| With the rapid development of modern science and technology, information transmission capacity of communication increases day by day. Optical fiber communication, which has advantages of large transmission capacity, high transmission velocity, excellent anti-jamming ability and good Signal-to-Noise value, is becoming a main method in communication researches at present. All-optical networks with good performances, such as big capacity, good transparency, wavelength routing characteristics, compatibility and extensibility, has become the first choice of next generation of wide-band net with a promising application. Accompanied by the deep research of wave division multiplex (WDM), switches have drawn more and more people's attention. In the existing optical-electronic-optical conversation apparatus of present communication net, disadvantages of slow switching speed and clock displacement have lead to a "bottleneck" of optical fiber communication systems. All-optical switches which can break through the transmission speed limits of electro-optical, acousto-optical, thermo-optical and micro-electro-mechanical switches, can serve as effective methods to solve these problems. Based on the third-order nonlinear optical (NLO) effect, phase all-optical switches use a controlled light to bring changes of refraction index and make phase difference when signal light passes through sample and thus carry out the function of "on" or "off' of optical switches. Its nonlinear phase difference is proportional to (2π/λ)n2IL, where I is intensity, L is length of interaction of wave and n2 is nonlinear refraction index. The properties, such as change speed, intensity loss, sensitivity to optical polarization and insert loss, all depend on third-order NLO materials used to synthesize apparatuses. At present, it is with great enthusiasm to emphasis on exploring and synthesis of materials for all-optical switches based on the continual discovery of varies kinds of new materials.There are other applications of third-order NLO materials, including optical limiting devices, Q-switch, passive mode locking, optical operation and light storage etc.. Laser weapons applied to military have special effects on optical-electro antagonism, aerial defense and military recovery. Laser blinding can make eyes blind temporarily or permanently, and laser can also destroy important apparatus in the satellite, such as detectors and sensors et al.. Meanwhile, corresponding antagonism has drawn high attentions of many countries. As a result, laser protection materials and devices have become a focus. The purpose of laser protection is to protect people and devices from damage of high intensity. These optical limiting devices are mainly based on the materials' third-order NLO properties, including self-focusing, self-defocusing, two-photon absorption, reverse saturable absorption and nonlinear scattering. Comparing to earlier laser protection devices, it has advantages of fast response, wide protected band, low optical limiting threshold, large damage threshold and high linear transmission, etc. The third-order NLO properties of materials can also be used in the compression (mode-locking) and shaping of laser pulses, optical bistability, etc.Third-order NLO materials also have many potential practical exciting applications, and these spur scientists to continually explore new materials with high third-order NLO properties. The demands of materials for all-optical information process and high-speed all-optical switches include large nonlinear refraction index, small linear and nonlinear absorption coefficient, fast response and low propagation loss. In the present study, on the basis of the demands for pragmatic apparatus, a series of new materials were explored, their NLO properties and propagation characters of third-order NLO composite polymer films were studied comprehensively.Establishment and optimization of the measurement techniques on the optical nonlinearity is very important in the process of exploring the novel NLO materials, which can not only reveal the ultimate origin of NLO properties but also supply important instruction for the synthesis of materials with more excellent performances as well as provide reliable data for further device designing.The thesis mainly comprises the following aspects:Firstly, a series of metal-organic DMIT complexes were explored and synthesized, BPAu, EtCu and EtCd etc. were novel optical materials and their single crystal structures, linear absorption and some other properties were reported by our research group for the first time.In recent years, the third-order NLO materials are one of the key focuses in NLO materials research field with the appearance of ultrafast and high power lasers producing picosecond and femtosecond pulses. The third-order NLO effects exist in all of the optical materials and are irrelevant to their structures. The materials with relatively strong third-order NLO effects can be divided into several categories, including semiconductors, metal oxides and organic materials, etc.. Organic materials are greatly attractive because of their advantages, such as ease of fabrication and integration into devices, tailorability which allows one to finely tune the chemical structures and properties, low dielectric constants, fast NLO response times, high laser damage thresholds, large off-resonance NLO susceptibilities and low cost. Generally speaking, these materials haveπelectron conjugated systems and the delocalizedπelectron will contribute dominantly to the third-order NLO effects. Our group explored and synthesized lots of novel metal-organic DMIT complexes, a series of metal-organic semiconductors with good performance. The part of "dmit" is an anion richly containing sulphur in the molecule, abbreviated as Metal(dmit)2. They mostly have centrosymmetric structures and the central metal atom can be Au, Cu, Cd, Ni and Co ions, etc.. Materials' properties can be changed by substituting different metal ions. From their molecular structures, we can see that they have excellentπelectron conjugated systems, which can extend through the overlap between the conjugatedπelectron and the d orbit of metal ions, and the charge transfer between the organic systems and the metal ions greatly enhances the NLO