Nonlinear optical processes in ic-electron organic and polymer systems have attracted considerable study because their fundamental understanding has led to observations of new phenomena and new theoretical findings and to the development of new materials and devices of considerable promise1. The ic-electron excitations occurring on the individual molecular, or polymer chain, units are the basic origin of the observed large nonresonant nonlinear optical coefficients. The coefficients are broad band and ultrafast, and, as shown by theory and experiment, their sign, magnitude, and dispersion are determined by many-body electron correlation effects1. The field has now arrived at a critical crossroad to realize actual technological applications. Table 1 summarizes many of the key features of nonlinear optical polymers. Activities have increasingly centered on high performance materials that comply with device manufacturing and end-use conditions. The main attractions for applications remain the low cost, practical materials processing associated with polymer films, fibers, and bulk components. In an important recent development in data communications networks, a new application area may be emerging for optical polymer materials in the form of high band width polymer optical fibers (POF). In this review, we briefly summarize several recent developments in organic nonlinear optics. The summary is intended to illustrate the rich variety of developments in the field. The topics include exciton strings, photoactive proteins, polymer optical fibers for data communications, two photon states in third order optical processes, electrooptic polymers, photorefractive polymers, octopolar organometallic complexes, and multigigahertz electrooptic modulators.

A series of new silicon phthalocyanine monomers containing two or more hydroxyl groups has been synthesized by axial etherification of [PcSi(OH)₂] with various polyfunctional alcohols, where R is a residue generated from an appropriate alcohol namely, ethylene glycol, glycerol, triethanolamine, triethylene glycol, 1,4-bis(2- hydroxyethyl)piperazine and N,N-bis(2-hydroxyethyl) isonicotinamide. All derivatives are soluble in common organic solvents such as chloroform and dioxane, and exhibit low absorptions in the visible spectral region. The dimer [RO(SiPcO)₂R] and trimer [RO(SiPcO)₃R] of triethanolamine have also been synthesized to investigate structure-property relationships. The above derivatives can be processes into thin polymeric films either by reacting with a diisocyanate compound or with a reactive polysiloxane. Third- order nonlinear optical properties of the above derivatives are described.

The dipole moments ((mu) ) of a series of zwitterionic nonlinear optical chromophores doped into poly(methyl methacrylate) have been determined. Values of between 34 D and 38 D have been measured through the fitting of a uncurtailed Langevin function to the incidence angle dependence of the p-p second harmonic intensity generated from corona poled films. It is shown that accurate values of dipole moment can only be determined when the poling fields are lower than approximately 100 MVm^-1 above which existing electric field poling models appear to be inadequate. The reasons for this are as yet unknown, possible mechanisms of the effect are presented.

We present preliminary results obtained from in-situ linear absorption spectroscopy of polymer fractal metal cluster formation. We discuss background material pertaining to the linear optical properties of a fractal cluster, present the experimental results, and interpret our findings.

We report on a second harmonic generation in a poled polymer waveguide using anomalous dispersion phase-matching. Blue light was produced by phase-matching the lowest order fundamental and harmonic modes over a distance of 32 micrometers . The experimental conversion efficiency was n equals 1.2 X 10^-4, in agreement with theory. Additionally, we discuss a method of enhancing the conversion efficiency for second harmonic generation using anomalous dispersion phase-matching to optimize Cerenkov second harmonic generation. Our modeling shows that a combination of phase-matching techniques creates largest conversion efficiencies and reduces critical fabrication requirements of the individual phase-matching techniques.

The enhancement of the third order susceptibilities (chi) ⁽³) and second order molecular hyperpolarizabilites < (gamma) > in a series of covanlently stacked dimer and trimer macrocycles (SiPc and SiNc) was observed throught he phase conjugated signals from DFWM measurements at both 1064 and 532 nm. The FWHM of the phase conjugated signals at 532 nm is much smaller than those at 1064 nm and those of the reference compound CS₂. The < (gamma) > values at both wavelengths as a function of number of the monomer units (n) have an approximate n³ dependence, differing only in the scaling constant. The origin of such enhancement is discussed and compared to those in 1D (pi) -conjugated systems.

