Heterostructures of a Pb(Zr,Ti)O3 (PZT) waveguide/(Pb,La)(Zr,Ti)O3 (PLZT) system buffer layer were grown on a Nb-doped SrTiO3 (Nb:ST) substrate by solid-phase epitaxy. The propagation loss in the PLZT heterostructure waveguides was on the order of I dB/cm. An electro-optic beam deflection device with an ITO prism electrode on the surface of the PLZT heterostructure waveguide presented efficient deflection of the coupled laser beam by applying a voltage between the electrode and the substrate. A beam deflection greater than 10 mrad at 5 V and frequency response as fast as 13 MHz were observed. An apparent electro-optic coefficient as large as 39 pmJV was estimated from the deflection characteristics for the TE mode and TM mode suggesting the polarization independent nature of the PZT waveguide. For integrating the electrooptic PLZT heterostructure waveguides, channel waveguides were fabricated in the PZT waveguides using a simple wet-etching process. Based on a low-voltage drive structure, lowloss waveguide process, and fine patterning process, a fabricated digital matrix switch showed a – 10 dB cross-talk at a voltage as low as 7.5 V.

The dynamic response of the electro-optic coefficients and the electronic polarizability for epitaxial thin films of KnbO3 and BaTiO3 are measured. For these two systems a logarithmic dependence of the electro-optic response and the polarization on time was observed after removal of an applied electric field. The dynamic response of the electro-optic effect and the polarization of the films are attributed to the same physical mechanism, which we associate with the dynamic response of ferroelectric nanodomains.

Recent advances in the techniques for preparation of Ce-doped yttrium iron garnet (YIG) films on gadolinium gallium garnet (GGG) and semiconductor substrates, hybrid material structures of YIG/GGG- gallium arsenide (GaAs) combination, and the resulting microwave and guided-wave magnetooptic (MO) devices are presented. For example, high-efficiency MO Bragg cell modulators using the YIG/GGG-alumina material structure have been realized using a non-uniform bias magnetic field as well as an electronic feedback. Such MO modulators are being used to construct integrated optic devices such as optical scanners, switches, and frequency shifters. Also, a wideband microwave bandstop filter with a carrier frequency tuning range as high as 2.5 to 23.0 GHz using the YIG/GGG-GaAs material structure has been realized. The same material structure can be employed to perform MO Bragg diffraction experiment at ultrahigh carrier frequencies.

Over the past 30 years, the need for transparent conducting oxide coatings has been met almost exclusively by tin doped indium-oxide. As the display market advances in complexity, the demand for alternative transparent materials exhibiting high conductivity and stability has become greater. In this paper, we discuss briefly the merits of using doped ZnO as a superior transparent conducting oxide. We report here our results in scaling our ZnO MOCVD reactor technology from 5° to 12° diameter susceptors. Using Rotating Disk Reactor-Low Pressure Metal Organic Chemical Vapor Deposition, we have been able to obtain large area uniformity on multiple (14 cm × 9 cm) glass sheets per deposition run. Promising film characteristics suggest significant application in the field of flat panel displays and other optical systems may be possible.

A novel stoichiometric vapor deposition process, Autostoichiometric MOCVD, was developed in this study to prepare stoichiometric thin films. Heterometallic alkoxides were used as single precursor for two different metal components in Autostoichiometric MOCVD. The molecular ratios of the metals were conserved through the precursor evaporation and the deposition reactions based on the chemical nature of precursors and the deposition reaction mechanisms. A non-stoichiometric factor K was defined to study the evaporation process of precursors. A precursor evaluation method using the K factor and the thermal decomposition analysis was introduced to quantitatively analyze the stoichiometric evaporation characteristic of a heterometallic alkoxide precursor. Single phase LiTaO3, LiNbO3, SrNb2O6 and BaNb2O6 films were successfully obtained using precursor LiTa(n-OBut)6 or LiTa(i-OBut)6, LiNb(n-OBut)6, SrNb2(n-OBut)12 and BaNb2(n-OBut)12, respectively. Solid solution Sr1-x.BaxNb2O6(SBN) films were also successfully obtained by a two-step Autostoichiometric MOCVD.

Within our program to develop ferroelectric thin film optical waveguides, we have studied the growth of epitaxial waveguides BaTiO3 on r-plane sapphire substrates with a MgO buffer layer. The films were prepared by pulsed laser deposition (PLD). Their structural properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS) in random and channeling (RBS-c) configuration and atomic force microscopy (AFM). They displayed good crystalline quality, characterized by an RBS-c minimum yield of about 4–6%, a full width at half maximum (FWHM) of the XRD rocking curve measurement of the BaTiO3(200) reflection of 0.32° and a rms roughness of 1.2 nm in a film of ∼ 1.0 μm thickness. The epitaxial relationship was found to be BaTiO3(100) // MgO(100) // A12O3(1102). The refractive index, the birefringence and the optical losses have been measured.

