By adding Polarization Maintaining Fiber on output terminal of SLD and Loyt depolarizer behind polarizer , the Degree of polarity can be reduced to 10 -3 ,and influence of outside conditions to light-wave′ state of polarization can be reduced too. And by calculating with Jones matrix,the relationship between four joint angles and polarization was discussed, and range of four joint angles was limited. In the end, how to link the fiber-optic and measure the joint angles was discussed.