A device for optically detecting and distinguishing airborne liquid water droplets and ice crystals includes an illumination portion and a detection portion. The illumination portion outputs a circularly polarized illuminating beam. The detection portion receives circularly polarized backscattered light from moisture in the cloud, in response to the illuminating beam. The circularly polarized backscattered light is passed through a circular polarizer to convert it into linearly polarized backscattered light, which is split into two components. Each of the two components is optionally subject to further linear polarization to filter out any leakage-type orthogonal polarization. The two components are then optically detected and the resulting detection signals are used to calculate one or more parameters reflective of the presence or absence of airborne ice crystals and/or water droplets.