Fiber optics is a major building block in the telecommunication infrastructure. Its high bandwidth capabilities and low attenuation characteristics make it ideal for gigabit transmission and beyond. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves.Optical fiber systems have many advantages over metallic-based communication systems. These advantages include:
1. Long-distance signal transmission
The low attenuation and superior signal integrity found in optical systems allow much longer intervals of signal transmission than metallic-based systems. While single-line, voice-grade copper systems longer than a couple of kilometers (1.2 miles) require in-line signal for satisfactory performance, it is not unusual for optical systems to go over 100 kilometers (km), or about 62 miles, with no active or passive processing.
2. Large bandwidth, light weight, and small diameter
Today’s applications require an ever-increasing amount of bandwidth. Consequently, it is important to consider the space constraints of many end users. It is commonplace to install new cabling within existing duct systems or conduit. The relatively small diameter and light weight of optical cable make such installations easy and practical, saving valuable conduit space in these environments.
3. Nonconductivity
Another advantage of optical fibers is their dielectric nature. Since optical fiber has no metallic components, it can be installed in areas with electromagnetic interference (EMI), including radio frequency interference (RFI). Areas with high EMI include utility lines, power-carrying lines, and railroad tracks. All-dielectric cables are also ideal for areas of high lightning-strike incidence.
4. Security
Unlike metallic-based systems, the dielectric nature of optical fiber makes it impossible to remotely detect the signal being transmitted within the cable. The only way to do so is by accessing the optical fiber. Accessing the fiber requires intervention that is easily detectable by security surveillance. These circumstances make fiber extremely attractive to governmental bodies, banks, and others with major security concerns.
5. Designed for future applications needs
Fiber optics is affordable today, as electronics prices fall and optical cable pricing remains low. In many cases, fiber solutions are less costly than copper. As bandwidth demands increase rapidly with technological advances, fiber will continue to play a vital role in the long-term success of telecommunication.
In most applications, optical fiber must be protected from the environment using a variety of different cabling types based on the type of environment in which the fiber will be used. Cabling provides the fiber with protection from the elements, added tensile strength for pulling, rigidity for bending, and durability. In general, fiber optic cable can be separated into two types. They are indoor and outdoor.
Indoor Cables
• Simplex cable—contains a single fiber for one-way communication
• Duplex cable—contains two fibers for two-way communication
• Multifiber cable—contains more than two fibers. Fibers are usually in pairs for duplex operation. A ten-fiber cable permits five duplex circuits.
• Breakout cable—typically has several individual simplex cables inside an outer jacket. The outer jacket includes a zipcord to allow easy access
• Heavy-, light-, and plenum-duty and riser cable
− Heavy-duty cables have thicker jackets than light-duty cable, for rougher handling.
− Plenum cables are jacketed with low-smoke and fire-retardant materials.
− Riser cables run vertically between floors and must be engineered to prevent fires from spreading between floors.
Outdoor Cables
Outdoor cables must withstand harsher environmental conditions than indoor cables. Outdoor cables are used in applications such as:
• Overhead—cables strung from telephone lines
• Direct burial—cables placed directly in trenches
• Indirect burial—cables placed in conduits
• Submarine—underwater cables, including transoceanic applications
Sketches of indoor and outdoor cables are shown in Figure 8-18.
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