Hello everyone!
Today, I want to write about optical amplifiers. I wrote about the topic in the article EDFA. Now, I will detail explain the operation of the optical amplifiers.
For very long optical traces, signal regeneration is required. Earlier repeaters were used, today they are optical amplifiers. The use of repeaters proved to be bad. It converted optical to electrical and electrical to optical signals, they introduced noise. They were made for the specific bit rate of transmission. Modern optical amplifiers do not have these problems –no signal conversion, no noise, etc. They operate at 1550 nm and use erbium-doped fiber. Praseodymium-doped fluoride fiber amplifiers (PDFFAs) are not a good solution, they do not have good performance for wide use. Gains of optical amplifier can be > 40 dB or > 20 dBm and that is a signal amplification of 10,000 times.
Figure 1. Block diagram of the optical amplifier
The most
efficient optical amplifiers are 1550 nm amplifiers that use
erbium-doped fiber, such as EDFA.
It is
a simple device. The laser emits light with a wavelength of about
1540 nm. Laser pumps emit light at 800 nm or 980 nm and stimulate
fiber doped with erbium. Stimulation of erbium releases a lot of
energy.
Er3 + ions have quantum levels. They allow them to be stimulated to emit in the range of 1540 nm. This wavelength was chosen because it has the least attenuation in the optical fiber. Laser pumps stimulate the doped optical fiber, resulting in high optical power output. This makes it possible to amplify the optical signal in the desired range.
Erbium can also be stimulated with laser pumps with a wavelength of 1480 nm, but it is not desirable. Because the process of pumping energy and stimulated signal emission is at approximately the same wavelength.
In WDM systems, EDFA uses Bragg gratings, which provide equal gain in the operation band.
In PON systems, optical amplifiers are EDFA amplifiers. They are used to amplify the video signal - CATV. The reason is the required high optical signal strength at the reception of the mini node or ONU.
Thank you!
