How BiDi (Single-Fiber) Transceivers Work — and How to Pair Them
BiDi modules send and receive on different wavelengths over one fiber strand. How WDM does it, which wavelength pairs are common, and the installation checklist that prevents down links.
One fiber, full duplex
A conventional transceiver pair uses two fiber strands — one to transmit, one to receive. A BiDi (bidirectional) module replaces the second strand with wavelength-division multiplexing (WDM): it transmits on one wavelength and receives on another, so both directions of traffic share a single strand of single-mode fiber. For ISPs and enterprises that lease fiber, that halves the strand count — and the cost — of every link.
Why wavelength pairing is not optional
A BiDi link only works when the two ends are mirror images: module A transmits on the wavelength that module B receives, and vice versa. If both ends transmit on 1310 nm, both signals collide on the same wavelength and the link never comes up — the fiber test passes, the optics pass, and the link stays down. This is the single most common BiDi installation mistake.
Every BiDi module we ship is labeled with its TX/RX wavelengths, and matched pairs are dispatched together in the same order. On the product page of each model you will find the exact pair module linked, so both ends can be ordered in one step.
Common BiDi wavelength pairs
The wavelength pair is chosen for the reach class. The combinations below cover the full catalog; the exact pair for your order is printed on the label and confirmed before shipping:
| Wavelength pair | Speed class | Typical reach | Typical use |
|---|---|---|---|
| TX 1310 / RX 1550 nm (and mirror) | 1.25G SFP | 3–60 km | FTTH access, ISP point-to-point, metro |
| TX 1310 / RX 1490 nm (and mirror) | 1.25G SFP | 10–40 km | Access rings and campus single-fiber links |
| TX 1490 / RX 1550 nm (and mirror) | 1.25G SFP | 60–120 km | Long-haul single-fiber spans |
| TX 1270 / RX 1330 nm (and mirror) | 10G SFP+ | 10–60 km | 10G backhaul and inter-site links |
| TX 1490 / RX 1550 nm (and mirror) | 10G SFP+ | 80–120 km | Long-haul 10G on a single strand |
Installation checklist
Four checks prevent almost every BiDi field problem. First, install the pair crosswise — the module labeled TX 1310/RX 1550 goes opposite the TX 1550/RX 1310 module. Second, run one simplex cord per end — a duplex cord leaves one strand unconnected, and if both ends land on the same-colored strand the two transmitters never meet. Third, clean and inspect the single LC/SC ferrule — a single strand carries both directions, so one dirty connector kills the whole link. Fourth, verify both directions with DOM/DDM readout on the switch: both RX powers should be within the module's rated range.
Browse BiDi modules
Our BiDi families cover 1.25G LC and SC interfaces and 10G SFP+, from 3 km to 120 km, always supplied as matched pairs. Open the BiDi catalog and share your switch model — we confirm coding for both ends before you order.