Hello, everyone!
Today, I want to explain the difference between EDFA and Raman optical amplifiers. Long optical links require amplification of the signal. There are two types of amplifiers - EDFA and Raman. The question is what are the differences between these two amplifiers? And which amplifier should be applied?
It depends on our optical link – type of optical fiber, length, wavelengths, and attenuation. But, let's first look at the basic information about these optical amplifiers.
EDFA
EDFA (Erbium Dropped Fiber Amplifier) is an optical amplifier that is widely used - PON, DWDM systems, long links, etc. It is composed of Erbium-doped fiber (EDF), a pump laser, optical isolators, WDM couplers, optical filters, etc (figure 1.).
Figure 1. The main elements of EDFA
EDFA is used in two bands:
C-band (Conventional), from 1525 nm to 1565 nm, and
L-band (Long), from 1570 nm to 1610 nm.
During the production of optical fiber, a very small amount of erbium (trivalent erbium ion) is inserted into the fiber core. In this way, the optical properties of the optical fiber are changed and they can be used to amplify the signal. Using laser pumps at 980 nm or 1480 nm, the doped erbium fiber is simulated. In this way, a large amount of energy is released and thus large optical power outputs are obtained. This is the working principle of amplifiers.
Figure 2. EDFA
The main advantages of EDFA:
gain can be bigger than 40 dB or bigger than 20 dBm,
low noise figure,
it has a flat gain in a wide wavelength band (> 80 nm) of about 1550 nm, and
low cost.
The main disadvantages of EDFA:
the problem is the size of the device, and
it cannot be an integral part of another semiconductor device.
Raman amplifier
Raman optical amplifier allows signal amplification at any wavelength. The working principle is based on stimulated Raman scattering (SRS). Undoped optical fiber is used. The photon that is inserted excites the electron and it goes into a vibrating state. Then, the stimulated emission occurs when the electron de-excites to the vibrational state of the glass molecules in the optical fiber.
Two types of this optical amplifier are currently available:
lumped type Raman optical amplifier (LRA) and
distributed type Raman amplifier (DRA).
The first type of optical amplifier has fiber gain media of 10 km. It requires very high power of pump lasers because it produces high output optical power.
DRA has longer fiber gain media than LRA, about dozens of kilometers. Its pump laser has power of about hundreds of megawatts.
Figure 3. Raman amplifier
The main advantages of Raman amplifier:
it is used in a wide range of wavelengths,
it is compatible with all singlemode optical fibers, and
it has a lower average output optical power but it can be good for lower crosstalk.
The main disadvantages of Raman amplifier:
high power laser pumps are required,
precise gain control is required,
there is a problem with noise, and
high cost.
The main difference between EDFA and Raman amplifiers is given in the following table.
Features | EDFA | Raman amplifier |
Working principle | It uses stimulated radiation of EDF fibers to amplify optical signals. It requires doped optical fiber. | It uses stimulated Raman scattering for the amplification of optical signals. It does not require doped optical fiber. |
Pump power | 25 dBm | > 30 dBm |
Amplification band | 1525 nm - 1565 nm and 1570 nm - 1610 nm. | All wavelengths |
Noise figure | 5 dB | 5 dB |
Gain | > 40 dB | > 25 dB, gain is smaller than EDFA, for about 5 –15 dB |
Cost factor | Low | High |
This is the end of this article. I hope you learned something new!
Thank you!
