磁光晶体GdYBiIG的磁致退偏效应

Depolarization Effect of Magneto-Optic Crystal GdYBiIG in Adjustable Magnetic Field

建立了磁光晶体磁致偏振特性测试系统。该系统采用中心波长为1538nm的WGY型半导体激光器,在0～1500mT的大范围可调磁场下,对光隔离器用磁光晶体GdYBiIG样品的退偏效应进行了测试。测试结果表明,达到磁饱和或接近磁饱和时,GdYBiIG晶体的偏振性能最优;达到磁饱和后,随着磁场的增强,出现了磁致退偏效应。分析了磁致退偏效应的产生机理,给出磁致圆二向色性及磁致线双折射是产生退偏的原因。实验测试与理论分析表明,根据磁光晶体GdYBiIG这种退偏效应的规律性,在利用该类晶体制作磁光器件时,外加磁场强度稍大于它的磁饱和强度即可。

The optical system has been established in which the changes of polarization state for magneto optic crystal can be measured. In this optical system, WGY model semiconductor laser is applied as the light source, and the tuning range of the intensity of magnetic field is 0～1500 mT. Depolarization effect in GdYBiIG crystal which often be used in optical isolator is measured in large variation range of adjustable magnetic field. The experiment result shows that polarization performance will be best in GdYBiIG crystal when it reaches saturated magnetization. And the depolarization effect occurs when the intensity of magnetic field increases over saturation intensity. The principle for magnetic depolarization effect is also given according to the experimental result. It presents that magnetic circle dichroism and magnetic linear birefringence are the reasons which cause depolarization effect. From these results, it is optimum to make sure that the magnetic field should be lager only a little than the saturation intensity of magnetic field.