High Precision Optical Quantitative Method Research

The advantages of digital technology in signal transmission and processing have encouraged rapid developments in VLSI circuit. In a highly-digitalized world, analog-to-digital converter (ADC) with high performance has become the key device in digital-signal-processing area. In recent years, advancements in digital-signal-processing technology require wider bandwidth and higher sampling rate of ADC. Due to its inborn limitation of electronic mobility, traditional electronic ADCs fail to satisfy the high speed and high resolution requirements for future applications. As a potential candidate to circumvent the problem, all-optical ADC can obtain high sampling rate. However, how to achieve high resolution remains a problem for all-optical ADC.In this thesis, a soltion-self-frequency-shift (SSFS)-based all-optical quantization scheme and several spectral-compression-based resolution-improvement methods were briefly introduced. Then two spectral-compression methods and their use in all-optical quantization were explored. Firstly, the spectral-compression method in comb-like profiled fiber (CPF) and in comb-like dispersion-profiled fiber (CDPF) were given, which were derived from adiabatic soliton propagation in dispersion-increasing fiber. Based on the average soliton propagation theory, a CPF with highly nonlinear fiber and single-mode fiber (SMF) were designed. Simulation results showed that, with the CPF the spectrum of250fs pulses in the wavelength range of1550nm～1670nm can be compressed to about1.2nm, indicating a resolution of6.4bits for all-optical quantization system. In experiments, a CDPF composed of dispersion-shifted fiber and SMF was sliced, with which the spectral width of a NPR passively mode-locked fiber laser can be compressed from9.6nm to6.7nm. The CDPF was applied to the experiment of quantization, where a resolution of4.11bits was obtained.At last, a spectral-compression method of frequency-shifting pulses was proposed, which is based on pulse SSFS effect and fiber third-order dispersion (TOD). Spectral compression can occur in anomalously-dispersive fiber with positive TOD. Simulation results were given, where a spectral-compression ratio of2.7was obtained. Analytic equations were derived and showed that the spectral-compression ratio is strongly dependent on the TOD value. With this method, the pulse spectrum can be compressed simultaneously with its center-wavelength shift. One can apply it as initial spectral-compression step in the SSFS part of all-optical quantization system.