Localization of light in an optical fiber with nanoscale radius variation

In optical fibers and photonic waveguides, reflection and localization of light is usually introduced with the periodic modulation of refractive index. Alternatively, in this paper, a quasi-one-dimensional slow axial propagation of light featuring reflection and localization is theoretically and experimentally demonstrated at the surface of an optical fiber having nanoscale radius variation. The test fiber (TF) is placed in contact with a microfiber (MF) positioned normal to the TF and used for excitation of whispering gallery modes in the TF and super-accurate sensing of its radius variation r(z)=r₀+Δr(z).