Research Of All-optical Analog To Digital Converter Based On Nonlinear Effect

With the rapid development of information technology,the amount of information that people get is exponentially increasing,which requires higher speed and bandwidth in the process of information transmission.As the basic component of communication network,the performance of traditional ADC is limited by the factors of maintaining circuit bandwidth,comparator relaxation and clock jitter,and its performance is difficult to meet the development of high-speed digital signal processing.All optical analog to digital converter takes three steps which mean sampling,quantization and coding into optical filed to overcome the "electronic bottleneck" of traditional ADC,therefore meeting the demand of high speed and high bandwidth for digital signal processing.The main work and achievements of this thesis are as follows:Initially,in this thesis,a variety of realization methods and development of all optical sampling and quantization are described,and then the advantages and disadvantages of them are summarized and analyzed,meanwhile the realizations and applications of all optical logic gates are also introduced.Furthermore,the time domain transmission equation of optical pulse is obtained based on the Maxwell electromagnetic theory.On the basis of this,the principle of the coupler is analyzed,and then the coupling mode equation of the coupler is derived.The transmission equation of the Sagnac ring and M-Z interferometer is deduced by using the transmission matrix of the coupler,and then the transmittance is obtained,and the condition of the optical switch is analyzed respectively.Additionally,based on the theory of optical pulse transmission,the second order dispersion is applied to stretch the sampling signal to reduce the requirement of sampling pulses repetition rate.In the thesis,the linear chirped Bragg fiber grating with high dispersion coefficient is used to replace the commonly used dispersive devices to reduce the transmission loss and simplify the whole sampling system.The analysis in chapter two has shown that the symmetry of the symmetric M-Z interferometer cannot achieve optical switch,so cross phase modulation in nonlinear optics field is used to change the refractive index of the medium.So that the phase difference between the signals transmitt on the two arms of the M-Z interferometer is occurred,the necessary conditions for the realization of optical switch is satisfied when the phase difference reaches ?,then the signal switches output in two output ports of the M-Z interferometer.The switching performance of the M-Z interferometer based on cross phase modulation effect are further studied,including the coupling coefficient,the peak power of the sampling pulses and the arm length of the interferometer.And then the all-optical sampling scheme based on M-Z interferometer is proposed,the all-optical sampling is achieved under the condition that the interferometer arms are equal,then the thesis analyzes the influence of unequal arm length on the performance of sampling scheme,and then concludes that the arm length of the interferometer must be identical based on the sampling scheme,otherwise the sampled signal suffers great distortion.Moreover,it is obviously that all optical sampling based on the cross phase modulation effect can realize the function of all optical wavelength conversion.Based on the characteristics of wavelength conversion,a scheme of all-optical logic gate based on M-Z interferometer is proposed in this thesis.By changing the system parameters and adjusting the system structure,four different logic operations are achieved.Finally,an all-optical quantization and coding scheme based on Sagnac rings and optical limiters is proposed,the transmittance curves of the system at all levels are obtained by optimizing each parameters of the system.Then by selecting the appropriate quantization threshold,the realization of 4bit encoding is achieved.