Five Reasons for Local Loop Fiber

Often we take for granted that fiber optics is a good match for broadband access. Copper has served us well, and it can provide several to tens of Mbps, but fiber optics is the future. Here are the top five reasons fiber is well-suited to broadband access services.

1. Fiber is inexpensive, and cost is everything in delivering local loop broadband. The cost of typical fiber cable is outweighed by the cost of installing that cable and other costs associated with delivering broadband service.
2. Fiber provides tremendous bandwidth. Bandwidth is the primary reason fiber is replacing copper in the local loop. Fiber has been shown to deliver thousands of Gbps in lab applications, and it is certainly under no stress providing the rates used in local loop applications. Copper local loops cannot provide anything approaching the bandwidth of fiber local loops. The constraining factor for local loop applications is the cost of the optical components required to provide a certain bandwidth. These components must operate in the rigorous environment that local loop equipment experiences, not just the friendly environment of the lab. Optical transceivers are much easier to manufacture to inside requirements of 0 – 50C than to the OSP requirements of –40C to + 65C, so the OSP rated components are more expensive. As rates increase (for instance from 2.5 Gbps to 10 Gbps), the cost difference can become even more prominent.
3. Fiber provides great immunity to crosstalk. With twisted pair copper local loops, crosstalk is always a factor to consider in link design. With fiber, crosstalk issues between different fibers are all but nonexistent. Light just does not couple between different fibers.
4. Fiber optic cables are very small allowing many to be packaged into a single, compact cable. In a multi-strand cable, the space taken up by a fiber is substantially less than that of a single copper local loop. Fiber optic cables are smaller but carry much more information than twisted pair copper cables used in the local loop.
5. Fiber is a very low loss medium. Optical splitters and cost effective transceivers can be used in fiber access networks because of the low losses of fiber. Splitters introduce a high level of attenuation that can only be marginally improved, and a typical 32x splitter introduces 16-17 dB of loss (15 dB of loss is a perfect 32x splitter). This is more than half of the typical link budget in a PON system. If fiber attenuation was considerably higher at the wavelengths used in local loop systems, then the cost of the necessary components would make implementing PON systems impractical.

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