How communication possible with single Fiber only!

In communication books we read that two path is required for two way communication but actually with single Fiber also it is possible. In traditional communication system we saw that we require two wire or fiber for transmission and reception of signal (information) but with modern technology it is possible to have bi directional communication with single fiber.

For example, In Bharat net project BBNL uses single Fiber to connect OLT (Optical Line Terminal) and ONT (Optical Network Terminal) end user. 

But this method is useful for only low bandwidth applications. But if you want to connect two big cities you need separate fibers for transmission and receiving the signal.

In today's digital Era Telecom companies play crucial role to provide 24×7 services to their users. Telecom companies have wide infrastructure of optical fiber between various cities, towns, states and even between countries.

As India is a developing country, a lot of development works always go on and underground optical fiber cable gets damaged. In such scenario any telecom company can not rely on one optical fiber cable. So to ensure 24×7 connectivity between two exchanges (cities) Telcos have more than one cable via different path. Suppose there are three ways to reach city B from city A, say path a,b,c. Then if Optical fiber cabld (OFC) laid on any two paths say b and c, such type of network topology called ring connection. But if three OFC laid on all three paths a,b and c then such network topology called mesh connection. So ring connection have two paths while mesh connection may have three or more paths available.

Actually In the technology called GPON (Gigabit passive Optical Network) which uses single fiber for both transmission and receiving, two wavelengths are used, one for downstream 1490nm and another 1350nm for upstream communication. This multiplexing is called Wavelength Division Multiplexing (WDM).

In this technology GPON passive splitter is used to split one fiber in upto 64 fibers so that single Fiber can serve 64 different customers.

 

This upper limit is because of the loss introduced by the splitter. If we try to split more than that limit power level received may be below threshold which will disrupt the communication.