Radio can be modulated or encoded to carry information. Light is electromagnetic radiation as well, but of a higher frequency. Because of the higher frequency, light can be used to carry much more information than radio.
Light travels in straight lines.
At least, that is what everyone knew until the nineteenth century, when it was observed that light would follow the path of a curving stream of water. When light passes from one medium to another, there is always some reflection. Now you know something about fibre optics. There is still an awful lot to know about how it works in practice, what the protocols are, how to control access to the media, how to interconnect it with copper cables, how to manage it, how to buy and install it, and how well to expect it to perform. Which is what this book is about.