Takeshi Akamatsu

Migration of Mo atoms across Mo–Si interface induced by Ar+ ion bombardment

Backscattering analysis is used to investigate the effect of 150‐keV Ar ion bombardment on Mo thin films evaporated on silicon. Ar ion bombardment induces the migration of Mo atoms into the underlying substrate. These migration phenomena are caused mainly by an atomic recoil process, and depend on implanted ion dose and on film thickness. These phenomena are also affected by the peculiarity of the Mo–Si interface. The migration of Mo atoms occurs most noticeably at a thickness of 450±50 A, where about five Mo atoms for every incident Ar ion are introduced.

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.

Continuous fabrication of phosphate glass fiber

A phosphate glass fiber is fabricated by continuous drawing using a quartz double crucible. The raw materials for core and cladding glass are prepared at almost 100-percent efficiency by a liquid-phase process using ultra-high-purity chloride solutions. The transmission losses of the fiber are 2.5 dB/km at 1.1μm wavelength and 5.8 dB/km at 0.85 μm. The numerical aperture of the fiber is 0.31, and the breaking stress at 50-percent failure on the Weilbull plots is 3.5 kg for a 150-μm outside diameter. The phosphate glass is sufficiently water-resistant for practical use. Costs are less than 4 cents/m when phosphate glass fiber is produced continuously in quantities greater than 105km per year. This is approximately half the estimated cost of doped silica fiber.

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.