The off-resonant (pi) -electronic component of the (beta) tensor, (beta) _(pi ), is calculated and analyzed for an octupolar molecule with D_3h point group symmetry, 1,3,5-triamino- 2,4,6-trinitrobenzene (TATB), and the related dipolar molecule with C_2v point group symmetry, para-nitroaniline (pNA). The (beta) _(pi )'s for TATB and pNA are calculated using the semi-empirical INDO/S Hamiltonian combined with single- and double-excitation configuration interaction of singlet (pi) -electron configurations, and Orr and Ward's sum- over-states expression for (beta) .

Electro-optic polymer waveguide modulators may be used in parallel modulation arrays supplied by branching structures providing fanout from a CW laser for a variety of applications, including CATV and data communications. This paper highlights some of the benefits of using EO polymer modulators in arrays for point-to-point digital data communications.

Ultrastructure synthesis techniques for stabilization of large second order optical nonlinearities of poled polymers are reviewed. These techniques include covalent attachment of chromophores onto polyimide backbones, use of double-end crosslinkable chromophores, crosslinking of main-chain polymers with chromophores as polymer backbone components, and in-situ poling and polymerization of chromophores with multiple functionalities. By using these techniques, second harmonic generation coefficients, measured at 1064 nm wavelength, on the order of 10^-7 esu and long term stability of optical nonlinearity at 90 - 125$DEGC have been realized.

In this paper we report the first experimental values for the hyperpolarisability of the octopolar molecules tricyanobenzene and trinitrobenzene. The experimental hyperpolarisabilities were obtained using the Hyper-Rayleigh Scattering technique. It is experimentally shown that octopolar molecules have nonlinear optical properties which compare favorably to those of their dipolar counterparts. All the experimental results were in excellent agreement with the results from quantum-chemical calculations.

We have synthesized silicon-based donor-acceptor compounds that are transparent in the visible and have moderate values of the first hyperpolarizability, (beta) , which are measured with Hyper-Rayleigh Scattering (HRS). The spectroscopic properties (UV-VIS) are studied by investigating the influence of the donor and acceptor strength and the chain length on the absorption maxima and (lambda) _cutoff values. We will focus the perfluorobutylsulfonyl in studies concerning functionalization and incorporation into a polymer matrix.

The properties of new, high temperature optical materials based on dye-doped Ultradel 9000D polyimides are presented. Ultradel 9000D is a soluble, pre-imidized, fluorinated polymer with properties optimized for integrated optical applications. When thermally or photochemically cross-linked, it has a Tg approaching 400$DEGC and retains excellent optical transparency as measured by both waveguide loss spectroscopy (WLS) and photothermal deflection spectroscopy (PDS). The agreement between WLS and PDS data indicates that losses in polyimides are due to absorption, not scattering. Two thermally stable, donor-acceptor oxazole-based dyes were designed, synthesized, and doped into the polyimide at concentrations up to 25 percent by weight. The Tg of the doped polymers decreased from the neat polymer, but remained above 300$DEGC. The effects of doping on the dielectric constant, refractive index, and coefficient of thermal expansion of the polyimide are presented.

Conjugated organic molecules and polymer systems are of interest due to the delocalized (pi) -electron systems which give rise to large values of (chi) ⁽³)(-(omega) ;(omega) ,(omega) ,-(omega) ), with extremely fast response times, in wavelength regimes where there is minimal background absorption. We have previously presented theoretical results demonstrating that (chi) ⁽³)(-(omega) ;(omega) ,(omega) ,-(omega) ) can be further increased for nonlinear optical processes originating from real population of electronic excited states in conjugated linear chains. In this paper, a dynamical model is developed for the time evolution of the degenerate four wave mixing susceptibility (gamma) (-(omega) ;(omega) ,(omega) ,-(omega) ).

Two complementary approached to the construction of poled, crosslinked second-order polymeric NLO materials are discussed. In the first, poly(p-hydroxystyrene) is functionalized with a nitroaniline chromophore having a protectable hydroxyl group for hydrogen bonding or epoxy crosslinking. Chromophore immobilization is most effective when crosslinks can be made directly at the chromophore substituent and when multifunctional crosslinking agents are employed. The second approach shows that matrices prepared from an aryldiamine chromophore and a bismaleimide co-monomer can achieve T_g values approaching + 240$DEGC and exceptional SHG temporal stability.

