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EDFA vs Raman Optical Amplifier

Although the fiber loss limits the transmission distance, the need for longer fiber optical transmission link seems never ending. In the pursuit of progress, several kinds of optical amplifiers are published to enhance the signals. Hence, longer fiber optical transmission link with big capacity and fast transmission rate can be achieved. As the EDFA and Raman amplifiers are the two main options for optical signal amplification. which one should be used when designing long fiber optical network? What are the differences of the two optical amplifiers? Which one would perform better to achieve the long fiber optical link? And which one is more cost effective? Let’s talk about this topics.

What’s EDFA Amplifier?

EDFA (Erbium-doped Fiber Amplifier), firstly invented in 1987 for commercial use, is the most deployed optical amplifier in the DWDM system that uses the Erbium-doped fiber as optical amplification medium to directly enhance the signals. It enables instantaneous amplification for signals with multiple wavelengths, basically within two bands. One is the Conventional, or C-band, approximately from 1525 nm to 1565 nm, and the other is the Long, or L-band, approximately from 1570 nm to 1610 nm. Meanwhile, it has two commonly used pumping bands, 980 nm and 1480 nm. The 980nm band has a higher absorption cross-section usually used in low-noise application, while 1480nm band has a lower but broader absorption cross-section that is generally used for higher power amplifiers.

The following figure detailedly illustrates how the EDFA amplifier enhance the signals. When the EDFA amplifier works, it offers a pump laser with 980 nm or 1480 nm. Once the pump laser and the input signals pass through the coupler, they will be multiplexed over the Erbium-doped fiber. Through the interaction with the doping ions, the signal amplification can be finally achieved. This all-optical amplifier not only greatly lowers the cost but highly improves the efficiency for optical signal amplification. In short, the EDFA amplifier is a milestone in the history of fiber optics that can directly amplify signals with multiple wavelengths over one fiber, instead of optical-electrical-optical signal amplification.

What’s Raman Amplifier?

As the limitations of EDFA amplifier working band and bandwidth became more and more obvious, Raman amplifier was put forward as an advanced optical amplifier that enhances the signals by stimulated Raman scattering. To meet the future-proof network needs, it can provide gain at any wavelength. At present, two kinds of Raman amplifiers are available on the market. One is lumped Raman amplifier that always uses the DCF (dispersion compensation fiber) or high nonlinear fiber as gain medium. Its gain fiber is relatively short, generally within 10 km. The other one is distributed Raman amplifier. Its gain medium is common fiber, which is much longer, generally dozens of kilometers.

When the Raman amplifier is working, the pump laser may be coupled into the transmission fiber in the same direction as the signal (co-directional pumping), in the opposite direction (contra-directional pumping) or in both directions. Then the signals and pump laser will be nonlinearly interacted within the optical fiber for signal amplification. In general, the contra-directional pumping is more common as the transfer of noise from the pump to the signal is reduced, as shown in the following figure.

EDFA vs Raman Optical Amplifier: Which One Wins?

After knowing the basic information of EDFA and Raman optical amplifiers, you must consider that the Raman amplifier performs better for two main reasons. Firstly, it has a wide band, while the band of EDFA is only from 1525 nm to 1565 nm and 1570 nm to 1610 nm. Secondly, it enables distributed amplification within the transmission fiber. As the transmission fiber is used as gain medium in the Raman amplifier, it can increase the length of spans between the amplifiers and regeneration sites. Except for the two advantages mentioned above, Raman amplifier can be also used to extend EDFA.

However, if the Raman amplifier is a better option, why there are still so many users choosing the EDFA amplifiers? Compared with Raman amplifier, EDFA amplifier also features many advantages, such as, low cost, high pump power utilization, high energy conversion efficiency, good gain stability and high gain with little cross-talk. Here offers a table that shows the differences between EDFA and Raman optical amplifiers for your reference.

Property	EDFA Amplifier	Raman Amplifier
Wavelength (nm)	1525-1565, 1570-1610	All Wavelengths
Gain (dB)	> 40	> 25
Noise Figure (dB)	5	5
Pump Power (dBm)	25	> 30
Cost Factor	Relatively Low	Relatively High

Considering that both EDFA and Raman optical amplifiers have their own advantages, which one should be used for enhancing signals, EDFA amplifier, Raman amplifier or both? It strictly depends on the requirement of your fiber optical link. You should just take the characteristics of your fiber optical link like length, fiber type, attenuation, and channel count into account for network design. When the EDFA amplifier meets the need, you don’t need the Raman amplifier as the Raman amplifier will cost you more.

