Temperature and bending simultaneous sensing properties of cascaded long- and short-period gratings

Based on the coupled-mode theory, temperature and bending sensing properties of cascaded long-and short-period grating (CLBG) are analyzed by using the transfer matrix method. Two resonance peaks are produced in the reflection spectrum of CLBG when the resonance wavelengths of the two gratings are approximately equal. The two resonance peaks shift along the longer wavelength as temperature increases, and the peak reflectivity at the longer wavelength decreases monotonically at the same time. When CLBG is bent, the peak reflectivity at the longer wavelength increases evenly while the resonance wavelengths remain unchanged. This tells us that CLBG can be used to sense temperature and bending simultaneously. Experimentally, the temperature and bending simultaneous sensing properties of CLBG are discussed. The temperature sensitivities corresponding to the peak reflectivity and the resonance wavelength are -0.03718  dB/°C and 0.011846  nm/°C, respectively; the bending sensitivities are 9.878  dB/m⁻¹ and 0, accordingly. This proves that CLBG has important application value in multiparameter sensing and measurement fields.