The success of optical fiber technology continues to enable great advances in telecommunications. Among the more recent commercial developments have included the erbium doped fiber amplifier, 10 GB/sec time division multiplexing, and dense wavelength division multiplexing (DWDM). In the near future two trends will dominate the continued growth of this technology (1) increased optical device functionality and (2) migration of increased bandwidth down to local loop and access levels of the network. Examples of increased functionality will include splitters and DWDMs with increased port counts, wavelength conversion, and matrix optical switching. Migration of bandwidth will require greater volumes of fundamental optical components such as power splitters and WDMs. We will discuss our polymeric optical device technology in light of both current and future telecom needs. We have developed a series of cross-linked polymers with intrinsic losses in the 1.55 micrometer window as low as 0.1 - 0.2 dB/cm. Singlemode waveguides can be made from these materials by photolithography or by molding. Our baseline materials, C20 and C21, are nonhalogenated polymers and exhibit waveguide losses at 1.55 micrometer of 1 to 1.5 dB/cm; by increasing the level of halogenation we can achieve waveguide losses as low as 0.3 dB/cm. These polymers exhibit excellent resistance to adverse environmental conditions, typified by the well-known Bellcore 85 degrees Celsius/85%RH soak test. One X sixteen and 1 X 8 power splitting devices made from C20/C21 have exhibited insertion losses of 11 dB and uniformities of plus or minus 0.3 dB at 1.3 micrometer. We have also invented a passive alignment technology that allows optical fibers to be 'snap-fit' aligned with the optical waveguide, which reduces the difficulty and cost of pigtailing. Finally, we discuss our approach to DWDM which takes advantage of our ability to precisely control the refractive index of our polymers by proper selection of the comonomers.

The use of polymer waveguides for the design and fabrication of devices for wavelength division multiplexing (WDM) at 1550 nm is described. Single mode 1 X 2, 1 X 4 and 1 X 8 splitters and combiners have been fabricated using photosensitive polyimide materials on silicon substrates. Good division of light was achieved in the devices, and waveguide facets could be cleaved to allow efficient coupling from optical fibers. The design of phased array wavelength demultiplexers for polymer waveguide technologies is described and compared to competitive technologies. Optimization of the trade-off between device size and waveguide cross-section is discussed and preliminary device designs for different polymer systems are presented.

The provision of a range of WDM network component functionality by ferroelectric liquid crystal (FLC) spatial light modulators (SLM) has already been demonstrated, but reconfigurration speed is limited to the order of 100 kHz by liquid crystal response time. A future generation of fast spatial light modulators might be based on a (chi) ⁽²) material, yielding a device response time limited only by electronic RC product. This paper presents device modeling and characterisation of single-pixel SLMs based on an approximately 2 micrometer film of commercially available nonlinear optical polymer (NLOP) in an asymmetric Fabry-Perot (AFP) cavity. Polymer films were poled at a low field of approximately 35 V/micrometer and a 10-V modulating signal applied. Intensity modulation of 0.3% was provided by a gold/gold etalon device at 633 nm, while 1.4% modulation was provided by a hybrid device having an ITO-coated dielectric rear mirror and gold front mirror. Transmitted intensity modulation of the former device around 1.55 micrometer was approximately 0.1% and had a 3-dB bandwidth of 10.8 nm. Modelled behaviour has been extrapolated to yield two significant performance indicators: (1) the diffraction efficiency (eta) of a multiple-pixel 1-D AFP NLOP-SLM is largely phase modulation-dependent, having a maximum value of approximately 13.5% cf. approximately 40% for a binary phase FLC-SLM; (2) the 3-dB bandwidth of (eta) ca. 1.55 micrometer is approximately 5 nm in this configuration, but an approximately 190 nm-thin cavity hybrid device could have an (eta) _3dB approximately 30 nm.

