Optical Fiber Communication

Type of optical fiber

            When we are selecting optical fiber for a specific application we have two types of optical fibers. They are Single mode and multi mode. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber is a type of fiber optic cable which is thick enough for light to follow several paths through the code. Multi-mode fiber is best suited for use in short lengths, such as those used in Local Area Networks (LANs). But single modes are standard choice for high data rates or long distance telecommunications which use laser diode based fiber optic transmission equipment. 

Dispersion

When we discuses about dispersion of fiber. Ever fiber has Inter modal or chromatic dispersion. Multi mode dispersion only occurs in multimode fibers. . But single mode fibers are having lower dispersion than multi mode fibers. Therefore we can use single mode fibers for long haul repeater/amplifier less optical communication links. 

Fiber non linearity

In this system it is difficult to maintain a linear fiber connection. The system has bending losses and signal transmitting distance may reduce. So, it is important to try to design a linear fiber optic transmission system as possible.

Operating wavelength

When we are selecting a suitable wave length for optical fiber communication we have to analyze the Optical window graph. In optical window there are three windows. We have  820 nm to 900 nm(1^st window), 1280 nm to 1350 nm (2^nd  window), and 1450 to 1650 nm(3^rdwindow) But 3^rd window is enhanced for long distance communication for the reason that, the attenuation is varying 0.15 - 0.25 dB/Km which is very low compare to other two windows.

Transmitting power

            For a high bit rate, long haul repeaters / amplifiers less fiber link communication we need to supply better and sufficient transmitting power to the source. Because of the attenuation of the signal when it is traveling more distance. 

Source type

For high-data-rate applications as like this, most fiber optic transmitters use laser diodes as sources. Fiber optic data link performance depends on the amount of optical power (light) launched into the optical fiber. Therefore using laser diode we can obtain high bit rate over long distance.

Receiver sensitivity

            We know in a long haul communication the transmitting signal is attenuated. Then the receiver gets weak signal. Therefore it should have the high receiver sensitivity for grab the receiving signal.

Detector type

In optical fiber communication there are three types of detectors. They are known as PIN, FET-PIN and APD. But long haul communication we need detector with higher sensitivity and APD has the highest sensitivity. Therefore we can use APD for communication.

Modulation technique

            We can use PSK, DQPSK, and PSBT as the modulation technique suit for this application. 

Bit Error rate

When the signal travels through the optical cable there are many inter symbol interferences. It confuses the receiving data. Therefore bit error happens. In order to avoid bit errors we need to reduce the base band data rate. But it is difficult to reduce the data rate because we nee high data rate.

Number of connectors

            When we have number of amplifiers and repeaters we also introduce loss to the system by increasing number of connectors. These losses will reduce the length of the high bit rate long haul fiber optical links. Therefore it is better keep the connectors in a low number.

Number of splicing points

If we increase the distance of the cable the splicing points will increase. In long haul fiber optical communication links number of splicing point may at a higher value. And we know each splicing point introduce a loss to the system. But we can’t control when the link is rising. 


    Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.