Augmented Reality (AR) and Mixed Reality (MR) glasses stand as pivotal technological advancements in contemporary society. However, maintaining a compact and lightweight design while ensuring high-quality image viewing remains a persistent challenge. Researchers endeavor to overcome the intricate optical hurdles associated with these glasses. They suggest that waveguides incorporating two in- and out-coupling Volume Holographic Optical Elements (VHOEs) has surfaced as a promising approach, addressing these requirements and providing high see-through transmittance due to Bragg selectivity. Nonetheless, in the case of a full-color VHOE-based waveguide, the crosstalk between the RGB gratings of three primary colors within a waveguide results in the ghost images that diminish image quality. In this paper, we propose a method to eliminate ghost images and offer precise simulations aligned with experimental observations.
In this paper, we will discuss about the color performance and image quality of the Volume-Holographic-Optical-Element (VHOE)-based AR devices using two different type of volume holograms: transmission or reflection-type VHOEs. The simulation results show that color distortion occurring in these two types of VHOE-based AR devices are quite different and resulting from different characteristics of Bragg diffraction from those VHOEs. The reflective VHOE-based AR devices show better overall performance in terms of color, field of view and image quality.
In this paper, we introduce an approach—multiplexing gratings plus drive signal management scheme implemented on a micro-display device within an optical engine—to precisely adjust the color uniformity of an Augmented Reality (AR) eyewear display. This display is based on Volume Holographic Optical Elements (VHOEs) and a waveguide. Our method simplifies the complexity of multiplexing, requiring only a single optical waveguide and three RGB gratings for primary colors to achieve a full-color eyewear display with an expansive horizontal field of view (FOV) of nearly 30° and less than 3% ΔELab color non-uniformity.
In this paper, we present theoretic modelling of color breaking in a holographic-optical-element based Augmented Reality (AR) display. We first build up a theoretic optical model of the AR display system using scalar diffraction method. The discussions about the design parameters of holographic optical elements (HOE) for Augmented Reality (AR) glasses, focusing on color uniformity as a function of the waveguide thickness are conducted. It can be used to evaluate the color breaking of a displayed white image from user’s point of view. The simulation results show that color breaking occurs due to the limitations of pupil size and image shifting caused by the extended eye-box. Moreover, the thickness of the waveguide also causes uneven color distribution. Our model can also provide a way to analyze the relationship between waveguide thickness and color uniformity. In addition, based on those results, we propose a color correction algorithm by applying a pre-compensation scheme to the R/G/B values of each display pixel. Results show light display colors can be better corrected in the wider region of user’s field of view. It demonstrates the feasibility of compensation of color breaking in a holographic-optical-element based AR display.
In this paper, we present a space division technique to multiplex communication channels in a regular step-index multimode fiber using holographic correlator. We consider a multimode fiber with a large diameter of core as highly scattering medium. Thus, the focusing laser spot at different position on the incident plane of the fiber excites different sets of modes, which gives a different speckle pattern at the output of the fiber. Hence, each focusing spot can be considered as a communication channel for data transmission. By combining the volume holographic techniques to form channel multi/demultiplexer in a transmission system, we demonstrate conceptually transmission of multichannel optical information by using a regular step-index multimode fiber for data transmission application.
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