In this letter we propose a multipurpose fiber optic sensor composed of a fiber, a spherical micro lens, and a sensing mirror. The analog sensor converts a physical quantity such as oscillation or displacement to a quantity of light. Replacing the lens with one of a different diameter makes it possible to use the new sensor several different ways, such as for sensing flow rate, pressure or temperature. Experimental results show that the dynamic range of the mirror's position displacement changes from 7.5 µm to 500 µm and that the dynamic range of the conversion gain changes about 20 dB when the lens is changed from 0.5 mm to 5.0 mm in diameter.