Concept of Optical Amplifiers and Regeneration

Concept of Optical Amplifiers and Regeneration : What is the importance of Regeneration and Amplifiers in optical networks will be discussed in this article. Regeneration is an amplifier with addition of 3-R function. It suppress the noise at intermediate station. Regeneration require at every 600Km distance.

Role of amplifiers in the optical network are that Pre-amplifier boosts signal pulses at the receive side. The post-amplifier amplifies the communication pulses on the transmitted side (post amplifier) ​​and the receiving side (preamplifier). Here we can also mention that a line amplifiers (ILAs) are placed at different distances from the source to provide recovery of the optical signal before it is degraded by loss.

What are 3R Regeneration?

In very simple words, we can say that amplifiers in optical networks are defined as type 1R, 2R and 3R, which we call 3R Regeneration.

1R- Re-amplification : Boost up the received weak signals to transmit further. It is done by the optical amplifier. In one word we can say that 1R = Re-amplify.

2R- Re-Shaping : Correcting noise and dispersion. Remove noise from a digital signal. It is done by DCF and OEO. In other word we can say that 2R= Re-amplify and reshape.

3R- Re-timing : Synchronizing with network clock. Using PLL and optical clock recovery. In simple word we can say that 3R = Re-amplify, reshape, and retime. 

Below given image shows the effect on a degraded optical signal once it has been 1R, 2R, or 3R regenerated.

Optical Network and Regeneration

With the help of the picture given below, it is shown that optical networks can have 1R, 2R, and 3R devices. In the optical network the 1R device only amplifies the received optical signal. Amplification and reshaping of the waveform are provided by 2R device to provide some data recovery.

Amplification, reshaping and retiming provided to the optical network by the 3R device, it can provide for the transponder. A transponders have asynchronous input, do not depend on timing and cannot be retimed. See the image below that consists of 3R devices in an optical network with 1R and 2R as well as 3R-

Erbium-Doped Fiber Amplifiers

For DWDM amplification gain mechanism provided by the Erbium-doped fiber amplifiers (EDFAs). Erbium amplifiers used in the DWDM system because it work very well and very efficient as amplifiers in the 1500 nm range.

The light is pumped to about 1400 nm (pumped laser diode) excite the erbium ions, and then amplify the 1500 nm light signal coming from the source system. Last active component in the DWDM system and erbium-doped fiber amplifier (EDFA) shows in the image on the transmit side (post amplifier). In the give image the first active component is on the receive side, the preamplifier (a receive EDFA).

In this article, we are discussing about Amplifiers and Regeneration, so it is also important to discuss about fiber bands. If the fiber band is not discussed here, then the information given will probably be incomplete, then let's talk about the fiber band in a very short time.

Fiber Bands

For fiber-optic DWDM networks there are three optical frequency bands are used today. These three bands are C- band,  L-band and S-band, which are considered the most useful. The bands are:

➤The range of C-band (conventional) is from 1530 nm to 1570 nm.

➤The range of L-band (long wavelength) is from 1570 to 1625 nm.

➤The range of S-band (short wavelength) is from 1450 to 1500 nm.

Why Amplifier Required?

Different types of amplifiers like C- and L-band amplifiers are required because EDFA must be adapted for either C-band or L-band amplification.

➤For C-band amplifiers used high pump power with short EDFA fiber.

➤For L-band amplifiers used the medium pump power with long EDFA fiber.

Thulium-doped fluoride-based fiber amplifiers (TDFAs) for the 1450–1490 nm S-band are used in conjunction with Raman fiber amplifiers (RFA). The S-band has recently undergone DWDM system design. Now it is important to discuss about Raman amplifier, so now let's discuss about Raman amplifier.

Raman Amplifiers

Originally Raman scattering was considered a detriment to fiber performance. However, recent discoveries have resulted in hybrid networks that use Raman amplification to achieve greater distance performance. Features include:

➤Silicon fiber used as the gain mechanism

➤The lower efficiency of optical signal is compensated for by the higher linear density of silicon in the fiber.

➤Amplifies over C-, L-, and S-bands.

Distributed Raman amplifiers general used to accomplish operation over longer spans with fewer regeneration sites.

Others Optical Amplifiers

The photo above shows the silicon optical amplifiers (sauce). These include rare-earth elements to make rare-earth-doped fibers in optical amplifiers such as:

TeO2- Tellurium- compound of Tellurite and Oxygen.

TmF3- Thulium- compound of Thulium and Fluoride.

Most amplifiers are still experimental and include:

EDFA: Erbium-doped fiber amplifier (1530–1565 nm)

➤GS-EDFA: Gain-shifted EDFA (1570–1610 nm)

➤EDTFA: Tellurium-based gain-shifted TDFA (1530–1610 nm)

➤GS-TDFA: Gain-shifted thulium-doped fiber amplifier (1490–1530 nm)

➤TDFA: Thulium-doped fluoride-based fiber amplifier (1450–1490 nm)

➤RFA: Raman fiber amplifier (1420–1620 nm or more)

Last Word

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