Raman amplifier

Introduction to Raman amplifier :

Raman amplifier is an optical amplifier based on main to be Raman gain, which results from the effect of stimulated called as Raman scattering. In this medium, the active medium is generated or often at an optical fiber, although it can also be a bulk crystal, a waveguide in a photonic integrated circuit, or a cell with a liquid or gas medium device. An input signal can be amplified while a counterpropagating with a pump of a beam, the wavelength of which is typically a few tens of nanometers shorter. For silica fibers, the maximum gain is obtained for a frequency offset of around = 10-15 THz between pump and signal depending on the composition of the fiber core. Here this article gives information about the most important amplifier known as the Raman amplifier to better understanding this topic.

Features of Raman amplifier :
  • It can be operated in the different wavelength region
  • Provided that a suitable pump source is available
  • In this amplifier the gain spectrum can be tailored by using different pump wavelength simultaneously
  • This amplifier also requires high pump power, it also requires high pump brightness but it can also generate high output powers
  • A greater length of fiber is required
  • It can have a lower noise figure
  • This amplifier also has a fast reaction to changes in pump power, particularly for copropagating pump and very different saturation characteristics 
Working principle :

It is based on stimulated Raman scattering effect. Power transferred in the optical signal is known as the Raman effect and amplification. In this above method, Raman amplification provides self-phase matching between the pump and signal with a broad gain bandwidth response generated. The pumping signal can be propagated in either direction of fiber called as forward and backward pumping.

Basically, the Raman gain is dependent on several terms following  given below :
  • Fiber length
  • Fiber length
  • Fiber attenuation
  • Fiber core diameter
  • Optical pump power 
The figure is shown that below a typical Raman amplifier. The circulator as well as a pump shown in the figure, it lases comprise the two key elements of the Raman optical amplifier. The circulator is basically used for injecting light back into the transmission path minimal optical loss.


Typical Raman amplifier configuration
Advantages of Raman amplifier :
  • Compatible with installed SM fiber.
  • Variable wavelength amplification possible.
  • A very broadband operation may be possible.
  • Lower crosstalk.
  • Can be used extends  EDFAs full form.
Disadvantages of Raman amplifier :
  • High pump power requirements.
  • Sophisticated gain control needed.
  • Noise is also an issue.