Theses supervised by Prof. Dr. Hakan Ürey
23 theses · Koç University
Full-color holographic near-eye displays
Near-eye displays (NEDs) for augmented reality (AR) applications are expected to be the next computing paradigm. NEDs offer to combine computer-generated visuals with our physical world in a seamless fashion. Depth cues and natural blurring of images are all critical for a comfortable 3D experience with near-eye displays. Holography for NEDs is a commonly accepted strong candidate in meeting the human visual system's demands by offering natural depth cues. Holographic near-eye displays (HNEDs) deliver virtual images using computer-generated holograms (CGHs) displayed on spatial light modulators (SLMs). Holographic displays allow for a vast range of optical architectures that are not possible with conventional microdisplay-based designs. However, due to the current technological limitations of SLMs, most existing HNEDs have a limited field of view (FOV) and viewing region around the eye pupil (i.e., eyebox size). However, improving SLMs have a positive impact on improving FOV and eyebox size in HNED design. In this thesis, we propose various solutions for overcoming the current technological limitations of SLMs and HNEDs. We start by offering a paraxial matrix optics-based analysis of a conventional HNED design to formulate the relation between eyebox, FOV, and SLM characteristics. We developed a CGH computation procedure that applies to arbitrary paraxial optical architectures, where the SLM illumination beam can be collimated, converging, or diverging. The virtual or real SLM image as seen by the eyebox plane may form at an arbitrary location. Using this approach, we designed full-color HNEDs with varying FOV and resolution characteristics and proper depth control. We demonstrated a lensless HNED architecture with diverging beam illumination, which provides 3D images within a wide FOV (70°) at retinal resolution (30 cycles-per-degree), exceeding 4,000 resolvable pixels on a line. The experiments using binary holograms imprinted on masks prove that the proposed CGH computation procedure eliminates chromatic aberrations and speckle noise observed in all other laser-based displays. We also designed two systems with 10° and 20° FOV using dynamic SLM. While the first design has a uniform resolution, the second design demonstrates a foveated display, which has gradually degrading resolution across the FOV. To further explore HNED architectures, we analyzed the light source coherence requirements and investigated HNED designs utilizing light-emitting diodes (LEDs). While laser light sources have the highest degree of spatial and temporal coherence, lasers' usage in direct contact with a human may cause health hazards. We show that under certain design restrictions, it is possible to utilize LEDs instead of lasers and get better quality holographic images. We analyzed the effect of LED emission areas on image resolution, quality, and depth perception. Lastly, we designed micro-mirror array (MMA) based thin components and demonstrated that those could be used as off-axis thin lenses in AR displays to reduce size and volume.
High quality computer generated hologram computation and display applications
Computer Generated Holographic (CGH) displays can be the ultimate three-dimensional (3D) display technology as they can match all the requirements of the human visual system. A CGH display goes beyond stereoscopic displays and offers a 3D experience with all the depth cues, including vergence and accommodation. CGH displays can satisfy all the demands of industrial, educational, and consumer applications. Despite its great potential, the visual quality of CGH displays is inferior to other display technologies. There remain many computational and implementation challenges that are needed to be resolved before fulfilling its promises. In this thesis, we developed two novel methods to improve the computation and the visual quality of holograms. First, we explored a new direction called learned holographic light transport models, where we improved hologram computation using machine learning approaches. Although traditional computational models offer excellent quality in simulation environments, experimental images from these models do not exhibit the expected visual quality. Our work addresses this mismatch by generating a holographic dataset and learning model that contains the reconstructed images for simulated and experimental results. We proved that our method mitigates the mismatch between simulated and experimental results while improving the visual quality of experimental results. The second challenge is the mismatch between the incoherent natural scenes and the holographically constructed scenes using coherent light such as lasers. While the blur due to defocus results in smoothed features in natural images, defocus blur in coherent images contains high-spatial frequency features, which can inadvertently disturbs the eye's accommodation in 3D holographic scenes. Such difference in defocus blur manifests itself as edge fringe artifacts in 3D holography. We investigated these artifacts, and proposed a novel phase only hologram generation method to mitigate this issue. Our method introduces a novel targeting scheme and loss function that is specifically tailored to improve the visual quality by reducing these artifacts. Furthermore, we propose a new optimization method we named the Dual Stochastic Gradient Descent method. Defocus blur is a well-known problem in coherent systems, but previous research has failed to show any enhancement. We showed for the first time that our method could reduce the edge-fringe artifacts both in simulations and experimental results. Finally, we developed a novel holographic vision simulator device to assess the post-visual acuity performance of cataract patients before going through surgery. The device contains a CGH display and pupil tracker cameras. We demonstrate that holographically shaped light beams can be programmed and directed through less dense cataractous regions of the crystalline lens to form crisp images on the retina. Our pre-clinical studies with 13 patients showed that patients' potential post-op visual acuity after surgery can be successfully predicted using the CGH display before the surgery. Such a simulator has enormous potential in the clinic.
Enhancing the performance of a coagulometer through optimization of microfluidic cartridge and fiber optic-based optomechanical systems
More than 800 million clotting tests are performed each year in hospitals and clinical laboratories for emergencies, surgical operations, and periodic monitoring of patients. Monitoring of adequate anticoagulant dosage is essential to maintain the delicate balance between bleeding and thrombosis. The primary means of monitoring the response to warfarin (VKAs) is the Prothrombin Time (PT) test and the international normalized ratio (INR) while activated partial thrombosplastin time (aPTT) is used for heparin monitoring. Current clinical laboratory tests used to routinely measure blood coagulation still lack in rapidity and simplicity. Whole-blood Point-of-Care (PoC) coagulation devices that respond to the exact needs of both clinicians and patients are still emerging in the field. Portable PoC and self- care PT/INR monitoring devices are gaining in popularity as they provide crucial advantages over traditional laboratory methods such as ease of use, instant results, rapid turnaround for timely anticoagulant dose adjustment and improved patient convenience by removing the need for routine hospital/laboratory visits and venipunctures. Moreover, PoC devices are using whole capillary blood usually from a finger prick while conventional laboratory methods utilize centrifuged plasma obtained from citrated venous blood. This thesis presents several optimization activities that was performed on the disposable cartridge unit of an opto-mechanical-based Point-of-care and Self-care coagulometer. This study demonstrates several design optimization and validation activities undertaken during the product development stage in order to move the initial cartridge design into a commercializable product. Thus, this work focused of increasing the manufacturability and usability of the previous cartridge design developed by our group in terms of passive capillary flow/Microfluidics, biochemical functionalization, optical fiber assembly, and reagent optimization. Furthermore, the final cartridge design was used to conduct a proof-of-concept study in the topic of heparin monitoring and aPTT measurement on control plasma and blood samples, suggesting a reliable and rapid testing as a PoC device. A preclinical trial was conducted with an n=42 sample size to assess the correlation between our device and the standard hospital method, further validating its efficacy and potential for clinical use.
