Study On High Resolutionoptical Sampling Technique For Optical Analog-to-Digital Conversion Systems

Analog to Digital Converter (ADC) is one of the important signal processing devices. It converts analog signal into digital signal to ensure easy signal storage and processing, providing an effective way to explore the real world. Although the performance of electronic ADC has been continuously improved in recent years, it still cannot meet the requirement of ultra-wideband systems. Due to the limitation arising from the so-called "electronic bottleneck" on main factors such as the dithering of sampling clock, it meets great challenge to further enhance the performance of electronic ADC.Photonics has many advantages such as ultra-wideband, high speed, high stability, etc. It provides an alternative method to improve the bandwidth and precision of ADC. In recent years, many systems of photonic ADC have been proposed to improve sampling rate, bandwidth, precision and resolution. Among them, high-resolution photonic ADC is expected to play important role in some applications. It may be implemented by combining the advantages of photonics (such as ultra-wideband and high stability) and electronics (such as with mature technology).This thesis mainly studies high-resolution optical sampling technique for phase-encoded photonic ADC system. The theory of the optical modulation scheme is analyzed. The basic principle and signal processing methods of dual-port push-pull MZ modulator are investigated. The nonlinearity caused by the asymmetry of the internal structure and the drift of the bias voltage is theoretically studied. Subsequently, a linearity correction method using the extinction ratio of the output ports is proposed, which is validated via simulation and experiment.The thesis also studies the correction of the intensity noise of the optical pulse in phase-encoded analog-to-digital conversion system. The theoretical analysis of the noise elimination is given and the relative experiment is carried out. After noise elimination, a 4.45-bit effective number of bits (ENOB) with 4.66-Gs/s sampling rate is successfully achieved in a system whose ENOB is only 3.02 bits. Some other factors limiting the ENOB of current system are also investigated.Finally, the thesis improves the numerical simulation of mode-locked ultra-short optical pulses based on the work already carried out in our group. The results show that the simulated femtosecond optical pulse sequences agree well with the actual laser both in frequency domain and in time domain. The impacts of timing jitter, amplitude fluctuation and pulse-width variation are also analyzed. Software of femtosecond pulse sequence generator with key parameters configurable is designed.