  While measuring the orbital angular momentum state of bright light beams can
be performed using imaging techniques, a full characterization at the
single-photon level is challenging. For applications to quantum optics and
quantum information science, such characterization is an essential capability.
Here, we present a setup to perform the quantum state tomography of photonic
qubits encoded in this degree of freedom. The method is based on a projective
technique using spatial mode projection via fork holograms and single-mode
fibers inserted into an interferometer. The alignment and calibration of the
device is detailed as well as the measurement sequence to reconstruct the
associated density matrix. Possible extensions to higher-dimensional spaces are
discussed.
