全息分散式聚合物液晶線上可調變式濾波器

Abstract

利用全息分散式聚合物液晶在光纖內部做通訊波段的可調變式濾波器在本工作中已經初步發展成功。我們利用抽絲技術將中空光纖的纖心直徑縮減到符合單模波導傳遞條件。將分散式聚合物液晶引入處理過的中空光纖後，把光纖放置在雙光干涉系統下曝光，做液晶與聚合物相分離，並形成週期性結構的布拉格光柵。外加電壓驅動內部液晶轉動，造成折射率上升使布拉格波段偏移，此結果在亦在本文做討論。為了避免耦合造成損耗過大，我們將單模光纖連接在完成的結構兩端。此外，由於單模光纖纖心與中空光纖纖心大小差距較大造成傳輸損耗，我們將單模光纖做抽細的動作使差距縮小降低損耗。又因為聚合物分散液晶的物質特性，我們也嘗試增加內部光柵數目來提升反射效率。

An in-line wavelength tunable filter based on holographic polymer-dispersed liquid crystal (HPDLC) working in the communication band is demonstrated. PDLC is infiltrated in a hollow-core fiber whose single-mode waveguiding operation is achieved by shrinking the hollow-core diameter to an appropriate value. To periodically separate polymer and liquid crystal, two-beam interference exposure is employed, and a Bragg grating (BG) is thus formed. The resultant Bragg wavelength is shown tunable by applying an external voltage to the BG region. To reduce the coupling loss, tapered single-mode fibers (SMFs) are directly connected to the input and output ports of the HPDLC-based filter to realize an in-line fiber device.