erbium doped fiber amplifiers principles and applications

Erbium doped fiber amplifiers principles :

EDFA stands for erbium doped fiber amplifier, An optical amplifier are also called erbium doped fiber amplifier or EDFA. This article also gives you  advantages and disadvantages of EDFA to know more details about EDFA.

The erbium atoms in silica are Er³⁺ ions with three lost electrons in its orbit. The raising of ions to higher energy levels is achieved by two pump level.

1. Meta stable state :

The meta stable state is a state from which the life time for the transitions from this state to the ground state are very long compared with the life times to the states that led to this level. 

 2. Stark splitting :

The meta stable, the pump band state and ground state levels are closely spaced energy levels form the manifold called stark splitting.

Erbium doped fiber amplifiers applications :

• Erbium doped is a double clad fibers can be used for generating very high output power of tens of watts or even more.
• It is also possible to amplify ultra short pulses in the 1.5 micro meter region to relatively high energies using EDFAs in the form of amplifier chains
• As a pump absorption efficiency can be weak in this case, an ytterbium sensitized core may again be useful.
• One exploits the relatively high saturation energy of such amplifier, particularly when erbium doped large mode area fibers.
• For proper choice of material composition of the fiber core this energy transfer can be fairly efficient.
• The use of pure erbium doped fibers is more common in the telecom area side.

Advantages and disadvantages of graded index fiber

Graded index fiber is one type of optical fiber. Here this article gives information about the advantages and disadvantages of graded-index fiber to know more details about it. 

Advantages of graded-index fiber :

• Losses are reduced
• The information-carrying capacity is increased
• Pulse distortion is reduced
• The data rate is very high 
• Attenuation is less

Disadvantages of graded-index fiber :

• Difficult to manufacture
• Costly compare to step-index fiber

Explore more information:

1. What are the advantages and disadvantages of optical fiber
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Linear and nonlinear systems examples

A linear model represents an accurate representation of the behavior of many systems where the non-linear system has steady state performance with a different kind of behavior. Here this article gives the information about the example of a linear and nonlinear system to know more details about it.

Example of linear systems :

• Electronics circuit such as amplifier 
• The unity system, where the output of a system is always equal to the input
• Multiplication by a constant that is the amplification of the system
• Linear system where the wave propagation produce such as sound as well as  an electromagnetic wave 
• Some electrical circuit composed of the resistor, capacitor, and indicator
• The null system where the output is always equal to zero regardless of the input system
• Differentiation and integration
• A signal must be changed such as a resonance and image blurring
• A mathematical operation like a convolution where each value in the output is expressed as the sum of values in the input multiplied by a set of some weighing coefficient, so here give some many more example of linear as well as a non-linear system

Example of a non-linear system :

• A system that does not have sinusoidal fidelity such as electronic circuit
• Common electronic distortion clipping and cross over distortion
• Saturation such as an electronic amplifier and transformer are driven too hard
• A system does not have static linearity
• A system with a threshold like digital logic gates 
• Multiplication of signal by another signal called as amplitude modulations

What is DTFT

The DTFT is the member of the Fourier transform family, it can operate on aperiodic, discrete signals. 

The DTFT stands for discrete-time Fourier transform, It is a member of the Fourier transform family that operates on an aperiodic discrete signal. 

The best way to understand the DTFT is how it related to the DFT.  In general, the DTFT is used for the analysis of non-periodic signals. Let us consider the discrete time signal x (n), its DTFT is denoted as X () is given is :

DTFT  = X (Ώ) = e ^{-j Ώn}

^{The inverse DTFT given as :}

^{IDTFT  =} X (n) = 1/2∏  * e ^{-j Ώn}  d Ώ

In this section, we will also study some  properties of  DTFT to learn better understand this topic. We know that x (n) and X (ω) are Fourier transform pair and is denoted as,

             DTFT

If  x (n)    ↔     X(ω)  

DTFT features :

• Used for finite and infinite sequence
• It is only theoretical
• Cannot be implemented practically
• DFT is derived from DTFT
• It is periodic and continuous 

DTFT properties

We already know about what is DTFT. In this section, we will study some properties of  DTFT to know a better understanding of this topic. We know that x (n) and X (ω) are Fourier transform pair and denoted as given below,

             DTFT

If  x (n)   ↔   X(ω)  

1. Linearity :

Fourier transform of a linear combination of signals then it will be the same as the linear combination of the Fourier transform of each of the individual signals.

