Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
1999-02-10
2001-06-26
Ngo, Hung N. (Department: 2874)
Optical waveguides
Optical transmission cable
Loose tube type
C385S112000, C385S113000, C385S103000, C385S106000
Reexamination Certificate
active
06253012
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to an optical fiber cable; and more particularly relates to an indoor/outdoor optical fiber cable that meets various competing industry standards such as peak flame, peak smoke, average smoke, compression and cold temperature bend tests.
2. Description of Related Art
Campus cables are known in the art and include four (4) categories, such as outdoor, outdoor-riser, riser and plenum cable designs. Balancing the industry specifications with current demand, results in strategic performance targets for such cables which include flame peak, smoke peak, average smoke, cold bend, compression, and temperature cycling attenuation.
Campus cables with components made of polyvinyl chlorides (PVC) have a difficult time consistently passing the average smoke requirement for the Underwriters Laboratory (UL) 910 test; while cables with components made of polyvinylidene fluorides (PVDF) generate very little smoke but do not process well when pressure extruded around fiberglass yarns.
Existing yarn-matrix units with or without water swellable powder are not flame and smoke retardant. Some yarn-matrix combinations exhibit low smoke and relatively low flame but do burn easily and are not considered flame retardant.
In the prior art, when running cable between buildings, an indoor plenum cable is used in combination with an outdoor cable. One of the major disadvantages of this approach is that the indoor plenum cable must be spliced to the outdoor cable and the cost of splicing is more expensive than the actual cost of the cable.
Patentability searches were conducted in the United States Patent and Trademark Office for patents related to an indoor/outdoor cable using plenum (i.e. flame retardant) material, as well as a combined indoor/outdoor cable using polyvinylidene fluoride (PVDF) in combination with flame retardant polyvinyl chloride (FRPVC). The results of the patentability searches are described in the aforementioned patent application Ser. No. 09/190,706.
Moreover, when cables are used in a riser application, the optical fiber must be held in a buffer tube so it does not fall out during installation. Many different methods are known in the art for holding the optical fibers inside the buffer tube in a cable.
Cables having buffer tubes without gel are known, but must be coiled intermittently at various elevations to prevent the optical fibers or optical fiber ribbons within from slipping to a lower level. However, even though coiling may be used, there is still the need to prevent water ingress and allow some coupling of the fiber to the tube for riser applications.
Cables are also known for having a tight structure or semi-tight structure such as a micro tube for holding optical fiber or optical fiber ribbon in place. However, such cables have the problem of requiring a stripping, scoring or shaving step of the buffer tube to access the fiber therein which causes damage to the fiber.
Cables are also known for having gel for holding optical fiber or optical fiber ribbon in place, preventing water ingress in the buffer tube and allowing for fiber helix movement as the cable expands and contracts due to temperature. However, such cables have the problem of removing the gel with a solvent wipe removal or other messy cleanup after working on the cable. See also U.S. patent application Ser. No. 09/090,169, filed Jun. 4, 1998, hereby incorporated by reference in its entirety, which shows cyclically placed grease segments for holding fibers in a determined position, separated by segments having no grease.
Many other U.S. Pat. Nos. 5,224,192; 5,187,763; 4,464,013; and 4,176,240 show and describe cables having a filling material or compound between a sheath and optical fiber, none of which are cyclically placed. See also European patent application no. 0157516. U.S. Pat. No. 4,232,935 (Alcatel Reference no. 90365) shows and describes a communications cable having an optical waveguide, a corrugated metallic tubular member and a filler material for continuously or discontinuously connecting the optical waveguide to the corrugated tubular member. As described in U.S. Pat. No. 4,232,935, column 2, lines 21-36, the filler material is a foamy material, a powder, petrolata that are vaseline-like and consist of waxes and oils (which has a thick consistency at room temperature and becomes more fluid at higher temperatures), high molecular polymers, plastic or material based on bitumen or polybutene. U.S. Pat. No. 4,232,935 does not describe that any filler material is a thermoset material. See also JP-56 039 503, which describes a cable having super hard ceramics which would not solve the problem of the need for movement during processing, yet yields a soft fiber-lock after processing.
A patentability search was also conducted in the United States Patent and Trademark Office for patents related to a cable having trace amounts of water swellable powder sprinkled on the optical fiber, and the following patents were found:
U.S. Pat. No. 4,401,366 discloses a fiber optic cable that includes a central core
12
with grooves
16
supporting optical waveguides
18
within an outer sheath
22
, as shown in
FIG. 1. A
mixture of hydrophilic powder and hydrophobic powder is included around the waveguides as described in column 3, lines 58-68.
U.S. Pat. No. 5,684,904 discloses an optical fiber cable that includes buffer tubes
20
wherein a coating formed from a mixture of moisture-absorptive powder and resin is applied to the inner buffer tube surface, outer buffer tube surface or both inner and outer surfaces.
FIG. 2
shows a coating
19
on the inner surface of a buffer tube
8
, and
FIG. 3
shows all of the suggested coating alternatives, as described in column 3, lines 42-60, and column 4, lines 35-42.
U.S. Pat. No. 5,698,615 discloses optical cables that include a filler material composed of water swellable powder and an additive powder, as shown in FIG.
7
and described in column 10, lines 57-64. The filling compounds have been used in electrical and optical cables, as described in the paragraph bridging columns 13 and 14.
Japanese Patent No. 58-10703 discloses an optical fiber cable that includes polyacrylamide powder in the spaces between fibers to function as a water blocking material.
Most of the prior art references, including U.S. Pat. No. 5,698,615, use composite material having water swellable powder which cause microbending in the fiber under certain cold temperature conditions. See U.S. Pat. No. 5,698,615,
FIG. 6
, filling compound FC2.
See also United Kingdom patent application no. 2 172 410 A that shows and describes an optical cable containing hydrogen trapping powder coated on a substrate tape.
The subject matter of all of the aforementioned United States and foreign patent applications and patents are hereby incorporated by reference.
SUMMARY OF THE INVENTION
In its broadest sense, the present invention provides a cable having an optical fiber, a buffer tube having the optical fiber arranged therein, and a thermoset material for frictionally-connecting the optical fiber to the buffer tube.
A thermoset material is capable of becoming permanently solid when heated or cured and is also known in the art as a crosslinked polymeric material. (Compare: A thermoplastic An material that is capable of softening or fusing when heated and of hardening again when cooled.) In the present invention, the thermoset material may be a flame-retardant product of Dow Corning named SYLJRD Silguard 184 silicone elastomer, base and curing agent, or a Liquid Rubber—Rubber Molded Compound (PMC-121/40, Parts A and B), which is not flame-retardant, but may be applied about every 0.5-30 meters. The thermoset material will not melt or appreciably soften and will maintain basic elastomeric flexibility in a temperature range from −40 to +85 degree Celsius. The thermoset material allows for fiber helix movement as the cable expands and contracts in the temperature range from −40 to +70 degrees Celsius, and is cyclically placed for fr
Keller David A.
Keller Leslie P.
Rosko John C.
Alcatel
Ngo Hung N.
Ware Fressola Van der Sluys & Adolphson LLP
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