BiDi SFP, known as Bi-Directional SFP, is the fiber optic transceiver for over 1 gigabit data transmission. The core technology of this kind of transceiver is BiDi transmission which uses Wavelength Division Multiplexing (WDM) technique for bidirectional transmission of two different waves with only one optical fiber. Since the BiDi module just has one port , it must be employed in pairs. For example, when one port is used for receiving 1310nm and transmitting 1550nm optical signals, the other should receive 1550nm and transmit 1310nm signals, and vice versa. In this way, BiDi products usually cost more money than ordinary ones, but it is a better way to use BiDi transceivers to save the optical fiber expenditure.