單層介電質次波長極化分光器之設計、製作與量測

Abstract

摘要 一維次波長光柵在許多文獻中已被證實對不同偏極化的光具有分光的效果。在以介電質次波長光柵來設計並製作極化分光器的文獻中，大多需要以多層次波長介電質光柵的結構來提升分光的效率。因此在本論文中提出一種新的設計，可以利用簡單的單層次波長介電質光柵來實現不錯的分光效率，具有在光纖通訊波長(1.55μm)上極化分光的效果以及製作複合型光學元件的潛力。 在設計次波長極化分光器上，主要是利用嚴格耦合波動理論(rigorous coupled wave analysis)來進行設計分析，再參考相關文獻調整次波長光柵的材質、週期、深度等參數，由模擬結果可知此一結構能在光纖通訊波長(1.55μm)下有效進行極化分光。 在製作次波長極化分光器上，我們使用干涉微影曝光來製作光阻的圖案，再利用鉻當做金屬擋罩進行活性離子蝕刻，將光阻的圖案轉移至非晶矽薄膜上，達成所需的次波長分光器的結構。 在量測次波長極化分光器上，主要是利用光譜儀量測不同極化光的穿透效率，來計算所製作的次波長極化分光器的分光效率，並且與結果做比較，分析製程上的誤差並驗證模擬結果的準確性。

Abstract In the literature, one dimensional subwavelength gratings have been proved to be able to separate light with different polarization. In most cases, to design a dielectric subwavelength grating polarizing beam splitter requires multilayer structure to improve diffraction efficiency. Here, we design a new structure utilizing single layer dielectric subwavelength grating for polarization beam splitting around wavelength of 1.55μm. It also has potential in fiber communication or hybrid optical elements. For such a polarization beam splitter, we use rigorous coupled wave analysis to design this structure and refer to related works to adjust its parameters. The simulation result shows it has polarizing-beam-splitting capability around wavelength of 1.55μm. In the fabrication of this polarization beam splitter, we use interference lithography to define photoresist pattern, followed by lift off to transfer pattern into Cr as a metal mask and then followed by reactive ion etch to fabricate the designed structure. In the characterization of this polarization beam splitter, we use a spectrometer to measure the transmission spectrum and calculate its diffraction efficiency. From the measured spectrum response, we can prove our design and analyze the fabrication error.