Cones-assembled grating for long-range fiber-optic linear displacement sensor

This paper presents the initial design of a new fiber-optic displacement sensor; it is used to measure the linear displacement of an actuator performing a helical movement. This sensor consists of a set of assembled cones, which constitute a reflective grating, and two fiber-optic probes. It is characterised by its ability to measure the displacement along a millimetric range, with a high sub-micrometric resolution. In this work, the geometric model of the sensor is presented as well in terms of single probe response in front of a curved reflective surface as in terms of grating shape which authorizes the measurement principle. This grating design makes the displacement measurement possible due to the overlap of the two probes simulated output signals. The single probe measurement in front of a curved reflective surface demonstrates a good agreement with simulation results. A prototype of the cones-assembled grating has been fabricated using a high precision turning machine and a single-crystal diamond tool on an aluminium alloy; the geometric parameters of the fabricated grating were evaluated with the help of a Nanofocus™ μscan optical profilometer. The agreement between the simulated geometric parameters and the real parameters is very good.