In this paper, we summarize detailed measurements of the frequency dependence of (gamma) ijkl(-(omega) 4;(omega) 1,(omega) 2,(omega) 3) for the third-order nonlinear optical processes dc-induced second harmonic generation (DCSHG) and third harmonic generation (THG) by wedge Maker fringe techniques recently completed for several important linear polyene structures.

Third harmonic generation (THG) experiments have been performed on a variety of conjugated organic materials over the energy range 0.5 - 1.5 eV. The measured dispersion of (chi) (3)(-3(omega) ;(omega) ,(omega) ,(omega) ) is presented and comparisons between structurally related materials are made to elucidate structure-property relationships. In the benzimidazobenzophenanthroline material series consisting of the fully fused ladder polymer BBL, the semiladder polymer BBB, and the model molecule cis-BB, the effects of polymerization and ring fusion are observed. The cis-BB displays an interference in the THG spectrum, while this feature is absent in the BBB and BBL. The difference in the nonlinearity of the BBB and BBL is attributed to the difference in the number density of the two materials. The effect of the ladder structure on the nonlinearity is demonstrated by comparing the nonlinearity of BBL with PPI, a polyazomethine possessing a similar backbone. The ladder structure increases the nonlinearity by a minimum factor of 5 throughout the energy range examined. The effect of donors on the polyazomethine backbone is examined using the hydroxy and methoxy donors. The methoxy donor increases the nonlinearity, while the hydroxy donor reduces the nonlinearity. The physical implications of these observations are discussed.

The tetrayne monomer with urethane groups in substituents, i.e., hexadeca-5, 7, 9, 11-tetrayn- 1, 16-diyl bis(N-(butoxycarbonyl)methyl)carbamate, was synthesized so as to check the generality of the polymerization scheme observed in a dialkyltetrayne. It was confirmed that the polymerization behavior of this urethane monomer is just the same as the dialkyltetrayne: Namely, the monomer was polymerized by (gamma) -ray irradiation to give a linear polymer of the polydiacetylene with diacetylenic substituents (polymer I), and the following thermal polymerization of diacetylenic moieties in side chains estimated to give a ladder polymer of the di(polydiacetylene) (polymer II) in which two polydiacetylene backbones are conjugated. Though the third-order nonlinear optical susceptibilities of the polymer I were evaluated to be the same order of magnitude as those of the polydiacetylenes with aromatic substituents directly bound to the main chain, no detectable third harmonic generation was observed for the polymer II. This may be due to the disappearance of the excitonic absorption in polymer II, caused by deterioration of the crystallinity and/or instabilization of excitons.

(alpha) , (omega) -Bis(9-anthracenyl) polyenes containing 3, 4, 5, and 6 ene repeat units have been synthesized. These polyenes can be oxidized to extremely stable bipolaronic charge states in solution by SbCl5. There is significant shift in oscillator strength attending the formation of these gap states with (lambda) max for the BP states shifting into the NIR. Stable polycarbonate composites of both the neutral polyenes and the bipolarons can be cast from solution to yield optical quality films for (chi) (3) characterization.

Guest-host polymeric materials combine the good optical quality of the host and the large nonlinear-optical susceptibility of the guest. In this contribution, we report on the fabrication of polymer fibers with an elevated refractive index as defined by a doped core that confines light to regions of high third-order nonlinear-optical susceptibility. The high intensities and long propagation lengths afforded to such a single-mode guide makes the all-optical device figure of merit large enough for certain device applications. The possibility of increasing the nonlinear-optical susceptibility -- thereby the figure of merit -- with metal sphere fractal clusters are presented along with results from quadratic electro-optic measurements of a silver/PMMA system.

Third order nonlinear optical properties of side-chain methacrylate copolymers incorporating 4-amino-4'-nitrostilbene, 4-oxy-4'nitrostilbene, and functionalized silicon phthalocyanine chromophores are measured by picosecond degenerate four wave mixing at 598 nm. The nonresonant stilbene system exhibits a pulse limited ultrafast response, while the resonant phthalocyanine system has a large excited state nonlinearity. Comparison of silicon phthalocyanine copolymers with solubilized guest/host systems dispersed in polymethylmethacrylate illustrate the importance of aggregation and phthalocyanine ring interaction in determining the linear optical properties and the magnitude and speed of the nonlinear optical response.