The longitudinal component of the static first hyperpolarizability per unit cell of model finite and infinite polymethineimine chains has been computed at the uncoupled Hartree-Fock level of approximation. Particular attention has been paid to the correspondence between the results associated with the large oligomers and the direct polymeric results. We have investigated as a function of increasingly large chain length the effects of the heteroatomicity and the bond alternation upon the electron density alternation and centro-symmetry which modulate the amplitude of the longitudinal first hyperpolarizability per unit cell.

A new class of thermally and chemically stable donor-acceptor substituted thiophenes is presented. It is shown that exceptionally large electro-optic activity (as high as 30 pm/V at 1.3 micrometers ) can be achieved by doping/covalently bonding highly efficient trycyanovinylthiophenes into high temperature polymers such as polymidies and polyquinolines. Monitoring the long-term stability of electro-optic activity at temperatures above 100 degrees C has revealed that the covalent bonding approach is quite superior to the guest-host approach in polymide as well as polyquinoline based materials.

Chromophore relaxation is still one of the major problems of NLO polymers. Two strategies have been developed to overcome this problem. One of them is crosslinking after poling. We synthesized new polymers with methylfuryl acryloyl side groups. Upon irradiation with UV- light, they undergo a (2 + 2) cycloaddition which leads to a highly crosslinked material. Compared to cinnamoyl gorups frequently used in such polymers, the absorption of the novel crosslinker is shifted to longer wavelengths. This allows to use a cutoff filter during irradiation and therewith minimizes chromophore decomposition. The second way to suppress chromophore relaxation is the use of polymers with high glass transition temperatuers. We have prepared a number of polymers by copolymerization of NLO-active methacrylates with the bulky adamantyl methacrylate. This leads to polymers with glass transition temperatures up to 190 degrees C. The synthesis and properties of these polymers are reported in detail. The polymers shown a good long term stability of the electro-optic coefficient (r₃₃) with its relaxation approximately following a KWW-function.

A new copolymer system with high, but still variable glass-transition temperatures was synthesized. The fixation of various NLO-chromophores is performed after the radical is performed after the radical copolymerization by a polymer analogous reaction. This was accomplished by copolymerizing various N-substituted maleimides with methylvinyl- or vinylisocyanate, so that a polymer with a 1:1 composition of the two monomers and reactive isocynate side-groups is obtained. With different substituents attached to the imide-ring, T_g can be adjusted between 100 and 200 degrees C. Two effects of the substituent at the imide-nitrogen are observed. Bulky gorups reduce the mobility of the chain and lead to high T_g values. A similar tendency is found for smaller less flexible substituents. In this case the intermolecular forces by hydrogen-bonding (urethanes) contibute ot the effects for high T_g's. A variety of different NLO-chromopores can be fixed on the polymer backbone by reaction of a hydroxyalkyl-spacer with the isocyanates, so that a urethane linkage between the chromophore and the polymer is formed. Based on the experience obtained with this first class of NLO-materials, new functionalized polymers were prepared. In order to further increase the T_g-values, while keeping a good processability (solubility), chemical modifications of the spin-coated polymer were prepared. In order to further increase the T_g-values, while keeping a good processablility (solubility), chemical modifications of the spin-coated polymer were performed. Monomers functionalized with tertiary butyl groups (esters or carbonates) allow it, to split off isobutene from the final (and processed) polymer, thereby reducing its solubility and increasing its T_g-value.

Summarized are two project areas: First, the development of a quantitative structure property relationship for analyzing thermal decomposition differential scanning calorimetry data of electro-optic dyes is presented. The QSPR relationship suggest that thermal decomposition can be effectively correlated with structure by considering the kinds of atoms, their hybridization, and their nearest neighbor bonded atoms. Second, the simple preparation of clad plastic optical fibers (POF) is discussed with the intention of use for nonlinear optical applications. We discuss preparation techniques for single core and multiple core POF, and present some recent data on index profiles and the optimization of thermal stability in acrylate-based POF structures.

