J. I. Chen

Photorefractive effect in a conjugated polymer based material

Abstract A new type of polymeric photorefractive material based on a conjugated polymer has been developed. Photorefractive effect was observed in a second order nonlinear optical polythiophene derivative with the addition of a photosensitizer. The linear and second order nonlinear optical properties, photoconductivity and photorefractivity for this material were investigated. Relatively large two-beam-coupling gain coefficient of 24.5 cm−1 was measured.

An interpenetrating polymer network for second-order nonlinear optics

Abstract The linear optical and second-order nonlinear optical (NLO) properties of an interpenetrating polymer network (IPN) have been investigated. For the poled and cured IPN samples, large second-order NLO coefficients, d 33 , were measured at 1.064 μm and 1.542 μm. The linear electro-optic coefficients, r 33 , were determined at various wavelengths. The opled and cured IPN samples showed no measurable decay of the second-order optical nonlinearity after being treated at 110°C for more than 1000 hours. This excellent long-term stability of the NLO property is ascribed to the novel interpenetrating crosslinked molecular structure of the IPN system.

Design and synthesis of interpenetrating polymer networks for second‐order nonlinear optics

There has been a tremendous recent interest in the development of second-order nonlinear optical (NLO) polymeric materials for photonic applications. However, a major drawback of second-order NLO polymers that prevents them from being used in device applications is the instability of their electric field induced dipolar alignment. The randomization of the dipole orientation leads to the decay of second-order optical nonlinearities. Numerous efforts have been made to increase the stability of the second-order NLO properties of polymers. The search for new approaches to develop NLO polymers with optimal properties has been an active research area since the past decade. A novel approach, combining the hybrid properties of high glass transition temperatures, extensively extensively crosslinked networks and permanent entanglements, based on interpenetrating polymer networks (IPN) is introduced to develop stable second-order NLO materials. Two types of IPN systems are prepared and their properties are investigated. The designing criteria and the rationale for the selection of polymers are discussed. The IPN samples show excellent temporal stability at elevated temperatures. Long-term stability of the optical nonlinearity at 100°C has been observed in these materials. Temporal stability of the NLO properties of these IPNs is synergistically enhanced. Relaxation behavior of the optical nonlinearity of an IPN system has been studied and compared with that of a typical guest/host system. The improved temporal stability of the second-order NLO properties of this IPN system is a result of the combination of the high rigidity of the polymer backbones, crosslinked matrices and permanent entanglements of the polymer networks. A slight modification of the chemical structure resulted in an improvement of the optical quality of the sample.

Nonlinear Optical Polymers Derived from Organic/Inorganic Composites

Abstract : A general approach to the development of multicomponent multifunctional stable NLO materials based on sol-gel reactions has been discussed. We have shown that these second order NLO organic/inorganic composites exhibit excellent room temperature stability of the second order optical nonlinearity. The final structure is an orientationally ordered organic/ inorganic network. After an initial decay, excellent long term stability at elevated temperatures, ranged from 100 to 120 deg C is observed for a number of different systems. The second order optical nonlinearities are reasonably large for radical device considerations. Sol-gel, Nonlinear optical polymers, Organic/ inorganic composites.

Infrared dielectric behaviour of polypyrrole doped with tosylate

Abstract Measurements of Reflection (R) and Transmission (T) for polypyrrole tosylate in the far infrared (10–200 cm−1) were performed. The dielectric constants are determined from these measurements through manipulation of the Fresnel equations. The magnitude and dispersive nature of the complex index of refraction is described as a function of conductivity. The applicability of these materials to new optical devices is demonstrated through the significant change in conductivity realizable by suitably reducing the oxidized film. Further evidence for alternative conduction mechanisms is given by the failure of the Drude free carrier model to fit our dielectric data in the 10–100 cm−1 region. An application exploiting the large real part of the index of refraction and relatively low loss observed in the microwave region is discussed.

A relaxation study of poled nonlinear optical polymers by infrared reflection-absorption spectroscopy

Abstract The relaxation of poled nonlinear optical (NLO) chromophores in polymer films was characterized by infrared (i.r.) reflection-absorption spectroscopy. Both a guest-host system and a photocrosslinkable polymer system were investigated. Polymethylmethacrylate doped with either 2-methyl-4-nitroaniline or 4(4′-nitrophenylazo)aniline was studied. The photocrosslinkable polymer system, polyvinylcinnamate doped with 3-cinnamoyloxy-4-[4-(N,N-diethylamino)-2-cinnamoyloxy phenyl azo]nitrobenzene was also investigated. Doped NLO active molecules were aligned using the corona poling technique. i.r. spectra as a function of time were used to monitor the relaxation behavior of the oriented dyes after poling. Relaxation of NLO molecules was followed at various characteristic vibrational frequencies. The relaxation behavior of both systems were found to be consistent with those studied by the second harmonic generation technique.

Synthesis and Characterization of Electroactive Polymers Based on Pyrrole

A novel method for polymerizing pyrrole has been identified which utilizes aqueous KI 3 solutions. This new synthesis technique enables a controlled method for incorporation pyrrole into composite systems to produce new electrically active polymers and to provide process control. Two electroactive systems were synthesized by this technique and characterized for their morphological and electrical properties. Electromembranes were fabricated from polypropylene and polycarbonate membranes and exhibited virtually no pore size restriction. Stable conductive coatings composed of ethylene-vinylacetate (EVA) copolymer and polypyrrole (PPy) were also developed

Polyimide/Norganic Composite - Interpenetrating Polymer Network For Stable Second-Order Nonlinear Optics

Abstract : A new class of IPN system has been prepared and investigated. This IPN system combines the polybismaleinimide network and the NLO-active phenoxysilicon network. The second-order NLO coefficients, d33, values of the samples range from 2.5 to 6.7 pm/V depending on the composition and the processing conditions. The temporal stability of the second-order nonlinearities for these samples at 110 deg C varies from 47 to 88% retention after 274 h.

Thermally Stable Polyimides for Second-Order Nonlinear Optics

A new class of nonlinear optical (NLO) polyimides incorporating a thermally stable chromophore has been synthesized and characterized. These polymers exhibit large and extremely

Semi- and Full Interpenetrating Polymer Networks as Stable Second-Order Nonlinear Optical Materials

Polymeric materials with second-order nonlinear optical (NLO) properties have been extensively studied for their potential applications in electro-optic modulation and frequency doubling devices.1,2 The second-order NLO properties in these polymer are present when the chromophores are aligned in a non-centrosymmetric manner. In order to be useful in practical devices, the alignment of NLO chromophores in the poled polymers must be sufficiently stable at temperatures above 100°C. Since the alignment of the chromophores resulting from poling is not in a state of thermodynamic equilibrium, the poled order would relax to a random configuration in an absence of electric field. In a prototypical guest/host system, Stahelin et al. demonstrated a fitting of the temporal relaxation to a Kohlrausch-Williams-Watts (KWW) equation establishing that the decay of the dipole alignment is explained by a single relaxation phenomenon.3 A fit of the relaxation times to the Williams- Landel-Ferry (WLF) equation pointed out that relaxation of the second order NLO properties is mainly related to the glass transition temperature (Tg) of the media. Thus NLO chromophores are usually incorporated in a polymer which has a high Tg in order to prevent the randomization of the poled (aligned) NLO molecules.