The effects of the reflective surface configuration and the refractive index of lubricating oil on the characteristics of the displacement sensor of two-circle reflective coaxial fiber

which is used to measure the thickness of the lubricating oil film

is analyzed. An output function of the fiber sensor with spherical reflective surface is gained and the effect of refractive index of lubricating oil on the maximum incidence angle is analyzed by geometrical optics. The refractive index of the lubricating oil decreases the maximum incidence angle of fibers. The simulation and the experiment indicate that the sensibility of sensors decreases when the reflector changed from flat to curved and in the propagation medium varying from gas into lubricating oil

which leads to the necessity of recalibration when the sensors are applied to monitoring the thickness of the lubricating oil film.