A refractive-index profile formation mechanism in the VAD method for optical fiber preform fabrication was investigated and practical techniques for precisely controlling the preform index profile are proposed. The GeO2 dopant distribution in the preform is found to be mainly caused by the porous VAD preform surface temperature distribution and by the raw material vapors mixing effect. By applying the surface temperature effect, the index profile can be controlled in the wide profile parameter range of d1-10. Further, by utilizing the maxing effect, it is possible to adjust the profile parameter precisely around a desired value. Transmission characteristics for graded-index fibers obtained with the above control technique are also presented.

In order to propose necessary raw material purity for obtaining low loss optical vapor-phase axial deposition (VAD) fibers, the contribution of impurities in raw materials to transmission loss for finished fibers has been investigated. Especially, the relation between both SiHCl3 and Fe impurity concentrations in raw materials and the absorption loss for final VAD fibers is clarified. As a result, the OH absorption loss, which is to be produced by SiHCl3 impurity, for VAD fibers is independent of the SiHCl3 impurity amount in raw materials, in contrast to MCVD fibers. In regard to Fe impurity, broadly Fe absorption loss of 0.3 dB/km at 0.8 µm appeared in the VAD fiber which was made from the raw materials containing saturated FeCl3 impurity. This Fe impurity contribution is discussed in terms of partial vapor pressure. Besides, low loss fiber with a 0.60 dB/km minimum transmission loss at 1.55 µm has been fabricated from unpurified SiCl4 with 99.17% purity. It is showed that low grade raw materials can be used to fabricate low loss fibers for practical use in the VAD process.

A wireless tag system has been designed and developed for maintaining and managing outdoor communication facilities. This system employs an infrared (IR) beam and an electromagnetic wave with a radio frequency (RF), and is constructed using IR-RF tags, an IR commander, and an RF receiver. The IR command radiation with strong directivity enables a maintenance operator to recognize a target facility, and the RF response without directivity enables a management system to obtain data from within a large circular area. Solar and secondary batteries are also adopted as the power module in the tag to allow easy maintenance at long intervals. IR signal communication is possible up to a distance of 9 m, and RF signal communication is possible within a circle with a radius of 9 m.

A new burner with a multi-flame structure is proposed for high-rate fabrication of optical fiber preforms in the vapor-phase axial deposition process (VAD). In this multi-flame VAD process, the synthesis of fine glass particles was clarified and the fabrication of soot preforms was investigated together with the consolidation process. As a result, a deposition rate of 4.5g/min was achieved using one double-flame burner. Graded-index core preform size was increased to 2500g. In addition, fibers with a high numerical aperture (N.A.) of 0.28 were fabricated using a double-flame burner. A transmission loss at 1.62µm was 0.54dB/km and the bandwidth at 1.3µm was 440 MHz km.