Optical Amplifier Overview

When it comes to optical fiber communication, we are impressed with its fast speed, large information capacity and bandwidth. To achieve this result, numbers of optical components play key roles in optical systems. Optical amplifier is one of them. When transmitted over long distance, the optical signal will be highly attenuated. On this situation, optical amplifier makes a difference. Today, this article will give a brief overview about optical amplifier to help you learn more about it.

What Is an Optical Amplifier?

Usually a basic optical communication link consists of a transmitter and receiver, with an optical fiber cable connecting them. Even if signals in fibers suffer less attenuation than in other mediums, there is still a limited distance about 100 km. Beyond this distance, the signal will become too noisy to be detected.

Optical amplifier is a device designed to directly amplify an input optical signal, without needing to transform it first to an electronic signal. And at the same time, it can strengthen the signal, which is conducive to transmission over long distances. Here is a comparison figure. In the (a), it is an electrical signal regeneration station. We can see all the channels are separated, signals detected, amplified and cleaned electrically, then transmitted and combined again. However, in the figure (b), it is an optical amplifier in which all channels are optically and transparently amplified together. Compared to electrical amplifier, optical amplifier is more cost-effective. Because it amplifies signals directly, and needs less cost.

comparison

Common Types

Generally, there are three common types optical amplifier: the erbium doped fiber amplifier (EDFA), the semiconductor optical amplifier, and the fiber Raman amplifier.

Erbium Doped Fiber Amplifier (EDFA)

The amplifying medium of EDFA is a glass optical fiber doped with erbium ions. The wavelength near 1550 nm can be amplified effectively in erbium doped optical fiber amplifiers. What’s more, EDFA has low noise and can amplify many wavelengths simultaneously, making EDFA widely used in optical communications. According to the functions, EDFA usually has three types: booster amplifier, in-line amplifier and pre-amplifier.

A booster amplifier operates at the transmission side of the link, designed to amplify the signal channels exiting the transmitter to the level required for launching into the fiber link. It’s not always required in single channel links, but is an essential part in WDM link where the multiplexer attenuates the signal channels. It has high input power, high output power and medium optical gain. The common types are 20dBm Output C-band 40 Channels 26dB Gain Booster EDFA, 16dBm Output C-band 40 Channels 14dB Gain Booster EDFA and so on. Of course, there are still different specification of booster amplifiers which cannot be listed here. Here is a picture of 23dB Output 1550nm Booster EDFA Optical Amplifier.

booster amplifier

An in-line amplifier typically operates in the middle of an optical link, which is designed for optical amplification between two network nodes on the main optical link. It features medium to low input power, high output power, high optical gain, and a low noise figure.

At the end a pre-amplifer makes a difference. Pre-amplifier is used to compensate for losses in a demultiplexer near the optical receiver. It has relatively low input power, medium output power and medium gain.

Semiconductor Optical Amplifier

Semiconductor optical amplifier (SOA) uses a semiconductor to provide the gain medium. It operates with less power and is cheaper. But its performance is not as good as EDFA. SOA is noisier than EDFA. Therefore, SOA is usually applied in local area networks where performance is not required but the cost is an important factor.

Raman Amplifier

In a fiber Raman amplifier, power is transferred to the optical signal by a nonlinear optical process known as the Raman effect. Distributed and lumped amplifiers are the two common types of Raman amplifier. The transmission fiber in distributed Raman amplifier is utilized as the gain medium by multiplexing a pump wavelength with the signal wavelength, while a lumped Raman amplifier utilizes a dedicated, shorter length of fiber to provide amplification. Here is a Raman amplifier.

Conclusion

Optical amplifiers perform a critical function in modern optical networks, enabling the information transmitted over thousands of kilometers and providing the data capacity which current and future communication networks are required. Amplifiers mentioned above are available in Fiberstore. If you are interested, please visit FS.COM for more information.

Optical Amplifier Is a Key Technology for Restoring Signals

Optical communications are more and more prevailing for the high demand for telecommunication, video and data transmission. The optical fiber is capable of transmitting many signals over long distance to meet people’s various requirements. But the signals are easily attenuated in the long-distance high speed networks. Amplifiers are a key enabling technology for strengthening optical signals. Electrical amplifiers are originally used but gradually replaced by optical amplifiers.

Optical amplifier is a device that can amplifier optical signals directly without the need to convert them into electrical ones. Electrical amplifier is originally used but gradually replaced by optical amplifier. It is a much cheaper solution in comparison with electrical amplifier which has costly conversions from optical to electrical signal. The longer the transmission distance is, the more electrical signals need to be converted, which makes the cost of electrical amplification higher and higher. So optical amplifier is used in an increasing number. More detailed information about it is as followed.

