| Our society is in the "Information Age".The traditional correspondence technique can not satisfy with people's demands,which has increased rapidly in the amount of information.In the present communication system,the optical fiber communication system(OFCS) used many electronic components with some disadvantages such as slow switching speed,clock displacement,serious crosstalk and high power loss which can easily lead to the "bottleneck" of the system.Under such conditions,it is necessary to construct the "all-optical network" while information exchange at points adopts all-optical switch(AOS).In general,AOS is based on nonlinear optical(NLO) effects.Taking advantage of the third-order nonlinear refraction of materials,AOS' work principle can be described as follows:With a control beam inducing the change of refractive index of material,the other signal beam transmitting in the material will produce an additional phase difference to realize the function "On" or "Off" of optical switches.There are two factors defined as W=n2I/α0λ.and T=βλ/n2,while n2 is the NLO refraction,I is the laser intensity,α0 is the linear absorption,λis the wavelength,βis the nonlinear absorption. To make the practicable all-optical switches,NLO materials must simultaneously satisfy |W|>>1 and |T|<<1.Therefore,the materials must satisfy:1.large nonlinear refractive index (n2) at the operating wavelength which can reduce the power density of control light; 2.minimal linear and nonlinear absorption which lower the information transmission loss,increase the switching speed and then enhance the reliability and stability of the system;3.ultrafast nonlinear refractive index responses and relaxation times (picoseconds or less);4.easy to make wave-guides.Currently,the investigations of AOS device,include not only the improvement and innovation of technologies and structures but also the exploration of new action mechanism and novel materials.Currently,people still do not discover such materials whose performances are comprehensively suitable to the development of these NLO devices.Therefore,it seems to be particularly important to explore and synthesize novel materials possessing excellent third-order NLO properties and good factors of merits.Our group has studied many materials,and found that the transition metal DMIT complexes possess largeπ-electron delocalization,charge transfer and high electromigration rate in the systems.Hence the characteristics should result in an ultrafast optical response capability and large third-order NLO effects.The AOS require materials with large NLO refraction and small NLO absorption,hence it is important to discover the rules which affect the NLO properties of the materials.This dissertation takes the Cu(dmit)2 and Au(dmit)2 as the object of the research. Researches the NLO properties of materials by Z-scan technique,and discussed the factors which affect the NLO refraction and NLO absorption for the purpose of raise the NLO refraction and NLO absorption of the materials.The dissertation mainly comprises the following aspects:Firstly,a series of metal-dmit complexes whose central metal ions are Cu and Au were explored,it is found that the NLO properties come of the central metal ions.The Cu(dmit)2 and Au(dmit)2 materials have small linear and NLO absorption at the correspondence wavelength(1.3～1.6μm),therefore this dissertation takes the Cu(dmit)2 and Au(dmit)2 as the object of the research,TPPPADTA,TPEPADT and TPPPADT were reported for the first time as new optical materials.In this dissertation,we investigated systematically the optical nonlinearities of DMIT materials by Z-scan technique and obtained the third-order nonlinear susceptibility,third-order nonlinear refractive index,nonlinear absorption coefficient, molecular second-order hyperpolarizability,absorption cross section of ground and excited states,and two-photon absorption cross section,etc..We also investigated the factors which effact the third-order NLO properties of materials:A.It is found that the central metal ions influence the NLO refraction of DMIT complexes.The materials with same central metal ion exhibited same NLO refraction, the Cu(dmit)2 materials with the concentration 1×10-3 mol/L have self-defocus at 1064 nm.B.The central metal ions also influence the NLO absorption.TMACDT and TMAADT with same cations and concentration have different NLO absorption, TMACDT has two-photon absorption and TMAADT without NLO absorption.C.The complex with same central metal ion and smaller cation represents large third-order NLO coefficients.TMACDT and TMAADT have larger NLO refraction than other materials with same central metal ion.It indicates that the central metal ion play an important role on the NLO properties and choose the materials with small cations can obtain the NLO properties with larger coefficients.Secondly,the third-order NLO refraction and absorption of DMIT materials were systematically studied.It is discovered that the materials exhibit larger NLO absorption at resonance region and at broad pulse width.In this dissertation,we investigated systematically the optical nonlinearities of DMIT materials in both 1064 and 532 nm.A.The wavelength and pulse width of the laser affect the NLO parameters.The NLO absorption coefficients of material that obtained at resonant wavelength are larger than those obtained at other range.The NLO absorption of Cu(dmit)2 is 10-12 m/W at 532 nm while 10-13 m/W at 1064 nm.B.The NLO properties for the same material at different pulse width are also distinct.TMACDT represent two-photon absorption at picosecond laser pulses while reverse saturation absorption at nanosecond laser pulsed.This can be explained by the five-level model:the nonlinear absorption was dominated by the singlet-singlet excited state transitions for picosecond laser pulses,while for nanosecond pulses it can be mainly attributed to the triplet-triplet excited state transitions.The different origins induced the results that obtained at nanosecond are larger.C.With 20 ps laser pulses at 1064 nm,Cu(dmit)2 possesses high third-order NLO refraction which is obtained as 10-13～10-12 esu and NLO absorption.Au(dmit)2 exhibits non-resonant third-order optical nonlinearities,the NLO refraction of TMAADT is -4.11×10-12 esu and with no NLO absorption which satisfy the requirements of AOS for materials' figures of merit,W=2.87 and T=0(|W|>>1 and |T|<<1).Thirdly,we prepared the composite film of DMIT complexes by sol-gel process and investigated the NLO properties of Au(dmit)2/PMMA film by Z-scan technique and obtained some conclusions.A.It is found the Au(dmit)2/PMMA film can satisfy the requirements of AOS.With 20 ps laser pulses at 1064 nm,Au(dmit)2 possesses high non-resonant third-order optical nonlinearities and the figures of merit are two orders of magnitude larger than which are measured in solution.Thus the Au(dmit)2 can satisfy the requirements of AOS for materials' figures of merit |W|>>1 and |T|<<1.B.Compared with the results that obtained in solution,the NLO parameters of composite film are two orders of magnitude larger than which are measured in solution, the NLO refraction of Au(dmit)2/PMMA film can attain as 10-10 esu.The phenomenon revealed that the concentration of DMIT materials in film is higher than that in solution. It is also found the NLO coefficients are enhanced with the doping concentration increases.Hence we can enhance the NLO properties by enhance concentration of DMIT materials in film.All the outcomes suggest that Cu(dmit)2 and Au(dmit)2 materials possess good NLO properties and Au(dmit)2 materials have large NLO refractions,small NLO absorptions and ultrafast response which can satisfy the requirements of AOS.All the conclusions can provide a basis and an important foundation for the preparation of waveguide devices in the future.
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