| With the appearance of the 3G era and the integration of telecommunications networks, cable television networks and the internet, the demand for bandwidth is greater and greater, so the high-speed broadband integrated service network has become the development trend of the modern communications network. As the signal transmits in all-optical network is in optical domain, therefore, all-optical network has the advantage of the transparency of the signal and achieves the routing selection through wavelength routing device. All-optical network becomes the first choice of the next-generation high speed (ultra-high speed) broadband network for its good transparency, wavelength routing feature, compatibility and scalability.As the key device of all-optical networks, all-optical switching can realize the functions of routing selection, wavelength selection, optical cross-connect and self-healing protection in all-optical layer. At present, the nonlinear optical material which is suitable for all-optical switching hasn't been found yet, hence its investigation has increasingly become the focus of the all-optical communication field.The principle of all-optical switching is taking advantage of the third-order nonlinear optical effect of materials, namely optical Kerr effect. With a control beam inducing the change of refractive index of materials, the other signal beam transmitting in the material will produce an additional phase difference, therefore to realize the function "on" and "off"of optical switching. All-optical switching devices require materials with high third-order nonlinear refractive index, lower linear and nonlinear absorption and faster response time.Therefore, the precise characterization of third-order nonlinear optical properties is significant to explore materials, optimize materials to satisfy the requirement of optical devices.My main work is as follows:Firstly, according to merit factors W(w=n2I/a0λ)and T(T=βλ/n2)of material which is suitable for all-optical switching, we designed and synthesized two materials with conjugation of theπelectron, one is multi-thione derivatives material 4,5-bis(benzoylthio)-1,3-dithiole-2-thione (BBDT) and the other is metal-organic material hexadecyltrimethylammonium bis(1,3-dithiole-2-thione-4,5-dithiolato) aurate(III), (CtAu).The third-order nonlinear optical properties of the CtAu material were first reported.In order to provide theoretical and experimental evidence for the device design, We mixed BBDT and CtAu with polymethyl methacrylate (PMMA) which has the advantage of high glass transition temperature, excellent optical transparency, ease of film forming polymer. We prepared CtAu/PMMA, BBDT/PMMA composite film by spin-coating method.Secondly, the linear refractive indexes and thicknesses of polymer composite film BBDT/PMMA and CtAu/PMMA were characterized by quasi-waveguide method. Quasi-waveguide method is developed from plane light wave interference theory and the Mie scattering cluster theory. The method is convenient and with high accuracy which only needs angle measurement. The nonlinear refraction and absorption properties of BBDT and CtAu solution and polymer composite film at the wavelength of 1064 and 532nm were characterized and studied using Z scan technique. Z scan technique is based on the principle of special fundamental mode Gaussian beam distortion, which measures the nonlinear optical properties of materials using the horizontal effect of fundamental mode Gaussian beam. The nonlinear refractive index, nonlinear absorption and third-order nonlinear susceptibility of the two materials can be calculated by fitting the data we got from closed aperture and open aperture Z scan experiment. The results show that BBDT solution and BBDT/PMMA exhibit self-focusing property and CtAu solution and CtAu/PMMA exhibit self-defocusing property.Thirdly, by characterizing and studying the nonlinear refraction and nonlinear absorption of BBDT and CtAu solution and polymer composite film at the wavelength of 1064 and 532nm using Z scan technique, a series of conclusions are as follows:Laser pulse width (20ps when wavelength is 1064nm,14ps when wavelength is 532nm) is small and repetition rate(lOHz) is low, so thermal effects can be neglected. The nonlinear refractive indexes of two materials are from the structure of largeπ-electron conjugation.The third-order nonlinear susceptibility of CtAu material is larger than BBDT because of the introduction of the metal atom, which results in the charge transfer state of metal to the ligand and ligand to metal.The third-order nonlinear susceptibility at the wavelength of 532nm is larger than that at the wavelength of 1064nm because of the nonlinear absorption at the wavelength of 532nm. The nonlinear optical coefficient of the film is larger than that of the solution because of the surface local field enhancement.The nonlinear optical coefficient increases as thin film doping concentration increases. The response time of CtAu/acetonitrile solution with the concentration of 1.O×10-3mol/L is measured to be 195fs.Short response time and large nonlinear susceptibility showed that these materials are promising photonic materials.The study is supported by the National Natural Science Foundation of China (Grant No.60778037) and the Foundation for the Author of National Excellent Doctoral Dissertation of P. R. China (Grant No.200539).
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