HIGH FIBER COUNT, COMPACT, LOOSE TUBE OPTICAL FIBER CABLE EMPLOYING RIBBON UNITS AND FLEXIBLE BUFFER TUBES

摘要

An optical fiber cable has a longitudinally extending central strength member and at least one substantially fluid impervious, flexible plastic buffer tube S-Z wound around said central member in an alternating hand helix, said alternating hand helix having a lay length of from about 400 mm to about 600 mm. Superimposed ribbon units in stack are loosely received in the tube, each ribbon unit comprising optical fibers held together in side-to-side relation in a non--conductive material. The stack of superimposed ribbon units has an axial length from about 0.1% greater than to about 0.2% less than the axial length of the tube and has a width transverse to the stack axis and a thickness transverse to the stack width. The ribbon units are helically twisted around the axis of the stack with a pitch of from about 250 mm to about 1000 mm in the tube. The ratio of the pitch of the superimposed ribbon units to the lay length of the tube is from about 0.5 to about 1.2. There is a clearance C between the superimposed ribbon units and the inner diameter of the tube wall between about 1 mm and about 2 mm with the relation; C = (T I2 - W R2)1/2 -H R where T I is the inner diameter of said tube, W R is the width of said stack and H R is a thickness of said stack. A sheath of plastic material encircles the central strength member and the tube wound around the central member. The ratio of the ribbon pitch to the tube lay length, the clearance and the axial length of the stack are selected to provide optical signal attenuation in the optical fibers of less than 0.30 average dB/km at a 1550 nm wavelength.