A Linear Optical Current Transducer Based on Newton’s Ring Sub-Wavelength Grating

Abstract

This paper presents a novel optical current transducer based on Newton’s ring sub-wavelength grating. It converts the Faraday rotation angle into synchronized rotation of the spot image and locates the spot with a four-quadrant detector to achieve real-time linear measurement of the current. The Newton’s ring grating is used instead of a radial grating as a polarization detection device so the extinction ratio is distributed uniformly in the radial directions and the polarization characteristics have no change with the radial direction, thereby a higher measurement accuracy has been achieved. The angle measurement range can reach ±40 degrees which breaks through the limitations of the intensity demodulation mode. The performance of the transducer has been verified by experiments and a 0.2 S class accuracy achieved with a linear measurement, no interference of optical power fluctuation, and minimized the effect of birefringence.