Research On The Fabrication And Characterization Of Long Period Grating(LPG)

With four main features including sensing, information converting, automated response and self- adaptation, Smart materials and structures become the new field of materials research, and which represents a direction of advanced new material of 21th century. Because of excellent characteristic, fibers are concern by more and more researcher, thereinto fiber grating is the most important part.Since A. M. Vengsarkar et al. wrote successfully Long-Period Fiber Gratings (LPG) in optical fibers in 1995, LPG have become increasingly popular as fiber-optic devices for optical fiber communication and sensing. LPG have been demonstrated as band-rejection and gain-flattening filters for improving Er-doped fiber amplifier systems, and also used as temperature/strain sensors, as well as sensing demodulators. One of their unique characteristics is the sensitivity to the refractive index of the cladding, which can be used as biochemical sensor.This dissertation deals with the fabrication, characterization, and applications of long-period gratings in optical fiber communications and sensing systems. The aim of this project is to assess long-period gratings as fiber-optic devices for optical fiber communication and sensing. A review of the properties and characteristics of fiber gratings associated with the simple silicate fibers is provided, which includes a theoretical analysis of the principles of operation for short-period gratings (fiber Bragg gratings) and long-period gratings. The simulations of the spectral response from these two types of gratings are also presented. A number of long-period grating fabrication methods and techniques, which were reported by some researchers, are reviewed. In this project, the normal long-period gratings are fabricated by using a KrF excimer laser combined with the metal amplitude mask technique and point-by -point exposure technique. The metal mask is made of a stainless steel sheet, and the slot width (periodicity) is processed by using high quality photographic tooling.Considered the refractive index changes caused by hydrogenmoecular, this paper developed a simple model based three-layer step index wave guide and coupled mode theory to analyze and simulate the annealing of LPG inscribed in hydrogen loaded fiber. The results agree well with the experiments.