Executive Summary : | Complex light fields with inhomogeneous phase and polarization in the transverse plane are popularly known to be scalar and vector vortices of light respectively. These structured light fields are gaining immense attention for their fascinating applications in the fields of microscopy, imaging, classical and quantum communication, non-linear optics, and Nano-optics to name a few. The main goal of the project is to develop an all-fiber device for generating such complex fields using special optical fibers and characterize the modal outputs with optical correlation technique for stability and efficiency. Here, special optical fibers refer to few-mode fibers (FMF), long-period fiber gratings (LPFG). Few-mode fibers are inherently capable of supporting a set of degenerate vector vortices, namely, TE01, TM01, and HE21o,e, also known as cylindrical vector beams (CVBs). Using an LPFG can lift the degeneracy between these modes and makes it easier for the excitation of selective modes. The coherent combination of these degenerate modes (TE01± i TM01 and HE21o ± i HE21e) would result in orbital angular momentum (OAM) modes in an optical fiber, which are analogous to Laguerre-Gaussian (LG) modes. In order to generate OAM modes, the FMF will be coupled to a tunable laser source and carefully spliced with an LPFG, which help in efficient coupling of power from fundamental LP01 mode to the LP11 mode family. The grating pitch, arc power, and length of the LPFG are simultaneously optimized for efficient coupling of power to the desired OAM modes by real time monitoring of the output mode profile. Further, the splicing conditions of LPFG with the FMF will be optimized via offset splicing to get pure and stable OAM modes. The generated output modes will be initially characterized by interferometry and Polarimetry and the detailed propagation characteristics and mode dynamics will be investigated using correlation technique. |