Modern communication networks are built on fiber optic cables. Optical fiber transmits data using light, enabling extremely reliable and high-speed communication. When choosing the right fiber optic cable for your network, you'll likely consider two main types: single-mode fiber and multimode fiber. These are the most common types of fiber optic cable, each designed for different applications. Understanding the differences and applications of single-mode and multimode fiber will help you make better choices for your home, business, and industrial networks.
Single-mode and Multimode Cores
What are the two main types of fiber optic cable?
Fiber optic cables are available in two types: single-mode and multimode. The primary difference lies in the core size and light transmission method. The core is the central portion of the fiber where light travels. Single-mode fiber has a very small core width of just 9 microns, allowing only one light path (mode) to travel. Multimode fiber, on the other hand, has a larger core diameter of 50-62.5 microns, allowing many optical channels to travel simultaneously. This difference in core size affects data transmission distance and speed.
Differences in the exterior color of single-mode and multimode optical fiber
What is single-mode optical fiber (SMF)?
Single-mode optical fiber has an extremely thin core diameter of just about 9 micrometers (thinner than a human hair!). Because the core diameter is so small, light can only travel a single path—directly toward the center, much like a laser beam. This simple path allows the optical signal to remain strong and undisturbed over extremely long distances, even hundreds of kilometers. To achieve this, single-mode optical fiber uses a powerful laser light source.
These cables are often seen with a yellow exterior jacket. Because light travels so cleanly in a single mode, single-mode optical fiber offers the highest speeds and longest distances.
Multimode optical fiber is ideal for large-scale networks.
It can be used for a variety of applications, including long-distance telephone lines and Internet backbones (such as intercontinental undersea cables),
cable television company trunk lines, connections between buildings across large university and corporate campuses, and
connections between distant data centers.
It's also ideal for future-proofing designs, especially if you know you'll need the highest possible speeds in the future.
What is multimode fiber (MMF)?
Multimode fiber has a very wide core, typically 50 or 62.5 micrometers in diameter. The large core diameter allows many different beams of light ("modes") to travel through the core simultaneously. As these beams of light travel down the cable, they reflect at slightly different angles—think of it as many beams of light zigzagging through a tube.
While this allows for higher speeds, it creates a problem over long distances, as the beams arrive at slightly different times (a phenomenon known as "modal dispersion"). This limits the distance and speed at which signals can be reliably transmitted compared to single-mode. Multimode is typically good for distances up to about 550 meters (about half a kilometer), although newer versions can reach even greater distances.
Multimode fiber can be identified by its jacket color: older types are often orange, newer, higher-speed versions are often aqua, and the latest designs are lime green.
Because the cable itself is cheaper than single-mode and the light source is also cheaper, multimode is the most cost-effective solution for short-distance cabling. As a result, multimode is widely used within buildings:
Connecting computers and phones in an office (local area network, LAN),
Connecting servers and switches in a data center,
Connecting security cameras within a building or campus,
Connecting factory machinery in a production environment,
It is also widely used in professional audio/video systems that require high-quality transmission over medium distances.