We have developed a flat type multi-fibers cable which is intended to use in data bus. As the broad-band characteristics is not necessarily required in such systems, we adopted the silicone cladding pure silica core fiber for the constitution unit of the flat type cable which has 10 optical fibers. The flat type cable is 5 mm wide and 0.5 mm thick and 1 km long. Core diameter and cladding diameter of silicone clad optical fiber is 150 µm and 360 µm respectively and refractive index difference between core and cladding is approximately 3.6%. In order to prevent silicone clad fiber from optical and mechanical damages due to handling and enviromental forces, they are jacketed with polyester elastomer of 0.5 mm in diameter. Mean value of the transmission losses of 10 fibers of the flat cable is 3.6 dB/km and the standard deviation of losses is 0.3 dB/km at 0.82 µm. This flat cable could be advantageous in solving the problems of inductive disturbance from electrical equipment and cable congestion in comparison with the usual cable with copper conductor. As the results of many optical and mechanical tests on the cable, we found it possible that the cable can be used pratically.

It is very important to choose appropriate fiber parameters such as core and outer diameters and refractive index difference of fiber for obtaining low loss and stable fiber cables for practical use. Several problems related to determine the fiber parameters must be taken into concideration for a design of fiber structures. Many theoretical and experimental studies on the relationship between fiber parameters and transmission characteristics to show fiber parameters dependence on excess loss useful for the design of practical fiber cables. In this paper, we made clear experimentally the relationship between excess losses and fiber parameters for jacketed step-index fibers with various combinations of core and outer diameters, index difference and jacket diameter. As the results, we found that the excess loss caused by winding uniformly on the mandrel is proportional to (a/)2-3 and is independent of fiber diameter and that the loss due to microbending by external forces remarkably affected by both a/ and the fiber and jacket diameters. The results obtained by the investigations are utilised for manufacturing low loss and stable optical fiber cables.