The Research On Electro-optic Guided-Wave Analog-to-Digital Converter Unit Based On Lithium Niobate Substrate

The goal of the thesis is to design and fabricate a 2-bit electro-optic A/D converter based on computer simulation and experiments. The detailed analysis of the optical waveguide parameters, electrode optimization, electrooptic response and so on is performed.The waveguide parameters of the device are optimized by the Finite Difference Beam Propagation Method (FD-BPM) based on Lithium Niobate (LiNbO₃) substrate including abrupt bending waveguides and Y-branching waveguides. Based on the cosine bend branching waveguides, the parameters of 2-bit M-Z electrooptic A/D converter are designed. The waveguide parameters of 2-bit M-Z electrooptic A/D converter based on phase compensation microprims are also optimized.Based on a free SC tool from University of Delaware, the electrodes structure of the electrooptic A/D converter is anylized by confromal mapping method in detail. The simulating results show that the structures with low refractive index buffer layer in substrate, thick electrode can improve the performance of A/D converter in some degree. But these parameters have different effects on bandwidth, characteristic impedance and conductor loss. The tradeoff between bandwidth, characteristic impedance and conductor loss must be adopted in practical design to gain perfect modulation performance.The effect of velocity mismatch and transmission loss on output optical pulse, including pusle shape, amplitude, and width is quantitatively analyzed using Fourier transform techniques. The simulating results show that phase velocity mismatch will decrease the pulse peak, broaden the pulse width. While microwave attenuation only decreases the pulse peak, it does not broaden the pulse width. In addition, the frenquency reponse of the lumped-parameter electrode and traveling-wave electrode electrooptic A/D converter is discussed.The factors, such as transmission time of laser pulse, laser pulse width, the jitter of the sampling interval that has effects on the performances of the electrooptic A/D...