All fiber compact bending sensor with high sensitivity based on a multimode fiber embedded chirped long-period grating

We investigated and prepared a chirped long-period grating for high sensitivity bending measurement. The novel fiber structure is composed of the multimode fiber (MMF) with fixed length and gradually longer single-mode fiber using the continuous splicing method. The powerful ability of refractive index modulation in the MMF renders the miniaturization of the sensor. The total length of the sensor is 3.45 mm. Chirped period arrangement is adopted to improve the bending sensitivity. Through numerical calculation, the chirp coefficient is determined, and the clear resonance peaks are obtained using the wavelength scanning. The experimental results of several samples show that the maximum bending sensitivity is 53.68 n m / m − 1 at 0 − 1.803 m − 1 . With the advantages of small size and high sensitivity, the sensor is especially suitable for bending sensing with a micro-structure.