應用於折射率感測的穩定封裝之微光纖線圈共振腔與其長時間穩定性提升

Abstract

近來，微光纖線圈共振腔在非線性光學和光纖感測吸引許多目光。和以半導體製作的微共振腔相比，微光纖線圈共振腔擁有例如低傳輸損耗，容易和一般光纖元件結合等特點。透過增加線圈數或堆疊線圈，微光纖線圈共振腔可以達到相當高的品質因子。然而，沒有保護的微光纖線圈共振腔很容易受到外界環境干擾，限制了微光纖線圈共振腔的應用。因此，微光纖線圈共振腔的保護方法是本篇論文的主要焦點。 在此論文中，首先我們介紹微光纖線圈共振腔的製作過程和保護方法。我們利用改良的小型光纖抽絲塔，以氫氧焰作為熱源製作直徑3微米的微光纖。接著我們展示微光纖線圈共振腔的製作架構。透過具有超長工作距離的物鏡和CCD元件，我們可以即時觀測繞線過程，有助於儘早檢測出錯誤。具有良好同心度和穩定性的繞線系統使我們可以準確地控制微光纖線圈共振腔每圈的間隔。我們使用以正己烷稀釋過的聚二甲基矽氧烷作為微光纖線圈共振腔的包裝材料。稀釋過的聚二甲基矽氧烷擁有較低的黏滯性，方便在繞線過程中調整線圈。以此方法製作的微光纖線圈共振腔品質因子可以達到5 x 10^5，而且頻譜表現可以維持5天。 接著我們嘗試以聚二甲基矽氧烷包裝之微光纖線圈共振腔進行折射率感測。將微光纖線圈共振腔放置在一壓克力架構中，並以葡萄糖水溶液作為折射率變化。微光纖線圈共振腔的偵測極限為7 x 10^-4。為了增加微光纖線圈共振腔應用的潛力，我們將剩餘微光纖部分以紫外光固化膠覆蓋，進一步提升微光纖線圈共振腔的穩定性。如此微光纖線圈共振腔的表現可以維持長達一個月沒有明顯劣化。

Recently, microfiber coil resonators (MCR) have attracted much attention in nonlinear optics and optical sensing. Compared with the semiconductor based micro resonators, MCRs have attractive properties such as low propagation loss and easy connection with conventional optical fiber devices through their tapered sections. Moreover, by increasing coil turns or stacking microfiber turns, MCRs can achieve very high quality factor. However, an unpackaged MCR is easily affected by surrounding disturbance, which limits its applications. Therefore the methods to protect MCRs is the main focus of this work. In this work, we firstly introduce fabrication process and protection method of MCR. A 3-μm diameter microfiber was produced by using a modified miniature fiber drawing tower. The hydrogen oxygen flame was applied as heat source. Then the experimental setup for fabricating MCR is demonstrated. With the extra long working distance objective and CCD, the coiling process could be observed in situ. This helps us early detect the faults during coiling process. The coiling system with good concentricity and stability helps us control the microfiber coil accurately. Polydimethylsiloxane (PDMS) diluted with hexane was used as package material for MCR. Hexane-diluted PDMS has lower viscosity so the microfiber coil could be turned around easily. The quality factor of PDMS-packaged MCR was 5 x 10^5 and could maintain for 5 days. Next, we tried to use PDMS-packaged MCR as refractive index sensor. PDMS-packaged MCR was put in a PMMA structure and glucose solutions were used for different refractive index. The detection limit of PDMS-packaged MCR was about 7×10^-4 RIU. To increase the potential of practical applications, long-term stability of MCR was further improved by protecting microfibers with UV glue. The performance of MCR could maintain over a month without degradation.