LAUSR

Abstract Fiber probe is a key component in absolute distance measurement system. It has dual tasks of delivery and collection of light. However, little information is given about how light coupling efficiency behaves as the target distance and tilt angle change, although it is of great importance to improve signal-to-noise ratio of the measurement system. In this paper, a theoretical model of fiber probe is proposed. Assuming that the target surface is a mirror, we deduce the coupling efficiency of the light reflected from target surface which is deviated from the ideal image plane with distance Δl. When Δl=-5 mm, the difference of the light coupling efficiency between Zemax simulation result and the theoretical calculation is 0.0017. In addition, Zemax is utilized to simulate the variation of coupling efficiency when target distance and tilt angle change both for reflective and diffuse target surface. It is concluded that the rate of descent for the coupling efficiency is greater when target surface is placed in front of the ideal image plane, and the working range of the fiber probe increases with the increase of ideal image distance. The variation of coupling efficiency with respect to target distance basically follows the same rule for both cases. Nevertheless, the coupling efficiency of diffuse target surface is less sensitive to the tilt angle. The findings will be helpful to guide us to make full use of fiber probe and provide a simple and economical approach to improve the measurement precision.