Long-period fiber gratings for core mode conversion

Abstract

This project is to investigate a possible writing method of Long-period fiber gratings (LPFGs) to realize the core mode conversion from guided LP01 mode to guided LP11 mode. Literature research on LPFGs is done at the very beginning, serving as a theoretical background for the project. Some characteristics of the LFPGs, like coupling coefficient, effective refractive index calculation and the correlation between resonant wavelength and grating pitch are studied in details. Different LPFGs writing methods, like mechanical deformation, UV light exposure and computer-controlled CO2-laser etching methods are also introduced and manipulated. With the studied theory, an originally designed experimental system is set up for realizing the mode conversion. Reasons for setting up the experiment, experimental procedures and experimental results are presented. A deep analysis on the experimental results and a further discussion on the improvements for the experiment are also given at the end.