Cladding gratings fabricated using femtosecond laser plane by plane inscription for vectorial curvature sensing

We present and demonstrate a compact and simple all-fiber one-dimensional vector curvature sensor based on writing a cladding fiber Bragg grating (CLFBG) next to the core of a single-mode fiber (SMF). The CLFBG is written using a femtosecond (fs) laser with a plane-by-plane (Pl-b-Pl) method. The refractive index modulation region (RIM) induced by the fs laser is similar in size to the fiber core, increasing the coupling efficiency of the CLFBG. The reflection spectrum of CLFBG changes in terms of wavelength and intensity based on the curvature and direction of the fiber bend. By combining the wavelength and intensity responses of CLFBG, it is possible to simultaneously measure the magnitude and direction of the curvature. Experimental results show that the sensor has a maximum wavelength sensitivity of 81.6 pm/cm^-1 and a maximum intensity sensitivity of -2.20 dB/m^-1$.$ This structure holds significant potential for applications in structural health monitoring, robotic movement, biomedical, and biomechanical fields.