Aaron W. Harper

Polymer electro-optic devices for integrated optics

Abstract Recent advances in polymer electro-optic polymers and in fabrication techniques have made possible advances in polymer optical guided wave devices which bring them much closer to system ready. The processing of a new thermal set FTC polymer and its incorporation into a high-frequency, low-Vπ optical amplitude modulator are reviewed. The design and fabrication of 100 GHz modulators and their integration with rectangular metal waveguides using an anti-podal finline transition with a flexible Mylar substrate is discussed. High-speed polymer modulators with balanced outputs and the in situ trimming of the output coupler is described. More complex guided wave devices using polymers are demonstrated by the photonic rf phase shifter. Techniques for integrating both passive and active polymers into the same optical circuit without the need for mode matching is presented and demonstrated. To reduce the Vπ of a polymer amplitude modulator to 1 V or under, a technique of constant-bias voltage is demonstrated. Finally, a technique to directly laser write electro-optic polymer devices is reviewed.

FORMYLATION OF DIETHYL 2-THIENYLMETHYLPHOSPHONATE FOR ONE-POT SYNTHESIS OF AMINOTHIENOSTILBENECARBOXALDEHYDE

Diethyl 5-formyl-2-thienylmethylphosphonate is synthesized via the formylation of 2-thienylmethylphosphonate, and has been demonstrated to beane efficientintermediate thienylvinylene elongation of electron-rich conjugate systems.

DC biased electro-optic polymer waveguide modulators with low half-wave voltage and high thermal stability

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 half-wave voltage. This technique makes use of the total achievable electro-optic coefficient, which can be more than three times the value that is used by the conventional devices of poled electro-optic polymer. As the result of the DC bias and with high-μβ chromophores, a low half-wave voltage of 1.5 V was achieved with 2-cm-long birefringent waveguide modulators at the wavelength of 1.3 μm. Results of a 200°C stability experiment indicate that this scheme also enables electro-optic polymer devices to meet the short-term high-temperature stability requirement because the polymer does not need to be poled prior to high-temperature steps.

Properties and chemical environment effects of alkylamino styryl pyrazine two-photon fluorophores

Advancement over the past decade of materials based on two-photon absorption has been phenomenal; yet, a need for greater understanding of multi-photon processes remains. Questions of design to maximize two-photon absorbance cross-sections and quantum yields have been addressed quantitatively. However, effects of the chemical environment on the absorption and emission processes in these chromophores are largely unexplored. This study presents the effects of 26 different solvents on the absorption and emission characteristics of a set of six new alkylamino-substituted styryl pyrazines. The solvatochromic comparison method is employed to derive structure-optical property relationships within this family of fluorophores, and the effects of solvent polarity, hydrogen bonding and inductive and dispersive forces are discussed. Electrostatic and transition moments are measured and their contributions to two-photon absorbance cross-sections (δTPA) are discussed. Symmetric D-π-A-π-D molecular architecture is thought to play a very important role in increasing δTPA by disrupting the degeneracy of excited states and increasing one- and two-photon transition probabilities. The coupling of strong electron donors to strong electron acceptors with symmetric D-π-A-π-D molecular architecture is shown to produce fluorophores with exceptional two-photon activities.

Chemically responsive fluorophores exhibiting large color changes

The design, synthesis, and characterization of a series of styryl pyrazine derivatives as chemically responsive fluorophores are reported. These styryl pyrazines were ideal for structure-property relationship studies designed to elucidate the role of molecular symmetry, polarity, planarity and cooperative and competitive intramolecular charge transfer interactions in determining their colorimetric or fluorimetric responses. These fluorophores were designed to exhibit large changes in emission in response to changes in solvent composition or addition of various analyte species. The large solvatochromic and analyte-induced changes in their spectra were related to the nature of molecular polarization upon excitation, as well as stabilization of the excited state by the molecular environment. Several of these molecules shared the structural and electronic features common to quadupolar two-photon chromophores, and were thus expected to function as chemically responsive two-photon fluorophores, as well. Calculations of their second hyperpolarizabilities (γ(-ω;ω,-ω,ω))and comparison to known two-photon molecules showed that these molecules were expected to be exceptional two-photon active molecules.

