Investigation On Third-order Optical Nonlinear Characteristics Of Organometallic DMIT Compounds Composite Films

With the development of fiber to the home (FTTH) and next generation broadcasting (NGB), the optical fiber communication comes into its second climax after dense wavelength division multiplexing. Subscriber's increasing demand for network bandwidth, making the construction of all-optical networks become increasingly urgent. In all-optical network, date signals in transmission and switching unit are all optical signals. Switch is no longer on the handling of user information carried by bit, but realized through wavelength routing device. All-optical networks with good transparency, high processing speed, low error rate, good compatibility and scalability will become first choice for next generation communication networks.As the key device in all-optical networks, all-optical switching (AOS) can be realized in all-optical layer routing, optical cross-connecting and optical self-healing protection and other important functions. Nonlinear refraction optical switch based on Mach-Zehnder interferometry is the use of optical Kerr effect, control the light beam caused by nonlinear refractive index changes, in order to achieve optical switching action. All-optical switching (AOS) devices with excellent performance require materials to have large third-order nonlinear refractive index, small linear absorption and nonlinear absorption. With the rapid development of high energy laser technology, the development of effective protective devices has become the urgent issue in grasping the initiative in modern war and in laser equipment protection. Compared to earlier devices, the new generation optical limiting (OL) devices take the advantage of third-order nonlinearities, such as reverse saturable absorption, two-photon absorption and so on. It has a fast response, wide-band protection, low limiting threshold and high damage threshold advantages.At present, the research of nonlinear optical (NLO) devices such as AOS and OL devices making the exploration of NLO properties become the focus of nonlinear materials research. Therefore, the precise characterization of third-order NLO is significant to explore materials, optimize materials to satisfy the requirement of optical devices. The results of a serious of experiments researched by our group indicated that the organic metal complexes DMIT materials have large conjugate structure prone to be polarized and transfer charge between metals and organic systems can further enhance material's third-order NLO properties. Therefore, NLO properties of three novel DMIT polymer composite films were studied and analyzed. My main work is as follows:Firstly, according to the demands of AOS and OL devices, we synthesized two novel DMIT organometallic compounds:PrCu, TPEPADT and a multi-thione derivative material:BBDT, and doped them into poly methyl methacrylate (PMMA) to prepare composite films by spin-coating and sol-gel methods. The third-order NLO properties of the PrCu and TPEPADT were first reported.Secondly, with the prism coupling method and transmission spectroscopy of polymer composite films, linear optical properties such as refractive index, thickness, absorption coefficient and extinction coefficient of three composite films were calculated and characterized; NLO properties of TPEPADT, PrCu and BBDT in acetonitrile solution and PMMA composite thin films were studied by Z scan technique at 1064 nm. The results show that, TPEPADT and PrCu solutions and PMMA composite films exhibit defocus effect and their nonlinear refractive indices were negative, PrCu has a slight two-photon absorption; BBDT solution and PMMA composite films show focus effect and its nonlinear refractive index is positive. In order to explore DMIT material's laser limiting effect, we investigated OL properties of PrCu solution at 1053 nm, the results show that two-photon absorption of PrCu in acetonitrile lead to a good laser limiting effect the near infrared waveband; we explored third-order NLO properties of PrCu sol-gel films..Thirdly, through investigating and studying third-order nonlinearities of TPEPADT, PrCu and BBDT solutions and polymer composite films at the wavelength of 1064 nm using Z scan technique, we discovered a series of conclusions:laser pulse width (1064 nm, the pulse width of 20 ps) is small, repetition rate (10 Hz) is low, the heat effects can be neglected. The large nonlinear refractive indices of three materials are from the structure of largeπ-electron conjugation; the NLO refraction and absorption properties of TPEPADT, PrCu and BBDT in solutions and polymer composite films were compared, the reasons of their difference were discussed, and their potential applications in AOS were evaluated.This work was supported by the National Natural Science Foundation of China (Grant No.:60778037 and 11004123) and the Foundation for the Author of National Excellent Doctoral Dissertation of P. R. China (No.200539).