Fiber Optic Fluid Level Sensor

Abstract

A fiber optic fluid level sensor based on transmission attenuation due to bending loss is described. Fibers formed with reverse curvatures of decreasing radii will induce an increasing amount of lower mode light loss to the cladding as the light propagates along the multimode fiber. The sensor is arranged in the fluid in a vertical orientation such that the light travels along the fiber from the bottom or low fluid point to the top or full point. As the fluid covers increasing lengths of the exposed fiber, it strips ever more power from the cladding (assuming the fluid refractive index is greater than the cladding). Data taken with a sensor of this configuration show a monotonic decrease of output intensity as a function of increasing fluid level. As much as a -14dB change occurred over a one-foot fluid level change. Comparison of these results with a mathematical model shows good agreement.