• Accelerated Ray Tracing for Headlamp Simulation

      Chipman, Russell A.; Kimura, Ryota; Chipman, Russell A.; Koshel, Richard J.; Takashima, Yuzuru (The University of Arizona., 2017)
      High speed ray tracing for a headlamp lens and advanced algorithms for ray analysis are investigated. First, the basics of ray tracing, Algorithm to search intersection points between a ray and surfaces and refraction are reviewed, including intersection search for a ray with aspheric surfaces. A spherical surface, a plane surface, and a point cloud are reviewed as objects. Snell’s law is introduced from Fermat’s principle in 2D. Then, it extended to three dimensional spaces. Second, photometry is reviewed for the post processing of ray tracing, due to the convolution effect of its area. To accelerate ray tracing, the Nvidia GPU and CUDA platform of general purpose computing is evaluated in this study. Its architecture and memory architecture is unique. In addition, Mathematica is used in this study for file IO and graphic output with unique CUDA interface. Then, the each ray tracing method is validated using a spherical lens, aspherical lens, and a headlamp lens. From the comparison, the double precision floating Nagata triangular patch method is best in accuracy. Acceleration of ray tracing using CUDA was successful having 2 times implement in 362 million rays traced, compared to commercially available ray trace packages under the same computing resources.
    • All-Polymer Based Fabrication Process for an All-Polymer Flexible and Parellel Optical Interconnect

      Takashima, Yuzuru; Yang, Jilin; Takashima, Yuzuru; Liang, Rongguang; Milster, Tom (The University of Arizona., 2015)
      This thesis proposed and demonstrated a new all-polymer based fabrication process for an all-polymer flexible and parallel optical interconnect cable having a vertical light coupler, which can not only cut down the cost by eliminating metallization process for alignment but also facilitate both in production and application. Throughout the process, polyimide was used as the substrate, coated by Epoclad as claddings, then AP2210B and WPR 5100 were used to fabricate waveguides and 45 degree mirror couplers, respectively. In addition, precisely aligned mirror couplers to waveguides are fabricated by using polymer-based, non-metallic, and transparent alignment marks. Conventional and metallic alignment marks are easy to be detected by camera, when a layer of high reflective material, generally Cr metal, is patterned. However, transparent polymer material is used in this process, as alignment marks made of it which are actually buried phase structures. Therefore, it is hardly to be observed by conventional microscopy system. Hence, to increase the contrast of the alignment marks, I proposed and tested a feature specific alignment camera system for which the shape and depth of the alignment marks are optimized for phase-based imaging, such as phase contrast and Schlieren imaging. The results showed a contrast enhancement of alignment marks image compared to that of a conventional microscopy system. By using the fabrication and alignment process, process for adding waveguides to the structure is identified by using the polymer based alignment marks on the WPR 5100 layer. Mask was made by etch down process using fused silica wafer plate, Cr and AZ 3312 photoresist. At last, the developed and proposed process provides means of all-polymer based fabrication process for a flexible and parallel optical interconnect.
    • Applications of Phase and Amplitude Spatial Light Modulators

      Takashima, Yuzuru; Chen, Guanghao; Hart, Michael; Cvijetic, Milorad (The University of Arizona., 2018)
      Spatial light modulators (SLM) have been widely adopted for applications such as optical data storage, optical tweezers, laser beam shaping including generation and detection of Optical Angular Momentum. In this thesis, we experimentally demonstrate two applications of Liquid Crystal (LC) SLM for eigenmode multiplexing for holographic data storage, and fast binary modulation by using MEMS and amplitude based SLM. In the holographic data storage system (HDSS) research, we successfully achieved nine holograms recording with angular multiplexing and eigenmode multiplexing methods using projector hacked low-cost SLM. In DMD (digital micromirror device) beam scanning, we realized beam scanning with single DMD binary amplitude holography and phase holography. With the phase modulator, total efficiency of the system reaches around 16% and is expected to be 32% with light recycling method. In the last part of the thesis, we also introduce our work on repurposing a commercial video projector as a ?? phase-only SLM for our research. Phase modulation accuracy was tested with a Linnik microscope interferometer. Detailed modification procedures are given at the end of the thesis for future application of the projector hacked SLMs.
    • Astigmatism in Systems With Double Plane Symmetry

      Sasian, Jose; Kirk, William Slater; Peng, Lei Lei; Takashima, Yuzuru (The University of Arizona., 2018)
      The waveform aberration equation is developed to sixth order and nodal aberrations are explored using combinations of the aberration terms.
    • Bessel-Gaussian Beams and Physical-Layer Security in a Free-Space Optical Channel

