Field Experience with Fiber-Optic Cable Installation, Splicing, Reliability, and Maintenance
The experience obtained during the installation of more than 700 sheath km of fiber-optic cable is summarized. These include in-building, underground (duct), aerial, buried, and underwater installations. In general, no special precautions are required except to maintain the specified pull tension and cable bend radius. Field splicing is discussed and results are given on splice losses with and without splice loss monitoring with the optical time domain reflectometer. A 28 percent learning curve for fusion splicing is derived. Reliability data on 312 sheath km of installed cable and field splices are presented. Most of the cable failures were in the "uncontrollable extrinsic category," and most of these were due to complete cable cuts. Finally, restoration is reviewed with emphasis on troubleshooting, repair, emergency restoration, and offset breaks.
Splicing of Fibers by the Fusion Method
Single-mode fiber splicing requires quite a precise core alignment for the adjustment of core eccentricity and outer diameter discrepancies. Several core alignment methods have been developed. The typical four methods are as follows: 1) remote injection and remote detection systems (RIRDS), 2) remote injection and local detection systems (LDS), 3) local injection and detection systems (LIDS), 4) core direct monitoring systems. The so-called prefusion method has been developed to prevent bubble growth during the fusion process. This method is widely used for both single and multimode fiber arc fusion splicing machines. The average splicing losses of 0.11 dB and 0.10 dB are reported for single-mode fiber splicings with RIRDS by NTT in Japan, and by Bell-Northern Research in Canada, respectively. With the LIDS method, the average splicing loss of 0.13 dB in the field was reported by PTT in The Netherlands. With the core direct monitoring method, average splicing loss of 0.08 dB in the field was reported by NTT in Japan. This method is one of the simplest on the most useful core alignment for single-mode splicing machine. Splicing of multimode fiber does not require a precise core alignment; that is, the alignment by the cladding is sufficient for the low-loss splicing. Therefore, the mechanism for the alignment of the fibers is much simpler than that of single-mode fibers. The average splicing loss of 0.07 dB was reported by NTT in Japan in 1982. As mentioned above, this paper reviews the field experience with these different splicing methods.
PRECISION FARMING APPROACHES TO SMALL-FARM AGRICULTRUE
Precision farming implies a management strategy to increase productivity and economic returns with a reduced impact on the environment. It is based on the application of information technology to a description of variability in the field, variable-rate operations and the decisionmaking system. There are three technology levels and three strategies in the development of precision farming. Precision farming practices can be used on small farms as well as big ones, and they play a core role in rural development programs which are integrated with industry. A real-time soil spectrophotometer was developed to describe soil variability in farmers' fields, to be used in precision farming.