Highly c-axis oriented SBN thin films with various compositions were obtained on MgO(100) and Pt(100)/MgO(100) substrates. The anisotropy of refractive indices (no and nc) of c-axis preferred oriented films on MgO(100) substrates decreases certainly as Sr content in the film composition increases. The optical propagation loss of the films decreases with increasing Sr content due to the reduction of the optical scattering by the anisotropy of refractive indices. The oriented films show the linear electro-optic effect with large electro-optic coefficients. The coefficient of the films increases as the Sr content increases because the linear electro-optic coefficient is dependent on the spontaneous polarization and the dielectric constant of the films.

In this study, the KLN thin films were prepared by RF-magnetron sputtering method onto Coming 1737 glass. The effect of working pressure, substrate temperature, RF-power, sputter gas ratio (Ar/O2) during deposition was investigated. For an optimum deposition condition, the postannealing, RTA(rapid thermal annealing) and IPA(in-situ post annealing)methods were employed. Both RTA and IPA processes, which were conducted at different deposition and annealing temperature influenced surface morphology and optical properties of the films. The films prepared by the IPA process showed a lower crystallization temperature and better optical transmittance.

Photorefractive (PR) materials are multifunctional materials which combine both photoconductivity and electro-optic response to show a new phenomenon: reversible modulation of the index of refraction by light. In the past years, our group has focused on the development of fully functionalized polymers, oligomers and small molecular materials. We have had success in identifying new materials and in gaining understanding in design principles of better materials. Several new PR material systems have been explored, including conjugated PR polymers containing transition metal complexes as photosensitizers, oligothiophene based PR systems and small molecular PR materials containing carbazole and methine dyes. Large net optical gain and minimized phase separation were achieved. The correlation between molecular structure and physical properties is the focal point of this paper.

A new mechanism for space-charge field formation in photorefractive liquid crystal composites containing poly(2,5-bis(2′-ethylhexyloxy)-l,4-phenylenevinylene) (BEH-PPV) and the electron acceptor N,N′-dioctyl-1,4:5,8-naphthalenediimide, NI, is observed. Using asymmetric energy transfer (beam coupling) measurements that are diagnostic for the photorefractive effect, the direction of beam coupling as a function of grating fringe spacing inverts at a spacing of 5.5 μm. We show that the inversion is due to a change in the dominant mechanism for space-charge field formation. At small fringe spacings, the space-charge field is formed by ion diffusion in which the photogenerated anion is the more mobile species. At larger fringe spacings, the polarity of the space charge field inverts due to dominance of a charge transport mechanism in which photogenerated holes are the most mobile species due to hole migration along the BEH-PPV chains coupled with interchain hole hopping. Control experiments are presented, which use composites that can access only one of the two charge transport mechanisms. The results show that charge migration over long distances leading to enhanced photorefractive effects can be obtained using conjugated polymers dissolved in liquid crystals.

The formation of holographic reflection gratings in polymer dispersed liquid crystals(H-PDLC) was investigated in real time both in reflection and transmission modes. Real time study is useful for obtaining information on the speed of grating formation, phase separation dynamics, host polymer shrinkage, polarization dependence of the reading beam, bleaching of the photointiator dye and scattering of the writing beam during grating formation. The real time studies showed that the formation of the grating is fast and reaches a maximum in a few seconds. The diffraction efficiency (DE) VS time curve shows an initial increase followed by a sharp decrease and a recovery to higher efficiencies. Variation of monomer functionality in the pre-polymer syrup resulted in a decrease of reflection efficiency as the functionality is lowered. Varying the writing power of the laser beam gave higher efficiencies at powers exceeding 10 mW/cm2. Liquid crystal (LC) loadings of >16% are needed to obtain measurable efficiencies. Varying the polarization of the probe beam (S vs P) revealed differences in the temporal evolution of DE. Morphology studies are indicative of the differences in the phase separation due to monomer functionality, LC concentration and also laser power. The growth dynamics of H-PDLC gratings are very different from the well known Du Pont photopolymer films which may be due to the phase separation process accompanying gelation in H-PDLC systems.

We report an investigation into the mechanism responsible for the optical limiting behavior in multiwalled carbon nanotubes. We conducted energy-dependent transmission measurements, picosecond time-resolved pump-probe, and nonlinear scattering experiments at 532-nm wavelength on multiwalled carbon nanotube suspension. For comparison, C60-toluene solution and carbon black suspension were also studied in the same experiments. The similarities that we observed between the multiwalled carbon nanotubes and carbon black suspension suggest that nonlinear scattering, which is known to be responsible for the limiting action in carbon black suspension, should play an important role in the limiting effect in multiwalled carbon nanotubes.

The scattering properties of polymer dispersed liquid crystal (PDLC) composites are studied and applied to optically addressed devices for the protection against continuous wave laser. The geometry of the device is chosen with respect to its scattering efficiency, linear transmission and response time. The optical limiting performances of this PDLC-based device are measured at 514 nm.

