IPIQ: Simplex/Duplex

Difficulty level:  • • •
By Lindsay Bull, technical writer

We’ve been on a fiber kick the past few weeks—our plumbing can tell you all about it. Or you could read our past two posts, “7 Reasons You Should Consider Fiber on Your Next Install” and “Fiber Optic Cable: Should You Use Singlemode or Multimode?

So you’re considering fiber, and you’ve seen the guide to help you determine whether you should use singlemode or multimode. What’s next?

There are two types of communication you should know about when dealing with fiber cabling—simplex and duplex. Both enable you to run much further lines of communication than copper wire. But there are several differences between the two we’d like to point out.


As applied to fiber cabling, duplex simply means there are two cables in use. But how does that affect communication between devices?

A duplex fiber cable will include two cables in an individual casing. When a connection is wired between two devices, that individual cable will allow traffic between those devices bidirectionally. So each device will be able to send data and receive data at the same time.


Alright, we’re switching up the prefix here—you probably guessed, based off duplex, that simplex means your communication is happening over a single cable.

Simplex fiber cable is slightly more pricey and a little more difficult to work with than duplex, and here’s why:

Simplex communication over fiber requires the use of singlemode fiber. With only one cable in use, simplex fiber cable relies on an even more advanced technology to enable bidirectional communication between devices: WDM, or wavelength division multiplexing. WDM takes the signal travelling across the wire and splits it into two wavelengths, thus enabling two lines of communication over a single cable. This further increases the amount of data that can be sent across the cable.

Whether you use simplex or duplex fiber cable, the increase in price can be justified by the fact that its ability to travel longer distances without losing strength means you’re less likely to need a signal booster. And based on the physical properties of fiber cables, they’re less susceptible to interference, which means you have less to worry about when running wire in your installs.

With improvements in speed, bandwidth, and performance, there’s little reason to not start using fiber cabling in your installs. Leave it out of your diet; we don’t care. But don’t leave it off your installs.

Lindsay Bull