Passive fibre-waveguide coupling is a promising alternative to expensive active coupling in single-mode fibre-optics. The idea to utilize replication techniques in transparent polymeric materials for waveguide and alignment structure fabrication has led to the SIGA-process (Silizium, Galvanik und Abformung) which allows a cost effective production of low loss polymer waveguides in the near IR. Major difficulties in passive fibre coupling are caused by the high lateral alignment accuracy (of about 1 micrometer) in fibre positioning. In the SIGA process, the exact position of the V- grooves relative to the waveguide trenches is defined by the etch mask for the silicon master wafer. The width of the V- grooves is determined by the KOH etching time. It is controlled precisely at various stages in the etching process by means of a microscope based piezo driven measurement system with a resolution better than 0.5 micrometer, thus allowing a final vertical precision of fibre positioning of 350 nm. In order to specify the capability of our technology we have measured the position of dozens of fibres glued into V- grooves. The result was that an amount of 55% of the fibre cores was closer than 1.5 micrometer to the waveguide centre. As the experience has shown, a two-step process for the fabrication of passively fibre coupled waveguides is necessary. First, the waveguides are produced by filling the waveguide trenches with an IR-transparent monomer and by polymerizing it using UV curing. The waveguides are inspected with visible and IR light by clamping a fibre ribbon mechanically into the integrated plastic V-grooves. In a second step the fibre ribbon is fixed irreversibly in the V- grooves. By that way we have reached an insertion loss of 3.5 dB at 1300nm and 1550nm for passively coupled 22mm single mode waveguides. Most of the losses are attributed to waveguide imperfections. More details concerning the coupling losses and the device performances will be reported at the conference.

We have proposed a highly scattering optical transmission (HSOT) polymer for use as a high luminance light source medium. This polymer contains specified internal microscopic heterogeneous structures for controlling light scattering properties. A LCD backlight using the HSOT polymer has twice the brightness of the conventional transparent PMMA-based backlight because of multiple scattering phenomenon inside the HSOT polymer. In this paper, such a light scattering phenomenon was quantitatively analyzed by a ray tracing based on Mie scattering and Monte Carlo simulations. Subsequently, we proposed the new HSOT backlight system having higher luminance and uniformity of white color illumination.

A beam deflector has been designed and fabricated that uses a nonlinear-optical polymer. The device is composed of a cascade of polymeric electro-optic prisms formed within a planar waveguide of the same polymer system. A laser beam, to be deflected, is coupled into and out of the planar waveguide by cylindrical lenses. The light path of the laser beam within the planar waveguide is adjusted to pass through the successive prisms of the cascade, where the Gaussian transverse-mode profile is centered (initially) within each of the prisms. The index of refraction of each prism in the cascade, but not of the surrounding polymer, is modified by the electro-optic effect when a drive voltage is then applied. The application of a drive voltage thus causes the planar waveguide to function as a sequence of prisms that change the path of propagation of the beam through the planar waveguide. The collimated beam formed by the output cylindrical lens deflects. The extent of deflection is proportional to the amount of refractive-index change induced in the prism cascade. A uniform electrode structure can drive the electro- optic prism cascade, which should enable the device to operate at high speeds when traveling-wave driven.

Recent progress of the graded-index polymer optical fiber (GI POF) is reviewed. Because the low attenuation of light transmission in the perfluorinated (PF) polymer base GI POF enables 500 to 1000 m transmission, more accurate analysis is required in the refractive index profile to realize the order of giga bit transmission. The analytical procedure of the bandwidth characteristics of the GI POF is described in this paper. Furthermore, recent improvement of the thermal stability of the GI POF is introduced. We clarified that the stability of the refractive index profile and the attenuation under high temperature and high humidity atmosphere can be improved by selecting the suitable dopant material.

A complete understanding of the propagation characteristics of plastic optical fibers (POFs) is crucial for their future applications in short-haul data transmission systems. In this article, we summarize the observation of strong mode coupling effect inside POFs through different experimental techniques. The optical pulse broadening measurements show characteristic change over from linear to square root length dependence. The equilibrium mode distribution (EMD) condition can readily be achieved in step-index (SI) POFs at lengths (approximately 15 - 20 m) much shorter than in glass optical fibers (GOFs). Our results are directly verified by independent measurements of the far-field radiation patterns and the mode coupling coefficient inside POFs, which is over two orders of magnitude larger than in GOFs.

