Glass fiber is the most common type of fiber available, with companies such as Corning and Siecor producing billions of meters per year. Common industry-standard glass fibers are differentiated by the diameter of the core: larger cores allow more modes to propagate; smaller cores allow fewer. Glass fiber is available in three common sizes: two multimode fibers and one single mode fiber. Multi-mode fibers have larger cores and allow many modes to travel through the fiber. The two standard sizes for multi-mode fiber are 62.5/125µm, and 50/125µm.
The first number indicates the core diameter and the second number indicates the cladding diameter. Single-mode fibers have cores so small that only one mode of light enters the fiber. Most single-mode fibers are 9/125 mm, but some have 8 mm cores.
Glass fibers are lightweight, durable, and fairly inexpensive. They make up most of the installed base of fiber-optics in the world. Single-mode fiber accounts for all of the long haul telecommunications fiber.
Plastic Optical Fiber (POF)
Plastic fiber has been around for about 20 years and makes up only a small percentage of the total fiber in the world today. Most plastic fiber is used in Japan and Europe. The two major manufacturer of POF today are Mitsubishi in Japan and Boston Optical Fiber in the US. Several other smaller Japanese vendors also manufacture POF.
POF is easy to work with because of its large 980/1000 mm diameter. As a result, component, connector, and labor costs are all minimal, making a plastic fiber-optic link comparable to the cost of copper wire.
Hard Clad Silica (HCS)
HCS fiber has a glass core and a plastic cladding, giving it the qualities of both materials. This fiber is used even less than plastic fiber: SpecTran Specialty Optics Corporation being the most prom-inent manufacturer in the US and Torray being the most prominent one in Japan. HCS is the most durable of fibers and is relatively easy to work with. It has a 200/240 mm diameter, and is available in riser and plenum versions that meet environmental standards.
If the diameter of the fiber core is smaller than the light emitter or larger than the photodiode detector, power coupled from the transmitter into the fiber or power coupled from the fiber into the receiver can be lost. For this reason, the transmitter and receiver must be optically matched to the fiber’s diameter.