Optimizing the performance of organic electro-optic modulator materials requires the consideration of many issues including the optimization of chromophore molecular hyperpolarizability, the effective translation of molecular electro-optic activity to macroscopic electro-optic activity, the stabilization of induced electro-optic activity, the processing of bulk materials into active buried channel waveguides of appropriate dimensions, and the integration of polymeric electro-optic circuitry with semiconductor electronics and silica fiber optics. The utilization of theoretical methods to design chromophores and optimize processing protocols is reviewed. Device performance is defined by material optical loss, thermal stability, photochemical stability, and processability as well as by electro-optic activity.

Simple fabrication technique of nonlinear optical waveguide components in polymer films based on simultaneous embossing and poling at elevated temperature (SEPET) is proposed and demonstrated. The master gratings which consist of polyimide die and metal base are fabricated by a single pulse two-beam interference technique using UV laser ablation. The master grating is found to be stable enough against heat and mold treatment cycles. The master molds nonlinear optical polymers at their Tg's. At the same time, high voltage is applied to the polymers to induce second-order nonlinearity. The grating profile as well as the nonlinearity is estimated. Moreover, formation of channel waveguide with grating based on the present process is also discussed.

Novel second order nonlinear optical (NLO) polymethacrylate or polyacrylate polymers with high glass transition temperatures containing an azo dye attached as side-chain have been prepared using a new approach from polymethacrylic acid or polyacrylic acid as starting materials. Glass transition temperatures of 150 approximately 170 degree Celsius were obtained for Disperse red 1 dye attached polymethacrylic acid. These are attributed to the hydrogen bonding between the residual carboxyl groups in the starting polymers. Poled films by corona poling exhibited large NLO susceptibilities, (chi) ⁽²)₃₃ up to 53 pm/V at a wavelength of 1.3 micrometer. Due to the high glass transition temperatures of the polymers, long-term stability of the optical nonlinearity at 100 degrees Celsius was observed for 200 hrs or more. However residual carboxyl groups caused absorbance decrease mainly by hydrolysis of the ester bonds of the polymers investigated by UV-Vis absorption measurement. The stability of induced polar order of the NLO polymer was enhanced by using aminoalkyl chromophore and imidizing it thermally to introduce imide structure into the polymer main-chain. This imidized polymer exhibited (chi) ⁽²)₃₃ of 45 pm/V at a wavelength of 1.3 micrometer and maintained about 90% of the initial value after 230 hrs or more at 100 degrees Celsius.

This paper describes the development and optimization of chiral, non-polar media with large second-order nonlinear optical responses. We employ molecular engineering, quantum- mechanical sum-over-states theory, and measurements of molecular hyperpolarizability by means of Kleinman-disallowed hyper-Rayleigh scattering in order to understand molecular properties. Then we analyze the appropriate arrangement of the chromophores that produce an optimum axial nonlinear optical medium. Chromophores with large Kleinman disallowed traceless symmetric second rank tensor hyper-polarizabilities (beta) can be aligned so as to result in large susceptibilities, (chi) ⁽²), in structures that lack polar order. We found that (Lambda) -shaped chromophores with C_2v or similar symmetry are good candidates for these materials as they can exhibit large second-rank components of the hyperpolarizability tensor. A wide variety of techniques can be used to fabricate bulk materials belonging to the chiral non-polar symmetry groups, D_(infinity ) and D₂. The microscopic chromophore alignment schemes that optimize the NLO response in such materials are deduced from general symmetry consideration for both molecules and bulk.

We fabricated and demonstrated a beam deflector implemented in an electro-optic polymer planar waveguide. An array of prism- shaped electrodes formed on the top of the waveguide induces selective refractive index change in the core polymer layer, which results in the tilt of the propagation direction of the guided beam. Waveguide beam deflectors have potential applications in the emerging photonics technologies such as optical storage systems, optical phased array antenna, and optical switching. The deflection sensitivity of 28 mrad/kV, and the maximum deflection angle of +/- 8.4 mrad at +/- 300 V were obtained for this first demonstrated device.

We fabricated spincoated films of squarylium dye (SQ) J- aggregates exhibiting femtosecond optical response at room temperature. Optical dynamics measurements revealed that the saturable absorption of the SQ J-aggregates film exhibited a decay time of less than 100 fs at a pump energy of 80 fJ/micrometer². With this ultrafast SQ optical film, four- output demultiplex operation for T bps pulses was demonstrated. A series of 4 optical pulses with 100 fs duration and 1 ps interval (corresponding to 1 T bps signals) were irradiated onto the SQ film synchronized with a 100 fs gate pulse at a finite angle. Four demultiplexed signals were clearly observed at different areas on the CCD camera. Multi- output serial-to-parallel demultiplexer for T bps optical signals can be formed using the SQ J-aggregates film.

