Fluorescent Fiber Implementation of a High-resolution Distributed Position Sensor

Fluorescent optical fibers employ the luminescence property of fluorescent dyes in order to radiate light as a response to incident illumination. When multiple dyes are used to dope the fiber, fluorescence results from the energy transfer between the donor and acceptor dyes and the reabsorption process. In this work we propose a high-resolution distributed optical sensor for position monitoring developed around a yellow fluorescent fiber. Immunity vs. ambient light variations is achieved by employing the spectral behavior of the donor-acceptor energy transfer mechanism and the reabsorption process. This consists in a red shift of the fiber emission peaks vs. distance. Extensive experimentation with the laboratory proof of principle validates the proposed solution. Measurements carried out in laboratory environment under ambient illumination show that the wavelength of the emission peaks is insensitive to the intensity of the incident light, but is dependent on the variation of the ambient light color. Accordingly, rather than monitoring the wavelengths of the emission peaks, the proposed positions sensor evaluates the spectral spacing between the peaks. This provides an accurate estimate of the distance between the fiber end and the incident light application point. The proposed sensor exhibits a monotonous decrease of the spectral spacing vs. distance, which is indeed insensitive to limited variation of the ambient light.