Transponder - Optical Communications

Optical Communications

In optical fiber communications, a transponder is the element that sends and receives the optical signal from a fiber. A transponder is typically characterized by its data rate and the maximum distance the signal can travel.

Different descriptions, with important functional differences, might be implicitly assumed across various academic and commercial literature:

• according to one description, a transponder and transceiver are both functionally similar devices that convert a full-duplex electrical signal in a full-duplex optical signal. The difference between the two being that transceivers interface electrically with the host system using a serial interface, whereas transponders use a parallel interface to do so. In this view, transponders provide easier to handle lower-rate parallel signals, but are bulkier and consume more power than transceivers.
• according to another description, transceivers are limited to providing an electrical-optical function only (not differentiating between serial or parallel electrical interfaces), whereas transponders convert an optical signal at one wavelength to an optical signal at another wavelength (typically ITU standardized for DWDM communication). As such, transponders can be considered as two transceivers placed back-to-back. This view also seems to be held by e.g. Fujitsu

As a result, difference in transponder functionality also might influence the functional description of related optical modules like transceivers and muxponders.