                 DTFT

If  x₁ (n) is    ↔   X₁(ω)  and  x₂ (n) is   ↔  X₂(ω)  then

              

                                      DTFT

a₁ x₁ (n)   +  a₂ x₂ (n) is    ↔    a₁ X₁ (ω)   + a₂ X₂ (ω)  

2. Time shifting : 

Time shifting shows that a shift in time is equivalent to a linear phase shift in frequency domain. Since the frequency content depends only on the shape of a signal generated, which is basically unchanged in a time shift, then only the phase spectrum will be altered. This   property is given below : 

 If 

            DTFT

x (n)  is    ↔    X(ω)  then 

              DTFT

x(n-k)  is   ↔    e ^–jωk  X(ω)  

3. Frequency shifting :

  If 

             DTFT                                           DTFT

x (n)  is   ↔    X(ω)  then  e ^–jω0ⁿ  x(n)   is   ↔    X ( ^ω - ω0)

4. Time reversal :

 If 

         DTFT

x (n)    ↔    X(ω) is  then 

   

            DTFT

x (-n) is    ↔    X(-ω)   

5. Differentiation :

It is a complicated differentiation equation, it is the easiest way to understand a better way to this topic, the equation is given below.  It is apparent with this property that converting to the frequency domain may allow the frequency domain may allow us to convert these complicated differential equations to easy simpler equations involving multiplication and addition. This property is given below :

If 

         DTFT

x (n)    ↔    X(ω)  then 

           DTFT

n x (n)    ↔    d/dω X(ω)  

6. Parseval's theorem : 

                DTFT                                 DTFT

If  x₁ (n) is  ↔   X₁(ω)  and  x₂ (n)  is   ↔      X₂(ω)  then

Parseval's relation tells us that the energy of a signal is totally equal to the energy of its Fourier transform.

  _{∞                                                ∏}

∑  x₁ (n)   x₂ (n)  is  = 1 /2∏  ∫  X₁(ω)  X₂(ω)  dω

n = - ∞                              -∏

7. Convolution theorem :

Convolution is one of the big reasons for converting signals to the frequency domain since convolution in time becomes multiplication in frequency domain.

                DTFT                                DTFT

If  x₁ (n) is  ↔   X₁(ω)  and  x₂ (n) is    ↔     X₂(ω)  then

                             DTFT

  x₁ (n) * x₂ (n)  is     ↔     X₁(ω) . X₂(ω) 

Space diversity

The space diversity method is also called the antenna diversity method. There was no guarantee of a direct path between the transmitter and receiver in the conventional method of wireless communications. Hence, the occurrence of Rayleigh fading signal was suspected. 

Now  let us talk about the different types of space diversity reception method given below :

• Selective diversity
• Feedback diversity
• Maximal ratio combining
• Equal gain diversity

1. Selective diversity :

Principle :

Selective diversity is one of the best signals among all the signals received from different branches at the receiving end.

In the selective diversity method, the branches that have the strongest received signal are combined and selected.

In this method suppose n number of the demodulator is used to provide n number of diversity branches. The gains of these n number of diversity branches can be adjusted to give the average signal to noise ratio for every diversity branch.

The antenna signal will be then sampled and the signal that possesses a good signal strength and the best signal is sent to the demodulator side.

2. Feedback diversity :

Principle :

The feedback diversity also referred to as the scanning type of diversity. In this method in a correct sequence n number of signals are scanned. The signals are continuously monitored so that they can pick up a signal in the sequence that is above some threshold value alpha.

For the signal received the process of scanning is initiated but the limitations of this method are that the decreases in the fading level were less than the diversity method.

The advantages of scanning diversity are easier implementation than other diversity techniques. It needs only one receiver.

3. Maximum ratio combining techniques :

Principle :

In this method is all the (N) branch signal are weighted with the necessary coefficients for each diversity branch signal and combined coherently in order that the decreases in fading will be more. This will improve the overall system of performance.

