Pal Sudipta Sarkar, Mondal Samir K, Tiwari Umesh, Swamy P Venu Gopala, Kumar Manish, Singh Nahar, Bajpai P P, Kapur Pawan
Central Scientific Instrument Organization (Council of Scientific and Industrial Research), Sector 30C, Chandigarh 160030, India.
Rev Sci Instrum. 2011 Sep;82(9):095107. doi: 10.1063/1.3633955.
We propose a novel refractive index sensor based on multimode microfiber knot-type loop (NL) interferometer. The middle portion (~5 cm) of a 15 cm long multimode fiber is etched in 48% hydrofluoric acid to reduce its diameter to ~12 μm. A NL of diameter <1 mm is made from the etched fiber. The ends of etched fiber are spliced with single-mode fibers for launching and detecting light from the NL interferometer. The NL introduces path differences to produce interferometric spectra with free spectral range ~16 nm. The spectrum shifts as the surrounding refractive index of the loop is changed by adding chemicals. We observe the highest sensitivity of the NL interferometer ~172 nm/RIU (refractive index unit) at a refractive index value 1.370 as obtained experimentally using commonly available chemicals. The design could be used as simple, low cost, and highly sensitive biological and chemical sensor.
我们提出了一种基于多模微光纤结型环（NL）干涉仪的新型折射率传感器。将一根15厘米长的多模光纤的中间部分（约5厘米）置于48%的氢氟酸中蚀刻，使其直径减小至约12微米。由蚀刻后的光纤制成直径小于1毫米的NL。蚀刻光纤的两端与单模光纤熔接，用于发射和检测来自NL干涉仪的光。NL引入光程差以产生自由光谱范围约为16纳米的干涉光谱。当通过添加化学物质改变环的周围折射率时，光谱会发生偏移。我们通过实验使用常见化学物质观察到，在折射率值为1.370时，NL干涉仪的最高灵敏度约为172纳米/RIU（折射率单位）。该设计可作为简单、低成本且高灵敏度的生物和化学传感器。
