Optimal design of MPD based fiber optic strain sensors and comparison of power-meter and CCD camera measurements

In this paper, we consider optimal sensor design problem and compare power-meter and CCD camera based techniques for strain measurements using Modal Power Distribution (MPD). MPD is a sensitive and low-cost fiber optic sensing technique which uses spatial intensity modulation in two dimensional setting. In a power-meter based fiber optic sensor, light intensity is measured at one or more points, and selection of these points is usually very critical in sensor design. Single point based sensors are not usually very successful, because of the time varying feature of a laser source output intensity. To the best of authors’ knowledge, most of the power-meter based MPD sensors utilize a single photo-detector, and there is only one known work where two photo-detectors are used with no optimization on measurement locations. In this work, we both consider optimal measurement location selection problem, and compare of power-meter and CCD camera based sensor measurements. We also show that there is an almost one-to-one relationship between CCD based and power-meter based fiber optic sensor measurements, which allows estimation of power-meter based measurements using CCD camera images. In our experimental setup, power-meter measurements and CCD camera images were recorded for different strain values. Power-meter measurements were estimated from CCD camera images with an average error of less than 4% by utilizing image processing techniques and non-linear least squares techniques.