| The demand for the capacity and speed of communications increases rapidly as our society has entered the information age. The traditional radio communication cannot satisfy the demand completely. As a representative of the optical communication technology, optical fiber communication technology has been widely used because of its high transmission rate, large information capacity, small transmission loss, strong anti-jamming ability, good confidentiality and resources saving. However, in the present optical fiber communication system (OFCS), optical signal and electrical signal must convert to each other at both the sending and receiving terminals. These photoelectric conversion devices have some disadvantages such as slow switching speed, serious crosstalk and high power loss which influence the signal transmission speed and lead to the "bottleneck" of the OFCS. In order to break the "bottleneck", people have put forward the concept of "all-optical network". In it the information transmission speed is improved greatly because pure optical devices are used to realize the information transmission, regeneration, optical cross connect (OCC), optical add and drop multiplexing (OADM) and exchange/routing without any photoelectric conversion devices. All-optical switch (AOS) is a key device for OCC, OADM as well as for wavelength exchange, therefore AOS is an importance kind of device in all-optical network.While submarines becomes an important part of national military weapon system because of its ability of covert activities and sudden attack, its capability for underwater communication and detection are poor. Reliable communication cannot be obtained by using radio communication or audio channel. The wavebands used in blue and green light communication as a kind of optical communication is450～700nm region. The absorption loss of the light in this band is very low in sea water, so the penetration and direction are excellent when blue and green light goes across the sea water. Blue and green light communication has become a predominant means for information exchange between the ground and submarines. However, in blue and green light communication, optical signal needs to be first modulated by electrical signal of the transmitter to carry the required information. At the receiver side, the optical signal is demodulated by the electrical signal again through optoelectronic detector, thus the "bottleneck" still existing. It is demanding to develop AOS which can be applied in blue and green light communication.A noticeable type of AOS aims to take advantage of the third-order nonlinear optical (NLO) properties of materials. Its work principle can be described as follows: with a control beam inducing the change of refrative index of materials, the other signal beam transmitting in the material will produce phase change to realize the function "On" or "Off" of optical switches. Researchers seek not only innovative technologies and structures but also novel materials to implement such kind of AOS. Up to now, people have not discovered ideal materials whose performance is perfectly suitable to prepare AOS devices. It appears to be fundamentally important to explore and synthesize novel NLO materials. Two quality factors:W=n2I/α0λ and T=βλ/n2are used to analyze the suitability of a material for application in AOS, where n2is the third-order nonlinear referative index,I the laser intensity, α0the linear absorption coefficient, λ the wavelength, and β is nonlinear absorption coefficient. To make practicable AOS, NLO materials must satisfy|w|>> and|T|<<1. Therefore, the NLO materials should possess large third order nonlinear refractive index, low linear and nonlinear absorption coefficients, fast response speed and stable physical and chemical properties at the operating wavelength. The first element can reduce the power density of control light and avoid damage to the device. The second one can reduce the information transmission loss and weaken the thermal effect. The third can increase the switching speed and the fourth one makes waveguide fabrication more easily.Our group devote ourselves to exploring and studying novel NLO complexes which have large third-order NLO effects and ultrafast response speed to satisfy the material requirements for AOS application. We have studied many materials and found that the chalcone and transition metal1,3-dithiole-2-thione-4,5-dithiolate(DMIT) complexes possesses large planar π electron conjugated structure. The π electron becomes delocalized in the incident laser, making polarization and charge transfer occur easily and materials have large third-order NLO effects. Especially when metal ions are introduced into the conjugated system of DMIT complexes, the charge transfer between metal and organic system makes the electron delocalization property of total conjugated system stronger. In addition, the anion in the molecules is rich in sulfur which can form effective orbital overlapping between molecules and make DMIT have fast response speed.This dissertation discusses the factors which affect the third-order nonlinear properties of materials from internal structure and external conditions. More than ten kinds of DMIT and chalcone complexes were explored and synthesized. DMIT complexes with central metal ions Au and Mn suitable for1064nm and NNDC belonging to chalcone complexes for532nm were investigated using laser Z-scan technique. DMIT