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Theoretical Study On Pulse Generation Based On Fiber Optical Parametric Amplifier

Posted on:2015-03-06Degree:MasterType:Thesis
Country:ChinaCandidate:Z WangFull Text:PDF
GTID:2268330428465124Subject:Electronics and Communications Engineering
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The technique of high repetition pulse generation and compression becomes one of the keytechnologies in all optical networks. In conventional telecommunication window, a reliable highrepetition pulse source appears to be a key technical support in many aspects such as wavelengthdivision multiplexing technology or time division multiplexing technology in backbone networks,flexible access technique in the development of FTTx and so on. Because the lack of efficient gainmedium, conventional lasers don’t meet the need of short pulse generation in non-conventionalwavelengths. On the other hand, with the development of optical fiber communication, fiber opticalparametric amplifier enters people’s field of vision because it offers ultra-fast response, wide-gainbandwidth, high gain and large wavelength detune from the pump. Based on these advantagesabove, the application of FOPA in the generation of pulses will have great prospects. The mainstudy in this paper is focused on the generation of short pulses based on FOPA, and the details areas follows:1. At first, the development of optical communication and some key techniques are introduced.One focuses on some optical pulse generation techniques. Some common nonlinear processes andknowledge about high nonlinearly optical fiber are introduced and the physical mechanism of FWMis interpreted. At the same time, the main terms that have significant effect on the phase matchingterm are introduced such as material dispersion, waveguide dispersion and nonlinear term. Thethesis also analyzes how the parametric gain changes when pump power takes different values.2. In small signal model, the analysis on single pump optical fiber parametric amplifier is madein detail by using two derivation methods. The amplitude of signal gain decreases and its edge partshift towards the center, which is caused by the diminution of pump power. That is the fundamentalof pulse generation and it is also prepared for the theoretical basis of numerical method latter. In thispaper, the common symmetrical split-step Fourier numerical method (SSFM) is used and some partis modified according to the particularities in our research contents. A new kind of SSFM isproposed: In the analysis of linear part, the general method is used. But when refer to nonlinear part,one uses the method of solving ordinary differential equations to deal with it which is based onRunge-Kuta method.3. Previous studies mainly focused on the wavelength conversion between signal and pump,but in this paper one mainly analyses the generation of idler wave when pump pulse is input. Onetakes the hyperbolic pulse for an example to study the characters of duty-cycle and peak power when the frequency detuning of between signal and pump changes. We show that when thefrequency detuning is small, the peak power of idler is high and so is the duty-cycle. In general, theduty-cycle of idler pulses is improved a lot. In addition, this paper analyzes the walk-off effectbetween pump pulse and generated idler pulse by using the definite parameters and proposedmethod. The result of previous study is proved. Based on this theory, we consider the effect ofsecond order dispersion. The character of idler pulses under different modulation frequency isanalyzed, when the pump power is modulated by sinusoidal signal. The result shows that how thegroup-velocity dispersion affects the generated pulses has something to do with the modulationfrequency. According to the parameters in this paper, idler pulse is broaden when the modulationfrequency is10GHz; when it is20GHz or40GHz, the combine of dispersion effect and walk-offeffect makes for good pulse shape.4. Based on the dual pump configuration FOPA, the analysis of two orthogonal pump waves ismade as well as corresponding argumentation. The character of signal gain is analyzed when pumppower decreases. Compared with the case in which the two pumps are linearly co-polarized in thesame direction, the features of parametric gain in both cases are discussed respectively. Meanwhile,the relation of phase matching term and the gain sensitivity are analyzed. When pumps are linearlyco-polarized, gain sensitivity reaches the maximum on condition that detuning Lapproaches to-0.12; In the case of orthogonal polarized pumps, one gets the maximum value when Lis about-0.09. In this paper, one also compares the walk-off effect between pumps and signal or idler withthat of single pump configuration in the condition that pump waves are linearly co-polarized. Whenone refers to get the same peak power pulses, the dual configuration FOPA suffers less impact, butgets broader pulses. Through the polarization effect in FWM process can be eliminated by usingtwo orthogonal pumps, the peak power of pulses can be impacted by the small signal gain. We showthat ideal pulses can be generated by increasing pump power. At last, by using the numericalmethod proposed in this paper, one analyzes the impact of pump phase modulation based on pulsegeneration with single pump FOPA. We verify the result in previous study. Furthermore, based onthe previous results, one studies the effect of pump phase modulation in dual pumps FOPA. Theexpression of signal gain that contains phase terms is derivate, and relevant analysis is made. Ourstudy shows that apart from the method that is taken in the case of single pump FOPA, we can getuniform pulse train by reversely modulating two pumps synchronously.
Keywords/Search Tags:pulse, parametric amplifier, walk-off effect, group-velocity, phase modulation
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