Organic dyes and rare earth chelates have been chosen and incorporated into the core regions of graded index (GI) polymer optical fibers (POF) as gain media. Since the synthetic polymer shows much better compatibility with organic fluorescent materials and is amenable to high active dopant concentrations, the doped POFs produce high gains in short lengths of fiber. We demonstrated that organic dye-doped polymer optical fiber amplifiers (POFA) cover a wide spectral range in the visible with a best observed gain of 37 dB in a Rhodamine B-doped POFA pumped at 550 nm. Also, with a GI POF doped with europium chelate of hexafluoroacetylacetone in tris form, we observed superfluorescence, evidenced by spectral narrowing and lifetime shortening. The prospect is that the wide choice of organic dyes and rare earth chelates offers optical amplifiers and superfluorescent sources for a variety of communication and sensor applications.

The full potential of second order nonlinear polymers can be utilized in electro-optic polymer modulators with a DC biased operation scheme to greatly reduce the V_(pi ). This technique makes use of the total achievable electro-optic coefficient, which can be more than three times as high as the residual value after the fast partial relaxation following corona or contact poling. As the result of the DC bias and with high (mu) (beta) chromophores, a low V_(pi ) of 1.5 V was achieved with 2 cm long birefringent waveguide modulators at the wavelength of 1.3 micrometer. Results of 200 degrees Celsius stability experiment indicate that this scheme also enables electro-optic polymer devices to meet the stability required for high temperature hermetic sealing because the polymer does not need to be poled before device packaging.

Throughout the paper, the concept of the planar 1-D lay-out (one layer) of kXk-switches and the concept of its compact double-layer/multi-layer counterpart will be presented and experimental results analysed for k equals 4. The paper presents the construction and treats of the working principles of switching system that can operate with minimum number of stages. A reduction of the number of stages is obtained due to combination of the electro-optic (EO) polymer films on the isotropic substrate. The optical switches are collected in one optical layer and each layer composes of at most two 2X2- switches simultaneously active. Poly (methyl methacrylate) (PMMA) film doped with azo dye and para-nitro- aniline/polyvinyl alcohol (p-N-An/PVA) were used for the EO films preparation. Thereby switching is applied horizontally (use one layer only) and vertically (between the two layers). The scheme of such a 4X4-switch in double-layer technique has been presented.

Electric field distribution and relaxation in a multi-layer polymer system are analyzed based on electromagnetic theory. Analysis showed that the steady state DC electric fields across polymer layers depend on the conductivity of each layer. When a step DC voltage is applied to the electrodes, the field across the waveguide layer will relax exponentially from an initial state to a steady state depending on the dielectric constants and conductivities of polymers. The AC field distribution generally depends on the dielectric constants of the polymer layers at high frequency. At low frequency, the AC field distribution is frequency dependent, and a phase delay occurs. To eliminate the AC/DC field relaxation, the materials used must have matching dielectric properties. The relaxation time (tau) of each polymer layer must be equal at the operating conditions. The analysis of the field relaxation can be applied to the design, fabrication, and test of electro-optic polymer devices. The field relaxation in multi-layer polymers can affect the device bias and operation stability in practical applications. Experimental results showed that stable DC bias can be achieved by optimizing or matching relaxation properties of polymers. Other applications of the field relaxation analysis include polymer poling, device characterization, and new device designs.

Alternating polyelectrolyte deposition (APD) in aqueous solutions may be used to process nonlinear optical polymers (NLOPs) into noncentrosymmetric ordered films at ambient temperature. Second-order NLOP films were prepared by alternately dipping a substrate into aqueous solutions of a polycation and a polyanion. Polyepichlorohydrin substituted with stilbazolium side-chain chromophore was used as the cationic NLOP. The inactive polyanion was polystyrene sulfonate. Uniform layer to layer deposition is observed as evidenced by a linear increase of UV-Visible absorbance and quadratic increase of second harmonic generated light intensity as a function of film thickness. Films have been uniformly deposited up to 24 bilayers. Films have been further characterized by contact angle measurements, interferometry, and polarized light microscopy. Work is in progress to deposit thicker films of the same quality and to quantify NLO figures of merit.

