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

Less than 1.5dB 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 0.5mm. The quenched
melt seems to be free of precipitates because they would bring about
larger loss if existed. 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.