Compact slotted core ribbon cable

A slotted core type optical fiber ribbon cable, comprising:

• a cylindrical rod having a longitudinal axis and having in the exterior surface thereof at least one slot having a helical pitch, said slot having a floor;
• an optical fiber ribbon having a major surface disposed adjacent to said slot floor in said at least one slot, said ribbon comprising a planar array of at least eight optical fibers which in cross-section span a width, thereby defining a midpoint of the width in the plane containing the optical fibers;
• and, a sheath containing the rod and the optical fiber ribbons, wherein the magnitude of the slot pitch is selected to be in the range
• P.sub.c <P<P.sub.s, with
• P.sub.c =(-6.718+76.094W.sub.r)+(-2.0467+0.33014W.sub.r)R.sub.r and
• P.sub.s =(340.92+1.3495W.sub.r +6.8775W.sub.r.sup.2)+(4.5417-0.07796W.sub.r -0.037W.sub.r.sup.2)R.sub.r,
• where P is the slot pitch, W.sub.r is the width spanned by the optical fibers in the ribbon, and R.sub.r is the radial distance between the rod longitudinal axis and the midpoint of the width spanned by the optical fibers in said ribbon.