Eyebox expansion of a lensless near-eye display using diverging spherical wave illumination and a multiplexed holographic optical element

• Published in: Optics and lasers in engineering 2024-10, Vol.181, p.108380, Article 108380
• Main Authors: Dashdavaa, Erkhembaatar, Erdenebat, Munkh-Uchral, Khuderchuluun, Anar, Darkhanbaatar, Nyamsuren, Kwon, Ki-Chul, Jeon, Seok-Hee, Kim, Nam
• Format: Article
• Language: English
• Subjects: Augmented reality; Computer-generated hologram; Holographic optical element; Near-eye display
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2024.108380

•We propose a design method to expand the eyebox size of lensless holographic near-eye-display (NED) system benefiting from the passive eyebox replication technique with the combinational use of the horizontally separated high-order diffractions of the SLM and holographic optical element (HOE) combiner.•When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be uniformly formed without the zero-order term under spherical wave illumination.•The proposed prototype system not only replicates the base eyebox size, also increases sufficient field of view (FOV) due to the benefit of the spherical divergence wave illumination of the SLM, breaking the trade-off relationship between the FOV and eyebox. We expand the eyebox size of a lensless holographic near-eye-display (NED) using passive eyebox replication technique that incorporates a spatial light modulator (SLM) and a holographic optical element (HOE). In holographic NEDs, the space-bandwidth product (SBP) of the SLM determines the exit pupil dimensions and corresponding eyebox size. The base eyebox size is replicated in the horizontal direction by using the horizontal high-order diffractions of an SLM under spherical wave illumination and a multiplexed HOE combiner. When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be uniformly formed without the zero-order term. When the eyebox size is expanded, the field-of-view (FOV) is not sacrificed; spherical divergence wave illumination alleviates the need for a tradeoff between FOV and eyebox size. The astigmatism introduced during HOE fabrication is counterbalanced by pre-correcting the target image using a computer-generated, holographic computation algorithm. The prototype system shows simple and effective, distortion-free eyebox expansion of a wide-angle, lensless, holographic NED.