A novel liquid crystal panel suitable for real-time holography and exhibiting a very high exponential gain coefficient is presented and discussed. It consists of a nematic liquid crystal layer sandwiched between photoconducting polymeric layers. Under exposition to sinusoidal light intensity pattern the panel shows an efficient formation of the refractive index grating. Three different photoconducting polymers were used: poly(3-octyl thiophene), poly(3-octyl thiophene) functionalized with disperse red #1 and polyvinyl carbazole (PVK) doped with TNF. The first order diffraction efficiency, measured in degenerate two wave mixing experiments, depends on the photoconductor used and reaches 44% with PVK:TNF. The panel shows also the ability to switch energy from beam to beam. In the two-wave coupling experiment multiple orders of diffraction are present and a very high two-beam coupling gain is obtained. The largest value of net gain g equals 12 and the corresponding exponential gain coefficient (Gamma) equals 3700 cm^-1 were again observed with PVK:TNF. This was achieved in samples biased by a dc external electric field and tilted with respect to the beam incidence bisector at 15 degrees. The time constants of grating formation and its erasing in the studied system depend on the applied voltage and can be made as short as few milliseconds in favorable conditions.

We present a study on the effects of the dark conductivity on the photorefractive performance of polymers doped with styrene-based chromophores. We find that reducing dark conductivity in such composites increases diffraction efficiency and at the same time decreases the response time. We use a polymer composite based on a polyvinylcarbazole matrix doped with 4-Homopiperidinobenzylidenemalononitrile (7- DCST), sensitized with C₆₀, and plasticized with N- ethylcarbazole (ECZ) and butyl benzyl phthalate (BBP). The reduction of the dark conductivity is achieved by coating one of the electrodes with a SiO blocking layer.

An organic electrically switchable holographic material and its applications to display and photonics components are outlined. This material is an extension of polymer dispersed liquid crystal (PDLC) technology. Consisting of liquid crystal (LC), prepolymer and photoinitiator, a holographic PDLC (HPDLC) mixture can form LC droplets in the polymer matrix 1 - 2 orders of magnitude smaller than those in regular PDLCs. Thin HPDLC films sandwiched between transparent electrodes such as ITO-coated glass can be used to record high-resolution holographic gratings. These gratings, the result of the index modulation due to the phase separation of the LC from the polymer matrix, can be easily switched on and off under an electric voltage at a high speed 1 - 2 orders of magnitude faster than that of a regular PDLC device or a bulk nematic/cholesteric LC based device. Two types of switchable diffractive gratings, transmissive and reflective gratings, will be discussed. Applications such as wearable displays, portable projectors and optical networking components will be described in the presentation. Prototypes of some of these devices will be demonstrated in the presentation.

We present the structure of electrically switchable diffraction gratings using low concentration polymer network stabilized pattern-forming state (fingerprint texture) of a host cholesteric liquid crystal. In this polymer-stabilized cholesteric diffraction grating (PSCDG)s, both the pattern- forming state and its diffraction state are the result of complex combinations of dielectric, flexoelectric, and electrohydrodynamic torques induced by applying an electric field at specific amplitudes and frequencies and for specific ratios of the sample thickness to cholesteric pitch. In each case, key structural features of the patterned distortion in orientational order of the liquid crystal can be recorded into the morphology and optical anisotropy of an internal polymer network, which is formed via photopolymerization of a low concentration monomer additive. The observed morphologies reported in this paper include one-dimensional arrays of thin parallel and zig-zag walls. We also discuss issues how the polymer network enhances the potential of complex pattern- forming states in liquid crystals for optical beam steering and switching applications.

The purpose of this paper is to present a grating-assisted nonlinear limiting method based on the principle of index mismatching and grating diffraction. In addition, various nonlinear organic materials have been tested in the optical limiting system. A few examples with experimental results are presented. Using a YAG nanosecond pulse laser at 532 nm as a simulated threat laser source, we tested the optical limiting characteristics of the methyl-red doped nematic liquid crystal films. In the meantime, we observed some quite interesting optical phenomena, such as self-defocusing diffraction rings, dark spots in the far-field behind the cell. Our experimental results presented in the paper show that the methyl-red doped nematic liquid crystal films posses a good optical limiting performance. When the input energy focused on the cell increases from approximately zero micro Joule to approximately 200 micro Joule, the output energy on the far-field exit plane is kept under 1 micro Joule. We will describe a completed optical limiting system with Q-switched frequency-doubled 12- ns Nd:YAG laser, dual-channel detectors, and computer processing units based on Lab-view software and its design considerations.

