Low-loss and large-tolerance fiber coupling of high- Delta silica waveguides by local mode-field conversion

Small mode-field silica waveguides with a high refractive index difference of 2% that were efficiently coupled to optical fiber using a local mode-field conversion technique are described. The waveguide end was heated locally at 1300 degrees C for 10 h and this had the effect of doubling the mode-field diameter from 5.0 mu m to about 10 mu m with a taper length of 8 mm. It is shown that, as a result, the fiber coupling loss was drastically reduced from 2.4 to 0.1 dB and the alignment tolerance was doubled.<
>