In fiber optic patch cords, "SX" can mean either "simplex" for single-fiber cables or "short wavelength" for multimode SFP modules, depending on context.

SX as Simplex in Patch Cords

When referring to a fiber optic patch cord, "SX" often stands for simplex, meaning the cable contains a single fiber rather than a duplex pair. Simplex cables are used for one-way transmission and are common in FTTH, telecom racks, and optical modules. For example, an LC/UPC–SC/UPC-SM-SX patch cord is a single-mode, single-fiber jumper that connects high-density LC ports to standard SC ports, providing a low-loss optical path without adapters . Simplex cables are cost-effective, space-saving, and suitable for short-distance or one-way links.

SX as Short Wavelength in SFP Modules

In the context of SFP transceivers, "SX" stands for Short Wavelength, typically around 850nm, and is designed for multimode fiber (MMF). 1000BASE-SX SFP modules operate at 1 Gigabit per second and are intended for short-range connections, usually up to 550 meters on modern OM3/OM4 multimode fiber . SX modules are strictly multimode and will not function properly over single-mode fiber. They are commonly used for intra-building or server-room connections.

Key Distinctions

• Simplex SX patch cord: Refers to single-fiber cable, can be single-mode or multimode, used for one-way transmission.
• SX SFP module: Refers to short-wavelength multimode transceiver, operates at 850nm, used for short-range 1G links.
• Compatibility: Simplex cables can connect SX SFP modules if the fiber type matches (multimode for SX SFP). Duplex cables are required for bidirectional links with separate Tx/Rx fibers . Understanding the context—whether discussing the cable itself or the transceiver module—is essential to correctly interpret "SX" in fiber optic systems.