In this paper, we report on the development of an intensity-modulated fiber-optic sensor for angular displacement measurement. This sensor was designed to present high sensitivity, linear response, and wide bandwidth and, furthermore, to be simple and low cost. The sensor comprises two optical fibers, a positive lens, a reflective surface, an optical source, and a photodetector. A mathematical model was developed to determine and simulate the static characteristic curve of the sensor and to compare different sensor configurations regarding the core radii of the optical fibers. The simulation results showed that the sensor configurations tested are highly sensitive to small angle variation (in the range of microradians) with nonlinearity less than or equal to 1%. The normalized sensitivity ranges from 0.25 × V max to 2.40 × V max mV ∕ μrad (where V max is the peak voltage of the static characteristic curve), and the linear range is from 194 to 1840 μrad. The unnormalized sensitivity for a reflective surface with reflectivity of 100% was measured as 7.7 mV ∕ μrad. The simulations were compared with experimental results to validate the mathematical model and to define the most suitable configuration for ultrasonic detection. The sensor was tested on the characterization of a piezoelectric transducer and as part of a laser ultrasonics setup. The velocities of the longitudinal, shear, and surface waves were measured on aluminum samples as 6.43, 3.17, and 2.96 mm ∕ μs, respectively, with an error smaller than 1.3%. The sensor, an alternative to piezoelectric or interferometric detectors, proved to be suitable for detection of ultrasonic waves and to perform time-of-flight measurements and nondestructive inspection.

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In this work, we present an analysis of the influence of geometrical parameters on the sensitivity and linear range of a fiber optic angular displacement sensor, through computational simulations and experiments. The geometrical parameters analyzed are the lens focal length, the gap between fibers, the fiber cladding radii, the emitting fiber critical angle (or, equivalently, the emitting fiber numerical aperture), and the standoff distance (distance between the lens and the reflective surface). Besides, we analyze the sensor sensitivity regarding any spurious linear displacement. The simulation and experimental results show that the parameters that play the most important roles are the emitting fiber core radius, the lens focal length, and the light coupling efficiency, whereas the remaining parameters have little influence on the sensor characteristics.