Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
2002-06-03
2003-12-02
Nguyen, Khiem (Department: 2839)
Optical waveguides
Optical transmission cable
Loose tube type
C385S113000
Reexamination Certificate
active
06658187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical fiber cables and, more particularly, to an improved geometrical arrangement and selection of elements forming an optical fiber cable that decreases the diameter, linear weight and cost of the optical fiber cable while, at the same time, improving its mechanical performance.
2. Description of Related Art
One type of prior art optical fiber cable assembly includes an optical core surrounded by one or more jackets. The optical core includes a plurality, e.g., six, buffer tubes surrounding a central member. Each buffer tube has a wall that encloses a plurality of optical fibers. The wall of each buffer tube is preferably formed from a synthetic thermoplastic compound, such as polybutylene-terephthalate (PBT), or polyester, such as nylon, or polyolefin, such as polyethylene. The central member is formed from a fiber reinforced plastic (FRP) rod formed from silica fibers encased in plastic coating.
The FRP rod forming the central member has a silica content between 70% and 85% and a plastic content between 30% and 15%. Because of the percentage of silica, the FRP rod is relatively rigid and has a relatively high modulus of elasticity, e.g., 50,300 N/mm
2
±10%.
As discussed above, the optical core is surrounded by a plurality of jackets. In an embodiment designed for aerial installations, the optical core is surrounded by an inner jacket formed from polyolefin, such as polyethylene, or polyester, such as nylon, an intermediate, strength layer formed from an Aramid yarn or other strength member, such as fiber glass, and an outer jacket, also formed from polyolefin such as polyethylene, or polyester, such as nylon. The optical fiber cable assembly may also include a Mylar tape and/or polyester binder disposed between the optical core and/or the inner jacket and between the strength layer and the outer jacket. In addition, polyester rip cords can be included between the inner jacket and the Mylar tape adjacent the optical core and/or between the outer jacket and the Mylar tape adjacent the strength layer.
Optical fiber cable assemblies designed for duct or premise applications are substantially the same as those designed for aerial installations except that the outer jacket and strength layer can be omitted whereupon the inner jacket becomes the outer jacket.
Problems with the prior art design of optical fiber cable assemblies include the inability to reduce the diameter of the optical core or reduce the number of Aramid yarns forming the strength layer surrounding the optical core while maintaining an acceptable degree of mechanical loading capacity of the cable assembly. Because of these inabilities, no reductions are available in the overall diameter of the optical fiber cable assembly, the circumferences and, hence, weights of the inner and outerjackets, the overall linear weight of the cable assembly or the overall cost of the cable assembly.
It is, therefore, an object of the present invention to overcome the above problems and others by providing an improved optical fiber cable assembly having an improved geometric design with improved mechanical performance over prior art fiber optic cable assemblies. This improved geometric design enables the same number of optical fibers to be received in an optical fiber cable assembly having a smaller diameter than prior art optical fiber cable assemblies while maintaining an acceptable degree of mechanical loading capacity, e.g., self loading and weather related mechanical loading, commensurate with its smaller outside diameter and lower linear weight Still other objects will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
SUMMARY OF THE INVENTION
Accordingly, I have invented an optical fiber cable assembly that includes an optical core having a plurality of elongated, hollow buffer tubes, a plurality of elongated outer interstitial members and an elongated central interstitial member. The plurality of buffer tubes is arranged with their axes extending in the same direction. When viewed from an end of the optical fiber cable assembly, the axis of each buffer tube is positioned at a corner of an imaginary triangle or an imaginary square. The plurality of buffer tubes is arranged with each buffer tube tangent to two other buffer tubes whereupon each pair of adjacent buffer tubes define an outer interstitial space therebetween. Each outer interstitial member is received in one of the outer interstitial spaces tangent to the two buffer tubes defining the outer interstitial space. The axis of each outer interstitial member extends in the same direction as the axes of the buffer tubes. The central interstitial member is received in a central interstitial space formed between the plurality of buffer tubes. The central interstitial member is positioned tangent to the plurality of buffer tubes with an axis of the central interstitial member extending in the same direction as the axes of the buffer tubes. The central interstitial member and the outer interstitial members have different moduli of elasticity, with the central interstitial member having a larger modulus of elasticity than the modulus of elasticity of each outer interstitial member.
In one exemplary embodiment of an optical fiber cable assembly, the central interstitial member is a fiber reinforced plastic (FRP) rod having silica fibers encased in a plastic coating, with a silica content between 70% and 85% by volume. It has been observed that FRPs having a higher percentage of silica fibers have a greater modulus of elasticity. In this exemplary embodiment, the FRP rod used as the central interstitial member has a modulus of elasticity of 50,300 N/mm
2
±10%. Moreover, in this exemplary embodiment, each outer interstitial member is also a FRP rod having silica fibers encased in a plastic coating, with a silica content between 50% and 70% by volume and with a modulus of elasticity of 37,700 N/mm
2
±10%.
The lower modulus of elasticity of the outer interstitial members make them less rigid than the central interstitial member and enables them to be spiral wound around the central interstitial member, together with the buffer tubes. The central interstitial member having a higher modulus of elasticity is not easily spiral wound. In an exemplary embodiment, the outer interstitial members and buffer tubes are wound spirally at a winding pitch between 8 and 20 times a diameter of the optical core. For aerial applications, the outer interstitial members and buffer tubes are preferably wound spirally at a winding pitch between 8 and 16 times the diameter of the optical core. For duct or premise applications, the outer interstitial members and buffer tubes are preferably wound spirally at a winding pitch between 10 and 20 times the diameter of the optical core.
The optical fiber cable assembly can also include a Mylar tape and/or a polyester binder disposed helically around the optical core tangent to the buffer tubes and outer interstitial members. An elongated polyester rip cord can be disposed on a side of the Mylar tape and/or polyester binder opposite the optical core. The longitudinal axis of the rip cord extends in the same direction, e.g. parallel, as the axes of the buffer tubes.
For optical fiber cable assemblies designed for duct or premise applications, a jacket comprised of, for example, polyolefin such as polyethylene, or polyester, such as nylon, surrounds the optical core. For optical fiber cable assemblies designed for aerial applications, an inner jacket comprised of, for example, a polyolefin, such as polyethylene, or polyester, such as nylon, surrounds the optical core, a strength layer comprised of, for example, Aramid or fiber glass yarn surrounds the inner jacket and a outer jacket comprised of, for example, a polyolefin, such as polyethylene, or polyester, such as nylon, surrounds the strength layer. In this latter assembly, a Mylar tape and/or a polyester binder can be disposed between
Alcoa Fujikura Limited
Beiriger Tracey D.
Nguyen Khiem
Notzen Randy A.
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