In our This vs. That series, we're comparing (and contrasting) two seemingly similar products. A lot of products seem the same at first glance but can greatly affect the outcome of your next application. Today, we're comparing single-mode and multi-mode fiber optic cables.

What is Single-Mode Fiber?

Single-mode fiber optic cable is the simplest type of optical fiber. Signals that are in single-mode fiber travel straight down the center of the core without bouncing off the edges. This type of fiber optic cable is very small with a very thin core. The core of a single-mode fiber optic cable is 5-10 microns in diameter, which translates to millionths of a meter.

Single-mode fiber optic cable is wrapped in a large bundle and used in telephone signals, cable TV, and internet applications. The signal from a single-mode fiber optic cable can travel over 100 km (60 miles). In a single-mode fiber optic cable, the MFD (mode field diameter) is large and easy to splice and/or connect, making it sensitive to micro bends. Microbends describe the source of signal loss or attenuation in fiber optic cable.

What is Multi-Mode Fiber?

Multi-mode fiber is a more complex type of optical fiber. These fibers are larger than single-mode fibers; they have a diameter of roughly ten times larger. This size allows light beams to travel through the core via a variety of different paths and modes. These paths can be straight through the core or bounced off the edges of the cable. Multi-mode cables are used in applications with short distances for transmissions, such as linking computer networks.

How Do They Compare?

When comparing single-mode and multi-mode fiber, the only real similarity between them is that they are both ways to send fiber optic signals. Single-mode is smaller and used in applications where a signal needs to be sent great distances. In contrast, multi-mode is used in applications where short distances are being used.

Single-mode only allows one signal to be sent straight down the core of the fiber, where multi-mode allows multiple signals to be sent and bounced off the edges of the core. In a single-mode fiber optic cable, the MFD (mode field diameter) is larger than in a multi-mode due to the core sizes. In a single-mode, the core is smaller, so the MFD is larger. In multi-mode cables, the core is larger, which means the MFD is smaller.

If you’re unsure about what cable or mode you’ll need in order to meet the needs of your application, consult with one of Allied’s knowledgeable sales reps by submitting an RFQ. Visit our website to learn more about fiber optic cable and all of our Prysmian/Draka Group products.