  Vortex fiber nulling is a method for spectroscopically characterizing
exoplanets at small angular separations, $\lesssim\lambda/D$, from their host
star. The starlight is suppressed by creating an optical vortex in the system
point spread function, which prevents the stellar field from coupling into the
fundamental mode of a single-mode optical fiber. Light from the planet, on the
other hand, couples into the fiber and is routed to a spectrograph. Using a
prototype vortex fiber nuller (VFN) designed for monochromatic light, we
demonstrate coupling fractions of $6\times10^{-5}$ and $>0.1$ for the star and
planet, respectively.