We report on the phenomenon of 'superquenching' observed for fluorescent polyelectrolytes -- conjugated and J-aggregate polymers -- in aqueous solution and in supported interfacial formats. Thus we find that for a number of substrates quenching by oppositely charged ions can occur with 'Stern- Volmer' quenching constants that are a million fold or greater than those for the quenching of similar 'molecular' chromophores by the same quenchers. The quenching can be tuned by a variety of techniques. The superquenching results from a combination of nonspecific but moderately strong association (due to a combination of Coulombic and hydrophobic interactions) between the quencher and polyelectrolyte with efficient excitonic or energy migration in the excited polymer. The effects reported here can be used in chemical and biological sensing applications.

Sol-gel hybrid glass (SGHG) films doped with various photoinitiators were prepared. Volatile photoinitiators are photolocked in SGHG matrix by photochemical reaction upon UV exposure. Refractive index and film thickness increases by UV exposure due to photoinduced polymerization and photolocking of high refractive index species. Using the photolocking of photoinitiators, channel waveguide was fabricated without using developing process step, which will be called photochemical self-developing.

Commercial application of organic light-emitting materials currently employs organic thin film deposition techniques including spin-coating, dip-coating, and evaporation. Broader technologies will also benefit from such organic optoelectronic materials. Emerging applications include on- chip light sources for integrated circuit (IC) optical signal transduction, on-chip microdisplays, and on-chip visible and infrared sources for integrated microsystems (MEMS). However, to fully adapt to the so-called cluster tool platform used for closed-loop manufacturing of IC's a remote vapor phase deposition scheme is required for low molecular weight organic light-emitting materials as opposed to conventional evaporation based techniques. We report the development of a remote organic vapor phase deposition process for growing high-quality aluminum tris-hydroxyquinoline (Alq₃) films. This process utilizes a remote reservoir for organic vaporization coupled with mass-flow controllers for delivery to the condensation zone. A load-lock equipped chamber, capable of 5' wafer transfer, is utilized to eliminate ambient contamination without restricting wafer loading/unloading or Alq₃ material loading. Data will be presented for a design-of-experiment (DOE) statistical process optimization investigation of Alq₃ thin film growth as a function of the system deposition parameters. Electrical characterization of the Alq₃ films and their applicability for optoelectronic device structures are presented and discussed.

The possibility to integrate an optical emitter at any point in a silicon integrated circuit would represent a major breakthrough in the field of optical interconnects between circuits or in the same circuit. The outstanding properties of luminescent organic semiconductors, such as their ability to be deposited on various substrates and their efficiency, make them good candidates for this kind of applications. In addition, microcavities limit the spectral and spatial distributions of the emitted light, which makes the integration of the light source easier in an optical interconnection system. We studied resonant-cavity organic light-emitting diodes (RC-OLEDs) such as Al/ITO/CuPc/TPD/Alq₃/Al which were made on silicon substrates. ITO was deposited by magnetron sputtering and the other materials by vacuum evaporation through masks. Aluminum was chosen to make the mirrors because it is widely used in CMOS technology. The thickness of each layer was chosen so that the optical length of the cavity is 3 * (lambda) _res/2 where (lambda) _res is the resonant wavelength. We described these planar multilayer microcavities using a transfer-matrix multiplication method. The devices were characterized by photoluminescence and electroluminescence, and the experimental results are in good agreement with the model. The current-voltage characteristics were measured while the electrical model is currently under study.

In this work we propose a genetic algorithm for the design of reflective filters consisting of organic materials. The algorithm chooses the materials of the layers from the list of available materials and chooses their thickness in order to obtain optimal reflectance characteristics. The wavelength dependence of the refractive index and the coefficient of extinction of the layers is taken into account.

Recent results obtained in the growth of organic materials by supersonic molecular beams (SuMBE) are presented. Compared to other vacuum deposition methods, it allows an accurate control on the initial state (kinetic energy, momentum, flux, etc.) of the molecules during the deposition process. We show that such feature can be efficiently exploited to prepare films, the structure and morphology of which resemble those single crystals, therefore achieving unprecedented control on their optical and electronic properties even for relatively thick samples (> 500 nm). We also report on the use of SuMBE for processes of co-deposition with the aim of functionalizing or doping organic semiconductors. We achieved co-depositions of a p-type semiconductor, as metal phthalocyanines, with an n- type semiconductor, as fullerenes, without phase segregation between the two compounds and with a high control on the deposition parameters. This aspect is very attractive for the growth of organic p-n junction in view of improving photovoltaic cells and gas sensors.