A general approach to the synthesis of second-order nonlinear optical (NLO) polymides exhibiting high thermal stability has been developed. Several selected NLO chromophores have been incorporated into the polyimide backbone. Detailed physical studies showed that these polymers are very promising for practical applications. Three of these polyimides are soluble in common orgainc solvents, offering the ease of processing. High glass temperatures, around 230 degrees C, ensured a long term NLO stability at elevated temperatures, such as 150 degrees C. Low optical loss was observed for those soluble polymers. The synthetic approach is also versatile and will allow the syntheses of many other functional polymers.

An inorganic methyl-siloxane based buffer material has been investigated that is suitable for nonlinear optical waveguides used in integrated electro-optic devices. Slab waveguide structures were fabricated to study the influence of buffer layers on poling mechanisms. Poling currents and second harmonic intensities were measured simultaneously under various poling conditions. Maximum poling efficiency for sandwich structures was found to be close to T_g being identical to samples without buffer. Poling currents first decreased with time following a t^-4 dependence and finally reached a steady-state value. Resistivities were determined from saturation currents for different temperatures and electric field strengths. An Arrhenius-like temperature dependence of the resisitivity was found for both buffer materials and NLO polymer in its glassy state. For both materials a Schottky-type dependence of the resisitivity on the elctric field strength was observed at poling tempertures. Charge injection currents into buffer were found to be one order of magnitude smaller than into the NLO polymer. Electro-optic coefficients of poled samples with and without buffer layer were measured providing that even higher degrees of chromophore orientational order can be achieved in samples with buffer due to an increased electrical breakdown limit. A low index of refraction and a high transmittance were determined for the whole visible to near infrared spectral region. Channel waveguides wer realized by photobleaching.

Possibilities and limitations of second-order nonlinear light scattering techniques in the determination of the components of the molecular hyperpolarizability tensor (beta) _ikl are discussed. The experimental feasibility of such measurements is demonstrated using para- nitroaniline as the nonlinear molecule. The number of independent measurements that can be performed on the hyperpolarizability tensor is limited by the number of rotational invariants of the isotropic orientational average ((beta) _ikl(beta) _jmn). For the cases of general nonlinear light scattering and hyper-Rayleigh scattering the maximum numbers of independent measurements are fifteen and six, respectively.

Photobleaching experiments on thin films of azo chromophore functionalized methacrylates were carried out to investigate bleaching kinetics and its underlying mechanisms. The polymer film's spatial index variation was measured and compared with a theoretical model of bleaching dynamics. From IR-spectroscopy and from GPC measurements it was found, that bleaching causes a destruction of the chromophore and a broadening of the polymer molecular weight distribution. The generated low molecular weight fractions from both polymer and chromophore photodecay evaporate during annealing above T_g, resulting in a reduction of the film's thickness. Surface roughness increases during photobleaching, causing an increase in waveguide loss. Film surface can be smoothed completely by annealing, thus lowering the optical loss induced by bleaching.

The first hyperpolarizabilities, (beta) , of bacteriorhodopsin, retinal, and related molecules were determined experimentally by using the hyper-Rayleigh scattering technique and compared to the calculated values obtained with the semiempirical intermediate neglect of differential overlap/configuration interaction/sum-over-states method. The experimental and theoretical results are in excellent mutual agreeement. The hyper-Rayleigh scattering technique is shown to be very sensitive to the degree of solubilization of bacteriorhodopsin. Theoretical and experimental data confirm the expected dependence of (beta) on the first transition energy as well as an exponential increase of (beta) with the number of double bonds. It was found that, upon trans to 13-cis or 9-cis isomerization of a retinal double bond, a constant fraction of the (beta) value is lost, regardless of the nature of the electron withdrawing group or the solvent of choice.

The electronic structure of conjugated polymers of current interest in the developemnt of novel organic light-emitting diodes, poly(p-phenylenevinylene) and its derivatives, has been studied experimentally by ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy as well as theoretically using quantum-chemical calculations. The focus of this work is on the (pi) -electronic structure near the Fermi level, which is of prime importance in the phenomena of charge carrier injection, interface formation, and light emission.

