Ultrasensitive refractive index sensor based on a Mach-Zehnder interferometer created in twin-core fiber.

We proposed and experimentally demonstrated a twin-core fiber (TCF)-based Mach-Zehnder interferometer (MZI) to develop an ultrasensitive refractive index (RI) sensor. This fiber MZI was constructed by splicing a short section of TCF between two sections of single mode fibers. A microchannel was drilled through one core of the TCF by means of femtosecond laser micromachining to create one arm of the proposed interferometer, and the other core worked as the second arm. Such a fiber interferometer exhibits an ultrahigh RI sensitivity of -10981  nm/RIU and a low temperature cross-sensitivity of 3.96×10(-6)  RIU/°C. Moreover, the ultra-compact device size and all-fiber configuration make it very suitable for highly sensitive RI sensing at precise location.