A strain gauge device employs a reflective base adapted to reflect a divergent optical signal, and a glass tube attached to the reflective base for optical communication therewith, the glass tube having a working length into which an optical fiber is inserted. The optical fiber is configured for transporting an optic signal indicative of the detected strain. The optic fiber has an outside diameter slightly smaller than an inside diameter of the glass tube for providing a slight tolerance. A distal end is disposed in slidable communication with an interior of the glass tube and accommodated by the tolerance, and a sensing circuit at the proximate end receives an optical signal indicative of strain or displacement. A resilient buffer layer made of soft silicone is disposed outside the glass tube to allow for large deformation measurements and reduce the distortion of the deformation by the introduction of the sensor.