  We experimentally demonstrate a quantum key distribution (QKD) protocol using
photon pairs entangled in orbit angular momentum (OAM). In our protocol, Alice
and Bob modulate their OAM states on each entangled pair with spatial light
modulators (SLMs), respectively. Alice uses a fixed phase hologram in her SLM,
while Bob designs $N$ different suitable phase holograms and uses them to
represent his $N$-based information in his SLM. With coincidences, Alice can
fully retrieve the key stream sent by Bob without information reconciliation or
privacy amplification. We report the experiment results with N=3 and the sector
states with OAM eigenmodes l=1 and l=-1. Our experiment shows that the
coincidence rates are in relatively distinct value regions for the three
different key elements. Alice could recover fully Bob's keys by the protocol.
Finally, we discuss the security of the protocol both form the light way and
against the general attacks.