Novel modified polyimide polymers with nonlinear optical chromophores as pendent side groups show high glass transition temperatures and large nonlinear optical coefficients up to d₃₃ equals 78 pm/V at (lambda) equals 1313 nm (electro-optic coefficient r₃₃ equals 18 pm/V). Due to the high glass transition temperatures of up to 190 $DEGC an excellent long term stability of the nonlinearity results. Extrapolation from measurements at elevated temperatures predict long term stabilities of the nonlinearity in excess of tens of years at 80 $DEGC and hundreds to thousands of years at room temperature. The structural (molecular weight, glass transition temperature) and optical (refractive index, nonlinearity) properties of these polyimides can easily be varied which allows to taylor active layer and buffer layer materials.

A new method of preparing oriented NLO main chain polymers is presented. We synthesized NLO-monomers that consist of donor acceptor substituted tolane molecules that can be poled in the low molar mass state. In the oriented polar state these monomers can be chemically linked using a thermally activated polyaddition reaction. This reaction links the donor head of one monomer to the acceptor tail of the next hibiting bulk noncentrosymmetry with the average direction of the molecular dipoles parallel to the aligning field.

Significant asymmetry and optical nonlinearity (second harmonic generation) can be produced by injection of electric charge into dye/polymer blends. The strength of the nonlinearity and its temporal stability depend on the electrical properties of the polymer and the polymer interface. It is shown conclusively that the mechanism for producing the nonlinearity does not arise from dipolar alignment of the dye in an electrostatic field; we even demonstrate production of nonlinearity under conditions of alternating current injection i.e. zero electrostatic field.

The realization of practical electro-optical devices based on the poled polymer waveguide approach is contingent on the simultaneous solution of a number of outstanding materials and fabrication issues. We have prepared and studied the molecular properties of a number of heterocycle containing chromophores with structures derived from high temperature polymer materials and further evaluated many of them as guests in polyimide polymer hosts. Correlations between the structure of these chromophores and their physical properties including optical nonlinearity, absorption, dipole moment and thermal stability have been made. Furthermore, a correlation between thermal stability and oxidation potential for some of these heterocyclic chromophores has been found and extension of this correlation to other types of nonlinear chromophores is suggested.

We report our study of a second-order nonlinear optical polymer in which the chromophores were first attached at one end to the polymer backbone as side chains and then crosslinked at the other end during electric field poling and thermal curing. The corona poled polymer films showed a sizable second-harmonic generation coefficient d₃₃ of 60 pm/V at 1.064 micrometers fundamental wavelength. The cured polymer film showed long-term stable nonlinearity from room temperature to 90 $DEGC. Improved thermal stability at 125 $DEGC was also obtained. A simple and quick method for measuring the short-term thermal stability of nonlinearity is presented.

After briefly introducing a modified Perot Fabry technique which enables to differentiate the true purely electronic Pockel effect from the piezoelectric induced electro-optic effect, we discuss the Electro Optical (EO) properties of a thermoplastic polymer and of a bismaleimide- based crosslinked network. Both polymers have large EO coefficients. However, the ratio R equals r₃₃ / r₁₃ is greater than predicted by the isotropic model. Values as high as 6.5 are observed in the crosslinked network. In the case of the thermoplastic polymer, the stability of the oriented chromophore is good up to 100$DEGC and disorientation is fitted reasonably well with a stretched exponential.

Nonlinear optical response of copolymers bearing pendant active mesogenic units have been studied. The A and C polymers are nematic and smectic A, respectively, while the B and D polymers resemble typical amorphous polymers. Spin-coated films have been activated using the corona poling technique. From the optical absorption spectra, order parameters in the range 0.4 - 0.6 have been determined. The rather large values obtained for the B and D polymers suggest that an isotropic/nematic transition occurs during poling. Second harmonic generation measurements relative to quartz have been performed to determine the values of second order coefficients d₃₃ and d₃₁.

The Electro-Optical (EO) effect has been studied in three different sidechain polymers (T_g: 140, 174 and 200$DEGC) both during poling and after poling. At the end of the poling process, when the poling field is switched off, a significant quasi-instantaneous decrease of the EO effect is observed, which--in our opinion--is indicative for motional hindrance during poling. The three polymers differ mainly in the flexibility of the coupling between the DANS- like sidechains and the backbone. A stronger coupling results in more hindered polability, but also in a higher T_g and better high temperature stability of the sidechain orientation. The role of hydrogen bonding is also discussed.

Electro-optically active planar waveguides of aromatic polyurea were prepared by simultaneous deposition of 4,4'-diamino-diphenyl-methane and 4,4'-diphenylmethane- diisocyanate from the vapor phase and subsequent corona poling. Attenuated total reflectance spectroscopy of the waveguide modes of the polymer films was used to measure the piezoelectric and electro-optic susceptibilities. It is found that the electro-optic response is not only determined by the nonlinear polarizability of the urea groups but also from their dipolar orientation in the applied field.

