Distance measurement by the low coherent interferometer

The obtained data was acquired by the interferometric fiber-optic sensor of distance. The setup was constructed of a broadband light source working at the central wavelength of 1560 nm, an optical spectrum analyzer and a fiber-optic 2x1 coupler (with the power split 50:50). All elements were connected by standard single-mode optical fibers. The measurement head was made by a polished fiber end-face and an external mirror placed parallel to the fiber, creating a Fabry-Perot cavity. The nitrogen-doped diamond film produced by a Microwave Plasma Enhanced Chemical Vapor Deposition method on a silica substrate played the role of the mirror. The diamond sample was made in the gas mixture of CH4 (3%), H2 (94%) and N2(3%). Measurements of distance were performed in the range of 0 – 200 µm with a step of 20 µm. The cavity length was changed by the use of a micrometer screw. Air was fulfilling the cavity during the whole experiment.