A method of assembling an optical sensor for measuring pressure and/or temperature is disclosed. The optical sensor is adapted for use in high temperature environments, such as gas turbines and other engines. The method comprises fabricating a sensor element formed of a pill having an enclosed cavity, bonding the pill to a front end of a spacer, bonding a lens to the back end of the spacer to form the optical assembly, aligning an optical fiber to the optical assembly, and fixing the fiber in position by fusing the fiber to the lens.