In continuation of our studies on donor-acceptor substituted heteroaromatic nonlinear optical chromophores, we have developed a new series of thiophene derivatives containing dialkylamino electron-donor and tricyanovinyl electron-acceptor substituents. EFISH measurements indicate that the combination of tricyanovinyl acceptors and thiophene conjugating moieties yields dramatically enhanced molecular nonlinear properties [(beta) (mu) (at (lambda) equals 1.907 micrometers ) equals 6000 - 9100 X 10^-48 esu].

Organic molecular crystals show some of the highest figures of merit performance for non- linear optical behavior and laser radiation damage. The use of these materials for device applications is limited however by the belief that they are difficult to prepare as high quality single crystalline bulk crystals and thin films. Even when obtained in this form, their mechanical properties are assumed to be unsuited for their preparation for incorporation in device systems. Over the past few years we have addressed these problems. Structurally and optically perfect crystals of large sizes have been prepared of a wide range of these materials despite their tendency to show extremely anisotropic growth behavior. Techniques have been developed which allow their orientation, cutting and polishing to optical standards. The work has also been extended to the preparation of high quality, single crystalline thin film samples by means of melt phase growth.

Hyper-Rayleigh scattering has been used to characterize the nonlinear optical properties of polymeric materials. This new technique has been applied both on synthetic polymers with nonlinear optical chromophores covalently attached to a polymer backbone and on biopolymers with one single chromophore embedded in a protein matrix. We demonstrate the hyper-Rayleigh scattering can be used to determine the molecular hyperpolarizability of the pending side chain chromophore in synthetic polymers. No evidence of orientational correlation between the side chains was observed for chromophore loading levels up to 22%. Hyper-Rayleigh scattering was also used to determine the first hyperpolarizability of a charged protein.

Experimental measurements of molecular hyperpolarizabilities can be useful in two ways. First, they allow comparison between different chromophores, so that structure-function relationships can be understood and increasingly nonlinear compounds synthesized. This application requires only good relative measurements. The second and ultimately more important application is prediction of the macroscopic nonlinear optical properties of custom materials. The latter application requires accurate absolute values for the molecular parameters. Examples of both types of comparisons are discussed below. We describe experimental measurements on several types of nonlinear optical chromophores, and the choice of conventions and reference standards that leads to accurate predictions of electro- optic coefficients in poled polymers. The degree to which nonlinearity and thermal stability are correlated is also discussed.

The refractive index dispersion of a nonlinear optical (nlo) polymer can be measured in a simple way with an accuracy of 0.001 by using an Abbe refractometer with the polymer in solution.

A new method to investigate the temporal stability of electric field poling induced polarization in polymers using piezoelectric effect is described. The results of two PMMA-based side chain copolymers are presented. A comparison with the results of Second Harmonic Generation (SHG) experiments is given. Glass transition ranges for the polymers were determined by thermal dependent SHG experiments.

Two nonlinear optical polymers, containing the active molecules in the main-chain and in the side-chain, have been characterized by dielectric spectroscopy in the frequency range from 0.05 Hz to 10 kHz. It is shown that dielectric spectroscopy is a powerful technique to monitor the mobility (relaxation) of active molecules. From the results a estimation about the poling temperature and -time can be made. In addition, the influence of absorbed water on the relaxation is established as well as the effect of UV-light exposure on the chromophores.

Approaches to reduce propagation loss in polymer waveguides for passive and active applications are discussed and demonstrated. Contrary to inorganic waveguide materials, the light loss in polymer waveguides is predominantly due to intrinsic absorption processes. In the telecommunication windows in the near-IR the absorption is due to vibrational overtones. The light loss can be decreased by reduction of the concentration of C-H, N-H and O-H groups in the polymers. Edge absorption by electronic transitions of charge transfer bands of nonlinear sidegroups in electro-optic polymers does not contribute to light loss in this region.

To induce macroscopic second-order nonlinear optical properties in polymers containing polar, hyperpolarizable groups like DANS or MONS, these groups have to be polarly aligned (poled) with a strong electric field at the glass transition temperature. Simple molecular statistical models, which neglect dipole-dipole interaction, predict an enhancement of the electric field induced polar order by axial order. Since axial order exists spontaneously in liquid crystals, the introduction of liquid crystalline properties into the poled polymer has been considered as advantageous. The presumed advantage for poling from axial order, in particular from liquid crystalline axial order, is discussed in the light of more recent theoretical calculations and experimental results.

This contribution deals with the application of some recently developed evanescent wave- optical techniques for the characterization of polymeric thin films as basic structures for integrated optics. Surface plasmon- and guided optical wave-spectroscopies and -microscopies are used to determine the linear and nonlinear optical properties of (chi) ⁽²)-active thin films prepared either by spin-casting from solution or by the Langmuir-Blodgett-Kuhn technique.

