LiNbO_3:Fe晶体中光写入波导时折射率的变化规律

The index changes of waveguides fabricated by light irradiation in LiNbO_3:Fe crystals

研究了利用光辐照法制作光折变波导时LiNbO3:Fe晶体中折射率变化的规律 .分别采用波长为 63 2 8nm和5 3 2nm的寻常偏振和非常偏振的细激光束和片状激光束 ,在LiNbO3:Fe晶体中进行了写入波导实验 .研究表明 ,制作波导的写入光宜采用寻常偏振光 .在利用由光束辐照LiNbO3:Fe晶体形成的正折射率变化区域作为波导结构时 ,必须严格控制辐照时间 .否则 ,由于长时间光辐照会带来较强的噪音栅以及折射率变化区域会发生扩展 ,而难以形成优质波导 .利用片光在“三明治”方式辐照下 ,以小曝光量制作波导时 ,可以避免噪音栅的影响 ,形成高质量的对称型光波导 .通过选择不同的光束宽度和片光间距 。

The refractive index changes of waveguides fabricated by light irradiation in LiNbO3 : Fe crystals were investigated by using ordinary and extraordinary laser beams at wavelengths of 632.8nm and 532nm. The experimental results show that the waveguide fabricated by ordinary light is better than that by extraordinary light, as the ordinary light causes much less light-induced scattering. The illuminated time must be strictly controlled when the region with a positive index change, formed by a single thin laser beam, is used as waveguide structure. This is beacuse the waveguide properties may be influenced by the strong noise grating and the shift of the waveguide region after the LiNbO3 : Fe crystal was irradiated for a long time. For avoiding the influence of the noise grating, the symmetric waveguide structure with high quality can be fabricated by sheet beam illumination employing the sandwich method at a relatively low exposure intensity. Moreover, waveguides with different index distributions and different dimensions can be fabricated by changing the width of the irradiating beam and the distance between twice irradiations.