Optical Engineering of Holography and Occlusion in Augmented Reality for Enhanced Depth Cues and System Practicality = 홀로그래피 및 폐색 효과 광학 설계를 통한 증강현실의 깊이 인식과 실용성의 향상

국문 초록 (Abstract)

증강현실 디스플레이는 현실 환경에 가상의 이미지를 융합시켜주는 디스플레이로, 사용자는 현실과 가상이 어우러진 전에 없던 시청 경험을 느낄 수 있다. 이러한 독특한 특징 덕분에 정보디스플레이의 중요도가 높은 의료, 교육, 엔터테인먼트 분야에의 활용이 활발하게 연구되고 있다. 특히 인공지능의 발달과 더불어 인공지능과 소통하고 인공지능의 데이터를 시각화하기 가장 효율적인 디스플레이 형태로 각광받고 있다. 하지만 이렇게 증강현실을 위한 소프트웨어와 그 어플리케이션의 개발이 활발히 이루어지고 있는 반면에, 현실적이고 몰입감 있는 증강현실 하드웨어는 여전히 광학적 발전이 필요한 상태이다. 본 학위논문에서는, 기존 증강현실 하드웨어의 광학적인 한계점을 해소하기 위한 새로운 접근법을 소개하고 실험적으로 검증하여, 사실적이고 실용적인 증강현실 디스플레이를 위한 길을 제시한다. 이를 위해 증강현실 디스플레이를 (1) 가상 이미지를 생성하는 라이트 엔진, (2) 아이박스를 형성하고 증강현실 장면을 구현해주는 이미지 컴바이너, (3) 몰입감과 실용성 향상을 위한 추가적인 모듈 세가지의 핵심 파트로 분류하고, 각각의 파트에서 몰입감 있는 증강현실 경험을 위한 발전된 광학적 기술을 소개한다.

다국어 초록 (Multilingual Abstract)

Augmented reality (AR) displays have a unique concept that merge virtual scenes with real-world environments to coexist seamlessly. Recently, AR displays have gained increasing attention in areas where information visualization is critical such as medicine, education, and entertainment. With the rapid advancement of artificial intelligence (AI), AR display has also emerged as an effective device to interact and visualize AI-generated data. However, in contrast to the rapid progress in AR software and applications, optical hardware engineering still shows significant challenges in delivering realistic and practical AR experiences. This dissertation presents novel optical engineering techniques that alleviate the limitations of existing AR hardware toward the realization of more realistic and practical AR display systems. In particular, this dissertation focuses on the enhanced depth cue and system practicality of AR displays. The AR displays consist of three fundamental optical modules and functionalities: (1) Virtual image generation by the light engine, (2) eye-box and AR scene generation by the image combiner, and (3) supplementary functions to enhance immersive AR by additional modules. For each process, advanced optical engineering approaches are introduced to enhance depth perception and device usability.

목차 (Table of Contents)

• 1 Introduction 1
• 1.1 Fundamentals of augmented reality displays 1
• 1.2 Review of conventional optical hardware 5
• 1.3 Motivation of this dissertation 8
• 1.4 Scope and structure 11
• 2 Holographic light engine using light pipe for enhanced AR viewing comfort 13
• 2.1 Introduction 13
• 2.1.1 Holographic displays for AR 15
• 2.2 Wavefront transfer methods for light engine 17
• 2.2.1 Conventional methods 17
• 2.2.2 Modeling propagation within light pipe 20
• 2.2.3 Hologram rendering via light pipe model 25
• 2.3 Experimental results 26
• 2.3.1 Implementation 26
• 2.3.2 Holographic image results 29
• 2.3.3 AR scene results 30
• 2.4 Misalignment analysis and its compensation 32
• 2.5 Discussion 35
• 2.5.1 Advantages 35
• 2.5.2 Challenges and future works 38
• 2.6 Conclusion 41
• 3 Etendue expansion through sparse eye-box generation using lens array eyepiece 43
• 3.1 Introduction 43
• 3.1.1 Fundamentals of etendue and its expansion 45
• 3.2 Sparse eye-box for holographic displays 48
• 3.2.1 Sparse eye-box generation 48
• 3.2.2 Etendue expansion by lens array eyepiece 51
• 3.2.3 SLM phase profile optimization 54
• 3.2.4 Near-eye display construction 56
• 3.3 Analysis on sparse eye-box 56
• 3.3.1 Modulation transfer function analysis 57
• 3.3.2 Holographic image quality analysis 59
• 3.3.3 Brightness uniformity analysis 61
• 3.4 Experimental results 64
• 3.4.1 Implementation 64
• 3.4.2 Holographic image demonstrations 66
• 3.4.3 AR scene demonstrations 68
• 3.5 Discussion 70
• 3.5.1 Advantages 70
• 3.5.2 Challenges 70
• 3.5.3 Future Works 72
• 3.6 Conclusion 72
• 4 Advanced occlusion techniques for immersive AR 74
• 4.1 Introduction 74
• 4.1.1 4f system-based occlusion 76
• 4.2 Refined 4f system occlusion using lens arrays 76
• 4.3 Varifocal occlusion using lens arrays and focus tunable lenses 82
• 4.3.1 Varifocal occlusion using focus tunable lenses 82
• 4.3.2 Experimental results 84
• 4.4 Photochromic occlusion without screen-door effect 87
• 4.4.1 Screen-door effect of conventional occlusion 87
• 4.4.2 Photochromic mask 88
• 4.4.3 Experimental results 89
• 4.5 Discussion 95
• 4.5.1 Advantages 95
• 4.5.2 Challenges and future works 95
• 4.6 Conclusion 96
• 5 Conclusion 98
• Appendix 122
• 초 록 123