Guide to Optical Amplifier

Optical amplifier is an significant device deployed for optical communication and laser physics. No need for converting optical signals into electrical signals first, optical amplifier can directly amplify the optical signals. It is considered to be a laser without optical cavity or with suppressed feedback from cavity. Optical amplifiers are often installed at places where optical signals are weak and need to be enhanced. This ensures the stable transmission of optical signals in the rest cables. Thus, we should attach greater importance to optical amplifier. And this article will guide you to know the secrets of optical amplifier.


Functions of Optical Amplifier

In an optical network, optical amplifiers can be used as booster amplifiers, pre-amplifiers or inline amplifiers. These functions are a little different from each other. When a optical amplifier acts as a booster, it is used to amplify the signals that leave the transmitter into the required level before entering into fiber links. The booster amplifier is especially important to a WDM link as the multiplexer attenuates optical signals. Pre-amplifier is used at the other end of a link to amplify the signal level for it to be detected over or above the thermal noise of the receiver. As for inline amplifier, it is used for links over 150 km in case signals become weak in long distance. Every 80 to 100 km, inline amplifier will be placed to make sure that the signal level is over the noise floor.


Three Types of Optical Amplifiers
1) Erbium Doped Fiber Amplifier (EDFA)

Erbium doped fiber amplifier or EDFA is now the most widely used optical amplifier for long range fiber communications. Its optical fiber (usually a single-mode fiber) at the core is doped with rare earth element erbium to absorb light at one frequency and emit light at another frequency. The light is pumped from laser diodes with a wavelength around 980 nm and sometimes around 1480 nm. EDFA has advantages of high gain, wide bandwidth, high output power, high pumping efficiency, low insertion loss and insensitive to polarization state which turns out to be a good solution for DWDM, CATV and SDH applications.

2) Roman Amplifier

Roman amplifier is designed based on the Roman gain which results from the effect of stimulated Roman scattering. When a lower frequency signal photon induces the inelastic scattering of a higher-frequency pump photon in an optical medium in the nonlinear regime, another signal photon is produced with the surplus energy resonantly passed to the vibrational states of the medium. Roman amplifier is often installed in the mid-stream of a signal or in front of the receiver to amplify signal levels. It has the advantages of greater operating wavelength range, constant optical gain and effective noise figure reduction.

3) Semiconductor Optical Amplifier (SOA)

Semiconductor optical amplifier or SOA is the optical amplifier based on a semiconductor gain medium. Light is sent through a semiconductor single-mode waveguide with transverse dimensions. SOA is usually connected to the output of 1310nm transceivers to amplify signal level before entering into optical fiber. It supports all format of 1310nm wavelength signals and is compatible with all data rates. Thus, SOA is an ideal solution for DWDM network optical amplification.


To sum up, optical amplifier enables the optical transmission over long distance by amplifying signals. This article introduces the fundamentals of its functions and some commonly used types. You may have an overall understanding about optical amplifier. For more information, please visit FS.COM.