turning occurring over the length of the manifold system. By color coding, notching or otherwise marking at least one of the conduit sections in a characteristic way at each end, the rela-tionship and identity of all conduit sections can be known.
The manifold system also permits longer pulls to be accom-modated than with the single conduit sections, and the corrugated interior wall assures that less surface area will contact the optical fibers inside the conduit sections, and thus less surface friction will be developed. The fibers thus can be pulled through the conduit sections more easily.
The conduit manifold system allows an overall reduction 3Q in fiber optic cable installation costs, and the manifolding aspect of the system maintains high structural integrity i3~

over the entire length of the conduit sections, and affor~s enhanced moisture protection to the entire system by reason of the overwrap employed.
Although a preferred embodiment of the invention has been illustrated and described in the foregoing description, it will be understood that various changes can be made in the illustrated and described structure without departure from the basic principles upon which the invention rests.
Thus, for example, many more than three duct or conduit sec-tions can be manifolded together over very long lengths.
Changes such as that described are nevertheless deemed to be characteristic of other embodiments of the invention which fall within the spirit and scope of the invention as the same is defined by the following claims or reasonable equivalents thereof.

Claims (9)

1. A multiple channel duct for optical fiber cable comprising:
a plurality of contiguous, co-directionally extending substantially parallel sections of elongated, tubular corrugated conduit in abutting contact with each other, each of said sections having a series of encircling contiguous convolutions extending over the length thereof to impart flexibility to the respective elongated conduit sec-tions; and a flexible, synthetic resin overwrap sheath encircling and jacketing the corrugated conduit sections to retain them in their contiguous relationship, said sheath having sufficient strength and flexibility to permit said conduit sections to undergo flexing without any substantial restriction of, or reduction in, the extent of flexibility of said sections resulting from encircling them with said sheath.

2. A multiple channel duct as defined in Claim 1 wherein said encircling contiguous convolutions are con-centric, circular internal and external corrugations made up of contiguous ridges and troughs, whereby the frictional resistance to the pulling of optical fibers therethrough is substantially reduced, and the resistance of said sections to longitudinal sliding movement against each other is substantially increased.

3. A multiple channel duct as defined in Claim 1 wherein said sheath comprises a sheet of polyvinylchloride.

4. A multiple channel duct as defined in Claim 1 wherein said multiple channel duct is further characterized as including a plurality of sets of said sections of conduit in which the conduit sections in the respective set are coupled to each other in co-linear, end-to-end relationship, each of said sets having the longitudinal axes of the con-duit sections therein extending parallel to, and spaced from, the axes of the conduit sections in each other set, and said sections being retained in tangential abutting con-tact by said flexible overwrap.

5. A multiple channel duct as defined in Claim 4 wherein said encircling, contiguous convolutions are con-centric, circular internal and external corrugations made up of contiguous ridges and troughs whereby the frictional resistance to the pulling of optical fibers therethrough is substantially reduced, and the resistance of said sections to longitudinal sliding movement against each other is substantially increased.

6. A multiple channel duct as defined in Claim 3 wherein said multiple channel duct is further characterized as including a plurality of sets of said sections of conduit in which the conduit sections are coupled to each other in co-linear, end-to-end relationship, each of said sets having the longitudinal axes of the conduit sections therein extending parallel to, and spaced from, the axes of the con-duit sections in each other set, and said sections being retained in tangential abutting contact by said flexible overwrap.

7. A multiple channel duct as defined in Claim 5 wherein said sheath comprises a sheet of polyvinylchloride.

8. A multiple channel duct as defined in Claim 7 wherein said sheet of polyvinylchloride has a thickness of from about 5 mils to about 15 mils.

9. An optical fiber duct manifold comprising:
at least three co-extending, parallel, individual elongated corrugated duct sections each of substantially round cross-section and including internal, circular corru-gations formed by adjacent ridges and valleys, each of said duct sections tangentially contacting at least two other duct sections;
a flexible overwrap sheath extending around said duct sections and manifolding them together in contiguous relationship so that said corrugated sections will con-currently bend through equivalent radii of curvature upon application of a bending force thereto; and at least one optical fiber extending through the entire length of each of the duct sections and contacting only the ridges of said internal corrugations.