The influence of impurities in performs and of the drawing condition on the hydrogen-induced loss increase in the OH absorption band and the radiation-induced loss increase is investigated. The loss increase is much larger in fibers contaminated by sodium. Moreover, the loss increase in fibers with natural SiO2 clad, which is contaminated by alkali ions, increases with increasing maximum temperature in the drawing furnace and with decreasing drawing speed. By thermodynamically analyzing these results, the origin of the loss increase is identified as follows:(1) The OH loss increase and the radiation-induced loss increase are ascribed to the same origin.(2) The structural reorientation from GeO4 tetrahedrons to GeO6 groups thermally occurs in the drawing process, when the perform is contaminated by alkali ions.(3) The loss increase is induced through the reaction of H2 and radiation with GeO6 groups.

This paper describes the design and performance of optical components for in-service fiber testing and monitoring in optical subscriber loops. As the number of test fibers increases, compact and cost-effective components are becoming more important. To meet this need, we have developed a highly-dense hybrid structure for optical couplers and filters, which both play key roles in testing systems. It was realized by utilizing a polyimide-base thin film filter and a waveguide-type wavelength insensitive coupler. This component operates by combining a signal and a test light with a ratio of 80/20% and isolating the test light with a value of 50 dB. The experimental samples were successfully fabricated with an excess loss of 1 dB, a return loss of 40 dB, a plolarization dependent loss (PDL) of 0.3 dB, and good environmental and mechanical stability. We successfully applied the samples to an optical branch module (OBM), and achieved a component density twice that of a conventional module. The optical characteristics of the OBM met our target values. The results we obtained for termination cords incorporating the polyimide-base filter were also satisfactory.

Natural quartz jacketed fibers showed a larger OH loss increase due to diffused H2 than synthesized silica jecketed fibers. This additional OH loss increased with an increase in the drawing temperature and a decrease in the drawing speed in the former, although it was not changed by the drawing conditions in the latter. From this result, it was estimated that impurities which diffused from the natural quartz into the core glass during the drawing process were related to the large OH loss increase.