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06 Oct 2015
What Are Optical Amplifiers

An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. Together with wavelength-division multiplexing (WDM) technology, which allows the transmission of multiple channels over the same fiber, optical amplifiers have made it possible to transmit many terabits of data over distances from a few hundred kilometers and up to transoceanic distances, providing the data capacity required for current and future communication networks.

Functions of Optical Amplifiers

Broadly speaking, optical amplifiers may be used within an optical network as boosters, in-line amplifiers, or pre-amplifiers. The following picture shows a simple WDM optical network, where a number of transmitted channels are combined using a WDM multiplexer (MUX), amplified using a booster amplifier before being launched into the transmission fiber, re-amplified using in-line amplifiers, and finally pre-amplified before being demultiplexed and received.

Optical Amplifier

A booster amplifier is used to amplify the signal channels exiting the transmitter to the level required for launching into the fiber link. In most applications this level is in the range of 0-5 dBm per channel, however, it can be higher for more demanding applications. A booster is not always required in single channel links, but is essential in a WDM link where the multiplexer attenuates the signal channels. A booster amplifier typically has low gain (in the range of 5-15 dB) and high output power, typically about 20dBm for a 40 channel WDM system. At the other end of a link, a pre-amplifier may be required to amplify the optical signal to the level where it can be detected over and above the thermal noise of the receiver. A pre-amplifier should provide high gain, often in the range of 30 dB, and have a low noise figure in the range of 4-5.5 dB, in order to assure error-free detection of the signal channels. The output power of the pre-amplifier need not be very high. For links up to about 150 km, the booster amplifier and pre-amplifier are usually sufficient to ensure error-free transmission. However, for links above 150 km, the performance deteriorates to such an extent that the signal becomes undetectable. To avoid this, in-line amplifiers are placed every 80-100 km to ensure that the optical signal level remains above the noise floor. In-line amplifiers typically require moderate gain in the range of 15-25 dB, and NF in the range of 5-7 dB. Output power requirements are similar to those of booster amplifiers.

Main Types of Optical Amplifiers

The most practical optical amplifiers include the SOA and EDFA types.

● Semiconductor Optical Amplifier (SOA) SOAs are amplifiers which use a semiconductor to provide the gain medium. They operate in a similar manner to standard semiconductor lasers (without optical feedback which causes lasing), and are packaged in small semiconductor packages. Unlike other optical amplifiers, SOAs are pumped electronically (i.e. directly via an applied current), and a separate pump laser is not required. Despite their small size and potentially low cost due to mass production, SOAs suffer from a number of drawbacks which make them unsuitable for most applications. In particular, they provide relatively low gain, have a low saturated output power and relatively high noise figure. Thus, they are suitable for applications such as single channel booster amplifiers which don't require high gain or high output power.

● Erbium-Doped Fiber Amplifier (EDFA) EDFA is mainly made of Erbium-doped fiber (EDF), pump light source, optical couplers, optical isolators, optical filters and other components. 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. 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 networks and may also be used for some types of equipment testing.

Conclusion

Optical amplifiers perform a critical function in modern optical networks, enabling the transmission of many terabits of data over long distances of up to thousands of kilometers. Optical amplifiers provided by Fiberstore are designed for all network segments (access, metro, regional and long haul) and applications (telecom, cable and enterprise). We have a series of erbium-doped fiber amplifier (EDFA) optical amplifiers, including DWDM EDFA for DWDM systems, CATV EDFA for CATV applications, SDH EDFA for SDH networks, etc.



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