Tag: EDFA

How EDFA (Erbium Doped Fiber Amplifier) Works

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When a normal optical fiber core is doped with trivalent ‘erbium’ ions, erbium doped fiber is formed. This erbium doped fiber act as a gain medium that amplifies an optical signal. Hence, it is named as EDFA (Erbium Doped Fiber Amplifier). The erbium doped fiber is pumped with a laser, at a wavelength of 980 nm or 1480 nm and produce optical gain in the 1550 nm region.
We can’t directly send laser light into EDFA. Before that, laser needs to be multiplexed into the erbium doped fiber. For that purpose, we use WDM (Wavelength Division Multiplexing) coupler to multiplex laser into EDFA.  After that EDFA is pumped with laser, to achieve optical gain.
EDFA uses population inversion technique to achieve optical amplification. Before we jump into EDFA, first let’s see how the actual laser works. LASER stands for Light Amplification and Stimulated Emission of Radiation. As the name suggests, laser amplifies the light by using a process called stimulated emission of radiation.
Shall we go deeper into the concept!
Every object in the universe is made up of tiny particles called atoms. However, atoms are not the smallest particles in the universe. There are some particles which are much smaller than atoms. These particles are electrons, protons and neutrons. Combining these particles make an atom. Each atom has a set of electrons, protons and neutrons. Electrons have negative charge, protons have positive charge and neutrons have no charge. Protons and neutrons always stick together because of the strong nuclear force between them.
The protons and neutrons which are stick together are known as nucleus. The overall charge of the nucleus is positive because of the positive protons (neutrons does not have charge). On the other hand, electrons have negative charge (opposite charge to protons). As we know that, there exists an attractive force between the opposite charges. So the electrons always rotate around the nucleus at different distances because of the electrostatic force of attraction between electrons and nucleus.
The electrons which are revolving at different distances from the nucleus have different energy levels associated with it. The electrons which are revolving at a very close distance from the nucleus have the lowest energy level whereas; the electrons which are revolving at a larger distance from the nucleus have the highest energy level.
The electrons at a larger distance from the nucleus have highest energy level because they reached that level by gaining additional energy from the external energy sources like light, heat and voltage. This process of gaining additional energy from the external energy sources to jump into higher energy level is called absorption of radiation.
The electrons in the higher energy level will not stay for a long time. After a short period of time, they fall back to the lower energy level by releasing energy in the form of heat or light. This process is called spontaneous emission of radiation. Laser works based on this concept.
Although, the electrons release energy in the form of light, there is no light amplification in this process. So the spontaneous emission process is not used to build a laser.
The laser works based on a special process called stimulated emission of radiation. To achieve light amplification, the number of electrons in the higher energy level (E2) must be greater than the number of electrons in the lower energy level (E1). In a two level energy system, the population of electrons in the higher energy level is always lesser than the population of electrons in the lower energy level. In some cases, the population of electrons in higher energy level will becomes equal to the population of electrons in the lower energy level. So the two level energy system is not useful for light amplification.
The light amplification is achieved by using a 3 or more energy level system. The greater the energy levels are, the greater will be the light amplification. For example, a 4 level energy system will produce more optical gain than the 3 level energy system.
The EDFA is pumped using two laser diodes (bidirectional pumping) or a single laser diode (unidirectional pumping). The EDFA pumped with a single laser diode is most commonly used. In this tutorial, EDFA pumped with a single laser diode is discussed.
EDFA is pumped with two different wavelengths of photons: 980 nm or 1480 nm.

Are You Familiar with EDFA?

