Fiber Optic Cable

Before you start

Objectives: learn the specifics about fiber optic cables and which connectors can be used.

Prerequisites: no prerequisites.

Key terms: mode, connector, fiber, optic, single, multi, light, core, cladding, type, ceramic


Design

The center of fiber optic cable is its plastic or glass core. In one cable we can have several cores. These cores are fine glass or plastic that transmit light. Around those plastic or glass cores is the cladding. The job of the cladding is to bounce the light back into the center of the core. For instance, when we bend the cable the light will go straight and then bounce off the cladding back to the center of the core. Surrounding the cladding are several layers of sheathing that protect the cladding and the inner glass core.

Fiber Optic Cable

Image 209.1 – Fiber Optic Cable Design

Advantages

One of the main advantages of fiber optic cabling is the fact that it is completely immune to electromagnetic interference (EMI), because it doesn’t use electricity. Because of that it also resists eavesdropping. One of the problems with unshielded twisted pair is the fact that it’s possible, if we have the right equipment, to capture data that is traveling on the twisted pair wiring.

Other main advantage is the fact that it supports high data transmission rates.

Disadvantages

It is very expensive when comparing to unshielded twisted pair wiring. Another disadvantage is that it’s harder to work with. Because we are dealing with a glass, or plastic core that’s fragile, it’s not as flexible as twisted pair wiring. Also, with fiber optic cabling we have to go to special training to learn how to put a connector on the end of a piece of fiber optic cabling.

Single Mode Cable

The first type of fiber optic cabling is called Single mode. Single mode cabling transmits data through central glass, or plastic core using a single ray of light.

Single Mode

Image 209.2 – Single Mode

That ray of light is also called a mode. The diameter of the single mode core is very thin, about 10 microns. Because of the way the cable is constructed, and because of its small diameter, the light is forced to stay in the center of the cable. Because of that, this type of cabling can support a large amount of data and it can be very long. It is used to connect networks in different cities, or in different parts of a geographic location.

Multi Mode Cable

The second type of fiber optic cabling is called Multi mode. It transfers data using multiple rays of light.

Multi Mode

Image 209.3 – Multi Mode

Each mode, or ray, is transmitted at a slightly different frequency. By doing that, we can split up the fiber optic channels and transmit multiple signals at the same time. This type of cable is thicker than the Single mode. It is about 50 to 100 microns in diameter.

When we have many channels going at the same time with different frequencies, the light rays bounce as they go around a corner and hit a cladding. The cladding that surrounds the inner core is designed to reflect the light of one frequency at a different angle than light of other frequency. Doing that, it’s able to keep the signal intact.

Multi Mode Bouncing

Image 209.4 – Multi Mode Bouncing

Multi mode cable does not allow us to go distances that Single mode will. With Single mode we’re talking kilometers but with multi mode we are talking less than 500 meters.

Connectors

ST Connector

The first type of connector is called the ST connector. It’s used with both single mode and with multi mode fiber optic cabling. The ST connector is a keyed bayonet type connector.

ST Connector

Image 209.5 – ST Connector

It is called a ‘push in and twist connector’. To connect this to another piece of fiber optic equipment we would push it in and give it a twist to lock it in place. The connector is nickel plated and it uses a ceramic ferrule down inside the connector. The purpose of ceramic ferrule is to ensure that we have the cable properly aligned, and to prevent light rays from being reflected as they pass through the connector.

SC Connector

The SC connector is also used with both Single mode and with Multi mode connectors. It is a ‘push on, pull off’ type of connector and it uses a locking tab to keep it plugged in.

SC Connector

Image 209.6 – SC Connector

It also uses ceramic ferrule down inside that ensures proper alignment and it makes sure that light doesn’t get reflected or bounced around as it passes through the connector.

LC Connector

The LC connector can be used with Single mode or Multi mode fiber optic cabling. It uses a plastic connector that uses a locking tab.

LC Connector

Image 209.7 – LC Connector

Just like other connectors, it uses a ceramic ferrule down inside that ensures that the connector is lined up properly as it’s plugged in, and to prevent light from being bounced around as it passes through the connector.

MTRJ connector

The MTRJ connector can also be used with Single mode or Multi mode fiber optic cabling. It’s a plastic connector and uses little tabs that make sure that the plug is aligned and locked in place properly.

MTRJ Connector

Image 209.8 – MTRJ Connector

It also uses the ceramic ferrule to make sure that the fiber optic cable is aligned properl.

Remember

Fiber optic cabling transmits light signals instead of electrical signals. The center of fiber optic cable is its plastic or glass core. It is completely immune to electromagnetic interference (EMI). We difirentiate Single mode and Multi mode cables. Single mode cabling transmits data using a single ray of light, and Multi mode uses multiple rays. Connectors which we can use are ST, SC, LC and MTRJ.

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