理论分析了隔离器在高功率多模激光入射时的自退偏特性.结果表明：线性双折射致退偏与圆双折射致退偏均与入射光功率的平方成正比，线性双折射致退偏与光斑大小无关，而圆双折射致退偏随光斑半径的增大而减小.当光斑半径与旋转晶体半径相比很小时（R0/r0≥80）圆双折射引起的退偏大于线性双折射引起的退偏，当光斑半径接近旋转晶体半径（R0/r0≤3）时，与线性双折射引起的退偏相比，圆双折射引起的退偏可以忽略.对比单模激光入射，在同种条件下，多模入射使得线性双折射致退偏减小了0.4倍， 最小圆双折射致退偏减小为0.05倍.

Self-induced depolarization in high power Faraday isolators was investigated theoretically when incidence lasers are Multi-mode.Research result shows that depolarization induced by linear birefringence and circular birefringence are also proportional to square of laser power,depolarization induced by linear birefringence has no dependence on beam radius,but depolarization induced by circular birefringence increases with reduction of beam radius.Depolarization induced by circular birefringence may be more than depolarization induced by linear birefringence when R0/r0≥80,and can be neglected when R0/r0≤3.In the same conditions,depolarization induced by linear birefringence with multi-mode incidence is 0.6 times of that with single mode incidence,and minimum of depolarization induced by circular birefringence is only 0.005 times of that with single mode incidence.