  We present an experimental study of higher-dimensional quantum key
distribution protocols based on mutually unbiased bases, implemented by means
of photons carrying orbital angular momentum. We perform (d+1) mutually
unbiased measurements in a classical prepare and measure scheme and on a pair
of entangled photons for dimensions ranging from d = 2 to 5. In our analysis,
we pay attention to the detection efficiency and photon pair creation
probability. As security measures, we determine from experimental data the
average error rate, the mutual information shared between the sender and
receiver and the secret key generation rate per photon. We demonstrate that
increasing the dimension leads to an increased information capacity as well as
higher key generation rates per photon up to a dimension of d = 4.