Several electroactive polymers, such as polyacetylene, polythlophene, poly (p-phenylene vinylene), and poly (2, 5-thienylene vinylene) have shown promise as NLO-active materials over the past few years. Extended conjugation pi-electron polymers, however, suffer from solubility and processability problems. Several recent experimental and theoretical studies have indicated that long conjugation sequences may not be necessary for enhanced (chi) (3) activity. During the past year we have utilized a suggestion of Wudl and coworkers and discovered that long, branched-chain alkyloxy groups can greatly enhance the solubility of various oligomers related to the above polymers. In this paper we present studies directed toward the incorporation of oligomeric subunits in formal copolymers and how stable bipolaronic charge states can be formed in NLO-active repeat units.

Two different liquid crystalline phases and the reversible phase transition between them have been found for the spin coated thin film of tetrakis(octylthio)phthalocyanines both with and without copper (II): Phase 1 of as-prepared films changed with time lapse at room temperature into phase 2 which had a new absorption maximum at the longer wavelength and the longer spacing of crystalline lattice, and the phase 2 returned to the phase 1 when heated up to 100 degree(s)C and cooled down to room temperature. The phase 2 gave several times larger (chi) (3) values than the phase 1 by THG measurements at the same resonant wavelengths. On the other hand, tetrakis(alkylthio)phthalocyanine with the alkylchain shorter than butyl and octakis(octylthio)phthalocyaninato copper (II) with symmetric molecular structure were found not to give the phase 2 and their (chi) (3) values were small, i.e., in the order of 10-12 esu. Thus, phthalocyanines that do not form a tight inclined stack but a loose dimeric aggregation due to permanent dipole and flexible alkyl chains are estimated to be better candidates for third-order nonlinear optics.

Using a two-state model, it was recently shown that there is an optimal combination of donor and acceptor strengths for a given bridge that will maximize the first molecular electronic hyperpolarizability ((beta) ). To date, molecules with sufficiently strong donors and acceptors have not been synthesized to reach this ideal point. Here we outline synthetic strategies that lead to molecules where (beta) is optimized by tuning the degree of bond alternation in the (pi) -electron system between the donor and acceptor. Implementation of this strategy relies on the realization that molecules with strongly aromatic end groups will not have the correct balance of two limiting charge transfer resonance forms in the ground state to achieve the degree of bond alternation required to optimize the molecular hyperpolarizability. Electric field induced second harmonic generation studies on organic molecules with various bridge structures support our hypothesis.

As interest in the quadratic nonlinear optical properties of organic molecules and materials keeps strongly increasing, experimental data start accumulating and provide a better understanding of the structure/property relationships. Compounds were usually developed according to the general recipe of having a push (electron donating) group and a pull (electron accepting) group linked by a conjugated segment.

In designing chromophores for second harmonic generation applications one would like to have a large hyperpolarizability (beta) and an absorption well away from the second harmonic frequency. Unfortunately, there appears to be a connection between the experimentally observed absorption maximum energy and the observed zero-frequency hyperpolarizability (beta) 0, when comparing different molecules within a class, such as donor/acceptor substituted benezenes and stilbenes, that makes this difficult to achieve. In this paper, the origins of this relationship are investigated by comparing results from semi-empirical calculations with experimental values. A significant contribution to the observed relationship between absorption maximum and (beta) 0 is seen to arise from frequency dependences of the ground and excited state dipole moments. Since the two-level model for (beta) is used both as an extrapolation technique to obtain (beta) 0 and as a tool for analyzing the data, a discussion of the validity of this model is also presented.

We report our continuing investigations of the cumulenes, a novel class of compounds proposed for use as the active second- and third-order nonlinear optical component materials for electro-optic and all-optical devices. Unlike conjugated organic nonlinear optical molecules based on alternating multiple and single bonds, these molecules contain a contiguous, or `cumulated' system of double bonds, leading to a highly rigid one-dimensional backbone of polarizable (pi) -electrons. A series of symmetrically- and asymmetrically-substituted tetraphenyl cumulenes has been synthesized and characterized. Direct-current electric field- induced second harmonic generation experiments show significant second-order nonlinear susceptibilities in a series of polar cumulenes. These experiments have been performed at 1.9 micrometers to avoid dispersion effects. Thermogravimetric analysis indicates survival of a butatriene to 300 degree(s)C.

