In-line microfiber MZI operating at two sides of the dispersion turning point for ultrasensitive RI and temperature measurement.

Schematics of the bare and the PDMS-coated in-line microfiber MZI for RI and temperature sensing are shown in Fig. 1 (a) and (b), respectively. The microfiber MZI which is fabricated by non-adiabatically tapering a single mode fiber is composed of two abrupt tapered regions and a uniform waist region. When the fundamental HE 11 mode is propagating through the first abrupt tapered region, only symmetrical high order modes (HE 1m) can be excited owing to the symmetry of the abrupt tapered regions. Besides the fundamental HE 11 mode, only the high order HE 12 mode is excited by the fabricated microfiber whose taper waist diameter is 4.8 μm. The mode profiles of HE 11 mode and HE 12 mode are shown in Fig. 1 (c) and (d). These two modes interfere with each other at the second abrupt tapered region, forming dual-path interference. • An in-line microfiber MZI is demonstrated for ultrasensitive surrounding RI and temperature measurement. • An ultrahigh RI sensitivity of 24,209 nm/RIU and a high temperature sensitivity of -2.47 nm/℃ are experimentally achieved. • By embedding this microfiber MZI into PDMS, the temperature sensitivity is improved from -2.47 nm/℃ to about 8.33 nm/℃. An in-line microfiber Mach-Zehnder interferometer (MZI) is demonstrated for ultrasensitive refractive index (RI) and temperature measurement by operating at two sides of the dispersion turning point (DTP), respectively. An ultrahigh RI sensitivity of 24,209 nm/RIU (RI unit) around 1.3320 and a high temperature sensitivity of -2.47 nm/℃ are experimentally achieved by a microfiber MZI with taper waist diameter of about 4.8 μm. By embedding this microfiber MZI into polydimethylsiloxane (PDMS), the temperature sensitivity is improved from -2.47 nm/℃ to about 8.33 nm/℃. The positive temperature sensitivity of this PDMS-coated microfiber MZI and the negative thermo-optic coefficient of PDMS show that this microfiber MZI has a negative RI sensitivity around the material RI of PDMS (about 1.405), which indicates that the microfiber MZI works at two sides of the DTP for RI measurement and temperature measurement, respectively. The PDMS-coated microfiber MZI could achieve a temperature measurement resolution of about 0.0024 ℃ if the resolution of the optical spectrum analyzer were 0.02 nm, making it suitable for temperature measurement applications with high precision requirement. The bare microfiber MZI is promising for liquid analytical measurement in fields like biochemistry for its advantages of ultrahigh sensitivity, small size, and little sample consumption. [ABSTRACT FROM AUTHOR]