The Reseach Of Spectral Compression Based On All-optical Quantization

With the continuous development of the science technology, digital signal process is present in every aspect of our life because of its many advantages. The application of digital signal processing technology has revolutionized modern communication and radar systems, highly digitalized, and greatly improved the signal’s transmission and processing capabilities. While people’s expectation of DSP getting higher, the wider bandwidth and higher sampling rate are required. But the traditional electronic ADC, due to the electronic bottleneck, fails to satisfy the requirement of the high speed and resolution. Consequently, all-optical ADC attracts widespread attention, as a method of breaking through the bottleneck of electronic ADC.This thesis’ s emphasis is to explore a new spectral compression method, which is based on the nonlinear optical loop mirror scheme, in order to improve the quantization accuracy of the soliton-self-frequency-shift-based-all-optical-quantization scheme. The feasibility of the scheme has been verified by numerical simulation and experiment. The main contents of the thesis are shown as follows:1. Introducing the photonic ADC’s development statues and its application, making an overview of the discovery of soliton self-frequency shifting and its development in all-optical quantization.2. The generalized nonlinear Schrodinger equation applicable to the pulse’s propagation in optical fiber is derived from the Maxwell equations. The split-step Fourier method, the mostly used numerical method to analyze the GNLS equation, is briefly introduced. Besides, the nonlinear effects, when pulses transmitting in optical fiber, are introduced, and the soliton-self-frequency-shift is emphatically elaborated.3. From the basic principle of the NOLM, the design of NOLM-based spectral compression scheme has been done. Researching the capability of this spectral compression scheme by numerical simulation, the results indicates that the spectrum width of 300 fs hyperbolic secant pulses without chirp can be compressed to about 1.59 nm, achieving the result that the compression ratio is 5.4 by changing the peak power of the initial pulses. Changing the length of SSMF and parameters of the NOLM, we can reduce the sideband(or pedestal),and achieving the results that the sideband energy ratio and spectrum width are 9.39% and 1.6 nm, respectively. In the experiment, considering the factors of sideband energy ratio and compression ratio, 1.52 nm of the spectrum width and 6.53 of the compression ratio are obtained, by compressing the sub-picosecond pulses form NPR mode-locked laser.4. Researching for the two-stage spectral compression numerically with NOLM, the pulses are defined as 200 fs hyperbolic secant pulses without chirp. Connecting the NOLM after different DIFs, we get the results that the spectrum is compressed further when soliton number equaled to 0.5、1、1.4, respectively. Connecting NOLM after the HNLF with anomalous dispersion, when it is HNLF in NOLM, improving the compression ratio from 7.33 to 11.9; when it is DSF in NOLM, achieving the result that the compression ratio can reach 46.67.