A hybrid grating sensing device based on a side-polished fiber Bragg grating (FBG) with a polymer overlay is proposed for simultaneous measurement of external refractive index and temperature. The side-polished FBG, which is insensitive to ambient index change, is utilized for detecting temperature variation, and the polymer overlay is coated on the side-polished FBG for measurement of ambient index change. The temperature sensitivities of the side-polished FBG and the polymer overlay were measured to be 0.01 nm/℃ and-0.58 nm/℃, respectively, in a temperature range from 30℃ to 100℃. The ambient index sensitivities of the polymer overlay were measured to be 498.8 nm/RIU in an ambient index range from 1.33 to 1.

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A reflection-type interferometer based on a polarization-maintaining photonic crystal fiber (PM-PCF) is investigated for simultaneous measurement of chemical vapor and temperature. The PM-PCF with a length of 2.6 cm is fusion-spliced to standard single-mode fiber and airholes of the PM-PCF are fully collapsed allowing the excitation of different core and cladding modes in the PM-PCF corresponding to two orthogonal polarization modes. Since airholes at the end of the PM-PCF interferometer are left open, a chemical vapor can be infiltrated into the voids. Different sensitivities corresponding to input polarization states are utilized for discrimination between chemical vapor and temperature effects.