Design And Fabrication of High Numerical Aperture And Low Aberration Bi-Convex Micro Lens Array

Micro lens array is crucial in various kinds of optical and electronic applications. A micro lens array with high numerical aperture (NA) and low aberration is in particular needed. This research is aimed to design and fabricate such a micro lens array with simple structure while keeps the same NA of a same-diameter hemisphere lens. A bi-convex semispherical micro lens array, with corresponding NA 0.379, by PDMS is first designed and analyzed. Experiments are further conducted to fabricate the designed micro lens array by the thermal reflow process. The formed profile is then sputtered with copper to serve as the mold. The front and the rear micro lens array are fabricated by plating PDMS to the mold and then assembled to form the designed micro lens array

Modeling and simulation of surface profile forming process of microlenses and their application in optical interconnection devices

Free space micro-optical systems require to integrate microlens array, micromirrors, optical waveguides, beam splitter, etc. on a single substrate. Out-of-plane microlens array fabricated by direct lithography provides pre-alignment during mask fabrication stage and has the advantage of mass manufacturing at low cost. However, this technology requires precise control of the surface profile of microlenses, which is a major technical challenge. The quality control of the surface profile of microlenses limits their applications. In this dissertation, the surface forming process of the out-of-plane microlenses in UV-lithography fabrication was modeled and simulated using a simplified cellular automata model. The microlens array was integrated with micromirrors on a single silicon substrate to form a free space interconnect system. The main contributions of this dissertation include: (1) The influences of different processing parameters on the final surface profiles of microlenses were thoroughly analyzed and discussed. A photoresist etching model based on a simplified cellular automata algorithm was established and tested. The forming process and mechanism of the microlens surface profile were explained based on the established model. (2) Microlens arrays with different parameters were designed, fabricated, and tested. The experiment results were compared with the simulation results. The possible causes for the deviation were discussed. (3) A microlens array based beam relay for optical interconnection application was proposed. A sequence of identical microlens array was fabricated on a single silicon substrate simultaneously and its optical performance was tested. A fast replication method for the microlens optical interconnects using PDMS and UV curable polymer was developed. A selective deposition method of micro-optical elements using PDMS ‘lift-off’ technique was realized. No shadow mask was needed during deposition process. With the continuous advances in the integration of micro-optical systems, direct lithography of micro-optical elements will be a potential technology to provide both precision alignment and low cost in manufacturing process. Microlenses and microlens array with precisely controlled surface profiles will be an important part in the micro-optical system

Array microscopy technology and its application to digital detection of Mycobacterium tuberculosis

Tuberculosis causes more deaths worldwide than any other curable infectious disease. This is the case despite tuberculosis appearing to be on the verge of eradication midway through the last century. Efforts at reversing the spread of tuberculosis have intensified since the early 1990s. Since then, microscopy has been the primary frontline diagnostic. In this dissertation, advances in clinical microscopy towards array microscopy for digital detection of Mycobacterium tuberculosis are presented. Digital array microscopy separates the tasks of microscope operation and pathogen detection and will reduce the specialization needed in order to operate the microscope. Distributing the work and reducing specialization will allow this technology to be deployed at the point of care, taking the front-line diagnostic for tuberculosis from the microscopy center to the community health center. By improving access to microscopy centers, hundreds of thousands of lives can be saved. For this dissertation, a lens was designed that can be manufactured as 4×6 array of microscopes. This lens design is diffraction limited, having less than 0.071 waves of aberration (root mean square) over the entire field of view. A total area imaged onto a full-frame digital image sensor is expected to be 3.94 mm2, which according to tuberculosis microscopy guidelines is more than sufficient for a sensitive diagnosis. The design is tolerant to single point diamond turning manufacturing errors, as found by tolerance analysis and by fabricating a prototype. Diamond micro-milling, a fabrication technique for lens array molds, was applied to plastic plano-concave and plano-convex lens arrays, and found to produce high quality optical surfaces. The micro-milling technique did not prove robust enough to produce bi-convex and meniscus lens arrays in a variety of lens shapes, however, and it required lengthy fabrication times. In order to rapidly prototype new lenses, a new diamond machining technique was developed called 4-axis single point diamond machining. This technique is 2-10x faster than micro-milling, depending on how advanced the micro-milling equipment is. With array microscope fabrication still in development, a single prototype of the lens designed for an array microscope was fabricated using single point diamond turning. The prototype microscope objective was validated in a pre-clinical trial. The prototype was compared with a standard clinical microscope objective in diagnostic tests. High concordance, a Fleiss’s kappa of 0.88, was found between diagnoses made using the prototype and standard microscope objectives and a reference test. With the lens designed and validated and an advanced fabrication process developed, array microscopy technology is advanced to the point where it is feasible to rapidly prototype an array microscope for detection of tuberculosis and translate array microscope from an innovative concept to a device that can save lives