Dynamic accommodation measurement using purkinje reflections and machine learning
Dynamic and precise measurements of eye accommodation and vergence are important for vision research, near-eye displays (NEDs), and the diagnosis of certain visual disorders and neurological diseases. Existing biomedical devices have important limitations because they are bulky and cannot be used to accurately measure eye accommodation dynamically. From an engineering perspective, implementing accommodation and vergence measurements in NEDs, such as augmented reality (AR) or virtual reality (VR) glasses, helps to address issues like vergence-accommodation conflict (VAC). Previous work on NEDs using adaptive focus techniques or retinal projection has reported reduced symptoms of VAC, but validating the accuracy of these systems remains challenging with current methods. Consequently, finding a simple, portable, and head-mountable method for measuring accommodation and vergence is an active area of research. There are existing approaches in the literature for measuring eye accommodation and vergence using Purkinje reflections from various layers of the eye, as well as machine learning (ML) methods. However, these methods generally do not measure accommodation but rather measure gaze and do not use all Purkinje reflections, which limits their accuracy. In this thesis, we present a simple and efficient method for measuring accommodation and vergence using four Purkinje reflections and ML techniques, specifically multilayer perceptron (MLP) networks. We employed a ZEMAX-based eye model to simulate the positions of the Purkinje reflections at various focal distances. Despite the system's sensitivity to environmental factors, we successfully collected experimental data from nine subjects. We employed two analytical approaches to train our MLP models: subject-specific analysis using the data of individual subjects and leave-one-subject-out cross-validation (LOSO-CV) complemented by two-point calibration. To the best of our knowledge, this is the first successful implementation of the LOSO-CV method for measuring accommodation and vergence. Our system demonstrated high accuracy, predicting accommodation within 0.22 diopters (D) using subject-specific data and achieving 0.40 D accuracy with two-point calibration using data from other subjects across nine subjects.
Non-faradaic sensing of cardiac biomarkers from interstitial fluid using microneedle arrays
In recent years, microneedle-based biosensors have emerged as a promising technology for continuous and minimally invasive health monitoring. Various sensing methods, including electrochemical and optical approaches have been successfully integrated into these platforms. However, the integration of non-faradaic sensing methods into microneedle platforms remains limited. Non-faradaic sensing detects analyte-induced changes in interfacial capacitance without charge-transfer reactions, making it well-suited for developing label-free biosensors for cardiovascular health, where early and accurate biomarker detection is essential. To address this gap, this thesis presents a novel microneedle-based interdigitated electrode biosensor employing non-faradaic capacitive sensing principles to quantify cTnI directly from interstitial fluid (ISF). Fabrication of the microneedle capacitive patch was carried out using a reproducible process, followed by functionalization of the surface with anti-cTnI antibodies. The analytical output is expressed as the normalized capacitance change (%∆C/C), which improves the consistency of sensor responses. By relying on the intrinsic electrical double layer (EDL) phenomenon at the electrode–electrolyte interface, the sensor demonstrated effective detection capabilities validated through in vitro and in vivo characterization. The sensor exhibits a limit of detection of 3.27 pg/mL, and a total assay response time of less than 15 minutes. Also, to address the system integration challenges in wearable and implantable biosensors, the microneedle sensor is successfully integrated with a passive antenna enabling wireless and continuous monitoring. Furthermore, since the proposed platform operates in ISF, it is inherently affected by variations in its composition, both between individuals and within the same individual over time. Given that such fluctuations in ionic strength can influence both interfacial capacitance and overall sensor performance, a calibration correction method is introduced. This approach incorporates the effect of medium ionic resistivity on EDL capacitance changes through real time impedance measurement, thereby enhancing the robustness and reliability of biomarker quantification under diverse physiological conditions. The effectiveness of the proposed model in improving the accuracy of cTnI detection with the microneedle sensor was assessed through spike-and-recovery experiments. Collectively, this work advances the field of minimally invasive biosensing by offering an integrated, non-faradaic, microneedle-based solution with enhanced physiological adaptability and accuracy for the monitoring of cardiac biomarkers.
Kırınım ızgaralı girişim ölçer temelli MEMS Fourier dönüşümü kızılötesi spektrometre
Fourier transform infrared (FTIR) spectroscopy is a widely used non-contact optical material characterization method that is used for chemical analysis of solids, fluids, gases, and process flows. FTIR utilizes a black body light source with broad spectrum, moving opto-mechanical components, and a detector. Current FTIR spectrometers offer good spectral resolution (few cm-1 or better); however, they are costly bench top laboratory instruments, require very high opto-mechanical precision, sensitive to vibrations due to interferometric detection principle, and have low measuring speed (few seconds to minutes). A portable FTIR system is needed as it would allow field use and has the potential to open up new research directions and applications.The aim of this project was to build a miniaturized handheld FTIR spectrometer with high measuring speed (1-2msec) and moderate spectral sensitivity (10cm-1) that works across a wide wavelength range in the mid-infrared (2.5-16µm) region. The project is done as a part of the European Commission funded project called MEMFIS within a consortium. A novel lamellar grating interferometer (LGI) based on micro-electro-mechanical-system (MEMS) technology and electrostatic actuation is at the heart of the FTIR system and offers the required precision, speed, and the vibration immunity for a portable system. LGI MEMS device was designed and microfabricated by our group prior to this thesis research. LGI is a dynamic diffraction grating operated at resonance and functions as a high-precision opto-mechanical interferometer with key important advantages compared to other types of interferometers.This thesis mainly focuses on the detailed optical and mechanical characterization of the LGI MEMS device and its integration into a fully functional FTIR system using the source, detector, and IR optics. For this purpose, MEMS devices fabricated in five separate runs are characterized mechanically and optically. For mechanical characterization, two automatized systems based on laser Doppler vibrometry and laser fringe counting are developed using a Labview based controller. Physical optics simulations of the system are performed in MATLAB and ray-tracing simulations are performed in ZEMAX to find the optimum combination of optical components. A fully functional LGI based FTIR spectrometer system is built on an optical table and successfully benchmarked with other FTIR systems using polystyrene film samples. The system can currently achieve about 30cm-1 spectral resolution. This is the best MEMS-based LGI system developed to date considering the spectral resolution and clear aperture size of 10mm2. To increase the mechanical deflection (i.e., improve spectral resolution) and to avoid problems related to electrostatic actuation such as pull-in and nonlinear frequency response, acoustic excitation using a speaker and mechanically-coupled excitation using a piezoelectric-vibrator are introduced as alternative actuation methods. As another application of the FTIR system, measurement of photovoltaic solar cell thin film thickness uniformity is exploited.
