Carbon-nanotube-deposited multi-mode fiber cavity for refractive index sensing applications

We present an optical fiber sensor fabricated by deposition of carbon nanotubes at the end face of a joint fiber segment, consisting of a short multi-mode fiber segment fusion spliced to a single-mode fiber. Optically-driven deposition is utilized as a simple and cost-effective method for carbon nanotubes coating. The sensing mechanism depends on the reflectance at the fiber-CNT interface, where the intensity of the reflected spectrum changes with a variation in refractive index of the ambient environment. A sensitivity of 29.3 dB/RIU was achieved for the fabricated fiber sensor within the RI range of 1.33-1.46, and a refractive index resolution of 3.4 × 10-4 RIU was also obtained based on a 0.01 dB intensity resolution of the optical spectrum analyzer.