In a linear optical current transducer(OCT)based on the radial grating polarizer detection

the faraday rotation angle is converted into synchronous rotation of a circular facula. Then

a charge coupled device camera(CCDC)is utilized to position the dark stripe of the facula to achieve a real time current measurement. The linear OCT overcomes some issues in the OCT of traditional light intensity detection mode

such as small dynamic measurement range

nonlinear detection

light intensity dependence

linear birefringence and temperature drift etc. However

the linear OCT still has some shortcomings

such as high cost

low resolution

big algorithm error

and not being capable of meeting 0. 2S accuracy class

especially in small current measurement. In order to fix these problems

a four-quadrant detector is employed to sense the rotation angle of the circular facular with the advantages of low cost

simple algorithm

high-resolution and high-accuracy. It has been verified that the resolution of measurement is increased nearly 100-fold by theoretical analysis and experimental derivation in the range of ±40°of the faraday rotation angles. The accuracy is improved from 0. 5% class to 0. 2S

and the cost of picture detection unit is reduced by more than 95%.