Cladding Modes Generation Through Highly Localized Bragg Grating in Polymer Optical Fiber

Thanks to the highly localized fiber Bragg grating obtained by a femtosecond laser and point-by-point inscription method, a cladding mode spectral range of over 80 nm is achieved in polymer optical fibers. After grating inscription, refractometric measurement is conducted within a range from 1.38 to 1.54 to measure the surrounding refractive index, and the evolution of the cladding mode resonances is analyzed accordingly. By monitoring the cutoff mode, the refractive index sensitivity is found to be 527 nm/RIU (refractive index unit). The originality of our work lies in the production of highly localized FBGs with a large spectral range of cladding mode resonances in polymer optical fibers, capable of measuring refractive indices in a wide range in aqueous solutions and (bio)chemical media.