Why Use EDFA with WDM Network?

EDFA (erbium doped fiber amplifier), commercialized in the early 1990’s, became a key enabling technology for optical communication networks, and has deployed in the field. It is usually used to improve the intensity of optical signals being carried through a fiber optical communication system thus enables the optical signals in an optical fiber to be amplified directly in high bit rate systems beyond Terabits. 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. So what is EDFA? Do you know EDFA working principle? Now I’d like to make a detailed introduction of EDFA.

EDFA Working Principle

How Does Signal Amplification Happen? In general, EDFA works on the principle of stimulating the emission of photons. With EDFA, an erbium-doped optical fiber at the core is pumped with light from laser diodes.The erbium-doped fiber (EDF) is at the core of EDFA technology, which is a conventional silica fiber doped with Erbium. It is a conventional silica fiber doped with erbium. EDFA usually has two used pumping bands 980nm and 1480nm. When the erbium is illuminated with light energy at a suitable wavelength (either 980 nm or 1480 nm), it is excited to a long lifetime intermediate state, following which it decays back to the ground state by emitting light within the 1525-1565nm band. If the light energy already exists within the 1525-2565nm band, for example due to a signal channel passing through the EDF, then this stimulates the decay process, resulting in additional light energy.

This type of setup in telecom systems can help with fiber communications, for example, boosting the power of a data transmitter. An EDFA may also be used to maintain long spans of a passive fiber network and may also be used for some types of equipment testing.The working principle of EDFA is same as that of lasers excepting that EDFA do not require a cavity where as cavity is required for laser oscillation.

Base Configuration of EDFA

In its most basic form, the EDFA consists of a length of EDF (typically 10-30m), a pump laser, and a component (often referred to as a WDM) for combining the signal and pump wavelength. Because 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 so that they can propagate simultaneously through the EDF. 

In principle, the most common EDFA configuration is the forward pumping configuration using 980nm pump energy, as shown in the picture below. This configuration makes the most efficient use of cost effective, reliable and low power consumption 980nm semiconductor pump laser diodes, thus providing the best overall design with respect to performance and cost trade-offs.

Besides the three basic components described above, this picture also shows additional optical and electronic components used in a basic single stage EDFA. 

Application of EDFA

• 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.
• EDFA can be employed in the high-capacity and high-speed optical communication system. The application of EDFA is very constructive todeal with the defect that the transmission distance without relay is not far enough due to the low sensitivity of the high-speed system receiver.
• 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.
• 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.
• 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 optical power splitters can significantly enlarge the scale of the distribution network and increase the number of subscribers.

Conclusion

A brief introduction to the EDFA, one of the most important components in WDM communications, is given in this article. Be equipped with the features of high output power, high gain, wide bandwidth, polarization independence and low noise figure, EDFA have become one of the key components used in the new-generation optical communication system. Lightoptics provides various EDFA, including DWDM EDFA, CATV EDFA, etc. Visit www.lightoptics.co.uk for more details.