Optik okuma ile tümleştirilmiş termo-mekanik kızılötesi algılayıcı dizinlerinin tasarım, üretim ve karakterizasyonu
Thermal imaging has been a useful tool in many thermal mapping applications such as medical imaging, target detection, surveillance, monitoring circuits and rescue. This thesis reports the design, fabrication and characterization of micro electro-mechanical system (MEMS) based uncooled thermo-mechanical infrared (IR) sensor arrays integrated with CMOS based optical readout.Pixelated sensor array operation is based on the conversion of incident IR radiation to mechanical displacement. The pixels are suspended membranes connected to a transparent substrate via bimaterial legs. Absorbed IR radiation modulates the temperature of the structure and this modulation causes the deflection of bimaterial legs that have a mismatch of coefficient of thermal expansion. This mechanical deflection is detected optically with sub-nm precision by monitoring the first diffracted order of the readout beam returning from the diffraction gratings that are embedded underneath each pixel. The main advantage of the designed sensors is that the MEMS die is passive, thus pixels are electrically and thermally isolated from the optical readout. Two options are exploited for the optical readout: (i) reimaging of diffracted light onto a CCD camera using Fourier filtering, (ii) integration of MEMS sensor array chip on a CMOS readout chip that contains a photodetector array and a through wafer via hole for each pixel for the illumination beam. This is a novel approach for optical readout and tried for the first time.Sensor arrays are designed and microfabricated in 640x480, 320x240 and 64x64 pixel formats with 35 µm sensor pitch using standard MEMS processes with SixNy/Al and Parylene/Al material combinations. Optical readout IC is fabricated using standard 0.18 µm CMOS process. As a post-process, the CMOS chips are thinned and through wafer holes are etched, which allow the readout laser beam to pass through. After the CMOS post-process steps, MEMS and CMOS dies are aligned and integrated, which enabled a novel integrated optical readout.
Lazer ekranlar için elektrostatik ve piezoelektrik MEMS tarayıcı geliştirme
Laser based displays have been under development over the last 50 years but commercial viability of the technology was limited mainly due to the large size and high cost of laser sources and scanners. The quest for miniaturization and higher efficiency is realized with the development of directly modulatable laser diodes and scanning mirrors based on micro electro mechanical systems (MEMS) technology. Integration of scanners and laser diodes offers a powerful combination for micro-display and imaging applications such as laser printers, barcode readers, and wearable micro-display systems.A displayed image is formed pixel by pixel using a mirror producing angular motion that scans a modulated light beam on a screen. The purpose of this thesis is to develop new MEMS two dimensional raster scanners for laser display applications.For the slow axis of the two-mirror display engine, an electrostatically actuated rotary scanner is conceived and developed to provide a linear ramp scan at 60 Hz. A novel spring design is proposed for linear in-plane rotary MEMS scanner. It offers over 98% linear motion up to 7 deg. mechanical rotation with the novel suspension design.For the fast axis, piezoelectric actuation that requires much lower voltages than electrostatic actuation is used to develop a high frequency resonant torsional MEMS scanner. Sinusoidal actuation with 24 V at a mechanical resonance frequency of 40 kHz provides a total optical scan angle of 38.5 deg. for the 1.4 mm wide mirror. It exceeds the performance specifications cited in the current literature and becomes a significant step towards achieving Full HD (1080p) resolution with mobile laser projectors.
Mikromercek dizini tabanlı şeffaf ve yüksek kazançlı projeksiyon ekranları
Tablet computers and smart phones have increased the mobility of the users but small screen size has been a major limitation for the productivity of the users. Mobile projectors, called pico-projectors, are emerging technologies and can project images to any distance and size from a tiny display engine that can be embedded in mobile computers and phones. While pico-projectors can overcome the screen size limitation, they are limited in brightness due to battery operation and laser safety concerns. The aim of this research was to develop reflective and transparent novel screen technologies that can provide high-efficiency and high-brightness when used together with laser scanning based pico-projectors. Such screens are needed in augmented reality displays, head-up displays, and head-mounted projection displays. When an image is projected on ordinary surfaces, such as walls or a piece of paper, the light is scattered onto the entire hemisphere. We developed special micro-structured screens that concentrate the scattered light only around the user?s eyes. As the projected energy is concentrated into a smaller area, the brightness of the image is increased and the screen has a gain compared to ordinary surfaces. Three different screen technologies have been developed that use microlens array (MLA) based diffusers: a single MLA screen, a dual MLA screen and a rotated MLA screen. The single MLA screen has a gain of 3 and it was designed for automotive head-up display applications. Due to its unique index matched structure the screen provides excellent transparency and high brightness at the same time. The dual MLA screen is an opaque screen with a gain of 9. It concentrates the diffused light more efficiently compared to the single MLA due to the telecentricity of the microlenses. A novel rotated MLA provides the highest gain of all the screens. It is designed specifically for a given application such that every pixel on the screen is reflected towards the user due to the rotation of the microlenses. It can provide gains on the order of 100.
Lazer taramalı pico projektör kullanan gelecek nesil 3B ekran uygulamaları
This thesis presents four novel 3D display methods and a number of new applications using commercial laser scanning pico projectors that have been developed with major contributions from our laboratory during the last decade. The new methods developed in this thesis are (i) mixed-polarization stereoscopic display using single-projector and passive polarized glasses, (ii) a new type of glasses that can relieve the accommodation and vergence conflict associated with all the stereoscopic displays, (iii) rotating screen based auto-stereoscopic display for a single-viewer using two pico-projectors, and (iv) multi-user multi-view auto-stereoscopic display using an array of pico-projectors. Furthermore, a head-mounted pico-projector is also demonstrated as a new augmented- reality application aimed at motion-capture actors. The first method introduces a new twist on glasses based stereoscopic projection displays as it utilizes polarization and color multiplexing simultaneously and avoids weaknesses associated with previous methods. This new method is named Mixed Polarization 3D. Color imbalance artifacts associated with anaglyph glasses are avoided by alternating the colors presented to each eye. In mixed polarization 3D, flicker is not observed even at 60 Hz since both eyes receive at least one color frame in every single frame. The second method, named Super Stereoscopic 3D Display (SS3D), introduces a major improvement on stereoscopic 3D displays for avoiding accommodation-vergence conflict. Our method provides at least two views to a single eye by using special apertures equipped with selective filters in front of the users' eye. Our designs can be embedded into conventional stereoscopic glasses or can be developed as special contact lenses. The third method introduces a single viewer multi-view autostereoscopic projection display, which is invented in our laboratory by a co-worker. The technique uses two mobile projectors, a rotating retro-reflective diffuser screen, and a head-tracking camera. As two dynamic viewing slits are created at the viewers position, the slits can track the position of the eyes by rotating the screen. The last method introduces a new modular multi-user multi-view autostereoscopic display architecture based on an array of pico-projectors and a vertical diffuser screen. A single projector provides a portion of the each perspective observed through the vertical diffuser. Unlike similar projector-array based displays, the screen assembly complexity and the size of the projection display hardware have been decreased dramatically. Our proposal has the capability to provide horizontal expansion in the screen size, and an increase in the number of different perspectives as well. Lastly, an augmented reality (AR) system is proposed and developed for supporting motion capture actors. This system allows seeing and exploring the digital environment without occluding the actors visual field. An in-house prototype is built by combining a retro-reflective screen that covers the walls and a headband consisting of a laser scanning projector with a smartphone. Built-in sensors on the smartphone provide navigation capabilities in the digital world.