New techniques of multiple integral field spectroscopy

The work of this thesis is to investigate new techniques for Integral Field Spectroscopy (IPS) to make the most efficient use of modem large telescopes. Most of the work described is aimed at the FMOS for the SUBARU 8m telescope. Although this is primarily a system for Multiple Object Spectroscopy (MOS) employing single fibres, there is an option to include a multiple-IFS (MIPS) system. Much of this thesis is therefore aimed at the design and prototyping of critical systems for both the IPS and MOS modes of this instrument. The basic theory of IFU design is discussed first. Some particular problems are described and their soludons presented. The design of the MIPS system is described together with the construction and testing of a prototype deployable IFU. The assembly of the pickoff/fore-optics, microlens array and fibre bundle and their testing are described in detail. The estimated performance of the complete module is presented together with suggestions for improving the system efficiency which is currently limited by the performance of the microlens array. The prototyping of the MIPS system is supported by an extensive programme of testing of candidate microlens arrays. Another critical aspect of the instrument is the ability to disconnect the (IPS and MOS) fibre input which is installed on a removable prime focus top-end ring from the spectrographs which are mounted elsewhere on the telescope. This requires high-performance multiple fibre connectors. The designs of connectors for the MOS and IPS modes are described. Results from the testing of a prototype for the MOS mode are presented. This work is supported by a mathematical model of the coupling efficiency which takes into account optical aberrations and alignment errors. The final critical aspect of FMOS which has been investigated is the design of the spectrographs. The baseline system operates in the near-infrared (NIR) but an additional visible channel is an option. Efficient designs for both the visible and NIR systems are presented. The design of the NIR spectrograph presents challenges in the choice of materials for the doublet and triplet lenses employed. The choice of material and the combinations in which they can be used are described. This thesis shows that all these critical aspects of FMOS have good solutions that will result in good performance of the whole instrument. For the multiple IFU system, the prototype demonstrates acceptable performance which can be made excellent by the use of a better microlens array. The multiple fibre connector prototype already indicates excellent performance. Finally, the spectrograph designs presented should result in high efficiency and good image quality

Compact microscopy systems with non-conventional optical techniques

This work has been motivated by global efforts to decentralize high performance imaging systems through frugal engineering and expansion of 3D fabrication technologies. Typically, high resolution imaging systems are confined in clinical or laboratory environment due to the limited means of producing optical lenses on the demand. The use of lenses is an essential mean to achieve high resolution imaging, but conventional optical lenses are made using either polished glass or molded plastics. Both are suited for highly skilled craftsmen or factory level production. In the first part of this work, alternative low-cost lens-making process for generating high quality optical lenses with minimal operator training have been discussed. We evoked the use of liquid droplets to make lenses. This unconventional method relies on interfacial forces to generate curved droplets that if solidified can become convex-shaped lenses. To achieve this, we studied the droplet behaviour (Rayleigh-Plateau phenomenon) before creating a set of 3D printed tools to generate droplets. We measured and characterized the fabrication techniques to ensure reliability in lens fabrication on- demand at high throughput. Compact imaging requires a compact optical system and computing unit. So, in the next part of this work, we engineered a deconstructed microscope system for field-portable imaging. Still a core limitation of all optical lenses is the physical size of lens aperture – which limits their resolution performance, and optical aberrations – that limit their imaging quality performance. In the next part of this work, we investigated use of computational optics-based optimization approaches to conduct in situ characterization of aberrations that can be digitally removed. The computational approach we have used in this work is known as Fourier Ptychography (FP). It is an emerging computational microscopic technique that combines the use of synthetic aperture and iterative optimization algorithms, offering increased resolution, at full field-of-view (FOV) and aberration-removal. In using FP techniques, we have shown measurements of optical distortions from different lenses made from droplets only. We also, investigated the limitations of FP in aberration recovery on moldless lenses. In conclusion, this work presents new opportunities to engineer high resolution imaging system using modern 3D printing approaches. Our successful demonstration of FP techniques on moldless lenses will usher new additional applications in digital pathology or low-cost mobile health

