While shopping for duplex fiber optic cable you’ll see a few terms that can be confusing. Namely, what’s the difference between simplex and duplex fiber, and what do “single mode” and “multimode” mean? We clarify this below, and also discuss some common applications of duplex fiber cables.

Simply put, simplex and duplex describe the number of physical fibers, while single mode and multimode refer to the fiber optic glass types that are used.

Simplex vs Duplex Fiber

A simplex fiber cable is one strand of glass or plastic fiber. It can operate either in half-duplex mode or full-duplex mode, depending on the transceivers it is attached to. In half-duplex mode, it can transmit data from Point A to Point B or from Point B to Point A, but not both directions at the same time. In full duplex, the single strand can send and receive data simultaneously.

A duplex fiber cable consists of two strands of glass or plastic fiber. Each fiber is jacketed separately but the two are often either molded together in “zip-cord” fashion or joined with clips. Like simplex, it also can operate in half-duplex mode or full-duplex mode depending on the equipment it is attached to. In half-duplex, one strand transmits in one direction, from A to B or B to A, but not in both directions at once. However, duplex fiber is most used in full-duplex mode, with a transmit signal on one fiber and a receive signal on the other fiber occurring simultaneously. Therefore, it connects devices that require the transmit and receive signals to be on separate fibers.

Uses for Duplex

One benefit of duplex fiber optic cable is that it can serve the function of two simplex cables but is easier to install and maintain because it is one cable. Typical uses for duplex fiber cables include workstations, fiber switches and servers, fiber modems, and other types of networking hardware. Duplex fiber cables are commonly used with standard optical transceivers such as GBIC, SFP, 10G SFP+, 40G QSFP+, and 100G QSFP 28. Duplex fiber cables may also be used to interconnect/cross-connect between fiber optic transceivers and MPO/MTP cassettes if there is a long enough distance between the two devices.

Single-Mode vs Multimode Fiber

Both simplex and duplex fiber cables are offered in either single mode or multimode. As stated, the mode refers to the type of fiber optic glass that’s used. Single mode has a narrower core and light travels a single path (mode) through it. Its smaller core minimizes reflection of light passing through, so there’s less signal attenuation, allowing it to transmit signals in some cases up to 100 kilometers or more. Multimode has a much larger core diameter and light travels multiple paths through it. It has more signal attenuation and thus is best for shorter distances, no farther than 550 meters in most cases. However, usually it costs less than single-mode fiber and operates with less expensive transceivers.


A duplex fiber cable has two fiber strands that can simultaneously carry two signals in opposite directions (full-duplex mode). It can serve the purpose of two single-strand simplex fiber cables but is easier to install and maintain because the two strands are housed or clipped together. Both duplex and simplex cables are available in either single mode or multimode. Single mode has a smaller glass core, is used for longer distances at faster speeds and usually costs more than multimode cable.

ShowMeCables offers both single-mode and multimode simplex and duplex fiber optic patch cables. We also carry bulk cable and connectors for on-site termination projects. Standard lengths of our patch cables range from 1 to 50 meters (3 to 164 feet), but custom options are available as well. If you have questions about any of our products, reach our sales team at 1-855-246-0657 or via email at Sales@ShowMeCables.com.