Nano etiketler ile işaretlenmiş sıvıların tanınması için optik sensör tasarımı ve gliştirilmesi
Barkod teknolojisi ürün tanımlama ve takibi için önemli bir kavramdır. Bununla birlikte, geleneksel barkod teknolojisi, sıvıların tanımlanması için kullanılamaz. Bu tezde, nano-etiketler kullanarak sıvıları tanımlayan optik sensörün tasarımı ve karakterizasyonu anlatılmıştır. önerilen sistemde, geniş absorpsiyon ve emisyon spektrumu, yüksek kuantum verimi ve florışıldama bozulmasına karşı yüksek direnci nedeniyle, etiketleme için Kuantum noktacıkları (QDs) kullanılmaktadır. Bu tezde, görüntüleme tabanlı sistem, tek detektöre bağlanmış yüksek sayısal açıklığa sahip olan lens ve fiber optik tabanlı sistem olmak üzere farklı ışık toplama mimarileri incelenmiştir. Bu araştırma, maliyet, taşınırlık ve hassasiyet açısından belirgin avantajları olan fiber optik tabanlı sistem üzerine odaklanmıştır. Önerilen fiber optik sensör, bir fiber optik kablo, bir algılama ünitesi ve bir aydınlatma birimi ile bir sinyal işleme biriminden oluşmaktadır. Sistemdeki her bir bloğun detaylı optimizasyonu ile su gibi saydam sıvılar içinde pM altı konsantrasyonlarında kuantum noktacıkları saptanabilmektedir. Öte yandan, saydam olmayan sıvılar içinde nano etiketlerinin tespiti, ortam ve kuantum noktacıkları arasındaki karmaşık etkileşimler nedeniyle oldukça zordur. Bu tez araştırmasında, bu sorunu aşmak için, yeni bir arka plan çıkarma algoritması uygulanmaktadır. Bu algoritma, 100 pM seviyesinde bir algılama sınırı ile saf kuantum noktacığı sinyalini yapılan okumalardan ayrıştırabilmiştir. Sistemin optik performansı sıvılar içinde dağılmış kuantum noktaları için Monte Carlo yöntemi kullanılarak simüle edilmektedir. Simülasyon sonuçları ölçüm verileri ile yakın korelasyon göstermektedir. Elde edilen sonuçlar, günümüz teknolojisiyle yapılan sistemlerin sonuçlarından çok daha iyi ve çeşitli değerli sıvıların, hat üzerinde izlenmesi için kuantum noktacıkları kullanımı yolunda, yeni araştırmalara yön vermek için potansiyele sahiptir.
Gerçek zamanlı kütle, özkütle, viskozite ve pıhtılaşma ölçümleri için mikroçubuk tabanlı mikroakışkan algılayıcılar
Miniaturization of sensor technologies and the development of lab-on-a-chip (LoC) devices in the last decade enabled new opportunities in diagnostics and therapeutics to improve human health. Despite the great technological advances in research labs, there are only a few commercially successful LoC devices used for point-of-care diagnostics applications. Such applications demand simple sensor readout and single-use disposable sensors, which are difficult requirements to achieve due to mechanical, fluidic, optical, and electronic interface and integration problems. This thesis focuses on the development of a fully integrated LoC measurement system that use micro-electro-mechanical-system (MEMS) based microcantilevers operated in a microfluidic cartridge with simple interface and simple sensor readout. Microcantilever biosensors developed in this research have been adapted for different point-of care applications (blood plasma viscosity and coagulation time measurements), liquid property monitoring and immunoassay detection purposes. The cantilevers are made of electroplated Nickel and fabricated with a simple process using Koç University Micro/Nano Fabrication Clean Room. Cantilever designs varied according to the application. The length of the cantilevers are between 60 µm and 200µm, the width varies between 5 µm and 100µm and the thickness is generally in the order 1- 2µm. They are fully immersed in liquid and actuated by an external electro-coil that operates close to cantilever resonant frequencies and sensing is conducted by means of an optical read-out. A unique optical interferometric method or a laser Doppler Vibrometer is employed for the optical read-out. Both actuation and read-out are conducted remotely. Thus electrical connections to the cantilevers are not required. This feature enables the use of the developed technology as a point of care device with disposable cartridges. The oscillation dynamics of the cantilevers change due to the variations in the liquid properties or the accreted mass on the cantilever surface. The changes in the dynamics are either tracked with lock-in amplifier or phase-locked loop (PLL) based electronics that follows the optical detector. The lock-in amplifier method tracks the phase difference between the actuation signal (coil drive current) and the sensor signal (photo detector output) whereas the PLL method tracks the oscillation frequency real-time by using a fixed phase difference between the actuation and the sensor signals. The cantilever biosensor platform has been used for four biological applications during this thesis research. First, the system is utilized as a viscosity sensor and viscosities blood plasma and blood serum are measured. Blood plasma viscosity can be used for the diagnosis of several diseases such as cardiovascular disorders, rheumatoid arthritis, and certain autoimmune diseases. The proposed system enables fast and convenient measurements with small sample volumes (~10µl), which is superior to common bench-top clinical devices and makes the system suitable for point of care use. New protocols are developed, the systems repeatability and reliability is also tested with reference measurements using commercial laboratory devices. For viscosity detection a detection limit of 0.01 mPa.s is achieved for blood plasma with error less than 6%. Second, a novel method is proposed and demonstrated to separate the coupled effects of density and viscosity on the cantilever oscillation dynamics. A set of equations and a simple algorithm is developed to relate the density and the viscosity to the frequency shifts of the cantilevers. We found that the effect of the density and the viscosity can be well separated if cantilevers have different widths. The method uses the PLL based system to track the resonant frequencies of two cantilevers with different widths immersed in the same liquid. Precise density and viscosity measurements are performed and compared with the reference measurements. The measurement error with the new method was lower than 3 % in density in the range 995 to 1150 kg/m3 and 4.6 % in viscosity in the range 0.935 to 4 mPa.s. Based on the signal-to-noise ratio, the minimum detectable difference in the viscosity is 1.6x 10-3 mPa.s and the density is 0.3 kg/m3. As the third application, the system is adapted for blood plasma coagulation time tests. Periodical coagulation time tests are required for patients who are receiving anticoagulant therapy, undergoing pre-operation evaluation or for patients under risk of embolism, stroke or atrial fibrillation. In general practice, patients need to visit a hospital or a central laboratory periodically for coagulation tests. Such a procedure puts a significant burden on the health-care provider and increases the return time and the cost of the test. Thus, fast, reliable and simple assays are needed to monitor the coagulation parameters. For this purpose the MEMS chips containing cantilevers are integrated with microfluidic channels and multiplexed coagulation time measurements are enabled from single cartridge. New protocols are developed for standard coagulation tests (Prothrombin time (PT) and activated partial thromboplastin time (aPTT)). The tests are conducted not only with standard control plasma samples but also with human plasma samples. The measurement system has an overall 7.28 % and 6.33 % CV (Coefficient of Variation) for PT and aPTT, respectively which are comparable with the commercial devices with different technologies. As the fourth application, the system is tested for immunoassay detection in parallel channels. The proteins of Hepatitis B, Hepatitis C, HIV and Syphilis antigens are detected with reasonable detection limits. The technology developed in this thesis is simple to use, label-free, can be integrated in a disposable cartridge, and suitable for multiple tests in the same cartridge; therefore, it has high potential for point-of-care and home diagnostics applications.
