Raman Self-frequency Shift Of The Pulse Width Of The All-fiber All-optical Quantization Compressor Design

Raman-self-frequency-shift-based (RSFS) high-speed all-optical analog-to-digital converters (ADC) need sub-picosecond sampling pulses for large frequency shift in order to achieve high resolution. Therefore, the pulses with the picosecond pulse-width from the mode-locked laser need to be compressed to realize higher quantization performance. All-fiber pulse-width compressors using the combination of the nonlinear effects and the dispersion effects in the optical fibers are good candidates to realize the above-mentioned purposes because of its compact structure and low loss etc.In this thesis, the interaction between the self-phase modulation (SPM) and the group velocity dispersion(GVD) in the nonlinear optical fibers is studied firstly, and then two kinds of all-fiber pulse-width compressors using single-stage comb-like dispersion fibers and anomalous dispersion varying fiber respectively are designed, both of which can be used in the Raman-self-frequency-shift-based all-optical analog-to-digital converters. The evolutions of the optical pulses in both of the compressors are simulated through numerically solving the generalized nonlinear Schr?dinger (GNLS) equation using the symmetrized split-step Fourier method, and the system parameters making both of the compressors useful for the above-mentioned analog-to-digital converters are given. Finally, the influence of the third-order dispersion on the compressor performance is analyzed.Simulation results show that, for the all-fiber pulse-width compressor using single-stage comb-like dispersion fibers, two kinds of fiber combination can achieve the pulse-width compression from 2 ps to 300 fs and 200 fs for the Gaussian pulses, which can greatly enhance the performance of the ADC. The compressor composed of high nonlinear fiber (HNLF) and polarization maintaining fiber (3M-FS-PM-7811) requires low incident pulse power, but has a larger pedestal in the output pulses. And the situation is the reverse for the compressor composed of HNLF and SMF-28 fiber. For the soliton-effect-based compressor using anomalous dispersion fiber (ADF), the performances of two-type fibers are also investigated. Compared with the anomalous dispersion-increasing fiber (AD-DIF), the anomalous dispersion decreasing-fiber (AD-DDF) achieves a larger compression ratio but leads to a larger output pulse pedestal, and the minimal pulse is realized when the GVD of the fiber is reduced to zero. Compared with the all-fiber pulse-width compressor using single-stage comb-like dispersion fibers, the one using AD-DIF outputs pulses with symmetrical pedestals.