多模干涉式光子晶體極化分光器之設計與分析

Abstract

摘 要

本研究探討正方晶格柱狀光子晶體架構之多模干涉波導,並藉以設計一極化分光器。在此光子晶體結構下，由於光子晶體禁帶的效應，橫向電場偏極化(TE)波與橫向磁場偏極化(TM)波可在此結構傳輸。由於TE波與TM波在光子晶體中色散關係不同，造成其拍頻長度(beat length)有很大的差異，利用此特性，可以在多模干涉元件長度大約82.5微米將兩不同偏極化光分開。此外，利用有限差分時域法(Finite-Difference Time-domain, FDTD)來觀察二維光子晶體多模波導中的成像現象和成像位置,發現其成像位置與模態傳輸分析(Modal Propagation Analysis, MPA)所得到的成像位置一致。利用有限差分時域法模擬設計的極化分光器， TE波之插入損耗(Insertion Loss) 為0.301dB及對比(Contrast)為13dB ，而TM波之插入損耗為0.515dB及對比為9.03dB。

ABSTRACT

A compact polarizing beam splitter (PBS) based on a photonic crystal (PC) multimode interference (MMI) with a square lattice of dielectric rods is designed and analyzed. In the applied PC structure, transverse-electric (TE) light and transverse-magnetic (TM) light are confined with the photonic bandgap effect. Due to the different dispersion relation, TE and TM light have a large difference in beat lengths, which is utilized to separate the two polarizations in a MMI device about 82.5 □m. In the PC MMI structure, the self-imaging phenomenon and the imaging positions along the propagation axis are observed, and it is found that the results are in good agreement with those derived from the modal propagation analysis (MPA) by the two-dimensional finite-difference time-domain (FDTD) computation The performance of the PBS is numerically simulated by FDTD computation. The results show that the insertion loss is 0.301 dB for TE, and 0.515 dB for TM. The contrast is 13 dB for TE, and 9.03 dB for TM, respectively.