İğne deliği görüntüleme temelli stereoskopik 3B ve başa takılan göstergeler için çözümler
Two well-known existing problems of stereoscopic displays are the accommodation-convergence conflict and the lack of natural blur for defocused objects. We present a new technique that we name Super Stereoscopy (SS3D) to provide a convenient solution to these problems. Regular stereoscopic glasses are replaced by SS3D glasses which deliver at least two parallax images per eye through pinholes equipped with light selective filters. The pinholes generate blur free retinal images so as to enable correct accommodation, while the delivery of multiple parallax images per eye creates an approximate blur effect for defocused objects. Experiments performed with cameras and human viewers indicate that the technique works as desired. In case two pinholes equipped with color filters per eye are used, the technique can be used on a regular stereoscopic display by only uploading a new content, without requiring any change in display hardware, driver or frame rate. Apart from some tolerable loss in display brightness and decrease in natural spatial resolution limit of eye due to pinholes, the technique is quite promising for comfortable and realistic 3D vision, especially enabling the display of close by objects that are not possible to display and comfortably view on regular 3DTV and cinema. We propose a simple virtual reality (VR) type head-worn display (HWD) system, where a pinhole array relays the image on a smart phone display to the retina of a user without requiring any lenses. The sub-images relayed through the pinholes are seamlessly tiled on the retina without ghost (double) images or blank regions by using an optimized pinhole design and by pre-processing the images shown on the cell phone. A proof-of-concept prototype with a 3 mm exit pupil successfully verifies the developed theory and demonstrates the delivery of full color images within a diagonal field-of-view (FoV) of 45 degrees at a resolution of about 4 cycles per degree. The experiments also demonstrate the interesting possibility that there are multiple options for the display content that generates a desired retinal image, including those obtained with random decisions. The system is low-weight, very low-cost, and can deliver diffraction-limited images across a wide FoV. However, the spatial resolution is moderate due to small pinhole size. Also, pupil tracker sensors and a dynamically configurable pinhole array are needed to handle changing pupil size and locations.
Döner perde kullanan 3 boyutlu gözlüksüz projeksiyon ekranı
A new technique for glasses free (autostereoscopic) and multiview 3D display is proposed and demonstrated in this thesis. The technique uses two mobile projectors, a rotating retro-reflective diffuser screen rotated by a mechanical unit, a pupil tracking camera and a computer. Two mobile projectors project stereo images onto a transfer screen composed of a retroreflector and a 1D diffuser. The transfer screen forms two viewing slits through each of which only one image of stereo image pair is seen. The mechanical unit rotates the transfer screen around its center according to the viewer's position obtained by the pupil tracker. As the screen is rotated accordingly, the viewing slits track the viewer's eyes. Thus, a single viewer can perceive 3D in a large viewing field. Images from different perspectives can be presented to the viewer using the information from the pupil-tracker. Advantages of the proposed technique compared to conventional autostereoscopic projection displays are as follows: it requires only two projectors rather than an array of projectors; there is no image registration problem on the screen once the projectors are aligned; the viewing slits remain aligned with the viewer's pupils, thus the viewer never perceives discrete transitions between different perspectives; the technique can provide high gain, and sufficient brightness using low power mobile projectors. In order to demonstrate capabilities of the proposed technique, a prototype was developed. The prototype consists of two laser based pico projectors using MEMS scanners , a retro-reflective diffuser screen as a transfer screen, pupil-tracker, rotating mechanism which rotates the transfer screen around its center, and a personal computer to provide content and closed-loop control of the tracker and the screen. The resulted prototype presents stereo images to a single viewer without need of any glasses. The screen is circular with 60cm diameter and the image is a rectangular image that fits on the screen and viewed from about 100cm distance. The prototype allows the viewer to move approximately 70 cm along the horizontal axis, and 50 cm along the vertical axis with an average crosstalk below 5 percent. The display quality in terms of brightness and crosstalk has been measured and reported for different types of light diffusers.
Fiber optik tabanlı kartuş ile çalışan taşınabilir kan pıhtılaşma zamanı ölçüm platformu
Advancements in sensor technologies have enabled miniaturized point-of-care (PoC) medical diagnostics devices and offer new opportunities in health care. Most of the new sensor platforms and lab on chip devices are still at laboratory level with only a few successful PoC implementations such as blood glucose monitoring devices. In this thesis, we focused on the development of a novel optical sensor platform and PoC device for periodic monitoring of blood coagulation, which is a critical need for cardiac patients on anticoagulant treatment. While the golden standard for coagulation measurements is direct mechanical measurement from plasma in clinical laboratories, existing commercial and research phase PoC devices employ electro chemical and MEMS based lab on chip devices. This is the first report of a direct mechanical coagulation time measurement system designed for self-testing. The proposed platform has two parts; a disposable cartridge and a reader unit. Disposable cartridge has small volume microfluidic channels for blood flow and fiber optic based mechanical sensor. This sensor is composed of two optical fibers facing each other. One of the fibers is vibrated in mechanical resonance via an electro coil embedded in the reader unit. The other fiber is fixed and receives the light passing through the vibrating fiber. An optical AC signal is obtained at the output of the fixed fiber due to mechanically induced optical modulation. The reader unit has an LED light source coupled to the large core of the vibrating fiber, and a photodetector coupled to the the fixed fiber. Lack of electrical connection to the cartridge, remote electromagnetic actuation and optical read out enable simple and robust POC platform. The proposed sensor platform is tested on a table top measurement set-up for activated-Partial-Thromboplastin-Time (aPTT) measurements on control plasma samples and human whole blood samples. Control plasma test results yielded <1% mean error and <1.36% relative standard deviation based on repeated tests. Then aPTT tests were successfully carried out with human whole blood samples. Proposed platform showed robust and repeatable results in both plasma and whole blood samples. A portable prototype based on table top measurement set up was developed in collaboration with SFO Technologies, India. aPTT test capability of the prototype was also demonstrated with human whole blood. Simplicity of the cartridge design and use of readily available materials enables low cost disposable cartridge and reader units. Future work will focus on reagent optimization, portable reader design, and validation of the system in clinical tests.