The nonlinear excitation of organic molecules in polymer matrices using dual-frequency beams permits the achievement of a large and permanent second-order nonlinearity. The so-called all-optical poling technique permits the patterning of 3- dimensional spatio-tensorial micro-structures in resonant and in transparent materials. Using appropriate combinations of circular polarizations, nearly perfect dipolar and octupolar orders is induced in a polymer consisting of linear molecules. Writing-beams phase retardation angle is coded into a rotation of the nonlinear pattern by the same angle. This permits the achievement of chirality gratings. This may also offer a polarization insensitive configuration for frequency conversion devices.

In an attempt to build single polymer film photovoltaic cells, we underline the intrinsic rectifying nature of an oriented polymeric material. Orientation of the initially symmetric structure is performed through DC-field ordering of the polar molecules contained in the polymer. The internal field induced in the polymeric material is evidenced by the induction of a rectifying current-voltage characteristic. Second harmonic generation is used as a probe of the molecular order. Orientation induced rectification is proportional to the molecular order. This preparation technique opens a new route for the improvement of organic-semiconductor devices efficiency.

An attractive and challenging approach to the construction of robust, structurally precise thin film materials with large second-order optical nonlinearities or electroluminescent characteristics is the covalent self-assembly of arrays of tailored molecular building blocks. In this contribution, we discuss the implementation of self-limiting siloxane self- assembly processes to achieve the fabrication of structurally regular organic LED (OLED) devices. Areas surveyed include: (1) the use of layer-by-layer self-assembly for ITO electrode modification/passivation/hole-electron carrier balancing in vapor deposited devices, (2) the synthesis of chlorosilane- functionalized precursor molecules for hole transport (HTL), emissive layer (EML), and electron transport layer (ETL) self- assembly, (3) the physicochemical and microstructural characterization of the HTL self-assembly process employing a triarylamine precursor, (4) the fabrication and characterization of a hybrid self-assembled + vapor deposited two-layer OLED, (5) the fabrication and characterization of a fully self-assembled two-layer OLED.

Ionic species in emissive polymer: The performance of polymer LEDs having the configuration Al/MEH-PPV/ITO (where MEH-PPV equals poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene- vinylene) have been improved by light iodine p-doping of the emissive MEH-PPV polymer layer to presumably produce (MEH- PPV)_x^+y(I₃)_xy^- whereby the turn-on voltage is reduced from approximately 10 V to approximately 5 V and the external quantum efficiency is increased by an order of magnitude. It differs from non-doped MEH-PPV LEDs in that light emission is observed in both forward and reverse bias modes. The presence of (MEH-PPV)_x^+y ions at the cathode facilitate electron injection due to (partial) compensation of the injected charge while I₃^- ions at the anode analogously facilitate injection of holes. Ionic species in non-emissive polymer: LEDs having the configuration Al/MEH-PPV/ITO, at a constant applied potential of approximately 11 V, reached maximum intensity of light- emission after approximately 0.07 minute. Those having the configuration Al/MEH-PPV/EB/ITO reached maximum intensity (at approximately 11 V) after approximately 4.2 minutes (where 'EB' equals emeraldine base, the non-doped form of polyaniline), while those having the configuration Al/MEH- PPV/EB.HCSA/ITO reached maximum intensity (at approximately 11 V) after approximately 7.2 minutes (where 'EB.HCSA' is EB completely doped by camphor sulfonic acid). In each case, decay in intensity began to occur after the maximum was reached. The behavior of both systems are consistent with a non-electrochemical model wherein the new phenomena are controlled by an electric field induced diffusion of positive and negative ions towards the appropriate electrodes.

Polymer and low molar mass liquid crystalline discotic materials display an unusually large hole mobility of the order of 10^-2 cm²/V^S which results from the formation of stacks with a strong one dimensional (pi) - electron overlap. Homogeneous films with the stacks being uniformly oriented along the film normal or perpendicular to it can be prepared by spin coating and multilayer films with a narrow control of the internal structure via Langmuir Blodgett techniques. We have used such discotic materials as hole transport layer in light emitting diodes both in single layer as well as in multilayer devices. The observation is that the onset fields are small compared with amorphous hole conducting materials, that the onset fields depend strongly on the orientation of the molecular stacks and finally that the onset field is significantly decreased and the quantum efficiency increased in the multilayer devices. Quantum well structures are available via the Langmuir Blodgett technique.

