Modeling, design and optimization of computer-generated holograms with binary phases

L’hologramme généré par ordinateur (HGO) a été démontré à jouer un rôle important depuis son invention par Lohmann dans les années 1960 dans de nombreuses applications telles que l’ingénierie du front d'onde, l’éclairage structuré et l’affichage optique, etc. Dans le travail de thèse ci-présent, la modélisation, la conception et l’optimisation d’HGO avec des phases binaires sont étudiées. Nous avons examiné un système pratique de projection d’image avec certaines spécifications de travail, par exemple, une distance de travail de 40 cm, une profondeur de champ de 10 cm et un angle de diffraction de 53 degré pour une longueur d’onde de travail de 632 nm, et ensuite conçu et optimisé un hologramme de phase binaire en passant par une recherche directe binaire pour ce système d’image. L’hologramme a été fabriqué par la lithographie à faisceau d’électrons. Pour atteindre l’angle de diffraction requis, nous avons discuté de l’architecture optique dans le système de projection d’image holographique. L’HGO conçu et le système de projection d’image holographique ont été validés expérimentalement par reconstruction optique. Étant donné que les pixels finiront par se regrouper pour former des ouvertures polygonales en hologramme, qui peut être vu clairement dans le processus de recherche directe binaire, nous avons proposé une nouvelle approche pour la conception directe des ouvertures polygonales basée sur la disposition triangulaire en HGO de grande taille en pixels. La diffraction de l’ouverture a été calculée par la transformation analytique d’Abbe. L’image reconstruite peut être exprimée comme une addition cohérente de motifs de diffraction à partir de tous les bords droits d’orientations et de longueurs différentes. Une optimisation en deux étapes comprenant l’algorithme génétique avec la recherche locale de codage des phases binaires des ouvertures, suivie par la recherche directe de co-sommets flottants des ouvertures triangulaires élémentaires a été développée. Nous avons en outre proposé une disposition d’ouverture quadrilatérale, qui fournit plus de degrés de liberté et peut former des ouvertures polygonales plus diverses en hologrammes. L’algorithme génétique parallèle avec la recherche locale a été adopté dans une première étape pour assigner des phases binaires, et la recherche directe a ensuite été utilisée pour optimiser des emplacements de co-sommets d'ouvertures quadrilatérales lors de la deuxième étape. Trois schémas différents pour l'algorithme en deux étapes ont été discutés pour fournir des moyens flexibles afin d’équilibrer la performance de l’optimisation et la durée nécessaire.The computer-generated hologram (CGH) has been demonstrated to play an important role, since its invention by Lohmann in 1960s, in many applications such as wavefront engineering, structured illumination and optical display, etc. In this thesis, the modeling, design and optimization of CGH with binary phases are studied. We considered a practical projection image system with certain working specification, e.g. working distance of 40 cm, depth of field of 10 cm and a diffraction angle of 53 degree for 632 nm working wavelength, and then designed and optimized a binary-phase hologram by direct binary search for this image system. The hologram was fabricated by E-beam lithography. To achieve the required diffraction angle, we discussed the optical architecture in holographic projection image system. The designed CGH and holographic projection image system were validated experimentally by optical reconstruction. Since the pixels will eventually cluster to form polygonal apertures in hologram, which can be seen clearly during the process of direct binary search, we proposed a new approach to directly design polygonal apertures based on triangular layout in CGH of a large number of pixels. The diffraction of aperture was calculated by analytical Abbe transform. The reconstructed image can be expressed as a coherent addition of diffraction patterns from all the straight edges of different orientations and lengths. A two-step optimization including genetic algorithm with local search for encoding binary phases of apertures, followed by direct search for floating covertices of the elementary triangular apertures was developed. We further proposed a quadrilateral aperture layout, which provides more degrees of freedom and can form more diverse polygonal apertures in holograms. The parallel genetic algorithm with local search was adopted to assign binary phases in the first step, and direct search was then used to optimize of locations of covertices of quadrilateral apertures in the second step. Three different schemes for the two-step algorithm were discussed to provide flexible ways to balance the optimization performance and time cost.Résumé en espagno

