An optical sensing device including a force-applying assembly for providing a force and a Fabry-Perot (FP) element including a large-diameter waveguide having a core and having a cavity in line with the core, the cavity having reflective surfaces and having an optical path length related to the distance between the reflective surfaces, the FP element being coupled to the force so that the optical path length changes according to the force, the FP element for providing an output optical signal containing information about a parameter that relates to the force. Sometimes the large-diameter waveguide is formed by collapsing a glass tube, having a bore and having an outer diameter of about one millimeter, onto a pair of optical fibers arranged in tandem in the bore and separated by a predetermined distance, and respective end faces of the optical fibers form the cavity and are coated with a wholly or partially reflective material.