New biconically tapered fiber star coupler fabricated by indirect heating method

A new biconically tapered fiber star coupler is developed. The fiber bundle is inserted in a quartz protection tube and the tube is heated with an oxyhydrogen burner while the fibers are twisted and pulled. The tube ends are then sealed with adhesive agent. Excess loss for the new coupler is approximately
\log_{10}m
for input/output fiber port number
m
. Furthermore, the coupling ratio is almost independent of wavelength and polarization of incident light. The new fabrication method offers high reproducibility and stability.