The thermal elimination conditions for more efficient poly(p- phenylene vinylene) polymer light-emitting diodes were established: the precursor films must be heated to 230 degrees Celsius and kept at that temperature for 5 min. under a N₂ flow of 50 ml/min. By the heat treatment the degree of conversion to PPV was about 70%. The external quantum efficiency of 0.0078% was achieved for the ITO/70% PPV/Al devices. The brightness of the device was calculated from the efficiency to be 2.3 cd/m² at 200 MV/m (current density of 0.2 mA/mm²).

In this paper, we demonstrate the enhancement in the performance of organic electroluminescent devices upon the insertion of an insulting layer or layers of LiF in the device structure. Highly efficient and bright organic light-emitting devices were fabricated with this approach. External quantum efficiencies approaching 3% and light output exceeding 45,000 cd/m² have been achieved for green light-emitting devices with Al cathode. This technique can be extended to fabricate efficient blue and sharp-red light-emitting devices. In this respect, using Al as the electron injecting electrode, blue light-emitting devices with external quantum efficiency of 1.4% and light output more than 4,000 cd/m² have been achieved without the use of dopants. For sharp-red light- emitting devices, record efficiency and light output were obtained when LiF was used. Devices without the LiF layer showed light output levels lower than 5 cd/m², whereas, with the insertion of LiF before the cathode, the external quantum efficiency exceeded 1% and light output was higher than 320 cd/m². All of these devices had lower operational voltage than similar devices without the LiF layer. Preliminary UPS-XPS results revealed a sharp decrease in the work function of aluminum upon the deposition of sub-monolayer of LiF. Although, the use of the LiF layer on the indium-tin- oxide anode showed some enhancement in device performance, the contribution to device performance is lower than the case with the same insulator deposited at the cathode side, indicating that the cathode is more problematic than the hole injecting indium-tin-oxide electrode.

We study the emission properties of various laser cavities under pulsed optical excitation of the active semiconducting conjugated polymer material. Physical origin, magnitude, and dynamics of optical gain in these novel active laser materials are discussed leading to a selection of suitable cavity configurations for laser applications. We demonstrate laser action for various planar and ring resonator configurations that can be achieved in the regimes of transient inversion and quasi stationary excitation of the polymer material pumping with femtosecond and nanosecond pulses, respectively.

We evidence optically pumped spectral narrowing in ultra thin (3.5 microns) single crystals of (alpha) -octithiophene ((alpha) -8T), the luminescent conjugated octamer of thiophene. Experiment is achieved in a transverse pumping mode. It occurs at a pump energy threshold of approximately 0.1 (mu) J per pulse (33 ps, 10 Hz) to yield an intense and narrow emission line peaking at 700 nm. At pump energies higher than 15 (mu) J per pulse, a second narrow line of weaker intensity emerges at 640 nm. Gain narrowing of these two lines can be easily described in the usual framework of stimulated emission (SE). Light amplification originates from the combination of a net dipole alignment and efficient wave-guiding towards the edges of the crystal. The (alpha) -8T molecules provide both the emitter and the optical cavity. Spectral SE selection of the two SE lines at 640 and 700 nm can be monitored by simply scanning the spatial position of the pump beam onto the surface of the crystal. Similar SE phenomena are also observed in the (alpha) -4T and (alpha) 6T crystals, showing that conjugated oligothiophenes ((alpha) -nT) constitute a family of monolithic organic single crystals naturally adapted to laser action. Additionally, in a longitudinal pumping gain guiding situation, nanojoule-threshold infrared two-photon pumped up- converted stimulated emission is demonstrated in the oligothiophene crystals.

