Research On A Novel Wireless Receiving For Super-broad Band With Integrated Optical Waveguides

A conventional wireless receiver is composed of devices with different parameter structures to obtain various frequency bands. In this dissertation, a novel wireless receiving way with super-broad band by using a waveguide electrooptic modulator and an electric field sensor is investigated theoretically and experimentally. The optical intensity is controlled by an electric field component of the electromagnetic wave received by the E-field sensor after the guided optical wave is modulated by one-frequency microwave signal. Therefore, the connection of the optical modulator and the E-field sensor has brought about wireless receiving of microwave subcarrier with super-broad band. The principal work done in the dissertation is described in the following sections:Ⅰ. Research on LiNbO3 waveguide modulator A LiNbO3 waveguide is optimized with the modified FD-BPM. As a result, a Ti: LiNbO3 modulator with low loss and high extinction ratio has been achieved. Then, with the microwave-cavity model proposed by some scholars, the effects of modulator electrodes composed of different sections (including: input/output, tapers, bends, and active section) on the device transmission performance have been studied in the four aspects, including characteristic impedance, microwave effective index, microwave loss coefficient and electrode length. Also, the electrode bend effects on the device transmission performance and microwave loss coefficient are analyzed, and the influences of the active section on the microwave loss coefficient, half-wave voltage and microwave effective index have both been studied. To test the effect of different bend length on the electric transmission performance, the experiment has been done. As a result, the theoretical analysis is almost agreed with the experiment result. In addition, the influence of electrode transverse size on the transmission performance has been discussed and the comparison of two different methods for calculating device transmission performance is analyzed.Finally, the frequency properties of characteristic impedance of the modulator electrodes are analyzed with Finite Element Method for different structures, such as CPW electrode structure, ridge waveguide structure, structure with different electrode shapes, electrodes on LiNbO3 substrate with channel, and dual-driving electrode structure. Meanwhile, the effect of each structure parameter on the device performance has been discussed. Ⅱ. Reverse-poled LiNbO3 and its applicationThe refractive-index change produced by Ti-diffusion is analyzed using the methods of photoelastic and electro-optical tensor matrixes. It is shown that the two factors contributing to the refractive-index change are in the same level. Also, the refractive-index change in reverse-poled LiNbO3 is validated and discussed based on spontaneous polarization, and the result shows that it satisfies the conditions of Δne >0 and Δno >0. Meanwhile, the refractive-index change in reverse-poled LiNbO3 after proton exchange has been analyzed and concluded. In addition, the refractive-index changes for an E-field sensor in LiNbO3 without electrodes are studied in the two aspects of experiment and theoretical calculation.Then, a periodic phase reversal LiNbO3 modulator with reverse-poled waveguide has been obtained. In order to obtain large broadband, a novel traveling-wave modulator with nonperiodic domain inversions and ridge structure is proposed. The composite structure is designed to achieve velocity matching between the optical wave and the microwave, to get a 50 Ω characteristic impedance and to reduce the loss of the microwave electrodes with finite element method. The calculation results show that the frequency response of the new device is flat up to 350 GHz with interaction length of 1 cm, characteristic impedance of 49Ω, and microwave refractive index of 2.5. In addition, a broadband LiNbO3 modulator with low frequency chirp has been obtained by using the reverse-poled waveguide and ridge structure. The device performance is analyzed and...