Category Archives: EDFA Amplifier

Differences Between Pre-Amplifier, Booster Amplifier and In-line Amplifier

Transmission distance has always been a key factor during deployment of fiber optic network. DWDM technologies, which are considered as the most cost-effective ways to increase the network capacity over long transmission distance, have been widely applied in our telecommunication network. To further extend transmission distance of optical signals transmission from the DWDM fiber optic transceivers, optical amplifiers are usually used in the DWDM network. Different types of optical amplifiers have been invented to meet the signal amplifying requirements at different situations. This post will introduce the differences between the three most commonly used optical amplifier: pre-amplifier, booster amplifier and in-line amplifier.

Basic of Optical Amplifier

In the past, if you want to extend the transmission distance of DWDM network, optical regenerator station is required to install in the fiber link every 80km to 100km. The regenerator station will electronically regenerate the optical signals to overcome the power loss and ensure that the optical signal can be detected at the receiver end. However, this requires a lot of money and is not easy to upgrade the whole network.

With optical amplifier, things become much easier. The optical amplifier can enlarge the optical signals without the regeneration. In addition, the network upgrading is more cost-effective with optical amplifier. Each optical amplifier has an important factor which is operation gain measured in dB. The operation gain of the optical amplifier should be carefully calculated to ensure the network performance. Pre-amplifier, booster amplifier and in-line amplifier are used in different places in the fiber optic network. And they support different operation gain according to the whole network requirement.

Pre-Amplifier, Booster Amplifier and In-line Amplifier

Pre-Amplifier is usually installed at the receiver end of the DWDM network to amplify the optical signal to the required level to ensure that it can be detected by the receiver. The following picture shows a typical diagram for a duplex 10G DWDM network which can support 80km. A pre-amplifier is installed at each receiving end of this network. There will be great power loss after the optical signal goes through the 80km optical fiber. Then, pre-amplifier installed at the receiver end is necessary. Generally, a pre-amplifier should offer high gain to ensure that the optical signal is detectable.

pre-amplifier

Booster Amplifier is installed in the transmitting end of the fiber optic network, which can amplifier the amplify the optical signal launched into the fiber link. It is usually used in DWDM network where the multiplexer attenuates the signal channels. The following picture shows a 10G DWDM network using booster amplifier (BA) at the transmitting end and pre-amplifier (PA) at receiving end. Thus, this 10G DWDM network can support a transmission distance much longer than the above mentioned one. Please note, a DCM (Dispersion Compensation Module) is added in this network to further ensure the transmission quality. A booster amplifier usually provides low gain and high output power.

booster amplifier

In-line Amplifier is easy to understand. The gain provided by the pre-amplifier and booster amplifier might not be enough due to the optical loss caused by long haul transmission. In-line amplifier is installed in the fiber optic link every 80-100km as shown in the following picture. It has moderate gain and has similar output power to those of booster amplifier.

in-line amplifier

Conclusion

Optical amplifier can help to amplifier the optical power during long haul transmission to ensure that the receiver can detect the optical signal without error. Three amplifiers are commonly used in DWDM network. Booster amplifier is used to amplifier optical power at the transmitting end and pre-amplifier is placed at the receiver end. If the transmission distance is longer than 150km or have great power loss during transmission, in-line amplifier is suggested to be installed every 80km to 100k in the fiber optic link. The gain of these amplifiers should be carefully calculated during practical use. Kindly visit DWDM EDFA Amplifier page for more details.

Related Article: Introduction of Optical Amplifier

Comparison Of Different Optical Amplifiers

Optical amplifier is an important technology for optical communication networks. Without the need to first convert it to an electrical signal, the optical amplifiers are now used instead of repeaters. As we know, there are several types of optical amplifiers. Among them, the main amplifier technologies are Doped fiber amplifier (eg. EDFA), Semiconductor optical amplifier (SOA) and Fiber Raman amplifier. Today, we are going to study and compare them in this paper.