We observed laser emission in whispering gallery modes using a microring composed of a light-emitting semiconducting polymer poly[2,5-bis-(2'-ethylhexyloxy)-p- phenylenevinylene] (BEH-PPV) coated on an etched fiber under transient and quasi steady-state pumping conditions. The threshold for laser oscillation was 1 mJ/cm² (0.1 MW/cm²) and 30 (mu) J/cm² (300 MW/cm²) for nanosecond and femtosecond excitation, respectively. The laser output showed superlinear dependence on the excitation energy above the threshold. The demonstration of lasing under quasi steady-state pumping shows the possibility to develop electrically pumped polymer lasers. Preliminary results on the line narrowing in tripheny dilamine (TPD) films under nanosecond optical pumping are also presented. 23

Hole mobilities have been measured in tri-p-tolylamine (TTA) doped poly(styrene) containing different concentrations of di- p-tolyl-p-anisylamine (DTA) or tri-p-anisylamine (TAA). DTA and TAA are traps with depths of 0.08 and 0.22 eV, respectively. For low concentrations of DTA or TAA, the transport processes are trap controlled and the mobilities decrease with increasing trap concentration. For high TAA concentrations, however, the transport processes are dominated by trap-to-trap hopping and the mobilities increase with increasing trap concentrations. The threshold concentration for the transition from trap controlled to trap-to-trap transport is approximately 10^-1. A transition to trap- to-trap hopping is not observed for TTA containing DTA. The results are discussed within the framework of the Hoesterey- Letson formalism and the recent simulations of Wolf et al. and Borsenberger et al.

The effect of charge carrier mobilities on EL performances in electroluminescent diodes were discussed. It is stressed that quantum EL efficiency is no direct relation with charge mobilities but power efficiency may concern with charge carrier transport processes, because power efficiency is inversely proportional to drive voltage. Hole and electron mobility data on both bulk films and polymer-dispersed films were summarized and some discussions on the relation between molecular structures and charge mobilities were added. In addition, the meaning of designing high mobility materials for EL diodes is discussed. Our recent studies on the introduction of molecular alignment by use of liquid crystalline textures for the increase of charge mobilities were mentioned.

Multilayer organic light-emitting diodes with a well-defined emission region are ideal systems to investigate the underlying mechanisms of device operation. In this paper we give a brief overview of our studies on the injection and recombination processes in blue organic light-emitting diodes. Our diodes consist of copper phthalocyanine as the hole- injection/buffer layer, the aromatic diamine N,N'- di(naphthalene-1-yl)-N,N'-diphenyl-benzidine as the hole- transport layer, a distyrylarylene derivative as the emitting layer, tris(8-hydroxy-quinoline)aluminum as the electron- injection/transport layer sandwiched between indium tin oxide (ITO) as the transparent hole injector, and low work-function metals as the electron-injecting electrode. To reveal the limiting mechanisms in device operation we investigated the influence of different anode (ITO, optimized ITO) and cathode materials (Mg:Ag, Ca, LiF/Mg:Ag) as well as different layer thicknesses on the device characteristics. These investigations revealed that the device characteristics in the low and medium voltage range are determined by the injection properties of the electrodes, whereas at higher voltages (i.e. at higher current densities) a transition from an electrode- limited injection to a bulk-limited conduction process is detectable.

The current-voltage relationships in organic electroluminescent devices are derived for the following two cases: (1) double-carrier injection trap-charge limited (TCL) regime, and (2) TCL conduction with internal photodetrapping. Several experimental observations are explained based on our equations. Location of the recombination zone is predicted. A numerical model is also developed to simulate the TCL conduction. Current-voltage characteristics, band and charge profiles are obtained to elucidate the conduction mechanism in the organic electroluminescent devices with large trap densities.

The charge carrier mobility in unsubstituted poly(p- phenylenevinylene) (PPV) is investigated by the time-of-flight (TOF) method and by the space-charge limited current transient (SCLCT) technique. Both methods are performed on devices with the configuration indium-tin-oxide/PPV/Al, which is typically used in light-emitting didoes. Hole mobilities in the range of 10^-5 cm²/Vs at room temperature for an electric field of about 10⁵ V/cm are obtained. Field and temperature dependent TOF measurements yield an exponential increase of the mobility with the applied field and thermally activated behavior with activation energies between 0.4 and 0.7 eV on different samples. The values of the mobility at room temperature are consistent with stead-state space-charge limited currents, but considerably larger than the data from transient electroluminescence measurements. This indicates that the transit times obtained by the latter method are dominated by the much lower electron mobility rather than by the hole mobility. Assuming luminescence quenching within a distance of 20 nm to the Al contact, an electron mobility of some 10^-9 cm²/Vs can be estimated at room temperature and fields in the range of 10⁵ V/cm.