In this method, the signal is also combining all the signals in a weighted manner and co-phased manner, so as to have the highest achievable signal to noise ratio (SNR) at the receiver at all the times.

Advantages :

• The maximal ratio combiner produces as acceptable SNR value
• The accuracy of this method is high
• In this method also maximal ratio combiner results in best decreases in fading

4. Equal gain combiner :

In these techniques, all diversity branches are coherently added with the same weighting factor. These techniques also based on co-phases all the diversity branches and finally adds them up.

As the signal are co-phased from all branches they provide an equal number of gain factor. So in this method combining all the signal in a co-phased manner with the unity based weights for all signals levels, so as to have the highest achievable signal to noise ratio (SNR ratio) at the receiver at all the times.

Advantages :

• Several diversity branches are allowed
• Space diversity applicable to macroscopic diversity
• No extra bandwidth or power is needed

Diversity concept

Diversity definition :

The simple concept of the terms of diversity is that even if a radio signal path experiences a deep face, there will be another independent signal path available for analysis. 

The concept of diversity encompasses acceptance and respect. It means understanding that each individual is unique, recognizing for our individual differences. 

Assume that there is two antenna with some specific separation between them. Both the antenna signal are located on the same terminal. As the mobile terminal moves the antennas signal side experience different fading levels.

The received signal level varies with their corresponding fading levels. Hence we need to select an antenna that has a higher signal level. This is done so that the probability of deep fading is to be avoided.

There are two kinds of diversity :

• Microscopic diversity
• Macroscopic diversity

1. Microscopic diversity :

The counteract small signal fading in the signal received under very small distance, microscopic, diversity can be used to exploit changing signal.

It can prevent the small signal fades in case of fewer antenna separations if two antennas are used.

By choosing the signal of higher strength most of the time, the receiver can reduce the fading effects.

2. Macroscopic diversity :

The signal strength is too much decreases in large scale fading because of the problems related to shadowing by selecting a base station that is not shadowed in comparison to the other base stations, the mobile unit in its forward path can get a better signal to noise ratio (SNR).

Such a diversity concept is used to decreases the large scale signal fades is called macroscopic diversity. At the base station receiver is to end, this diversity method is useful.

Advantages and disadvantages of nuclear power

The main uses of nuclear energy is electric power generation and it can be also used scientific research, space page, medicine, nuclear fission, food, and agriculture etc.  Here this article gives the information about advantages and disadvantages of nuclear power to know more details about it.

Advantages of nuclear power :

• No green house gases
• Conserves fossils fuel
• Fuel has low cost
• High density
• Sustainable
• Clean energy
• High qualities
• Contentiously generate electricity
• A little makes a lot of  energy
• High electricity output
• Reliable
• A small amount of fuel used so less transport needed
• Cheap to run once built
• No sulfur dioxide emission
• No carbon dioxide emission
• Safe under normal condition
• Does no emit green house gases

Disadvantages of nuclear power :

• Expensive to built and start to maintain power plants
• High operating maintenance cost
• Mining uranium cause pollution
• The west of radioactive and also is harmful thus having to be disposed of carefully
• Risk of disaster or accident
• Safely concerns
• Waste that remains toxic for many years
• Supplies will run out in 50 years
• No renewable
• Expensive to decommission
• A power station is at risk of being attacked
• Link with cancer
• Product radio active waste
• If it is needed, it takes days to shut down a total power plant
• In a nuclear meltdown, high dosages of radioactivity are exposed

Advantages and disadvantages of transformer

A transformer is a static electrical device which can transfer the electrical energy between two or more many circuits through electromagnetic induction. This article gives information about the advantages and disadvantages of a transformer to know more details about it.