Computer-Generated Holography for Areal Additive Manufacture

With a market of approximately $10B, additive manufacture (AM) is an exciting next-generation technology with the promise of significant environmental and societal impact. AM promises to help reduce emissions and waste during manufacture while improving sustainability. Widely used in applications from hip implants to jet engines, AM remains the domain of experts due to the material and thermal challenges encountered. AM in metals is dominated by Laser Powder Based Fusion (L-PBF). Powder is spread in layers 10s of microns thick and selectively melted by scanning a small laser spot heat source over the bed. Traditional AM systems have limited ability to manage or compensate for heat generated. The rapidly moving heat source spot results in high thermal cycling and is a major influence on residual stress and distortion. Mechanical limitations in the galvoscanner mean that over or under-heating is common and can lead to voids, boiling and spatter. The scale difference between the part size and the spot size means that predictive modelling is beyond the scope of even today’s best computing clusters. These factors have led to frequent inability to ensure part quality without physical prototyping and destructive testing. This thesis sets out initial research into creating a radically new AM process that uses computer-generated holography (CGH) to produce complex light patterns in a single pulse. Projecting power to the whole layer at once will mean that the thermal properties of the powders before and after writing can be factored into the processed hologram and part design. It will also significantly reduce thermal gradients and melt-pool instability. The fields of additive manufacture and computer-generated holography are introduced in Chapter 1. Chapters 2 and 3 then provide more detail on CGH and AM modelling respectively. The first deliverable, a reusable software package capable of generating holograms, is presented in Chapter 4. Algorithms developed for the project are introduced in Chapter 4.3. The first project demonstrator, an AM machine capable of printing in resins using holographic projection is discussed in Section 6.2. This shows performance comparable to modern 3D printing machines and highlights the applicability of computer-generated holography to areal processes. Section 6.3 then discusses the ongoing development of a metal powder demonstrator. As this PhD forms the first stage of a larger project, only preliminary work on the powder demonstrator is discussed. Chapter 7 then draws conclusions and outlines the way forward for future research. The thesis appendices then discuss an in-depth discussion of algorithm performances in Appendices A and B. Appendices C and D then discuss digressions into the implementation. Appendices E and F present a laser induced damage threshold (LIDT) measurement system developed. Finally, Appendices G and H provide more detail on the software developed and Appendix I gives links to additional project resources.EP/T008369/1; EP/L016567/1; EP/V055003/