Doctor of Philosophy

dissertationOptics is an old topic in physical science and engineering. Historically, bulky materials and components were dominantly used to manipulate light. A new hope arrived when Maxwell unveiled the essence of electromagnetic waves in a micro perspective. On the other side, our world recently embraced a revolutionary technology, metasurface, which modifies the properties of matter-interfaces in subwavelength scale. To complete this story, diffractive optic fills right in the gap. It enables ultrathin flat devices without invoking the concept of nanostructured metasurfaces when only scalar diffraction comes into play. This dissertation contributes to developing a new type of digital diffractive optic, called a polychromat. It consists of uniform pixels and multilevel profile in micrometer scale. Essentially, it modulates the phase of a wavefront to generate certain spatial and spectral responses. Firstly, a complete numerical model based on scalar diffraction theory was developed. In order to functionalize the optic, a nonlinear algorithm was then successfully implemented to optimize its topography. The optic can be patterned in transparent dielectric thin film by single-step grayscale lithography and it is replicable for mass production. The microstructures are 3?m wide and no more than 3?m thick, thus do not require slow and expensive nanopatterning techniques, as opposed to metasurfaces. Polychromat is also less demanding in terms of fabrication and scalability. The next theme is focused on demonstrating unprecedented performances of the diffractive optic when applied to address critical issues in modern society. Photovoltaic efficiency can be significantly enhanced using this optic to split and concentrate the solar spectrum. Focusing through a lens is no news, but we transformed our optic into a flat lens that corrects broadband chromatic aberrations. It can also serve as a phase mask for microlithography on oblique and multiplane surfaces. By introducing the powerful tool of computation, we devised two imaging prototypes, replacing the conventional Bayer filter with the diffractive optic. One system increases light sensitivity by 3 times compared to commercial color sensors. The other one renders the monochrome sensor a new function of high-resolution multispectral video-imaging

