What is EDFA Optical Amplifier?

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EDFA stands for Erbium Doped Fiber Amplifier and it is one type of many different optical amplifiers.

Optical amplifiers amplify an optical signal directly, without the need to first convert it to an electrical signal. This process is significantly cheaper and started a fiber optic revolution.


Put simply, EDFA stands for Erbium Doped Fiber Amplifier and it is one type of many different optical amplifiers.

When an optical signal is transmitted over a long distance, such as from New York to San Francisco, the optical signal has to be amplified many times in between. This is because of signal loss from fiber attenuation, connector losses, fiber splice losses, etc.

Before optical amplifier was invented, the optical signal had to be first converted to electrical signal, amplified, and then converted back to optical signal again. This process was very complicated and expensive.

Then optical amplifiers such as EDFA were invented. Optical amplifiers amplify an optical signal directly, without the need to first convert it to an electrical signal. This process is significantly cheaper and started a fiber optic revolution.

Now let's take a close look at how EDFA works.


The top left picture shows a simple diagram of how EDFA works.

The optical signal, such as a 1550nm signal, enters an EDFA from the input. The 1550nm signal is combined with a 980nm pump laser with a WDM device. The signal and the pump laser pass through a length of fiber doped with Erbium ions. The 1550nm signal is amplified through interaction with the doping Erbium ions.

This Erbium ion interaction process is shown at the right picture.

The 980nm pump laser excites Erbium ions from lower energy level 1 into a higher energy level 3. From level 3, the Erbium ions rapid decay to level 2. From Level 2, the Erbium ions interacts with 1550nm signal and jumps back to lower energy level 1. In this process, it emits a 1550nm photon. This process is called Stimulated Emission.

Actually EDFA has an amplification window. It is the range of optical wavelengths for which the amplifier yields a usable gain. This wavelength range is determined by the properties of the dopant ions, the glass structure of the optical fiber, and the wavelength and power of the pump laser.

The lower left picture shows a more detailed schematic diagram of EDFA. It is composed of isolators, WDM, Erbium Doped Fiber, 980nm pump laser, and more.