Before the comparison of the different optical amplifiers, let’s take a closer look at fiber optic amplifer. In general, a repeater includes a receiver and transmitter combined in one package. The receiver converts the incoming optical energy into electrical energy. The electrical output of the receiver drives the electrical input of the transmitter. The optical output of the transmitter represents an amplified version of the optical input signal plus noise. Repeaters do not work for fiber-optic networks, where many transmitters send signals to many receivers at different bit rates and in different formats. However, unlike a repeater, an optical amplifier amplify optical signal directly without electric and electric optical transformation. In addition, an ideal optical amplifier could support multi-channel operation over as wide as possible a wavelength band, provide flat gain over a large dynamic gain range, have a high saturated output power, low noise, and effective transient suppression. Several benefits of optical amplifiers as the following:

  • Support any bit rate and signal format
  • Support the entire region of wavelengths
  • Increase the capacity of fiber-optic links by using WDM
  • Provide the capability of all-optical networks, not just point-to-point links

OK, after a brief introduction of the optical amplifiers, we formally begin today’s main topic. As we talk above, there are three main types of today’s amplifier technology. Each of them has their own working principle, features and applications. We will describe them one by one in the following paragraphs.

Doped fiber amplifier (The typical representative: EDFA)
Erbium-doped fiber amplifier (EDFA) is the most widely used fiber-optic amplifiers, mainly made of Erbium-doped fiber (EDF), pump light source, optical couplers, optical isolators, optical filters and other components. Among them, a trace impurity in the form of a trivalent erbium ion is inserted into the optical fiber’s silica core to alter its optical properties and permit signal amplification.

the components of EDFA

Working Principle
The working principle of the EDFA is to use the pump light sources, which most often has a wavelength around 980 nm and sometimes around 1450 nm, excites the erbium ions (Er3+) into the 4I13/2 state (in the case of 980-nm pumping via 4I11/2), from where they can amplify light in the 1.5-μm wavelength region via stimulated emission back to the ground-state manifold 4I15/2.

EDFA

Advantages & Disadvantages of EDFA
Advantages

  • EDFA has high pump power utilization (>50%)
  • Directly and simultaneously amplify a wide wavelength band (>80nm) in the 1550nm region, with a relatively flat gain
  • Flatness can be improved by gain-flattening optical filters
  • Gain in excess of 50 dB
  • Low noise figure suitable for long haul applications

Disadvantages

  • Size of EDFA is not small
  • It can not be integrated with other semiconductor deviecs

Semiconductor optical amplifier (SOA)
Semiconductor optical amplifier is one type of optical amplifier which use a semiconductor to provide the gain medium. They have a similar structure to Fabry–Perot laser diodes but with anti-reflection design elements at the end faces. Unlike other optical amplifiers SOAs are pumped electronically (i.e. directly via an applied current), and a separate pump laser is not required.

design of SOA

Working Principle
1.Stimulated emission to amplify an optical signal.
2.Active region of the semiconductor.
3.Injection current to pump electrons at the conduction band.
4.The input signal stimulates the transition of electrons down to the valence band to acquire an amplification.

SOA

Advantages & Disadvantages of SOA
Advantages

  • The semiconductor optical amplifier is of small size and electrically pumped.
  • It can be potentially less expensive than the EDFA and can be integrated with semiconductor lasers, modulators, etc.
  • All four types of nonlinear operations (cross gain modulation, cross phase modulation, wavelength conversion and four wave mixing) can beconducted.
  • SOA can be run with a low power laser. This originates from the short nanosecond or less upper state lifetime, so that the gain reacts rapidly tochanges of pump or signal power and the changes of gain also cause phase changes which can distort the signals.

Disadvantages
The performance of SOA is still not comparable with the EDFA. The SOA has higher noise, lower gain, moderate polarization dependence and high nonlinearity with fast transient time.

Fiber Raman amplifier (FRA)
Fiber Raman Amplifier (FRA) is also a relatively mature optical amplifier. In a FRA, the optical signal is amplified due to stimulated Raman scattering (SRS). In general, FRA can is divided into lumped type called LRA and distributed type called DRA. The fiber gain media of the former is generally within 10 km. In addition, it requires on higher pump power, generally in a few to a dozen watts that can produce 40 dB or even over gains. It is mainly used to amplify the optical signal band of which EDFA cannot satisfy. The fiber gain media of DRA is usually longer than LRA, generally for dozens of kilometers while pump source power is down to hundreds of megawatts. It is mainly used in DWDM communication system, auxiliarying EDFA to improve the performance of the system, inhibiting nonlinear effect, reducing the incidence of signal power, improving the signal to noise ratio and amplifing online.