To manifest a photorefractive effect, the polymer must possess a photocharge generator, a charge transporter, a charge trapping center and a nonlinear optical chromophore. We have synthesized two types of novel photorefractive (PR) polymers. The type I PR polymers contain the NLO chromophore, the charge generator and the transporting compound covalently linked to the polymer backbone. The type II photorefractive polymers contain a conjugated backbone and a second order NLO chromophore. The design idea behind the structure of the type II polymers is the expectation that they will possess photorefractivity. Since the conjugated backbone absorbs photons in the visible region and is photoconductive, it is expected to play the triple roles of charge generator, charge transporter and backbone. Thus, the four functionalities necessary to manifest the PR effect will exist simultaneously in a single polymer.

The photorefractive effect has been observed in a 1/1 side chain copolymer of N- methacryloxyethyl-N-methylaminonitrostilbene and methylmethacrylate. Holographic gratings were written in this polymer at 633 nm in 4 - 8 micrometers thick films at low laser powers and detected using four wave mixing and two beam coupling. The polymer which has a high linear electro-optic coefficient was intrinsically photorefractive and did not require the addition of photoconducting or charge generative components. Diffraction efficiencies on the order of 10^-5 - 10^-4 were measured by four wave mixing. Two beam coupling provided conclusive evidence that the observed effect was photorefractive in nature.

Photorefractivity, or reversible photoinduced refractive index change, was first observed about twenty-five years ago in inorganic crystals. The photorefractive effect involves generation, transport and trapping of charges and a change of the refractive index through the electro-optic effect. We have synthesized a photorefractive crosslinked polymer material in which the active components, derivatives of diethylaminobenzaldehyde diphenylhydrazone and para- nitroaniline, are chemically linked into the polyurethane network. During the crosslinking of the polyurethane the para-nitroaniline groups were aligned (poled) by an external electric field, which resulted in a non-centrosymmetric polymer material. This material was shown to be photorefractive by the two beam coupling experiment, without the application of an external electric field.

The results of photorefractivity studies in newly developed polymer composite C₆₀/PVK/DEANST are presented. The composite contains fullerene (C₆₀) photosensitizing molecules, second-order active molecules of diethylaminonitrostyrene (DEANST) and charge transporting polymeric matrix of poly[N-vinylcarbazole] (PVK). Photorefractive properties of the material were investigated using erasable volume holography and two-beam coupling techniques. Additional information was obtained from the results of photoconductivity, electro-optic modulation and the angular dependence of holographic diffraction. The kinetics of the effect, as well as the writing beams and the external dc field switching of the refractive grating are discussed. A previously developed theory of space-charge field gratings formation in photoconductive polymers is used to calculate four-wave mixing diffraction efficiency.

In this paper, we examine the nonlinear optical properties of molecular systems undergoing cis-trans photoisomerization process. Such a process gives rise to dynamic photochromism on a picosecond time scale. A kinetic analysis of a general cis-trans nonlinear organic absorber is performed. The analysis is used to derive an expression for the complex nonlinear-molecular index of refraction. The properties of a molecular SLM based on such an absorber are discussed by examining the azo type molecular system. These calculations predict an optimum contrast ratio and fast on-off switching for the SLM performance, achieved at low read-write laser intensities.

The development of a stable self-oscillatory system based on the alignment response times of liquid crystals is reported. A simple phenomenological mathematical model has been developed and solved numerically which produces results in accord with the observations, namely that the frequency of oscillation increases as the temperature increases. The model is extended and solved numerically to describe a mixture of two liquid crystal species.

We report on a scheme for phase-matching second harmonic generation in polymer waveguides based on the use of anomalous dispersion to optimize Cerenkov phase matching. We have used the theoretical results of Hashizume et al. and Onda and Ito to design an optimum structure for phase-matched conversion. We have found that the use of anomalous dispersion in the design results in a 100-fold enhancement in the calculated conversion efficiency. This technique also overcomes the limitation of anomalous dispersion phase- matching which results from absorption at the second harmonic. Experiments are in progress to demonstrate these results.

The third order susceptibility of a polydiacetylene polymer was investigated by three different nonlinear spectroscopic techniques in order to test two existing microscopic theories which predict the nonlinear response of such molecular systems. We previously found good agreement between a four essential state model and the THG spectra of (pi) -electron conjugated backbone polymers. However, when such a model was extended to two additional third order susceptibility spectra, poor agreement was found. In contrast the recently developed anharmonic oscillator model fitted well all four experimentally obtained spectra of the third order susceptibility.

