179 research outputs found
νΈκ΄ λ€μ€νλ₯Ό μ΄μ©νμ¬ ν₯μλ κΈ°λ₯μ μ 곡νλ λνκ΄ κΈ°λ°μ κ·Όμ λμ€νλ μ΄
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Όλ¬Έ (λ°μ¬) -- μμΈλνκ΅ λνμ : 곡과λν μ κΈ°Β·μ 보곡νλΆ, 2021. 2. μ΄λ³νΈ.This dissertation presents the studies on the optical design method that enhances the display performance of see-through waveguide-based near-eye displays (WNEDs) using the polarization multiplexing technique. The studies focus on the strategies to improve the crucial display performances without compromising a small form factor, the most attractive merit of the WNEDs. To achieve this goal, thin and lightweight polarization-dependent optical elements are devised and employed in the WNED structure. The polarization-dependent devices can allow multiple optical functions or optical paths depending on the polarization state of the input beam, which can break through the limitation of the waveguide system with the polarization multiplexing.
To realize the function-selective eyepiece for AR applications, the proposed devices should operate as an optically transparent window for the real scene while performing specific optical functions for the virtual image. The proposed devices are manufactured in a combination structure in which polarization-dependent optical elements are stacked. The total thickness of the stacked structure is about 1 mm, and it can be attached to the waveguide surface without conspicuously increasing the form factor of the optical system.
Using the proposed polarization-dependent devices, the author proposes three types of novel WNED systems with enhanced performance. First, the author suggests a compact WNED with dual focal planes. Conventional WNEDs have an inherent limitation that the focal plane of the virtual image is at an infinite distance because they extract a stream of collimated light at the out-coupler. By using the polarization-dependent eyepiece lens, an additional focal plane can be generated with the polarization multiplexing in addition to infinity depth. The proposed configuration can provide comfortable AR environments by alleviating visual fatigue caused by vergence-accommodation conflict. Second, the novel WNED configuration with extended field-of-view (FOV) is presented. In the WNEDs, the maximum allowable FOV is determined by the material properties of the diffraction optics and the substrate. By using the polarization-dependent steering combiner, the FOV can be extended up to two times, which can provide more immersive AR experiences. In addition, this dissertation demonstrates that the distortion for the real scene caused by the stacked structure cannot severely disturb the image quality, considering the acuity of human vision. Lastly, the author presents a retinal projection-based WNED with switchable viewpoints by simultaneously adopting the polarization-dependent lens and grating. The proposed system can convert the viewpoint according to the position of the eye pupil without mechanical movement. The polarization-dependent viewpoint switching can resolve the inherent problem of a narrow eyebox in retinal projection displays without employing the bulky optics for mechanical movement.
In conclusion, the dissertation presents the practical optical design and detailed analysis for enhanced WNED based on the polarization multiplexing technique through various simulations and experiments. The proposed approaches are expected to be utilized as an innovative solution for compact wearable displays.λ³Έ λ°μ¬νμ λ
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λ° μλ‘μ΄ κ°λ₯μ±μΌλ‘ μ μν μ μμ κ²μ΄λΌ κΈ°λλλ€.Abstract i
Contents iii
List of Tables vi
List of Figures vii
Chapter. 1 Introduction 1
1.1 Augmented reality near-eye display 1
1.2 Key performance parameters of near-eye displays 4
1.3 Basic scheme of waveguide-based near-eye displays 22
1.4 Motivation and purpose of this dissertation 33
1.5 Scope and organization 37
Chapter 2 Dual-focal waveguide-based near-eye display using polarization-dependent combiner lens 39
2.1 Introduction 39
2.2 Optical design for polarization-dependent combiner lens 42
2.2.1 Design and principle of polarization-dependent combiner lens 42
2.2.2 Prototype implementation 48
2.3 Waveguide-based augmented reality near-eye display with dual-focal plane using polarization-dependent combiner lens 51
2.3.1 Implementation of the prototype and experimental results 51
2.3.2 Performance analysis and discussion 57
2.4 Conclusion 69
Chapter 3 Extended-field-of-view waveguide-based near-eye display via polarization-dependent steering combiner 70
3.1 Introduction 70
3.2 Optical design for polarization-dependent steering combiner 73
3.2.1 Principle of polarization grating 73
3.2.2 Principle of polarization-dependent steering combiner 76
3.2.3 Analysis and verification experiment for real-scene distortion 77
3.3 Waveguide-based augmented reality near-eye display with extended-field-of-view 81
3.3.1 Field-of-view for volume grating based waveguide technique 81
3.3.2 Implementation of the prototype and experimental results 84
3.3.3 Performances analysis and discussion 87
3.4 Conclusion 92
Chapter 4 Viewpoint switchable retinal-projection-based near-eye display with waveguide configuration 93
4.1 Introduction 93
4.2 Polarization-dependent switchable eyebox 97
4.2.1 Optical devices for polarization-dependent switching of viewpoints 97
4.2.2 System configuration for proposed method 100
4.2.3 Design of waveguide and imaging combiner 105
4.3 Compact retinal projection-based near-eye display with switchable viewpoints via waveguide configuration 114
4.3.1 Implementation of the prototype and experimental results 114
4.3.2 Performance analysis and discussion 118
4.4 Conclusion 122
Chapter 5. Conclusion 123
Bibliography 127
Appendix 135Docto
Descending premotor target tracking systems in flying insects
The control of behaviour in all animals requires efficient transformation of sensory signals into the task-specific activation of muscles. Predation offers an advantageous model behaviour to study the computational organisation underlying sensorimotor control. Predators are optimised through diverse evolutionary arms races to outperform their prey in terms of sensorimotor coordination, leading to highly specialised anatomical adaptations and hunting behaviours, which are often innate and highly stereotyped. Predatory flying insects present an extreme example, performing complex visually-guided pursuits of small, often fast flying prey over extremely small timescales. Furthermore, this behaviour is controlled by a tiny nervous system, leading to pressure on neuronal organisation to be optimised for coding efficiency.
