Fabry–Perot Sensor Using Cascaded Chirped Fiber Bragg Gratings With Opposite Chirp Directions

We report a fiber-optic strain sensor that can simultaneously achieve high resolution and large dynamic range. The sensor is a fiber-optic Fabry-Perot cavity formed by cascaded high-reflection chirped fiber Bragg gratings with opposite chirp directions. The reflection spectrum of the sensor features a series of narrow spectral notches with unequal spacings. The sensor is demodulated by the wavelength scanning of a distributed feedback laser diode through the current-injection modulation. The narrow spectral notch leads to high measurement resolution; while the unambiguous identification of the spectral notches through their unique spectral spacings results in large measurement range without the need for fringe counting. We have demonstrated a linear axial strain response of the sensor with strain resolution of 0.033 με over a range of 1000 με.