相位移長週期光纖光柵之設計及製作

Abstract

在本論文中，我們研究如何由理論配合實驗去設計及製作相位移長週期光纖光柵。在實驗上，我們用紫外光逐點曝照光纖的方式，使其產生週期性的折射率改變。藉由控制不同的曝照時間，可製作出各種不同折射率變化的均勻長週期光纖光柵。由所得到的均勻長週期光纖光柵的頻譜，再配合模態耦合理論，可推得折射率變化與時間的關係和折射率對波長的變化率與波長的關係。 利用所得到的參數，我們使用演化演算法來設計最佳化長週期光纖光柵的耦合係數函數，並藉由控制不同的曝照時間和每段均勻光纖光柵之間的相位移，來試製複雜且能實際應用於光纖通訊中的平坦化長週期光纖光柵濾波器。

In this thesis, we investigate the design and fabrication of phase-shifted long-period fiber gratings (LPGs). To periodically modulate the refractive index of the fiber core, the fiber is sequentially irradiated point-by-point by a UV laser beam. The refractive index change of fabricated long-period fiber gratings can be changed by adjusting the UV exposure time. Using the coupled-mode theory to analyze the measured data, we calibrate the relationship of the fiber core refractive index change with the wavelength as well as with the exposure time. With the calibration parameters, an Evolutionary Programming (EP) algorithm is then used to design a flat-band LPGs by optimizing the coupling coefficient distribution function. By controlling the UV exposure time and the phase shifts between each uniform LPGs, complex LPGs with advanced characteristics can be fabricated.