Reconfigurable homodyne detector for vortex beams

We review the general properties of balanced optical homodyne detectors (BHD) that provide a physical implementation of the quantum field quadrature observable. Then, we discuss the particular case of a BHD designed to span a prescribed sub-space of vortex optical modes carrying orbital angular momentum. By properly tailoring the geometrical features of the local oscillator, mode matching with the signal to be detected is achieved guaranteeing a visibility around 97%. This performance has recently allowed the detection of continuous-variable entanglement between structured modes. Homodyning structured light may pave the way to its use in optical coherent communication and quantum communication protocols.