基於二維傾斜光柵的色彩極化分光器之設計

Abstract

極化分光器是一種在光學系統中常使用的元件，其作用是將傳播的電磁波依照不同的偏振分離，其應用如: 光纖通訊多工分光、生化檢測以及光學顯微鏡等。近年來，隨著製程技術的進步，奈米等級的光電元件由於符合其輕薄短小的優點，逐漸成為趨勢。其中，次波長介電質光柵藉由優異的操縱光的能力，以及相對簡單的製程，因此受到大家的關注。這幾年，一維傾斜光柵被應用在擴增實境，在該領域上展現了極大的應用價值，特別是頭戴式顯示眼鏡商品問世後。 本研究利用數值模擬方法設計二維傾斜光柵，完成對單一波長擁有高耦合效率以及高消光比的垂直耦合極化分光器。其耦合效率可達70%以上，消光比30 dB以上。接著，再對兩種不同中心波長設計出高耦合效率的色彩極化分光器，可將兩個在不同垂直極化的不同波長分別轉成繞射的TE-1,0 和TE0,-1 階的穿透繞射。兩種波長耦合效率，在最佳化結構皆可高達90%，我們並考慮製程容易性，設計出效率也不錯的波長分光器。

Polarization beam splitters are frequently used in optical systems. They can split propagating electromagnetic waves according to their polarizations. Their applications include wavelength division multiplexing (WDM) in optical communications, bio-chemical testing, optical microscopy, etc. With the rapid advancement of semiconductor process technology, nano-level optoelectronic devices become more popular due to their advantages of slimness and light-weigth. Among them, sub-wavelength dielectric gratings are attractive due to their excellent light-manipulating capability and relatively simple manufacturing. Recently, one-dimensional slanted gratings are adopted in augmented reality (AR), which shows their superior value, especially with the introduction of commercially available head-mounted display goggles. In this research, we use numerical simulation to design polarization beam splitters with high efficiency and extinction ratio, based on two-dimensional slanted gratings. The coupling efficiency can be more than 70%, the extinction ratio can be higher than 30 dB. Thereafter, we design high efficiency chromatic splitter based the 2D slanted gratings, which convert two central wavelengths of two polarizations into two directions, i.e., TE-1,0 and TE0,-1, transmitted diffractions, respectively. The coupling efficiency can be as high as 90% in optimized structures. We also design wavelength splitters with acceptable efficiency considering the easiness of process.