Photoinduced depoling in a crosslinked side-chain polyurethane-disperse red 19 thin film is investigated. Using an electro-optic grating modulator, we have investigated the electro-optic coefficients and depoling rates of the poled polymer films as a function of incident fluence at different wavelengths from 543 to 795 nm. Our experiments showed that when the incident wavelength approaches the absorption peak of the nonlinear optical chromophore attached to polymer backbone, the depoling effect becomes more and more severe. The photoinduced relaxation rate increased approximately 5 orders in magnitude from 670 nm to 543 nm. The photoinduced depoling was observed even at wavelengths 200 nm away from the peak absorption wavelength of the chromophore. A polarization microscope showed that chromophores were randomized and rotated by the excitation laser beams after exposure. However, no significant photoinduced depoling was detected during the time span of the measurement of 795 nm near infrared wavelength which is approxiamtely 320 nm away from the absorption peak.

Since the introduction of hyper-Rayleigh scattering (HRS) as a measurement technique for the first hyperpolarizability (second-order polarizability) of molecules in solution, the importance of fluctuations in the orientational distribution was realized. For isotropic solutions, a combination of the spatial and temporal fluctuations causes the instantaneous and local deviation from macroscopic centrosymmetry, which allows the observation of a second-order HRS signal. Femtosecond HRS has been used to probe the spatial orientational distribution function of nonlinear optical chromophores. The fluctuations in this function cause an HRS signal that fluctuates as a function of position. The decay of the autocorrelation function of this fluctuating signal is characterized by a correlation length. The correlation length indicates the degree of spatial correlation between the chromophores in the solid state. The development of femtosecond HRS was instrumental for the study of orientational correlations.

A novel measurement technique for characterizing both the real and imaginary parts of the electro-optic r₃₃ and r₁₃ coefficients of in-plane poled polymer thin films is proposed and demonstrated. Efficient in plane poling with applied DC fields up to 200 V/micrometers was achieved. A r₃₃ of 12.5 pm/V at the 1.3 micrometers wavelength was measured for a polyurethane disperse red 19 polymer. 'Push-pull' modulation was demonstrated.

We report on the studies of three photorefractive (PR) polymeric systems: two different multifunctinal polymeric composites and one doped polymer. The doped polymer system consisted of charge transporting polymer, a plasticizer, a photocharge generation sensitizer, and a second-order nonlinear optical chromophore. The measurements of the electric field and light fluency dependencies of charge photogeneration efficiency, response speed, carrier mobility and diffraction efficiency provided information about the kinetics of the photorefractive effect. The two new multifunctional photorefractive polymers each contains a second-order nonlinear chromophore and a charge transporting molecule covalently attached to the polymer backbone (methacrylate chain or silica). The charge transporting and the second- order NLO segments of the polymer are the N-alkylated carbazole group and the stilbene derivative, respectively. Fullerene C₆₀ or charge transfer complex of trinitrofluorenone:carbazole was utilized as charge generating sepcies. The specific advantages of sol-gel processing of organically modified silanes render optical quality materials having the properites of both oxide glass and organic compounds. Electro-optic and PR responses in these composites have also been measured.

The imaginary part of the third order nonlinear optical susceptibility is evaluated for several squaraine dyes to determine the characteristics of their excited states. Quadratic electroabsorption and linear absorption spectroscopy are used for this evaluaiton as well as to determine mechanisms responsible for the nonlinear optical properties of these dye-doped polymers. THe value of (chi) ⁽³) (in which we use an optical field to probe the effect of a static field) is of importance in evaluating the applicability of these thin-films dyes to all- optical devices. The nonlinear responses are compared to the three- and four-level models to help determine which models are most suitable for predicting nonlinear behavior.

The transient behavior of photorefractive gratings in the polymer composite poly(N-vinyl carbazole) (PVK), 2,4,7-trinitro-9-fluorenone doped with the electro-optic molecules 4- (hexyloxy)nitrobenzene or N,N-diethyl-para-nitroaniline is presented. It is shown that despite the dispersive character of charge transport in polymers, information that allows the estimation of the hole drift mobility is obtained. The change in the hole drift mobility for samples with various trap densities, induced by 4-(diethylamino)benzaldehyde diphenylhydrazone, was measured.

