Speed Comparison: FSO vs Fiber


Fiber-optic cables must be installed from one point to the next to enable optical communications. The quality of those cables is important to the performance of an optical communications system, as is the integrity of the splices between sections of optical cable. Whereas a fixed microwave link sends information through the air between two points, a fiber-optic link depends upon these cables, which must be installed with care and then maintained over time, since they can deteriorate and wear out. Optical cables can break or be cut and must be repaired, but first the fault must be found, often in many miles of optical cable, and this is not a trivial task. Business models for laying fiber-optic cables typically assume a 50-year lifespan for the capital investment of installing the optical network equipment, which may also include links to individual subscribers, known as fiber-to-the-hole (FTTH) optical communications. Although the speed of light through a vacuum is well known (186,000 miles/s), light slows down when it is not in a vacuum (such as outer space). It can slow down significantly when it travels through a medium such as the glass or plastic fibers used in optical cables. While fixed wireless systems are designed for LOS links between transmitter and receiver, optical communications systems typically do not have the luxury of a straight path and must often wind around corners through a city or in an office building for their signal paths. As with light reflecting off walls around a corner, every bend in the cable decreases the speed of the light propagating through that cable. As a result, in terms of pure communications speed, fixed wireless links typically provide faster connections than optical links. [1]

Along with the speed advantage FSO has over RF transmissions, FSO also has a speed advantage over optical fiber; 3.3 µs per kilometer of link distance versus 5 µs per kilometer length of fiber. [2]


Related Links

Paper: Free Space Optical Communication

CableFree: FSO Technology Comparisons