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Reaserch and Applications on Long-period Fiber Gratings

Author: GaoXia
Tutor: FengDeJun
School: Shandong University
Course: Radio Physics
Keywords: long-period fiber grating (LPG) coupled mode mechanically deformation method sensing refractive index
CLC: TN253
Type: Master's thesis
Year: 2009
Downloads: 435
Quote: 3
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Abstract

Since the first practical fiber grating was fabricated with phase mask technology in optical sensitive fiber by G. Meltz in 1989, the study of fiber grating have attracted more and more attentions around the globe. The fiber grating based components have played and will play an important role in the fiber communication and fiber sensing region. Compared to fiber Bragg grating, long-period fiber grating has such advantage as no back-scattering and more sensitive to the outward physical quantity changes, a wide range of applications in optical fiber communication and sensor region have been proposed. So long period fiber grating also becomes one of the burning research issues.In this thesis, the coupling mechanism of long period gratin, fabrication methods and its applications in communications and sensing are involved.Chapter I gives a brief introduction of the basic concepts, development and classification of long period fiber grating. Starting from Maxwell’s equations, chapter II explains the reasons for mode coupling and derives the electric field amplitudes. Then the magnitude and phase of fiber Bragg grating and long period fiber grating are derived with two mode coupling analysis, respectively. A simulation analysis on the different types of long-period gratings was made and how the parameters affected the spectrum was studied. This part of work will be the theoretic basis for sending applications.Capter III mainly introduces the fabrication methods of long period fiber grating, specially, a new ultraviolet （UV） laser point-by-point exposure mechanism is proposed. Several commonly used production methods of long-period fiber grating in the recent years, such as ultraviolet laser exposure method, hydrofluoric acid solution etching corrugated structure method, residual stress relaxation by electric arc discharge method, ion implantation, CO₂ laser-induced method and mechanically deformation method et al. are introduced.This thesis presents a new mechanically deformation method by pressing a plate with periodic grooves against a short length of fiber. The long period fiber grating fabricated by this method, presents many advantages such as simple fabrication procedure, inexpensive, erasable, and several LPFGs on different fibers simultaneously. Chapter IV gives performance analysis of the tunable long-period fiber grating filter based on the mechanically deformation method mentioned above. Theoretical simulation and experimental verification are done to find the impact on grating transmission spectrum when changing parameters such as the grating tilt angle and the pressure change et al. Some important conclusions are drawn.Chapter V studies the applications of long-period fiber grating in the sensor fields. This chapter presents the theoretical analysis for refractive index sensing and factors which will affect the sensitivity are discussed. In addition, for cascaded long-period fiber grating, e.g. LPG based M-Z interferometer structure and its performance is analyzed in particular.Finally, this thesis summarizes the work carried out and gives introduction and prospects to the work follow-up.In conclusion, commenced with the coupled-mode theory, this thesis analyzes the various working characteristics of long-period fiber grating. Research work was done both on various simulation analysis and some basic experiments. For temperature and stress sensing of long-period fiber grating, simulation and experimental results are analyzed separately. Meanwhile, the thesis sums up the applications in the refractive index sensing systematically. A tunable long-period fiber grating filter based on mechanically deformation method was proposed and experimentally studied, which can produce several LPGs simultaneously.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Optical waveguide and integrated optics > Fiber optic components
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