We report on the photorefractive properties of polymer composites based on the dye 2, N, N-dihexylamino-7- dicyanomethylidenyl-3, 4, 5, 6, 10-pentahydronaphthalene (DHADC-MPN). At 633 nm and with 2,4,7-trinitrofluorenone as a sensitizer, the polyvinylcarbazole-based composites show complete internal diffraction at applied electric fields as low as E_(pi /2) equals 30 V/micrometer. The sensitivity of the composite could be extended into the infrared by using (2,4,7-trinitro-9-fluorenylidene)malonitrile as a sensitizer, and at 830 nm complete internal diffraction occurred at an applied field of E_pi/2 equals 59 V/micrometer. Finally, by using DHADC-MPN as a trifunctional dopant in an inert matrix, we have achieved a dynamic range of (Delta) n equals 0.0085 and a net two-beam coupling gain of (Gamma) equals 202 cm^-1 at an applied field of 50 V/micrometer and at 633 nm. The composites are thermally stable or have shelf lifetimes of at least several years at room temperature.

Photorefractive polymer materials were tested for speed and magnitude of response, using degenerate four wave mixing, Mach-Zehnder interferometry and transmission ellipsometry. Two polymer materials with an electro-optic dye of identical molecular mass were tested, one with a straight chain aliphatic group, the other with a branched chain. The orientational response tends to be hindered by an increase in the amount of branching of the electro-optic dye molecule, which reduces both the degree of poling that is due to the external field and the enhancement due to the internal space- charge field. Although the composites containing ODNPB show faster and greater photorefractive response, they exhibited more phase instability, with devices showing advanced crystallization after short periods. The EHDNPB composite offered slightly less photorefractive response at a reduced rate but offered crystallization free devices over many months even at high dye concentrations.

Single arm dual mode optical waveguide interferometer utilizes interference between two modes of different order. Sensing effect results from the change in traveling conditions of the modes caused by the environment. The waveguide is made as an open asymmetric structure containing a dye-doped high temperature polyimide film onto a silica substrate. It is more sensitive to the change of environment than its conventional polarimetric analog using orthogonal modes (TE and TM) of the same order. The sensor still preserves the option of operating in polarimetric regime using a variety of mode combinations such as TE₀/TM₀ (conventional), TE₀/TM₁, TE₁/TM₀, or TE₁/TM₁ but can also work in nonpolarimetric regime using combinations TE₀/TE₁ or TM₀/TM₁. Experimental temperature sensor based on TE₀/TE₁ combination demonstrates 2(pi) -phase shift between interfering modes in response to 2 degree Celsius-change of the ambient temperature. Utilization of different mode combinations simultaneously makes the device more versatile. Application of the sensor to gas sensing is based on doping polymer film with an organic indicator dye targeting a particular gaseous reagent. Change of the optical absorption spectrum of the dye caused by the gas results in change of the reactive index of the dye-doped polymer film which is detected by the sensor. We propose to use indicator dyes based on temperature durable metal substituted phthalocyanines (such as Octadecyloxy copper phthalocynaine) which demonstrates a significant change of the absorption spectrum being exposed to acidulous or alkaline atmosphere. We discuss the design of the experimental gas chamber for testing the interferometer as a NOX sensor.

Light emitting diodes made of a single spin-coated layer of poly(9-vinylcarbazole) doped with coumarin-515 dye have been studied. The influence of dye concentration on emission and electrical characteristics is evidenced. Two different regimes are identified. At low concentrations, apparent hole injection barrier raises, holes are trapped and mobility decreases. External quantum efficiency increases with concentration. At concentrations larger than 10%wt, coumarin aggregates, photoluminescence yield drops and electroluminescence yield increases up to 0.1%-photons per electron. We show that using coumarin dye in a single-layer diode improves electron-hole injection and recombination balance more than using an additional hole-blocking layer.

