Monitoring of oxidation phases of copper thin films using long period fiber gratings

•Real time monitoring of Cu oxide phase transitions using Long Period Fiber Gratings.•Production of two stable oxide phases of copper using the annealing process with an air atmosphere.•Study of different spectral properties of Long Period Fiber Gratings coated with distinct oxide phases of the same material (Cu).•Possibility of tuning the sensitivity to the external medium by choosing the appropriate oxidation phase.