홀로그래픽 프린터를 이용한 증강현실 디스플레이의 맞춤형 홀로그래픽 광학 소자 제작

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 이병호.This dissertation presents the studies on the design and fabrication method of a holographic optical element (HOE) for augmented reality (AR) near-eye display (NED) by using a holographic printing technique. The studies enable us to manufacture HOEs based on the digitalized design process and allow more freedom to design HOEs, beyond the conventional HOE manufacturing process. The manufactured HOE can play the role of the image combiner of the AR NED and can be designed precisely according to each users distinctive characteristics. The prototype of the HOE printer is presented and the structure is analyzed. The HOE printer can record a hogel with 1900 × 1900 pixels in 1 mm2 and can give complex wavefront information via using an amplitude SLM and sideband filtering technique. The author adopts an index-matching frame with a passive optical isolator, which consists of quarter waveplates and linear polarizers, to eliminate the internal reflection noise. With the HOE printer, a lens HOE with field of view (FOV) 50° is manufactured, and a holographic AR NED is implemented with the lens HOE. The experimental result shows the lens HOE and the HOE printer work properly as our purpose. Using the prototype HOE printer, the author proposes two types of novel AR NEDs. First, the author suggests a customized HOE for an eye-box extended holographic AR NED. The limitation of the conventional holographic AR NED is that the eye-box becomes very narrow when large FOV is implemented due to the limited spatial bandwidth product. By using the proposed HOE printer, the eye-box can be extended along with both horizontal and vertical directions without any mechanical scanning devices. Also, the position of the extended eye-box can be designed to fit with the movement of the eye pupil. This prevents the vignetting effect due to the eye-box mismatch. Second, the author presents a freeform mirror array (FMA) HOE and implement a retinal projection AR NED with the HOE. By using the FMA HOE, the holographic mirrors no longer block the sight of the observer. Also, the freeform phase function allows the FMA HOE to float the display to the desired location without any additional optics, such as a lens. In this way, a wide depth of field and extended eye-box retinal projection AR NED with a compact form factor is implemented. It is expected that this dissertation can help to develop a customized AR NED based on the customers needs. Furthermore, it is believed that this work can show new possibilities for research on the design and fabrication of HOEs.본 박사학위 논문에서는 근안 증강현실 디스플레이의 홀로그래픽 영상 결합 소자를 홀로그래픽 프린팅 기술을 이용하여 설계 및 제작하는 방법에 대하여 논한다. 이를 통하여 기존의 아날로그 방법에 의존한 홀로그래픽 광학 소자 제작 기법을 디지털화 할 수 있다. 또한 홀로그래픽 광학 소자의 설계 자유도가 증가하여 사용자 특징에 따른 근안 증강현실 디스플레이의 맞춤형 영상 결합 소자를 제작할 수 있다. 이 박사학위 논문에서는 홀로그래픽 광학 소자 프린터의 프로토타입을 제작 및 소개한다. 해당 프로토타입은 1 mm2의 면적 안에 1900 × 1900 복소 광파 정보를 표현 할 수 있다. 광파의 복소 변조를 위하여 진폭 변조 공간광변조를 이용한 sideband filtering 기법이 사용된다. 또한 굴절률이 보상된 프레임에 1/4 파장판 및 선형 편광자를 이용한 수동 광분리소자를 적용하여 홀로그래픽 광학 소자를 기록 할 때 발생하는 내부 반사 노이즈를 효과적으로 제거할 수 있다. 이와 같은 홀로그래픽 프린터의 프로토타입이 의도한 대로 제작되었음을 검증하기 위하여 홀로그래픽 광학 소자 렌즈를 제작 및, 해당 홀로그래픽 광학 소자 렌즈가 근안 홀로그래픽 증강현실 디스플레이의 영상 결합 소자로 사용될 수 있음을 보인다. 제작된 홀로그래픽 광학 소자 프린터를 이용하여 두 가지의 새로운 근안 증강현실 디스플레이를 제안한다. 첫 번째는 시청영역이 증가한 근안 홀로그래픽 증강현실 디스플레이로, 공간대역폭에 의하여 제한된 시청 영역을 수직 및 수평 방향으로 동시에 확장할 수 있다. 또한 확장된 시청 영역은 사용자의 안구 길이 및 회전 각도에 맞춰 설계되어 시청영역 불일치로 인한 비네팅 등의 이미지 왜곡을 최소화한다. 마지막으로 망막투사 형태의 근안 증강현실 디스플레이에 사용될 수 있는 프리폼 거울 어레이 홀로그래픽 광학 소자를 제안한다. 이를 이용하여, 기존 거울 어레이 기반의 망막투사 디스플레이의 문제점 중 하나인 거울이 시야를 가리는 문제를 해결한다. 또한 홀로그래픽 거울 배열에 위상 변조 패턴을 기록하여 추가적인 렌즈 등의 광학계 없이 원하는 깊이에 디스플레이 평면을 띄울 수 있게 된다. 이를 이용하여 작은 폼팩터의 넓은 깊이 표현 범위를 지니는 망막투사형 근안 증강현실 디스플레이를 구현한다. 본 박사학위 논문의 결과는 사용자의 필요에 기반한 맞춤형 근안 증강현실 디스플레이의 개발에 도움이 될 것으로 기대된다. 나아가, 본 연구는 홀로그래픽 광학 소자의 설계와 제작에 관한 연구의 새로운 가능성을 보여줄 것으로 기대된다.1 Introduction 1 1.1 Image combiners of augmented reality near-eye display 1 1.2 Motivation and purpose of this dissertation 8 1.3 Scope and organization 10 2 Holographic optical element printer 12 2.1 Introduction 12 2.2 Overview of the prototype of holographic optical element printer 16 2.3 Analysis of the signal path 21 2.4 Considerations in designing an HOE 27 2.5 Removal of the internal reflection noise using passive optical isolator 32 2.6 Manufacturing customized lens holographic optical element 37 2.7 Discussion 41 2.7.1 HOE printer to modulate both signal and reference beams 41 2.7.2 The term "hogel" used in this dissertation 41 2.8 Summary 44 3 Holographically customized optical combiner for eye-box extended near-eye display 45 3.1 Introduction 45 3.2 Proposed method and its implementation 51 3.3 Implemented prototype 57 3.4 Experiments and results 61 3.5 Discussion 63 3.5.1 Vignetting effect from mismatched pupil position along axial direction 63 3.5.2 Diffraction efficiency simulation according to incident angle 65 3.6 Summary 67 4 Holographically printed freeform mirror array for augmented reality near-eye display 68 4.1 Introduction 68 4.2 Retinal projection NED based on small aperture array 70 4.3 Proposed method 72 4.4 Design method of FMA HOE 75 4.4.1 Depth of field analysis 75 4.4.2 The size of the mirror 77 4.4.3 The distance between the mirrors 79 4.5 Experiments and results 82 4.6 Discussion 86 4.6.1 Eye-box of the system via the angular selectivity of the HOE 86 4.7 Summary 89 5 Conclusion 90 Appendix 104 Abstract (In Korean) 105Docto