In dragonflies, a population of eight pairs of bilaterally symmetric Target Selective Descending Neurons (TSDNs) relay visual information about small moving objects from the brain to the thoracic motor centres. These neurons encode the movement of small moving objects across the dorsal fovea region of the eye which is fixated on prey during predatory pursuit, and are thought to constitute the commands necessary for actuating an interception flight path. TSDNs are characterised by their receptive fields, with responses of each TSDN type spatially confined to a specific portion of the dorsal fovea visual field and tuned to a specific direction of object motion. To date, little is known about the descending representations mediating target tracking in other insects. This dissertation presents a comparative report of descending neurons in a variety of flying insects. The results are organised into three chapters:
Chapter 3 identifies TSDNs in demoiselle damselflies and compares their response properties to those previously described in dragonflies. Demoiselle TSDNs are also found to integrate binocular information, which is further elaborated with prism and eyepatch experiments.
Chapter 4 describes TSDNs in two dipteran species, the robberfly Holcocephala fusca and the killerfly Coenosia attenuata.
Chapter 5 describes an interaction between small- and wide-field visual features in TSDNs of both predatory and nonpredatory dipterans, finding functional similarity of these neurons for prey capture and conspecific pursuit. Dipteran TSDN responses are repressed by background motion in a direction dependent manner, suggesting a control architecture in which target tracking and optomotor stabilization pathways operate in parallel during pursuit.echnology and Biological Sciences ResearchCouncil (BB/M011194/1
Change blindness: eradication of gestalt strategies
Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149β164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by Β±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task
Chromatic processing in the zebrafish (Danio rerio) inner retina: bipolar cell physiology and open hardware designs for spectrally accurate stimulation under two-photon
Colour vision describes the ability of animals to differentiate objects based on their spectral reflectance properties independent of light intensity. It is an essential evolutionary trait that allows species to efficiently forage for food, avoid predation, break camouflage, communicate with conspecifics, or to find mates. Zebrafish is a powerful model for studying colour vision as it possesses four cone-photoreceptor types which can be categorised as Red-, Green-, Blue- and UV-sensitive. From first principles, its retina therefore holds the potential to process diverse chromatic computations. In the presented work, the focus was on retinal bipolar cells (BC). These are the retinaβs first projection neurons. They receive inputs from the photoreceptors in the outer retina, and send their axon terminals to the inner retina, the inner plexiform layer (IPL). Diverse types within this class of interneuron shape light responses collected by the photoreceptor array into parallel channels with diverse spectral properties. BCs also make connections with all other neuron types within the retina, including horizontal cells in the outer retina, and amacrine as well as retinal ganglion cells in the inner retina. This makes them a central hub for spectral processing within the retina.
By combining genetically encoded calcium indicator and two-photon microscopy, light-driven activity from larval zebrafish BC synaptic terminals was systematically recorded in vivo. Synaptic responses to tetrachromatic light stimulation unveiled an unprecedented degree of visual specialisation, including retinal regions dedicated to distinct light-guided behaviours. These regional characteristics were further correlated to functional BC types which were strongly associated with specific retinal positions and axonal stratification depths. Overall, BC projections to the inner plexiform layer displayed a sophisticated level of organisation, structured into chromatic and achromatic functional layers which systematically adjusted their response profiles across the eye to match natural spectral input statistics.
