Research On Precision Small-Angle Measurement Tecnology Based On Total Internal-Reflection

Beam steering characteristics of Liquid Crystal Optical Phased Array (LCOPA) is an important index evaluating its optical performance, and beam steering angle is the direct parameter indicating this. The beam steering angle is always small, about 2~3°, and high resolution and orientation precision are required, so a high-precision optical small-angle measurement technique and system is imminently required to develop. This paper is presented aiming at meeting this need.Small-angle measurement based on total internal reflection effect is a high-precision method. The s- and p-polarized components in reflection beam has different phase shift when total reflection occurs, which could be used to measure the incident angle. The relative phase shift between s- and p- light is a function of the incident angle, and changes highly with the incident angle in the vicinity of the critical angle. This paper designs an optical system based on above to measure the small angle of the laser beam. A non-polarized beam splitter (NPBS) is used to split the incident beam into two branches, and a rhombic prism agglutinated by two right-angle prisms is placed to realize total internal reflection twice in each branch. It not only improves the measurement sensitivity and linearity, but also increases antinoise ability by the differential optics. According to current experimental condition, we let s- and p- components with relative phase shift interfere with each other, and receive the interference intensity to measurement the angular displacement. An approximately linear signal versus angular displacement is defined as the system output. A man-machine interface is designed using Labview8.0 to communicate between the dual-channel power meter and RS-232 serial port of personal computer, which improves measurement efficiency dramatically.Four groups'measurement data are given based on built system, and the results and the error analysis of measurement range of±1.5°, angle step of 0.06°is discussed in detail. A list table of fitting curve and angular displacement is given as well. At last this paper explains the unperfect factors of the system and compensates some of them.