Near infrared operation of femtosecond laser micro-machined in-fiber Mach Zehnder interferometers (uIMZI) for refractive index sensing

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.