The choice between optical fiber cables and copper telephone cables for transmission for a particular telecommunication system is made based on a number of trade-offs. Optical fiber is generally chosen for systems requiring higher bandwidth or spanning longer distances than copper based electrical cables can accommodate.
The main benefits of optical fiber are its exceptionally low loss that allows long distances between amplifiers/repeaters, its absence of ground currents and other parasite signal and power issues common to long parallel electric conductor runs (due to its reliance on light rather than electricity for transmission, and the dielectric nature of fiber optic), and its inherently high data-carrying capacity.
Thousands of electrical links would be required to replace a single high bandwidth fiber cable. Another attractive benefit of optical fibers is that even when run alongside each other for long distances, optical fiber cables do not show crosstalk, in comparison with some types of copper telephone cables. Fiber can be installed in areas with high electromagnetic interference (EMI), such as alongside utility lines, power lines, and railroad tracks. Nonmetallic all-dielectric cables are also ideal for areas of high lightning-strike incidence.
While single-line, voice-grade copper telephone systems longer than a couple of kilometers require in-line signal repeaters for satisfactory performance, optical systems go typically over 100 kilometers, with no active or passive processing. Single mode fiber cables are available for purchase in more than 12 km lengths per drum, thus minimizing the number of splices required over to achieve long cable run. Multi-mode fiber is available in lengths up to 4 km, although industrial standards only mandate 2 km unbroken runs.
Though copper electrical cables offer short distance and relatively low bandwidth applications, electrical transmission is often preferred because of its
- Lower material cost, where large quantities are not required
- Lower cost of transmitters and receivers
- Capability to carry electrical power as well as signals (in appropriately designed cables)
- Ease of operating transducers in linear mode.
Because of the above benefits of electrical transmission, optical communication is not common in short box-to-box, backplane, or chip-to-chip applications; however, optical systems on those scales have been demonstrated in the laboratory.
It is common for some people to campaign against optical fibers using the following
– Optical fibers are more difficult and expensive to splice than electrical conductors.
– At higher powers, optical fibers are susceptible to fiber fuse, resulting in catastrophic destruction of the fiber core and damage to transmission components.
In certain situations fiber may be used even for short distance or low bandwidth applications, due to other important features:
- Immunity to electromagnetic interference, including nuclear electromagnetic pulses (although fiber can be damaged by alpha and beta radiation).
- High electrical resistance, making it safe to use near high-voltage equipment or between areas with different earth potentials.
- Lighter weight-important, for example, in aircraft.
- No sparks-important in flammable or explosive gas environments.
- Not electromagnetically radiating, and difficult to tap without disrupting the signal—important in high-security environments.
- Much smaller cable size-important where pathway is limited, such as networking an existing building, where smaller channels can be drilled and space can be saved in existing cable ducts and trays.
- Resistance to corrosion due to non-metallic transmission medium.
Optical fiber cables can be installed in buildings with the same equipment that is used to install copper and coaxial cables, with some modifications due to the small size and limited pull tension and bend radius of optical cables. Optical cables can typically be installed in duct systems in spans of 6000 meters or more depending on the duct’s condition, layout of the duct system, and installation technique. Longer cables can be coiled at an intermediate point and pulled farther into the duct system as necessary.