  Vector modes are spatial modes that have spatially inhomogeneous states of
polarization, such as, radial and azimuthal polarization. They can produce
smaller spot sizes and stronger longitudinal polarization components upon
focusing. As a result, they are used for many applications, including optical
trapping and nanoscale imaging. In this work, vector modes are used to increase
the information capacity of free space optical communication via the method of
optical communication referred to as mode division multiplexing. A mode
(de)multiplexer for vector modes based on a liquid crystal technology referred
to as a q-plate is introduced. As a proof of principle, using the mode
(de)multiplexer four vector modes each carrying a 20 Gbit/s quadrature phase
shift keying signal on a single wavelength channel (~1550nm), comprising an
aggregate 80 Gbit/s, were transmitted ~1m over the lab table with <-16.4 dB
(<2%) mode crosstalk. Bit error rates for all vector modes were measured at the
forward error correction threshold with power penalties < 3.41dB.
