A pair of gigabit single-mode single-fiber optical modules

Single-fiber single-mode gigabit optical modules (BIDI SFPs) transmit and receive data over a single fiber strand and must be used in matched pairs for proper operation.

Overview

Single-fiber, single-mode optical modules, also known as BIDI (bidirectional) SFPs, allow 1 Gbps data transmission over a single strand of single-mode fiber. Unlike traditional duplex SFPs that require two fibers (one for transmit, one for receive), BIDI modules use different wavelengths for transmitting and receiving on the same fiber, reducing cabling requirements and simplifying network deployment .

Key Specifications

• Transmission Distance: Typical gigabit BIDI SFPs support distances from up to 3 km (Ubiquiti 1G BIDI module) to 10 km or more depending on the module and fiber quality .
• Connector Type: Most modules use simplex LC UPC connectors, which are standard for single-mode fiber .
• Power Consumption: Modules are generally low-power, often classified as Class 1 laser products, requiring standard safety precautions .
• Form Factor: Small Form-Factor Pluggable (SFP) modules are compact, hot-swappable, and compatible with MSA-compliant switches and routers .

Operational Requirements

• Paired Modules: BIDI SFPs must be used in matched pairs, with one module transmitting at wavelength A and receiving at wavelength B, and the other module reversed (transmit at B, receive at A). For example, Huawei's SFP-10G-BXD1 must be paired with SFP-10G-BXU1 .
• Compatibility: Modules are generally compatible with MSA-compliant SFP ports, but it is recommended to verify vendor interoperability, especially when mixing brands like Cisco, Juniper, or Intellinet .
• Inline Attenuation: For short single-mode fiber spans, an inline optical attenuator may be required to prevent receiver overload, particularly for long-range modules like 40 km or 70 km SFPs .

Examples of Gigabit Single-Fiber Single-Mode Modules

• Cisco SFP-1G-LH: Supports 1 Gbps over single-mode fiber up to 10 km, compatible with 10G-capable ports .
• Ubiquiti 1G BIDI SFP: Supports 1 Gbps over single-mode fiber up to 3 km with simplex LC UPC connector .
• Intellinet SFP Transceiver: MSA-compliant, compatible with Cisco GLC-LH-SM-20, suitable for 1 Gbps single-mode fiber networks .

Practical Considerations

• Ensure fiber type and quality match module specifications to achieve maximum distance.
• Always use matched BIDI pairs to maintain bidirectional communication.
• Verify switch/router port compatibility, especially if using dual-rate or tri-rate ports.
• Consider future scalability; some modules support higher speeds (10G) but operate at 1G when needed . These modules are ideal for fiber-constrained environments, long-distance gigabit links, or network upgrades where minimizing fiber usage is critical.