The core of the fiber-optic cable is made of one or multiple glass or plastic fibers. Central fibers are used as media for transmitting data, which is being sent in light beams from a laser or a LED. The core is surrounded by layer of plastic or glass with different density, which is called cladding. Its purpose is to reflect the light back to the core depending on the transmission mode. This allows light beam to bend together with cable, where necessary. Cladding is surrounded by the plastic buffer that protects the fiber and absorbs any light that might escape through the cladding. Plastic buffer is covered in Kevlar that is used for protection and to avoid cable stretching. Last layer in the fiber-optic cable is the plastic sheath that keeps everything together.
There are many different types of the fiber cable available on the market. Large sized fibers may contain up to 1000 fibers in one cable with heavy sheath. This cable will be developed for extreme outdoor conditions. Small sized fibers (patch cables) can have two strands of fiber and will be flexible enough for short connectivity. Data is being transmitted only in one direction in the single strand of glass. That makes necessary to use two strands for full-duplex communication in case fiber transmitters and receivers use only one wavelength. In such case, for example you can see dual fiber media converters having duplex fiber connector on board. It is done in the zipcord cable, where strands are combined side by side in conjoined jackets. This type of cable is shown in Figure 1 and is usually used for short distances, like equipment interconnection. However, in case WDM typesingle fiber strand media converters are used, then receiving and transmitting directions will use same fiber strand. Usually for distances less than 60 km 1310 nm and 1550 nm will be used, for higher distances 1490 nm instead of 1310 nm will be used. By the wayEPON OLT and EPON ONU’salso use only one fiber between them, and directions for transmit and receive are split using 1490/1310 nm. And then if CATV overlay is needed over same fiber, 1550 nm wavelenght is added, using CATV 1550 nm transmitter at the headend.
Figure 1. Zipcord fiber-optic patch cable.
Obvious benefits of the use of fiber cable are high throughput, great noise resistance, increased security, longer transmission distances, and high-speed networking standard. On the other hand fiber is more expensive for short distances, more difficult to splice than copper, and require experienced specialist for splicing.
Optic-fiber cable is using light beams, so in theory throughput is only limited by physics of light traveling through the glass. In practice it gives us data rates of up to 100 gigabits. Another benefit of using light beams is the noise, that has been almost completely removed. Optic fibers specifications make it best choise for the network backbone and high traffic applications, such as video and audio streaming.
Optional fiber cable is using 10 types of connectors. Most common are shown in Figure 2. The SC and ST connectors are used and deployed commonly, while LC and MT-RJ are latest development for today. They are smaller size, and MT-RJ is having double strands of fiber in single ferrule. This makes MT-RJ able to transmit full-duplex signal. Variety of connectors allows purchasing cables with different connectors on the each end.
Figure 2. ST, SC, MT-RJ, LC and connectors.
Fiber can be used for different distances, from 150 to usually 120,000 – 150,000 meters. It is limited by 120 – 150 km due to signal degradation after this point. However, Fiberbit have a special cases when our adapted 2.5G rate sfp fiber transceivers were made to fit for a 200 km distance. Degradation is resulting in data errors and data loss. Optical loss also appears with every connection point in the fiber. Dust or oil in the connection might increase signal loss. Depending on the light wavelength and the type of cable (single mode/multimode) maximum distance might reduce.
