Study of Long-Period Fiber Grating and Its Application on Optical Add-Drop Multiplexer and Optical-Fiber Surface-Plasmon-Resonance Sensor
| Autor: | Yue-Jing He, 何岳璟 |
|---|---|
| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 In the recent years, utilizing the spectrum characteristic of long-period fiber grating (LPG), numerous components extensively applied on optical fiber communication system have been proposed such as band rejection filters, gain flatteners, and dispersion compensators. In contrast to fiber Bragg grating, it is well-known that the LPG has considerable spectrum bandwidth. So far, on the optical communication component design, the researches as to LPG are all to emphasize the coupling characteristic between core mode HE11 and low order cladding modes. Obviously, it is almost impossible to use LPG to design the optical communication components that possess the narrow bandwidth and conform Wavelength Division Multiplexing standard (WDM), not to mention Dense Wavelength Division Multiplexing standard (DWDM). In this dissertation, we use strict coupled-mode theory to study and quantify the spectrum characteristic of LPG in detail with the aim of supplying a concrete concept to design narrow-bandwidth optical communication components. In contrast to the wide spectrum bandwidth resulting from the coupling between core mode and low order cladding modes, we will prove that a 0.4 nm FWHM can be achieved as long as the period of LPG is properly designed to choose some high order cladding. Then, we will further apply this new concept to design the narrow bandwidth optical add-drop multiplexer (OADM) based on two parallel LPGs. In addition, in order to obtain the maximal power transmission, we also derive the structure parameters of OADM such as the distance between two parallel fibers and the length of two LPGs according to four-mode coupled-mode equations. As for the application on optical fiber sensor, we combine the advantages of traditional LPG sensor and present optical-fiber surface-plasmon-resonance (SPR) sensor and further propose a new type of optical-fiber SPR sensor. It simply employs a long-period fiber grating with proper period to couple a core mode (HE11) to the co-propagating cladding mode that can excite surface plasmon wave (SPW) and monitors the change of the transmitted core mode power, which is operating at a fixed wavelength, to determine the variation of the refractive index of analyte. As far as the excitation of SPW, the model of numerical simulation, and the complexity of measurement equipment are concerned, it is obvious that this new structure is superior to the proposed SPR sensor, consisting of a bent polished single-mode SPR optical fiber. In this dissertation, we derive the dispersion relation of guiding modes in this four-layer optical-fiber SPR sensor, and the unconjugated form of coupled-mode equations. In addition, in order to increase greatly the efficiency on analyzing this new SPR sensor, further simplifications on the integration form of coupling constants are proposed. The numerical results will demonstrate that this new and simple configuration may be used as a highly sensitive amplitude-sensor. Furthermore, it can be easily adapted for a SPR fiber optical probe by depositing a mirror on the fiber tip. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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