An optical combiner, configured for use in a mixed-reality display system that combines holographic and real-world images, includes an assembly of see-through waveguides that are arranged in a stack to provide full color holographic images from constituent RGB (red, green, and blue) color components received from a holographic image source. Each waveguide—one per RGB color component—includes an in-coupling DOE (diffractive optical element), an intermediate DOE, and an out-coupling DOE that are disposed on internal surfaces of the stacked waveguides in the optical combiner. Each of the out-coupling DOEs incorporates a diffractive lens functionality to render the out-coupled holographic images at a set depth on the mixed-reality display. In an illustrative non-limiting example, the out-coupling DOE may provide a half diopter of negative lens power to set the optical focus of the holographic images at 1.33 m.