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The bottom shape control of optical fiber soot preform by a modified VAD method is proposed to realize the indirect control of the refractive index profile exponent during soot deposition. This proposal is based on the discovery of a close correlation between the refractive index profile exponent and the bottom shape profile exponent of the soot preform. Diameter and refractive index profile fluctuations of the preform with control and without control are analyzed. In the case of no control, these fluctuations are larger with unstable growth of the soot preform. By controlling the bottom shape, axial fluctuations in the refractive index profile of a transparent preform are reduced to half the magnitude of preforms with no control, and axial diameter fluctuations of the soot and transparent preform are reduced to below f 0.5 percent. As a result, fibers with a bandwidth of about 1 GHz . km at a wavelength of 0.85 pm can be stably fabricated.

We have tried to develop the technology for selective bleaching of core patterns of waveguides on polysilane films by UV light irradiation without wet development and RIE process. Furthermore, we have examined heat treatment of films in order to make transmission loss low instead of introducing fluorine groups in the polymer structure which conventional polymeric material are applied. As a waveguide device, evaluation of low loss straight-line waveguides and multilayered laminating type waveguides at 850nm for MM, and splitter of 8 branches (1×8) at 1550nm for SM was carried out. This new technology is expected to establish the low-cost manufacturing process of optical waveguides which are important components of passive optical devices for PON (passive optical network) system and optical interconnects.