Light is a form of electromagnetic radiation and as such it can be conveyed through a waveguide. The cross-sectional size of any waveguide depends on the wavelength of the energy that it will carry. Because light is at the high-frequency end of the spectrum, the waveguide through which it travels is slender although it may be quite long.
Any waveguide consists of two materials, the inner portion through which the radiation travels, and the outer container, often rectangular or cylindrical. In a microwave waveguide, as in the ubiquitous satellite dish used for TV reception and Internet two-way connectivity, the inner medium is air and the outer container is metal. It’s highly polished inner surface serves to contain the signal, which zigzags as it reflects from side to side, always staying inside the inner part of the medium.
Optical fibers are made of extruded glass or plastic having the same order of thickness as a human hair. Due to the high frequency of the light conveyed, both inner core and outer cladding are transparent. But the index of refraction of the two materials differs, and that is what makes the assembly work. The internal reflection is near total.
There are two major types of optical fiber, both used extensively: single-mode and multimode. Multimode optical fiber is capable of carrying diverse signals that follow out-of-phase paths. In this mode there is an accumulating loss over distance, so the length cannot exceed 1 km. Single-mode optical fiber is for handling longer distances. Multimode is used for runs within one building. If a piece becomes damaged or tests badly, it is customary to replace the entire length rather than cutting and splicing to eliminate the bad segment.
Splicing, in fact, is kept to a minimum because any imperfection will cause loss. When there is no alternative, splicing involves precise cleaning and polishing of the cut ends and joining the cores so they perfectly align. Mechanical or fusion methods are used to make a high-performance permanent joint.
Multimode (indoor) installations generally employ a minimum of tools because splicing is rare. Electricians and cabling technicians have found they can expand into this subtrade, but the work is sensitive and exacting. Any kinking, pinching, abrasion or other damage will compromise the installation. When laying out a run of fiber, it is important to not let anyone step on it. Hangers and securing hardware must not be tight and installations must observe the minimum-bending radius.
Generally, however, installation is straightforward and user friendly. Electromagnetic interference from nearby motors and ballasts is not an issue for fiber optic signals. For protection and ease of replacement, it is always a good move to install optical fiber in electrical metallic tubing (EMT) where budgeting permits.
Single-mode optical fiber in outdoor runs greater than 1 km generally goes underground in raceways. Underground runs are far more expensive and demanding than hangers or conduit. Utilities maintain installation crews or subcontract-out this work. It is immensely profitable, but takes a large capital investment in equipment and worker training. Necessary at a minimum are an excavator, bulldozer, dump truck and flatbed trailer to haul the earthmoving machinery, temperature controlled mobile building for making splices, time domain reflectometer for verifying product and locating faults, advanced high-bandwidth oscilloscope, and a full range of mechanical and electrical tools, not to mention blasting equipment and licensing.
As time passes, data and communication utilities are replacing ever greater lengths of copper media with optical fiber, and it is anticipated that everywhere there will eventually be underground fiber to the home and business, and it will be universally used inside buildings. That will result in higher speed connectivity that is immune to RF interference and weather-related outages.