Grating Coupling to Polymer Optical Waveguides

We describe the production and optical characterization of planar dielectric waveguides of the organic polymers Poly-(alpha) -Methyl-Styrene and Poly-Phenyl-Acetylene. Single mode waveguides, at (lambda) equals 1.064 micrometers , were obtained by the use of the spin-coating technique. Propagation losses were measured through detection of the out of plane scattered light are as low as 0.7 dB/cm. The waveguiding films were spun over fused silica substrates that were previously etched in order to obtain two grating couplers with a 0.55 micrometers period. Nonlinear grating coupling was investigated in the case of Poly-Phenyl-Acetylene, with a 70 ps pulsed source at (lambda) equals 1.064 micrometers at high repetition rate (frep equals 76 MHz)

CRYSTALLINE PROPERTIES AND COLOR-CENTERS IN ALKALI-HALIDE THIN-FILMS

Thin films of KCl, KBr, RbCl have been obtained by thermal evaporation on amorphous substrates with different deposition parameters. The crystalline structure and orientation have been determined, and the films resulted to be policrystals with high uniformity of orientation. Production of colour centres, achieved by irradiation with low-energy electrons, leads to F center concentrations barely observed in large crystals. The colouration kinetics is similar to that in the bulk, and shows after a maximum an exponential decay at high doses because of centre aggregation coupled to thermal effects. The films exhibit a bleaching process of the colour centres at room temperature, whose kinetics depends on the irradiation damage