A method by using magnetooptical modulation and light source modulation techniques was proposed to measure the extinction ratio of a polarizing prism precisely

and an extinction ratio measurement system was also established based on the two modulation techniques. Firstly

the systems measurement model was derived according to the Jones matrix describing manner of polarized light. By using a magnetooptical modulator

the optical axis angle between a polarizer and a measured polarizing prism was precisely located. Then

by using a chopper to modulate the square wave of a light source

the impact of noises on the system measurement accuracy was eliminated and the system could measure the light intensity value accurately after the measured polarizing prisms axis was located precisely. Finally

the polarizing prism was measured for a number of times and the data were averaged. The experimental results indicate that the measurement accuracy of extinction ratio for the polarizing prism can be 10

-6

which verifies the effectiveness and stability of the method. The system is characterized by high stability

high accuracy

and can offer the references for the performance test and engineering applications of polarized devices.