Mechanism of refractive index increase in silica glass for the development of fiber-optic photodevices

紫外光光子或离子辐照在透明材料中引起的折射率变化，保证了可以直接绘制出可用作光学光栅的波导。用显微光致发光、拉曼散射、光学显微镜和原子力显微镜(AFM)测量了离子微束作用下石英玻璃的结构变化。原子力显微镜对微束辐照区域的测量表明，微束表面形成了一条凹槽。此外，在平行于入射平面的表面上的横截面观察揭示了沿离子轨迹的表面变形，在离子的投射范围内是最深的。考虑到能量沉积可能引起的二氧化硅结构的变化，测量到的前表面和侧表面的拓扑变化是由于石英玻璃的内部致密造成的。折射率变化由Lorentz-Lorenz关系估计，使用AFM测量估计的内部压实分布。在PECVD制备的a-SiO_xN_y：H薄膜中，除了在投影范围内有较强的折射率变化外，沿离子轨迹还观察到很小的折射率变化，这表明电离和原子碰撞引起的能量沉积都是由KrF准分子激光产生的紫外光引起的。利用高质量的熔融硅板制作了位相掩模，制作了衍射光栅。用扫描电子显微镜(SEM)观察了制作的光栅片的表面。可以观察到周期在1μm左右的清晰的方齿图案。此外，从夫琅和费衍射图中估计出该光栅的周期约为1μm，这与扫描电子显微镜的图像相吻合。这简单地证明了a-SiO_xN_y：H可以被紫外光辐照处理。

The refractive index change induced in a transparent material by UV photon or ion irradiation promises direct drawing of a waveguide that can be used as optical gratings. Structural changes in silica glass induced by ion microbeam were evaluated using microscopic photoluminescence and Raman scattering, and optical and atomic force microscopes (AFM) measurements. The AFM measurements on the microbeam irradiated area show the formation of a groove on the surface. In addtion, a cross sectional observation on the surface parallel to the incident plane reveals surface deformation along the ion tracks, which is deepest at the projected range of ions. Taking into account the possible structural changes of silica induced by energy deposition, the measured topological changes at the front and side surfaces result from internal compaction of silica glass. Refractive index changes were estimated from the Lorentz-Lorenz relationship using the distribution of the internal compaction estimated by the AFM measurements. A small refractive index change was observed along the ion tracks besides a much stronger index change at the projected range, suggesting that energy depositions by the ionization as well as by the atomic collision should be taken into account.It has also become clear that the refractive index change can be induced by UV photons from a KrF excimer laser in a-SiO_x N_y : H films prepared by PECVD. Fabrication of a diffraction grating was performed using a phase mask made of a high quality fused silica plate. The surface of the fabricated grating observed by scanning electron microscopy (SEM). A clear square-toothed pattern with periodicity of around 1 μm can be observed. Furthermore, from the Fraunhofer diffraction pattern, the periodicity of the grating pattern was estimated to be around 1 μm, which agrees with the SEM image. This simply demonstrates that a-SiO_xN_y : H can be processed by UV photon irradiation.