Together, these findings bolster our understanding of βcolour-processingβ in this animalβs inner retina and suggest that unlike in mammals, teleost fish BCs already encode complex chromatic responses in the inner plexiform layer before driving retinal ganglion cells.
Additionally, the study of colour vision from an organism requires precise control over the light stimuliβs temporal, spatial and spectral features. Therefore, chromatic stimulators, designed to be combined with two-photon microscopy, were developed throughout this work. These devices allowed circumventing experimental limitations, such as spectral crosstalk between the microscope and the stimulus light. Furthermore, they were conceived as open source projects to be easily replicated and adapted to any organismβs retina with different spectral sensitivities through the free control over the number and spectra of stimulation light sources. These open source projects originated from the desire to set up a stimulation standard for the field of visual neuroscience
High Performance Three-Dimensional Display Based on Polymer-Stabilized Blue Phase Liquid Crystal
Autostereoscopic 2D/3D (two-dimension/three-dimension) switchable display has been attracting great interest in research and practical applications for several years. Among different autostereoscopic solutions, direction-multiplexed 3D displays based on microlens array or parallax barrier are viewed as the most promising candidates, due to their compatibility with conventional 2D display technologies. These 2D/3D switchable display system designs rely on fast switching display panels and photonics devices, including adaptive focus microlens array and switchable slit array. Polymer-stabilized blue phase liquid crystal (PS-BPLC) material provides a possible solution to meet the aforementioned fast response time requirement. However, present display and photonic devices based on blue phase liquid crystals suffer from several drawbacks, such as low contrast ratio, relatively large hysteresis and short lifetime. In this dissertation, we investigate the material properties of PS-BPLC so as to improve the performance of PS-BPLC devices. Then we propose several PS-BPLC devices for the autostereoscopic 2D/3D switchable display system designs. In the first part we evaluate the optical rotatory power (ORP) of blue phase liquid crystal, which is proven to be the primary reason for causing the low contrast ratio of PS-BPLC display systems. Those material parameters affecting the ORP of PS-BPLC are investigated and an empirical equation is proposed to calculate the polarization rotation angle in a PS-BPLC cell. Then several optical compensation methods are proposed to compensate the impact of ORP and to improve the contrast ratio of a display system. The pros and cons of each solution are discussed accordingly. In the second part, we propose two adaptive focus microlens array structures and a high efficiency switchable slit array based on the PS-BPLC materials. By optimizing the design parameters, these devices can be applied to the 2D/3D switchable display systems. In the last section, we focus on another factor that affects the performance and lifetime of PS-BPLC devices and systems: the UV exposure condition. The impact of UV exposure wavelength, dosage, uniformity, and photo-initiator are investigated. We demonstrate that by optimizing the UV exposure condition, we can reduce the hysteresis of PS-BPLC and improve its long term stability
Visual Cortex
The neurosciences have experienced tremendous and wonderful progress in many areas, and the spectrum encompassing the neurosciences is expansive. Suffice it to mention a few classical fields: electrophysiology, genetics, physics, computer sciences, and more recently, social and marketing neurosciences. Of course, this large growth resulted in the production of many books. Perhaps the visual system and the visual cortex were in the vanguard because most animals do not produce their own light and offer thus the invaluable advantage of allowing investigators to conduct experiments in full control of the stimulus. In addition, the fascinating evolution of scientific techniques, the immense productivity of recent research, and the ensuing literature make it virtually impossible to publish in a single volume all worthwhile work accomplished throughout the scientific world. The days when a single individual, as Diderot, could undertake the production of an encyclopedia are gone forever. Indeed most approaches to studying the nervous system are valid and neuroscientists produce an almost astronomical number of interesting data accompanied by extremely worthy hypotheses which in turn generate new ventures in search of brain functions. Yet, it is fully justified to make an encore and to publish a book dedicated to visual cortex and beyond. Many reasons validate a book assembling chapters written by active researchers. Each has the opportunity to bind together data and explore original ideas whose fate will not fall into the hands of uncompromising reviewers of traditional journals. This book focuses on the cerebral cortex with a large emphasis on vision. Yet it offers the reader diverse approaches employed to investigate the brain, for instance, computer simulation, cellular responses, or rivalry between various targets and goal directed actions. This volume thus covers a large spectrum of research even though it is impossible to include all topics in the extremely diverse field of neurosciences
Aerial Vehicles
This book contains 35 chapters written by experts in developing techniques for making aerial vehicles more intelligent, more reliable, more flexible in use, and safer in operation.It will also serve as an inspiration for further improvement of the design and application of aeral vehicles. The advanced techniques and research described here may also be applicable to other high-tech areas such as robotics, avionics, vetronics, and space
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