About optical "cables", which are actually optic fibers. There is no advantage to a fiber being thicker. The transmission of light from one end to the other depends chiefly on the smoothness of the fiber surface, because the light actually reflects off of the inside of the surface as it travels along the interior.

Another thing that affects transmission quality is the squareness of the cut and polishing of the fiber ends where they are fitted to the 'plugs' that terminate the fiber and lock it into the SPDIF (Sony-Philips Digital InterFace) connectors.

If some fibers are thicker than others, the difference is most likely the jacket, which protects the fiber from nicks, which seroiusly reduce the transmission quality, and, of course, being snapped in two, which usually renders the fiber useless.

Larry
www.fineelectricco.com