1.5 Fiber-Optic Cabling

Answer 1

Optical fiber cable transmits data over longer distances and at higher bandwidths than any other networking media. Unlike copper wires, fiber-optic cable can transmit signals with less attenuation and is completely immune to EMI and RFI. Optical fiber is commonly used to interconnect network devices.

Optical fiber is a flexible, but extremely thin, transparent strand of very pure glass, not much bigger than a human hair. Bits are encoded on the fiber as light impulses. The fiber-optic cable acts as a waveguide, or “light pipe,” to transmit light between the two ends with minimal loss of signal.

Question 2

Types of Fiber Media

Answer 2

Fiber-optic cables are broadly classified into two types:

Single-mode fiber (SMF)
Multimode fiber (MMF)

Question 3

Single-mode fiber (SMF)

Answer 3

SMF consists of a very small core and uses expensive laser technology to send a single ray of light, as shown in the figure. SMF is popular in long-distance situations spanning hundreds of kilometers, such as those required in long haul telephony and cable TV applications.

A cross-section of a single-mode fiber optic cable consisting of a center glass core of 9 microns in diameter, surrounded by a glass cladding of 125 microns in diameter, surrounded by a polymeric coating. An x-ray vision sideview shows that this type of cable construction produces a single straight path for the light.

Question 4

Multimode fiber (MMF)

Answer 4

MMF consists of a larger core and uses LED emitters to send light pulses. Specifically, light from an LED enters the multimode fiber at different angles, as shown in the figure. MMFs are popular in LANs because they can be powered by low-cost LEDs. It provides bandwidth up to 10 Gbps over link lengths of up to 550 meters.

A cross-section of a multi-mode fiber optic cable consisting of a center glass core of 50/62.5 microns in diameter, surrounded by a glass cladding of 125 microns in diameter, surrounded by a coating. An x-ray vision sideview shows that this type of cable construction allows for multiple paths for the light.

Question 5

DISPERSION

Answer 5

One of the highlighted differences between MMF and SMF is the amount of dispersion. Dispersion refers to the spreading out of a light pulse over time. Increased dispersion means increased loss of signal strength. MMF has a greater dispersion than SMF. That is why MMF can only travel up to 500 meters before signal loss.

Answer 6

Fiber-optic cabling is now being used in four types of industry:

Enterprise Networks - This is used for backbone cabling applications and interconnecting infrastructure devices.
Fiber-to-the-Home (FTTH) - This is used to provide always-on broadband services to homes and small businesses.
Long-Haul Networks - This is used by service providers to connect countries and cities.
Submarine Cable Networks - This is used to provide reliable high-speed, high-capacity solutions capable of surviving in harsh undersea environments at up to transoceanic distances. Search the internet for “submarine cables telegeography map” to view various maps online.

Question 7

Fiber-Optic Connectors

Answer 7

An optical-fiber connector terminates the end of an optical fiber. A variety of optical-fiber connectors are available. The main differences among the types of connectors are dimensions and methods of coupling. Businesses decide on the types of connectors that will be used, based on their equipment.

Note: Some switches and routers have ports that support fiber-optic connectors through a small form-factor pluggable (SFP) transceiver.

Question 8

STRAIGHT TIP connectors

Answer 8

ST connectors were one of the first connector types used. The connector locks securely with a ‘twist-on/twist-off’ bayonet-style mechanism.

Question 9

SUBSCRIBER CONNECTOR connectors

Answer 9

SC connectors are sometimes referred to as ‘square connectors’ or ‘standard connectors’. They are a widely-adopted LAN and WAN connector that uses a push-pull mechanism to ensure positive insertion. This connector type is used with multimode and single-mode fiber.

Question 10

LUCEN CONNECTOR SImplex Connectors

Answer 10

LC simplex connectors are a smaller version of the SC connector. These are sometimes called little or local connectors and are quickly growing in popularity due to their smaller size.

Question 11

DUPLEX MULTIMODE LC connectors

Answer 11

A duplex multimode LC connector is similar to an LC simplex connector, but uses a duplex connector.

Answer 12

Until recently, light could only travel in one direction over optical fiber. Two fibers were required to support the full duplex operation. Therefore, fiber-optic patch cables bundle together two optical fiber cables and terminate them with a pair of standard, single-fiber connectors. Some fiber connectors accept both the transmitting and receiving fibers in a single connector known as a duplex connector, as shown in the Duplex Multimode LC Connector in the figure. BX standards such as 100BASE-BX use different wavelengths for sending and receiving over a single fiber.

Question 13

Fiber Patch Cords

Answer 13

Fiber patch cords are required for interconnecting infrastructure devices. The use of color distinguishes between single-mode and multimode patch cords. A yellow jacket is for single-mode fiber cables and orange (or aqua) for multimode fiber cables.

Note: Fiber cables should be protected with a small plastic cap when not in use.