A monolithic interferometer for high-sensitive strictly-local detection of orbital angular momentum states of light

We propose an innovative monolithic interferometer to distinguish the topological charge of radiation carrying orbital angular momentum. Remarkably, our method requires to access only a small portion of the entire wavefront. The proposed scheme relies on a monolithic birefringent crystal, and as such it is intrinsically stable and does not require any feedback or thermal drift compensation. An experimental setup has been realized to prove the effectiveness of the proposed method down to the photon counting regime.