Working Principle
The principle of FRA is based on the Stimulated Raman Scattering (SRS) effect. The gain medium is undoped optical fiber. Power is transferred to the optical signal by a nonlinear optical process known as the Raman effect. An incident photon excites an electron to the virtual state and the stimulated emission occurs when the electron de-excites down to the vibrational state of glass molecule. The Stokes shift corresponding to the eigen-energy of a phonon is approximately 13.2 THz for all optical fibers.

FRA

Advantages & Disadvantages of FRA
Advantages

  • Variable wavelength amplification possible
  • Compatible with installed SM fiber
  • Can be used to extend EDFAs
  • Can result in a lower average power over a span, good for lower crosstalk
  • Very broadband operation may be possible

Disadvantages

  • High pump power requirements, high pump power lasers have only recently arrived
  • Sophisticated gain control needed
  • Noise is also an issue

Summary
After talking about these three types of optical amplifiers, we make a comparison of them as the following table.

Optical amplifier Comparison

Related Article: Differences Between Pre-Amplifier, Booster Amplifier and In-line Amplifier

DWDM System Amplifiers

DWDM EDFA is key component in DWDM network. It uses an optical supervisory channel power adjustment and extends the power link budget for long distance DWDM communication systems.

There are three main types of optical amplifiers: fiber amplifiers (EDFAS), semiconductor optical amplifiers(SOAs), and Raman amplifiers. Fiber amplifiers use rare earth elements usually erbium, but also oraseodymium, tellurite, neodymium, and others as dopant that are pumped with a laser of either 980 to 1480nm. The most commom used for WDM network are the EDFAs.

Types of EDFAs used for DWDM

1 Erbium-doped fiber amplifiers-EDFA. They are low nosie figure approximately 5dB and wide amplitication bandwidth. The EDFA is pumped at 980nm 0r 1480 nm.
2 Erbium-doped fluoride fiber amplifiers(EDFFA) provide for flatter gain spectrum without any gain flattening that introduces loss. They can absorb more erbium than silica producing flatter
band across the erbium passband, allowing the 1530 nm to 1542 region to be used for DWDM. SNR remains the same, or nearly the same for each channel. Howerver, fluoride EDFAs have higher noise from being pumped at 1480nm. DWDM channels must have flat gain through means of an amplifier to properly function. They have proved durable with wavelength stability better than 0.02nm per year.

In DWDM systems amplifiers are an enabling component. For 32 channel DWDM systems optical amplifiers will need to provide at least 25nm of usable bandwidth. 80Gbt/s with 10 Gbt/s channels need 8 wavelengths; 2.5 Gbt/s channels need 32 wavelengths. These must have high outout power and low noise and high signal to noise ratio(SNR). Network spans now at 360km are expected to extend to 600 km then to 2000 km with use of EDFAs. With optical amplifiers the optical signal does not have to be converted and is amplified optically in passing through the amplifier. Optcial fiber amplifiers generate stronger signals than regenerators and transmission can be for extended distances. This takes the place of the SONET regenerator.

PS: 600 km span with DWDM only using 4 optical amplifiers over on fiber pair

dwdm edfa

There are three types if optical amplifiers used in DWDM system. These are:
1 Post amplifier are placed immediately after transmitter to increase optical power to the receiver.
2 In-line amplifiers boost the power level after transmission through a length of fiber permitting the signal to pass through another fiber segment. They are used to compensate for signal attenuation in long segments of fiber. 
3 Pre-amplifiers boost the power of a signal just prior to the receiver.

FiberStore can provide DWDM EDFA amplifiers in different channel from 40~80 channels. These amplifiers offer high optical gain, low noise figure and high saturation optical power which are fully integrated with various kinds of DWDM system.

DWDM EDFA 40 channel BA Module Optical Amplifier

See the video introduction about this products:

This product is spectrum flat EDFA for DWDM system. The stability Pump laser and unique ATC (automatic temperature control) and APC (automatic power control) circuit are employed in it as the key component to ensure the high stability and reliability of output power.The unique optical circuit design ensures the excellent optical character. The high stability and high precision MPU system are employed to ensure the control adjustment and display are intelligent and easy. Professional design GFF (gain flattening filter) with excellent optical path design make flatness and noise reach the best optimization. It can provide 40~80 channels, and above 35nm flatness.

