251 research outputs found
높은 공간 대역폭을 위한 복소 진폭 이미징 및 디스플레이 시스템
학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2021. 2. 이병호.빛을 파동으로 이해하면 간섭과 회절을 포함한 다양한 광학 현상을 해석 할 수 있다. 미래 기술이라 불리는 홀로그램, 3차원 이미징 및 3차원 디스플레이 시스템들은 파동의 복소진폭을 이해하고 변조함으로써 구현될 수 있다. 현존하는 광공학 장치를 넘어서는 파동 광학에 기반한 광공학 장치들을 상용화 및 발전시키기 위해 많은 연구가 진행되어왔지만, 지금껏 구현된 장치들은 공간 대역폭 (space-bandwidth product)의 제한으로 인해 그 성능이 대중의 기대에 부합하기 어려움을 겪고있다.
본 논문은 복소 진폭 이미징 및 디스플레이 시스템에서 공간 대역폭을 향상 시키는 방법을 제안한다. 복소 진폭 변조 시스템의 성능은 광학 시스템의 정보량을 나타내는 공간 대역폭에 의해 제한된다. 이 공간 대역폭을 향상시키기 위하여 저자는 다양한 다중화 기술을 적용하며, 동시에 다중화된 정보를 분리하는 알고리즘과 장치를 고안한다. 첫번째로 디지털 홀로그래피 기술에 공간 주파수를 다중화해 대역폭을 효율적으로 활용하는 방법을 고안하여 획득된 홀로그램의 촬영 영역을 증가시킨다. 두번째로, 단일 촬영 푸리에 타이코그래피 (single-shot Fourier ptychography) 기술에서는 광 조사 다중화를 사용하여 이미지 센서에 기록되는 정보의 양을 확장시킨다. 다중화 된 정보를 분해하고 복소 진폭을 획득하기 위하여 새로운 광학 시스템과 전산 알고리즘을 고안하여 해상도가 향상된 복소 진폭을 획득한다. 세번째로, 저자는 홀로그램 디스플레이에 조명 다중화 및 시분할 기술을 적용한다. 다중화 된 정보는 인간의 인지적 시간 대역폭과 제안된 시스템의 공간 필터링의 결합으로 분해된다. 구현된 홀로그래픽 디스플레이는 공간 대역폭이 확장되어 더 넓은 시야각에 삼차원 홀로그램을 제공한다.
본 논문은 작은 공간대역폭이라는 공통된 문제를 공유하는 이미징 및 디스플레이 분야의 발전에 기여할 것으로 기대된다. 저자는 본 연구에서 제안된 방법이 다양한 복소 진폭 변조 시스템의 성능 향상에 영감을 주며, 나아가 삼차원 계측, 홀로그래피, 가상 및 증강현실을 포함한 다양한 미래 산업에 발전에 기여할 수 있기를 기대한다.Understanding light as a wave makes it possible to interpret a variety of phenomena, including interference and diffraction. By modulating the complex amplitude of the wave, hologram, three-dimensional imaging, and three-dimensional display system, called future technologies, can be implemented that surpass the currently commercialized optical engineering devices. Although a lot of research has been conducted to develop and commercialize the wave optical system, state-of-the-art devices are still far from the performance expected by the public due to the limited space-bandwidth product (SBP).
This dissertation presents the studies on high SBP for complex amplitude imaging and display systems. The performance of a complex amplitude modulating system is limited by the SBP, which represents the amount of information in the optical system. To improve the SBP of the complex amplitude in a limited amount of information, the author applies various multiplexing techniques suitable for the implemented system. In practice, the spatial frequency multiplexed digital holography is devised by efficiently allocating frequency bandwidth with dual-wavelength light sources. The author also applies illumination multiplexing to the single-shot Fourier ptychography to expand the amount of information recorded in the image sensor. Computational reconstruction algorithm combined with novel optical design allows the acquired multiplexed information to be decomposed in the imaging system, leading to improvement of size of the image or resolution. Furthermore, the author applied illumination multiplexing and temporal multiplexing techniques to holographic displays. The multiplexed information is decomposed by a combination of human perceptual temporal bandwidth and spatial filtering. The SBP enhanced holographic display is implemented, providing a more wide viewing angle.
