Basic Research On Electro-Optic Characteristics Of Poled Polymer Thin Films

Recently, with the rapid development of high-speed optical communication and all-optical networks, the higher requirements for optical communication devices and photonic integrated has been put forward. And the study of poled polymer materials has also been promoted greatly. The inorganic materials ,which are currently used, such as LiNbO3, III-V compound semiconductor materials(GaAs/GaAlAs,InGaAsP/InGaAs), silicon-based semiconductor materials(Si,SOI,SiO2), are difficult to meet the key requirments of high-speed, large capacity, wide-bandwidth, high-density for the actual system. In contrast, poled polymer materials have rised a wide concern of scientific researchers and businessmen because of their fast response speed, large electro-optic (E-O) coefficient, low dielectric constant, easy process and so on. Therefore, the study to the poled polymer is extremly valuable for research and applications on a wide range.Currently, the research on the poled polymers is mostly concentrated in their preparation, poling, and E-O testing. For different polymer systems, the methods of their preparations are also different, for example, the organic / inorganic hybrid E-O material which now attracts most attention is based on Sol-Gel method, while the host and guest doped E-O materials are just simple physical doping. As to the poling method of polymers, it has been developed from electrode-contact poling at first, to today's corona poling, all-optical poling, and auxiliary poling of light. The corona poling and contact poling are the two most widely used poling techniques. In the E-O testing, the focus is on measuring the E-O coefficient of the poled polymers. In recent years, there have been many ways for measuring the E-O coefficient of the poled polymers, such as Mach-Zehnder interferometer method, waveguide technology based on Fabry-Perot cavity method (F-P resonant cavity method), attenuated total reflection(ATR) method, secondary harmonic generation method (SHG method), and the simple reflection method. Compared with other methods, the simple reflection method is becoming a widely used measuring methods because it can be achieved more quickly and easily. Thus, the research on the test system and calculating method is particularly important. Firstly,the concept, main advantages and classification of poled polymer are introduced in this thesis. Secondly, the E-O effect of poled polymer is studyed, the method to enhance the E-O coefficient, and the principle and techniques of polarization. Then, the basic research focused on setting up and adjustment of the simple reflection system for measuring the E-O coefficient is carried out. And the formula for measuring the E-O coefficient of poled polymer is also deriveded and adjusted. Finaly, a kind of organic/inorganic hybrid E-O material via sol-gel method is analyzed by both theory and experiment. And the waveguide based on this material is fabricated and measured successfully. The main results are listed as follows:1. The simple reflection system for measuring the E-O coefficient of poled polymer is set up, and the calibration is placed on this system based on its principle. Then, we derived the formula of calculating the E-O coefficient for the single layer E-O material and the GaAs. Because of the error resulted from the testing system, we derived a adjusted formula for calculating the E-O coefficient of single layer E-O material.2. The formula is derived for calculating the E-O coefficient of two-layer film which contains one layer top caldding on the E-O film. And according to optical configuration of the laser beam propagation in this structure, the influence of impedance and dielectric constant of the top cladding at the AC modulated voltage is analysed, which is important for designing E-O devices such as E-O modulation, E-O switch and so on.3. With the testing system, we measure the E-O coefficient of poled polymer DR1/PMMA, and obtain stronger signals at the frequency of 30KHz and 50KHz. The accuracy for measuring E-O coefficient in the high-frequency is demonstrated. And we measure E-O signals in different frequencies at the range of 70KHz to 130KHz, and the EO coefficient is about 11.45pm/V at 1310 nm wavelengh which is measured by our system and formula adjusted. Thus, it proves that the testing system and the formula adjusted for calculating the E-O coefficient of the poled polymer materials are accordant.4. We synthesize a kind of silane coupling agent KH560-based organic / inorganic hybrid E-O material by Sol - Gel method. The reaction mechanism of hydrolysis and condensation of KH560 in the case of hydrochloric acid as a catalyst is analysed. Then we characterize the surface morphology, refractive index and E-O properties of the E-O thin films by means of atomic force microscopy (AFM), ellipsometry, and simple reflection method. At last, we obtain the poled polymer films that have good shape and alterable refractive index. The electro-optic coefficient is measured to be 3.5pm / V at the wavelength of 1310nm wavelengh based on the simple reflection method.5. By utilizing silane coupling agent KH560 as the silicon source, we successfully enhance the the flexibility of organic/inorganic hybrid E-O materials. According to the feature, we design the structure of the strip-loaded waveguide guided by the simulating results of the two-dimensional and three-dimensional light fields by the Opti-BPM software. After exploring the processing technology, we complete the fabrication of the waveguide with strip-loaded structure. Finally the near-field images of this waveguide are obtained by through the measurment system.