  Ultra-compact, densely integrated optical components manufactured on a
CMOS-foundry platform are highly desirable for optical information processing
and electronic-photonic co-integration. However, the large spatial extent of
evanescent waves arising from nanoscale confinement, ubiquitous in silicon
photonic devices, causes significant cross-talk and scattering loss. Here, we
demonstrate that anisotropic all-dielectric metamaterials open a new degree of
freedom in total internal reflection to shorten the decay length of evanescent
waves. We experimentally show the reduction of cross-talk by greater than 30
times and the bending loss by greater than 3 times in densely integrated,
ultra-compact photonic circuit blocks. Our prototype all-dielectric
metamaterial-waveguide achieves a low propagation loss of approximately 3.7
dB/cm, comparable to those of silicon strip waveguides. Our approach marks a
departure from interference-based confinement as in photonic crystals or slot
waveguides, which utilize nanoscale field enhancement. Its ability to suppress
evanescent waves without substantially increasing the propagation loss shall
pave the way for all-dielectric metamaterial-based dense integration.
