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Distance, interferometers, Fabry-Perot cavities, optical fiber, optical fiber sensor, optical path length abstract In this work, Fabry-Perot (FP) interferometers were built by terminating an optical fiber with an angle. These were used to measure transverse distances to the principal axis of the fibers. These cavities were created in two types of optical fiber: single-mode fiber (SMF), for measuring unidirection distance, and multicore fiber (MCF) for measuring radial and axial distance. In order to reflect electromagnetic radiation perpendicularly to the principal axis of the fiber, a numerical model was created to identify the angle of the fiber terminal for which the reflectivity was maximum. Experimentally, the FP cavities were fabricated by polishing the terminal of the optical fibers at the optimised angle. In the case of SMF, the polishing process allowed the creation of an FP cavity at the cladding region which was due to the reflection in the angled polished terminal and in the cladding-air interface. Furthermore, by placing a reflective surface at a distance “d” from the fiber surface, it allowed the observation of a second cavity, whose optical path depends on the imposed distance, thus, allowing the determination of its value. On the other hand, reproducing the polishing process for three of the six radial cores of an MCF (separated 120° between each other) allowed the measurement of the distance in three directions. This was explored, not only to measure the internal diameter of hypodermic needles, but also to determine the radial location of the MCF inside the needle. This feature can be explored in future three-dimensional navigation applications, namely through the use of the MCF central core region, which can be used for the measurement of axial distance. |