Interest in organic materials for applications in photonics is based mainly on their fast, electronic in origin, and large nonlinear optical response which is due to the large hyperpolarizability of delocalized ii electrons. On the other hand the organic materials are characterized by some interesting physico— chemical properties, such as: processability, versatility and good optical quality. They are also expected to integrate well with semiconductor technolo gy. Quasi one dimensional conjugated polymers like polydiacetylenes, polyacetylene and polythiophenes [1] are indeed characterized by a large nonlinear optical response and fast response time, but on the other hand it is difficult to obtain good optical quality, stable thin films of these materials. Polydiacetylenes are of repute for their excellent crystallinity, which leads to unwanted light scattering, and consequently to large propagation losses. Polyacetylenes are know to be unstable in air.On the other hand these po— lymers are characterized by a residual absorption in the near infrared due to overtones of C-H and 0-H stretching vibrations. Consequently it limits interest of their application in the interesting for practical purposes (telecommunication window) operation wavelength range. For these reasons the fullurenes in general, and C in particular are interesting materials for applica— tions in photonics because of lack of the low energy stretching vibrations. Moreover, the electronic bands in C are narrower [21 than in conjugated po lymers, where they are broadened due to conformations and conjugation length distribution. Consequently one expects the resonances to be narrower too. Large nonlinear optical response in C6 has been reported by third harmo nic generation in thin films [31 and in solution[4] as well as by degenerate four wave mixing [51 in solution, differing by two to four orders of magnitude from the last determinations (cf. Table 1). All these measurements have been performed almost at one wavelength only (mostly 1.064 jim). Also very recently a significant second order nonlinear optical response from C6 thin films has been reported by Wang et al [6] by optical second har monic generation. This result is in contrast with what one could expect for presumably centrosymmetric thin films. In fact, no bulk quadratic susceptibility in these films should be observed, at least at dipolar approximation. A second order activity of C thin films has been also observed by Hoshi et al [3]. There is much less data on a higher fullerene which is C . The nonlinear 70 optical properties of this molecule have been studied almost in solution and at discrete wavelength (cf. Table 1). In this paper we report the results of a systematic study of nonlinear optical properties of C60 thin films by optical third (THG) and second (SHG) harmonic generation techniques. The THG measurements have been done as a function of fundamental wavelength. The tecique allows a precise determination of the electronic cubic susceptibility x (-3w;w,w,w) and to learn more about the electronic structure of these materials. In fact, this technique gives not only the magnitude of the nonlinear susceptibility, but when done as a function of fundamental wavelength, allows also to locate the allowed and forbidden for one photon transition excited states. The SHG measurements have been performed at 1.064 im funcnental wavelength leading to the determination of quadratic susceptibility x (-2w;w,w).

Research aimed at addressing materials issues relevant to making doped polymer optical devices is well known.[1,2] Poled doped polymers that exhibit second harmonic generation were first demonstrated by Singer and coworkers.[3] In these materials, the polar order of the dopant chromophores is stabilized when the polymer composite is cooled below its glass transition temperature in the presence of a static electric field. Later studies found that the polar order of such a poled polymer - as probed with second harmonic generation - relaxes over time and that the characteristic time of decay depends on the free volume of the polymer host.[4J Early work aimed at decreasing relaxation rates focused on attaching the dopant molecules to the polymer.[5] In these second-order susceptibility studies, stabilization of slow molecular reorientation was of interest. The faster reversible reorientational effects of molecular dopants on millisecond time scales were first studied by Kuzyk and coworkers using second harmonic generation. Both isotropic and poled polymers were investigated below their glass transition temperature. [6] Later, Boyd and coworkers did similar mobility experiments but modeled the response as a free volume effect.[7] The temperature dependence of Boyd's free volume model and Kuzyk's elastic model showed the same qualitative behavior. In contrast to the slow relaxation process which has impact on the stability of an electrooptic device, the faster reorientational response is of interest owing to its contribution to the third-order nonlinear-optical susceptibility. While this reorientational response may be large in many material systems, materials in which faster mechanisms dominate - such as the fast electronic response would find applications in ultra-high speed devices. The reorientational response in organic liquids is well characterized.{8] Elastic reorientational mechanisms in polymers have only recently been addressed with quadratic electrooptic modulation (a third-order effect).[9,10J When the contribution of these reorientational effects are properly accounted for and removed from quadratic electrooptic measurements, the third order nonlinear-optical susceptibility so determined is found to be consistent with third harmonic measurements.[9,10][1 1] Because the third harmonic measures only the electronic response, it follows that the electrooptic modulation experiment can be used to estimate the third-order response if the reorientational effects are properly accounted for. In retrospect, the agreement between the low frequency electrooptic technique (1 3kHz) and the fast third harmonic results (w 1015Hz) is astounding considering that the comparison spans twelve decades of frequency. Q uadratic electroabsorption studies were first applied to doped polymers by Havinga and coworker to study the orientational order of the dopants.[llJ More recently, Poga and coworkers have reformulated this response as the imaginary part of the third-order susceptibility and applied the technique . . . . (3) (3)to study molecular mobility.[12,13,14] In these studies, the value of the tensor ratio a =X3333/Xii is found to be an indicator of the mechanism of response. Such experiments are well suited for materials physics investigations of the microscopic properties of a polymer as well as how these microscopic properties affect the third-order response. In this contribution, we extend the quadratic electroabsorption technique by measuring the magnitude and phase of the response over a broad range of wavelengths (modulating frequency dependence will be reported later); and, show that quadratic electroabsorption spectroscopy is a useful tool at shedding light on response mechanisms. As an example of how this technique can be used to study the nature of excited states that leads to a nonlinear-optical response, we show that a temperature-independent peak in the quadratic electroabsorption spectrum (which is not observed in the linear spectrum) is evidence of a two-photon state in the squarylium dye ISQ doped in poly(methyl methacrylate) (PMMA). A significant observation is that the different mechanisms dominate at different wavelengths. Indeed, it is this dispersion in the mechanisms that allows them to be more easily separated. Given the high signal-to-noise ratio of our data, we show that a Kramers-Kronig transformation can be used to obtain the real part of the thirdorder susceptibility. Furthermore, the relationships between the phase of the response and the electrostrictive contribution is briefly discussed.

