Integrated Waveguide-Type Red-Green-Blue Beam Combiners For Compact Projection-Type Displays

We studied the red-green-blue combiners with optical waveguides to obtain compact projection-type displays. Three combiners based on whispering-gallery mode, multi-mode interference and directional-coupler were designed. In these combiners, we concluded that the combiner based on the directional-coupler is the best candidate, giving 96% efficiency and the size of 0.06x6 mm.