  We present numerical simulations and laboratory experiments on an
eight-octant phase-mask (EOPM) coronagraph. The numerical simulations suggest
that an achievable contrast for the EOPM coronagraph can be greatly improved as
compared to that of a four-quadrant phase-mask (FQPM) coronagraph for a
partially resolved star. On-sky transmission maps reveal that the EOPM
coronagraph has relatively high optical throughput, a small inner working angle
and large discovery space. We have manufactured an eight-segment phase mask
utilizing a nematic liquid-crystal device, which can be easily switched between
the FQPM and the EOPM modes. The laboratory experiments demonstrate that the
EOPM coronagraph has a better tolerance of the tip-tilt error than the FQPM
one. We also discuss feasibility of a fully achromatic and high-throughput EOPM
coronagraph utilizing a polarization interferometric technique.
