Cellular-Dimension Picoliter-Volume Index Microsensing Using Micro-Abrupt-Tapered Fiber Mach–Zehnder Interferometers

We report a micro Mach-Zehnder index sensor with a device length of 179.5 using two micro-abrupt-tapers in a cladding-reduced strongly-guiding fiber based on a focused laser beam. The cladding of strongly-guiding fiber is chemically etched before irradiation by a focused laser beam. The index sensitivity is 600 and 4000 nm/refractive index unit, respectively, at around 1.34- and 1.61-wavelength with a volume of 65.5-pL liquid over a refractive index range of around 1.45. A 72-pL glucose liquid with the concentration of 200 mg/dL over a refractive index range of around 1.33 can lead to a red-shift of 0.8 nm at 1.3.