Signals travel through fibers over large distances with attenuation. Then the optical amplifiers are needed in the CWDM (corse wavelength divsion multiplexing) and DWDM (dense wavelength divsion multiplexing). Optical amplifiers are devices that can amplify optical signals directly without the need to convert them to electrical signals. EDFA (erbium doped fibre amplifier) is the most common optical amplifiers.
Introduction of EDFA
EDFA is doped with element erbium and with the core of a silica fiber. It is one of DWDM equipment that amplifies optical fiber signals as signals will be attenuated when the transmission distance is over hundreds kilometers. The term “doping” refers to the process of using chemical elements to facilitate results through the manipulation of electrons. It is employed in the telecommunications field and in various types of research fields.
Principles of EDFA
In general, EDFA works on the principle of stimulating the emission of photons. Pump lasers, known as pumping bands, insert dopants into the silica fiber, resulting in a gain, or amplification. EDFA amplification occuring as the pump laser excites the erbium ions, which then reach a higher energy level. The excited ions make transition to the ground state either by CWDM, DWDMequipmentamplified spontaneous emission or stimulated emission. The amplified spontaneous emission is a major source of noise in the system. And the stimulated emission could amplify signals by generating photons. With EDFA, an erbium-doped optical fiber at the core is pumped with light from laser diodes. This type of setup in telecom    systems can help with fiber communications.
Advantages of EDFA
EDFA has many advantages. First, it can provide in-line amplification of a signal without the need for E-O and O-E conversions. Second, it can directly and simutaneously amplify a wide wavelength band (>80nm) in the 1550nm region with a relatively flat gain. Third, it provides high power transfer efficiency from pump to signal power. At last, EDFA has low noise, which is suitable for long haul applications.
Although EDFA has so many advantages, it has disadvantages as well. For example, EDFA is usually limited to no more than 10 spans covering a maximum distance of approximately 800 kilometers (km). When the distance is longer, an intermediate line repeater to retime and reshape the signal and filter accumulated noise from various light dispersion forms in the optical fiber would be required. So EDFA still needs to be improved.

The Application of EDFA

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Optical amplifiers are the critical technology for the optical communication networks, enabling the transmission of many terabits of data over distances from a few hundred kilometers to thousands of kilometers by overcoming the fiber loss limitation. As the first optical amplifier commonly used in optical communications systems, EDFA has resulted in a dramatic growth in transmission capacity with the deployment of WDM systems. Be equipped with the features of high output power, high gain, wide bandwidth, polarization independence and low noise figure, EDFAs have become one of the key components used in the new-generation optical communication system. So what is EDFA? Do you know EDFA working principle?
What Is EDFA?
Erbium-doped fiber amplifier (EDFA) is an optical repeater device that is utilized to boost the intensity of optical signals being carried through a fiber optic communications system. An optical fiber is doped with the rare earth element erbium so that the glass fiber can absorb light at one frequency and emit light at another frequency.
EDFA Working Principle
The erbium-doped fiber (EDF) is at the core of EDFA technology, which is a conventional silica fiber doped with Erbium. When the Erbium is illuminated with light energy at a suitable wavelength (either 980 nm or 1480 nm), it is motivated to a long-lifetime intermediate state, then it decays back to the ground state by emitting light within the 1525-1565 nm band. The Erbium can be either pumped by 980 nm light, in which case it passes through an unstable short lifetime state before rapidly decaying to a quasi-stable state, or by 1480 nm light in which case it is directly excited to the quasi-stable state. Once in the quasi-stable state, it decays to the ground state by emitting light in the 1525-1565 nm band. This decay process can be stimulated by pre-existing light, thus resulting in amplification. EDFA working principle is shown in the Figure 1.
Baisc configuration of EDFA
EDFA configuration is mainly composed of an EDF, a pump laser, and a component (often referred to as a WDM) for combining the signal and pump wavelength so that they can propagate simultaneously through the EDF. In principle, EDFAs can be designed such that pump energy propagates in the same direction as the signal (forward pumping), the opposite direction to the signal (backward pumping), or both direction together. The pump energy may either be 980 nm pump energy, 1480 nm pump energy, or a combination of both. Practically, the most common EDFA configuration is the forward pumping configuration using 980 nm pump energy, as shown in the Figure 2.
Application of EDFA
After learning what is EDFA, and EDFA working principle. Next, we’ll discuss application forms and application fields of EDFA.
Forms of application
Booster Amplifier
When used as the booster amplifier, EDFA is deployed in the output of an optical transmitter to improve the output power of the multi-wavelength signal having been multiplexed, as shown in Figure 3. In this way, distances of optical communication transmission can be extended. This application form places a demand of higher output power on EDFA.
Fields of application
EDFA has the following fields of application:
(1) EDFA can be employed in the high-capacity and high-speed optical communication system. The application of EDFA is very constructive to deal with the problems of low sensitivity of receivers and short transmission distances owing to a lack of OEO repeater.
(2) EDFA can be utilized in long-haul optical communication system. By utilizing EDFA, we can dramatically lower construction cost by increasing the repeater spacing to reduce the quantity of regenerative repeaters. The long-haul optical communication system mainly includes the land trunk optical transmission system and the submarine optical fiber cable transmission system.
(3) EDFA can be used in the optical fiber subscriber access network system. If the transmission distances are too long, EDFA will function as the line amplifier to compensate for the transmission losses of lines, thus greatly increasing the number of subscribers.
(4) EDFA can be employed in wavelength-division multiplexing (WDM) system, especially dense wavelength-division multiplexing (DWDM) system. Utilization of EDFA in WDM system is able to solve the problems of insertion loss and reduce the influences of chromatic dispersion.
(5) EDFA can be utilized in community antenna television (CATV) system. In CATV system, EDFA functions as the booster amplifier to greatly improve the input power of an optical transmitter. Utilizing EDFA to compensate for the insertion loss of opt

