1. A depth detection system that illuminates a scene with infrared radiation in order to obtain depth images of the scene based on reflections of the infrared radiation that are within a narrow infrared band, comprising: a depth image detector, comprising: an illumination source adapted to output collimated infrared illumination radiation sufficient to illuminate a scene including multiple objects; a circular polarization structure including a quarter wave plate positioned to receive collimated linearly polarized infrared illumination radiation having a first linear polarization orientation and to output a circularly polarized collimated infrared beam; a diffractive optics structure positioned adjacent to the circular polarization structure and adapted to receive the circularly polarized collimated infrared beam and adapted to output a pattern of circularly polarized infrared illumination radiation to the scene to illuminate the multiple objects; and a detector adapted to receive a reflection of the pattern from the multiple objects, the detector including an array of collector elements covered by a filter tuned to the infrared illumination radiation output by the illumination source; the circular polarization structure, the illumination source and the diffractive optics structure positioned relative to one another such that the circular polarization structure blocks from being incident on the illumination source, at least a portion of the infrared illumination radiation that, after being output by the illumination source, is scattered back from the diffractive optics structure towards the illumination source; and the circular polarization structure, the illumination source and the diffractive optics structure positioned relative to one another such that at least a portion of the infrared illumination radiation that is scattered back from the diffractive optics structure towards the illumination source, by the diffractive optics structure, is converted from circularly polarized infrared illumination radiation to linearly polarized infrared illumination radiation having a second linear polarization orientation that is orthogonal to the first linear polarization orientation.