Anomalous-dispersion phase-matching (ADPM) offers large enhancements in the effective hyperpolarizabilities of nonlinear optical processes such as second harmonic generation (SHG) in organic materials. The principal barrier to the practical application of this approach is the residual absorption of asymmetric organic chromophores at the second harmonic which is shown by calculation to inherently limit the efficiency of SHG. Resonance Raman experiments on a nonlinear optical (NLO) dye optimized for doubling 800 nm light indicate that the residual absorbance is probably due to vibronic levels associated with the electronic absorption. Recent work with thin films of PMMA doped with this ADPM dye showed zero dispersion at approximately 6% concentration.

In the design of new organic materials with enhanced nonlinear optical activity, it has been predicted that (gamma) , the third order hyperpolarizability (second hyperpolarizability) will not increase indefinitely in a regular fashion as the conjugation length increases. In regular polyenes, for example, (gamma) has been predicted to level off after circa 10 - 15 repeat units. However, very few experimental systems have been investigated in which the number of repeat units approach these limits. Synthetic difficulties and the lack of solubility of longer oligomers has precluded accurate measures of (gamma) in polyenylic series of well- characterized compounds. In the present study, we discuss how long, and branched-chain alkyl groups attached via alkoxy-substituted phenyl rings can greatly increase the solubility of long polyene oligomers for D,D- and D,A- substituent patterns. This allows, for the first time, a comprehensive study of how (gamma) varies with conjugation length and symmetrical versus asymmetrical substitution.

The nonresonant (pi) -electronic component of (gamma) (- 3(omega) ;(omega) ,(omega) ,(omega) ), (gamma) (pi) , is calculated for all-trans, linear symmetric cyanine, and streptocyanine cations with no double-single bond-length alternation, and for cyanine cations with asymmetric geometries resulting from the artificial imposition of double-single bond-length alternation. These (gamma) (pi) are compared with those previously calculated for all-trans linear polyenes with double-single bond-length alternation, and for a new set calculated with geometries resulting from the artificial imposition of no double-single bond-length alternation. Bond-length alternation is found to dramatically affect (gamma) (pi) for the linear cyanines: the (gamma) (pi) for the symmetric cyanines are calculated to be negative; the (gamma) (pi) for the asymmetric cyanines change from negative to positive with increasing chain length. The (gamma) (pi) for the linear polyenes are always positive regardless of the extent of bond-length alternation; the (gamma) (pi) for the linear polyenes increase with decreasing bond-length alternation. The (gamma) (pi) for the symmetric linear cyanines increase more rapidly with the number of (pi) -electrons than the (gamma) (pi) for the linear polyenes: (gamma) (pi) (symmetric cyanines) varies as N(pi -e)8 and (gamma) (pi) (linear polyenes) varies as N(pi -e)4, where Npi-e equals 4, 6, 8, 10, 12. The (gamma xxxx component along the chain axis is the most dominant one of (gamma) (pi) for all linear molecules studied. The salient 1(pi) (pi) * states and the important terms in the sum-over-states expression that define (gamma) xxxx, and hence (gamma) (pi) , are identified for the molecules. The dependence of (gamma) (pi) and (beta) (pi) on the geometric asymmetry of a pentamethine cyanine cation is investigated. The polymethines in general, and the cyanines in particular, comprise a very interesting class of nonlinear optical, (pi) -electron molecules that merit further experimental study.

The molecular design and assembly of metallophthalocyanine systems that have the enhanced macroscopic third-order nonlinear susceptibility (chi) (3)ijkl(-(omega) 4; (omega) 1, (omega) 2, (omega) 3) and show ultrafast responses are described. Enhancement of the third harmonic susceptibility (chi) (3)1111(-3(omega) ; (omega) , (omega) , (omega) ) was observed in vanadyl phthalocyanine vacuum-deposited film with the staggered stacking arrangement induced by thermal treatment. Processable polymeric system based on tert-butyl mono-substituted rich vanadyl phthalocyanine was developed and the favorable staggered stacking arrangement was induced in a polymer matrix to enhance (chi) (3)1111(- 3(omega) ;(omega) ,(omega) ,(omega) ). Femtosecond-time-resolved spectroscopy was performed on vanadyl phthalocyanine thin films with different morphological forms in order to elucidate the exciton dynamics. The exciton decay kinetics consists of three processes: exciton-exciton annihilation, exciton-phonon coupling, and much slower triplet state formation. The decay rate of the exciton population via exciton-exciton annihilation was found to have a time dependence of t-1/2. The vacuum-deposited film and spin-coated film of vanadyl phthalocyanine derivatives showed similar decay behavior, whereas molecular beam epitaxy film showed a faster decay with a time constant of several hundreds of femtoseconds.

