A single-mode optical module connects via LC connectors to single-mode fiber, with transmit (TX) and receive (RX) lines properly aligned, often using APC or UPC polished ends depending on the module type.

Basic Wiring Principles

1. Module Ports: Single-mode SFP or SFP+ modules have two optical ports: TX (transmit) and RX (receive). The TX of one module must connect to the RX of the other module to establish communication .
2. Fiber Type: Use single-mode fiber (SMF) only. Do not mix with multimode fiber, as this will prevent signal transmission .
3. Connectors and Polishing:
   • LC connectors are most common for single-mode modules.
   • Polishing types:
     • APC (Angled Physical Contact, green): typically used for wall outlets or long-distance links.
     • UPC (Ultra Physical Contact, blue): often used on SFP modules.
   • Always match polish types: APC to APC, UPC to UPC. Mixing APC and UPC will result in poor or no connection .
4. Polarity: Maintain correct polarity:
   • TX of module A → RX of module B
   • RX of module A → TX of module B
   • For bidirectional (BiDi) SFPs, a single fiber can carry both TX and RX using different wavelengths, but standard single-mode modules require two fibers .
5. Attenuation and Distance: Ensure the fiber length does not exceed the module's maximum supported distance. Signal loss depends on fiber type, splices, and connectors .

Example Wiring Setup

[Device A SFP Module]TX (UPC) ──┐ │ LC Single-Mode FiberRX (UPC) ──┘ ┌── TX (UPC) │[Device B SFP Module] RX (UPC)

• For wall outlets, APC connectors are recommended:

[Device SFP Module (UPC)]TX ──┐ │ LC SMFRX ──┘[Wall Outlet (APC)]TX ──┐ │ LC SMFRX ──┘[Device SFP Module (UPC)]

• Use a fiber patch panel if multiple connections are needed.

Installation Tips

• Avoid bending fiber beyond its minimum bend radius (e.g., 10 mm for G.657.A1 fiber), .
• Pre-terminated fibers simplify installation, but ensure conduit size allows pulling them through.
• Short fiber runs may require attenuators to prevent signal overload .
• Secure modules in their slots and avoid touching the fiber endfaces to prevent contamination . By following these wiring principles, single-mode optical modules can be reliably connected for high-speed, long-distance communication.