Fiber Optical Basic

What is fiber optical and why use it?

In an simple word, using the light traveling in the fiber optical cable and transmitting the data instead of using electric traveling in the copper. As fiber optics use light as opposed to electrical signals, it is immune to electrical interface. Unlike the copper cable such as Cat 5, the fiber cable works very well in noisy environments. The other major advantage is less resistant in the signals traveling. The data can be transmitted to much further distances, up to 80 km, as oppsed to the transmission on copper cables.

Key Components for fiber communication.

1. Transceiver
A fiber communication request transceiver, which is both a transmitter and receiver. There are usually two strands in one fiber cable, one for transmitting and the other is for receiving. Two factors need to be considered when looking at the maximum distance in fiber applications, the power for the transmission end, and the sensitivity of the receiving end. The higher the numbers on the transmit power and receive sensitivity, the longer the transmission distance.

2. Connector
There are so many types of fiber connectors available for the fiber communications. The most popular connectors for the industrial applications are LC, SC and ST connectors. The ST and SC are widely used in 100Mbps communication, where the LC is usually used for the Gigabit but not limited to that.

3. Cable Types (Core and Clad)
There are two type of fiber cables, Single Mode (SM) and Multi Mode (MM). The cable type is determined by the diameter of the core and the clad. A 50/125 cable rating mean a 50 µm core with 125 µm which 125 µm is the typical clad of fiber cable.  The quality of cable will determine the distance the light signals can travel. The core of the fiber cable is made of glass or plastic. Glass is considered a better material to reflect the light. In general, Single Mode cable is made of glass, and the Multi Mode cable can be made of either glass or plastic.

4. Operating Mode
There are two operating modes for fiber, Multi Mode and Single Mode. Since the way to transmit the signals are different, the cable mode must be matched with the fiber transceiver.

The core of Multi Mode fiber is large which allow for reflections and deflections. This makes the cable less expensive. The core of Single Mode cable is narrow to keep minimum reflections in the cable. This allows the singles to travel much further distances than Multi Mode. Thus the Single Mode is much better for long distance communication but more expensive.

5. Small Form Factor (SFP)
Small Form Factor (SFP) is an industrial standard for the transceiver module. It is mostly used for Gigabit applications but also can be used for 100Mbs. The benefits of using SFP are the flexibility (single mode or multi mode upon the applications), hot swappable for maintenance, and plug & play.
There is a memory map on the SFP. It contains the information such as transceiver interfaces and manufacturer. In order to provide the best performance, manufacturers usually lock the SFP module. The SFP and switch have to be provided by the same manufacturer.

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