We present results on nonlinear optical properties of newly-synthesized diazo-dye-substituted methacrylate polymers. These dye-substituted polymers, which have been developed for EO devices, contain a dicyanovinyl-terminated, dimethyl-substituted diazo (3RDCVXY) dye exhibiting a larger hyperpolarizability (beta) than that of nitro-terminated diazo (3RN) or monoazo dye. In order to describe the relationship between a bulk susceptibility (chi) (2) and the (beta) value in the presence of electric poling field, a molecular statistical model is proposed. In the model the intermolecular potential due to the van der Waals forces in transitory aggregates is considered. As the 3RDCVXY dyes, which have the central benzene ring substituted by methyl groups, are prevented to come close to each other, the intermolecular interactions influence more weakly on the 3RDCVXY polymers than the 3RN polymers. As a result, the corona-poled 3RDCVXY polymer exhibits a large (chi) (2) value of 1 X 10-6 esu at 1.06 micrometers , whose thermal stability is excellent even at 80 degree(s)C. The poled 3RDCVXY polymer film exhibits a linear EO coefficient as high as 40 pm/V at 0.633 micrometers . An electro-optical light modulation in the channel 3RDCVXY polymer waveguides with half-wave voltage as low as 5 V is also presented.

Using polyimide as host in a guest-host electro-optic thin film a thermally stable poled electro- optic response is demonstrated at temperatures at 150 degree(s)C and 300 degree(s)C. A coplanar-electrode poling geometry is used so that the guest molecular alignment between the electrodes is coincident with the free volume of the host. Electric field poling during curing process including imidization (170 - 230 degree(s)C) and densification (340 - 380 degree(s)C) accounts for the highly thermally stable electro-optic response.

Numerous studies have shown that the orientational decay rate of nonlinear optical (NLO) polymers increases as the glass transition temperature is approached. A high glass transition temperature is thus beneficial to long-term poling stability. Here we report on the synthesis and nonlinear optical properties of poly(N-MNA Acrylamide), which as a glass transition temperature of 205 degree(s)C. This side-chain polymer has the NLO organic molecule 2- methyl-4-nitroaniline (MNA) attached through a carbonyl group to an acrylic polymer backbone. Second harmonic Maker fringe measurements used to evaluate the second-order optical nonlinearity in corona-poled thin films resulted in a second harmonic coefficient d33 approximately equals 3 pm/V at 1064 nm. Thin films were quite transparent with an absorption maximum for poled samples occurring near approximately 320 nm.

Poled polymer thin films are studied by SHG, THG, and ATR experiments. The ATR method is used for determining the linear and quadratic electro-optic (chi) (2) (-(omega) ; 0, (omega) ) and (chi) (3) (-(omega) ; 0, 0, (omega) ) coefficients. The part due to the piezoelectricity and electrostriction is characterized and it is shown that in some cases the mechanical strains are more important than the direct electro-optic effect. From SHG experiments, the degree of orientation linked to the (chi) (2) (-2 (omega) ; (omega) , (omega) ) susceptibility can be evaluated. The various results are presented in this paper.

Second order nonlinear optical properties of doped polymer thin films are studied by optical second harmonic generation and electro-optic coefficient measurements. The studied thin films are guest-host systems and cross linked polymers with charge transfer noncentrosymmetric amines as curing agents. The in situ second harmonic generation (SHG) measurements during poling optimize the poling process and give corresponding components of (chi) (2)(- 2(omega) ;(omega) ,(omega) ) tensor depending on the fundamental harmonic electric field polarization configurations. At the same time they follow the stability of induced dipolar orientation by poling. Obviously, crosslinked polymers are more stable, whereas orientation in guest-host systems decay rapidly with time. The electro-optic measurements in thin films by reflection using the technique proposed by Teng and Man and by Schildkraut measures r33 coefficient even in the doped polymer absorption band and give its real and imaginary parts.

