Transceivers Versus Transponders
- Transceivers – Since communication over a single wavelength is one-way (simplex communication), and most practical communication systems require two-way (duplex communication) communication, two wavelengths will be required (which might or might not be on the same fiber, but typically they will be each on a separate fiber in a so-called fiber pair). As a result, at each end both a transmitter (to send a signal over a first wavelength) and a receiver (to receive a signal over a second wavelength) will be required. A combination of a transmitter and a receiver is called a transceiver; it converts an electrical signal to and from an optical signal.
- Transponder – In practice, the signal inputs and outputs will not be electrical but optical instead (typically at 1550 nm). This means that in effect we need wavelength converters instead, which is exactly what a transponder is. A transponder can be made up of two transceivers placed after each other: the first transceiver converting the 1550 nm optical signal to/from an electrical signal, and the second transceiver converting the electrical signal to/from an optical signal at the required wavelength. Transponders that don't use an intermediate electrical signal (all-optical transponders) are in development.
See also transponders (optical communications) for different functional views on the meaning of optical transponders.
Read more about this topic: Wavelength-division Multiplexing