الفهرس 
CHAPTER I: General IntroductionOnly 14 pages are availabe for public view
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Abstract
This study has presents different advanced techniques for gain flattening that are namely hybrid amplifier, gain flattening filter (GFF), fiber Bragg grating (FBG), glass composition (GC) and Fabry-Perot filter (FPF). Finally, the combination of them are used as the best optimized technique of gain flattening. The overall study in this work is done using optiwave simulation software program version 13 and version 7. Starting from erbium doped fiber amplifier (EDFA) alone and adding Raman amplifier followed by GFF then FBG then glass composition then getting the hybrid modified model after adding Fabry-Perot filter. This study shows that the largest value of gain flatness can be achieved with the hybrid modified model and this occurs under changing the different operating parameters of EDFA. Using 300 channels in this model and changing the different EDFA parameters and then comparing it with other models that uses different number of channels. This model shows that it has the greatest value of gain flatness compared to the other models by about 40±5 dB and this is obtained after changing the pump power of both EDFA and Raman amplifier. Also, the proposed model shows that it is better than the model of using EDFA and Raman amplifier after changing the values of both the signal wavelength and the lengths of EDFA and Raman amplifiers.
The gain flatness of EDFA is achieved also using two different proposed methods that are namely: Gain Flatting Filter and Fiber Bragg Grating. Using various numbers of channels up to 196 channels and getting an optimized value of gain flatness by changing the different EDFA parameters such as core radius, doping radius, ion density, numerical aperture, ambient temperature, and pumping power. In GFF method, the value of gain flatness with and without GFF can be shown by using both five stages of EDFA and different modulation formats. In case of FBG, the effect of using the different apodization functions of FBG is studied by changing both the number of channels with the different EDFA parameters. In case of FBG, the gain flatness is improved from about 40±5 dB to nearly 75±5 dB. But, in the case of GFF, the value of gain flatness is improved from 15±5 dB to nearly 40±5 dB.
Eighty channels dense wavelength division multiplexing can be developed with optimum length based EDFA and dispersion compensating fiber. Different fiber media with different effective areas such as single mode fiber (SMF), highly nonlinear fiber (HNLF), highly nonlinear dispersion- flattened fiber (HNL-DFF), nonreturn to zero dispersion shifted fiber (NRZDSF) and a two types of large effective area fiber (LEAF Step core and LEAF Ring core) are used with dispersion compensating fiber and EDFA amplification. Optimum fiber length can be obtained using minimum and maximum bit error rates with different number of channels and different values of bit rates.
Also, by using different materials of optical fibers, two of them are plastic optical fibers that are namely polysulfone (PSU) / vinyl-phenyl acetate (VPAC) with refractive indices of 1.63/1.567, the second plastic material namely sapphire (S) / polysulfone (PSU) with refractive indices of 1.77/1.63. The other materials consist of fluorite (FT)/ poly-tetra-fluoro-phenyl methacrylate (PTFPMA) with refractive indices of 1.433/1.422, where the second material consists of fluoride (FD) / poly methylmethacrylate (PMMA) with refractive indices of 1.56/1.49, Finally, third material consists of silica (Si)/ tetra-fluoro-propyl-methacrylate (TFPMA) with refractive indices of 1.46/1.373. This study is based on the selection of best candidate material for the highest transmission bit rate under the same operating conditions. Gain, noise figure, bit rate, quality factor and bit error rate are the major interesting performance parameters in this study. We have employed two different optical sources that are namely continuous wave laser (CW) and vertical cavity surface emitting laser (VCSEL) in the comparison to get the highest bit rate distance product.
Dense Wavelength Division Multiplexing (DWDM) for upgrading optical communication systems capacity can be used with different modulation formats that are namely: NRZ (non-return to zero), RZ (return to zero) and On-Off Keying (OOK) and change the number of channels then showing the effect of this on the three different optical pumping techniques. Here, the simulation program can be used with changing the following parameters: EDFA length, pumping power, pumping wavelength, input signal power and also fiber length. Then we measure the quality factor, bit error rate (BER), input power, output power, gain, noise figure and bit rate. Based on the simulation results, the best pumping technique and the best modulation format for the different number of channels are determined.