Types of Optical Amplifiers - Technopediasite

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Monday, July 13, 2020

Types of Optical Amplifiers

Types of Optical Amplifiers : We will discuss about amplifiers used in optical networks, optical amplifier especially those used in long distance networks. Here it will also be discussed what are the types of optical amplifiers and what does optical amplifier work in optical networks. When optical fiber network has a distance of up to 10 km or 100 km, that transmission loss cannot be ignored. Then optical amplifier is required in optical network.

The transmission loss of light passing through optical fiber is a very small value of less than 0.2 dB per km with light wavelengths at the 1,550 nm band. However, when the optical fiber has a distance of up to 10 km or 100 km in length, the transmission loss cannot be ignored. When the signal propagating through long-distance optical fiber that signals becomes extremely weak, it is necessary to amplify the signals using an optical amplifier.


Types of Optical Amplifiers details
Optical Apmlifiers

Types of Optical Amplifier

When the signal propagating through long-distance optical fiber that signals becomes extremely weak, it is necessary to amplify the signals using an optical amplifier. We can say that an optical long-distance network is not possible without an optical amplifier.

There are two types of optical amplifiers used in optical networks-

1. Solid state Optical Amplifiers
➤Semiconductor Optical Amplifiers

2. Fiber Amplifiers
➤Erbium Doped Fiber Amplifiers ( EDFAs )
➤Raman Amplification ( RA )



Semiconductor Optical Amplifier (SOA)

As the name suggests, an SOA is a semiconductor element. By performing antireflective processing on the crack plane of a semiconductor laser and eliminating the resonant structure, light can penetrate from outside the semiconductor and amplify the signals (Light) through excited emission.

An SOA can be built in a compact size and its low running cost compared to EDFA means that it is economically more efficient. Until recent years, SOA's input light was highly dependent on polarization, but research into low polarization dependence has progressed in recent years.

An SOA can be built in a compact size and its low running cost compared to EDFA means that it is economically more efficient. Until recent years, SOA's input light was highly dependent on polarization, but research into low polarization dependence has progressed in recent years. But currently the use of SOA is not common in the telecom sector.

Use of SOA

SOA is used for embedding in 100G CFP / CFP2 ER4. Light sources are used for optical communication in the 1.3 μm band for 40 km transmission between data centers and between mobile phone base stations and data centers.

However, SOAs are required as pre-amplifiers for attenuation in communication light when performing long-distance transmission. SOASs are embedded in 100G CFP / CFP2 ER4 transceivers, and are now playing an important role in the market.

Fiber Amplifiers

There are mainly two types of fiber amplifier which widely used in optical network for DWDM system. 
1. EDFA (Erbium-Doped Fiber Amplifier)
2. FRA (Fiber Raman Amplifier)

Erbium-Doped Fiber Amplifier (EDFA)

I have already written an article on the concept of EDFA, to understand the concept of EDFA, please read this article first, whose link is given below.

Concept of EDFA ( Erbium-Doped Fiber Amlifier )

Here we can say with strong concept that EDFA is a type of OFA and is an optical amplifier with erbium ions added to the core of the optical fiber. It features high gain and low noise, independent polarization , and can amplify optical signals in the 1.55 μm band or 1.58 μm band.

It was first necessary to use an optical repeater to temporarily convert light into an electrical signal, to amplify and regenerate the wave electrically, then to turn back into light and send back. In the 1990s, the introduction of EDFA amplified the signals as light.

Configuration of EDFA

An optical amplification is performed with the help of an optical pump laser of selective wavelengths. Arbium ions are excited by the pump signal and reach high energy states, driven by the need for an erbium ion signal in the high energy state of these ions. Leads Return to a low-energy state called the geo-energy state.

Configuration of EDFA
EDFA

During this transition, these ions emit radiation similar to the signal. Erbium doped fiber amplifiers have a short length of doped optical fiber by small controlled amounts of the rare earth element erbium. This rare earth element contributes to the amplification process in the presence of a pump signal. Pump laser excitium erbium ion that gives additional energy to the signal. The principle of operation is similar to the principle of laser.

Irradiating a coupling module with light at 1.48 µm enables the light to be internally stored as energy, and light in the 1.55 µm band causes optical amplification when it propagates, and obtains a gain of 20 to 30 dB.

Keep in mind these important points, An erbium doped fiber amplifier consists of a short length of doped optical fiber by small controlled amounts of the rare earth element erbium. This rare earth element contributes to the amplification process in the presence of a pump signal. Pump laser excitium erbium ions that give extra energy to the signal. The principle of operation is similar to the principle of a laser.

It is clear that pumping with 980 nm laser is more effective than 1480 nm pumping. Commonly used in submarine systems, and rapidly on land. Possible amplification at several wavelengths around 1550 nm. The profit profile is not flat with EDFA and requires some flat mechanism.

Raman Fiber Amplifier

Raman Amplification process
Raman Amplification process


Raman fiber amplifier is also a type of OFA. This causes excited emission based on SRS when strong excitation light enters the optical fiber. The light is then amplified into a wavelength range that is approximately 100 nm longer than the excitation light wavelength. It has a broad amplification wavelength region, and can be determined independently by the wavelength of the excitation light.

The basic principle of Raman fiber amplifier is excited Raman scattering (SRS). When the strong optical pump makes contact with the medium it produces a new signal (a Stokes wave) in the same direction. The new generated frequency is lower then the pump frequency by13.2 THz. In normal fibers this effect is very small and has a relatively long length for significant amplification.

Raman gain strongly depends on the power of the pump and the frequency offset between the pump and the signal. Amplification occurs when the pumped photon leaves its energy to form a new photon at the signal wavelength and some residual energy that is absorbed as photons ( vibration energy).

The low frequency signal is then pumped up and optimal amplification occurs when the difference in wavelength is around 13.2 THz. Any signal less then the pump can be amplified but the efficiency may not be the same for all efficiency by adding FBG (Fiber Bragg Grating) reflector for all waves. Thus any frequency can be generated from this event.


Advantages of Raman Amplifier over EDFA

Low noise build up
Simple design, since direct amplification in optical fiber is achieved and no special transmission medium is required. on the basis of background flexible assignment of signal frequencies, because Raman amplifier gain depends on pump wavelength and not on wavelength sensitive material parameters, such as emission cross section of dopants in erbium doped fiber (EDF).

The broad gain bandwidth is achieved by combining the Raman amplification effect of multiple pump waves that are carefully placed in the wavelength domain.


Disadvantages of Raman Amplifier over EDFA 

Disadvantages of Raman Amplifier over EDFA not only specifically launched pump waves but also that some WDM channels can provide power to amplify other channels, which will result in power to amplify other channels and thus for de-gradation The leading cross will cross.

Degrading effects like Raman scattering and backward Rayleigh scattering also affects the performance.

Comparison of Raman Amplifier and EDFA 

Raman amplifier and EDFA are compared in a very simple way by the table below so that you can understand very easily-
Comparison of Raman Amplifier and EDFA
Raman Amplifier and EDFA

Last Word

Dear Telecom Friends, how did you like this article " Types of Optical Amplifiers ", please tell me by commenting. I have tried my best to discuss the commonly used amplifiers in optical networks. If you have any suggestion related to this article, then also let me know. Stay connected with me to get any information related to telecom technical support.

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