HoloBeam: Paper-Thin Near-Eye Displays

An emerging alternative to conventional Augmented Reality (AR) glasses designs, Beaming displays promise slim AR glasses free from challenging design trade-offs, including battery-related limits or computational budget-related issues. These beaming displays remove active components such as batteries and electronics from AR glasses and move them to a projector that projects images to a user from a distance (1-2 meters), where users wear only passive optical eyepieces. However, earlier implementations of these displays delivered poor resolutions (7 cycles per degree) without any optical focus cues and were introduced with a bulky form-factor eyepiece (50 mm thick). This paper introduces a new milestone for beaming displays, which we call HoloBeam. In this new design, a custom holographic projector populates a micro-volume located at some distance (1-2 meters) with multiple planes of images. Users view magnified copies of these images from this small volume with the help of an eyepiece that is either a Holographic Optical Element (HOE) or a set of lenses. Our HoloBeam prototypes demonstrate the thinnest AR glasses to date with a submillimeter thickness (e.g., HOE film is only 120 um thick). In addition, HoloBeam prototypes demonstrate near retinal resolutions (24 cycles per degree) with a 70 degrees-wide field of view.Comment: 15 pages, 18 Figures, 1 Table, 1 Listin

Holographic video : design and implementation of a display system

Thesis (M.S.V.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1989.Includes bibliographical references (leaves 86-89).by Mary Lou Jepsen.M.S.V.S

Apparatus and Method for Focusing a Light Beam in a Three-Dimensional Recording Medium by a Dynamic Holographic Device

An apparatus is disclosed for reading and/or writing information or to from an optical recording medium having a plurality of information storage layers. The apparatus includes a dynamic holographic optical element configured to focus light on the optical recording medium. a control circuit arranged to supply a drive signal to the holographic optical element, and a storage device in communication with the control circuit and storing at least a first drive signal and a second drive signal. The holographic optical element focusses light on a first one of the plurality of information storage layers when driven by the first drive signal on a second one of the plurality of information storage layers when driven by the second drive signal. An optical switch is also disclosed for connecting at least one light source in a source array to at least one light receiver in a receiver array. The switch includes a dynamic holographic optical element configured to receive light from the source array and to transmit light to the receiver array, a control circuit arranged to supply a drive signal to the holographic optical element, and a storage device in communication with the control circuit and storing at least a first drive signal and a second drive signal. The holographic optical element connects a first light source in the source array to a first light receiver in the receiver array when driven by the first drive signal and the holographic optical element connects the first light source with the first light receiver and a second light receiver when driven by the second drive signal

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 structured light

Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.Peer ReviewedPostprint (published version

