  The prospect of rendering objects invisible has intrigued researchers for
centuries. Transformation optics based invisibility cloak design is now
bringing this goal from science fictions to reality and has already been
demonstrated experimentally in microwave and optical frequencies. However, the
majority of the invisibility cloaks reported so far have a spatially varying
refractive index which requires complicated design processes. Besides, the size
of the hidden object is usually small relative to that of the cloak device.
Here we report the experimental realization of a homogenous invisibility cloak
with a uniform silicon grating structure. The design strategy eliminates the
need for spatial variation of the material index, and in terms of size it
allows for a very large obstacle/cloak ratio. A broadband invisibility behavior
has been verified at near-infrared frequencies, opening up new oppotunities for
using uniform layered medium to realize invisibility at any frequency ranges,
where high-quality dielectrics are available.
