基於二維傾斜光柵的極化分光器之研究

Abstract

極化分光器是非常重要的光電元件，因可分離兩相互垂直偏振之特性，可以運用在光纖通訊之多工分光、光學顯微鏡、生化檢測等。近年來隨著半導體製程技術的進步，可見光波長等級的各種光電元件成為趨勢。次波長介電質光柵對於光的操控性有十分的競爭力，在製程上又相對簡單可以量產，其中一維傾斜光柵即在擴增實境頭戴式眼鏡領域展現其價值。 過去傾斜光柵並未受到重視，缺乏理論分析傾斜光柵結構，大多以數值模擬方法求得。本研究利用簡化模態法，快速推測出一維傾斜光柵結構參數，並以模擬軟體驗證，負一階穿透率可超過92%。後介一維傾斜光柵結構特性，引入極化分光器概念，將一維光柵延伸至二維光柵，應用對稱性，最終成功設計出高耦合效率且高消光比的垂直耦合型極化分光器。針對可見光532 nm之綠光，利用二維傾斜光柵，可以將單一偏振方向正向入射光柵平面，透過T-1,0階穿透傳播，耦合效率可達70%以上，消光比20 dB以上。

Numerous optical information processing, routing and imaging systems employ different polarization states to increase the information bandwidth and to reduce crosstalk between channels. Applications include, for example, free-space optical switching networks, optical microscopes and biosensors. In these systems, the polarizing beam splitter is a key element for separating two orthogonally polarized light beams. With the progress of semiconductors manufacturing technology, visible wavelength scale structure’s optoelectronic devices have become a rapidly growing field of research in recent years. Light manipulations capability of subwavelength dielectric gratings is substantial, manufacture wise are relatively easy and have the probability of mass production. The one dimensional slanted gratings used in augmented reality head-mounted display is one good example. Few theoretical analyses are focusing on such slanted gratings in the pass due to the lack of interest, mostly, the geometry was calculated mainly via mass parameter scan and simulation. In this thesis, one dimensional slanted gratings geometry was predicted using the Simplified Modal Method, achieving a transmittance rate as high as 92%. We also present how, by the use polarizing beam splitters, we can promote this one dimensional result to two dimensions. The two dimensional slanted gratings we successfully designed and can achieve a coupling efficiency as high as 70%, with an extinction ratio above 20 dB.