We report second harmonic generation studies of an amorphous polymer (polymethylmethacrylate) containing hyperpolarizable dye species poled in an in-plane geometry where the electrodes are thinner than the polymer film. It is found that polymers poled in this geometry exhibit optical nonlinearity both parallel and perpendicular to the direction of the poling field. It is determined that charge injection into the film is responsible for the nonlinearity in the perpendicular direction. This nonlinearity is much stronger than that predicted solely on the basis of dipole moment -- poling field interactions.

Photoconductivity and third order optical nonlinearity measurements on a dye doped photocrosslinkable nonlinear optical (NLO) polymer -- PVCN (polyvinylcinnamate)/CNNB-R (3-cinnamoyloxy-4-[4-(N,N-diethylamino)-2-cinnamoyloxy phenylazo] nitrobenzene) are presented. Photoconductivity was measured in this polymer system, in both photocrosslinked and uncrosslinked states, without introducing any photosensitizer and photocharge transport agents. Absorption of CNNB-R, peaked at 518 nm, leads to photocharge generation and it is conjectured that CNNB-R also plays a role in the photocharge transport. Additionally, no phase segregation was observed with CNNB-R concentration up to 33wt%. Large quadratic electro-optic coefficients were measured at 633 nm with a modified Michelson interferometer at different CNNB-R concentrations.

Sol-gel processing has been used to prepare a new class of multicomponent inorganic oxide:organic polymer composites which show great promise for both second- and third-order nonlinear optics. Special processing techniques have permitted the preparation of SiO2/TiO2/organic polymer composites in which the relative composition can be judiciously varied to select the linear refractive index for applications in integrated optics. Furthermore, this composite has been doped with both inorganic and organic dopants. The composite film doped with paranitroaniline (PNA) has been successfully poled. Both second-harmonic generation and electro-optic modulation have been achieved in such a poled four-component SiO2/TiO2/Polymer/PNA composite. For third-order nonlinear optics, composites of SiO2, V2O5 with poly-p-phenylene vinylene and the derivatives have been prepared. Femtosecond degenerate four-wave-mixing studies have been conducted on such third-order materials.

This paper describes the properties of a new class of materials exhibiting the photorefractive effect, doped nonlinear organic polymers. Photorefraction (at 647.1 nm) was established by a combination of hologram erasability, correlation with photoconductivity and electro-optic response, and enhancement by external fields in numerous samples (178 to 533 micrometers thick) of two nonlinear epoxy materials doped with hole transport agents based on p- diethylaminobenzaldehyde-diphenyl hydrazone (DEH). Diffraction efficiencies up to 0.1% were observed at bias fields near 100 kV/cm. A useful property of these materials is that poling of the nonlinear chromophores is partially reversible, permitting partial control of the grating readout independent of the space-charge field formed. The polarization anisotropy of grating readout is consistent with the photorefractive mechanism. Two-beam coupling measurements of both absorption and index gratings show (1) the absorption gratings are approximately 10 times smaller than the index gratings, and (2) the phase shift of the index grating is near 90 degree(s), which cannot occur via photochromism, heating, or any other process except photorefractivity.

Single crystals of the electro-optic compound 2-cyclo-octylamino-5-nitropyridine (COANP) doped with small amounts of 7,7,8,8-tetracyanoquinodimethane (TCNQ) have been shown to be the first organic material exhibiting the photorefractive effect. Measurements of light induced gratings and beam coupling proved that the electro-optic response originates from photocarrier generation, charge separation, and the electro-optic effect driven by the space charge field.

The linear and nonlinear optical properties of N-(4-nitro-2-pyridinyl)-phenylalaninol (NPPA) single crystals have been investigated. The refractive indices were measured in the visible and near infrared for wavelengths up to 1318 nm. The nonlinear optical coefficients were measured for the second harmonic generation of 1064 and 1318 nm light. The largest coefficient d23 was found to be 31 pm/V. The phase matching conditions for frequency doubling and sum frequency generation are discussed.

Single crystals of the organic salt 4'-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) are shown to exhibit large second harmonic generation and electro-optic coefficients. Maker fringe second harmonic generation measurements at 1907 nm give d11 equals 600 +/- 200 pm/V and electro-optic modulation measurements at 820 nm give r11 equals 400 +/- 150 pm/V. These initial results as well as preliminary results on the refractive indices, dielectric constants, transparency, and thermal stability of DAST suggest that it and related organic salts are promising materials for electro-optic device applications.