The electronic structure of neutral and singly charged conjugated molecular clusters is investigated by means of quantum-chemical calculations. We first assess the influence of interchain interactions on the nature of the singly charged species (polarons) in organic conjugated polymers. In a two- chain model aggregate, the polaron is found to be delocalized over the two conjugated chains for short interchain separation. Such a delocalization strongly affects the geometric and electronic relaxation phenomena induced by charge injection, which in turn lead to a dramatic spectral redistribution of the linear absorption cross section. We then consider pentacene clusters built from the experimental crystal structure and compute the HOMO and LUMO bandwidths, which are decisive parameters for charge transport in the limiting case of band-like motion (i.e., complete delocalization of the excess charge over a large number of interacting molecules). Very large bandwidths are obtained, in agreement with the remarkable electron and hole charge-carrier mobilities reported recently for ultrahigh purity pentacene single crystals.

Two types of excitons with different dynamics are observed in poly(p-phenylene-vinylene) thick films pumped by the intense 0.2 ps light pulses. The films are prepared from soluble sulphonium polyelectrolyte precursor polymer using different thermolysis temperatures between 240 degrees Celsius and 350 degrees Celsius. Narrowing of emission spectra accompanied by lifetime shortening is observed in the films formed at low temperature thermolysis at 240 degrees Celsius and 300 degrees Celsius when the films are pumped at their absorption edge of 500 nm with high intensity pulses. Contrary to the spectral narrowing pumped at the absorption edge, no spectral narrowing occurs and the quenching of the emission is observed when the samples are pumped at their absorption peaks around 400 nm. Sufficient concentration of the excitons responsible for the luminescence is needed to obtain the spectral narrowing which can be attributed to both amplified spontaneous emission and cooperative radiation or superfluorescence. The quenching of photoluminescence without any spectral narrowing is ascribed to the quenching of excitons by photoproducts such as free carriers. We propose a novel application of the phenomena of the spectral narrowing and the quenching in PPV films as an optical logic element with an exclusive OR function.

It has been demonstrated that in IR spectra of vacuum- deposited poly-para-phenylene (PPP) film an extremely strong band at 1375 cm^-1 is observed, which is not typical of currently known PPP modifications. High intensity of the band at 1375 cm^-1 was associated with the change in the bond order of the 'defect' C-C bond between adjacent quinoid and benzenoid units. Mechanism of quinoid fragments formation in process of PPP film grows is here suggested. The p- phenylene radicals generated during thermal destruction of PPP powder are extremely active. However, when they appear included in the solid phase, they lose much of their initial reactivity, and recombination may be kinetically hindered. In this case, the macromolecules with 'stuck' terminal phenyl radicals could form. The vacuum-deposited poly-para-phenylene solid phase exhibits high crystallinity. Therefore, the recombination of 'stuck' radicals can be essentially hampered. In this case the isomerization of 'stuck' radicals gives delocalized defects. The possibility of practical applications of vacuum-deposited PPP films with delocalized defects is discussed.

Nonlinear optical properties of (pi) -conjugated organic systems based on polyimide and 2-cyclooctylamino-5- nitropyridine have been studied. The nano-pulsed Nd lasers for holographic recording and optical limiting experiments has been used as irradiation sources. The drastic change of refractive index in the fullerene-doped structures in comparison with the fullerene-free systems has been observed. The nonlinear coefficients n₂ and (chi) ⁽³) for fullerene-doped compounds have been estimated. It has been shown that the fullerene-doped systems could be used as reversible real-time holographic materials and laser nonlinear absorbers with high laser strength.

The high efficient optical phase conjugation was successfully observed in a photorefractive mesogenic composite. The photorefractive mesogenic composite consists of a functionalized copolymer, low-molar-mass liquid crystal mixture (E7) and 2-4-7-trinitro-9-fruorenone (TNF) as a sensitizing dye. Experiments of optical phase conjugation were carried out under the degenerate four wave mixing (DFWM) configuration using a frequency-doubled Nd-YAG laser of 532 nm (on-resonant) or a He-Ne laser of 633 nm (off-resonant). The refractive index modulation was estimated to be around 2.5 X 10^-3 from the phase conjugate reflectance on the basis of the coupled wave theory including the absorption loss of the photorefractive media.

