Where copper cabling uses electricity to transmit signals from one end to another, fiber optics use light pulses to accomplish the same purpose. The fiber optic cable is made of a transparent glass core surrounded by a mirror like covering called cladding. Light passes through the fiber optic cable, bouncing off the cladding until it reaches the other end of the fiber channel – this is called total internal reflection. In today’s high speed networks, Graded Index Multimode fiber or Step Index Single mode fiber cable is used to improve light transmission over long distances. Multimode fiber optic cable has a larger core and is typically used in short runs within buildings. Single mode fiber optic cable has a smaller core and is used in long distance runs typically outside between buildings
Fiber Optical Transmission
Fiber specifications list the core and cladding diameters as a ratio. The top example shows the ratio of core to cladding as 62.5/125 microns. Below, the ratio is 9/125 microns. Multimode fiber is commonly 62.5/125 or 50/125 micron, single mode fiber is commonly 9/125 micron.
In Single mode applications the amount of back reflection on assemblies can be critical. L-com offers both PC and APC Single mode assemblies off the shelf. UPC finishes are available by custom order.
Stepped Index Fiber relies on the reflection of light whereas in Graded Index Fiber, the properties of the glass are changed in layers to “bend” the light as it travels down the cable. This reduces modal dispersion within the cable allowing for higher transmission rates.