The Difference Between Fiber Optic Cable, Twisted Pair and Coaxial Cable

The main components of a transmission system are: the transmitter (TX), the communication channel and receiver (RX).

Today we will focus on the communication channel. This can be materialized in the form of either a physical wired medium or a wireless medium such as air. The wired medium can be found in today’s data center dense cabling in the form of twisted pair or optical cable and in the last mile loop as a coaxial cable.

Twisted Pair

Twisted pair cables as the names implies, consists of a pair of cables twisted together, which has been utilized in telecommunication field for a long time. The twisting can avoid noise from outside sources and crosstalk on multi-pair cables, so this cable is best suited for carrying signals. Basically, twisted pair cable can be divided into two types: unshielded twisted-pair (UTP) and shielded twisted-pair (STP).

UTP stands for unshielded, twisted pair, while STP is for shielded, twisted pair. UTP is what's typically installed by phone companies and data communication (though this is often not of high enough quality for high-speed network use) and is what 10BaseT Ethernet runs over. However, STP distinguishes itself from UTP in that it consists of a foil jacket which helps to prevent crosstalk and noise from outside source. It is typically used to eliminate inductive and capacitive coupling, so it can be applied between equipment, racks and buildings.

Coaxial Cables

Coaxial cable is composed of an inner solid conductor surrounded by a paralleled outer foil conductor that is protected by an insulating layer. A coaxial cable has over 80 times the transmission capability of the twisted-pair. Coaxial cable has also been the mainstay of high speed communication and has also been applied to network with 10 Gigabit links data centers, because it is proved to be cost efficient for short links within 10 m and for residential network.

There are two coaxial cables: 75 Ohm and 50 Ohm. The former is primarily used to transmit a video signal, like television signals over cable. While the main application of the latter is the transmission of a data signal in a two-way communication system. Other typical applications include computer Ethernet backbones, wireless antenna feed cables, GPS (Global Positioning Satellite) antenna feed cables and cell phone systems.

While deciding whether to use coaxial cable, twisted-pair, or fiber optic cable for transmission, it’s imperative to collect the basic information about them, and take the cost, cable runs and other external conditions into consideration.

Fiber Optic Cable

Fiber optic cable is the complete assembly of fibers, it uses light pulses to transmit information down fiber lines instead of using electronic pulses to transmit information down copper lines. Each of the optical fiber elements is individually coated by plastic layers and contained in a protective tube. A fiber optic cable can accommodate many wavelengths (or channels), able to accommodate ever-increasing data capacity requirements. When terminated with LC/SC/ST/FC/MTRJ/MU/SMA connectors on both ends, such as LC-LC, LC-ST, SC-SC, ST-ST, LC SC cable, fiber optic cables can achieve fiber link connection between equipment during fiber cabling.

A single-mode optical fiber is a fiber that has a small core, and only allows one mode of light to propagate at a time. So it is generally adapted to high speed, long-distance applications. While a multimode optical fiber is a type of optical fiber with a core diameter larger than the wavelength of light transmitted and it is designed to carry multiple light rays, or modes at the same time. It is mostly used for communication over short distances because of its high capacity and reliability, serving as a backbone applications in buildings.

Advantages of fibers over copper wiring

• Broad bandwidth: a single optical fiber can carry over 3,000,000 full-duplex voice calls or 90,000 TV channels.
• Immunity to electromagnetic interference: light transmission through optical fibers is unaffected by other electromagnetic radiation nearby. The optical fiber is electrically non-conductive, so it does not act as an antenna to pick up electromagnetic signals. Information traveling inside the optical fiber is immune to electromagnetic interference, even electromagnetic pulses generated by nuclear devices.
• Low attenuation loss over long distances: Attenuation loss can be as low as 0.2 dB/km in optical fiber cables, allowing transmission over long distances without the need for repeaters.
• Electrical insulator Optical fibers do not conduct electricity, preventing problems with ground loops and conduction of lightning. Optical fibers can be strung on poles alongside high voltage power cables.
• Security of information passed down the cable. Copper can be tapped with very little chance of detection.