Optical fiber ribbon cable and assembly thereof with a connector

An optical fiber ribbon cable having a specified space between the first and second optical fibers, a guide piece to fit onto the cable against the web of jacket between the first two optical fibers, and an assembly of the cable and guide piece with an optical fiber connector to supply accuracy and predictability of dimensions for assembly of optical fiber cables to connectors of close dimensional tolerances.

FIELD OF THE INVENTION 
The invention pertains to optical fiber ribbon cables having precisely 
aligned and oriented optical fibers therein for termination to a connector 
having close tolerance termination requirements. 
BACKGROUND OF THE INVENTION 
In the field of optical fiber cables, the mating thereof to very precise 
connectors having very close dimensional tolerances renders it 
increasingly difficult to manufacture optical fiber cables to the 
dimensional precision required for termination to those connectors. The 
invention provides optical fiber ribbon cables having precisely spaced 
optical fibers which can meet the dimensional tolerances required for 
termination to such connectors. 
SUMMARY OF THE INVENTION 
The invention comprises an optical fiber ribbon cable in which a 
multiplicity of optical fibers are cabled together within a jacket of 
dielectric material at precise distances apart, there being at least one 
optical fiber width space between an edge fiber and the next adjacent 
fiber, preferably two fiber widths space therebetween. The first optical 
fiber from the edge of cable is positioned in a location within the cable 
such that the other optical fibers can be easily and precisely positioned 
in the cable with reference to the first fiber. 
By separating the first and second optical fibers from each other by at 
least one and preferably two center-to-center spacing units (such as 0.01 
inch per unit), in the form of a groove, the cable with the aid of one or 
two, upper and/or lower, guide pieces can track the groove into a 
connector to position the cable correctly and precisely in the connector 
for termination of the individual optical fibers. 
The guide pieces are in the form of small flat molded polymer pieces of 
about the width of the cable which have a protruberance or ridge molded 
accurately into one side to exactly match the groove in the cable between 
the first and second optical fibers. One or two guide pieces are laid on 
the top and/or bottom of the cable end and together the guide pieces and 
cable inserted as a unit into an optical fiber connector. 
The optical fiber ribon cables of the invention are manufactured by 
standard cabling techniques used in the cabling art. The optical fibers 
used therein are those known to be useful in the art, made of glass or 
plastic, coated or uncoated, and covered or not covered by buffering 
layers of soft or hard materials. A high-temperature embodiment of the 
cable may be formed of sheets of unsintered PTFE or unsintered expanded 
PTFE around the optical fibers and the PTFE sintered at the end of the 
cabling process. The sheathing of the cable which holds the optical fibers 
in position precisely spaced apart from each other may be porous expanded 
polytetrafluoroethylene (PTFE) coated with a thermoplastic polyester to 
seal and hold the PTFE layers together at the edges of the cable or in 
between the optical fibers in the form of webs between the fibers. The 
expanded PTFE useful in the invention is that disclosed in U.S. Pat. Nos. 
3,953,566, 3,962,153, 4,096,227 and 4,187,390. Other equivalent materials 
of similar insulation properties to the above preferred PTFE materials may 
also be utilized. The guide pieces may be any commonly useful moldable 
thermoplastic insulation material or thermosetting insulation material if 
needed for a high-temperature resistant cable.

DETAILED DESCRIPTION OF THE INVENTION 
The invention is now described, but not limited, by reference to the 
drawings to more carefully delineate the scope of the invention which will 
be described by the appended claims. 
FIG. 1 shows a partial perspective view of a portion of ribbon cable 13 of 
the invention in which one optical fiber 1 near an edge of ribbon cable 13 
is separated by web 7 within the polymeric insulation 4 by at least one 
fiber diameter, preferably at least two fiber diameters from the second or 
next adjacent optical fiber 2. The remaining optical fibers 3 of ribbon 
cable 13 may be adjacent each other without intervening webs of 
insulation. As shown in FIG. 2, there may be intervening webs 14 of 
insulation separating the optical fibers 2 and 3 from each other at 
carefully controlled distances apart. Web 7 of insulation separates and 
holds in place optical fibers 1 and 2 at the specified one or two fiber 
width distance apart. 
Cable 13 is manufactured by well-known cabling methods used in cabling 
electric signal conductors and fiber optic cables together into flat 
ribbon cables. In this invention, insulation 4 is preferably made from 
sheets of the porous expanded PTFE described above which have on one 
surface an adhesive layer of thermoplastic polyester for easy adherance of 
two layers of expanded PTFE to each other around the optical fibers 3 of 
the cable in the cabling process. This method allows close dimensional 
control of the spacing of the optical fibers within the cable during and 
after the process. 
Where a high temperature cable is being made the insulation may be sheets 
of PTFE insulation extruded from emulsion prepared fine PTFE powder 
particles which are placed around the optical fibers by the cabling 
process and the resulting ribbon cable heated in a salt bath or sintering 
oven for the requisite time at a temperature to fully sinter the PTFE to 
full-density PTFE insulation. 
In the cabling process, optical fiber 1 is carefully spaced at preferably 
two optical fiber diameters from the second or next adjacent optical fiber 
2 so that the spacing of fiber 2 and the remaining optical fibers 3 such 
that a known spacing between fibers 1, 2, and 3 is achieved and maintained 
within the cable with fiber 1 being the reference fiber for that spacing. 
Such carefully controlled spacing between optical fibers is necessary to 
match the termination grooves of more modern optical fiber connectors for 
accurate termination to those connectors. As shown in FIG. 3, the second 
and third grooves of the connector remain empty to correspond to the gap 
of controlled size between fibes 1 and 2 of cable 13. 
To aid in maintaining the required spacing while cable termination is being 
performed, a guide piece 8 is placed either above or below or both above 
and below the end of cable 13. The guide piece 8 is relatively short and 
corresponds to the length of cable which is to be inserted in connector 11 
as shown in FIG. 3. The grooves 12 in connector 11 aid in maintaining the 
spacing in the connector of the optical fibers of the cable. A protruding 
portion 9 of guide piece 8 fits down into web 7 when guide piece 8 is 
placed in abutment with cable 13 for insertion into connector 11. A cover 
(not shown) fits over cable 13 and guide piece 8 to hold them in the 
completely assembled connector. The cable 13 and guide piece 8 when fully 
assembled to connector 11 form an assembly of the invention. The guide 
piece may be manufactured from any moldable plastic dielectric material, 
usually a thermoplastic polymer being preferred for convenience and ease 
of manufacture. 
The cable 13, the guide piece 8 provide a simple easy to assemble means to 
overcome the spacing problems and supply the needs for accuracy and 
predictability of dimensions for assembly of optical fiber cables to 
modern connectors having close dimensional tolerances.