Fiber-Optic Pressure Sensor Based on π-Phase-Shifted Fiber Bragg Grating on Side-Hole Fiber

We present a fiber-optic pressure sensor based on a p-phase-shifted fiber Bragg grating (pi FBG) fabricated on a side-hole fiber. Due to the resonance effect of a pi FBG, its reflection spectrum features two notches that are dramatically narrower than the linewidth of a regular FBG of similar length. The narrow spectral notches allow high-resolution measurement of their spectral separation, significantly improving the pressure detection limit (defined herein as the minimum detectable pressure change) compared to sensors based on a regular FBG of a similar length and on the same fiber. The pi FBG demonstrated in this letter is 8.3 mm long and the linewidth of each spectral notch is only 3.6 pm, corresponding to a quality factor of 4.3 x 10(5). The spectral notch separation exhibited a sensitivity of 20 pm/kpsi to pressure, which was limited by the geometry of the fiber holes, and little sensitivity to temperature. The Bragg wavelength shift exhibited a sensitivity of 11.4 pm/degrees C to temperature. In practice, a spectral resolution of 0.028 pm can be easily achieved for the pi FBG demonstrated in this letter, leading to a pressure detection limit of 1.4 psi and a temperature detection limit of 0.0025 degrees C.