  The ability to perfectly guide surface electromagnetic waves around
ultra-sharp corners without back-scattering and radiation is in great demand
for various photonic and plasmonic applications. This is fundamentally
difficult to realize because of the dramatic momentum mismatch and wave nature
of radiation at the sharp corners. Here we experimentally demonstrate that a
simple photonic structure, a periodic square array of metallic cylinders
standing on a metal surface, can behaves as a surface-wave photonic crystal
with complete photonic band gap to overcome this bottleneck simply. A
line-defect waveguide can support and guide surface waves around ultra-sharp
corners without perceptible radiation and reflection, achieving almost perfect
transmission efficiency in a broad frequency range. We also demonstrate an
ideal T-shaped splitter to split input surface waves equally into two arms and
a square radiation-suppressed plasmonic open resonator with high quality
factors by simply inducing line-defects in this fully open surface-wave
photonic crystal.
