  Graphene with its dispersion relation resembling that of photons offers ample
opportunities for applications in electron optics. The spacial variation of
carrier density by external gates can be used to create electron waveguides, in
analogy to optical fiber, with additional confinement of the carriers in
bipolar junctions leading to the formation of few transverse guiding modes. We
show that waveguides created by gating graphene with carbon nanotubes (CNTs)
allow obtaining sharp conductance plateaus, and propose applications in the
Aharonov-Bohm and two-path interferometers, and a pointlike source for
injection of carriers in graphene. Other applications can be extended to
Bernal-stacked or twisted bilayer graphene or two-dimensional electron gas.
Thanks to their versatility, CNT-induced waveguides open various possibilities
for electron manipulation in graphene-based devices.
