Research On Several Key Technology Of High Speed All-optical Analog-to-digital Conversion

With the rapid development of science and technology,the human society has stepped into the era of mass information.The digital signal processing system with higher performance and more stability is playing an increasingly important role in information processing.However,in the nature,most of the signals exist as analog signals.Analog-to-digital converter(ADC),as a bridge between analog and digital signals,is a very critical and indispensable front device in digital information system.All-optical analog-to-digital conversion(AOADC)directly digitizes analog signals in the optical domain,solving the inherent electronic bottleneck of traditional electronic ADC,so as to obtain digital performance with higher rate,wider bandwidth and higher stability than that of electronic ADC.However,from the current research and research results of AOADC at home and abroad,there are still some key problems need to be solved,such as,how to take into account ultra-high speed sampling rate,broadband width and high quantized resolution;how to realize low power consumption,integration and miniaturization of devices.Aiming at the problems existing in AOADC,this paper focuses on nonlinear optical effect and electro-optical modulation technology,and makes an in-depth study and analysis of the AOADC that can be integrated and has high performance.The main research contents and innovative research r-esults can be summarized as follows:1.An all-optical demultiplexing scheme based on FWM with chirped pump and multicast parametric in real time with double pump are proposed.By using a MLLD pulse source with a repetition rate of 10 GHz to sample the OTDM signal multiplexing of RZ-OOK with a rate of 10Gb/s,a resolution rate of 160 GSa/s is obtained.The demultiplexing ratio is up to 16 times.Compared with the traditional all-optical sampling scheme,the scheme greatly improved the efficiency of multiplexing,reduces the stringent requirements for MLLD pulse repetition rate and reduces the number of broadcast for parametric broadcasting.2.Comparison of several typical silicon based waveguide structure are carried out by simulations and the results show that the horizontal slot waveguide has more robust light confinement ability.Then,the advantages of horizontal slot waveguide on dispersion and nonlinearity is analyzed and a chalcogenide silicon slot waveguide with small effective mode field area and high nonlinear coefficient in As2S3 is designed.The mechanism of all-optical quantization with SSFS effect is introduced and a scheme of all-optical quantization based on As2S3 slot waveguide at the wavelength of 1550 nm is proposed.Numerical simulation of the proposed scheme is implemented,simulation results show that,when the hyperbolic-secant pulse with input pulse width of 100 fs and peak power of 21.4 W is used,the frequency shift of 425 nm can be achieved by using the As2S3 waveguide with a length of 6 cm.For a 4-bit quantization scheme,the ENOB is calculated to be 3.29-bit.The ENOB can be improved by spectral compressing after SSFS.Supercontinuum generation and its application in AOADC at mid-infrared region in AlGaAs strip waveguide are numerically investigated.Owing to the high nonlinear coefficient of the III-V waveguide at the mid-infrared region in this scheme,the input pulse peak power will be reduced to reach the appropriate SCG for low power consumption and integrated quantization scheme.The generated SC with high coherence can be used in the application on AOADC to reduce the coding error and enhance the ENOB.The simulation results show that,as the input pulse,compared with hyperbolic-secant pulse and gaussian pulse,the parabolic pulse not only has advantage in broader and higher coherence of SCG,but also has a higher ENOB of AOADC.For a 4-bit quantization scheme,a AlGaAs strip waveguides with the length of 1 cm is used and the pump center wavelength is 3 ?m at the normal dispersion region,in addition,the pulse width is 100 fs and the input power is 200-760 mW.For the parabolic pulse,hyperbolic-secant pulse and gaussian pulse,the ENOB is 3.99-bit,3.87-bit and 3.93-bit,respectively.To M-bits {M>4)quantization scheme,the advantages of the parabolic pulse will be more obvious.The modulation principle of the MZ electro-optic modulator is studied,and a new all-optical quantization scheme with cascading UMZMs is proposed.In this scheme,the theory of cascading UMZMs in the quantization scheme is firstly analyzed,and then the factors that may affect the quantization performance of the quantization scheme are discussed.It can be seen from the theoretical analysis that,when the number of input pulses M is the same,the resolution of traditional phase-shifting quantize-tion scheme is log2(2·M),while the resolution of this scheme can reach log2(2·M·T),where T is the number of periodic multiplication after cascade UMZMs.In this scheme,the 5-bit quantization resolution can be achieved by using 4 input pulses and 4 UMZMs,the ENOB is 4.86-bit.The proposed cascade quantization scheme provides more possibilities for achieving high resolution of AO ADC.3.A coding scheme of AOADC based on polymer material waveguide structure is studied.Firstly,several common coding schemes are compared and analyzed.However,they cannot meet the development trend of integration and miniaturization.A new waveguide branching structure similar to F-type is designed by combining EIM and FD-BPM.The waveguide splitter structure uses the organic polymer material,so it is easier to process,has good compatibility,and has low loss;the cross section of the brancher selects a ridge structure which is more easily coupled.The simulation results show that the two output ports of the splitter structure have a split ratio of 1:1.The encoding structure was designed by using the straight waveguide,curved waveguide and the F-type branching structure.And the encoding structure was applied to the all-optical quantization scheme based on SSFS.The simulation results showed that the encoding effect of the encoding structure was good,and the ENOB of the whole quantization and encoding scheme could reach 3.91-bit.