In this paper, we introduce a novel liquid crystal structure, the Inverse Twisted Smectic Structure (ITSS), which has several advantages over the previously reported twisted smectic structure. Both these structures are capable of high-speed, gray scale modulation and phase modulation capability. Additionally, the easy fabrication of the ITSS makes it more attractive for practical applications. We discuss the use of this structure and the fabrication devices using the ITSS. Possible applications, such as the birefringence wavelength filter (BWF), and the digital wavelength filter (DWF) are also discussed and demonstrated experimentally.

Optical limiting properties of singlewall carbon nanotubes suspended in water have been evaluated with 7 ns pulses at 532 and 1064 nm and compared with those of other materials. In order to determine the origin of optical limiting, we carried out a Z-scan experiment at 532 nm and 1064nm at different input energies. We evidenced strong nonlinear scattering and a refractive effect with a negative nonlinear index. The kinetics of nonlinear transmission, from the nanosecond to millisecond time scale, was studied using a pump-probe set-up at 1064nm. We observed cavitation bubbles growth at low input energy. The different nonlinear effects evidenced are discussed in terms of physical origin and in terms of broadband optical limiting efficiency.

Iron doped lithium niobate (Fe:LiNbO3) in a simple focal plane geometry has demonstrated efficient optical limiting through two-beam coupling. The performance is largely independent of the total Fe concentration and the oxidation state of the Fe ions, providing the linear optical transmission of uncoated crystals is between 30% and 60%. Fe has been found to be the best dopant for LiNbO3, giving the widest spectral coverage and the greatest optical limiting. Optical limiting in Fe:LiNbO3 has been shown to be very much greater than predicted by simple diffusion theory. The reason for this is a higher optical gain than expected. It is suggested that this may be due to an enhancement of the space-charge field arising from the photovoltaic effect. The standard two-beam coupling equations have been modified to include the effects of the dark conductivity. This has produced a theoretical intensity dependence on the ΔOD which closely follows the behaviour observed in the laboratory. A further modification to the theory has also shown that the focusing lens f-number greatly affects the optical limiting characteristics of Fe:LiNbO3. A lens f-number of approximately 20 gives the best results.

We investigate the optical limiting capabilities of composite materials consisting of nematic liquid crystal inclusions within a polymer matrix in the millisecond and CW regime. Preparation of the composite has been optimized to decrease the operation voltage. Clear evidence of light induced reorientation is observed. A numerical model is proposed to describe multiple linear and nonlinear light scattering in the time domain in this medium. Numerical simulations are compared to experiment and confirm promising limiting characteristics of such materials.

Nonlinear absorption processes in an extremely nonlinear optical fiber core liquid, and recently observed supra-optical-nonlinearity in dopant modified nematic liquid crystals, are discussed in the context of optical limiting and anti-laser dazzling application.

There is a maximum value for any nonlinear process, which can be found on the basis of fundamental quantum mechanics. With regard to single photon processes, there is a maximum absorption cross section, σa, which any molecule may reach. The maximum is 1.13 × 10-17 λ is the wavelength of the light, n is the refractive index of the host medium, and Q is the quality factor ascribed to the absorption line width. Thus large cross sections can only be obtained at the expense of a narrow operating range. The maximum is set by fundamental physics. Since nonlinear phenomena are highly resonant, the maxima of higher-order processes are also a strong function of the width of the resonance and the peak wavelength. In the case of twophoton absorption the peak value of the maximum cross section, σ2N or δ, is roughly 3.5 × 10-32 λ4nQ cm4/GW, or about 7 × 10-57 λ3 nQ cm4/photon. No value for a nonlinear coefficient is meaningful in the absence of the width of the resonance, the wavelength, and the refractive index of the medium at the wavelength of the measurement.

The basic quantity of interest is the linear electronic polarizability. This fundamental quantity determines not only the absorption for the various processes of interest, but also the surface tension and the closely related solubility parameter. All scale with the polarizability a. The polarizability has a maximum value of e2/mω2; consequently the absorption cross sections have a corresponding ceiling. The maximum value for the peak in a resonant polarizability curve is set by a balance between the Coulomb potential energy of the electron and its kinetic energy. Hence it is an inherent property of the electron itself, irrespective of the molecular orbital in which it finds itself. All that the particular quantum configuration of the molecule does is partition the line strength for absorption among various possible transitions. The extreme case is when virtually all the strength is concentrated in a single transition, an inherently resonant condition.

Many studies have focused on the computation of the structural and electronic properties of liquid crystal molecules in a single static conformation. However, a complete and quantitatively accurate description of the macroscopic optical properties of liquid crystals must also include effects due to the long-range nematic order, the anisotropic local environment surrounding the molecules, and the dynamical fluctuations of the molecules. In this paper, we explore methods to simplify computation of the molecular average second hyperpolarizability of the nematogen 4-n-pentyl-4-cyanobiphenyl (5CB). The model we develop relates changes in the geometrical parameters of the molecule to corresponding changes in the hyperpolarizability. The model is first applied to a simple donor-acceptor substituted polyene, and then to 5CB. Use of a small set of geometrical variables results in a slight increase in the RMS deviation of the predicted hyperpolarizability over the deviation obtained from a complete set. We then discuss the importance of this work for the development of means to calculate macroscopic optical properties.