TP-Link SM321A 1000Base-BX WDM Bi-Directional SFP Module, LC connector, TX:1550nm/RX:1310nm, single-mode, 10km

1000Base-BX WDM Bi-Directional SFP Module
Up to 20 km transmission distance with 9/125 μm SMF (Single-Mode Fiber)
Bidirectional WDM communication on a single fiber
Compatible with Small Form Pluggable Multi-Source Agreement (SFP-MSA)
Supports Digital Diagnostic Monitoring (DDM)
Hot-swappable module design
Work with TL-SM321B as a pair