  On-chip nanophotonics serves as the foundation for the new generation of
information technology, but it is challenged by the diffraction limit of light.
With the capabilities of confining light into (deep) subwavelength volumes,
plasmonics makes it possible to dramatically miniaturize optical devices so as
to integrate them into silicon chips. Here we demonstrate that by cascading
nano-corrugation gratings with different periodicities on silver nanowires atop
silicon, different colors can be spatially separated and chronologically
released at different grating junctions. The released light frequency depends
on the grating arrangement and corrugation periodicities. Hence the nanowire
acts as a spectral splitter for sorting/demultiplexing photons at different
nano-scale positions with a ten-femtosecond-level interval. Such nanowires can
be constructed further into compact 2D networks or circuits. We believe that
this study provides a new and promising approach for realizing
spatiotemporal-sensitive spectral splitting and optical signal processing on
nanoscales, and for general integration of nanophotonics with microelectronics.
