Self-assembled colloidal photonic crystal on the fiber optic tip as a sensing probe

This paper presents an effective and efficient method to fabricate novel fiber optic sensing probes. The new, simple and low cost approach is based on a 3D photonic crystal (PhC) dielectric structure directly deposited on the tip of a multimode optical fiber through the self-assembly of colloidal crystals (CCs) via a vertical deposition technique. Here, the colloidal crystal (CC) is made of polystyrene (PS) nanospheres with 200 nm diameter, and the optical fiber is a UV-VIS fiber with a core diameter of 200 μm. The obtained fiber probes exhibit a resonant peak at 480 nm and an amplitude enhancement of 3.7 with respect to the bare fiber, these results being highly repeatable. A numerical tool based on finite element method (FEM) analysis has been developed to study and analyze the 3D sub-wavelength structures. Numerical results are in good agreement with the observed experimental spectra. Moreover, refractive index measurements have been carried out revealing a sensitivity of up to 445 nm/RIU in the 1.33-1.36 values range. The achieved performances, obtained by using very small active areas and an easy and reliable fabrication procedure, demonstrate the future perspectives of these fiber-optic probes for chemical and biological sensing applications.