Low-loss fusion splices of optical fibers

A low-loss splicing method, based on discharge fusion of optical fibers by a simple apparatus and by applying pressure between fibers before fusion, was developed. Average splice losses of about 0.07 and 0.15 dB for single-mode (SM) fibers having core diameters of 10 and 7μm, respectively, and 0.02 dB for 50-μm core diameter graded-index (GI) fibers are obtained. Fusion loss and fusion time are obtained minimum for better end preparation having low initial alignment losses at critical pressure and temperature. Mathematical expressions for the variation of fusion time and splice loss with effect of applied pressure between the fibers, for different practical axis alignment, showing the optimum condition to have minimum splice loss are made. Experimental fusion losses are analyzed in terms of residual misalignment of off axis, angular tilt of the fibers during aligning, and air gaps in the splicing zone. Optimum fusion time is obtained by considering the forces due to applied pressure, thermal expansion, and surface tension in the viscous melted glass of the fiber. Theoretical curves of fusion times and splicing losses versus applied pressure agree with the experimental results. The decrease of fusion time to about 1.3 times and splice loss to about two times were found when applied pressure is varried from low to its critical value of 20-25 g. The splice losses are found at a minimum for the operating temperature range of 1980°C to 2140°C for silica fibers. Experimental results of the histogram of bar chart of splice losses agree with the derived mathematical expressions assuming a statistical distribution function of splice losses.