Internally curved long period gratings for improved refractive index sensitivity

A long period grating (LPG), characterized by a specially designed refractive index (RI) profile, is proposed. Each grating plane of the LPG is tilted at increasing angles, as moving away from the center of symmetry of the structure (grating plane with no tilt) towards its both edges. The RI sensitivity of an LPG to the external medium increases by means of this internally manufactured geometric structure, which mimics the external bending of an optical fiber. A three-fold improvement in the RI sensitivity has been experimentally showed for the sixth-order cladding mode. Therefore, this kind of LPGs displays the same spectral behavior of standard LPGs, with the advantage of increased RI sensitivity. The achieved results offer a novel and real scenario concerning the attainable improvements in the field of optical fiber LPG-based RI sensors.