Investigation Of High-speed Electro-optic Modulator Based On Polymer

Electro-optic (EO) modulators are the key devices in large-capacity and high-speed fiber communication system. Electrical signal is loaded to optic signal via EO modulator, so optical communication is realized. Recently, with the popularization of computer and development of information industry, the amount of data transmitted by network increases rapidly. The new generation of optical network based on wavelength division multiplexing (WDM) systems achieves that single fiber can transmit multichannel signals, which breaks through the limit of optical fiber transmission systems capacity. So the speed of EO modulator becomes the constraint in high-speed optical communication. Polymer materials possess characteristics such as low permittivity, high response speed, large EO coefficient, low cost, easy process and so on. EO modulator based on polymer material has a competitive advantage of high speed, anti electromagnetic interference and conducive to large-scale integration. So it becomes the research focus gradually.The main work of this thesis focuses on the investigation of high-speed EO modulators. The content and innovations of this thesis are listed as follows:The significance of modulators in optical communication and several applications of EO modulators are expatiated. The progress of polymer EO modulator is introduced. Different materials for EO modulator are contrasted in performance. The advantages of polymer EO modulator in high-speed optical communication are explained.The theory of EO modulation is expounded in detail. The configuration and principle of M-Z (Mach-Zehnder) interferometer and directional coupler are introduced. Considering the experiment and test of polymer EO modulators, the relation between output modulation waveform and direct current bias voltage is analyzed. When the direct current bias voltage changes from 0 to 2Vπ, the characteristic of output modulation waveform is discussed. The causation of side lobes phenomenon during testing process is explained. Several Vπ-testing methods via direct current bias voltage are introduced.The strip-loaded waveguide and quasi-rectangular waveguide based on SU-8 material is designed. The field distribution of the fundamental mode in waveguide is calculated when the width and thickness of the strip core are 4μm and 3μm, respectively, and the thickness of the EO layer is 0.5μm. The Y-branch waveguide of the modulator is optimized utilizing BPM (Beam Propagation Method) software. When the span of the Y-branch is 20μm and the length of Y-branch is longer than 2000μm, the bending loss of Y-branch can reach 0.03dB. The M-Z modulator with directional coupler branch is designed. When the length of the coupling area is 926.5μm, the optical power can realize 1:1 distribution ratio. The M-Z modulator with nonsymmetrical Y-branch structure is designed. When the spans of the two branches are 20μm and 27.5μm, respectively, the modulation is located at the linear operating point. That means the modulator can achieve linear modulation without direct current bias voltage. The relative photo-masks of waveguides and electrodes are designed according to the configuration of EO modulators. We analyzed the effect of multiple electrodes structure to the performance of the directional coupler electro-optical modulator based on coupled mode theory. The relationship between multi-electrodes is presented and the status curves equations with multi-electrodes are found.The preparation process of organic/inorganic hybrid material is introduced. Polyvinyl alcohol is added to improve the mechanical properties of the film. The thickness of the film increases from 0.5μm to 0.8μm. The preparation process and test system of polymer EO modulator are introduced. The sample of nonsymmetrical M-Z modulator is fabricated and tested.