Fiber Optic Cables:
Fiber optic cable is a type of network cable in which the core is one or more glass or plastic strands. The core is between 5 and 100 microns thick and is surrounded by cladding, which reﬂects light back to the core in patterns determined by the transmission mode. A buffer, often made of plastic, surrounds the cladding and core. To add strength (or “pull strength”) to the cable, strands of Kevlar®surround the buffer. An outer jacket, sometimes called armor, wraps and protects the whole assembly. Light pulses from a laser or high-intensity LED are passed through the core to carry the signal. The cladding reﬂects the light back into the core, increasing the distance the signal can travel without being regenerated.
Figure: A fiber optic cable.
Fiber Optic Costs and Beneﬁts
Fiber optic cables are expensive, fragile, and difficult to install. However, ﬁber optic transmissions are fast and reliable over extremely long distances. Also, ﬁber optic cables are impervious to electromagnetic interference.
Fiber Optic Cable Mode Types
Fiber optic cables can be single-mode or multimode ﬁber.
Mode Type and Description
Carries a single optical signal. Has a small core, which allows only a single beam of light to pass. A laser, usually operating in the infrared portion of the spectrum, is modulated in amplitude (intensity) to transmit the signal through the ﬁber.
Step index multimode ﬁber:
Contains a core surrounded by cladding, each with its own uniform index of refraction. When light from the core enters the cladding, a “step down” occurs due to the difference in the refractive indices. Step-index ﬁber uses total internal reﬂection to trap light.
Graded index multimode ﬁber:
Possesses variations in the core glass to compensate for mode path length differences. Provides up to 2 GHz of bandwidth, which is signiﬁcantly more than step-index ﬁber.