Information Modulation Schemes

The modulations scheme encodes the information to be transported.  Encoding information can improve the integrity of the transmission, allows more information to be sent per unit time, and in some cases, take advantage of some strength of the communication medium or overcome some weakness.  Modulating video signals can become complicated. The television signal uses many horizontal lines to form a video image. The video signal contains the information to draw these lines, detailing what parts of the line should be dark or light and how to represent colors. Sound is also encoded in the signal. Three basic techniques exist for transmitting information such as video signals over fiber optics.  Amplitude modulation, AM, includes baseband AM, RF Carrier AM and vestigial sideband AM. Frequency modulation FM include sign wave FM, square wave FM, pulse FM and FM coded this digital sidebands. Digital modulation correctly modulates the optical light source with the ones and zeros of a digital data stream.  A simplified explanation is that the light or laser source is off for a digital zero and on for a digital one.  In actual practice, the light source never completely shuts off.   The light source modulates darker and lighter for digital zero and one information.

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