Since 2-methyl-4-nitroaniline(MNA)1 was found as an attractive material for SHG, a large amount of organic nonlinear materials have been synthesized and studied'. Among them, not so many materials were investigated in their properties in bulk or crystal states2. Linear as well as nonlinear optical properties of these materials in their crystal states, for example, refractive indices and their anisotropy and dispersion, d-constants are essential for application of these materials in SHG. In this pager we describe these crystal properties for the material we previously reported in its molecular and powder state.

We have studied the various nonlinear optical processes that can be described in terms of a third-rank (chi) (2)-tensor or a fourth-rank (chi) (3)-tensor: signals of frequency 2(omega) as in second-harmonic generation due to (chi) (2), and signals of frequency (omega) , 2(omega) , 3(omega) due to (chi) (3). (chi) (3)-type difference-frequency generation is also discussed. Structural information is derived in all frequency domains by analysis of the elements of the respective orientation dependent susceptibility tensor.

We demonstrate resonant third harmonic generation as a powerful tool for analyzing the quasi 2-D molecular orientational order in a Langmuir-Blodgett film of poly(bis-m- butoxyphenylsilane). By recording Maker-fringes at different angles between the polarization of the fundamental beam and the dipping direction, we were able to determine the order parameters *2> and *4> simultaneously. We found *2> equals 0.466 +/- 0.030 and *4> equal to -0.12 +/- 0.10.

We demonstrate phase-matched frequency-doubling in Langmuir-Blodgett film waveguides of 2-docosylamino-5-nitropyridine (DCANP). Using the Cerenkov-type configuration we can generate light in the absorption region of DCANP (at least down to 410 nm). The largest nonlinear optical coefficient d33 could be used by exciting TE modes propagating in the film. Coupling of the fundamental beam into the waveguide is demonstrated by means of gratings and prisms.

Some new azobenzene functionalized DMA-copolymers were prepared and their monolayers at the air-water interface characterized by (pi) -A isotherms. Measurements of second harmonic generation from floating and deposited monolayers were performed and the tilt angle and hyperpolarizability of the pendant NLO-phores in the polymer were derived. The apparently low value of the hyperpolarizability obtained for the active groups is attributed to interaction effects between the NLO-phores and their orientational distribution in the copolymer films.

This contribution reports on the chemical generality of processes employed to construct self- assembled chromophoric multilayer materials with high second-order optical nonlinearities. These robust materials can be assembled on a variety of amorphous and single crystal substrates. Furthermore, there is significant breadth in the scope of coupling layer reagents and chromophore precursors that can be employed. These elaborations lead to enhancements in multilayer construction efficiency as does the use of in situ SHG measurements to directly monitor the assembly process. The chromophoric layers undergo facile ion exchange and the chromophore `capping' step in the construction process has been streamlined. Although these multilayer assemblies are chemically rather inert, they can be etched with HF solutions.

Multilayer assembly of organic chromophores with inorganic interlayers is a facile technique for the preparation of nonlinear optical materials with well-defined architectures. Recent reports of T. M. Mallouk (University of Texas-Austin) have indicated that zirconium organodiphosphonates form particularly stable surface multilayers that can be constructed straightforwardly one monolayer at a time. We have synthesized a series of chromophores with shapes and functional groups designed for layerwise deposition as zirconium phosphonates. These include electron donating thiophene oligomers, electron accepting quinodimethanes, and dipolar azo dyes. Cohesive, electrically insulating, thermally stable films of these compounds as layered phosphonates on various substrates were prepared with predictable thicknesses and, in some cases, polar order. Second harmonic intensity from the polar azo dye films was proportional to the thickness squared, consistent with theory. The dielectric and optical responses of a variety of other kinds of samples are discussed.

Langmuir-Blodgett films have been fabricated of a prepolymerized amphiphile containing a chromophore of high second-order nonlinear optical activity. Thick films, containing as many as 262 layers of noncentrosymmetric structure have been prepared by alternate deposition of the dye polymer and several different materials. In contrast to previous literature reports on Langmuir-Blodgett films of other polymeric dyes, these films show the theoretically expected quadratic dependence of second harmonic generation with film thickness. Polarization studies of the second harmonic generation demonstrate that the chromophores are highly ordered in these films. In addition, by using all-polymeric materials it has been possible to fabricate a waveguide of these films with optical attenuation of about 1 dB cm-1, substantially lower than has been previously reported for Langmuir-Blodgett films even without a noncentrosymmetric structure.