The withdrawal technique is used to obtain the 9-BCMU polydiacetylene (PDA) in the red and blue phases. The ordered blue phase film has an exciton band edge which is shifted by 0.3 eV from that in the less ordered red phase film. The chiral 3-SMBU PDA is found to only exist in an amorphous form in the solid state and films of this polymer are obtained by casting onto a glass substrate. Its absorption edge is intermediate between those obtained in the 9-BCMU films. Refractive indices of 1.65 +/- 0.01 are obtained at 632.8 nm and 1.57 +/- 0.01 at 1.3 micrometers in the red phase 9-BCMU film using a prism coupling technique.

We experimentally investigate the origin of the nonlinear refractive index, n2, of dye-doped polymeric films. We observe large positive or negative values of n2 for different dyes and conclude that it is due to two photon absorption resonant enhancement of the nonlinearity.

We have investigated some aryl substituted dithiolenes which show enhanced nonlinearity and their incorporation into polymer films. These neutral molecules show strong near infra-red absorption whose position is determined primarily by the extent of electron delocalization and the metal atom to which the sulphur ligands are attached. The presence of electron donating groups bathochromically shifts the band and selective detuning from the band is possible to arrive at optimum values for the important ration of nonlinear susceptibility to linear absorption, (chi) ⁽³)/(alpha) . Nonlinear optical characterization of these materials by degenerate four wave mixing and z-scan is described.

Third order nonlinear optical susceptibility of solutions of a triphenodithiazine derivative in dichloromethane has been measured at several different wavelengths utilizing sub-picosecond degenerate four-wave mixing. The values of the second hyperpolarizability, (gamma) , for the neutral and for the oxidized form (dication) are reported. The measurements performed at the wavelengths corresponding to the absorption maxima of the neutral and the dication forms (578 nm and 800 nm, respectively) indicate a twofold increase of the (gamma) /(sigma) figure of merit (where (sigma) is the absorption cross section) for the dication molecule. Time resolved experiments reveal different dynamics of photoexcitation relaxation in the neutral and the oxidized molecules.

The former part of this paper present two types of copolymer systems, paranitroaniline (p- NA)/polyvinylalcohl (PVA) and disperse red 1(DR1)/polymethylmethacrylate (PMMA) were synthesized for frequency doubling (second harmonic generation; SHG) in corona-poled waveguides. Remarkable blue SHGs from waveguides were observed by Cerenkov-type phase matching. The latter part of the paper describes characterization of a novel organic nonlinear crystal : 2-Furyl-Methacrylic-Anhydride (FMA) which has superior transparency ((lambda) _cutoff equals 380 nm), larger SHG coefficient (d₃₃ equals 24 pm/v) and stable physical property.

The electric field induced dynamic phase-matching of SHG waveguide was first demonstrated using a main chain type NLO polymer. The optimum phase-matching thickness was controlled by applied an electric field to polymer waveguide. The effective phase-matching thickness variation induced by poling is about 0.025 micrometers which is 6 times larger than FWHM of phase-matching thickness in conventional slab waveguide. The efficient phase-matched SHG was observed from taperless slab waveguide. No decay of SH conversion efficiency is observed in the presence of electric field.

