Three dimensional Multi-layred Optical Strage System

我们研制了一种三维多层光学条带系统。该系统将沿光轴方向的三维凹坑记录到厚材料中。在记录方面，我们使用了体全息记录中使用的光折变材料，如光致聚合物和光折变晶体(LiNbO_3)。凹坑被记录为折射率变化。我们使用了激光扫描显微镜来记录和访问凹坑。扫描显微镜允许我们记录和读取多层数据。我们结合使用了相差显微镜和共聚焦显微镜来成像折射率分布，以减少不需要的散射光，特别是在阅读过程中。采用40x、N.A=1.0、油浸式物镜和Ar+激光，以每平面50×50比特的速度每2um×2um写入比特数据。以10微米的纵向间距记录了30个平面，分析了激光聚焦到光折变晶体中一个很小的区域时局部产生的三维折射率分布。折射率分布的形成是从非稳态条件下晶体中电子密度分布的时间行为推导出来的。密度分布是使用一组递归关系来计算的，这些递归关系是从描述电子在时间上的输运的库赫塔雷夫方程中推导出来的。特别计算了掺铁LiNbO_3晶体的折射率分布。为了验证我们分析的有效性，我们用相差显微镜读取了铁掺杂LiNbO_3晶体中记录的折射率点。当考虑成像系统的特性时，实验结果与计算的相衬图像有很好的一致性。

We have developed a three-dimensional multi-layred optical strage system. The system records pits into the thick material in three dimensions along the optical axis direction. For recording, we used photorefractive materials such as photopolymer and photorefractive crystal (LiNbO_3), which are used in volume holographic recording. Pits are recorded as refractive index changes. We employed a laser scanning microscope to record and access the pits. The scanning microscope allows us to record and read multi-layred data. We employed in combination a phase contrast microscope for imaging refractive index distribution and a confocal microscope to reduce unwanted scattered light particularly during reading. By using 40x, N.A = 1.0, oil immersion type objective lens and Ar+laser, bit data were written every 2mum x 2mum at 50 x 50 bits per plane. A total of thirty planes was recorded at a longitudinal separation distance of 10mum between plane.We analyze the three-dimensional refractive-index distribution that is induced locally when a laser beam is focused unto a very small region in a photorefractive crystal. The formation of the index distribution is deduced from the temporal behavior of the electron density distribution in the crystal under non-steady state conditions. The density distribution is computed using a set of the recurrence relations that were derived from Kukhtarev's equations describing the transport of electrons in time. In particular, we calculated the index distribution formed in Fe-doped LiNbO_3 crystals. To verify the validity of our analysis, we read using a phase contrast microscope, refractive index dots that were recorded in Fe-doped LiNbO_3 crystals. A good agreement was obtained between experimental results and the calculated phase contrast image when the characteristics of the imaging system is taken into account.