Advantages of transformer :

• A transformer will increase or decrease  basically AC voltage, current or independence 
• It is efficient for high-frequency range
• The available power cannot change but will slightly too much decrease depending on the efficiency of the transformer 
• It has the advantage of preventing condensed flux leakage as well as iron loss
• It offers good mechanical strength
• The transformer is widely used in power transmission

Disadvantages of transformer :

• A transformer will not work with DC voltage under any condition
• The transformer size become un widely
• The physical size of the transformer is directly related to the amount of power to be desired
• It is not good to use outdoors
• It can be noisy

Microphone advantages and disadvantages

A microphone can be used a telephone, hearing aids, public address system for the concert hall and public event, radio and television broadcasting, megaphone etc.  Here this article gives information about the advantages and disadvantages of a microphone to know more details about it. 

Advantages of a microphone :

• In uses microphone greater freedom of movement for the artist or speaker 
• Reduction of cable trip hazards in the depends upon performance space
• Avoidance of cabling problems common with wired microphones, caused by constant moving as well as stressing the cables
• It is faster to read in text than to type it in using a keyboard type
• It can improve both safety and security when used in the voice activation system
• Sound can be manipulated in real time rather than a recording done at the earlier stage

Disadvantages of a microphone :

• Noise or dead spots 
• The limited number of operating microphones at the same time and place
• The limited number of radio channels 
• Sound files can use up a lot of computer memory in a device
• Voice recognition system software is not as accurate as typing manually 

Advantages and disadvantages of ac generators

AC generator stands for an alternating current generator, It is a device that produces an electromotive force. Here this article gives information about the advantages and disadvantages of AC generator to know more details about it.

Advantages of ac generators :

• AC is very easy and efficient to transmit over a long distance rather than DC
• The design of the AC generator is fairly simpler than DC generator type
• No need for matching a voltage 
• Cost of ownership is lower
• They have a quiet operation
• This also makes easier to maintain this generator 
• An AC generator allows users to convert its current to other voltage with the use of transformers
• AC generator is compatible only with an AC generator and not with a DC generator
• AC motors do not have a smell that is very typical of DC motors; in the latter, this is caused by and also these are compatible with an AC generator and not with a DC generator type

 Disadvantages of ac generators :

• This poses a challenge when it comes to handling because of the greater voltages needed to supply a fixed level of power
• In these systems require additional insulation because of the greater voltages needed to supply a fixed level of power
• In addition to all these risks, an AC generator is not as durable as a DC generator type
• Working with alternating current system has some distinct risk and difficulties  as compared to what can be expected from DC motors
• In addition to all these risks, an AC generator is not durable as a DC generator type

Advantages and disadvantages of FSK

FSK stands for Frequency shift keying. This technology is used for a communication system such as caller ID and emergency broadcast. Here this article gives information about the advantages and disadvantages of FSK to know more details about it. 

Advantages of  FSK :

• It has a lower probability
• Easy to implement
• High data rate 
• It has better noise immunity than ASK method, so the probability of error-free reception of data is high
• Easy to decode
• Operate in virtually any wires available
• FSK transmitter, as well as FSK receiver implementations, are simple for low data rate application
• It provides high SNR
• Used in long-distance communication
• Power requirement is constant
• Good sensitivity
• It has higher immunity to noise due to a constant envelope. Hence it is robust against variation in attenuation through a channel
• Low noise

Disadvantages of FSK :

• The BER performance in the AWGN channel is worse compared to PSK modulation
• Extensively used in low-speed modems having bit rates below around 1200 bits/sec
• This increases the channel bandwidth required to transmit the FSK signal type
• It uses larger bandwidth compared to other modulation techniques like ASK and PSK. Hence it is not bandwidth efficient
• FSK is not preferred for the high-speed modems because with increases in speed and also have the bit rate increases
• When in the telecommunication media, the telephone lines have very low bandwidth, it is not possible to satisfy the bandwidth requirement of FSK at a too much higher speed. So in a method of FSK is preferred only for the low-speed problem

Explore more information:

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2. Advantages and disadvantages of OFDM
3. Advantages and disadvantages of FDM
4. Advantages and disadvantages of QPSK
5. Advantages and disadvantages of delta modulation
6. Advantages and disadvantages of ASK

Advantages and disadvantages of electricity

We all know that electricity is a set of physical phenomena associated with the presence and motion of electric charge. Here this article gives information about the advantages and disadvantages of electricity to know more details about it.