비등방성 광학 소자를 이용한 광 시야각 근안 디스플레이

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2019. 2. 이병호.Near-eye display is considered as a promising display technique to realize augmented reality by virtue of its high sense of immersion and user-friendly interface. Among the important performances of near-eye display, a field of view is the most crucial factor for providing a seamless and immersive experience for augmented reality. In this dissertation, a transmissive eyepiece is devised instead of a conventional reflective eyepiece and it is discussed how to widen the field of view without loss of additional system performance. In order to realize the transmissive eyepiece, the eyepiece should operate lens to virtual information and glass to real-world scene. Polarization multiplexing technique is used to implement the multi-functional optical element, and anisotropic optical elements are used as material for multi-functional optical element. To demonstrate the proposed idea, an index-matched anisotropic crystal lens has been presented that reacts differently depending on polarization. With the combination of isotropic material and anisotropic crystal, the index-matched anisotropic crystal lens can be the transmissive eyepiece and achieve the large field of view. Despite the large field of view by the index-matched anisotropic crystal lens, many problems including form factor still remain to be solved. In order to overcome the limitations of conventional optics, a metasurface is adopted to the augmented reality application. With a stunning optical performance of the metasurface, a see-through metasurface lens is proposed and designed for implementing wide field of view near-eye display. The proposed novel eyepieces are expected to be an initiative study not only improving the specification of the existing near-eye display but opening the way for a next generation near-eye display.근안 디스플레이는 높은 몰입감과 사용자 친화적인 인터페이스로 인해 증강 현실을 구현하는 가장 효과적인 기술로 최근 활발한 연구가 계속되고 있다. 이러한 근안 디스플레이의 중요한 성능 중 시야각은 매끄럽고 몰입감 있는 경험을 사용자에게 전해줌으로써 가장 중요한 광학적 평가지표 중에 하나이다. 본 논문에서는 기존의 반사형 아이피스 (eyepiece) 를 대신하는 투과형 아이피스를 제안한다. 이러한 투과형 아이피스를 구현하기 위해서는 외부 정보에 대해서는 투명한 유리와 같이 투과시키며, 동시에 가상 정보는 렌즈로 작동하여 먼 거리에 띄울 수 있는 광학소자를 개발하여야 한다. 이러한 투과형 아이피스를 구현하기 위해서 편광에 따라 다르게 반응하는 굴절률 정합 이방성 결정 렌즈 (index-matched anisotropic crystal lens) 를 제안하였다. 이방성 결정 구조 (anisotropic crystal)로 이루어진 렌즈와 이를 둘러싼 등방성 물질 (isotropic crytal) 로 이루어진 굴절률 정합 이방성 결정 렌즈는 편광에 따라 다르게 작동한다. 이러한 투과형 아이피스는 기존의 근안 디스플레이에 비해 넓은 시야각을 제공할 수 있지만 이방성 결정 구조의 낮은 굴절률 차이로 인해 시스템의 크기가 커지는 단점을 가지고 있다. 본 논문에서는 이러한 단점을 개선하기 위해 메타 표면을 증강 현실 디스플레이 분야에 적용하였다. 메타 표면의 기존 광학 소자를 능가하는 놀라운 광학 성능을 이용하여 넓은 시야각을 가지는 근안 디스플레이를 구현하기 위해 투명 메타 렌즈를 제안하였다. 편광에 따라 다르게 반응하는 투명 메타렌즈는 넓은 시야각과 경량화 시스템 구현이 가능하며 이를 입증하기 위해 투명 메타렌즈의 설계 방법 뿐 아니라 실제 구현을 통한 가능성을 입증하였다. 이러한 새로운 아이피스에 대한 개념은 기존의 근안 디스플레이의 사양 개선에 유용하게 사용될 뿐 아니라 차세대 근안 디스플레이를 위한 선도적인 역할을 할 것으로 기대된다.Abstract Contents List of Tables List of Figures Near-eye displays with wide field of view using anisotropic optical elements Chapter 1 Introduction 1.1 Near-eye displays for augmented reality 1.2 Optical performances of near-eye display 1.3 State-of-the-arts of near-eye display 1.4 Motivation and contribution of this dissertation Chapter 2 Transmissive eyepiece for wide field of view near-eye display 2.1 Transmissive eyepiece for near-eye display Chapter 3 Near-eye display using index-matched anisotropic crystal lens 3.1 Introduction 3.2 Index-matched anisotropic crystal lens 3.2.1 Principle of the index-matched anisotropic crystal lens 3.2.2 Aberration analysis of index-matched anisotropic crystal lens 3.2.3 Implementation 3.3 Near-eye displays using index-matched anisotropic crystal lens 3.3.1 Near-eye display using index-matched anisotropic crystal lens 3.3.2 Flat panel type near-eye display using IMACL 3.3.3 Polarization property of transparent screen 3.4 Conclusion Chapter 4 Near-eye display using metasurface lens 4.1 Introduction 4.2 See-through metasurface lens 4.2.1 Metasurface lens 4.3 Full-color near-eye display using metasurface lens 4.3.1 Full-color near-eye display using metasurface lens 4.3.2 Holographic near-eye display using metasurface lens for aberration compensation 4.4 Conclusion Chapter 5 Conclusion Bibliography AppendixDocto

Various Applications of Methods and Elements of Adaptive Optics

This volume is focused on a wide range of topics, including adaptive optic components and tools, wavefront sensing, different control algorithms, astronomy, and propagation through turbulent and turbid media