Fabrication and characterization of micro fluidic based fiber optic refractive index sensor

•RI sensor fabricated by grayscale lithography technique is demonstrated in this paper.•The tapered optical fiber is embedded in a closed microfluidic channel.•The RI measurement is done by tested the sensor with different concentration of NaCl.•The transmission spectra are shifted with different concentration of NaCl.•The RI sensor achieved a reliability and high sensitivity of 1457 nm/RIU.

A refractive index sensor was proposed by using 3 dimension (3D) grayscale lithography technique. Optical fiber with taper diameter of 12 μm was embedded in a closed microfluidic channel. Taper area of optical fiber is in floating condition at the center of micro channel. Grayscale variation range used for this sensor was 70%-74% and thickness variation 430 μm-694 μm was achieved. The dimension of the sensor was 7.5 cm in length and 2 cm in width. Fabricated sensor was characterized with air condition and solution concentration from 0.1 M to 1 M. A sensitivity of 1457 nm/RIU is achieved. The measured results show a good repeatability and low temperature cross-sensitivity.