      Djordjevic, Ivan; Wang, Tyan-Lin; Kolesik, Miroslav; Takashima, Yuzuru (The University of Arizona., 2018)
      Physical-layer security in free-space optical communications channels can be compromised when an eavesdropper performs optical beam-splitting attacks over an atmospheric channel. In this scenario the free-space optical communications channel is referred to as an optical wiretap channel, which is an extension of Wyner’s wiretap channel model. For secure communications, Shannon's classical solution requires the transmitter and receiver to share a common secret key of length greater than or equal to the message length. This can become intractable as the message length grows in size. On the other hand the wiretap channel model proposed by Wyner is based on the premise that secrecy can be obtained even without a shared key if the noisy and degraded channel conditions experienced by the eavesdropper can be exploited. The primary metric to analyze physical-layer security is secrecy capacity, the highest data capacity at which the eavesdropper is unable to obtain information sent from the transmitter to the receiver. Positive secrecy capacity is possible when the main channel to the receiver is of better quality than the channel to the eavesdropper in the sense of signal-to-noise ratio. In this thesis we study how transmitting data using orbital angular momentum modes such as Laguerre-Gaussian and Bessel-Gaussian beams can achieve higher secrecy capacities compared to that of ordinary Gaussian beams within the turbulent conditions of an optical channel. Using computer simulations and experiments with spatial light modulators we demonstrate that Bessel- Gaussian beams provide 10 to 30 bits/sec/Hz higher secrecy capacity over their corresponding Laguerre-Gaussian counterparts in the weak to medium turbulence regimes, indicating a better resilience to atmospheric turbulence effects. We follow this with another experiment exclusively conducted with Bessel-Gaussian beams onto which we encode a pseudo-random binary sequence to emulate data transmission over an optical wiretap channel. Bit-error rate curves for the intended receiver and the eavesdropper are calculated from which estimates of secrecy capacity are derived. We demonstrate that the bit-error rate curves for the eavesdropper are consistently worse than those of the intended receiver under several turbulence conditions and find further evidence of an error floor even when the eavesdropper uses an optical amplifier. While these results show promise for secure communications further research will be needed to optimize the quality of these beams to help realize a practical system.
    • Diffusers in Coherently Illuminated, Wide Field of View Applications

      Takashima, Yuzuru; Odom, Garret; Milster, Tom; Fest, Eric (The University of Arizona., 2016)
      Diffusers are devices that are designed to spread or scatter light. Many different types of diffusers are readily available in the commercial and scientific industries, but most are designed with a specific application in mind. Thus, when attempting to use a diffuser in an unconventional way, it is important to understand how it will behave in the system it will be used in. One example is a diffuser in a coherently illuminated, wide field of view system such as a laser spot tracker. For some diffusers, coherent illumination and/or off-axis illumination can have a major impact on their diffusing properties, which may or may not be acceptable to system performance. This project evaluates the pros and cons of several types of diffusers in order to identify the most effective solution based on the parameters of a system, using a laser spot tracker as an example. First, three diffusers are down selected from the list based on their refractive and diffractive properties. Next, the candidates are evaluated analytically and/or experimentally to characterize their behavior when illuminated by a collimated laser over a wide range of incident angles. Results suggest that a computer generated diffractive diffuser is the most flexible design option for the described laser spot tracker, but some drawbacks such as diffraction efficiency and maximum diffusion angle do need to be considered. This selection method can be extended to serve as a guide for making the proper diffuser choice in many different applications.
    • Overview of the Microscope Objective

      Sasian, Jose M.; Niu, Ruijuan; Sasian, Jose M.; Takashima, Yuzuru; Hua, Hong (The University of Arizona., 2017-06-14)
      Microscopes are widely used in research and industry. The objective lens is the most significant part of the microscope. Some characteristics and different types of microscope objectives are discussed in this thesis. The markings on the objective indicate some main optical characteristics. However, it is not always possible to know the materials, the radius or the thickness of each surface in an objective lens and it is not easy to simulate an objective without this data. In this thesis, we build a first order model which can simulate a refractive microscope objective when the magnification and numerical aperture are known. The model contains a thin lens made by two standard surfaces and also simulates the principal planes. This model provides more accurate ray heights and it is aplanatic. Some design examples of an objective lens are also discussed in order to get a better understanding of design and optimization considerations.
    • Radiometric Calibration of a Hybrid RCWT Imaging Model

      Milster, Thomas D.; Pratap Kadam, Poonam; Milster, Thomas D.; Takashima, Yuzuru; Kim, Young-Sik (The University of Arizona., 2014)
      The applications of low-light imaging are widespread in areas such as biomedical imaging, remote sensing, ratiometric imaging, lithography, etc. The goal of this work is to develop a radiometrically scaled hybrid RCWT calculator to count the photons detected for such applications. The rigorous computation of different imaging models are discussed. An approach to calibrate the radiometry of the hybrid RCWT model for partially coherent illumination is presented. The diffraction from the object is evaluated rigorously using the hybrid RCWT model. A test bench is set up to validate the radiometrically scaled simulations. In all the cases considered, simulation and experiment agree within a 40% difference.
    • Scalable and Controllable Fabrication Process for Membrane Mirrors