The exceptional electro-optic properties of poled polymer films, coupled with the power and flexibility of thin film fabrication and photolithographic processing, may make possible a new class of integrated optic systems: photonic large scale integration (PLSI). PLSI systems are characterized by the hybrid integration of electronic and photonic devices, combining the processing power of VLSI with a dense, high bandwidth, photonic interconnection and switching network in a single, large format, package. In this paper, we describe the potential applications and benefits of PLSI and present a review of some of the relevant progress to date in electro-optic polymer materials and devices, including the demonstration of polymer switch based 100 Mbit/sec digital signal transmission for optical interconnection and a 20 GHz electro-optic polymer modulator.

Planar waveguides were made from a linear epoxy copolymer of bisphenol-A diglycidyl ether and amino-nitro-tolane. The refractive indices, nTM and nTE, and the electro-optic coefficients, r33 and r13, of the poled nonlinear optical polymer films were determined by measurements of the waveguide modes of these films at a wavelength of 632.8 nm, and the results are reported for both electrode and corona poling. The ratio of the second order susceptibilities was found to exceed significantly the theoretically expected value of 3. Restricted motion of the nonlinear chromophores during poling provides a possible explanation of this discrepancy.

Reflection-mode interference modulators can be used in electrical-to-optical interconnects. Prototype devices were implemented using poled nonlinear polymer films. The modulators were characterized and analyzed. It is shown that a modulation depth exceeding 10% is feasible using existing nonlinear polymers.

A novel passive optical device type is described yielding enhanced reflectance with increasing optical intensity at visible wavelengths. The device is a multilayered thin film Bragg structure, consisting of alternating layers of a transparent polymer and a transparent polymer doped with organic nonlinear optical (NLO) materials. The device operates through the intensity dependent charge of the optical index of refraction of the NLO material. Multilayer optical thin film computer codes were developed and used in the design, modeling, and fabrication of this device. The Bragg structure transmits under low intensity conditions and changes to a reflector with increasing intensity. Present devices were fabricated with poly- (methylmethacrylate) PMMA and PMMA doped with silicon naphthalocyanine (SiNc), an off- resonant electronic third-order organic NLO material. Intensity dependent increases in reflectivity were measured on picosecond time scales with fractional reflectance changes greater than 40% being observed. Along with the device performance results, characterization efforts on the NLO materials are discussed.

Optically nonlinear side chain polymers have been used to make a number of polymeric electro-optic and thermo-optic switching devices. The following devices are described and their performances discussed: a 2 X 2 electro-optical directional mode coupler; a 1 X 2 Mach-Zehnder switch comprising a Y-splitter combined with 2 parallel arms and a directional coupler section; a polarization and wavelength independent switch comprising a Y- junction; and an electro-thermo-optical Mach-Zehnder interferometer. In addition, the stability of some of the devices is presented and discussed. The directional mode coupler shows -17 dB modulation depth for 7.5 Volts switching voltage; the Mach-Zehnder switch required 10 Volts for 14 dB switching ratio; the Y-junction switch needed 50 mW for >20 dB modulation; the electro-thermo-optical Mach-Zehnder required as low as 0.5 mW to achieve (pi) -phase shift. The results show that optically nonlinear side chain polymer are attractive materials for the realization of polymeric switching devices.

Optical switches, bistable optical devices, and spatial modulators (SLMs) are important key elements in optical computers and in optical data processing systems. In recent years this field has advanced tremendously; however, the lack of appropriate materials to implement theoretical design of optical hardware is often considered as a bottleneck in realizing the potential of this field. Organic materials may provide the ideal medium needed for this optical hardware. It is already known, for example, that such materials exhibit the extremely high nonlinear optical susceptibilities that are necessary for optical data processing. An all-optical device based on appropriate organic materials will operate on the intensity induced changes in the complex index of refraction, i.e., the absorptive and dispersive properties of the medium due to intensity induced population changes. Theory predicts that optical bistability can be observed in such materials. In this paper we examine the possibility of producing nonlinear optical devices based on organic nonlinearly absorbing materials.