and NNDC were doped with PMMA polymer separately to prepare composite films using polymer spin coating method. The third-order NLO properties of the composite films were studied by Z-scan technique and the refractive index, light absorption, thermal effect and light transmission loss of the composite films were systematically studied by prism coupler, photographic technique and spectroscopic techniques. The purpose is to explore ways to enhance third-order nonlinear refractive index, weaken linear and nonlinear absorption, improve optical quality of composite film, and provide experimental basis for final device manufacture. The work of this dissertation will be described in the following aspects:Firstly, we explored and synthesized more than ten kinds of DMIT and chalcone organic π electron conjugated compound materials. The Mn(dmit)2materials with central metal ion Mn were synthesized for the first time. The crystal structure, linear optical absorption and the other physical-chemical properties of benzyltriethylamine bis(2-thioxo-1,3-dithiole-4,5-dithiolato)aurate(Ⅲ)(BTEAADT), benzyltriethylamine bis(2-thioxo-1,3-dithiole-4,5-dithiolato)nickel(Ⅲ)(BTEANDT), bis(tetrabutylammoniu-m)bis(2-thioxo-1,3-dithiole-4,5-dithiolato)manganate(Ⅱ)(BAMDT) and (2E)-1-(2,4-dichloro-5-fluorophenyl)-3-[4-dimethylamino)phenyl]prop-2-en-1-one (NNDC) were reported for the first time.Secondly, we established Z-scan experimental apparatus which was used to characterize the third-order NLO properties of the materials. Photographic technique apparatus was also built up to characterize the optical transmission loss of compound films. Experimental data processing method was complemented and perfected as well.Z-scan technique is a commonly used method to characterize the third-order NLO properties of materials. It has the advantages of simple experimental device, high measuring sensitivity, distinguish ability third-order nonlinear refraction and nonlinear absorption part, and so on. We established a set of Z-scan experimental apparatus to investigate the third-order NLO properties of the materials synthesized by us. A program was developed using Labview to realize controlled sample translation during the experiment and automated experimental data collection. Mathcad program was also written to realize the automation of data processing, which shortened the time of experiment and data analysis and increased the precision of experimental data collection. The photographic technique can characterize the optical transmission loss of composite films conveniently and exactly. We established photographic experemental apparatus, developed a program to realize the data processing, and characterized the optical transmission loss coefficient of the compound films.Thirdly, we studied the impact of central metal ions and external cations of materials on third-order NLO properties of DMIT complexes.The third-order NLO properties of Au(dmit)2. Ni(dmit)2and Mn(dmit)2were studied by Z-scan technique. The optical parameters, such as third-order nonlinear refractive index, nonlinear absorption coefficient, molecular second-order hyperpolarizability and the performance parameter such as all-optical quality factor were obtained after calculation. We obtained some important results after studying the properties of DMIT complexes:1. The third-order NLO properties of DMIT complexes were closely related to its central metal ions.Au(dmit)2materials exhibited self-defocusing effect and negligible nonlinear absorption at1064nm. Ni(dmit)2materials exhibited self-focusing effect and saturable absorption effect at1064nm. Mn(dmit)2materials exhibited self-defocusing effect and negligible nonlinear absorption at1064nm. The third-order NLO parameters of Au(dmit)2and Mn(dmit>2satisfy the requirements of AOS to the material quality factor. But the parameters of Ni(dmit)2materials did not satisfy the requirements because its|T|>>1.2. The third-order NLO properties of DMIT complexes is relevant to its external cations.Some Au(dmit)2materials with the same central metal ion, such as:BTEAADT, tetraphenylphosphonium bis(2-thioxo-1,3-dithiole-4,5-dithiolato)aurate(Ⅲ)(TPEPADT) tetrapropylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolato)aurate(Ⅲ)(TPAADT) and tetraethylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolato)aurate(Ⅲ)(TEAADT) exhibited similar nonlinear refraction at1064nm, but their third-order nonlinear refractive indexes were different when external cations changed.Fourthly, we studied the impact of external factors (laser wavelengths, intensity) on the third-order NLO properties of DMIT materials.1. The same material exhibited different third-order NLO effects when measuring at different linear absorption ranges of the materials. Strong linear optical absorption enhances the NLO effect when measuring at the resonance wavelength or in the region near it. Au(dmit)2materials exhibited self-defocusing effect at both1064and532nm, but the nonlinear absorption could be neglected at1064nm and exhibited reverse saturation absorption at532nm. The third-order NLO parameters of Au(dmit)2at532nm are larger than those at1064nm. The reason is that532nm is in the near resonance region in the material's linear optical absorption spectra. Strong linear optical absorption induced nonlinear absorption easily and enhanced materials' NLO effect.2. The third-order NLO parameters of the materials were different under different