Hızlı kaliteli beneklenme yapmayan bilgisyarda yaratılan faz hologramlı görüntü projeksiyonu
Computer generated holography based image projection, 3D television, head-up and near-to-eye (N2E) display systems offer unique advantages over conventional schemes and constitute a promising option for the future of display technology. Such systems provide much higher light efficiency, eliminate the need for bulky optics and provide natural 3D experience. Computer generated holograms (CGHs) are displayed on spatial light modulators (SLMs) illuminated by coherent light. Ideally, each pixel of an SLM should provide simultaneous and independent amplitude and phase modulation since CGHs are in general complex-valued functions. However, current state of the art SLM technology allows the implementation of only a constrained set of complex values depending on the device type, such as binary amplitude, binary phase, amplitude-mostly or phaseonly. Among various types, liquid crystal-on-silicon (LCoS) phase-only SLMs provide the most convenient option due to their smaller pixel pitch, higher diffraction efficiency and 8-bit modulation depth. Yet, these devices become useful only when they are combined with algorithms that encode a full-complex SLM pattern into a phase-only SLM pattern. In the context of holographic image projection, existing algorithms for phase CGH computation are iterative optimization procedures that require successive transformations with high computational costs. As higher pixel counts are attained, the computational load of iterative methods become increasingly excessive, hindering real-time video applications. Despite their high cost though, the reconstruction performance of these algorithms are only moderate, with generated images suffering significantly from speckle noise. In this thesis, two novel phase CGH computation algorithms are proposed. The first algorithm removes the iteration requirement and provides a direct solution, significantly improving the computational efficiency. The second algorithm processes a given desired image and non-iteratively calculates a phase CGH which, when used as a starting point, lets iterative algorithms to converge to almost global optimum, significantly improving reconstruction quality. The first algorithm is based on the observation that two phase-only pixels are equivalent to a full complex pixel; thus, the SLM is expected to reconstruct half of the desired image samples exactly. Simple Discrete Fourier Transform (DFT) and multirate signal processing relations are utilized to non-iteratively determine a phase CGH that exactly reconstructs the even (or odd) rows (or columns) of a given image. By requiring only a single Fast Fourier Transform (FFT) and a few additional trivial matrix operations, the algorithm offers 6 to 20 times improvement on computational efficiency compared to conventional procedures. The simulation results and proof-of-concept experiments indicate that our algorithm can provide full field-of-view (FOV), low speckle image reconstructions with maximized light efficiency when the reconstructions of 4 CGHs are averaged. High quality frames in the interlaced video format is already deliverable with 60Hz SLMs when the FOV in one direction is reduced to half. In the second algorithm, we developed a procedure for designing an image specific phase function that leads to an ideal CGH that is almost readily unit magnitude, resulting in a very low quantization error to begin with. When the phase CGH obtained in the described way is used as the starting point for existing iterative algorithms, much quicker convergence and unprecedentedly low reconstruction errors are achieved. The simulations and experiments reveal that reconstruction quality improves by about 20 times compared to iterative algorithms starting from random guesses. The reconstructions are almost speckle free, while allowing maximum light efficiency and FOV. The developed methods are particularly novel over existing approaches in that full physical as well as mathematical insight is exploited in their development. In particular, while most approaches formulate the phase CGH computation problem as a purely mathematical optimization problem, our methods recognize and utilize the correspondence between phase functions, ray directions, lenses, prisms and so forth. As a result, we can non-iteratively determine phase CGHs that are almost ready, i.e., can perform the desired reconstructions already with low error. In this way, we significantly reduce the number of iterations required, i.e., our methods require iterations just for fine-tuning, whereas in existing algorithms iterations are required for both coarse and fine tuning. Meanwhile, we can get much closer to global optimums than any other method. In this respect, we believe that this thesis also contributes significantly to the understanding of the fundamental limits of phase-only computer holography.
Göze yakın ekranlar için kompakt arka ışık aydınlatıcı
The advancements in micro-electronics, optics and fabrication during the recent decades have led to an ever rising miniaturization, personalization and mobility trend in technology. Just as the headphones that replaced loudspeakers; large televisions and monitors are getting substituted by personal and portable displays, including the wearable near to eye displays (NEDs). Immersive NEDs present users virtual reality (VR), while optically see-through NEDs present augmented reality (AR), with dozens of niche applications in entertainment, education, medical and military domains. The ultimate NED should simultaneously provide high resolution, wide field-of-view (FOV), thin form-factor, large eye box, sufficient brightness and light efficiency, which are all competing requirements. Existing solutions indeed meet merely a subset but not all of the listed objectives. In this thesis, a novel fiber based point source illuminator for near to eye displays capable of presenting wide field of view is presented. The proposed technology is suitable for both immersive (virtual reality) and optical see-through (augmented reality) applications. Proposed design is a coherent backlight illuminator that combines a fiber, scattering nanoparticles and a concave or ellipsoidal mirror which converts the wave from fiber to a converging wave. It is also possible to minimize the volume and to use the demonstrated technology in equipment where small form factor is important. The technology is also adjustable for different illumination profiles (collimated, converging, diverging etc.). Point source fabrication and three different configurations for point source usage are presented. Images captured with a computer generated holograms are presented to support the validity of the design.
