Transmit and receive wavelengths of single-core optical modules

Single-core (BiDi) optical modules transmit and receive simultaneously over one fiber using two distinct wavelengths, typically 1310 nm and 1550 nm, with each module's Tx and Rx wavelengths reversed at the opposite end.

How Bi

Di Modules WorkBiDi (bidirectional) SFP modules enable full-duplex communication over a single strand of single-mode fiber by using Wavelength Division Multiplexing (WDM). Each module contains a transmitter (Tx) and receiver (Rx) that operate on different wavelengths, allowing simultaneous sending and receiving of optical signals on the same fiber ( ). Inside the module, a BOSA (Bi-Directional Optical Sub-Assembly) integrates the TOSA (transmitter) and ROSA (receiver) with an optical filter to separate the wavelengths ( ).

Typical Wavelength Pairs

Common configuration: One module transmits at 1310 nm and receives at 1550 nm, while the paired module transmits at 1550 nm and receives at 1310 nm ( ). Alternative configurations: Depending on the network and module type, some BiDi modules may use other wavelength pairs, but the principle remains the same: opposite wavelengths at each end to ensure proper signal separation and avoid interference ( ).

Deployment Considerations

Matched pairs: BiDi modules must be deployed in matched Tx/Rx pairs; using two identical modules at both ends will prevent the link from initializing ( ). Laser type: High-speed networks (10G+) often require DFB lasers to mitigate chromatic dispersion over longer distances ( ). Thermal drift: Low-cost FP-based BiDi modules may experience wavelength shifts (~0.

1 nm/°C), which can cause intermittent packet loss if not accounted for ( ). Optical isolation: Integrated filters or WDM components prevent crosstalk between Tx and Rx wavelengths, maintaining signal integrity ( ).

Advantages

Fiber savings: Only a single fiber is needed for bidirectional communication, reducing infrastructure costs by up to 50% compared to traditional dual-fiber setups ( ). Simplified cabling: Fewer fibers and connections reduce potential failure points and streamline network upgrades ( ). Compatibility: BiDi SFPs are available in multiple speeds, including 1G, 10G, and legacy 155M networks, making them suitable for various enterprise and metro applications ( ).

In summary, single-core BiDi optical modules achieve simultaneous transmit and receive over one fiber by using two distinct wavelengths, typically 1310 nm and 1550 nm, with reversed roles at each end, and careful pairing and laser selection are essential for reliable operation.