In the films made of p-nitroaniline (pNA) and methacrylate polymers, the highly efficient second harmonic generations (SHGs) were observed. These are due to the spontaneous growth of the noncentrosymmetric pNA crystals in the particular region of the pNA composition. The SHG intensity depended on the film fabrication conditions. Furthermore, the above films showed long-term stability in the SHG property over 400 hours.

Block copolymers are materials where control over luminescence can be achieved by means of adjusting the length of the active ((pi) conjugated) block. We report on electroluminescent devices from poly[(Silanylene)Thiophene] block copolymers.

We present an extensive photoinduced absorption study of alkyl substituted poly (2,5- thienylenevinylene)s in both the solid state and in solution. The optical and conformational properties of the samples are monitored with UV-Vis absorption and emission, IR absorption and Raman scattering. Three photoinduced states are detected under steady state condition which display lifetimes of the order of 100 ms in the solid state. The two low-energy bands are assigned to bipolarons, while a third band peaked near the band edge has a different origin. In solution very lone-lived photoexcitated states are observed and they are assumed to recombine via a solvent-assisted photo-doping mechanism.

Nonlinear optical polymers offer substantial potential for improvement over inorganic crystals such as LiNbO₃ for the fabrication of electro-optic modulators. In this paper, we discuss the challenges and progress in the area of E-O modulator design and fabrication, with particular emphasis on the requirements of the fiber-optics communications industry. In communications, E-O modulators must compete with direct-current modulation of diode lasers--a well established technology with strong industry support. E-O modulators in general, and polymer modulators in particular, must offer improvements such as increased optical powers, higher bandwidth and lower cost, while maintaining high reliability and good environmental performance. These challenges require substantial improvements in materials and device design, as well as the modulator fabrication and processing. We will discuss these challenges and some of the ways that improvements in polymer materials have addressed (and continue to address) these issues.

This paper describes the properties and applications of some recent polymers in the field of electro-optics. We describe the properties of polyacrylates copolymer with a pending group with large hyperpolarizability. These amorphous copolymers show high optical nonlinear coefficients after poling under an electric field. We have used these copolymers for the manufacture of an electro-optic modulator working at 1.3 micrometers at a frequency of 1 GHz. We also look at the nonlinear absorption of the C₆₀ fullerene for applications in the field of optical limiting. Finally, we deal with ferroelectric polymers and their pyroelectric properties. We describe the realization and performance of an IR pyroelectric sensor using copolymers of poly(vinylidene fluoride-ethylene trifluoride).

A digital thermo-optic (t.o) 2X2 switch based on nonlinear optic (nlo) polymer is presented. The switch exploits a favorable combination of several attractive properties of nlo- polymers: a strong sensitivity for photochemical bleaching, a poor heat conduction and a large t.o.-effect. The bleaching is used to fabricate optical channel waveguides. Mode-sorting waveguides are used to obtain a digital switching behavior. Switching is performed by utilizing the t.o.-effect. For polymers this effect is an order of magnitude larger than for other materials used in integrated optics. The poor heat conduction of polymers results in switching with a low power dissipation.

Practical applications of electro-optic polymers require thermally stable materials with high electro-optic coefficients and low absorption loss. In this report, we first review the properties of some azo-based electro-optic polymer materials and devices. We then describe a new class of electro-optic cardo polymers with glass transition temperatures greater than 200$DEGC.

Phase modulation and optical heterodyne detection were used to transmit and receive six cable television signals at 832 nm using a new polymeric electro-optic material. The electro-optic slab waveguide layer of the phase modulator consisted of a spin-coated, amorphous polyimide film doped with a nonlinear chromophore which had been poled in an electric field. The cladding layers, which confined the optical field within the waveguide, were composed of a photo-crosslinked acrylic polymer. Our television transmission system serves as a stringent test of the utility of the electro-optic polymer for lightwave data transmission.

Recently interest has been growing in exploiting the advantageous fabrication properties of electro-optic polymer materials for optical interconnect applications. For many of these applications a technology for fabricating multilevel registered waveguide structures will be required. Described here is the use of a projection printing technique of waveguide fabrication which has been used to demonstrate a registered two level Mach-Zehnder modulator array. The details of this fabrication technique and design considerations for the multiple level device are presented.

This paper reports on the performance of devices based on current generations of photonic polymers, including passive devices, high-speed electro-optic devices and slow-speed thermo- optic devices. A better understanding of polymer waveguide design and processing resulted in a considerable improvement in device performance. The active devices now show high extinction coefficients (> 27 dB), and low switching voltages (5V) and switching powers (30 mW) for electro-optic and thermo-optic devices respectively.

