Yoichi Ueda

Fabrication of graded‐index fibers without an index dip by chemical vapor deposition method

When optical fibers are prepared by the (CVD) technique, an index dip often appears at the core center. The index dip reduces the coupling efficiency to optical sources and also it reduces the transmission bandwidth. This index dip in the core with germania‐doped silica could be eliminated successfully with a flow of the vapors of controlled proportion of GeCl4 and O2 during the collapse. The graded‐index fibers without dip were prepared by this technique. The bandwidth was increased from 500 to 800 MHz : km and the coupling efficiency by 20% when the index profile was controlled and the index dip was eliminated.

Fabrication of long fibers by an improved chemical vapor deposition method (HCVD method)

An improved (CVD) method was developed to fabricate long fibers. He gas mixed with O2 and raw material vapors were introduced into the CVD gas system to increase the deposition rate. This produced a sixfold increase compared to the conventional method. In addition to GeO2, a small amount of P2O5 was added as a dopant to the fused silica to lower the fusion temperature of the deposited soot and minimize tube deformation during the deposition process. Step index fibers 8.5 km long were prepared. These exhibited a mean loss of 4.4 dB/km at a wavelength of 0.85 μm. The outer and the core diameters were 125 and 62.5 μm, respectively.