It is of considerable interest to study the vortex behavior of a multiply connected superconductor for potential applications of vortex devices. Our sample is made of a type-I superconductor Pb and a capillary plate. The nominal sizes are 1-µm in hole diameter and 1.8-µm in lattice pitch. The microholes form triangular lattice while a superconducting network consists of a honeycomb lattice. When each hole accommodates a single vortex 0, an applied magnetic field becomes a nominal matching field (7.83 G). We measure the magnetization curve of sample by means of a SQUID (superconducting quantum interference device) magnetometer in the accurate small fields on the order of Gauss. We find a sharp magnetization peak at 8.2 G at temperatures near the critical temperature Tc.

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.