We present side induced fluorescence (SIF) results on laser dye doped unclad plastic optical fibers. The SIF data can be used to obtain optical loss spectra for the low loss region of the absorption tail of the laser dye that has been doped into the fiber. Dyes which have been examined include derivatives of rhodamine and pyromethene. SIF deduced loss results in combination with cutback loss measurements on undoped fibers suggest that the electronic absorption of the laser dye dominates the loss far (> 200 nm) from the peak of the dye absorption (the order of 0.5 cm-1 at 750 nm). Loss measurements of unclad undoped fibers suggest that loss is dominated by scattering and defect mechanisms. In fact these losses are quite high compared to literature measurements of analogous clad fibers. Thus intrinsic loss of the polymer (PMMA in most cases) is minor compared to scattering and defect losses when dealing with unclad fibers. We also present the fit of our dye-doped fiber loss data to homogeneous and inhomogeneous broadening equations and show that broadening is dominated by inhomogeneous mechanisms as is expected.

Polymer dispersed liquid crystals are successfully used in display technique because they are of high film-forming capability and photoconductivity inherent in a polymer matrix and of electro-optical and aligning effect in a liquid crystal mesophase. The laser modulation and the holographic recording in the polymer dispersed liquid crystal composites based on some (pi) -conjugate organic compounds doped with fullerenes C₆₀ and C₇₀ have been investigated with a use of cw He-Ne and picosecond pulsed Nd lasers. Both the 80% modulation of laser beams at repetition frequency of 0.2 - 3 Hz and 20% one at 35 Hz have been obtained. The laser induced refractive index in the picosecond range was 0.75 X 10^-3 at laser power density of 33 mJ(DOT)cm^-2, that was larger than the one for polymer dispersed liquid crystal doped by dyes.

The use of a Tris-(8-hydroxyquinoline) Aluminum (Alq₃) organic active region within a distributed Bragg reflector (DBR) mirror-cavity structure is described. The resultant device showed a narrowing of spectral output with increasing DBR usage significantly purifying the broadband emission of Alq₃. Higher excitation intensities resulted in the production of lasing with a threshold of 3.2 kW/cm².

This paper studies the characteristics of the nonlinear optical system in a model, which may be considered as that containing conjugate polymer, such as polydiacetylense. The dynamic equations are established through the approach of density matrix elements. The parameter conditions of laser and lasing without inversion (LWI) are discussed and the thresholds of pumping and probing fields to produce LWI are determined. The nonlinear susceptibility of the system is deduced from the density matrix equations and the forced oscillation model of laser and bistability is used to study the bi- or multi-stability of the system under lasing, or inversion without lasing (IWL) and LWI conditions. The results indicate that to realize OB or OM output in IWL or LWI situation, there must be some additional conditions on the relaxation and transition rates, also the critical output light intensity. Finally, theoretical analysis and numerical computing show that there exists unstable critical point of second kind phase transition, in such tri-stable state.

Cationic-induced two-photon photopolymerization is demonstrated at 710 nm, using an isopropylthioxanthone/diarylidonium salt initiating system for the cationic polymerization of an epoxide. The polymerization threshold J_2th is found to be approximately 1 GW/cm², with a dynamic range of > 100, i.e. the material can be fully polymerized at intensities > 100 times the threshold level without damage. The polymerization rate R is found to be proportional to the m equals 1.7 power of the intensity, or R equals [C (J-J_2th)]^m equals [C (J-J_2th)]^1.7, which implies a significantly stronger localization of the photochemical response than that of free radical photoinitiators. R and J_2th significantly improve when the concentration z of the initiator (onium salt) increases.

We report on a new polymer light emitting diode (PLED) based on a blend of immiscible polymers. The device shows high efficiency and current density over a broad range of driving voltage, therefore exhibiting very high brightness. The polymer film morphology plays a very important role in determining the device performance, and it can be controlled by changing the blend ratio as well as the polymers molecular weight. The high performance are discussed in terms of 'barrier free' injection into excitonic states. A predicted lifetime in excess of 10,000 hours has already been achieved, making this device structure an ideal candidate for backlighting and monochromatic application.

Organic electroluminescent diodes (OLED) were fabricated on a polymeric optical waveguide for use as an optical interconnector in data communication systems. The OLED were fabricated on an ITO sputtered polymer waveguide with a 45 degree mirror by vacuum deposition. The OLEDs, with an emission peak center at 520 nm consist of diamine derivative as a hole transporting layer and tris(8-hydroxyquinoline) aluminum (Alq₃) as an emissive layer. We estimated the propagation losses of the waveguide to be 1.35 dB/cm at 520 nm. However, it decreases as increasing the wavelength of the light source and is estimated as 0.37 dB/cm at the wavelength of 614 nm. The optical pulse of more than 5 Mb/s has been obtained from the OLED with Alq₃ and diamine derivative. We discuss the properties of the OLED for the light source for polymeric integrated devices.