New nonlinear optical polymers (NLOP) having potential utility in waveguides for the modulation and switching of optical signals are reported. A new class of chromophoric polymers which assume a folded, polar conformation of the backbone have been prepared. The polymers have a syndioregic arrangement of chromophores within the backbone (i.e., a head-to-head, tail-to-tail configuration). Polymers were synthesized by the polymerization of difunctional, precoupled pairs of chromophores and difunctional, bridging groups. Glassy, noncentrosymmetric films were prepared by electric field poling and by Langmuir-Blodgett (LB) deposition. Characterization of multilayer LB films by null ellipsometry to determine the anisotropic refractive parameters was performed at different angles of incidence and at a wavelength of 1.0 (mu).

The linear optical and electro-optical properties of new guest-host poled polymeric thin films are reported based on combined ellipsometric and modulated reflection measurements. Wavelength dispersion of the electro-optic coefficient and comparison between second harmonic generation and electro-optic coefficients are in keeping with a two-level model of the quadratic nonlinearities. The large extension of the conjugated systems may account for the remarkable quasi-absence of relaxation of the electro-optic coefficient over a period of months, when incorporated in PMMA. Operation of a waveguide phase modulator has been demonstrated at 1064 nm in a multilayer strip waveguide architecture over a GaAs substrate, and shown to correspond to r33 equals 1.76 pm/V. Further optimization is underway.

The simultaneous measurement of the xxz and zzz components of the quadratic susceptibility of Non Linear Optical functionnalized polymer films is performed by Fabry Perot under Oblique Incidence technique.Precise results are obtained without any accurate knowledge of the complex dielectric constant and the thickness of each layer.The deorientation of a non linear optical unit is compared in three main chain functionnalized polyurethanes at a constant difference of temperature below the glass transition temperature. Independently of the absolute value of the Tg, the rate of deorientation is very dependant of the monomer structure.

The dielectric relaxation characteristics of narrow molecular weight distribution polystyrene (PS) films containing the second order nonlinear optical dyes, 4-[N,N- dimethylamino]-4'-nitrostilbene (DANS) and 4-[N-ethyl, N- hydroxyethylamino]-4'-nitroazobenzene (DR1), at a level of 0.19 mole percent, are reported using time domain dielectric spectrometry. Measurements ranging from 10-4 to 10+4 Hz have allowed us to closely examine sub-Tg dipolar losses that are associated with the dye. It is seen that the frequency range over which dye relaxations occur are similar to those characteristic of the sub-Tg (beta) transition of polystyrene though with grossly different dispersion amplitudes. The dye relaxation time activation energies are 131 kJ/mol and 79 kJ/mol for DANS and DR1 respectively. The dye relaxation amplitudes do not follow predicted T-1 behavior. Extremely broad dispersion curves imply a broad distribution of relaxation times. With physical aging, little change in (beta) amplitude is seen though a narrowing of the relaxation time distribution function seems to occur. Our results indicate that in a poling experiment with near ambient temperature aging, sub-Tg (beta) losses will account for losing 17 - 20% dye orientation within a matter of seconds after field removal. Relaxations occurring over longer times arise from a combination of (alpha) and (beta) losses.

Resonant enhancement can greatly influence a materials third order optical nonlinearity and therefore (chi) (3) values can be highly wavelength dependent. The increased flexibility of a frequency tunable optical parametric oscillator (OPO) with a tuning range of 420 - 2500 nm has allowed us to measure, with relative ease, (chi) (3) dispersion curves in a THG experiment thereby identifying and quantifying resonant enhancement. The OPO is based on a (beta) -BBO crystal and is pumped by the third harmonic of a Q-switched Nd:YAG laser yielding a total output efficiency of greater than 15%. Conjugated polymers have been shown to display an order of magnitude enhancement of the cubic susceptibility due to 2 or 3 photon resonances. In this paper we display (chi) (3) values between 1 - 2.1 micrometers for polyacetylene, all trans-(beta) -carotene and Manganese phthalocyanine, which all show evidence of resonance effects in this wavelength region. The dispersion of (chi) (3) can be measured by tuning the OPO by crystal rotation to the appropriate resonant or nonresonant wavelength.

Newly synthesized polymer ion-dye complexes, poly-(2-acrylamide-2- methylpropanesulfonic acid) (AMPS)-hemicyanines (HC-1, 2), are investigated by the electroabsorption. The relation between (chi) i(3)(-(omega);(omega),0,0) and (chi) (3)(-3(omega);(omega),(omega),(omega)) is compared with a three-level model. Good agreement between the estimation and the experimental results of the third harmonic measurements is obtained.