低損耗光纖角錐和電弧融接技術應用於微奈米導光線及微光學元件製作

Abstract

微奈米導光線具有體積小且漸逝波大的特性，有潛力被廣泛應用在各種光學感測器或是微光學元件中。其中，要將光源從一般通訊用單模光纖導引入微奈米導光線並同時維持低的耦合損耗是一件困難的事。在本文中，我們使用氫氟酸動態蝕刻法將一般單模光纖加工成漸細光纖角錐，用來降低單模光纖到微奈米導光線的耦合損耗。我們可以藉由步進馬達來達成光纖角錐長度的控制，因為越長的光纖角錐具有越低的耦合損耗。我們成功地製造了損耗低於1.4dB的光纖角錐。 此外，我們發展了一套電弧融接系統，先利用凡德瓦力操控導光線，並成功的融接了2微米直徑的導光線。此電弧融接法可以維持低於1.1dB的耦合損耗，相較於一般常用的漸逝場耦合法，電弧融接法的耦合損耗通常更低。因為耦合損耗的降低，我們進而使用2微米的導光線製造1x2耦合器和Mach-Zehnder干涉儀。耦合器的分光比分布可以從47/53到91/9，並實現接近1:1的分光比；而經由頻譜的量測與比對，可確認我們製作的的確是Mach-Zehnder干涉儀。

A micro-nano optical wire (MNOW) has some attractive properties such as small size and large evanescent field; therefore it is potentially useful for fabricating micro optical sensors and micro optical devices. However, it is not easy to couple light to an MNOW from a conventional single mode fiber (SMF) with low loss. In this thesis work, we fabricate a fiber taper by using dynamic HF wet etching method to reduce the coupling loss between an SMF and an MNOW. Because the coupling loss becomes lower when the taper is longer, we can obtain the control of fiber taper length via a high-precision stepping motor. We also develop an arc splicing system to connect two MNOWs with 2μm diameter after manipulation of MNOWs into place by using van der Waal’s force. The splicing loss, which is the same with coupling loss in splicing case, is smaller than 1.1dB, and the coupling loss by using splicing technique is often smaller than the one of evanescent coupling. Such low loss tapers enable us to make two kinds of MNOW based devices, 1x2 coupler and Mach-Zehnder interferometer (MZI). The coupling ratios of couplers can be varied from 47/53 to 91/9 and a near 1:1 coupling ratio can be realized. The measured spectra confirm optical characteristics of the devices are indeed of MZIs.