      Takashima, Yuzuru; Phan, Phuoc Andy; Kim, Dae Wook; Walker, Chris (The University of Arizona., 2019)
      With the future need of larger telescopes, membrane mirrors are an option to create large-scale reflectors needed for space base observation at a lower cost than conventionally made mirrors. Proposed methods of how membrane mirrors have been put into place with ideas such as Dr. Chris Walker’s inflatable spherical telescope and the L’Garde Inflatable Antenna Experiment (IAE). With data from L’Garde, Dr. Aden Meinel presented the curvature of a membrane mirror does not produce a spherical curvature. From there a look into what sort of aberrations that curvature produces and attempts to correcting it or processing it to other benefits by altering the material. Procedures will be done on a small-scale in a process that can be applied to larger-scale systems.
    • Single Chip LIDAR with Discrete Beam Steering by Digital Micromirror Device

      Takashima, Yuzuru; Smith, Braden James; Takashima, Yuzuru; Milster, Tom; Kim, Young-Sik (The University of Arizona., 2017)
      A novel method of beam steering that utilizes a mass-produced Digital Micromirror Device (DMD) enables a large field of view and reliable single chip Light Detection and Ranging (LIDAR). Using a short pulsed laser, the micromirrors' rotation is frozen mid-transition which forms a programmable blazed grating which efficiently redistributes the light to a single diffraction order, among several. With a nanosecond 905nm laser and Si avalanche photo diode, measurement accuracy of < 1 cm for 3340 points/sec is demonstrated over a 1 m distance range and with a 48° full field of view.
    • Single Element Multiplexing and De-multiplexing System for Free Space OAM Communications

      Takashima, Yuzuru; Winkler, Paul Sebastian; Takashima, Yuzuru; Milster, Thomas D.; Cvijetic, Milorad (The University of Arizona., 2017)
      Orbital Angular Momentum (OAM) modes promise an exciting future for communications due to the infinite number available and their orthogonal nature. However modern implementations of OAM mode communications utilize a multi-element approach to multiplexing. This multi-element approach wastes power and becomes increasingly complex and expensive as the number of modes in the system increases. This makes the multi-approach method not scalable. In this thesis we explore single element OAM multiplexing and de-multiplexing. A system utilizing single element multiplexer and de-multiplexer, was designed built and qualified. We have demonstrated that such a system can easily achieve a BER of less than 1% and is thusly feasible.
    • Single-Chip LiDAR by Multi-Order and Multi-Pulse Beam Steering with Digital Micro Mirror Device

      Takashima, Yuzuru; Rodriguez, Joshua Miguel; Kim, Dae Wook; Kim, Young Sik (The University of Arizona., 2019)
      We demonstrate the feasibility of enhancing the scanning rate for MEMS and diffraction based beam steering employing Digital Micromirror Device (DMD) by one to two orders of magnitude, which is configured as a programmable blazed grating. The tilt movement of micromirrors synchronizes with multiple pulses from multiple laser sources that sequen- tially redirect the pulses to multiple diffraction orders within μs. The approach opens up a pathway to achieve a LIDAR system with a scanning rate over 1M samples/s while leveraging a state of the art DMD and a moderate number of laser sources.
    • Study of the Impact of Nonlinearities on Advanced Modulation Formats in Optical Systems and Networks

      Cvijetic, Milorad; Wang, Yi-Ping; Cvijetic, Milorad; Kieu, Khanh; Takashima, Yuzuru (The University of Arizona., 2017)
      Chromatic dispersion, Kerr nonlinearity, and amplified spontaneous emission (ASE) noise are three common problems for the optical communication systems. For the systems using direct detection scheme, we detect the power of the signal. Therefore, the information is carried by the signal power, which is pulse amplitude modulation (PAM). In this system, chromatic dispersion and Kerr nonlinearity will broaden the pulse and cause intersymbol interference, while ASE noise will degrade the signal to noise ratio and increase the error rate. For the system using coherent detection, we can detect not only the power but also the phase of the signal. Thus, the information can be carried by the power and the phase of the signal, which is quadrature amplitude modulation (QAM). In this system, the signal will see a phase shift during the propagation induced by the Kerr nonlinearity, which will cause an error if the phase shift is not corrected on the receiver side. In order to optimize the performance or design the solution for the system, a careful study of the impact of these three effects on the signal is needed. In this thesis, I study the theory of the pulse broadening effect caused by chromatic dispersion and Kerr nonlinearity, and as well as the bit error rate performance with the accumulation of ASE noise. Moreover, I use split-step Fourier method to solve the nonlinear Schrödinger equation in MATLAB and simulate the propagation of 2-PAM and 4-QAM signal. The impact of these three effects and the bit error rate behavior of the coherent detection system are demonstrated and discussed.