A Fabry-Perot optical sensor for sensing a parameter such as pressure or the like is provided. The sensor includes a lead optical fiber from the end of which projects a spacer having an end surface curving inwardly. A diaphragm extends across the forward end of the spacer. The diaphragm is flexible in response to the parameter to be measured and defines a forward reflector of the Fabry-Perot cavity within the optical sensor. A method for manufacturing such a sensor is also provided.