It is expected that this thesis will contribute to the development of the imaging and display fields, which share a common problem of small SBP. The author hopes that the proposed methods will inspire various researchers to approach the implementation of complex amplitude modulating systems, and various future industries, including 3-D inspection, holography, virtual reality, and augmented reality will be realized with high-performance.Abstract i
Contents iii
List of Tables vi
List of Figures vii
1 Introduction 1
1.1 Complex Amplitude of Wave 1
1.2 Complex Amplitude Optical System 3
1.3 Motivation and Purpose of the Dissertation 5
1.4 Scope and Organization 8
2 Space-Bandwidth Product 10
2.1 Overview of Space-Bandwidth Product 10
2.2 Space-Bandwidth Product of Complex Amplitude Imaging Systems 11
2.3 Space-Bandwidth Product of Complex Amplitude Display Systems 13
3 Double Size Complex Amplitude Imaging via Digital Holography 15
3.1 Introduction 15
3.1.1 Digital Holography 16
3.1.2 Frequency Multiplexed Digital Holography 22
3.1.3 Adaptation of Diffractive Grating for Simple Interferometer 24
3.2 Principle 26
3.2.1 Single Diffraction Grating Off-Axis Digital Holography 26
3.2.2 Double Size Implementation with Multiplexed Illumination 29
3.3 Implementation 32
3.4 Experimental Results 34
3.4.1 Resolution Assessment 34
3.4.2 Imaging Result 36
3.4.3 Quantitative 3-D Measurement 38
3.5 Conclusion 42
4 High-Resolution Complex Amplitude Imaging via Fourier Ptychographic Microscopy 43
4.1 Introduction 43
4.1.1 Phase Retrieval 45
4.1.2 Fourier Ptychographic Microscopy 47
4.2 Principle 52
4.2.1 Imaging System for Single-Shot Fourier Ptychographic Microscopy 52
4.2.2 Multiplexed Illumination 55
4.2.3 Reconstruction Algorithm 58
4.3 Implementation 60
4.3.1 Numerical Simulation 60
4.3.2 System Design 64
4.4 Results and Assessment 65
4.4.1 Resolution 65
4.4.2 Phase Retrieval of Biological Specimen 68
4.5 Discussion 71
4.6 Conclusion 73
5 Viewing Angle Enhancement for Holographic Display 74
5.1 Introduction 74
5.1.1 Complex Amplitude Representation 76
5.1.2 DMD Holographic Displays 79
5.2 Principle 81
5.2.1 Structured Illumination 81
5.2.2 TM with Array System 83
5.2.3 Time Domain Design 84
5.3 Implementation 85
5.3.1 Hardware Design 85
5.3.2 Frequency Domain Design 85
5.3.3 Aberration Correction 87
5.4 Results 88
5.5 Discussion 92
5.5.1 Speckle 92
5.5.2 Applications for Near-eye Displays 94
5.6 Conclusion 99
6 Conclusion 100
Appendix 116
Abstract (In Korean) 117Docto
Roadmap on holography
From its inception holography has proven an extremely productive and attractive area of research. While specific technical applications give rise to 'hot topics', and three-dimensional (3D) visualisation comes in and out of fashion, the core principals involved continue to lead to exciting innovations in a wide range of areas. We humbly submit that it is impossible, in any journal document of this type, to fully reflect current and potential activity; however, our valiant contributors have produced a series of documents that go no small way to neatly capture progress across a wide range of core activities. As editors we have attempted to spread our net wide in order to illustrate the breadth of international activity. In relation to this we believe we have been at least partially successful.This work was supported by Ministerio de Economía, Industria y Competitividad (Spain) under projects FIS2017-82919-R (MINECO/AEI/FEDER, UE) and FIS2015-66570-P (MINECO/FEDER), and by Generalitat Valenciana (Spain) under project PROMETEO II/2015/015
Roadmap on optical security
Postprint (author's final draft
Coherent and Holographic Imaging Methods for Immersive Near-Eye Displays
Lähinäytöt on suunniteltu tarjoamaan realistisia kolmiulotteisia katselukokemuksia, joille on merkittävää tarvetta esimerkiksi työkoneiden etäkäytössä ja 3D-suunnittelussa. Nykyaikaiset lähinäytöt tuottavat kuitenkin edelleen ristiriitaisia visuaalisia vihjeitä, jotka heikentävät immersiivistä kokemusta ja haittaavat niiden miellyttävää käyttöä. Merkittävänä ratkaisuvaihtoehtona pidetään koherentin valon, kuten laservalon, käyttöä näytön valaistukseen, millä voidaan korjata nykyisten lähinäyttöjen puutteita. Erityisesti koherentti valaistus mahdollistaa holografisen kuvantamisen, jota käyttävät holografiset näytöt voivat tarkasti jäljitellä kolmiulotteisten mallien todellisia valoaaltoja. Koherentin valon käyttäminen näyttöjen valaisemiseen aiheuttaa kuitenkin huomiota vaativaa korkean kontrastin häiriötä pilkkukuvioiden muodossa. Lisäksi holografisten näyttöjen laskentamenetelmät ovat laskennallisesti vaativia ja asettavat uusia haasteita analyysin, pilkkuhäiriön ja valon mallintamisen suhteen.
