Mechanically Induced Long Period Gratings (LPGs) in Standard and Unconventional Optical Fibers

This paper presents mechanically induced long-period gratings (MILPGs) realized in standard and unconventional optical fibers, like not-photosensitive double-clad and photonic crystal fibers. The periodic modulation of the geometry and refractive index along the length of the optical fibers is induced by pressure applied transversely to properly grooved plates and leads to light coupling among the core mode and forward propagating cladding modes at specific resonance wavelengths. The proposed method employs stereolithography (SLA) 3D printing technique to realize the periodic grooved plate with an interdigitated almost sinusoidal shape. The results have significant implications for silica optical fibers that possess different geometrical and optical properties, including: (i) the standard single mode fiber (SMF-28); (ii) double cladding fibers such as (a) Thorlabs DCF-13, and (b) Nufern S-1310; and (iii) Photonic crystal fiber. The obtained devices present high quality spectral features, i.e., trivial power losses, deep and narrow attenuation bands and are achieved with a cost-effective and simple technique. Such devices are valuable candidates for different applications ranging from sensing to optical communications.