Simultaneous Measurement of Strain and Temperature Using Long-Period Fiber Grating Written on Polarization-Maintaining Photonic Crystal Fiber.

Here we propose a novel optical fiber sensor capable of simultaneous measurement of strain and temperature by utilizing a long-period fiber grating (LPFG) inscribed on polarization-maintaining photonic crystal fiber (PMPCF) as a sensor head. The sensor head was fabricated by irradiating CO₂ laser pulses to one side of PMPCF with line-by-line technique. The LPFG written on PMPCF (referred to as the PMPC-LPFG) exhibits two different wavelength-dependent loss bands, obtained at two orthogonal input polarization states. For two resonance wavelengths of these two wavelength-dependent loss bands, designated as Dips A and B, strain and temperature responses were investigated in a strain range of 0 to 2058 μɛ with a step of 98 μɛ and a temperature range of 30 to 85 °C with a step of 5 °C. Strain sensitivities of Dips A and B were measured and found to be approximately -0.82 and -1.43 pm/μɛ, respectively, at room temperature (25 °C). Similarly, temperature sensitivities of Dips A and B were measured and found to be ~7.89 and ~4.76 pm/°C without applied strain (0 μɛ), respectively. Owing to their linear and independent responses to strain and temperature, strain and temperature changes applied to the PMPC-LPFG can be simultaneously estimated from the measured wavelength shifts of the two resonance dips (Dips A and B) using their premeasured strain and temperature sensitivities. The experimental results prove that the PMPC-LPFG can be used as a sensor head for simultaneous measurement of strain and temperature.