In this article, we demonstrate an on-demand two-step fabrication strategy for optical microfiber couplers (OMCs) with precisely controlled dispersion turning points (DTPs). Firstly, an OMC with a relatively thick width is obtained through the fusion elongation method. Secondly, the as-fabricated OMC is placed in a low-concentration hydrofluoric acid solution whose refractive index (RI) is adjusted to match that of the target working environment to fine etch the width of the OMC. During the etching process, the real-time output spectrum of the OMC is monitored in-line to track the position of the OMC. The etching process is terminated once the desired DTP appears. Our study shows that by accurately controlling the reaction time, the DTP can be tuned from 1600 to 900 nm with high precision better than 1 nm in both water and a liquid medium with a high RI of 1.365. Finally, we experimentally demonstrate that the OMC fabricated by the proposed method can work as an ultrasensitive RI sensor with a sensitivity of −1.61×105±0.15×105 nm/RIU at 1.333 and a biosensor for carcinoembryonic antigen (CEA) with a limit of detection of 2 pg/mL.

中文翻译：

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按需制造具有精确控制色散转折点的光学微纤维耦合器：面向液体中的传感应用

在本文中，我们展示了具有精确控制色散转折点 (DTP) 的微型光纤耦合器 (OMC) 的按需两步制造策略。首先，通过熔合延伸法得到宽度较厚的OMC。其次，将制作好的 OMC 放置在低浓度氢氟酸溶液中，其折射率 (RI) 被调整为与目标工作环境相匹配，以精细蚀刻 OMC 的宽度。在蚀刻过程中，在线监测 OMC 的实时输出光谱以跟踪 OMC 的位置。一旦所需的 DTP 出现，蚀刻过程就终止。我们的研究表明，通过准确控制反应时间，DTP 可在 1600 至 900 nm 范围内进行调谐，精度优于 1 nm，在水和液体介质中均具有 1.365 的高 RI。最后，我们通过实验证明，通过所提出的方法制造的 OMC 可以用作超灵敏 RI 传感器，灵敏度为 -1.61×105±0.15×105 nm/RIU 在 1.333 和癌胚抗原（CEA）的生物传感器，极限为检测 2 pg/mL。