Optical Fibers
From Engineering and Operations in the Bell System, page 134 (copyright 1977):
For applications such as interoffice trunks in metropolitan areas, it may be possible to use a cable in the order of a centimeter thick that contains a few hundred fibers, each of which carries a channel of a few megahertz bandwidth.
From Fiber-optic communication on Wikipedia:
Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 80 channels to support a combined bit rate into the range of terabits per second.