Thursday, June 27, 2013
There are two important components of a fiber optic network namely passive star coupler and active repeaters.
Passive Star in Fiber Optic Network
- Passive star couplers are single mode fiber optic couplers with reflective properties.
- These couplers are used for optical local area networking at very high speeds.
- These couplers are made from very simple components such as mirrors and 3 db couplers.
- Besides this, these star couplers save a lot of optical fiber when compared to its trans-missive counterpart.
- They are free of any multi-paths so as to avoid any interference.
- A fiber optic network may consist of any number of passive star couplers and each of them is capable of connecting a number of users.
- The input and output from every passive star coupler is given to the output and input of an active coupler.
- The round trip transmission tile is stored by the active star coupler.
- When it receives a signal from a passive star coupler, it stops the output to that coupler for the duration of the signal.
- It also inhibits the incoming data from all the other passive star couplers for the round trip transmission delay plus signal duration.
- The purpose of a star coupler is to take one input signal and then splitting it in to a number of output signals.
- In telecommunications industry and fiber optics communication, this coupler is used in network applications being a passive optical device.
- If an input signal is introduced to one of the input ports, it is distributed to all of the output ports of the coupler.
- As per the construction of the passive star coupler, the number of ports it will have is given by the power of 2.
- For example, in a two port coupler or in a directional coupler or splitter, there are 2 input ports and 2 output ports.
- In a four port coupler, there are 4 i/p ports and 4 o/p ports and so on.
- The digital equipment corporation also sold a device by the name of star coupler which was used for interconnecting the links and computers through coaxial cable instead of using optical fibers.
Active Repeater in Fiber Optic Network
- Active repeater is an important telecommunications device used for re transmitting the signal it receives to a higher level and with higher basically to the other side of an obstacle so that long distances can be covered.
- Repeater is an electro-mechanical device that helps in regenerating the telegraphy signals.
- It may be defined as an analog device for amplifying the input signal, reshaping it, re-timing it for re-transmission.
- A re-generator is a repeater that can perform the re-timing operation.
- Repeaters just tend to amplify the physical signal without interpreting the data transmitted by the signal.
- The 1st layer i.e., the physical layer is where the repeaters operate.
- Repeaters are employed for boosting the signals in optical fiber lines as well as in twisted pair and coaxial cables.
- When a signal travels through a channel, it gets attenuated with the distance and time because of the energy loss (dielectric losses, conductor resistance etc.).
- When light travels in optical fibers, it scattered and absorbed and hence is attenuated.
- Therefore, in long fiber lines, repeaters are installed at proper intervals for regenerating and strengthening the signal.
Repeater in optical communication performs the following functions:
Ø Takes the input signal
Ø Converts it in to electrical signal
Ø Regenerates it.
Ø Converts it in to optical signal
Ø Re-transmits it
- These repeaters are usually employed in submarine as well as transcontinental communication cables as the loss is unacceptable in these cases.