laser intensities. As the probing laser intensity becomes larger in a certain range gradually, Ni(dmit)2materials' nonlinear saturable absorption effect becomes weaker correspondingly. The nonlinear absorption coefficient, the third-order nonlinear refractive index and the peak-valley differentials of Z-scan curves all become smaller at1064nm. This is because the excited state absorption cross sections of Ni(dmit)2materials decreased gradually when the light intensity increase, and thereby made the third-order optical properties of Ni(dmit)2weaker.Fifthly, Au(dmit)2/PMMA and NNDC/PMMA composite films were prepared using polymer spin coating method. Their third-order NLO properties were studied by Z-scan technique. The impact of nonlinear element and doping concentration on the parameters were studied such as third-order NLO properties, refractive index, light absorption, thermal effect and light transmission loss of the composite films.1. Au(dmit)2materials were selected and doped with PMMA to prepare the composite films. Their third-order NLO properties were investigated using Z-scan technique at1064nm. The results revealed that composite films have negligible nonlinear absorption. The magnitudes of other third-order optical parameters were three orders larger than those in solutions of Au(dmit)2materials. The composite films satisfy the requirements of AOS for material quality factor, i.e.|W|>>1and|T|<<1and can be potentially applied in AOS device manufacture.2. NNDC/PMMA composite films with five different doping concentrations were prepared. Their third-order NLO properties were studied by using Z-scan technique at532nm. The results revealed that the linear light absorption, refractive indexes, third-order nonlinear refractive indexes and the quality factor|W|of the composite films increases with the doping concentrations. These composite films still have negligible nonlinear absorption effect. The composite films satisfy the requirements of AOS for materials quality factor, i.e.|W|>>1and|T|<<1. At the same time, the response time of chalcone materials was about2.0ps. These results showed NNDC had application potentials in AOS device manufacture in the blue and green light communication.3. The thermal effects of Au(dmit)2/PMMA composite films were larger than those for pure PMMA films. The thermo-optic coefficients of Au(dmit)2/PMMA composite films were calculated to be in the magnitude order of10-5/℃by using temperature-controlled prism-coupler system. The change of the refractive index induced by the thermal effect is the major factor that hinders the ultrafast response speed of AOS devices because its response time is much larger than that of refractive index change induced by electron cloud aberration. The influence of thermal effect can be depressed effectively by reducing the linear and nonlinear absorption of films or controlling the working conditions of films.4. The light transmission loss coefficients of NNDC/PMMA composite films were measured by using photographic technique. The results revealed that light transmission loss coefficients increased approximately linearly with the doping concentration. Reducing the light transmission loss of films can improve the optical stability and practicality of the films. The effective method to reduce the light transmission loss of the films is to improve the optical quality by virtue of appropriate fabrication technique and surface treatment technology.Sixthly, we investigated the time response properties of DMIT complexes. The response time of optical Kerr signal of dmit materials were measured by using optical Kerr method with the sensitivity of femto-second. The response time of some materials was firstly reported. The response time of DMIT materials was all about200fs which was4-6orders of magnitude faster than that of the current popular electro-optic switch. The results show DMIT materials satisfy the requirements for material response speed of AOS.In conclusion, in this dissertation we analyze various aspects which affect the third-order NLO properties of the materials from internal structures and external conditions based on the requirements for materials of AOS. The NLO phenomenon of chalcone and transition metal DMIT materials which have large planar n electrons conjugated structures were investigated in different conditions such as:(a) with different metal ions;(b) with the same metal ion but different cations, and (c) the same material at different laser intensity or wavelengths. The influence of cations and metal ions on NLO effects of materials was investigated. We found Au(dmit)2materials and NNDC have large third-order nonlinear refractive indices, small linear and nonlinear absorption coefficients and fast response speed. They can satisfy the requirements of AOS for material quality factor in optical fiber communication and blue and green light communication respectively. The impact of nonlinear element and different doping concentrations on the third-order NLO properties, refractive indexes, light absorption, thermal effects and light transmission losses of composite films were systematically studied in the prepared composite films. We found some effective methods of solving problems and provided important experimental basis for performance optimization of waveguide devices and for AOS device design and manufacture in the future study.
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