MEMS çubuk tabanlı algılayıcılar için optik okuma yöntemleri
Optical readout methods are attractive for micro-electro-mechanical system (MEMS) based sensors as they allow remote readout without electrical connections to the sensor chip and scalable architectures for sensor arrays. Optical readout noise is often the limiting factor in sensor applications. This thesis presents different optical readout methods that can improve the detection sensitivity and decrease the optical readout noise for MEMS sensors specifically for infrared (IR) detection and MEMS oscillator applications. MEMS based thermo-mechanical IR detection technology with optical readout can play a significant role for wide adaption of thermal detectors due to its low cost. In order to achieve sensitivities near the thermal noise limit, optical readout noise need to be reduced dramatically. For this purpose, firstly we demonstrated sensitivity improvements using a number of single sensor optical readout methods. Secondly, we developed both integrated and free-space based optical readout architectures for sensor arrays. Interferometric and optical beam deflection methods have been explored for a variety of single MEMS IR detectors. We developed AC-coupled detection methods to reduce the DC noise and increase the sensitivity to detect the thermal or spatial changes in the scene. Detailed noise characterizations of thermo-mechanical MEMS detectors with 35 µm pixels were performed. In addition, a single MEMS pixel with Fabry-Perot cavity type optical readout method was designed and fabricated. Lastly a novel prism-based optical-readout is proposed and demonstrated for a single lever MEMS pixel. The noise equivalent temperature differences (NETD) for different sensor designs were measured below 200 mK, with a best NETD performance of 150 mK. The measured noise levels were comparable to the state-of-the-art thermo-mechanical IR sensors for very small pixels. In order to improve the performance of the thermo-mechanical MEMS detector arrays, we developed two new approaches: i-) Compact optical Fourier filtering system. A convergent illumination system was developed, which reduced the size of the system and improved the SNR compared to the conventional 4f optical system. ii-) Two-wavelength based optical readout system. This method provided spatial auto-registration of two different color images on a single RGB camera. The sensitivity and dynamic operation range can be enhanced significantly by using two wavelengths for a non-uniform array. Integration of MEMS devices with CMOS electronics enables large array operation in a small low-cost package. MEMS-based sensor array with a large number of elements (64x64) is bonded at chip level with CMOS readout IC for the first time. A diffraction grating interferometer-based optical readout is realized by pixel-level illumination of the MEMS chip through the through-silicon via holes and by capturing the reflected light using a photodetector array on the CMOS chip. Lastly, two non-linear optical readout methods were developed for biological and chemical sensor arrays using dynamic MEMS cantilevers. A single controller is desired to monitor the entire array for tightly packed high density sensor arrays. A separate saturation mechanism and nonlinearity is required for each oscillating cantilever sensor. We used optical non-linearities to drive and sense multiple oscillators with a single controller. In the first method, MEMS cantilevers with embedded diffraction gratings were used in order to parallelize the array for multiple oscillations. In the second method, a prism-based optical readout method was proposed for simple cantilevers. Both methods were successfully implemented to actuate and monitor two nearly identical cantilevers with one actuation coil and photodetector.
Pasif optik yüzeylere dayalı artırılmış gerçeklik 3D ekran ve ışık alan görüntüleme sistemleri
This dissertation presents new display and imaging techniques where a number of micro-structured passive optical surfaces are developed and then combined with mobile projectors and cameras to achieve novel display and imaging modalities. Three types of novel optical surfaces are developed: (i) a transparent AR screen, which is a transparent retroreflective surface developed for augmented reality and automotive head-up display (HUD) applications, (ii) a 3D imaging surface, which is a handheld lens array sheet used for mobile light-field capture when combined with a regular camera, and (iii) an integrated dual-purpose screen, which combines the first two surfaces to achieve 3D display and 3D imaging on the same screen simultaneously. The transparent AR screen provides high optical gain within a small viewing window and enables the use of low lumen output head-mounted laser projectors to produce a bright content. Higher see-through performance is achieved through partial covering of a clear substrate with retroreflective microspheres. The screen transparency and optical gain is varied by changing the retroreflective fill factor, and three versions of the screen providing 50%, 75% and 90% transparency are developed. The transparent retroreflective AR screen was first used with a pair of head-mounted laser projectors (pico-projectors) for 3D vision. We achieved good stereoscopic vision providing down-to 1% crosstalk between two eyes and up-to 1,000 cd/m2 brightness using 30 lumen projectors. For automotive 3D head-up-display applications, we performed a user study to test the simulated collimation and provide the virtual image perception at different screen distances. The user study focused on the visual acuity response under the see-through condition and the simulated collimation condition that shows the relation of visual acuity with the distance of HUD screen and amount of accommodation-convergence (AC) conflict. We showed that the visual acuity is slightly dropped (from 20/20 to 20/25) when the HUD screen is placed between the driver/user and a real-scene. For the simulated collimation condition, an inverse relationship between the amount of AC conflict and the visual acuity is observed, which shows the minimum effect on the visual acuity and viewing comfort when AC conflict is less than 0.85 diopters or when the screen distance is >100 cm. The 3D imaging surface introduces a light-field imaging platform that can turn a regular camera into a multi-perspective 3D capture system. The 3D imaging surface contains an array of lenses and tracking markers to capture the 3D perspective views of a scene. The camera image provides an array of sub-images; each corresponding to a different perspective view. The location of the mobile surface is determined by tracking the distinct markers attached to the corners of the surface. A computational ray tracing tool is developed using OpenGL to perform the real-time light-field reconstruction and demonstrate digital image refocusing and partial occlusion capture. Lastly, a novel integrated dual-purpose screen is introduced for simultaneous display and imaging. The screen mainly consists of patterned retroreflective microspheres as the top layer and an array of curved mirrors as the bottom layer for 3D display and multi-perspective imaging, respectively. The simultaneous display and imaging are performed by using an intermediate polarization selective layer and performing polarization multiplexing to separate the projected and captured light. A telepresence demonstrator is built where user-1 uses a pair of head-mounted projectors and a camera while across the integrated dual-purpose screen and user-2 uses a VR headset, where user-2 can watch user-1 in real-time and from arbitrary perspectives. The display and imaging characteristics of the developed prototype are also evaluated. While mobile 3D telepresence is not possible using existing head-mounted AR and VR displays, our proposed solution offers a unique alternative and can be the future of mobile telepresence.
Bakış-noktası izleyicili, interaktif, geniş görüş-açılı, ikili-odak-düzlemli artırılmış gerçeklik ekranı
Stereoscopic displays have a fixed focus plane and they suffer from visual discomfort due to the mismatch between the focus and vergence of the eyes, known as the vergence-accommodation conflict (VAC). VAC is unavoidable in conventional stereoscopic head-mounted displays (HMDs). In this thesis research, I proposed a biocular (i.e, common optics for two eyes), two focal-plane based augmented reality (AR) system with real-time gaze tracker, which provides a novel interactive experience. Two separate liquid crystal displays (LCDs) are placed at slightly different distances to a Fresnel relay lens such that virtual images of LCDs appear at 25 cm and 50 cm to the user. Both LCDs are totally viewed by both eyes. While the system is limited to two depths and discontinuity occurs in the virtual scene, it provides correct focus cues and natural blur effect at the corresponding depths. This allows the user to distinguish virtual information through the accommodative response of the eye, even when the virtual objects overlap and partially occlude in the axial direction. Displays are driven by a single computer and the objects in the virtual scene are distributed over the LCDs according to their depths. Furthermore, a road scene simulation is realized as a convenient use-case of the proposed display so that a large monitor is used to create a background scene and the rendered content in the LCDs is augmented into the background. Field-of-view (FOV) is 60 x 36 degrees and the eye-box is larger than 100 mm, which is comfortable enough for two-eye viewing. The system includes a pupil and gaze tracker, which is implemented with a single camera and using computer vision algorithms. The gaze tracker, which is experimented on different users, is able to select the correct depth plane based on the shift in the interpupillary distance when the convergence angle of the user's eyes changes. The rendered content can be distributed to both depth planes and the background scene simultaneously. Thus, the user can select and interact with the content at the correct depth in a natural and comfortable way. The prototype system can be used in tasks that demand wide FOV and multiple focal planes and as an AR and vision research tool.