Low-Vπ high-thermal-stability electro-optic polymer waveguide modulators using the full potenetial of high-μβ chromophores with a DC bias voltage

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.

A Facile Synthesis of 5-N, N-Bis(2-Hydroxyethyl)Amino-2-Thiophenecarboxaldehyde

Abstract Amination of 5-bromo-2-thiophenecarboxaldehyde with an acyclic secondary amine - bis(2-methoxyethyl)amine was effected by using weak base sodium bicarbonate. The resulting 5-N,N-bis(2-methoxyethyl)amino-2-thiophenecarboxaldehyde was treated with boron tribromide to give 5-N,N-bis(2-hydroxyethyl)amino-2-thiophenecarbox- aldehyde.

The role of intermolecular interactions in fabricating hardened electro-optic materials

Until recently, the product of chromophore dipole moment, β, and molecular first hyperpolarizability, p, divided by chromophore molecular weight was considered to be an appropriate chromophore figure of merit. Substantial progress has been made designing and synthesizing chromophores characterized by large μβ values. If such high pp chromophores could be translated to hardened acentric polymer lattices with the same efficiency achieved for disperse red (azobenzene) chromophores then optical nonlinearities in excess of 50 pm/V could be expected. Although high μβ chromophores have been available for several years, such macroscopic optical nonlinearities have only beat recently realized. We demonstrated that the problem of translating microscopic to macroscopic optical nonlinearity can be traced to the attenuation of electric field polinginduced order by chromophore-chromophore electrostatic interactions. Such interactions are frequently treated within the approximations of London theory. We extend theoretical analysis to take into account the size and shapes of chromophores; such theory permits essentially quantitative prediction of variation of electro-optic coefficient with chromophore loading. Theory also suggests structural modification of chromophores to improve the maximum realizable optical nonlinearity as a function of chromophore loading and theoretical predictions have been experimentally realized in a number of cases leading to doubling and tripling of previously realized maximum electro-optic coefficient values. Chromophore-chromophore electrostatic interactions also contribute to aggregation and phase-separation which result in unacceptably high values of optical loss. Such interactions can also inhibit lattice hardening (e.g., thermosetting) reactions. A systematic analysis of such effects is presented.

Techniques for Ultrastructure Synthesis: Preparation of Second Order Nonlinear Optical Materials

Pi-electron organic materials have long been considered promising candidates for the fabrication of nonlinear optical devices such as electro-optic modulators and frequency doublers.1 The main advantages of organic materials have been stated to be their large optical nonlinearities together with ease and low cost of processing into various device forms. Other advantages include relatively high laser damage thresholds.

Photophysics of novel conjugated polymers with alternating heteroaromatic rings: synthesis and applications

We report the design, syntheses, structure-property relationships, and applications of alternating copolymers containing heteroaromatic rings. Polymers with different structures were synthesized by Suzuki couplings of 1,4-phenyldiboronic acid with various dibromoarenes. The effect of heteroatoms was studied by comparing polymers containing biphenyl, bipyridine, bithiazole, or thienyl moieties. The changes in the polymer structure led to changes in singlet and triplet energies, absorption and emission properties, as well as energy transfer parameters. The effect of polymer structure on absorption maxima, emission properties, excimer formation, aggregate formation, as well as singlet and triplet energies were studied. Alternating copolymers of bipyridyl moieties gave rise to blue-emitting polymers with emission maxima at 410nm, where as the use of bithiazole moieties red-shifted the emission. All of these polymers can be used in polymer light-emitting devices as the emitting layers, where thienyl containing polymers can be used as hole transport layers. The polymers transferred energy efficiently to Coumarins and europium complexes, allowing for their potential use in longer wavelength emitting applications. The ability of bipyridine containing polymers for use as metal ion sensors was studied.