In this paper, we present a concept for speckle reduction using optical superposition instead of temporal superposition. The proposed speckle reduction method does not contain any mechanical movement nor time-multiplexing technique. Therefore, the system is stable and free from the frame rate degradation or additional computation load. In addition, the angle diversity method is adopted with the proposed method to intensify the speckle reduction. In order to apply the angle diversity method, the required minimum angle difference is analyzed theoretically. To realize the proposed speckle reduction concept, the system is implemented with practical optical components. The system includes an echelon, which is a stair-shaped glass and a static diffuser. The echelon is employed to decrease the spatial coherence of the incident beam. The static diffuser imposes the band-limited random phases on each of the split beams that have passed through the echelon. Also, the static diffuser is used to combine mutually incoherent split beams into a single speckle-reduced beam. The proposed speckle-reduced light source is applied to the holographic display to demonstrate the speckle reduction effect. Experimental results show that the speckle contrast of the reconstructed image is reduced by 55%.

We introduce an augmented reality near-eye display dubbed "Retinal 3D." Key features of the proposed display system are as follows: Focus cues are provided by generating the pupil-tracked light field that can be directly projected onto the retina. Generated focus cues are valid over a large depth range since laser beams are shaped for a large depth of field (DOF). Pupil-tracked light field generation significantly reduces the needed information/computation load. Also, it provides "dynamic eye-box" which can be a break-through that overcome the drawbacks of retinal projection-type displays. For implementation, we utilized a holographic optical element (HOE) as an image combiner, which allowed high transparency with a thin structure. Compared with current augmented reality displays, the proposed system shows competitive performances of a large field of view (FOV), high transparency, high contrast, high resolution, as well as focus cues in a large depth range. Two prototypes are presented along with experimental results and assessments. Analysis on the DOF of light rays and validity of focus cue generation are presented as well. Combination of pupil tracking and advanced near-eye display technique opens new possibilities of the future augmented reality.

We propose a see-through additive light field display as a novel type of compressive light field display. We utilize holographic optical elements (HOEs) as transparent additive layers. The HOE layers are almost free from diffraction unlike spatial light modulator layers, which makes this additive light field display more advantageous when modifying the number of layers, thickness, and pixel density compared with conventional compressive displays. Meanwhile, the additive light field display maintains advantages of compressive light field displays. The proposed additive light field display shows bright and full-color volumetric images in high definition. In addition, users can view real-world scenes beyond the displays. Hence, we expect that our method can contribute to the realization of augmented reality. Here, we describe implementation of a prototype additive light field display with two additive layers, evaluate the performance of transparent HOE layers, describe several results of display experiments, discuss the diffraction effect of spatial light modulators, and analyze the ability of the additive light field display to express uncorrelated light fields.