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Investigation On Electro-Optic Organic/Polymer Optical Waveguide Modulator Visual Cortex

Posted on:2016-03-11Degree:DoctorType:Dissertation
Country:ChinaCandidate:J K LiaoFull Text:PDF
GTID:1108330482979904Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
With the rapid developments of wideband fiber optic communication technologies, the demands of high-performance optical waveguide electro-optic (EO) modulators are urgently increased due to the widespread applications. As an indispensable device in optic communication system, the modulator of high modulation rate is required in advanced networks, meanwhile the as low as possible VÏ€ and high stability are also expected for the modulator.Organic/polymer electro-optic materials have prominent advantages over inorganic materials such as low dielectric constant, large EO coefficient that they have promising potential to fabricate high-speed, low drive voltage EO modulators. Moreover, polymer EO materials are broadly applied in optical waveguide devices duo to the simple fabrication process, low propagation loss and low coupling loss with optical fiber. At present, organic/polymer EO materials have been successfully used in optical devices such as EO modulator, optical switch, tunable attenuator, optical filter and MI splitter etc., enhancing the performances of optical devices substantially.Besides being applied to optic communication systems, EO modulator is also used in advanced opto-electronic systems such as microwave photonics and optical phase controlled array radar systems. Generally, the unit modulator is used in optic communication system, while the arrayed device is demanded intensely in optical phase controlled array radar system. Organic/polymer EO materials are apt to realize planar and vertical integration of optical waveguide devices by spin-coating process, which is favorable for the fabrication of arrayed EO modulator.Considering the characteristics of organic/polymer materials, a novel Mach-Zehnder EO modulator with slope transition electrode is proposed to propagate broadband microwave signal in X band. Based on the results of synthetical design and simulation, the unit device of EO modulator has been fabricated successfully. The measurement indicates that the VÏ€ is 11.4 V. Furthermore, the feasibility of fabrication process for arrayed modulator is verified by organic/polymer EO materials.The main research work in the thesis is as follows:1. The dominent factors affecting propagation loss in organic/polymer optical rib waveguides are investigated, i.e., the mechanism of propagation loss involves absorption and scatter mainly. Also, the measurement system of propagation loss in organic/polymer waveguides has been established. The physical mechanism of optical activity of organic/polymer EO material is analyzed, and the principles and errors of simple reflection method to measure EO coefficients of polymer materials are studied. Moreover, the expression of EO coefficient with high precision is deduced strictly, and the measurement system of EO coefficient is set up successfully. A novel EO organic/polymer material FFC/PSU has been synthesized and characterized. The EO coefficient of FFC/PSU is as large as 130pm/V.2. The distributions of optical field and dispersion characteristics are analyzed for fundamental and higher order modes of organic/polymer optical rib waveguides. The distributions of optical field are analyzed by variational effective refractive index method. The dispersion characteristics are modified by vector wave equation considering the polarization of TE and TM modes. For Mach-Zehnder (M-Z) interferometer constructed by rib waveguide, the propagation characteristics of TM mode are analyzed by finite difference beam propagation method (FD-BPM). Moreover, operator expansion beam propagation method (OE-BPM) is applied to investigate M-Z interferometer waveguide in detail with fast speed. Based on the work above-mentioned, the structure parameters of M-Z interferometer are designed and optimized for the EO modulator operating in single mode.3. The propagation characteristics of microstrip line and coplanar line are studied, and the relationship between characteristic impedances and structure parameters is analyzed. After the simulation of the broadband transition from microstrip line to coplanar line, the specific structure parameters of high speed travelling wave electrode satisfying requirements are obtained. Meanwhile, a novel transition from microstrip line to coplanar line with slope is proposed to realize broadband transition. The simulation indicates that the performances of the electrode have been enhanced dramatically.4. The operation principle of organic/polymer M-Z OE modulator is discussed by its physical model, and the interaction between microwave and optical wave is investigated in detail. In the design of EO modulator, the performances have been analyzed and compared among rib waveguides and electrodes of different structure parameters to optimize the device.5. The fabrication processes and procedures of organic/polymer EO modulator are investigated by amounts of experiments. The low loss optical rib waveguide is fabricated by spin-coating, photolithography and reactive ion eatching. The thick Au electrode is fabricated by sputtering (evaporation), corrosion and electroplate. Careful research work has been conducted for poling process and stability to acquire as large as possible EO coefficient.In conclusion, the object of this thesis is the investigation of EO organic/polymer optical waveguide modulator. The main research work includes:1) A novel EO polymer material FFC/PSU is synthesized and characterized, the EO coefficient of which is 130pm/V; 2) Single parameter variational effective refractive index method with polarization modification is proposed to analyze the optical distributions and dispersion characteristics of optical rib waveguide, and the OE-BPM has been accelerated to shorten the computation time greatly; 3) A novel broadband slope transition from microstrip line to coplanar line is proposed to improve the propagation property of electrode, which enhances the modulation band of EO modulator obviously; 4) Based on the theoretical results above-mentioned, EO organic/polymer modulator and arrayed modulator are fabricated and measured to verify the validity and rationality of theoretical results.
Keywords/Search Tags:electro-optic organic/polymer, Mach-Zehnder electro-optic modulator, variational effective refractive index method, operator expansion beam propagation method, slope transition travelling electrode
PDF Full Text Request
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