  Graphene has shown great potentials for high-speed photodetection. Yet, the
responsivities of graphene-based high-speed photodetectors are commonly limited
by the weak effective absorption of atomically thin graphene. Here, we propose
and experimentally demonstrate a plasmonically enhanced waveguide-integrated
graphene photodetector. The device which combines a 6 micron long layer of
graphene with field-enhancing nano-sized metallic structures, demonstrates a
high external responsivity of 0.5 A/W and a fast photoresponse way beyond 110
GHz. The high efficiency and fast response of the device enables for the first
time 100 Gbit/s PAM-2 and 100 Gbit/s PAM-4 data reception with a graphene based
device. The results show the potential of graphene as a new technology for
highest-speed communication applications.
