The Evolution of Optical Amplifiers For DWDM

With the requirements of longer transmission lengths, fiber optic amplifier have become an essential component in long-haul fiber optic networks. Semiconductor optical amplifier (SOA), EDFA optical amplifier, and DWDM system amplifiers relif the effects of dispersion and attenuation, allowing improved performance for long-haul optical systems.


The evolution of EDFA has significantly miniaturized the loss of optical fiber. However dispersion is severely affecting the performance of fiber-optic systems. The light signal is severely distorted by dispersion, due to which signal quality, data rate and distance covered are greatly lessened. Therefore the techniques for effectively controlling the dispersion become burning concern in these systems.

EDFAs allow information to be transmitted over longer distances without the need for conventional repeaters. The fiber is doped with erbium, a rare earth element, that has the appropriate energy levels in their atomic structures for amplifying light. EDFAs are designed to amplify light at 1550 nm. The device utilizes a 980 nm or 1480nm pump laser to inject energy into the doped fiber. When a weak signal at 1310nm or 1550nm enters the fiber, the light stimulates the rare earth atoms to release their stored energy as additional 1550 nm or 1310 nm light. This process continues as the signal passes down the fiber, growing stronger and stronger as it goes.

The photons amplify the incoming signal optically, boosting the wavelength, and avoiding almost all of the active components. The output power of the EDFA is large, and thus, fewer amplifiers may be needed in any given system design. The amplification process is independent of the data rate. Because of this benefit, upgrading a system means only changing the launch/receive terminals.

As demands for wider bandwidth grow there is a call for more efficient and reliable optical amplifiers. The usable bandwidth of an EDFA is only about 30 nm (1530 nm-1560 nm), but the minimum attenuation is in the range of 1500 nm to 1600 nm. The dual-band fiber amplifier (DBFA) solves the usable bandwidth problem. It is broken down into two sub-band amplifiers. The DBFA is similar to the EDFA, but its bandwidth ranges from about 1528 nm to 1610 nm. The first range is similar to that of the EDFA and the second is known as extended band fiber amplifier (EBFA). Some features of the EBFA include flat gain, slow saturation, and low noise. The EBFA can achieve a flat gain over a range of 35 nm which is comparable to the EDFAs. EBFAs have the advantage of reaching a slower saturation keeping the output constant even though the input increases.

DWDM System Amplifiers

The explosion of dense wavelength-division multiplexing (DWDM) applications make DWDM optical amplifiers an essential fiber optic system building block, also forced the fiber optic manufacturers to develop DWDM multiplexer and demultiplexer that can handle closely spaced optical wavelengths. Due to DWDM systems handle information optically rather than electrically, it is imperative that long-haul applications do not suffer the effects of dispersion and attenuation.

Raman amplifier has been found to be an attractive candidate for DWDM system. Improved systems and methods for optical amplification of DWDM signals are provided by FiberStore.