Fabrication of an expanded core fiber having MFD of 40 /spl mu/m preserving outer diameter

A thermally-diffused expanded core (TEC) fiber with the mode field diameter (MFD) of 40 μm has been fabricated by improving the diffusion process using an electric furnace. The outer diameter of any TEC fiber is preserved and the excess loss (normal-TEC-normal) is as low as 0.1 dB.