The optical circuit is designed especially for digital optical fiber communication system including
(1) lower noise figure;
(2)high output booster and high sensitivity Pre-Amplifier improve the system loss budget;
(3)Broad input power range and output power adjustable make it use easily.
The design of dual Power Mixed and hot swap make it has longer MTBF. Also, the power system can be backup.Employ the intelligent temperature control system,the fan is on when the module temperature over 45℃, meanwhile it will stop as the temperature is under 40℃, which makes sure the thermal stability and fan’s long life-time, meanwhile, the professional air flow design can also ensure the best temperature stability.Intelligent network management system. Perfectly network interface: Ethernet, RS-485 and RS-232 network interface,and the open mib ensure the connectivity with all other network management system.

Applications
Pre-Amplifier Online Amplifier
Booster
DWDM Optical System

Features
1.Low Noise Figure:Typical 4.5dB High Flatness: Typical 1dB
2.Cover Whole C-Band: Carrie 40 or 80 chs
3.Redundancy hot swap power module: 110/220VAC and 48VDC can plug Mix
4.Perfect Network Interface:Ethernet, RS-485 and RS-232 port
5.Support Telnet and SNMP network management
6.Gain can be adjustable by network and manual
7.High Precise AGC and ATC Circuit
8.High saturation output power
9.Flexible Mechanics and Circuit structure (Module, 1U rack and Gain Block)
10.OEM is available Compatible with Telecordia GR-1312-CORE

DWDMEDFAFS

Technology Of Fiber Optic Amplifiers

In fiber optic communication, the visible-light or infrared (IR) beams carried by a fiber are attenuated as they travel through the material. Then there comes to the fiber optic amplifier which is used to compensate for the wakening of information during the transmission.

Amplifiers are inserted at specific places to boost optical signals in a system where the signals are weak. This boost allows the signals to be successfully transmitted through the remaining cable length. In large networks, a long series of optical fiber amplifiers are placed in a sequence along the entire network link.

Common fiber optical amplifiers include Erbium-Doped Fiber Amplifier (or EDFA Optical Amplifier), Raman fiber amplifier, and silicon optical amplifier (SOA). Erbium doped fiber amplifier is the major type of the fiber amplifier used to boost the signal in the WDM fiber optic system, as we know it is WDM that increase the capacity of the fiber communications system and it is the erbium-doped fiber amplifier that makes WDM transmission possible. Fiber amplifiers are developed to support Dense Wavelength Division Multiplexing (DWDM) which is called DWDM EDFA amplifier and to expand to the other wavelength bands supported by fiber optics.

There are several different physical mechanisms that can be used to amplify a light signal, which correspond to the major types of optical amplifiers. In doped fibre amplifiers and bulk lasers, stimulated emission in the amplifier’s gain medium causes amplification of incoming light. In semiconductor optical amplifiers (SOAs), electron-hole recombination occurs. In Raman amplifiers, Raman scattering of incoming light with phonons in the lattice of the gain medium produces photons coherent with the incoming photons. Parametric amplifiers use parametric amplification.

When light is transmitted through matter, part of the light is scattered in random directions. A small part of the scattered light has frequencies removed from the frequency of the incident beam by quantities equal to the vibration frequencies of the material scattering system. Raman fiber optic amplifiers function within this small scattering range. If the initial beam is sufficiently intense and monochromatic, a threshold can be reached beyond which light at the Raman frequencies is amplified, builds up strongly, and generally exhibits the characteristics of stimulated emission. This is called the stimulated or coherent Raman effect.

EFDA fiber optic amplifier functions by adding erbium, rare earth ions, to the fiber core material as a dopant; typically in levels of a few hundred parts per million. The fiber is highly transparent at the erbium lasing wavelength of two to nine microns. When pumped by a laser diode, optical gain is created, and amplification occurs.

Silicon or semiconductor optical amplifier functions in a similar way to a basic laser. The structure is much the same, with two specially designed slabs of semiconductor material on top of each other, with another material in between them forming the “active layer”. An electrical current is set running through the device in order to excite electrons which can then fall back to the non-excited ground state and give out photons. Incoming optical signal stimulates emission of light at its own wavelength.

Fiber optic repeater also can re-amplify an attenuated signal but it can only function on a specific wavelength and is not suitable for WDM systems. That is the reason why fiber optic amplifier plays a much more important role in communication systems.