Low-loss optical coupling structure between two ends of silica glass optical fibers by inserting TeO2 melt

Less than 1.5 dB of insertion loss was realized in an optical coupling structure in which two TEC (thermal-diffusion expanded core) fibers are spliced via quenched TeO2 melt whose length was 0.5 mm. The quenched melt seems to be free of precipitates because they would bring about larger loss if present. The loss due to imperfect optical coupling between the fibers is estimated to be about 1 dB, which can be reduced by introducing some refractive index modulation into the present structure.