光柵濾波元件之設計

Abstract

本論文中，我們探討窄頻光濾波器之特性。我們分析同向耦合、反向耦合 、以及諧振傳輸式光柵輔助之光波導濾波器。我們也探討了用平板型光波 導與立體背脊式光波導做光濾波器之特性與可行性。為配合目前積體電路 技術，我們選擇以矽材料為波導基片，以氮化矽和摻磷玻璃做為光波導材 料.我們利用模耦合理論 (coupled-mode theory) 來探討光柵輔助之光波 導濾波器的頻譜響應。我們發現在設計同向耦合光波導濾波器時，我們必 須考慮到不同波之間的干涉效應。在非對稱耦合光波導情形，只有二個波 導同調性差異較大時，能量傳輸才能達到百分之百。我們也發現在反向耦 合立體背脊式光波導濾波器的頻譜響應中，中心波長以外的地方也會有反 射,而這些直接布拉格反射 (direct-Bragg reflection) 可經由將光柵之 相位平移來消除。諧振傳輸式光柵的頻寬可以做得很窄，適合用於高密度 多波長分工系統 (WDM)中□ Narrow band wavelength selective devices were simulated. Spectral properties of codirectional, contradirecional, transmission resonant grating-assisted waveguide coupler filters were studied. The simulations we performed were based on waveguides made of Si3N4 and p-glass with SiO2 as clading layers. Planar waveguide couplers and ridge waveguide couplers were studied. Our goal is to design optical filters compatible with silicon IC technology. Coupled-mode theory was used to derive spectral response of the grating-assisted directional couplers. A 24angstrom bandwidth could be achieved with a forward coupling grating filter at 1.3 um center wavelength. For backward coupling grating filters the bandwidth was about half as narrow. Even narrower bandwidths could be achieved with transmission rsonant grating filters with the bandwidth determined by the coupling coefficient. We showed that interference between waveguide modes have to be considered in codirectionally coupled waveguide filters. Near ideal power transfer efficiency could be achieved only if the two waveguides are far from synchronous. We showed that side lobes in the reflection spectrum of contradirectionally coupled grating filters were significant for ridge waveguide couplers. These direct-Bragg-reflection induced side lobes could be suppressed by using a phase shifted grating. Transmission resonant grating filters were showed to have a narrow transmission peak inside the stopband, and so could be used in dense WDM systems.