Development of highly efficient polymeric frequency doubler using novel fabrication technique of domain inversion.

近年来，有机非线性光学（NLO）材料因其大的二阶非线性光学系数和超快的响应速度而在光电子学领域得到了广泛的研究。倍频器的转换效率与基频光的光密度成正比。波导几何形状对于非线性光学（NLO）应用具有优势，因为可以在长传播长度上实现高功率密度并且利用对角张量分量。为了获得高效的二次谐波产生（SHG），材料在基波和谐波的光的长传播距离上匹配相速度。通过仔细调节波导厚度，介质的色散允许在两个波长处的不同模式具有相同的有效折射率n_<eff>，这被称为模式色散相位匹配（PM）。波导的有效折射率主要取决于波导的尺寸。因此，满足相位匹配条件的波导尺寸的制造公差被限制为小于几nm。此外，传播波导模式之间的光场重叠必须大，以提高转换效率。一般情况下，很难获得大的尺寸公差，以及高的重叠积分模式色散相位匹配。在这里，我们报告的五层有机波导制备的LB技术表现出高的重叠积分以及大的制造公差的厚度高达56 nm。这种大的相位匹配制造公差是传统三层波导的8.6倍。

Recently organic nonlinear optical (NLO) materials have been extensively investigated because of their large second-order nonlinear optical coefficients and ultra fast response in the field of optoelectronics. A conversion efficiency of frequency doubler is proportional to the optical density of fundamental beam. The waveguide geometry has advantages for nonlinear optical (NLO) applications, because of the high power density that can be achieved over a long propagation length and utilization of diagonal tensor components. In order to obtain a highly efficient second harmonic generation (SHG), the materials match the phase velocity over the long propagation distance for light at fundamental and harmonic waves. By carefully adjusting the waveguide thickness the dispersion of the medium allows different mode at the two wavelengths to have the same effective refractive index n_<eff>, which is called as modal dispersion phase-matching (PM). The effective refractive index of waveguide critically depends on the waveguide dimensions. Therefore fabrication tolerance of waveguide dimension to fulfilll phase-matching condition is limited to less than a few nm. Furthermore optical-field overlap must be large between the propagating waveguide modes to improve a conversion efficiency. In general, it is difficult to obtain large dimension tolerance, together with high overlap integral for modal dispersion phase-matching. Here we report that five-layr organic waveguides prepared by Langmuir-Blodgett techniques exhibit high overlap integral as well as large fabrication tolerance of thickness up to 56 nm. This large fabrication tolerance for phase-matching is 8.6 times larger than that of conventional three layr waveguide.