The magneto-optical effect (Faraday effect) was discovered in the middle of the 19^th century. In the latter half of the 20^th century, the practical use of isolators using single crystals (Faraday rotators) using the melt growth method began. One century after Faraday's discovery of the magneto-optic effect, R.L. Coble proved translucency of polycrystalline ceramics. Ceramics may have many scattering sources due to their polycrystalline microstructure, and even from the viewpoint of scattering theory, it was considered impossible to apply them to the generation of coherent light (laser). However, 40 years later, A. Ikesue demonstrated laser ceramics for the first time with performance comparable to that of optical single crystal counterparts. The possibility of laser application of polycrystalline ceramics also makes it possible to apply it to Faraday rotators (optical isolators) that utilize coherence light. A magneto-optical single crystal composed of a single crystal orientation was considered to be superior in that it provided excellent optical performance and an accurate Faraday rotation angle. However, polycrystalline ceramics composed of random crystal orientations can not only provide accurate Faraday rotation angle but can also have a higher extinction ratio than single crystal isolators. A ceramic medium with extremely low scattering and extremely low insertion loss, which cannot be achieved with a single crystal material, has been developed. In addition, new materials, which have Verdet constants several times higher than those of main commercial crystal for isolator, have made it possible to reduce the size of isolator devices. However, these materials cannot be synthesized by the conventional melt-growth method. In the 21^st century, polycrystalline ceramics are paradigms for Faraday rotating elements, and are about to enter a period of change from single crystals to polycrystalline ceramics.

磁光效应（法拉第效应）是在 19 世纪中叶发现^的。^20世纪下半叶世纪以来，使用熔体生长法的单晶隔离器（法拉第旋转器）开始实用化。在法拉第发现磁光效应一个世纪后，RL Coble 证明了多晶陶瓷的半透明性。陶瓷由于其多晶微观结构而可能具有许多散射源，即使从散射理论的角度来看，也被认为不可能将其应用于相干光（激光）的产生。然而，40 年后，A. Ikesue 首次展示了性能可与光学单晶对应物相媲美的激光陶瓷。多晶陶瓷的激光应用的可能性也使其有可能应用于利用相干光的法拉第旋转器（光隔离器）。由单晶取向组成的磁光单晶被认为是优越的，因为它提供了优异的光学性能和准确的法拉第旋转角。然而，由随机晶体取向组成的多晶陶瓷不仅可以提供准确的法拉第旋转角，而且还可以具有比单晶隔离器更高的消光比。已开发出一种具有极低散射和极低插入损耗的陶瓷介质，这是单晶材料无法实现的。此外，Verdet 常数比用于隔离器的主要商业晶体高几倍的新材料使得减小隔离器设备的尺寸成为可能。然而，这些材料不能通过传统的熔体生长方法合成。在 21 由随机晶体取向组成的多晶陶瓷不仅可以提供准确的法拉第旋转角，而且还可以具有比单晶隔离器更高的消光比。已开发出一种具有极低散射和极低插入损耗的陶瓷介质，这是单晶材料无法实现的。此外，Verdet 常数比用于隔离器的主要商业晶体高几倍的新材料使得减小隔离器设备的尺寸成为可能。然而，这些材料不能通过传统的熔体生长方法合成。在 21 由随机晶体取向组成的多晶陶瓷不仅可以提供准确的法拉第旋转角，而且还可以具有比单晶隔离器更高的消光比。已开发出一种具有极低散射和极低插入损耗的陶瓷介质，这是单晶材料无法实现的。此外，Verdet 常数比用于隔离器的主要商业晶体高几倍的新材料使得减小隔离器设备的尺寸成为可能。然而，这些材料不能通过传统的熔体生长方法合成。在 21 已开发出一种具有极低散射和极低插入损耗的陶瓷介质，这是单晶材料无法实现的。此外，Verdet 常数比用于隔离器的主要商业晶体高几倍的新材料使得减小隔离器设备的尺寸成为可能。然而，这些材料不能通过传统的熔体生长方法合成。在 21 已开发出一种具有极低散射和极低插入损耗的陶瓷介质，这是单晶材料无法实现的。此外，Verdet 常数比用于隔离器的主要商业晶体高几倍的新材料使得减小隔离器设备的尺寸成为可能。然而，这些材料不能通过传统的熔体生长方法合成。在 21^世纪以来，多晶陶瓷是法拉第旋转元件的典范，即将进入单晶向多晶陶瓷的转变时期。