Tag Archives: Fiber optic cables

Cable Basics: Fiber Optic Cable Construction

Fiber optic cable provides one of the most effective means today for safe, and long-distance communications, and it offers a number of advantages over copper. Fiber optic cable construction consists of a core, cladding, coating, strengthening fibers, and a cable jacket.

Fiber optic cable constructionCore
This is the physical medium that transports optical data signals from an attached light source to a receiving device. The core is a single continuous strand of extruded silica glass or plastic that’s measured in microns (µm) by the size of its outer diameter. The larger the core, the more light the cable can carry.

All fiber optic cable is sized according to its core’s outer diameter. The two most common multimode sizes are 50 and 62.5 microns. Single-mode cores are 8.5–9 microns.

The cores of OM1 and OM2 multimode cable are made differently than the cores of laser-optimized OM3 and OM4 cable. OM1 and OM2 have a small defect in the core called an index depression. This enables them to be used with LED light sources. OM3 and OM4 are manufactured without the center defect to enable them to be used directly with VCSELS for greater speeds and distance.

Cladding
This is the thin layer that surrounds the fiber core and serves as a boundary that contains the light waves and causes the refraction, enabling light to travel the length of the fiber segment. Typical fiber cladding is 125 microns.

Coating
This is a layer of plastic that surrounds the core and cladding to reinforce and protect the fiber core. Coatings are measured in microns and can range from 250 to 900 microns.

Strengthening fibers
These components help protect the core against crushing forces and excessive tension during installation. The materials can range from aramid yarn (Kevlar®) to wire strands to gel-filled sleeves.

Cable jacket
Just like copper cable, fiber cable comes with PVC and Low Smoke Zero Halogen jackets. Whether you choose PVC- or Low Smoke Zero Halogen cable depends on where you are going to use the cable. PVC cable is typically used for patch connections in the data center, wiring closet, and at the desktop. Low Smoke Zero Halogen cable is used when you need to route a cable through the buildings air plenum. Low Smoke Zero Halogen cable has a flame-resistant jacket to inhibit the spread of fire.

Fiber cable and connector colors
To easily recognize what type of fiber cable you have in the data center, the cable jackets, connectors, and connector bodies are color-coded.

OM1 62.5-/125-Micron Multimode Fiber
Jacket: Orange
Connector: Beige
Connector Body: Beige

OM2 50-/125-Micron Multimode Fiber
Jacket: Orange
Connector: Black
Connector Body: Black

OM3 Laser-Optimized 50-/125-Micron Multimode Fiber
Jacket: Aqua
Connector: Aqua
Connector Body: Black

OM4 Laser-Optimized 50-/125-Micron Multimode Fiber
Jacket: Aqua/Violet
Connector: Black
Connector Body: Aqua/Violet

OS2 8.5-Micron Single-Mode Fiber
Jacket: Yellow
Connector: APC: Green, MPO: Black; UPC: Blue
Connector Body: APC: Green; UPC: Blue

Additional Resources:
White Paper: Fiber Optic Technology
Blog post: 8 advantages to choosing fiber over copper cable
Webinar: High-Density Fiber Connectivity for Data Centers