A pair of single-mode single-fiber optical modules

Single-fiber single-mode optical modules, also known as BiDi SFPs, transmit and receive data over a single strand of fiber using different wavelengths and must be used in complementary pairs for bidirectional communication.How Single-Fiber Modules Work

Single-fiber modules, or BiDi (bidirectional) transceivers, enable full-duplex communication over a single strand of single-mode fiber by using Wavelength Division Multiplexing (WDM). One wavelength is used for transmitting (TX) and a complementary wavelength for receiving (RX) on the same fiber. For example, one module may transmit at 1310 nm and receive at 1550 nm, while the paired module at the other end uses the opposite configuration (TX1550/RX1310) to complete the bidirectional link .

Why Modules Must Be Used in Pairs

Because each single-fiber module only handles one TX and one RX wavelength, a matching module with complementary wavelengths is required at the other end of the fiber. Without this pairing, the transmitted signal would not be received correctly, and bidirectional communication would fail . Common wavelength pairs include TX1310/RX1550 and TX1550/RX1310 for standard SFPs, and TX1270/RX1330 and TX1330/RX1270 for 10G or 100G SFP+ and QSFP28 modules .

Advantages of Single-Fiber Modules

• Fiber conservation: Only one fiber is needed instead of two, reducing infrastructure costs and simplifying network expansion .
• Cost efficiency: Lower CAPEX and OPEX due to reduced fiber deployment and maintenance .
• Simplified cabling: Less congestion in patch panels and fiber trunks, ideal for high-density or metro networks .

Compatibility Considerations

When deploying single-fiber modules in pairs, ensure:

• Correct wavelength pairing: TX/RX wavelengths must be complementary.
• Power budget: Verify that the optical power and link distance are supported.
• Connector type: LC or other compatible connectors must match.
• Vendor interoperability: Modules from different vendors may require testing to ensure proper operation .

Applications

Single-fiber single-mode modules are widely used in metropolitan area networks (MANs), telecom access networks, enterprise campus links, and high-density data centers, especially where fiber resources are limited or expensive . They are suitable for both short and long-distance links, leveraging single-mode fiber for minimal signal loss over extended distances . By using these modules in pairs, network operators can maximize fiber utilization, reduce costs, and maintain reliable bidirectional communication without laying additional fiber.