Waveguiding in electrooptic Langmuir-Blodgett films
This thesis describes work on the waveguiding and second-order nonlinear optics of Langmuir-Blodgett (LB) films. A number of new monomeric materials are assessed for their LB deposition and their second-order nonlinear properties. Both the Pockels effect and second harmonic generation are studied. One new chromophore, diphenyl butadiyne is shown to possess exceptional nonlinear effects in monolayer form with x((^2))(-w; w, 0) = 2.7 x 10(^-10) mV(^-1) A novel aminonitrostilbene carboxylic acid with x((^2))(-w;w,0) = 1.43 x 10(^-10) m V(^-1) is also described. Polymeric LB materials have been found to possess greater stability than monomers but the deposition properties are often poor. Two oligomers are investigated, these both form high-quality LB layers and one gave X((^2))(-w;w,0) = (3.4-1-1.0j) x 10(^-11) m V(^-1). Two alternate-layer systems are considered. The first, of an amidonitrostilbene and a novel functionalised diarylalkyne deposits to 150 bilayers, but the nonlinear coefficients are shown to diminish after fewer than ten layers. X-ray diffraction, waveguiding and Fourier transform infra-red measurements are also performed. The second system alternates the two oligomers; only films of fewer than seven layer are studied due to the low value of Pockels effect and second-harmonic generation detected. A novel method of waveguide fabrication combining solution dipped polymer layers with LB films is introduced. This technique allows the rapid fabrication of waveguides with nonlinear properties. Monomode waveguides are produced and their electrooptic properties measured. These are the first such measurements on an LB film waveguide. It is shown theoretically that such waveguides could be used to produce modulators of similar figures of merit to those made from poled-polymers but that an order of magnitude improvement in X((^2))(-w; w, 0) is needed to match lithium niobate systems.