Fiber amplifies are used to amplify the signal inside the fiber optic core to prevent the loss of data.

1. FIBRE AMPLIFIERS:
• Enables direct amplification on light.
• By facet reflectivity  SLA is classified into (1)Resonant Fabry-perot Amplifiers.
• (2)Non-resonant travelling wave Amplifiers
• In SLA exhibiting high gain, low polarisation sensitivity & high saturation power.
• The major advantage in fibre amplifier: 1) spliced into the system fibre with low loss.
• The coupling loss in SLA is large, therefore the gain is higher in -fibre amplifier
Wavelength division multiplexing

2. .
• The gain medium consist of single mode fibre connected to a wavelength division
multiplexing couple called dichroic coupler.
• The coupler provide 1)low insertion loss at both signal & pump wavelength. The
excitation through optical pumping – achieved by high semiconductor laser
combined with input signal……..The output signal emerged on the other end .
Erbium doped fibre amplifier: This type is operate near 1.55µm 1)which
the attenuation is minimum. 2)The bandwidth is around 300GHz. 3)It is a linear
characteristic amplifier and provides a 3 level lasing scheme.

3. .
• Parts: 1)erbium doped fibre 2)pump laser 3)wavelength selective coupler(combine
signal with pump wavelength)
•
1)The input signal and pump laser A are co-propagating. 2) The pump laser B at other
end propagate opposite direction & results counter propagation of beam. 3)Optical
filters remove unused pump light.
Advantages:

4. NON- LINEAR CHARACTERISTIC LASER:
• Non-linear effect: Change in optical properties such as refractive index in the
intensity of propagating light beam is large.
• Low – linear scattering & refractive index is constant.
• High – inelastic scattering results non linear phenomena such as 2nd hormonic
scattering, rectification, kerr effect, Raman scattering, Brillouin scattering &
Fraday effect.
• The variation of refractive index with light intensity :
n = n0 + n1 I2
n1= non linear component
I2 = light Intensity
n0 = refractive index of linear medium

5. RAMAN FIBRE AMPLIFIER:
• Working principle:  Stimulated Raman Scattering (SRS) – interaction between
optical and vibrational energy.
• 2)which cause energy transfer from pump to the signal.
• 3)RFA is based on the scattering of photon to lower energy
level. Diagram is similar to EDFA.
Parts: pump laser, wavelength selective coupler & fibre.
4)Major difference is using standard single mode fibre.
The pump signal is calculated from the signal on the laser beam.

6. BRILLOUIN FIBRE AMPLIFIER:
• Working principle is same as RFA but difference in optical gain obtained by
stimulated Brillouin scattering
• Each pumped photon creates a signal photon & remaining energy used to excite an
acoustic phonon.
• Amplification occur only when signal beam propagates in opposite direction of pump
beam.
• Difference in signal and pump frequency for SBS is smaller by 3 times in madgitude
to SRS.
• Pump power 5mW --- give gain 25dB
• Narrow bandwidth less than 100MHz, so less suitable for power amplifier,
preamplifier or in – line amplifiers.
• Application used in coherent & multichannel communication system.

7. BY
G.Shenbaga Rajan
A8UPH042
III B.Sc Physics
“Department of
physics”