The method of increasing the resolution of an optical addressing system is offered. A dynamic lens which is induced by a controllable light beam in a photochrome dye is used. The performance of the dynamic lens formed in the photochrome medium has been investigated. The findings of an investigation into a reversable light-sensitive crown-bearing medium are presented. It has been found experimentally that the resolution of the optical addressing system can be increased by an order of magnitude if the solution of a phitichrome crown-bearing dye is used.

The transient multiple diffraction rings associated with self-phase modulation is observed from PMMA doped with different dyes. The phenomenon is shown to be the result of laser-induced refractive-index change. The experiment is done on three different films fo PMMA doped with sulfrodamine, DCM, and Accriden yellow. The films were fabricated using the spin coating technique. The Ar⁺ laser at 514 nm was used as the exciting beam to the thin film. The transmitted laser formed interference fringes on a projection screen. It is observed that by increasing the thickness of the film, the number of rings increased. The relation between the thickness of the thin film and the number of rings was found to be different for the three films. This could be explained as the induced thermal refractive index coefficient in each of the samples depending on the strength of absorption of the 541 nm line by each material. It is also found that the third order nonlinear susceptibility enhanced with increasing the thickness of PMMA doped with Accriden yellow. The results also indicate the sensitivity of the transport phenomena in PMMA by changing the guest/host combination and the polymer doped with dye could be optimized for certain applications.

Transient third-order nonlinearity is induced by electronic resonances of excited molecules. Intensity of a signal, which is generated due to transient nonlinear susceptibility, strongly depends on a relaxation pathway and rate of high excited molecular electronic states, and on molecular dynamics in a low-lying excited state. Experimental and theoretical data, concerning a transient susceptibility dependence on dynamics of excited polyatomic organic molecules (ultrafast dephasing and depopulation processes, orientation anisotropy, time-dependence of transient absorption spectrum), are discussed. Obtained results demonstrate a high sensitivity of transient third order susceptibility to dynamics of excited molecules.

Among the different possibilities to generate a beam conjugated to an incident one, saturable absorption is presented as the most simple method. Recently, several authors have, however, described the use of Xanthene dyes (XD) as good candidates for degenerate four-wave mixing at low laser powers. This paper deals with the description of the systematic study of six XD compounds: Fluorescein and five of its halogenated derivatives. The rigid matrix in which the dyes are embedded is made of a poly(vinyl alcohol) film prepared from an aqueous solution. The measurements of the saturation intensities as well as reflectivities of phase conjugation mirrors are obtained by an original experimental set-up connected to a data acquisition system. Different parameters such as sample thickness, optical density or beam ratios are investigated. The results for the six dyes are presented and compared.

Conjugated polymers and oligomers are very interesting materials, with a number of possible electronic, optoelectronic, and photonic applications. New synthesis techniques allow the preparation of extremely pure soluble poly(paraphenylenes), showing a steepness at the bandedge comparable to conventional semiconductors. One consequence of this high purity is an improved photoluminescence quantum yield, higher than 24% for thin films. Copolymers of stepladder poly(paraphenylenes) are presented, which can be understood as the polymeric version of quantum well structures. Oligomers of poly(paraphenylene), like p-hexaphenyl can be produced as highly pure, well ordered thin films, which show a high photo-luminescence quantum yield in excess of 30%. All these materials, including an improved poly(phenylenevinylene), are applied as the active layer in light-emitting devices, giving bright light emission in the visible range and we report on their performance and efficiencies. Finally, we present a new preparation technique to produce highly ordered self assembled aromatic oligoazomethines, which are applied as transport layers in multiheterolayer electroluminescence devices.

The effect of axial ordering in determining macroscopic second order nonlinear optical response is investigated by the second harmonic generation measurement. Maier-Saupe mean field theory was employed to estimate the axial ordering contributions. The magnitude of second harmonic generations as a function of a dc external field suggests that the effect of axial ordering is negligible while polar ordering is dominant.

