Depressed cladding optical fiber cable

摘要

An optical fiber cable (20) includes a core (21) comprising plurality of units (22-22). Each unit is formed by a plurality of optical fibers (24-24) which are assembled together without intended stranding. Each of the optical fibers includes a core, and inner and outer claddings with the inner cladding characterized by an index of refraction depressed from that of the outer cladding. The ratio of the inner cladding diameter to the core diameter and the ratio of the difference in the indices of refraction of the inner and outer claddings to the difference in indices of refraction between the core and the inner cladding are such that each optical fiber is capable of operation in a single mode fashion at a predetermined wavelength. Also, the difference between the indices of refraction of the core and the inner cladding is sufficiently high to cause each fiber to be substantially insensitive to microbending. The plurality of units are enclosed in a common tube (34) which provides a predetermined packing density. In one embodiment, a waterblocking material (46) is disposed within the tube to fill the interstices between the optical fibers and between the units. The waterblocking material is such that its critical yield stress does not exceed about 70 Pa at 20 DEG C. and such that it has a shear modulus of less than about 13 KPa at 20 DEG C. The common tube is enclosed with a sheath system. This arrangement is such that the optical performance of the cable is not degraded at temperatures as low as -40 DEG F.