Ultrafast interfacing of electrical and optical signals
at the
nanoscale is highly desired for on-chip applications including optical
interconnects and data processing devices. Here, we report electrically
driven nanoscale optical sources based on metal–insulator–graphene
tunnel junctions (MIG-TJs), featuring waveguided output with broadband
spectral characteristics. Electrically driven inelastic tunneling
in a MIG-TJ, realized by integrating a silver nanowire with graphene,
provides broadband excitation of plasmonic modes in the junction with
propagation lengths of several micrometers (∼10 times larger
than that for metal–insulator–metal junctions), which
therefore propagate toward the junction edge with low loss and couple
to the nanowire waveguide with an efficiency of ∼70% (∼1000
times higher than that for metal–insulator–metal junctions).
Alternatively, lateral coupling of the MIG-TJ to a semiconductor nanowire
provides a platform for efficient outcoupling of electrically driven
plasmonic signals to low-loss photonic waveguides, showing potential
for applications at various integration levels.