Phase-Matched Wavelenght-Conversion in Nonlinear-Optical Waveguide of Organic Crystal Based on Thickness Control of LB Film

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We studied Langmuir-Blodgett (LB) films in a viewpoint of thickness control of top layrs on guideing layrs of organic nonlinear-optical crystals. The LB film as a top layr can be stacked layr by layr and the thickness can be precisely controlled, since, generally, on LB layr has thickness of nm-order. In the research, by means of stacking LB layrs, we experimentally achieved optical second-harmonic generation (SHG) under the condition of thickness-controlled phase-matching with practcally large tolerance and theoretically designed how to obtain larger tolerance in guided-to-guided mode SHG for given thickness of the guiding layre.In the experiment, we tried to stack Z-type LB layrs of N-dococyl-N^1- (4-nitrophenyl) urea (DONPU) on the inorganic nonlinear-optical LiTaO_3 epitaxially grown on the inorganic LiNbO_3 substrate. As a result, we could attain SHG under the tolerable phase-matching within a thickness range of 45 nm of the LiTaO_3 layr, which is wide enough in comparison with the usual thickness range of 1 nm-order. We also found that the stearic acid has to be used as the intermediate layr on the LiTaO_3, since DONPU can be stacked on the hydrophobic substrate.In the theory, we treated the organic nonlinear-optical (-) 2- (alpha-methylbenzylamino) -5-nitrophyridine (MBANP) and 3,5-dimethyl-1- (4-nitrophenyl) pyrazole (DMNP) as the guiding layrs on the glass substrates with the appropriate buffer layrs. We could predict that the wide thickness-range of the guiding layr can provide the tolerably phase-matched SHG,where the phase matching is controlled by stacking the DONP film layr by layr according to the thickness of the guiding layr.