To solve the problems of nonlinear measurement of Faraday rotation existing in the power optical sensing, a new type of circular polarization grating is designed, in which the grating grooves are arranged along the radial direction in a ring. For the polarization grating, the TE wave (parallel to the grooves) has a high reflection and the TM wave (perpendicu-lar to the grooves) has a high transmission. Therefore, according to the Malus' law, when a linearly polarized light is transmitted through the grating, the output light gets the maximum and minimum intensities at the directions perpen-dicular and parallel to the polarization direction of the LP light, respectively. Because the grating is ring-shaped and the average space between adjacent grooves is in nanometer size, a linearly polarized light with any polarization direction can generate a ring-shaped intensity distribution image with dark and bright stripes after passing through the grating. In brief, the grating can be described as a radial polarizer in which the transmission axis is perpendicular to the azimuth angle that can be varied within 0~360 degree. When the azimuth angle changes, the intensity distribution will rotate accordingly, and its rotation angle is equal to the azimuth angle. Therefore, the polarization rotation can be linearly measured by detecting the rotation of the dark stripe center.