Three dimensional computational imaging with single-pixel detectors

Computational imaging with single-pixel detectors utilises spatial correlation of light to obtain images. A series of structured illumination is generated using a spatial light modulator to encode the spatial information of an object. The encoded object images are recorded as total intensities with no spatial information by a single-pixel detector. These intensities are then sent to correlate with their corresponding illumination structures to derive an image. This correlation imaging method was first recognised as a quantum imaging technique called ghost imaging (GI) in 1995. Quantum GI uses the spatial correlation of entangled photon pairs to form images and was later demonstrated also by using classical correlated light beams. In 2008, an adaptive classical GI system called computational GI which employed a spatial light modulator and a single-pixel detector was proposed. Since its proposal, this computational imaging technique received intensive interest for this potential application. The aim of the work in this thesis was to improve this new imaging technique into a more applicable stage. Our contribution mainly includes three aspects. First an advanced reconstruction algorithm called normalised ghost imaging was developed to improve the correlation efficiency. By normalising the object intensity with a reference beam, the reconstruction single-to-noise ratio can be increased, especially for a more transmissive object. In the second work, a computational imaging scheme adapted from computational GI was designed by using a digital light projector for structured illumination. Compared to a conventional computational GI system, the adaptive system improved the reconstruction efficiency significantly. And for the first time, correlation imaging using structured illumination and single-pixel detection was able to image a 3 dimensional reflective object with reasonable details. By using several single-pixel detectors, the system was able to retrieve the 3 dimensional profile of the object. In the last work, effort was devoted to increase the reconstruction speed of the single-pixel imaging technique, and a fast computational imaging system was built up to generate real-time single-pixel videos

Development of Holographic Phase Masks for Wavefront Shaping

This dissertation explores a new method for creating holographic phase masks (HPMs), which are phase transforming optical elements holographically recorded in photosensitive glass. This novel hologram recording method allows for the fast production of HPMs of any complexity, as opposed to the traditional multistep process, which includes the design and fabrication of a master phase mask operating in the UV region before the holographic recording step. We holographically recorded transmissive HPMs that are physically robust (they are recorded in a silicate glass volume), can handle tens of kilowatts of continuous wave (CW) laser power, are un-erasable, user defined, require no power to operate, can work over a wavelength band ranging from 350 to 2500 nm, and can modify the wavefront of narrow line or broad band coherent sources. The HPMs can be wavelength-tunable by angular adjustment over tens or even hundreds of nanometers. The HPMs incorporate the phase information in the bulk of a volume Bragg grating (VBG) resulting in only a single diffraction order and up to 100% diffraction efficiency. Recording in thick photosensitive medium also enables the multiplexing of HPMs in a single monolithic element. While these HPMs are physically overlapped in the space, they provide independent phase profiles, efficiencies, spectral and angular acceptances. Multiplexing HPMs allows splitting or combining of multiple beams while affecting their wavefronts individually. We also developed a new holographic phase mask of reflective-type. This device provides us the ability of recording RBGs with transversely shifted parts in the larger aperture which upon reconstruction will produce different phases to different parts of the diffracted beam. RBG\u27s diffraction spectrum possesses a very narrow bandwidth, and the holographic recording technique allows to multiplex multiple gratings into a single volume of PTR glass. If each of these Bragg wavelengths is assigned with a specific spatial mode, it can be achieved simultaneous spatial and spectral multiplexing. As a separate research topic, we look at how holographic optical elements (HOEs) can be used for improving the capabilities of the existing generation of head-up displays (HUDs), resulting in smaller, lighter units with a larger eye-box. Currently, surface relief gratings recorded in photosensitive polymers that are susceptible to the environmental conditions are used in HOE-based HUDs. This has an impact on their reliability and overall lifespan. We investigated a specific holographically recorded in the volume of photo-thermo-refractive glass transmissive gratings that generated multiple diffracted beams due to their operation in Raman-Nath regime. The Raman Nath gratings were successfully used to create an array of images because in augmented reality systems, this approach can be used to enhance the size of the exit pupil. These image splitting elements, due to the features of PTR glass, have a great resistance to temperature gradients, mechanical shocks, vibrations, and laser radiation