Abstract: An optical fiber cable includes a flexible pipe of a plastics material, and a group of optical fibers loosely mounted within an axial bore of the pipe and held in contact with an inner surface of a peripheral wall of the pipe. At least one elongated flexible reinforcing member is embedded in the peripheral wall of the pipe and extends along a longitudinal axis of the cable, the reinforcing member being disposed in the vicinity of the group of optical fibers and made of a material having a higher Young's modulus than that of the plastics material of which the pipe is made. The optical fiber cable has a neutral axis extending through the bore of the pipe and defining a line of zero stress when the cable is bent longitudinally in a direction to dispose the reinforcing member radially inwardly of the group of optical fibers. The group of optical fibers are disposed on the neutral axis, so that the optical fibers are not subjected to axial contraction or elongation when the cable is bent in the direction.

Abstract: A water penetration-detecting apparatus includes an optical fiber sensor having an optical fiber, and a water-absorbent material disposed along the optical fiber in contiguous relation to the fiber. The water-absorbent material, when absorbing water, expands volumetrically so as to apply a pressure to an outer peripheral surface of the optical fiber to bend the fiber. A detecting means is connected to the optical fiber sensor for detecting a bending of the optical fiber.

Abstract: An optical fiber of a silica-based material includes a coating of cured silicone rubber covering an outer surface thereof. The cured silicone rubber coating, when subjected to an infrared spectroscopic measurement, has a transmissivity of not less than 70% at a wave number of 2100 to 2200 cm.sup.-1 at a coating thickness of 0.1 mm due to the infrared absorption due to the stretching and vibration of SiH. The coating of cured silicone rubber contains a neglibible amount of SiH so that the transmission loss of the optical fiber can be prevented from increasing over a long period of time.

Abstract: An optical fiber for communication comprises an optical fiber covered with a coating of a high-molecular elastomer having a flexural modulus of not less than 200 kg/cm.sup.2 at room temperature, the difference between the flexural moduli of said elastomer at room temperature and about -50.degree. C being not more than 1000 kg/cm.sup.2.