Online phase tracking of an extrinsic Fabry-Perot interferometer (EFPI) and experimental vibration control of a composite beam with a sensing patch are investigated. EFPI sensors have nonlinearity due to their interferometric characteristics. We propose a new sensing patch for compensation of this interferometric nonlinearity. This newly developed sensing patch consists of an EFPI sensor and another sensor that can produce directional information. Therefore, it uses the advantages of their components used in conjuction in order to overcome the disadvantages of the components used separately. A sensing patch that comprises an EFPI sensor and a piezoceramic is fabricated, and the characteristics are experimentally investigated. A simple and practical logic is applied to real-time tracking of the optical phase of an interferometer. The experimental results show that the proposed sensing patch does not suffer from the nonlinear behavior of conventional EFPI sensors and the hysteretic behavior of piezoelectric materials. Moreover, it has excellent strain resolution and a wide dynamic sensing range. The application of a sensing patch has been also investigated: vibration control with this sensing patch has been performed using a fuzzy logic controller (FLC), and the possibility of using a sensing patch as a sensoriactuator is considered.