Applications of the secondorder Bragg interaction in a thinfilm optical waveguide for the transverse electric mode

Guided-mode resonance optical filters are made from thin-film structures which consist of azopolymer films deposited on top of slab waveguides. Surface relief gratings can be optically induced on the azopolymer films. The transmission and reflection spectra as a function of the angle of incidence of the probe beam exhibit very sharp resonance features which correspond to coupling into the waveguide modes. Coupling into the overlying azopolymer film is also observed.

Novel cross-linkable, highly fluorinated poly(arylene ether ketones/sulfones) have been prepared by copolycondensation reactions of perfluorinated aromatic ketone/sulfone with 4,4′-(hexafluoroisopropylidene)diphenol and a tetrafluorostyrol-containing bisphenol (i.e., 1,1-bis(4-hydroxyphenyl)ethyl-1-phenyl 2,3,5,6-tetrafluorostyrol ether). The reactions were conducted at low temperature in the presence of calcium hydride and cesium fluoride. The resulting polymers have number-average molecular weights in the range of 25 000-36 000, excellent solubilities in common organic solvents, high glass transition temperatures (T g ) in the region of 150-185 °C, and good thermal stabilities (T d up to 480 °C). Tough, flexible, and transparent thin films of these polymers can be readily prepared by both solution casting and spin-coating. By adjusting the feed ratio of monomers, the refractive index and cross-linking density of the polymers can be readily controlled. Cross-linking of these polymers has been demonstrated by both thermal heating and UV irradiation. The cross-linked polymer thin films exhibit low optical loss (∼0.5 dB/cm) and low birefringence (∼2 × 10 -3 ) at 1550 nm, demonstrating that they are promising candidates for optical waveguide materials.

Highly fluorinated poly(arylene alkylene ether sulfone)s: synthesis and thermal properties Ding, Jianfu; Du, Xiaomei; Day, M.; Jiang, Jiaren; Callender, C.; Stupak, Jacek Process and EnVironmental Technology, National Research Council of Canada, 1200 Montreal Road, Ottawa, Ontario, Canada K1A 0R6; Communications Research Centre Canada, Ottawa, Ontario, Canada K2H 8S2; and Institute for Biological Sciences, National Research Council of Canada, 100 Sussex DriVe, Ottawa, Ontario, Canada K1A 0R6 ReceiVed January 3, 2007; ReVised Manuscript ReceiVed February 28, 2007 ABSTRACT: A simple procedure has been developed for the preparation of highly fluorinated poly(arylene alkylene ether sulfone)s using a nucleophilic polycondesation reaction of decafluorodiphenyl sulfone (DPSO) with a series of fluorinated linear or branched alkylene diols containing 4-12 carbon atoms. The reactions are activated using cesium fluoride (CsF) or potassium fluoride (KF) as a base in N,N-dimethylacetamide (DMAc) at room temperature and are completed in a few hours or a few days, respectively. Polymers with numberaverage molecular weights (M n ) around 50 000 Da have been prepared. A broad molecular weight distribution and a low dependence of the reaction rate on temperature are observed and attributed to the heterogeneous nature of the reactions. Because of low solubility, CsF and KF exist in the reaction solution mainly in the form of solid particles, and the adsorption of the polymer on the surface of the particles hinders the diffusion of CsF and KF from solid into solution. This effect causes the polymers close to the solid surface to have greater growth rates and higher molecular weights than those in solution. Polymers with linear alkylene spacers display a marked tendency to crystallize, which increases with the length of the alkylene spacer. In fact, the polymer with the longest alkylene spacers (P12C F SO) crystallizes during the polymerization reaction, preventing the polymer chains from growing, resulting in a low molecular weight (M n < 8000 Da). Raising the reaction temperature to 70°C slightly decreases the crystallization tendency and allows the M n to increase to 17 000 Da. The crystallization of P12C F SO is fast enough to be completed during a quenching process induced by immersing the molten sample in liquid nitrogen. However, the polymer with branched alkylene spacers does not show any crystalline structure even when annealed at a temperature slightly higher than its glass transition temperature (T g ). A secondary crystal peak is also found in the DSC curves of the crystalline polymers with linear alkylene spacers. The position of this peak can be shifted to higher temperatures by annealing and has been attributed to incomplete crystallites formed between the primary lamellar crystals.