The nonlinear optical properties of diphenylacetylene and bis(4-biphenyl) acetylene have been investigated using the Z-scan technique. In these experiments the solid materials were heated above their melting points into the isotropic liquid state using a temperature controlled hot stage. Using this method, the nonlinear optical properties of materials with low solubility or where the solvent may have a significant contibution to the observed nonlinearity can be measured. Nonlinear absorption and refraction have been measured to be 1.4 cm/GW at 532 nm which gives a two-photon absorption cross-section (sigma) ₂ equals (17 +/- 6) X 10^-50 cm⁴s/photon-molecule. The nonlinear absorption coefficient of molten refraction for both of these materials has also been investigtaed. Molten diphenylacetylene has a nonlinear refractive index n₂ equals 3.9 X 10^-12 esu. Surprisingly, the bis(4-biphenyl)acetylene appears to have a very small nonlinear refractive index. The optical limiting behavior of molten bis(4-biphenyl) acetylene has also been studied.

Second-harmonic generation from chiral surfaces has different responses to fundamental beams that are left- and right-hand circularly polarized. This form of nonlinear optical activity can occur within the electric-dipole approximation. However, second-order nonlinearities involving magnetic-dipole transitions, which can be strong in chiral media, also contibute to the circular-difference response. We describe a new measurement technique that is based on continuous variation of the state of polarization of the incoming fundamental field, which allows us to assess the relative importance of the electric- and magnetic-dipole contributions to the circular-difference response. We will report the results of our measurements on second- harmonic generation from surfaces consisting of thin films of chiral polymers.

The charactertization of light guiding and nonlinear optical properties of thin films based on poly(methyl methacrylate) doped with organic dyes 4-dicyanomethylene-2-methyl-6-p- dimethylaminostyryl-4H-pyran (DCM), Pyrromethene 567, and sulforhodamin was done using the prism coupling technique and nonlinear optical spectroscopy. Stimulated light emission in DCM doped waveguide with apparent pump threshold and spectrum narrowing was observed at transverse pumping with frequency doubled Q-switched Nd:YAG laser. PM-567 doped waveguide being transversely pumped with CW Ar⁺ laser at 514 nm demonstrated fluorescence with 0.19% energy conversion slope efficiency at 616 nm spectral peak. Upconverted fluorescence was found in the same waveguide at longitudinal CW infrared pumping. Sulforhodamin doped films demonstrated multiphoton excited fluorescence and surface enhanced second harmonic generation.

We report on a novel class of optically nonlinear polymeric materials realized by processing onto a substrate a combination of molecules and polymers comprising hyperpolarizable and thus optically nonlinear molecular groups, liquid crystal moieties, and chiral moieties. Since processing of this combination of materials leads to a spontaneously noncentrosymmetric bulk orientation of the hyperpolarizable moieties in its thermodynamically most stable state, the material exhibits second-order nonlinear-optical properties that can be used for second-order nonlinear-optical effects such as frequency doubling of optical radiation, the linear electro- optic of Pockels effects, magneto-optic effect, nonlinear dichroism, etc. We will present and discuss the experimental results concerning the nonlinear-optical properties obtained via frequency doubling of light in these materials.

