  Dense wavelength division multiplexing (DWDM) is one of the most successful
methods for enhancing data transmission rates in both classical and quantum
communication networks. Although signal multiplexing and demultiplexing are
equally important, traditional multiplexing and demultiplexing methods are
based on passive devices such as arrayed waveguides and fiber Bragg cascade
filters, which, although widely used in commercial devices, lack any active
tuning ability. In this work, we propose a signal demultiplexing method based
on sum frequency generation (SFG) with two significant features: first, any
signal from the common communication channel can be demultiplexed to a single
user by switching the pump wavelength; second, a cheap high-performance
detector can be used for signal detection. These two features were demonstrated
by demultiplexing multi-channel energy-time entanglement generated by a
micro-cavity silicon chip. High interference visibilities over three channels
after demultiplexing showed that entanglement was preserved and verified the
high performance of the demultiplexer, which will find wide application in
high-capacity quantum communication networks.
