Diffractive optical Elements based on subwavelength high-contrast Gratings

We report on novel concepts for reflective diffractive elements based on high-contrast gratings. To demonstrate the possibilities for such devices reflective cavity couplers with three output ports are investigated. A diffracting period is superposed to a highly reflective subwavelength grating in order to realize diffractive elements. This superposition can be realized with a periodic depth, fill factor or period modulation of the reflector. Further, to limit the total transmission of the device it is necessary to enhance its angular tolerance. We discuss different approaches in order to realize this increased reflectivity in broad range of the angular spectrum. The contribution focuses on the material combination silicon-silica, but the presented concepts also hold for other material combinations with large index contrast and even for monolithic silicon structures.