SBIR PHASE I: Novel Bridgman Growth of Tungsten Bronze Crystals for Emerging Nonlinear Optical Applications

这个小企业创新研究的第一阶段项目涉及铁电钨青铜材料的新型垂直布里奇曼生长，这种材料已知具有大的电光和光折变效应。它们包括一类非常有前途的光学材料，如可调谐全息波长滤波、全息海量数据存储、电光调制和光束转向、相位共轭和集成光开关。目前，大多数钨青铜晶体都是用Czochralski法生长的，其主要问题是折射率条纹、直径不稳定以及有害成分易挥发损失。条纹会引起明显的光散射，降低器件性能。它们产生于虚假的生长速率波动，主要是由于熔体-固体界面的温度变化。这些变化的主要来源是晶体在非轴对称温度分布中的旋转。我们建议开发一种垂直Bridgman系统来生长SBN和PBN，因为这种方法固有地避免了晶体旋转，最小化了浮力驱动的熔体对流，从而最小化了条纹。此外，晶体直径由坩埚壁决定，因此直径不稳定不是一个问题，并且可以通过使用密封坩埚技术来消除挥发。SBN、PBN和其他钨青铜晶体的垂直布里奇曼生长将提供更高光学质量的样品，尺寸更大，成本显著降低。这项技术将有助于进一步推进许多电光和光折变应用。

This Small Business Innovation Research Phase I project addresses novel vertical Bridgman growth of ferro-electric tungsten bronze materials which are known to have large electro-optic and photorefractive effects. They comprise a class of optical materials that are very promising for applications such as tunable holographic wavelength filtering, holographic mass data storage, electro-optic modulation and beam steering, phase conjugation, and integrated optical switching. Most tungsten bronze crystals are currently grown by the Czochralski method where the main problems are refractive index striations, diameter instability, and susceptibility to volatilization loss of hazardous constituents. Striations can cause significant light scattering and degrade device performance. They arise from spurious growth rate fluctuations, principally due to temperature variations at the melt-solid interface. The dominant source of these variations is crystal rotation in a non-axisymmetric temperature profile. We propose to develop a vertical Bridgman system for growing SBN and PBN because this method inherently avoids crystal rotation and minimizes buoyancy-driven melt convection, thereby minimizing striations. Furthermore, the crystal diameter is determined by the crucible walls so that diameter instability is not an issue, and volatilization can be eliminated by using a sealed-crucible technique. Vertical Bridgman growth of SBN, PBN, and other tungsten bronze crystals will provide higher optical quality samples with larger sizes and significantly lower cost. This technology will help to further advance numerous electro-optic and photorefractive applications.