Işığı Verimli Kullanan ve Foveated Gözlük Mimarileri
Augmented reality (AR) displays in eyeglass form are seen as the future of information displays. The image generation unit within the AR glasses, which is called a spatial light modulator (SLM), and optical architectures are among the major limitations of current AR displays. For the ultimate AR experience, the viewer should see high resolution images that cover a large portion of their viewing angle. With the current SLM technology either large viewing angle with low resolution images or high resolution images with small viewing angle can be provided. This trade-off is one of the key limitations of AR glass technology. Considering that the human eye has high resolution only at its central vision and the rest of the view gradually seems blurred towards the periphery, more efficient displays can be designed by mimicking the human eye. These architectures that show sharp images only to the central vision and low resolution images to the rest of the viewing angle are known as foveated displays in the literature. Foveated displays require eye tracking and special optical architectures that can change the position of the high resolution image within the larger viewing angle of the user, depending on the user's viewing direction. In this thesis, we present three different foveated AR glass architectures and a fast, reliable and computationally light pupil tracker algorithm that we developed for foveated display architectures. In our pinhole display we extended the eyebox using an array of light sources (LEDs), which are individually turned-on based on the pupil position in real-time. We demonstrated a 37° circular field-of-view (FOV) with a luminance of 360 cd/m2 using an LED with only 0.42 lumen output. We achieved an extended eyebox of 14x10 mm in size with 1 mm static eyebox per LED and the static eyeboxes are spaced 2 mm apart. The resulting display is super light-efficient as most of the LED light is captured by the eye. In our holographic display with rotating beam splitters, a static 7x4° instantaneous FOV is mechanically steered in sync with the rotations of the eye, so that the viewer always sees a high resolution image at the central vision. We demonstrated 37x4° extended FOV, which is the first holographic foveated head-worn display that works in closed-loop with a pupil tracker in the literature. In our eye-centric design, we eliminated the moving parts by imaging the SLM to the rotation center of the eye. With this architecture, the SLM automatically follows the central vision by design and the holographic image is projected on to fovea by updating the hologram on the SLM. We demonstrated 28x28° instantaneous FOV, which is extended to 60x40°.
Holografik ve foveated göze yakın ekran
Augmented reality (AR) displays are attracting more and more attention due to their potential in industrial, medical and consumer-level applications. The ability of embedding computer-generated information with the physical world seamlessly is unique to AR displays in glass-like form factor, which is the reason why they are considered the next-generation of display devices. Increasing the field-of-view (FOV) while providing viewing comfort and true 3D vision are the most important challenges in state-of-the-art AR display design. Computational holography is the only technology that can offer true 3D with all the required depth cues. Holographic near-eye displays (HNED) can provide continuous depth planes with the correct accommodation for a comfortable 3D experience. Existing approaches for HNEDs have small FOV and exit pupil size, which are limited by the number of pixels on the spatial light modulator. As an example, conventional holographic head-worn display architectures are limited to about 20×10 degrees FOV using a 4K resolution SLM panel and have fixed FOV. Dynamic foveated displays with a steerable FOV across the visual field are desired. Proposed architectures require multiple moving components, which are not practical for head-worn displays due to speed, size, and power requirements. We present a new optical architecture that can overcome those limitations and substantially extend the FOV supported by the SLM. Our architecture automatically follows the gaze of the viewer's pupil without any moving parts. Moreover, it mimics human vision by providing varying resolution across the FOV resulting in better utilization of the available space-bandwidth product of the SLM. We achieved 28×28 degrees instantaneous FOV within an extended FOV of 60×40 degrees using a 4K SLM, effectively providing a total enhancement of >3× in instantaneous FOV area, >10× in extended FOV area. Furthermore, we have developed a novel hologram computation algorithm for the display and developed a software-based hologram correction procedure that can correct for undesired aberrations. Computer-generated holograms were used to provide 3D depth cues such as focus blur within the instantaneous FOV.
Ultra hızlı ışık modülasyonu için manyetooptik malzemeler ve cihaz mimarileri
Magnetooptical (MO) Faraday and Kerr effects lead to rotation of the polarization plane of light in interaction with a magnetized matter. In combination with the intrinsic high speed of magnetization reversal which can go down to femtosecond time scales, MO effects enable magnetooptical spatial light modulators (MOSLMs), promising for nonvolatile, ultrafast, and high-resolution spatial modulation of light. The recent developments in low-power magnetization switching bring about major breakthroughs in MOSLMs benefiting beyond state-of-the-art holography, heads-up displays, virtual and augmented reality systems, data storage, optical communications, solid-state light detection and ranging (LIDAR), and emerging optical devices. The inherent weakness of the MO effects and difficulty in producing high-quality MO materials are the main obstacles on the way of the practicality and industrial development of the MOSLMs. This thesis addresses the challenges associated with MOSLMs and introduces novel solutions for realizing practical MO devices. The advancement of MOSLMs in different aspects including materials engineering, driving system, and device architecture is reviewed in the thesis to locate the present state in this research field. The MO figure of merit for various MO materials reported in the literature is calculated and compared using finite-difference time-domain (FDTD) simulations, suggesting bismuth-substituted yttrium iron garnets (Bi:YIG) with Bi1Y2Fe5O12 composition as the superior MO component for MOSLMs. Growth of Bi:YIG thin films on different substrates, by pulsed laser deposition using different growth parameters, is studied in order to optimize the growth conditions. The structural and optical characterization of the Bi:YIG films reveal the accomplishment of epitaxial growth on the garnet substrates and growth of poly-crystalline single-phase films on quartz substrates. In addition to the study of the materials prospect, photonic devices for the enhancement of MO effects are designed. Various magnetophotonic crystal (MPC) structures are investigated for high-contrast MOSLMs. By optimization of the MPC configuration and layer thicknesses, a three-defect MPC is demonstrated capable of simultaneous enhancement of Faraday rotation at three fundamental wavelengths of red, green, and blue (RGB) within a pixel. Rotation values of 20-55° are achieved in an overall thickness smaller than 1.5 μm including submicron garnet layers, whereas the optical loss is retained below 20 dB. The resonant approaches for enhancing the MO effects generally result in a narrow operation band and limit the applications. In this study, a magnetoplasmonic metasurface is designed for the broadband enhancement of the Faraday effect. While Faraday rotation in a bare Bi:YIG film is below 0.02° in the studied range of 600-1600 nm, the proposed metasurface yields few degrees of rotation in a broad spectral range, with a maximum exceeding 6.5°. It is shown that the MO response of the metasurface and the operation band can be further improved by optimizing the geometry and excitation parameters, leading to rotation values higher than 20° for a total thickness of 15 nm. Finally, the guidelines for designing a desired magnetoplasmonic metasurface are presented and the application of plasmonic metasurfaces in sensing systems is discussed. Different metasurface designs are modeled, fabricated, and tested for surface-enhanced Raman spectroscopy (SERS) and enhancement of the Raman signal by over three orders of magnitude is experimentally demonstrated.