Studies On Several Key Technologies Of All Optical Analog-to-digital Conversion

As the interface between the analog signals and digital ones, analog-to-digital converter (ADC) is a key device in lots of systems. However, with the fast development of digital signal processing technology, the electronic ADCs are now becoming a bottleneck in many applications with extremely high bandwidth requirement. All optical analog-to-digital conversion makes use of photonic technologies to sample and quantize the electrical analog signal, which has the potential to realize high sampling rate and high resolution at the same time. It is a promising technology to break through the bottleneck of electronic ADCs. This thesis studied several key technologies of all optical analog-to-digital conversion, including phase-shifted optical quantization, sampling optical pulse train, and optical spectral encoding.In this thesis, phase-shifted optical quantization is theoretically analyzed and experimentally studied, which can realize optical quantizing and encoding using only one electro-optic modulator. It has great feasibility to realize all optical analog-to-digital conversion. Three new schemes are presented in this thesis, including phase-shifted optical quantization using fiber squeezers, dispersion effect in a phase modulator and dispersion effect in an unbalanced M-Z (Mach-Zehnder) modulator. Experiments are carried out for the two former schemes, measuring their continuous waveforms of 16-channel phase-shifted optical quantization, and obtaining resolutions of 4.42 and 4.3bits for 2.5GHz electrical sinusoidal signal, respectively.The influence of nonideal optical sampling pulses on the performance of all optical analog-to-digital conversion is studied, including the timing jitter, amplitude fluctuation, and limited pulse width. 11ps stable mode-locked optical pulses are obtained, which can realize sampling rate of 40GS/s with time division multiplexing technology. Time- and wavelength- interleaved sampling pulse train are experimentally achieved, with a high repetition rate of 40GHz. To realize a potential high sampling rate of 100GS/s, 5.1ps optical pulses are also experimentally demonstrated.System experiments of all optical analog-to-digital conversion are carried out. Sampling rate of 40GS/s is realized through time division multiplexing and time- and wavelength- interleaving. 2.5GHz electrical sinusoidal signal is sampled and quantized through 8-channel phase-shifted optical quantization, respectively, obtaining a resolution of 3.68 and 3.45bits. Pre-compensation technology is proposed, which can dramatically improve the bandwidth of optical analog-to-digital conversion. An improvement of phase-shifted optical quantization is also presented.Spectral encoding all optical analog-to-digital conversion technique is studied in this thesis. A novel approach to realize spectral encoding is presented, using the tunable filtering characteristic of cascaded unbalanced M-Z modulators with doubling path imbalances. Different amplitudes of electrical analog signal will be linearly converted to different transmitted peak wavelengths of the cascaded modulators. Without requirement of any nonlinear effects, this presented scheme can break through a serious limitation of the formerly proposed spectral encoding schemes.