1.25G BiDi SFP 80 km Pairing Guide: 1490/1550 nm A/B Modules

An 80 km BiDi link uses two 1.25G SFP modules on one strand of single-mode fiber. The A end transmits on 1490 nm and receives on 1550 nm; the B end is the mirror image. Because the two directions use different wavelengths, full-duplex traffic fits on a single fiber. The 80 km figure is the module's reach class — confirm the real link budget against fiber loss, splices and connectors, or ask us with your distance and fiber type.

The two ends are not interchangeable. Every 80 km link needs one A module (TX 1490 / RX 1550) and one B module (TX 1550 / RX 1490), and the pair must be ordered together so both ends arrive with matching coding. The two stocked LC 1.25G ends are linked below. If your link uses SC housings or 10G SFP+, send the interface and speed and we will match the corresponding pair.

Use one simplex LC patch cord at each end, cross the pair (A opposite B), clean both LC ferrules, and verify both directions with DOM/DDM on the switch. A duplex cord leaves one strand unused and can put both transmitters on the same strand. If the RX reading is missing or out of range, check the wavelength pairing and the connector before replacing hardware.

80 km BiDi is intended for long single-fiber spans where only one strand is available — ISP backhaul, campus-to-campus links and metro extensions. The same 1490/1550 pairing is used across our 60, 80, 100 and 120 km LC BiDi family, so the installation rules are identical; choose the reach class that leaves margin in your link budget. Share the distance and fiber type and we will confirm the model.