Heterodyne interferometer with two parallel-polarized input beams for high-resolution roll angle measurement

We have proposed an improved heterodyne interferometric roll measurement system with enhanced resolution in this paper. Two beams with different frequencies but with the same polarization state input to the interferometer are provided by two acousto-optic modulators. A quarter-wave plate is employed in each path before the two beams are combined to generate a beat frequency. A mathematical model for the measurement system is established based on Jones' calculus. The measurement resolution is doubled because the sensitive areas of the two beams appear simultaneously. Experimental results show that in the range of 0.1° the gain coefficient reaches 229 which is twice that of the traditional method.