S-shaped refractometer based on dual tapered no-core fiber for low-range refractive index measurement

Authors：Fang Wang; Kaibo Pang; Tao Ma; Xu Wang; Heng Lu; Yufang Liu

Source：Optics Communications, 2020, 463: 125419.

DOI：10.1016/j.optcom.2020.125419

• S-shaped fiber
• Dual tapered no-core fiber
• Mach–Zehnder interferometer
• Low refractive index range
• Simultaneous measurement

In this paper, a refractometer based on an S-shaped dual tapered no-core (SDTN) fiber structure is proposed for low-range refractive index (RI) measurement. The SDTN comprises two Mach–Zehnder interferometers that are introduced within the dual tapered no-core fiber, thereby establishing a composite interference. The results of experimental evaluation demonstrate that maximum sensitivities of 460.66 nm/RIU within a linear RI range of 1.3387∼1.3516 are achieved. In addition, the two interference dips A and B in the transmission spectrum exhibit the temperature sensitivities of −0.0386 nm/∘C and −0.0429 nm/∘C, respectively. By fabricating an S-shaped cascade of tapered areas on the no-core fiber (NCF), RI sensitivity in the low RI range is improved and simultaneous measurements of RI and temperature are achieved. With its low cost, compact structure, and convenient manufacture, the proposed refractometer has broad application prospects in the field of RI measurement.