| Recent years, the rapid development of optical communication brings on the development of the research of photo-electronic materials and devices. Electro-optical polymer composite thin film with some nonlinear chromophore dopants have many excellent advantages, such as intrinsic low dielectric constant, rapid responsibility, ease of processing into thin films and compatibility with microelectronic devices, so they can be fabricated into electro-optic waveguide switches and modulator/demodulator. Especially due to the fast responsible characteristics of the nonlinear optical (NLO) polymers, it is a promising material in the wavelength-division multiplexing (WDM) all-optical communication network.EO merits Fm(Fm =n3γ/εr, where n is refractive index,γis electro-optical coefficient,εis dielectric constant) and transmission loss are the key parameters to characterize the polymer films. The material is better when it has larger EO merit and smaller transmission loss. This requires that the material has high EO coefficient, large refractive index, and low dielectric constant. So it is very important to setup some proper methods to research these properties of the films, because they can guide the design of the materials and the devices.Disperse Red 13(DR13)/poly-(methylmethacrylate) (PMMA) is a guest-host polymer system. The guest chromophore molecule DR13 is a highly conjugated molecule and a widely developed azobenzene dye, which has many advantages such as good dissolvability, ease of composition with polymer, and large electric-induced anisotropy. The host polymer PMMA is a highly transparent polymer whose glass transition temperature (Tg～105℃) is relative high and it has some other advantages, for example, excellent compatibility with guest NLO organic molecules and normally having no strong interaction with organic molecules.Lead lanthanum titanate (PLT) compounds is a kind of ferroelectric material which has received much recent attention for its applications in nonvolatile memory, optical switches, passive and active waveguides in integrated optics, piezoelectric devices and pyroelectric detectors. These materials typically yield large values of linear and quadratic electro-optic coefficients. PLT nano-crystal is used as guest chromophore and mixed with PMMA to form another guest-host polymer system. This composite thin film obtained large electric-induced anisotropy by poling and has large refractive index n, low dielectric constantεand good film quality, it is a promising EO material.The composite thin films were prepared onto indium-tin-oxide (ITO) glass substrate (n=1.51637 atλ=589.3nm) by a spin coating technique and poled by corona-onset poling at elevated temperature (COPET).All the work we have done include:I. The refractive indexes of the DR13/PMMA polymer composite films were investigated by the quasi-waveguide coupling technique. The quasi-waveguide coupling technique only requires angle measurement, which is convenient and very accurate. But it has its own limitations, i.e., it requires that the refractive index of the sample must be larger than that of the substrate. It is difficult to satisfy this requirement for some samples whose refractive indices are low. The thicknesses of the DR13/PMMA films are about 1-2μm, the error amounts of thickness and refractive index of the films are about 3.2×10-1μm and 1.5×10-3. It can be seen that at the same input laser wavelength, the refractive index becomes greater as the weight ratio increases, and when the wavelength of the input laser increases, the refractive index of the same weight ratio reduces.II. Some optical properties of inorganic/organic composite thin film were studied by transmittance spectrum method. Ultra-fine PLT (～40-50nm) nano-crystals with pure perovskite tetragonal phase were synthesized by a sol-gel method. It is mixed with PMMA and prepared into PLT/PMMA composite thin film. Some optical constants including the absorption coefficientα, the extinction coefficientκ, loss factor tanδand the real and imaginary parts of the complex dielectric constant,εr andε, were obtained using the data from the transmittance spectrum. The calculation using the data of the transmittance spectrum of the PLT composite film was simple, fast and very accurate by the computer. But it has high requirements on the film quality, the film sample should be homogeneous and parallel-faced.III. According to the video camera method proposed by Okamura et al., a new experimental apparatus for measuring transmission losses in the thin-film wave-guides was set up. It includes a prism-coupling system, a digital camera and corresponding image-processing software. We use this setup to investigate the transmitting characteristic of polymer composite thin film. The amounts of the transmission losses of three different weight rations (10%, 15% and 20%wt) are 1.5269, 2.7601 and 3.6291dB/cm, respectively. Transmission losses of PLT/PMMA composite thin film were also investigated, the amounts of three different weight rations (5%, 10% and 15%wt) are 1.986dB/cm, 2.971dB/cm and 3.752dB/cm, respectively. So we can see that the transmission loss increases as the weight ratio increases, that is, DR13 and PLT are more important for the transmission loss than PMMA, because more DR13 or PLT can induce larger scattering. The method eliminates the impacts of surroundings and the laser instability. The use of the scale ensures the accurate measurement of transmission length and its measurement scale is very large (0.5dB/cm～100dB/cm).IV. At last, we derived the relatively accurate equation for the linear EO coefficientγ33 of simple reflection technique and measured the EO coefficient of DR13/PMMA composite thin film at three different concentrations (10%, 15% and 20%wt) with simple reflection technique. When we calculated the difference of optical length and phase difference between s wave and p wave caused by the modulated electric field, we dealt with the two refractive anglesαs andαp more reasonably. The simple reflection technique has some advantages, such as, it is simple to prepare the film and need no waveguide, so it is especially suitable to materials that have weak absorption and large transmission loss. However, this method has certain limitation because the birefringence is ignored andγ33 is considered to be equal to 3γ13.All of above measurements estimate the properties of the films completely and accurately, they can not only guide the design and preparation of materials but also guide the design and manufacture of devices.
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