The purpose of CF2T project is to develop a competitive foundation, immerse it as part of a precommercial project and validate the concept in a real sea environment. The innovative foundation will be designed to decrease construction costs, with modular interfaces to allow an installation in several packages (foundation parts, ballasts, turbine) in order to limit the installation vessel’s crane capacity requirement, which will also reduce installation costs. The different alternatives to reduce the structure construction costs and modularity will be evaluated including the design of a hybrid foundation combining concrete and steel. The new foundation should also have an adaptive interface with the seabed in order to avoid any seabed preparation. In addition, the project will develop a monitoring system to have a better understanding of loads applied to the structure for future foundations developments. This monitoring will allow to carry out a survey of the structural health for preventive maintenance which will contribute to improve reliability of the foundation. This report is the second deliverable in WP6 (Foundation Monitoring), namely D6.2 Sensor implemented and calibrated in proof-of-concept. RISE led the work with collaborative efforts from ALKIT. The proof-of-concept was proposed by RISE to enable the implementation of the proposed and developed monitoring system based on fibre optics in a representative reinforced concrete test object. This report covers the implementation in the proof-of-concept, the execution of experiment with mechanical loading on the test object, as well as the calibration of the given sensors and verification using secondary measuring techniques. The results show a complete characterization of the structure strain response along several loading cycles and the compatibility between the fibre optics-based sensors and the strain gauges validating the optical solution for structural monitoring. The system showed its capability for crack detection and also showed a good consistency of the measurements under repeated cycles. Lastly, a description of requirements and details for taking this proof-of-concept to the next phase of offshore monitoring of the concrete foundation is provided.