This paper presents the geometric design and the performances of a high precision fiber-optic linear displacement sensor. Its original characteristic is the ability to measure the linear displacement of a rotating spindle. This sensor consists of two fiber-optic probes and a grating of assembled cones. First, the measurement principle is introduced. Then, the geometric model for sizing the first prototype grating is presented. The high precision fabrication technique of this initial prototype is illustrated. Finally, the sensor was used to measure the linear displacement of a rotating spindle.