Data Multiplexing

Data Multiplexing is the practice of sending multiple signals or streams of information on a carrier at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end.
In analog transmission, signals are commonly multiplexed using frequency-division multiplexing (FDM) in which the carrier bandwidth is divided into sub channels of different frequency widths, each carrying a
signal at the same time in parallel.
In digital transmission, signals are several common multiplexing techniques. These include time-division multiplexing (TDM) in which the multiple signals are carried over the same channel in alternating time slots; frequency-shift keying (FSK) in which the frequency of the transmitted signal is varied and phase-shift keying (PSK) in which the phase of a transmitted signal is varied to convey information.
Electrical signals can also be converted to optical signals. A fiber optic transmitter consists of an interface circuit, a source drive circuit and an optical source. The interface circuit accepts the incoming electrical signal and processes it to make it compatible with the source drive circuit. The source drive circuit intensity modulates the optical source by varying the current through it. The optical signal is coupled into an optical fiber through the transmitter output interface. Multiple optical signals can be carried together as separate wavelengths of light in a multiplexed signal using dense wavelength division multiplexing (DWDM). Very high data rates can be achieved with DWDM.