EDFA Selection Guide

An EDFA is an optical amplifier based on Erbium-doped optical fiber, that amplifies optical signals without converting them into electrical form. EDFAs use semiconductor lasers to pump Erbium Doped Fiber to amplify light in 1.5 μm wavelength region where telecom fibers have their loss minimum. It has low noise and can amplify many wavelengths simultaneously, which makes DWDM possible and becomes a key enabling technology for optical communication networks. Since the realization of EDFA, it has developed rapidly and has become the amplifier choice for most applications in optical communication.

Basic of EDFA

The structure and working principle of an EDFA are simple. EDFA consists of a glass optical fiber doped with Erbium ions, WDM coupler, isolators, optical filter and pumping supply.EDFA

The picture above shows how an EDFA works. When a beam of light that carrying signals passes the Erbium-doped optical fiber, a pump laser provides the amplifier energy at Erbium absorption peaks of 980 and 1480 nm, through the use of WDM couplers. Then an optical filter removes the remaining traces of the pump beam so that it doesn’t interfere with reception of the signal. Isolators are inserted into the amplifiers to minimize the reflections on the EDFA

How to Choose the Right EDFA

First of all, you should make sure the network type in which you need to use EDFA. Depending on the network application, EDFA are generally designed into the following types:

  • DWDM EDFA: for this type of network, EDFA needs to be not only high power low noise, but also gain flattened such that all wavelength channels can be amplified equally.
  • SDH EDFA: For SDH network, EDFA design should allow maximum power budget to achieve the highest detection sensitivity.
  • CATV EDFA: There is also EDFA designed for CATV application, which has low noise with heat dissipation and ventilation in mind to ensure a long operation life.

The way in which EDFA used is to enhance the performance of optical data links is also important in selecting EDFAs. Depending on this, three types of EDFAs can be found in the market:

  • Booster EDFA: this EDFA is used to increase the optical output of an optical transmitter just before the signal enters an optical fiber.
  • Inline EDFA: as the optical signal is attenuated as it travels in the optical fiber. The inline amplifier is used to restore the optical signal to its original power level.
  • EDF pre-amplifier: this kind of EDFA is used at the end of the optical link in order to increase the sensitivity of an optical receiver.

Some other important elements should be considered before selecting EDFAs.

  • Wavelengths: you should make certain how many wavelengths will go through the EDFA and the beginning and ending wavelengths, for example 1530 to 1562 nm. For single wavelength link, you should know clearly the exact wavelength.
  • Power or loss budget: the budget tells us how much amplification you require for the whole link.
  • The location of EDFAs: After the transmitter, before the receiver, or in the mid-span.

Fiberstore DWDM EDFASelecting the right EDFA seems not an easy thing. However, if you are not sure about the types and numbers of EDFAs, you can visit Fiberstore which supplies various EDFAs with high quality and low price, as well as free EDFA solutions meeting customers’ requests.

Dual Stage EDFA with DCM Mid-Stage Access – DCM-optimized EDFA

Besides optical amplifiers, modern optical networks also require other components to be place along the link, such as the Dispersion Compensation Module (DCM) used to correct signal distortion due to Chromatic Dispersion of the transmission fiber. Since the attenuation of DCM can be quite large, in the range of 5 to 10 dB, additional amplification is needed to accommodate them. In order to minimize the Optical Signal Noise Ratio OSNR and cost impact of this addition amplification, it is beneficial to place the DCM between two amplifiers.

A dual stage EDFA amplifier is basically two amplifiers in one package, where there is access for an optical component such as a DCM to be placed between them. In this configuration, it is called a DCM-optimized EDFA. Most often the first amplifier (pre-amplifier) is variable gain, and the second (booster amplifier) is fixed gain, such that the amplifier as a whole provides variable gain operation. The control of both amplifiers is combined, in other words the user sets the required net gain of the entire combination (including the DCM), and the control units sets the gain of each of the two amplifier in order to achieve the net gain.

Note: DCM-optimized EDFA is named because of using DCM as the mid-stage access. The DCM EDFA can be generally provided as a stand-alone module or in a managed 1RU package with the DCM integrated within. Fiberstore’s Dual Stage DCM-optimized EDFA is a stand-alone module without the DCM which need to be bought separately. In this way, customers could choose the right dispersion compensation modules to meet their own requirements.

DCM-optimized EDFA

Dispersion Compensation Module (DCM)

Here is the basic scheme for a dual stage EDFA amplifier with DCM mid-stage access. The two amplifiers are packaged in the same module and are controlled together with the mid-stage device (i.e. the DCM) as a single unit. Additionally, each amplifier also has its own local control loops.

Dual Stage EDFA with DCM Mid-Stage Access

The amplifiers are designed apriori to take into account the DCF loss. For example, the dynamic range of the input detectors of both amplifiers is set accordingly, and the optical performance, such as Noise Figure (NF), is specified already taking the DCM loss into account. Since the DCM is often implemented using special Dispersion Compensation Fiber (DCF), there can be a large optic al delay between the first and the second stage of the amplifier. For this reason transi ent suppression of each amplifier ne eds to be performed separately, and consequently each amplifier has its own pump and own local control mechanism (in addition to the overall control used to set the net gain).