  There have been some significant advances in optical-fiber multimode
communications. And important effort in on-chip communication has also been
recently reported for realizing mode-division multiplexing (MDM). Because of
the difficulty in lack of mode converter which can freely perform mode
converting function among different waveguide modes, flexible on-chip
mode-division switching communication has been rarely reported. Here we show
the first demonstration of mode converter which can convert an arbitrary
waveguide mode into any other modes with the help of phase tuning. With that
mode converter, two flexible on-chip mode-division switching architectures are
proposed. That architecture is compatible with wavelength-division multiplexing
(WDM) and can enable further scaling of the on-chip communication bandwidth.
Our demonstration suggests great potential of mode-divisional switching in the
vision of fully flexible, dense, on-chip optical networks.
