Concentration and temperature sensing accurately in a concatenated FBG and LPG

The concatenated strong fiber Bragg grating and a weak long period grating are presented for simultaneous temperature and solution concentration measurement in the methods of both detailed coupled-mode theory and experimental analysis, and find two ways which include dual wavelength method and dual parameter method to solve the cross sensitivity problem to ensure higher accuracy and sensitivity. Two peaks appear in reflection spectrum of CLBG device, and the higher peak is determined by FBG while the other peak is influenced by FBG and LPG. Temperature and solution concentration are adopted to test the performance of multi-parameter sensing simultaneously. By comparing two schemes, using wavelength shifts of the two peaks may solve the cross-sensitivity problem, but its resolution is still very low. Here, another scheme based on light intensity changes and wavelength shifts of the two peaks in reflection spectrum is designed to improve the resolution further. Experiment result proves that the resolution of the proposed method is higher than that of the improved way, and the CLBG device keeps higher sensitivity with our proposed method.