Orbital angular momentum filter based on multiple-beam interference

By virtue of multiple-beam interference, periodic structures such as photonic or phononic crystals can be used to separate an incident polychromatic light or acoustic beams, respectively, into their constituent frequency components. In addition, it is widely acknowledged that a light beam that is carrying orbital angular momentum (OAM) also has a spatial angular frequency in the azimuthal zone. Here we demonstrate that multiple-beam interference in the azimuthal zone can be used to modulate the transmission of the OAM state and; can thus serve as an OAM filter. The 2D transmission spectrum is analyzed and the mode resolution is discussed in detail. We anticipate that this OAM filter will be promising for use in applications such as optical switches, mode de-multiplexing in mode-division multiplexing communications and single-photon discrimination when using linear optical elements.