What is BiDi?
BiDi stands for bidirectional. A BiDi transceiver transmits and receives at different wavelengths through the same fibre. A built-in wavelength filter separates the traffic directions. The result is full duplex over a simplex connection instead of two fibres.
The technology is particularly useful when fibre pairs are a scarce resource, when new blowing is costly, or when an existing connection needs to free up fibres for more services.
The modules must be used in pairs
A BiDi link consists of a complementary pair. If module A transmits at 1270 nm and receives at 1330 nm, module B must transmit at 1330 nm and receive at 1270 nm. Therefore, two identical modules do not normally work with each other.
Label both ends with location, direction and Tx/Rx wavelength. This reduces the risk of a future service change inserting the wrong half of the pair.
When BiDi provides the greatest business benefit
In access networks and metropolitan networks, BiDi can provide more capacity without needing to install new fibre directly. In enterprise and campus networks, the technology can resolve a bottleneck in an existing cable route. It is also a practical alternative for a backup link when there is only one available fibre.
The savings should be compared with requirements for inventory and operation. Since the ends are different, a clear spare parts strategy is needed. For critical links, a complete A/B backup pair should be available, not just an unspecified BiDi module.
Technical checks before ordering
- The port's form factor and data rate must be supported in both devices.
- The Tx/Rx wavelengths should be complementary.
- Both modules should be intended for the same nominal range and power class.
- The link's attenuation, connector and receiver level must be within the specifications.
- Encoding, FEC and compatibility must be verified against the respective platform.
- Reflection and contact uniformity are particularly important in singlemode connections.
BiDi versus CWDM
Both technologies use different wavelengths, but solve different problems. BiDi typically pairs two directions over a fibre with filters in the transceiver. CWDM combines several separate optical channels over the same fibre with external or integrated mux/demux.
BiDi can be part of more advanced wavelength plans, but it requires careful control of passband, wavelengths and budget. Do not treat every BiDi module as automatically compatible with an existing CWDM system.
Common errors and troubleshooting
No link at both ends: first check that the A and B modules are correctly paired and that the simplex patching goes to the right fibre.
Link up but unstable: read DDM/DOM, clean and inspect contact surfaces and compare received power against the limits.
Works on one platform but not the other: check encoding, port mode, software support and alarms for unsupported transceiver.
Too low power: verify that actual link loss and any passive filters are included in the budget.
Order documentation
- Platform and port at end A and B.
- Data rate and desired range.
- Available fibre: one singlemode fibre and connector type.
- Desired or existing Tx/Rx wavelength pair.
- Estimated or measured link loss.
- Temperature class and need for DDM.
Next step
Verify speed, distance and existing or desired Tx/Rx wavelengths. We ensure a matching A/B pair for your equipment.