Wideband modulators based on organic nonlinear optical (NLO) polymers are reviewed. The material properties, design guidelines, fabrication, and performance of a modulator with a > 40 GHz of 3 dB electrical bandwidth in an organic NLO polymer are reported.

A number of new thermally crosslinkable second-order nonlinear optical polymers have been developed and characterized. These polymers are designed for stable nonlinear optical activities since both ends of the rod-like chromophores are locked into a polymer matrix by covalent bonds. Sizable nonlinearities were measured in these polymers and the thermal stability of both main chain and side chain polymers were improved significantly by thermally induced crosslinking. These thermosetting polymers, with the chromophores either included in the main chain or as side chain pendants, have been used in a number of device applications. Waveguide structures can be defined in these polymers by reactive ion etching or ultraviolet bleaching. Thin film integrated optical devices, such as high frequency electro-optic modulators and birefringent directional couplers have been fabricated with reactive ion etching and photo bleaching methods. Waveguide fabrication techniques for multi-layer structures are discussed in detail.

Electro-optic waveguide elements are fabricated in the polymer-on-silicon technology. Measured field distributions of the inverted rib waveguides show excellent agreement with vectorial FEM calculations. This method is also used for electro-optic phasemodulator design. The dynamics of electrode poling is studied by reflectrometry. An integrated waveguide interferometer with lateral electrodes allows the determination of the r₃₃/r₃₁ equals 3.5.

Two types of spatial light modulators are described. One is optically addressed CdS/CdTe- LCLV. Another one is electrically addressed CRT-LCLV. Detailed description is given of the structure and fabrication. To demonstrate their ability of application in optical data processing. Some practical examples are shown.

Polymeric traveling-wave phase modulators have been fabricated to assess the applicability of organic devices as the external modulating elements in coherent optical communication systems. The organic nonlinear optical material in our device was a PMMA-DR1 pendant side-chain polymer. The electrode geometry, used to drive the 1 cm long active region, consisted of a microstrip electrode on top of a poled single transverse mode channel waveguide made by photobleaching at a visible wavelength. This modulator, for which a 3 dB bandwidth in excess of 1 GHz has been demonstrated, was used to transmit a color television signal in a simulated communication system operating at 1.32 micrometers .

The first second-harmonic generation field-induced molecular reorientation experiments in a dye-doped polymer in the 100 K to 500 K temperature range is reported. The (alpha) transition, related to the mobility of the polymer backbone, is easily observed. We also see evidence of the (beta) transition (attributed to side-chain mobility). We demonstrate the low- temperature end of our data suggests that the polymer acts as a rigid elastic constraint to the chromophore. We also observe what appears to be a spontaneously ordered phase of the doped polymer that ma be associated with the polymer/substrate interface. We report on the temperature-dependent phase transition of the transparent indium tin oxide electrode. Suggestions are made on separating the ITO contribution from the polymer response.

Surface potential technique was applied to determine the orientational order of NLO chromophores in poled polymers. The technique is sensitive enough to detect the electro-optic coefficient of the order of 10^-3 pm/v and it is simple because it does not use any optics. It is purely electrical in contrast with other techniques. Relaxation behavior of poled DR1(1wt%)/PMMA was investigated using the surface potential technique. When the surface of the poled polymer was free from a metal electrode, the surface potentials decay monotonically with time. However, the surface potential measured on a metal electrode which was used as an electrode for poling showed an abnormal decay behavior. It was explained by the charge trap centers at the metal-polymer interface.

The polymer poly(methyl methacrylate) (PMMA) doped with the active photoinitiator dimethoxyphenalacetophenon (DMPA) is a well known material to form permanent gratings by uv-holographie. An additional doping with the photochromic material E-(alpha) (2,5- dimethyl-3-furyl)ethylidene(adamantylidene)succinic anhydride (Aberchrome 670) leads to a one step fabrication of a nonlinear optical grating. After the permanent grating is fixed, the refractive index of the grating can be tuned by a homogenous illumination. The diffraction efficiency of the grating can be tuned because the fulgide Aberchrome 670 undergoes a reversible transition from its bleached to its colored form by homogeneous uv illumination and back again by irradiating the film with a wavelength near the absorption maximum (here (lambda) equals 514.5 nm).

We have used the z-scan technique to determine the sign and magnitude of the off-resonant n₂ and two photon absorption coefficient of PTS-polydiacetylene. The sign of n₂ is negative and the magnitudes of nonlinearities are consistent with our previous reports on waveguide measurements.