Simultaneous Two-Parameter Sensing Using a Single Tilted Moiré Fiber Bragg Grating With Discrete Wavelet Transform Technique

We propose and demonstrate using a single tilted moiré fiber Bragg grating (TMFBG) with the discrete wavelet transform (DWT) technique for simultaneous measurement of refractive index (RI) and temperature. The particular feature of interest is that the spectrum consists of two separate parts associated with the phase-shifted main Bragg mode and discrete cladding modes, and that they have distinctive responses to RI and temperature. Our results showed that the cladding modes are, while the Bragg mode is not, sensitive to the surrounding RI. On the other hand, both the Bragg and cladding modes have the same linear temperature response. Hence, temperature can be obtained from the Bragg mode shift, and RI from the differential shift between the Bragg and cladding modes. In our experiment, the measured shifts of the Bragg and cladding modes can be unambiguously determined by applying the DWT technique. Thus, simultaneous two-parameter sensing using only a single TMFBG sensor is realized.