In this paper, we have demonstrated two types of polymer waveguide switches with nematic liquid crystal cladding. Although the higher propagation loss in LC materials hinders them from serving as the waveguide film, it has been common that LC exhibiting a large optical anisotropy and an electrically controllable molecular alignment are applied to investigations of slab-waveguide cut off switching as active medium claddings. For this type of switching geometry, a higher contrast ratio is obtainable because simple TE or TM polarized waves may be supported in the planar polymer waveguide.

We report the results of study of upconverted emission in the band 520 to 600 nm from waveguides made of poly(methyl methacrylate) (PMMA) doped with laser dye 4- (Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)4H-pyran known as DCM. The emission could be excited using CW laser pumping within the range 630 nm to 800 nm with intensity below 1 kW/cm². The excitation mechanism, instead of the two- photon absorption, more likely involves exciton-like localized states below the S1 singlet state. These localized states, being excited by low energy photons can assist in populating upper singlet states according to the scheme of the excited state absorption. We also pay special attention to material photobleaching that accompanies upconverted emission. This effect leads to refractive index decrease at the wavelength of the pump. Computer simulations based on numerical solutions of nonlinear propagation equation as well as experiments show that photobleaching leads to irreversible branching of optical pump beam that propagates through a dye-doped polymer waveguide.

Third-order nonlinear optical susceptibilities (chi) ⁽³) of polysilanes were estimated both at molecular and crystalline levels, in order to establish a molecular design strategy of (chi) ⁽³) of polysilanes, by using an ab initio coupled perturbed Hartree-Fock (CPHF) method and the oriented-gas approximation. Molecular calculation results showed the main chain conformation of polysilanes directly affects second hyperpolarizabilities (gamma) of polysilane oligomers, and the trans planar oligomers have larger (gamma) than the 7/3 helical or alternating trans gauche (TGTG') oligomers, due to a stronger (sigma) -electron delocalization in their trans planar main chain. On the other hand, it was found that crystalline (chi) ⁽³) of polysilanes are influenced not only by the main chain confirmation, but also by the molecular weight of polysilane repeating unit M_Si. Based on those molecular and crystalline results, a strategy of molecular design of polysilane (chi) ⁽³) was proposed which predicts trans planar poly[dimetylsilane] may have the largest (chi) ⁽³) among polysilanes investigated so far, owing to its trans planar main chain and smallest M_Si.

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) thin films dispersed molecularly with N,N'-diphenyl-N,N'-di(m- tolyl)benzidine (TPD) were applied as a hole-transporting layer (HTL) for the fabrication of organic electroluminescent (EL) devices. Vacuum-sublimed molecular film of tris(8- hydroxyquinolinato) aluminum (Alq3) was used as an emissive/electron-transporting layer (EM&ETL). The devices have the typical double layer structure of glass substrate/ITO/TPD:PVdF-HFP/Alq3/Al. Two different compositions, 30/70 and 50/50, of TPD in PVdF-HFP film were employed to investigate the dependence of device performance with the contents of the hole-transporting molecule. The turn- on voltage of OELD fabricated with 30/70 composition of TPD was lower than that with 50/50. In addition, the device with lower TPD concentration was more stable and efficient than that with higher concentration. The 30/70 device driven at 9 V emitted a bright green light with a peak wavelength of 511 nm (2.43 eV) under air ambient condition. At 10 V, the brightness was above 5,000 cd/m².

The polymeric light-emitting diodes (PLEDs) in the present work consist of a double layer organic structure, i.e. ITO/hole transport material (HTM)-dispersed polymer/emitter/cathode. Fully aromatic polyimide, poly(4,4'- oxydiphenylene pyromellitimide) (PMDA-ODA PI), with outstanding thermal stability and high glass transition temperature of 377 degrees Celsius was introduced as a matrix polymer for binding the HTM. N,N'-diphenyl-N,N'-di(m- tolyl)benzidine (TPD) and bis(8-hydroxyquinolinato)zinc(II) (Znq2) were used as a HTM and an emitter, respectively. The turn-on voltage was ca. 7 V. Bright greenish yellow light was observed at 11 V under room light.