Passive CWDM VS DWDM – Which to choose?

With current industry advancements trend that has equalized costs of transceivers, in technical battle of CWDM vs DWDM more advancements are in DWDM.

With current industry advancements trend that has equalized costs of transceivers, in technical battle of CWDM vs DWDM more advancements are in DWDM.

 

Lets compare passive CWDM vs DWDM from pure technical application viewpoint:

 

CWDM vs DWDM – Channel Uniformity:

As CWDM spectrum for 18 channels spans from 1260nm up to 1620nm compared to DWDM C-band 1530 – 1565 nm, CWDM has weakness from channel uniformity aspect. Attenuation in wide spectrum is different based on wavelength – for example, typical attenuation of G.652.C optical fiber is 0.38 dB/km at 1310nm wavelength and 0.22 dB/km at 1550nm. So in CWDM system You can get quite great disparity of channel optical performance using different CWDM wavelength. Uniformity of optical channels across whole 1260-1620nm spectrum depends on fiber cable specification. – we suggest checking carefully if You plan using passive CWDM. Especially it is very important for old G.652 specification fiber – it has so called “water-peak” phenomena in range of 1390 and 1490 nm that are not usable for CWDM connections at all. DWDM is clear winner here – due it’s narrow spectrum channel properties on same fiber will be almost identical.

 

CWDM vs DWDM – Capacity:

It’s clear winner here – while maximum capacity of CWDM system is 18 wavelengths all spectrum, DWDM using traditional C-Band 1530 – 1565 nm allow to have 45 100GHz spaced DWDM channels, but with introduction of 50 GHz spaced transceivers we can double number of channels up to 90. In future, we can expect to have 25 GHz and even 12.5 GHz frequency offset even multiplying number of possible channels to 180 or 360. If that is not enough – there is S-band (1460-1530 nm) and L-band (1565-1625 nm) which can be used with DWDM as well, just is not mainstream yet.

 

CWDM vs DWDM – Distance:

Maximum distance of xWDM connection depends on two main factors – maximum budget of optical transceivers and attenuation of all passive elements – fiber itself, number of joints and splices, attenuation of passive filters (Chromatic dispersion as well, but we don’t consider it much a factor up to 80km). If looking on 10G connection data rate, with both, CWDM and DWDM, passive technologies You can have up to 23 dB guaranteed budget using popular SFP+ transceivers (With XFP You can have 26dB budget), what is enough to have 80km WDM link with both technologies. But big advantage of DWDM is, that due it’s narrow spectral width it’s possible to use cost efficient and widely available EDFA (Erbium Doped Fiber Amplifier) boosters, which is one very cost efficient way allowing extension of DWDM reach.

 

CWDM vs DWDM – Spare Parts:

Even optical transceivers are mature elements and failure-rates are very uncommon, introducing WDM technology You would like to have backup stock of all active elements. If You are planning to have just small scale deployment and connect just two or few network nodes, it could mean that You basically need to back up everything – resulting on doubling up of your investment. DWDM is a winner here as well, due availability of Tunable DWDM transceivers, with can replace all Your different wavelength DWDM transceivers with one or two units.

 

Conclusion

CWDM still has price advantages for connection rates below 10G and for short distances with low data rates it’s currently most feasible technology. For more information,welcome to visit www.fiber-mart.com, pls feel free to contact me at service@fiber-mart.com