  We report the fabrication and characterization of photonic structures using
tapered optical nanofibers. Thanks to the extension of the evanescent
electromagnetic field outside of the nanofiber two types of devices can be
built: a ring interferometer and a knot resonator. We propose a general
approach to predict the properties of these structures using the linear
coupling theory. In addition, we describe a new source of birefringence due to
the ovalization of a nanofiber under strong bending, known in mechanical
engineering as the Brazier effect.
