The present invention introduces a concept of "smart" ribbons, which use functionally
tensioned optical fibers during the manufacture of fiber optic ribbons to create
fiber ribbons with controlled geometrical configuration, optimized strain distribution
and reduced attenuation. The ribbons may have flat or bowed cross section and be
straight along the length or curved in its plane, or twisted unidirectionally,
or periodically. These shapes and residual stress-strain state are induced and
controlled by using tension functions instead of traditional constant-value tension
per fiber during the ribbon manufacture. Further, the present invention reduces
signal loss and/or attenuation in ribbon fibers caused by an increase in the strain
variation from tensile strain to compressive strain along the length of the individual
fibers when ribbons are manufactured, stacked, stranded around a strength member
or twisted and bent during cable installation. In a first embodiment of the present
invention, either a symmetric or non-symmetric load distribution is applied across
the fibers being placed or drawn into a ribbon structure to eliminate or control
residual twist in a completed fiber ribbon. Additionally, in the present invention,
the load distribution on the fibers of a ribbon can be varied (e.g. periodically
changed) along the length of the ribbon to provide a ribbon with the required design
characteristics for any particular application. In a second embodiment of the invention,
a fiber optic ribbon is made up of a plurality of sub-unit ribbons arranged in
substantially the same plane. Each sub-unit ribbon includes a plurality of optical
fibers coated by sub-unit matrices.
