Immersion-based holographic wave front printer setup for volume holographic retinal projection elements

The recording of computer-generated holographic optical elements (HOEs) via the concept of holographic wave front printing has been a topic of rising interest in many research groups over the last years. Especially for applications in augmented reality (AR), holographic wave front printing has the potential to realize HOEs with complex optical transformations and high diffraction efficiencies while maintaining excellent transmittance. Here, we present a novel immersion-based holographic wave front printer setup, which allows the recording of reflection volume holographic optical elements (vHOEs) in both on-axis and off-axis configurations. HOEs fabricated via our wave front printing process are made up of individual sub-holograms, so called Hogels. Each sub-hologram is recorded via two phase-only reflective spatial light modulators (SLMs). Large-area vHOEs are achieved by adjacent recording of multiple Hogels in a step-wise fashion. Our immersion-based holographic printer setup ensures a high numerical aperture for the recording configuration, that is directly linked to a wide angular range in which recorded wave fronts can be replayed in air configuration. As a possible AR application, we demonstrate the recording of a holographic combiner for retinal projection. A single eye box is projected in the user's field of view (FOV) by means of a scanned laser projector source. Each Hogel of the holographic combiner performs an individual wave front transformation of large off-axis to on-axis angles, which contributes to the global holographic transfer function of the vHOE. Haze and clarity analysis of the recorded vHOE confirm high transmittance, which is crucial for AR applications.