  We demonstrate a 10Gb/s Graphene Phase Modulator (GPM) integrated in a
Mach-Zehnder interferometer configuration. This is a compact device, with a
phase-shifter length of only 300$\mu$m, and 35dB extinction ratio. The GPM has
modulation efficiency of 0.28Vcm, one order of magnitude higher compared to
state-of-the-art depletion p-n junction Si phase modulators. Our GPM operates
with 2V peak-to-peak driving voltage in a push-pull configuration, and it has
been tested in a binary transmission of a non-return-to-zero data stream over
50km single mode fibre. This device is the key building block for
graphene-based integrated photonics, enabling compact and energy efficient
hybrid Si-graphene modulators for telecom, datacom and other applications
