Carbon Nanotubes Deposited Optical Fibers for Continuous Refractive Index Sensing Applications

Abstract

An optical fiber-based refractive index (RI) sensing probe fabricated through optical deposition of carbon nanotubes (CNTs) onto the cleaved end face of a multimode fiber (MMF) segment, fusion spliced at one end to a single mode fiber (SMF), is presented. The interference of the excited higher order modes in the MMF segment with the fundamental mode led to the formation of various spectral features in the resulting output spectrum which were then used as reference points for RI measurements. RI perturbations in the external environment of the sensing probe could then be characterized by variations in intensity of these spectral features with little wavelength dependence. The deposited CNTs extended the continuous measurement range of the sensor and the achievable sensitivity was calculated to be approximately 35.8 dB/RIU for the RI range of 1.33–1.40 and approximately 98.8 dB/RIU for the RI range of 1.40–1.46. The sensing probe also exhibited good stability with little fluctuations in intensity of the output spectrum for a constant RI.