Research On Pulse Repetition Rate Multiplication Technology Based On Temporal Talbot Effect In Fiber

The expansion of bandwidth and capacity of mobile communication system by virtue of a fiber broadband and low loss advantage is the core idea of RoF technology, which is also the trend of next generation wireless communication technology. There are many methods in generation macrowave sigals with higher frequency. Among them, multipulicating optical pulse repetition rate in the optical domain by optical methods is one of the effective methods to obtain higher carrier frequency of the microwave signal.This thesis makes a brief introduction to the spatial Talbot effect and the spectrum Talbot effect. Three ways of introducing dispersion in the temporal Talbot effect are introduced in this thesis. The principle of time domain Talbot effect is analyzed in the view of the variation of the spectrum of the pulse sequence with the dispersion of fiber. The theory of the Talbot effect in the optical fiber is derived. And the relative phase relationship of each spectral line in the spectrum of several key points in the time domain is analyzed in the light of the change of the dispersion medium before and after the dispersion medium. The process of the optical pulse sequence in the self-imaging, the two times and the four times multiplication is analyzed in detail.In the simulation, the repetition rate of a 10 GHz pulse source is integer times multiplicated to 20 GHz, 80 GHz, 40 GHz and 160 GHz and fractional times multiplicated to 15 GHz. The time domain waveform and spectrum of the pulse sequence before and after pulse repetition rate multiplication are analyzed. After that, the influence of the pulse-width and the dispersion deviation on the quality of the multpulicated pulse sequence is analyzed. By the simulation of the pulse sequence of the different shapes of the same pulse-width, it is found that the quality of the multiplicated pulse is related to the shape of the input pulse. When the bottom of the input pulse is wide, the adjacent pulse may be overlapped and affecting the frequency quality in the multiplicated pulse train. By analyzing the relative phase of each spectral line in the spectrum affected by the dispersion deviation, it is found that the three-order dispersion will have a great influence on the multiplication of the pulse train with wider spectrum.In the experiment, the accurate value of the group velocity dispersion parameter of single mode fiber is measured by frequency sweeping method. The light source in the experiment is a mode locked laser that produces a pulse train with the repetition rate of 9.9519 GHz. The time domain diagram of the optical pulse sequence in the single mode fiber with length 20.675 km and 25.284 km are analyzed, and the similar results are obtained in the simulation. Three times multiplication realized in single mode fiber with 25.284 km length, and quality of the pulse train is very good. Fifteen times multiplication realized in single mode fiber with 20.675 km length, but the quality of the multiplicated pulse train is not so good. The simulation analysis shows that the reason why the quality of the pulse sequence is poor after the fifteen times multiplication is that the dispersion value in the optical fiber is not the optimal dispersion value of the fifteen times multiplication.