الفهرس 
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Abstract
The present work deals with the improvement of the performance of
optical fiber amplifiers, which are major components in optical
communication systems by studying, the characteristics of Raman
amplifier and the characteristics of Erbium-Doped Fiber Amplifiers
EDFA/Raman hybrid amplifier and comparing their performance.
The main interest of the study is devoted to fiber amplifiers like Raman
amplifiers and erbium doped fiber amplifier hybrid with Raman
amplifier. The main idea is to study and improve the gain and noise of the
amplifier through parameters which control it like input signal power,
Raman pump power, Raman amplifier length in Raman amplifier and
EDFA pump power and EDFA length with the last parameters in
EDFA/Raman hybrid amplifiers. The thesis provides a numerical
investigation of the performance of Raman amplifier and EDFA/Raman
hybrid amplifiers.
The performance parameters that have been investigated and compared
are gain spectrum, optical noise figure, optical signal to noise ratio
(OSNR). OSNR depends on the pump power of both types of amplifier,
signal power and fiber length of both types. EDFA can be forward
pumped and Raman amplifier can be reverse pumped. The parameters are
calculated for different values for the pump power, fiber length and signal
wavelengths and input signal power. The gain using these amplifiers
covers the range 1.45-1.65 μm which is S, L and C bands.
from the obtained results,
It is found that, the performance of nonlinear optical amplifiers depends
strongly on both the signal and pump wavelengths and the host material
through the values of the emission and absorption cross sections.
It is found also that, the gain in the case of EDFA/Raman Hybrid Optical
Amplifier (HOA) is large for the signal wavelength 1.53 μm rather than
Raman amplifier or EDFA.
For the gain and noise figure, we found that both depend on the signal
wavelength and input signal power as well as the pump power and the
fiber length.
It is found that, the optimum values of the parameters, which give higher
gain and lower noise figure for EDFA/Raman HOA, are EDFA length of
15 m with Raman amplifier length 25 km at input signal power, -30 dBm
for EDFA and Raman pump power of 100 mW. The broadening in the
gain curve is 0.041 μm.
Optical amplifiers could be pumped using either forward pumping
schemes in erbium and backward pumping in Raman. We found that, for
low pumping power levels, even though both forward and backward
pumping methods provide the same gain. The forward pumping is better
as its equivalent input noise figure is lower for erbium and the backward
is better for Raman in the EDFA/Raman HOA.
The higher gain obtained was 41.1 dB for EDFA/Raman hybrid amplifier
at -30 dBm input signal power, 100 mW of both EDFA and Raman pump
power and signal wavelength of 1.53 μm and the lower noise figure was
3.8 dB for EDFA only at -30 dBm input signal power, 100 mW of EDFA
pump power at signal wavelength of 1.53 μm.