Basically two types of transmission Analog(usually Freq. Division Multiplexing) and Digital(Time Division Muxing and Wavelength Division Muxing, in the case of Fiberoptic) transmission can occur in 3 mediums, 1.Coaxial, 2.Fiber and 3.Microwave.
This link give the basics of transmission such as Modulation, Coding etc. and introduces the fiber optics,
http://www.fiber-optics.info/transmissionbasicstOC.htm
The basics of Digital Transmission starts from “Pulse Code Modulatio'” and grows as E1, T1 technologies and it’s higer
hierarchies commonly known as “Plesiochronous Digital Hierarchy” (PDH)…. Then comes it’s superior “Synchronous Digital Hierarchy” (SDH). There are some verygood websites which provides useful information… for basics u can try in http://www.howstuffworks.com, it has a vrygood illustration too……
Check out these too….
http://www.infosyssec.org/infosyssec/teletut1.htm
Hope this helps.