Tässä väitöskirjassa tutkitaan laskennallisia menetelmiä lähinäytöille koherentissa kuvantamisjärjestelmässä käyttäen signaalinkäsittelyä, koneoppimista sekä geometrista (säde) ja fysikaalista (aalto) optiikan mallintamista. Työn ensimmäisessä osassa keskitytään holografisten kuvantamismuotojen analysointiin sekä kehitetään hologrammien laskennallisia menetelmiä. Holografian korkeiden laskentavaatimusten ratkaisemiseksi otamme käyttöön holografiset stereogrammit holografisen datan likimääräisenä esitysmuotona. Tarkastelemme kyseisen esitysmuodon visuaalista oikeellisuutta kehittämällä analyysikehyksen holografisen stereogrammin tarjoamien visuaalisten vihjeiden tarkkuudelle akkommodaatiota varten suhteessa sen suunnitteluparametreihin. Lisäksi ehdotamme signaalinkäsittelyratkaisua pilkkuhäiriön vähentämiseksi, ratkaistaksemme nykyisten menetelmien valon mallintamiseen liittyvät visuaalisia artefakteja aiheuttavat ongelmat. Kehitämme myös uudenlaisen holografisen kuvantamismenetelmän, jolla voidaan mallintaa tarkasti valon käyttäytymistä haastavissa olosuhteissa, kuten peiliheijastuksissa.
Väitöskirjan toisessa osassa lähestytään koherentin näyttökuvantamisen laskennallista taakkaa koneoppimisen avulla. Kehitämme koherentin akkommodaatioinvariantin lähinäytön suunnittelukehyksen, jossa optimoidaan yhtäaikaisesti näytön staattista optiikka ja näytön kuvan esikäsittelyverkkoa. Lopuksi nopeutamme ehdottamaamme uutta holografista kuvantamismenetelmää koneoppimisen avulla reaaliaikaisia sovelluksia varten. Kyseiseen ratkaisuun sisältyy myös tehokkaan menettelyn kehittäminen funktionaalisten satunnais-3D-ympäristöjen tuottamiseksi. Kehittämämme menetelmä mahdollistaa suurten synteettisten moninäkökulmaisten kuvien datasettien tuottamisen, joilla voidaan kouluttaa sopivia neuroverkkoja mallintamaan holografista kuvantamismenetelmäämme reaaliajassa.
Kaiken kaikkiaan tässä työssä kehitettyjen menetelmien osoitetaan olevan erittäin kilpailukykyisiä uusimpien koherentin valon lähinäyttöjen laskentamenetelmien kanssa. Työn tuloksena nähdään kaksi vaihtoehtoista lähestymistapaa ristiriitaisten visuaalisten vihjeiden aiheuttamien nykyisten lähinäyttöongelmien ratkaisemiseksi joko staattisella tai dynaamisella optiikalla ja reaaliaikaiseen käyttöön soveltuvilla laskentamenetelmillä. Esitetyt tulokset ovat näin ollen tärkeitä seuraavan sukupolven immersiivisille lähinäytöille.Near-eye displays have been designed to provide realistic 3D viewing experience, strongly demanded in applications, such as remote machine operation, entertainment, and 3D design. However, contemporary near-eye displays still generate conflicting visual cues which degrade the immersive experience and hinders their comfortable use. Approaches using coherent, e.g., laser light for display illumination have been considered prominent for tackling the current near-eye display deficiencies. Coherent illumination enables holographic imaging whereas holographic displays are expected to accurately recreate the true light waves of a desired 3D scene. However, the use of coherent light for driving displays introduces additional high contrast noise in the form of speckle patterns, which has to be taken care of. Furthermore, imaging methods for holographic displays are computationally demanding and impose new challenges in analysis, speckle noise and light modelling.
