Multimode fiber optic cable supports high bandwidths, works great at shorter distances, has a larger core size that is easy to terminate and is usually cheaper than single-mode fiber cable.

So, why do so many people prefer single-mode fiber?

This blog post explains the benefits and uses of single-mode fiber optic cable, as well as the differences between single-mode simplex and duplex.

Single Mode: Stronger Signal, Longer Distance

Single-mode fiber optic glass has a narrower core than multimode and light travels a single path (mode) through it. Single mode’s smaller core minimizes reflection of light passing through, so there is less signal attenuation, or loss of strength. This allows single-mode fiber cable to transmit over distances up to 62 miles or more, and with virtually unlimited bandwidth. Applications include longer distance LANs, telephony and cable TV, although it is used in data centers as well.

Multimode fiber 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, typically a maximum of 1,000 to 1,800 feet. Also, it is generally less expensive than single mode, which requires the use of pricier single-mode fiber optic transceivers. A fiber optic transceiver converts an electrical signal to an optical (light) signal and vice versa.

Simplex vs Duplex Fiber

If you choose a single-mode fiber optic cable, you can get it in either simplex or duplex. 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.

Uses for Simplex

Because simplex fiber cable offers a one-way data transfer, it is used in applications that don’t require two-way communication. Examples include measuring and monitoring equipment that sends data or video to a central location, such as:

  • Flow meters at a wastewater treatment plant
  • Temperature or vibration sensors on factory machinery
  • Highway traffic flow sensors
  • Video surveillance cameras

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
  • Telephones
  • Fiber switches and servers
  • Fiber modems
  • 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.

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