This paper describes the transmission characteristics of a graded-index fiber fabricated by CVD method. First, baseband frequency responses are discussed to be related with local bumps in refractive-index profiles. It is indicated that even a slight local bump causes serious deterioration of frequency response. Second, transmission loss characteristics are discussed as to four types of graded-index fibers. It is concluded that transmission loss is mainly originated from Rayleigh scattering loss and that in order to decrease scattering loss it is needed to reduce the fractional index differences caused by doping oxides. Finally, the transmission characteristics of long-length graded-index fibers are discussed. It is experimentally indicated that the dependency of bandwidth B on length L is nearly expressed as BL-0.7-0.8 and that bandwidth of 160 MHz and transmission loss of 30 dB over 10 km are achieved.

This method can reduce the measuring time considerably and can improve spatial resolution by using a Q (quasi)-fiber in comparison with an usual fiber-polishing method. The overall measuring error was less than 0.03% for the case of index difference1%.