This thesis examines computational methods for near-eye displays in the coherent imaging regime using signal processing, machine learning, and geometrical (ray) and physical (wave) optics modeling. In the first part of the thesis, we concentrate on analysis of holographic imaging modalities and develop corresponding computational methods. To tackle the high computational demands of holography, we adopt holographic stereograms as an approximative holographic data representation. We address the visual correctness of such representation by developing a framework for analyzing the accuracy of accommodation visual cues provided by a holographic stereogram in relation to its design parameters. Additionally, we propose a signal processing solution for speckle noise reduction to overcome existing issues in light modelling causing visual artefacts. We also develop a novel holographic imaging method to accurately model lighting effects in challenging conditions, such as mirror reflections.
In the second part of the thesis, we approach the computational complexity aspects of coherent display imaging through deep learning. We develop a coherent accommodation-invariant near-eye display framework to jointly optimize static display optics and a display image pre-processing network. Finally, we accelerate the corresponding novel holographic imaging method via deep learning aimed at real-time applications. This includes developing an efficient procedure for generating functional random 3D scenes for forming a large synthetic data set of multiperspective images, and training a neural network to approximate the holographic imaging method under the real-time processing constraints.
Altogether, the methods developed in this thesis are shown to be highly competitive with the state-of-the-art computational methods for coherent-light near-eye displays. The results of the work demonstrate two alternative approaches for resolving the existing near-eye display problems of conflicting visual cues using either static or dynamic optics and computational methods suitable for real-time use. The presented results are therefore instrumental for the next-generation immersive near-eye displays
Depolarized Holography with Polarization-multiplexing Metasurface
The evolution of computer-generated holography (CGH) algorithms has prompted
significant improvements in the performances of holographic displays.
Nonetheless, they start to encounter a limited degree of freedom in CGH
optimization and physical constraints stemming from the coherent nature of
holograms. To surpass the physical limitations, we consider polarization as a
new degree of freedom by utilizing a novel optical platform called metasurface.
Polarization-multiplexing metasurfaces enable incoherent-like behavior in
holographic displays due to the mutual incoherence of orthogonal polarization
states. We leverage this unique characteristic of a metasurface by integrating
it into a holographic display and exploiting polarization diversity to bring an
additional degree of freedom for CGH algorithms. To minimize the speckle noise
while maximizing the image quality, we devise a fully differentiable
optimization pipeline by taking into account the metasurface proxy model,
thereby jointly optimizing spatial light modulator phase patterns and geometric
parameters of metasurface nanostructures. We evaluate the metasurface-enabled
depolarized holography through simulations and experiments, demonstrating its
ability to reduce speckle noise and enhance image quality.Comment: 15 pages, 13 figures, to be published in SIGGRAPH Asia 202
Panoramic, large-screen, 3-D flight display system design
The report documents and summarizes the results of the required evaluations specified in the SOW and the design specifications for the selected display system hardware. Also included are the proposed development plan and schedule as well as the estimated rough order of magnitude (ROM) cost to design, fabricate, and demonstrate a flyable prototype research flight display system. The thrust of the effort was development of a complete understanding of the user/system requirements for a panoramic, collimated, 3-D flyable avionic display system and the translation of the requirements into an acceptable system design for fabrication and demonstration of a prototype display in the early 1997 time frame. Eleven display system design concepts were presented to NASA LaRC during the program, one of which was down-selected to a preferred display system concept. A set of preliminary display requirements was formulated. The state of the art in image source technology, 3-D methods, collimation methods, and interaction methods for a panoramic, 3-D flight display system were reviewed in depth and evaluated. Display technology improvements and risk reductions associated with maturity of the technologies for the preferred display system design concept were identified
근안 홀로그래픽 디스플레이의 개선에 관한 연구: 폼 팩터, 시약 각, 스페클 노이즈
학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2018. 2. 이병호.This dissertation presents solutions targeting on the three fundamental issues on near-eye holography: 1. Form factor, 2. Field of view (FOV), and 3. Speckle noise.
