What Is the Difference Between Optical & Coaxial?

Coaxial cables transmit radio frequencies.

Optical fibers and coaxial conductors are used in communications cables to send information from point to point. The first coaxial cable was patented in England in 1880; optical fibers emerged in the late 1950s. Both technologies have myriad uses and sometimes work in tandem. For example, cable TV companies use fiber optics to carry the signal from their transmitters to your home connection cabinet and then use coaxial cables to carry the signal from the connection cabinet to your cable box. Fiber optics have helped revolutionize the Internet and the field of medicine.

Uses

Fiber optic cables transmit light waves.

Fiber optic cables and coaxial cables both transmit audio, video, and data. In medicine, optical fibers--because they permit the "piping" of light--uniquely let doctors peer inside a patient's body to make diagnoses without surgery.

How They Work

Fiber optic cables used for long-distance communications.

In fiber optic cables, an electrooptic modulator converts electrical signals into laser- or electrode-generated light bursts that shoot down the length of the cable's glass core. The light waves convert back into electric current for decoding at the receiving end. Glass fibers can transmit clean signals over distances of up to 13,000 miles (20,917 kilometers).

Coaxial cable conducts encoded alternating electric current between locations at radio frequencies of 50 megahertz and above. The current travels outward from the source and returns, reversing direction millions to a billion times a second. To send radio frequency signals over long distances without signal loss requires boosting the current repeatedly.

How They Are Built

An active fiber optic bundle.

Optical fiber is a very thin coated strand of transparent glass or plastic capable of transmitting light. Cables bundle these fibers around a central, hard wire in a core tube that is wrapped with layers of protective material. Cables are coated with a polyethylene or Teflon housing.

In the coaxial cable, the inner copper conductor is surrounded by a tubular, typically semi-rigid insulating dielectric layer which in turn is sheathed in a conductive so-called “shield” of fine woven wire or thin metallic foil. Next comes the cable's outer surface, a thin insulating layer made of PVC or other impervious material. Coaxial cables are usually connected with radio frequency connectors.

Types

Both types of cables work well over short distances.

There are two common types of fiber cables--single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive.

The many types of coaxial cables available are classified according to impedance, dimensions, and intended use. The RG-6 type is the most commonly-used coaxial cable for home TV use. Don't confuse coaxial cable with other shielded cable only suitable for carrying audio signals.

Which is Better?

Fiber optics has displaced coaxial in many applications. Fiber optics are not plagued by electrical interference. Because they deliver unattenuated signals over much longer distances and carry more data faster, they are the standard for connecting computer networks over large areas and delivering broadband-hungry web services like video conferencing and interactive gaming. Cost is comparable to that of copper cabling. Coaxial cable technically is still competitive for wiring home audio, video and computers, but there, too, fiber optics as well as WiFi are helping to make coaxial an obsolescent technology.

References

• ePanorama.net: Coaxial Cables
• Florida Center for Instructional Technology: What is Network Cabling?
• Fiberlink: Application Briefs

Resources

• Belden: Residential
• FiberOptic: Product
• "Encyclopedia of Science and Technology"; James Trefil, 2001