Separation of coherent and incoherent light by using optical vortex via spatial mode projection

We present a spatial light filter method which can distinguish light by its coherency. The unique orbital angular momentum and spiral phase front properties of the vortex beam generate a null intensity center area that can serve as a spatial window to filter out incoherent light. A spatial light modulator can be used to modulate the wavefront of the incident light beam. Thanks to diffraction, the spectra from the coherent and incoherent part are spatially separated at the backfocal plane of a lens. The coherent part forms a ring, and the incoherent part forms a spot in the null intensity center of the ring. This method offers a new perspective to enhance the signal-to-noise ratio in the field of applied optics, such as optical communication, and active remote sensing, such as light detection and ranging.