利用光纖熔拉及側耦合技術來製作長週期光纖光柵

Abstract

在本論文中，我們利用光纖熔拉及側耦合技術來製作易於調變且高靈敏度的長週期光纖光柵。將單模光纖(SMF-28)熔拉至直徑20µm與鍍上金屬的長週期光柵側向接觸，利用熔拉光纖的消逝場與金屬光柵的相互作用，沿著光在光纖中傳播方向產生模態耦合，在穿透頻譜上產生帶狀的能量損失。利用外在環境的溫度與折射率變化來調變相位匹配，我們發現與一般利用單模光纖製作的光纖光柵相比，利用熔拉光纖所製作的長週期光纖光柵有相反的共振波長漂移方向。我們所得到的中心波長對折射率之調變效率(dλ/dn)最高約為773nm，中心波長對溫度之調變效率約為-0.24 nm/ °C，與傳統光纖光柵相比(約為+0.06 nm/ °C)，溫度調變效率提升了四倍。因為熔拉光纖和單模光纖的色散曲線特性不同，所以擁有不同的調變趨勢和效率。

In this thesis, we experimentally demonstrate a simple LPFG structure based on fiber-tapering and side-coupling techniques to form a flexible and high-sensitivity sensing device. The LPFG is composed of a fiber taper with a uniform waist of 20 μm in diameter and a side-contacted metal grating. The overlap of the evanescent field with the surface of metal grating leads to modal coupling along the propagation direction and provides an enhanced but opposite dip wavelength tuning tendency with respect to the temperature and refractive index change when compared to conventional LPFGs. The highest average refractive index tuning efficiency (dλ/dn) is 773 nm. The average temperature tuning efficiency is estimated to be about -0.24 nm/ °C, which is greatly improved when compared to that of conventional LPFGs (around +0.06 nm/ °C). The temperature and refractive index tuning characteristics of the LPFGs attributes to the unique material and waveguide dispersion characteristics of the proposed structure.