Optical amplifiers can be used as power boosters, in-line amplifiers and detector pre-amplifiers in fiber optical data links. Booster amplifiers are used to increase the optical output of optical transmitters when signals haven’t entered the optical fibers. Once transmitted, the optical signals are attenuated by 0.2dB/km. In-line amplifiers are then used to restore the optical signals to its original power level. At the end of the data link are pre-amplifiers which are used to increase the sensitivity of an optical receiver.

optical amplifier: functions

There are three most important types of optical amplifiers including erbium-doped fiber amplifier(EDFA), semiconductor optical amplifier (SOA) and Raman amplifier. Here will introduce them briefly.

Erbium-Doped fiber amplifier: it is an optical or IR repeater that amplifies a modulated laser beam directly without optical to electrical conversion. It uses a short length of optical fiber doped with the rare-earth element erbium. The signals-carrying laser beams are usually at IR wavelengths with application of external energy. It has low noise and capable of amplifying many wavelengths simultaneously, which is an excellent choice in optical communications.

Semiconductor optical amplifier: it is an optical amplifier which uses a semiconductor to provide the gain medium. The gain medium is undoped InGaAsP. This material can be tailored to provide optical amplification at wavelengths near 1.3 µm or near 1.5 µm which are important wavelengths for optical communications. It makes fewer noises than EDFA and generates less handle power. But it is more suitable to be used in networks where the best performance is not required for it is less expensive.

Raman amplifier: it is an optical amplifier based on Raman gain created by Raman scattering, which works entirely differently from EDFA or SOA. Raman optical amplifier have two key elements: the pump laser and the directional coupler. The pump laser has a wavelength of 90 nm to 1500 nm. The circulator provides a convenient means of injecting light backwards in to the transmission path with minimal optical loss. Raman amplification occurs throughout the length of transmission fiber, which makes Raman amplifier known as distributed amplifier.

For more information about optical amplifier, please visit www.fs.com.

Costs of the Comparison in the DWDM and SDH Network Construction

When we choose the fiber optic devices for our fiber optic networks, cost is necessary factor that we have to consider, almost all the consumers want good quality and affordable products for their network, but there is a point we need to know that is not reasonable to judge which costs of system or technology is more expensive only by the fiber optic devices. Therefore, this page will focus on DWDM system and SDH networks.

The fact that channel spacing’s and frequency stability of CWDM results that EDFAs could not be utilized. As though the DWDM can. The DWDM EDFA Booster amplifier?(shown as the figure) is a cost efficient solution for DWMD fiber optic link amplification which operates at the transmission side of the link. SDH EDFA Booster Amplifier?is designed for the SDH applications which installed after the optical transmitter to increase transmission distance for single wavelength optical module system.

As we know, the fiber optic module is integrated EDFA, it is divided into optoelectronic integrated EDFA and optical gain module, which has the characteristics of small size, low power consumption and easy to use. Can be installed in various systems easily according to users requirements, such as SDH frame, CATV machine box and DWDM system chassis. In fact, it is the specific infrastructure not only in DWDM system but also SDH networks. Although DWDM EDFA is more expensive than SDH EDFA from the diagram, can we say that the cost we need for DWDM system application is more expensive? No, the answer is negative.

Product Category	Product Model	Price
CATV Booster Amplifiers	CATV-EDFA-BA-24	US$ 1,625.00
	CATV-EDFA-BA-23	US$ 1,387.00
	CATV-EDFA-BA-22	US$ 1,300.00
	CATV-EDFA-BA-21	US$ 1,213.00
	CATV-EDFA-BA-20	US$ 1,148.00
	CATV-EDFA-BA-19	US$ 1,105.00
	CATV-EDFA-BA-18	US$ 1,062.00
	CATV-EDFA-BA-17	US$ 1,018.00
	CATV-EDFA-BA-16	US$ 975.00
	CATV-EDFA-BA-15	US$ 932.00
	CATV-EDFA-BA-14	US$ 888.00
	CATV-EDFA-BA-13	US$ 845.00
SDH Booster Amplifiers	SDH-EDFA-BA-O20	US$ 1,517.00
	SDH-EDFA-BA-O10	US$ 1,062.00
	SDH-EDFA-BA-O6	US$ 975.00
	SDH-EDFA-LA-O20	US$ 1,733.00
	SDH-EDFA-LA-O10	US$ 1,408.00
	SDH-EDFA-LA-O6	US$ 1,127.00
	SDH-EDFA-PA-G30	US$ 1,473.00
	SDH-EDFA-PA-G20	US$ 1,300.00
	SDH-EDFA-PA-G16	US$ 1,127.00
DWDM Booster Amplifiers	DWDM-EDFA-BA-O23	US$ 3,683.00
	DWDM-EDFA-BA-O22	US$ 2,665.00
	DWDM-EDFA-BA-O21	US$ 2,492.00
	DWDM-EDFA-BA-O20	US$ 2,383.00
	DWDM-EDFA-BA-O19	US$ 1,820.00
	DWDM-EDFA-BA-O18	US$ 1,733.00
	DWDM-EDFA-BA-O16	US$ 1,625.00
	DWDM-EDFA-BA-O17	US$ 1,690.00
	DWDM-EDFA-BA-O15	US$ 1,517.00
	DWDM-EDFA-BA-O14	US$ 1,300.00
	DWDM-EDFA-BA-O13	US$ 1,408.00

