As a fundamental parameter of the optical crystals, birefringence plays a vital role in many optical applications, such as phase modulation, light splitting, and polarization, especially the phase matching process of the nonlinear optical crystals. The big birefringence not only benefits to the miniaturization of related devices, but also broadens the phase-matching wavelength range of nonlinear optical crystals. The design and synthesis of crystals with large birefringence becomes a hot research topic due to its more and more important applications in the optical modulation and laser technology fields. Herein, crystals with birefringence greater than 0.05 in the borate system are reviewed and classified according to different birefringent active groups, and the relationship between structure and properties is thoroughly explored. It is hoped that this review will provide a clear understanding of what kinds of building units and arrangements would have more opportunity to get adequate birefringence in borate systems and provide the statistical references to encourage the emergence of better crystal materials with large birefringence.

双折射作为光学晶体的基本参数，在相位调制、分光、偏振等许多光学应用中发挥着至关重要的作用，尤其是非线性光学晶体的相位匹配过程。大的双折射不仅有利于相关器件的小型化，而且拓宽了非线性光学晶体的相位匹配波长范围。大双折射晶体的设计与合成因其在光调制和激光技术领域越来越重要的应用而成为研究热点。本文对硼酸盐体系中双折射大于0.05的晶体进行了综述，并根据不同的双折射活性基团进行了分类，并深入探讨了结构与性能之间的关系。希望本综述能够清楚地了解什么样的建筑单元和布置更有机会在硼酸盐体系中获得足够的双折射，并为鼓励出现更好的大双折射晶体材料提供统计参考。