Mode-field adaptor between large-mode-area fiber and single-mode fiber based on fiber tapering and thermally expanded...

We report a method to fabricate a mode-field adaptor (MFA) for a large-mode-area (LMA) fiber and single-mode fibers (SMFs) based on fiber tapering and the thermally expanded core (TEC) technique. Through adiabatically tapering a LMA fiber by an oxygen-hydrogen flame, the mode-field diameter is decreased effectively with nearly no extra loss, which makes it possible to realize mode-field adaptation between the LMA fiber and SMFs. Both numerical calculation and experimental results show it is workable to realize fundamental mode propagation in LMA fiber and get a low insertion loss by this method. For a LMA fiber (d=25  μm, NA=0.06) and a SMF (d=4  μm, NA=0.2), a low loss with less than 0.4 dB has been obtained both in the forward and backward directions experimentally.