The SFP-7002-WA is a BiDirectional single strand fiber Gigabit Ethernet / 1.25G rate SFP transceiver using a 1310nm wavelength laser and a 1550nm photo-diode and reaching up to 2Km distance. The SFP uses the so called WDM technology, that mixes two wavelengths simultaneously over same unique fiber strand.
\When using WDM transceivers, they must always be matched in order to get a working fiber link. For instance, the SFP-7002-WA using Tx:1310/Rx:1550nm must be matched with SFP-7002-WB using Tx:1550nm/Rx:1310nm. For ease of understanding, transceivers are marked A and B and they must always be used together.