This paper discusses refractive index (n) measurement capabilities of interferometers based on micro-cavities of various diameters (d = 50 and 60 μm) fabricated in optical fibers by a femtosecond laser. In comparison to previously presented structures, the reported sensor operates in the near-infrared spectral range. Bottom of the cavity intersected the fiber’s core (5.2 μm in diameter), which induced the Mach-Zehnder interferometer effect. After filling the cavity, a set of minima can be observed in the transmission spectrum, and they shift in wavelength with a change in n. The fabricated sensors exhibit high and linear sensitivity and can measure sub-nanoliter volumes of liquids, what make this sensor perfect for various diagnostic medical or biochemical applications.
Monika Janik, Tinko Eftimov, Marcin Koba, Mateusz Śmietana, and Wojtek J. Bock, "Near infrared operation of femtosecond laser micro-machined in-fiber Mach Zehnder interferometers for refractive index sensing," Proc. SPIE 10544, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics XI, 105440F (Presented at SPIE OPTO: January 28, 2018; Published: 22 February 2018); https://doi.org/10.1117/12.2291120.
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