DWDM are technologies that improve the capability of optical cable in carrying data by multiplexing many channels of wavelengths, and SDH are technologies that are used as a buffer interfacing layer for higher layers access the huge capability of Optical transmission system. DWDM is multiple signal transmit over a single fiber called DWDM or Different frequencies (colors/wavelengths/lambdas) for different connections over the single fibre. Full featured DWDM equipment can comprise the same range of cards as SDH. They can support fully configurable cross connect features. DWDM technology provides very high bandwidth long haul inter-connect links. Let’s say in microwave or fiber of point to point terms, SDH equipment is used when you need to connect several site/clients towards star topology. It is conventional TDM based and traffic is dropped and collected in SDH and rerouted towards desired point destination in form of electrical or light signals. Where as DWDM is mostly used at the core and is of fiber, traffic gathered from different equipments (SDH or others) and transported over fiber for analyzing billing or interpretation.

Due to the different characteristics between DWDM and SDH and then they cannot be compared logically. A DWDM ring may be equivalent to 40 SDH rings. But we can compare two rings of different capacities. Well, the only cost savings we will notice is that on the same fiber, we will be able to send multiple lambdas (SDH equipments / routers), using DWDM. SDH costs will be the same and you will add DWDM systems costs, maybe tens or hundreds of thousands of dollars and it all depends on the complexity. If you do not use DWDM, you will have to install more fibers for each SDH link. Well, fiber installation costs are high and they depend on the distance and geography. If the operators could transport the data using only SDH which would imply bigger costs for fiber infrastructure, more power consumption. In fact, there are also so many other elements in the network that for monitoring the network, more workers would be needed, they are both in monitoring and field intervention. Except this, DWDM systems are usually more reliable than SDH. So maybe the cost of maintenance would be cheaper. However, you need to keep in mind that DWDM systems amplification can save the use of many SDH repeaters or regenerator. In a word, if you wonder that which infrastructure costs are more reasonable, judge not only by the devices’cost, you need a combination of various factors to have a decision.

The Influence Factors of EDFA in the Optical Transmission System

One of the goals that being received in any telecommunication connections to offer the longest distance between transmission systems such as undersea, intercontinental and terrestrial connections. In common sense, components employed between transmission ends are appropriate to be reduced to keep up an expensive performance. Fiber Optic Amplifiers in optical communication become significant as there is not an expensive repeater.

Optical transmission systems designed for making are a selection of network application. Usually, unreported optical system connects an island to the mainland via undersea outdoor fiber optic cable as well as a group of islands. Transmission connections along coasts of a mainland are more favorable as well as a group of islands. Transmission connections along coasts of a mainland are more propitious as most of the population around the globe are located near the ocean. Unregulated systems are significantly complete the repeated system. Furthermore, mixing it with other types of connections within a terrestrial network can be made where the optical transmission systems allow a transmission crossing the wet area.

A locally pumped post EDFA or Booster Amplifier boosts the signal level before launching it into transmission fiber connections. The boosted signal amplifier, similar product: CATV signal amplifier, can be further amplified using forward distributed Raman amplifier (DRA). A post R-EDFA is located a few tenths of kilometers from the transmitter ti amplify the weak signal. This EDFA pumped via a amplify the weak signal. This EDFA pumped via a dedicated pump fiber. The figure displays the signal power evolution, represented by a dashed line along transmission distance utilizing forward DRA and post R-EDFA.

On the other hand, the figure shows that signal power evolution with respect to backward DRA and pre R-EDFA. At the receiver terminal, a deceived pre EDFA is used to amplify the received signal, this local pumped EDFA followed by optical filter and an optical to electrical converter.

System configurations show a practical implementation and typical positions of the R-EDFA and DRA in order to improve the transmission performance. Furthermore, two principal factors affect the optical transmission performance. The first factor is the system configuration, where various system configurations were examined and criticized. It shows that the configuration has a direct impact on the performance. The second factor is the total pump power injected into the system. By increasing the total pump power, the transmission distance can be expanded. On the other hand, improving the total injected pump power increases the non-linear effects of the transmission fiber, which degrades the system performance. Until now, there are not any clear and structured design rules for optical transmission systems. Therefore, design rules for optical transmission systems have become indispensable in this field. Finally, future researchers are asked to focus on reducing the noise figure at high pump powers.

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