effects. Moreover, as organic semiconductor or superconductor metal-organic complexes, DMIT materials possess fast NLO effects due to their good conducting properties, namely large electron mobility. Our group synthesized more than twenty metal-organic DMIT complexes, and the single crystal structures and linear absorption and some other properties of several novel optical materials, such as BPAu, EtCu and EtCd, are reported for the first time.Secondly, a set of Z-scan experimental setup was established and the third-order NLO properties of metal-organic DMIT complexes were studied. We characterized comprehensively a series of performance parameters, such as nonlinear refractive index, nonlinear absorption, third-order nonlinear susceptibility, molecular second-order hyperpolarizability, and ground-state and excited-state absorption cross sections etc.. We also studied deeply the influences of different factors, including molecular structures, laser wavelengths, and pulse widths, on the third-order NLO properties.There are some techniques to characterize the third-order optical nonlinearity of the materials, including nonlinear interferometry, three-wave mixing, degenerate four-wave mixing, ellipse rotation and beam distortion measurements, etc.. In 1989, a technique, Z-scan method, to measure both the nonlinear refractive index and nonlinear absorption of materials was proposed by M. Sheik-Bahae et al.. The method not only has simple experimental apparatus and high sensitivity but also can distinguish the real and imaginary parts of nonlinear susceptibility. The thesis provides detailed theory analysis process and commonly used formulas to obtain their performance parameters by experiment. We established a set of Z-scan experimental apparatus in the laboratory by ourselves independently and compiled a program to collect experimental data and control displacement device using Labview software. The work procedures were harmonized to save a lot of time. The laser energy's fluctuation can be setting within some scope. If overstepping the range, the laser pulse is not adopted. At one point of the Z-scan trace, several laser pulses were collected and averaged. All the above measures can minish experimental errors and improve the accuracy of measurements. Using our Z-scan experimental setup, we studied systematically the third-order NLO properties, measured the open-aperture and closed-aperture Z-scan normalized transmittance curves, analyzed the significations of different Z-scan configurations, calculated and obtained a series of performance parameters such as nonlinear refractive index, nonlinear absorption, third-order nonlinear susceptibility, molecular second-order hyperpolarizability, ground-state and excited-state absorption cross sections, etc.. We further analyzed the influences of different factors on the third-order NLO properties, including molecular structures, measurement wavelengths, and laser pulse widths. It has been found that the third-order NLO properties strongly depend on the laser wavelengths as the absorption of materials may enhance the NLO effects. Under the irradiation of picosecond laser pulses, EtCu exhibits saturable absorption at 532 nm while two-photon absorption at 1064 nm. The third-order NLO properties also relate to the laser pulse widths and different nonlinearity origins have different response times. Therefore, when illuminated by picosecond pulses at 532 nm, EtCd shows saturable absorption while reverse saturable absorption when irradiated by nanosecond pulses. Under the irradiation of picosecond laser pulses at the wavelength of 532 nm, we obtained the third-order NLO performance parameters of such novel materials as EtCu, EtCd and BPAu. The values of nonlinear refractive indexes lie in 10-11～10-12 esu and those of molecular second-order hyperpolarizability lie between 10-31～10-29 esu .Thirdly, several kinds of DMIT composite polymer films were studied; a set of experimental apparatus was established; a soft of data processing was written. There are many techniques to characterize the optical propagation loss. The method of quasi wave-guide prism coupler was used to obtain refraction index of the films. In this thesis, the method of measurement on composite polymer films using prism coupler was deduced in detail and the deduced process of experimental and theoretic principle and method were given. In addition, using method of quasi wave-guide prism coupler, the refraction index of DMIT thin films in TE mode was measured, and thus the accuracy was proved. There are many methods to measure the propagation loss of film. One of these methods was the end-fire coupling method including the prism double method, the three-prism method which has high demand to light collimation and cross disposition. Another method, fiber detected technique, was used to collimated. The technique of the hybrid technique, also one of these methods to measure the propagation loss of film, highly demands surface of wave guide and adjusting light path, and can only measure propagation loss of several positions in wave-guide surface. The photographic technique was chosen in the present study because of its good properties such as simple structure, easy manipulation, non-contact measurement, high accuracy and getting the loss of any parts of the films. Through establishing experimental apparatuses by ourselves, several kinds of DMIT complex polymer films were studied. To improve the accuracy, as to the hardware, the quality of composite polymer films and adjustment of light path were controlled strictly, including cleanout of base, synthesis of solvent, filtering of solvent, preparation of the films and control of picturing. As to the process of picturing, adding gauge, foreground and background, many exposals in same angle were used, and the area of the films to measure was also chosen. As to software, picture analysis was mainly used to improve accuracy. The results of measurement showed that, with the increase of content of composed polymer film, propagation loss increased linearly.Proved by the present experiments, materials of DMIT with high third-order nonlinear polarizability, fast response and low propagation loss are a kind of potential third-order optical materials.
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