For the form factor reduction of the holographic display, a multifunctional holographic optical element (HOE) is developed to replace the beam splitter and the eyepiece lens of the conventional holographic display. As a result, it enables us to build a compact see-through holographic display for augmented reality (AR). The feasibility of using HOE in the holographic display is verified by analyzing some optical characteristics of the HOE, based on the Kogelniks coupled-wave theory. In addition, a compensation method is introduced to compensate the wavefront aberration caused by use of the HOE.
To build a wide FOV holographic head mounted display, I proposed two methods to increase the space bandwidth product (SBP) which can widen the FOV without losing eyebox size. In each optical path of +1st, 0th, -1st diffraction order of a spatial light modulator (SLM), I place a shutter synchronized with the SLM to display different holograms by temporally dividing the frames of the SLM. The second proposed method is called polarization selective holography which is a brand new hologram calculation and encoding method. In this work, an SLM can modulate waves in different modes through different states of wave retardation and polarization optical elements. Two sets of wave plates and polarizers with optimized states are placed in the path of +1st and -1st different diffraction orders of an SLM, so that the SLM reconstructs two different holograms via each path. As a result, the system achieves a two-fold increase in terms of SBP for a single SLM. Furthermore, a curved hologram can provide wider FOV comparing to a planar one, when they have the same SBP. A curved surface hologram can provide wider FOV. Thus, curved holographic display has a great potential to the near-eye holography. Since the curved surface SLM has not been developed yet, as an example, I also proposed a numerical method of spherical hologram computation of real objects in this chapter.
For the speckle noise issue, some analyses are carried out to compare the quality of holographic reconstruction images using different light source such as a light-emitting diode (LED) and a laser diode (LD). Both of them have pros and cons. The main advantage of use of the LED in the holographic display is it can reconstruct the holographic image with significantly less speckle noise compared to laser or LD. However, an inherent problem caused by use of the LED is that it is difficult to reconstruct images located far away from the SLM. This problem is mitigated using a magnifier optical system. As a result, I demonstrate an LED based near-eye holographic display system not only to reduce the speckle noise but also to provide sufficient expressible depth range.Chapter 1 Introduction 1
1.1 Overview of near-eye displays 1
1.2 Motivation of this dissertation 7
1.3 Scope and organization 9
Chapter 2 Form factor reduction of near-eye holography using a multifunctional holographic optical element 11
2.1 Introduction of form factor issues in near-eye holographic display 11
2.2 Introduction of volume hologram 13
2.2.1 Diffraction efficiency: Coupled-wave theory 14
2.2.2 Condition to be met for using holographic optical element in holographic display 19
2.3 Multifunctional holographic optcal element fabrication and application 27
2.3.1 Design of mirror-lens holographic optical element 27
2.3.2 Fabrication of mirror-lens holographic optical element 30
2.3.3 System implementation and experimental results 33
2.4 Wavefront aberration compensation method for holographic optical element 37
2.5 Summary and discussion 44
Chapter 3 Field of view expansion of near-eye holographic display 45
3.1 Overview of field of view expansion for near-eyeholography 45
3.1.1 Investigation on constrains in expanding field of view for near-eye holography 45
3.1.2 Previous space bandwidth product enhancement methods for holographic display 50
3.2 Temporal multiplexing of high-order diffraction guided by holographic attenuating mirror 53
3.2.1 Design of holographic attenuating mirror 54
3.2.2 System imprelentation and expperiment results 60
3.3 Polarization selective holography 67
3.3.1 Principle of polarization selective holography 67
3.3.2 Amplitude combination map optimization using genetic algorithm 71
3.3.3 Simulation and experimental results 73
3.4 Synthesis of computer generated spherical hologram 76
3.4.1 Spatial spectral bandwidth of spherical hologram 76
3.4.2 Spherical hologram calculation of real objects 81
3.4.3 Simulation and experimental results 88
3.5 Summary and discussion 95
Chapter 4 Light source selection for near-eye holography 97
4.1 Coherence of light source 97
4.1.1 Temporal coherence 97
4.1.2 Spatial coherence 98
4.2 Image sharpness for holographic display 101
4.3 Ideal optical design for LED based near-eye holography 105
4.4 Summary and discussion 108
Chapter 5 Conclusion 109
Bibliography 111
Appendix 121Docto
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