The mission and scope of the National Science Foundation (NSF) and lightwave technology will be very briefly discussed. The focus of the presentation will be directed toward changes in research support that are taking place and the opportunities we have for aiming our research to meet the challenges and needs that face the nation. In the USA it is very clear that defense oriented research is downsizing and is being redirected into economy driven aresas, such as manufacturing, business, and industry. For those researchers who are willing to move into these areas and find a niche, the rewards may be very great. Industrial research partners should also seize these opportunities to enhance their resources in an otherwise bleak future for industrial support of basic research in lightwave technology and many other reserach disciplines. These activities of bringing together industry and academia will have the value added benefit of providing increased job opportunities for students. An outline of some of these opportunities and incentives will be presented. On the international front, there has never been a better time for the encouragement of joint research and collaboration across borders. The economic potential for involvement in Eastern Europe and Asia are enormous. Agencies like ourselves are open to help support of visiting scientist/engineer exchange, international conferences and forums and support of innovative ideas to help further enhance economic developemnt of the world and hence the quality of life. The presence of the Russian delegation here at these SPIE meetings in in part the result of NSF support. Concomitant with these changes is a growing interest in education. Academia is gradually realizing that education includes training for students to acquire jobs and hence we complete the cycle of the importance of interacting with industry. At the NSF a major new initiative is being introduced in Optical Science and Engineering (OSE). This effort has been created as an outgrowth of the NRC study being conducted in parallel under the same name. OSE is based on the fact that optics is a very interdisciplinary area and special emphasis on the interface between the relevant areas is where the action is. Lightwave technology and the implementation of organic materials to optoelectronic applications is clearly an area which has tremendous potential for economic impact and it fits the criteria for the OSE initiative. It is also exciting, challenging, and personally rewarding. But organic materials have been promising for quite some time and some are getting impatient. To provide credibility to those who support this research (governement, idustry, etc.), we must turn our attention to ways in which we can accelerate the transition from the laboratory discovery to the consumer. In this way everyone will become a winner.

To demonstrate the feasibility of integrating polymer electro-optic devices on Si circuitry, we have vertically integrated a demonstration slab phase modulator on nonplanar VLSI circuitry. Optical loss measurements for waveguides fabricated on planarized circuits demonstrate that more practical devices like channel phase and Mach-Zehnder amplitude modulators can easily be integrated onto the circuits.

We report on the progress of constructing a mesoscopic photomechanical unit (MPU)-a miniaturized device that acts as a sensor, all-optical logic unit, and mechanical positioner/actuator. We have to date made MPU's in polymer optical fiber (PMMA doped with DR1) that are 1 cm-4 cm long and have a diameter of 110 micrometers . This MPU is powered with a 18 mW laser diode at 685 nm or a 30 mW laser diode at 690 nm. These MPU's exhibit optical and mechanical bistability, multistability and regions of unstable oscillating/chaotic behavior. We report on both theoretical and experimental confirmation of these effects. In our MPU's, the fiber ends are shaped in an approximately retroreflector geometry to provide a higher reflectivity. The ends then form two reflectors that define a Fabry-Perot cavity. The refractive index, absorption and the length all change (through the photothermal heating mechanism) with light intensity: a nonlinear response. We also discuss the role of light induced isomerization. Aside from regions of multistability we also find unstable oscillating/chaotic behavior that is possibly caused by the mixing of the various nonlinear effects, stimulated Brillouin scattering and/or from the coupling of weaker Fabry- Perot cavities in the fiber caused by fiber imperfections. Polymers are better suited for devices based on the photomechanical mechanism since their coefficient of thermal expansion is typically an order of magnitude greater than most other materials. For example PMMA has a coefficient of thermal expansion roughly 90 times greater than that of fused silica and twice that of aluminum. We will also discuss how such devices can be built into optical logic units and smart materials.

We describe the performance of our packaged integrated optic switches based upon single- mode polymer waveguides.

Passive and active polarization converters have been designed and fabricated using electro- optic poled polymers. The devices utilize the controllability of the poling induced optic axis by using specially designed poling electrodes. In the passive TE-TM polarization mode converter, the optic axis of the poling induced waveguide is slowly rotated by using a slowly varying structure of poling electrodes. The polarization conversion is achieved as the guided mode propagates through the waveguide. Complete TE to TM mode conversion is observed and the polarization extinction ratio of the output light is higher than 30 dB. Because the device does not contain any periodic structure, it is wavelength insensitive and easy to fabricate. An active TE-TM mode converter utilizes a 45 degree off poling configuration, which can be obtained by arranging upper and lower stripe poling electrodes with proper lateral displacement. The poling electrodes themselvees can be used as driving electrode. The mode conversion properties and electro-optic effects are demonstrated by using a vector beam propagation method.

We report on the all-optical switching characteristics of a single-mode polymer optical fiber with a squaraine dye-doped poly(methyl)methacrylate core using a Sagnac interferometer.