Advantages of electricity :

• It is a clean, safe, cheap and convenient source of energy
• Lower maintenance cost
• More efficient
• No tailpipe emission
• We all know that it  can be set up in many sizes
• It doesn't require as many employees
• Reduces greenhouse emission
• Makes barely any pollution compare to other ways of creating or generating electricity
• Relatively low maintenance cost
• Hydroelectric station are inexpensive to operate
• Hydroelectricity produces no gas emissions or waste
• A station can operate and run for long periods of time
• It is renewable

Disadvantages of electricity :

• More expensive than gasoline
• Loss of fish species
• Sometimes messes up wildlife
• Dependent on precipitation
• More power plants and more pollution
• Damming can cause loss of land suitable for agriculture as well as recreation
• Cost for construction
• Change in river or stream quality
• An electric vehicle is not completely emission free
• In electricity, there are a limited number of feasible sites for a large number of dams
• Drought can affect power production
• Hydroelectric natural seasonal changes in river and ecosystems can be destroyed

Advantages and disadvantages of centrifugal pump

Centrifugal pump was fairly simple in nature. This article gives the information about the advantages and disadvantages of the centrifugal pump to know more details about it.

Advantages of centrifugal pump :

• Simple in construction and cheap
• Steady delivery
• Handle liquid with a large amount of solid
• Uniform pressure without shock or pulsation
• Direct coupling to the motor
• Maintenance cost is lower 
• Can be mounted horizontally or vertically
• No valve involve in pump operation
• No metal to metal fit 
• Discharge line may be closed
• Therein almost no noise 
• In these pumps, there is no drive seal so there is no leakage in the pump
• It can pump hazards liquids
• A pump has almost 100 % efficiency
• This pump has minimum wear with respect to other
• This pump is used magnetic coupling which breakup on high load eliminating the risk of damaging the motor

Disadvantages of centrifugal pump :

• Can not handle viscous fluids efficiently
• Can handle a small number of gases in liquids
• Primary offer needed before startup
• Can not be operated at a high head
• Must be primed
• This pump has not effective for high velocity but multistage configuration are expensive
• Can not be operated at high discharge pressures
• Maximum efficiency is to be hold over a narrow range of conditions

Advantages and disadvantages of switch

A switch is a network device which transfers data only to the host where it is being addressed. This article gives the information about the advantages and disadvantages of a switch to know more details about it.

Advantages of a switch :

• It can make use CAM table for a port to MAP mapping
• It helps in logical segmentation by supporting VLANs
• The number of broadcast domains gets decreases
• Support centralized management
• They help in reducing the workload on individual host PCs
• Permit multiple simultaneous conversations
• Fairer than connection based technology
• Switch interconnected individual node and also controlled access to media
• Switches can be connected directly to work station
• A network which uses switch will have fewer frame collisions
• They increase the available bandwidth of the network

Disadvantages of a switch :

• High cost 
• Failure of switch bridge down the network
• When we use a switch, a network connectivity problem can be difficult to trace through a switch
• Broadcast traffic may be troublesome
• While uses a limited broadcast, they are not as good as routers
• Proper design and most important configuration is needed in order to handle multicast packets
• If a switch is in promiscuous, they are vulnerable to security attacks

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3. Advantages and disadvantages of modem
4. Advantages and disadvantages of router
5. Advantages and disadvantages of ethernet

Advantages and disadvantages of hub

Hub is a network device used to connect multiple Ethernet devices uses a twisted pair. Here this article gives information about the advantages and disadvantages of a hub to know more details about it.

Advantages of hub :

• Easy to install
• Very little delay
• It is used for internal connectivity between the system
• Can different media type
• Cheaper
• Hub device does not affect the performance of the network seriously
• It can extend the total distance of the network

Disadvantages of hub :

• It runs half-duplex
• Can not filter information
• It can not connect different type of network architecture such as a token ring and Ethernet extra
• It does not have a mechanism to reduce the network traffic
• Passes packet to all connected segment
• Can not reduce network traffic
• It will broadcast to all the port
• Extend the collision

Explore more information:

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2. Advantages and disadvantages of wifi
3. Advantages and disadvantages of ethernet
4. Advantages and disadvantages of a router
5. Advantages and disadvantages of the bridge