Optical Fiber

Fiber Specifications

The usual fiber specifications you will see are size, attenuation and bandwidth. While manufacturers have other specs that concern them, like numerical aperture (the acceptance angle of light into the fiber), ovality (how round the fiber is), concentricity of the core and cladding, etc., these specs do not affect you.

Fiber Itself

Fiber Optics, as we said, is sending signals down hair-thin strands of glass or plastic fiber. The light is "guided" down the center of the fiber called the "core". The core is surrounded by a optical material called the "cladding" that traps the light in the core using an optical technique called "total internal reflection." The core and cladding are usually made of ultra-pure glass, although some fibers are all plastic or a glass core and plastic cladding. The fiber is coated with a protective plastic covering called the "primary buffer coating" that protects it from moisture and other damage. More protection is provided by the "cable" which has the fibers and strength members inside an outer covering called a "jacket".

Multimode & Singlemode Fibers

Multimode & Singlemode fiber are the two types of fiber in common use. Both fibers are 125 microns in outside diameter - a micron is one one-millionth of a meter and 125 microns is 0.005 inches- a bit larger than the typical human hair. Multimode fiber has light traveling in the core in many rays, called modes. It has a bigger core (almost always 62.5 microns, but sometimes 50 microns ) and is used with LED sources at wavelengths of 850 and 1300 nm (see below!) for slower local area networks (LANs) and lasers at 850 and 1310 nm for networks running at gigabits per second or more. Singlemode fiber has a much smaller core, only about 9 microns, so that the light travels in only one ray. It is used for telephony and CATV with laser sources at 1300 and 1550 nm. Plastic Optical Fiber (POF) is large core ( about 1mm) fiber that can only be used for short, low speed networks.

Step index multimode

was the first fiber design but is too slow for most uses, due to the dispersion caused by the different path lengths of the various modes. Step index fiber is rare - only POF uses a step index design today.

Graded index multimode

fiber uses variations in the composition of the glass in the core to compensate for the different path lengths of the modes. It offers hundreds of times more bandwidth than step index fiber - up to about 2 gigahertz.

Singlemode

fiber shrinks the core down so small that the light can only travel in one ray. This increases the bandwidth to almost infinity - but it's practically limited to about 100,000 gigahertz - that's still a lot!

Size Matters

Fiber, as we said, comes in two types, singlemode and multimode. Except for fibers used in specialty applications, singlemode fiber can be considered as one size and type. If you deal with long haul telecom or submarine cables, you may have to work with specialty singlemode fibers.

Multimode fibers originally came in several sizes, optimized for various networks and sources, but the data industry standardized on 62.5 core fiber in the mid-80s (62.5/125 fiber has a 62.5 micron core and a 125 micron cladding.) Recently, as gigabit and 10 gigabit networks have become widely used, an old fiber has been revived. The 50/125 fiber was used from the late 70s with lasers for telecom applications before singlemode fiber became available. It offers higher bandwidth with the laser sources used in the gigabit LANs and can go longer distances. While it still represents a smaller volume than 62.5/125, it is growing.

Featured Fiber Optic Products

Fiber Optic Patch Cable Assemblies

Patch Cables, Mode Conditioning, Pre-Terminated Assemblies, MTP Cables & Modules

Fiber Optic Test Instruments

Test Kits, Power Meters, Length Testers, Fault Locators, Talk Sets, & Connector Adapters

Fiber Optic Hardware & Accessories

Test Kits, Power Meters, Length Testers, Fault Locators, Talk Sets, & Connector Adapters

Read on for more fiber optic tutorial information..

Jargon This guide will help you get started by providing very basic information (we will also point you to more advanced studies)...

Basics This guide will help you get started by providing very basic information (we will also point you to more advanced studies)...

Fiber The usual fiber specifications you will see are size, attenuation and bandwidth. While manufacturers have other specs that...

Cable Fiber optic "cable" refers to the complete assembly of fibers, strength members and jacket. Fiber optic cables...

Termination We terminate fiber optic cable two ways - with connectors that can mate two fibers to create a temporary joint and/or connect...

Network In the telcos, singlemode fiber is used to connect long distance switches, central offices and SLCs (subscriber loop...

Estimating Estimating is necessary to figure out what the job will cost you. First of all you'll need to set up a simple chart of all the details...

Testing After the cables are installed and terminated, it's time for testing. For every fiber optic cable plant, you will need to test...

Training This guide has provided you with the basics, you need to decide where to go from here. There are many options...

Glossary Here's an alphabetical glossary of fiber optic terms. You can search the list using the alphabetical index below...