  Integrated photonic network-on-chip (NoC) fabrics can provide multiple
terabits per second (Tbps) bandwidth for high-performance computing servers
supporting the latest artificial intelligence. To maximize the utility of the
photonic hardware, these optical networks can multiplex data streams in
multi-dimensional channels encoded in optical wavelengths, modes, and
polarization states. A generic photonic platform that can be reconfigured to
implement functionalities in those dimensions is highly desirable to streamline
the design and manufacturing of integrated photonic networks. Here, we
demonstrate a multi-functional photonic device using phase-change material
Sb2Se3 that can be reconfigured from a wavelength-division demultiplexer to a
mode-division demultiplexer. The reconfiguration is achieved by direct laser
writing of phase patterns optimized with the inverse design technique. The
demonstrated programmable phase-change photonic devices hold immense promise
for a wide range of photonic applications requiring adaptable functionalities,
including on-chip and in-package optical interconnects, optical signal
processing, photonic tensor cores, and future optical computing for artificial
intelligence.