Recently developed photobleachable polymers show a loss of < 0.1 dB/cm at 1300 nm and < 0.15 dB/cm at 1550 nm. Nonchromophore containing polymers show film waveguide losses of < dB/cm at 1300 nm and 1550 nm. Refractive indices in these materials can be tuned within a range of 0.05 by changing the polymer composition. Multilayers of cross-linked (solvent resistant) layers, each 2-10 microns have been deposited by multiple spinning steps. Using these multilayers, fully embedded, fiber-compatible strip waveguide structures have been created by masked bleaching of multilayers with chromophore containing corelayers. The lateral refractive index contrast is thereby tuned by changing the chromophore content of the corepolymer. Poling-induced loss has been investigated by wavelength and polarization dependent measurements of losses in films. The results indicate that this loss is due to increased scattering. Bleached channel waveguides in a poled (at 125 V/micrometers ) nonlinear optical polymer have been made showing losses of < dB/cm at 1300 nm. Rapid photodegradation at 1300 nm has been observed in stilbene containing channel waveguides. In a nitrogen atmosphere no degradation was seen. The same is true for waveguides in air at 1550 nm. This suggests the attack of the stilbene chromophores by singlet oxygen. Therefore a new generation of low-loss, linear, and nonlinear optical polymers based on singlet oxygen resistant molecules has been developed. The linear optical polymers are used for the realization of low-insertion loss (< 2 dB), digital (switch voltage 3-6 V) and efficient (switching power < mW, cross talk - 20 dB) pigtailed and packaged 1 X 2 switches. They utilize the strong thermo-optic effect in polymers. Their switching time is therefore limited to 1 ms whereas their polarization dependence is < 0.3 dB.

Materials to be used for optoelectronic, photorefractive, or frequency doubling applications must have high nonlinearities, good thermal stabilities, and low optical loss (high transparency). Organic compounds synthesized for incorporation into poled nonlinear polymers typically exhibit tradeoffs between nonlinearity and each of the other two qualities. By judicious use of arylamino donor groups and cyano-containing acceptor groups, a small set of chromophores that are both highly nonlinear and stable at high temperatures has been prepared. By selecting delocalized bridging moieties that are either tuned for optimum hyperpolarizability or exhibit two charge-transfer excited states, highly transparent chromopohores with excellent nonlinearities can be prepared. The results suggest that thermal stability and nonlinearity are jointly achieved by modifying donor and acceptor groups, while transparency and nonlinearity are jointly achieved by modifying bridging groups.

Surface irregularities on a waveguide are influenced by material composition, the process by which polymer was made, and the technique used to fabricate the end-face. Different end-face preparation techniques (laser ablation, sawing, cleaving, reactive ion etching) produces different kind of surface terrain. Surface features, big compared to the wavelength of light, are represented as phase distortions superimposed on the Gaussian excitation beam, optimized to get maximum coupling efficiency. Similarity between the excitation beam and the fundamental waveguide mode is a measure of coupling loss due to different type of surface errors. To investigate the effect of surface roughness on coupling efficiency, several different surfaces were considered. These included sinusoidal phase gratings, spherical groove, cylindrical groove, wedges and delamination of the waveguide layers. For each tupe of surface error, a critical parameter was identified, and the associated value for that parameter was determined for a given tolerable coupling loss.

Third order nonlinear optical coefficients were obtained for a new chromophore 4(4'-N,N'- dimethyl amino phenyl)-1-, 1-bis(trifluoromethyl sulfonyl)-1,3-butadiene (MAG) doped in poly(ethyl)methacrylate (PEMA). The real and imaginary parts of the third order response were investigated at wavelengths close to and far from the resonant absorption maximum by quadratic electro-optics and quadratic electro-absorption (QEA) techniques. From these data real and imaginary parts of the Kerr coefficient are obtained. At room temperature the QEA measurement was also used to determine the ratio of the two contributing tensoral components of the third order response at wavelengths near the resonant absorption maximum. The tensor ratio suggest that an electronic mechanism dominates the third order response at room temperature for the MAG/PEMA system.