Three Dimensional Optical Data Storage in Polymeric Systems
Total Page：16
File Type：pdf, Size：1020Kb
THREE DIMENSIONAL OPTICAL DATA STORAGE IN POLYMERIC SYSTEMS By CHRISTOPHER J. RYAN Submitted in partial fulfillment of the requirements For the degree of Doctor of Philosophy Dissertation Adviser: Dr. Jie Shan Department of Physics CASE WESTERN RESERVE UNIVERSITY May, 2012 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of Christopher James Ryan candidate for the Doctorate of Philosophy degree Dr. Jie Shan Dr. Kenneth Singer Dr. Rolfe Petschek Dr. Lei Zhu January 20, 2012 Table Of Contents List of Tables 4 List of Figures 5 Acknowledgements 7 Abstract 8 Chapter 1 Introduction to Optical Data Storage 9 1.1 Motivation 9 1.2 Features of Optical Data Storage 9 1.3 A Brief History of Optical Data Storage 12 1.4 New Techniques for Optical Data Storage 15 1.5 3D Optical Data Storage 19 1.6 Multilayered Films as Storage Media 22 1.7 Coextruded Polymeric Films 23 1.8 Chapter Content 24 Chapter 2 Two‐Photon Induced Aggregate Switching of Excimer‐Forming Dyes 25 2.1 Introduction 25 2.2 Materials 27 2.3 TPA of C‐18 RG Dye 30 2.4 Experiment 31 2.5 Results and Analysis 32 2.6 Chapter Conclusion 34 Chapter 3 High Density Optical Data Storage in Multilayer Polymer Films 36 3.1 Introduction 36 3.2 Sample Fabrication 39 1 3.3 Film Properties 41 3.4 Optical Patterning and Reading 42 3.5 Determination of the Crosstalk 47 3.6 Modeling of the Layer Crosstalk 48 3.7 Comparison to Crosstalk Model 50 3.8 Chapter Conclusion 52 Chapter 4 The effect of Multilayering on the Contrast of 3D Data Storage Media 53 4.1 Introduction 53 4.2 Geometric Restriction to the Data Density 55 4.3 Determining the Signal Contrast and Background Noise 57 4.4 Comparing Multilayered Films to Monoliths 61 4.5 Results 63 4.6 Shot Noise and Dark Current 66 4.7 Chapter Conclusion 68 Chapter 5 Thermal Influence on Biexciton Annihilation in Zinc Phthalocyanine 69 5.1 Introduction 69 5.2 Materials 70 5.3 Experiment 72 5.4 Results 73 5.5 Physical Interpretation of the Time Dependence of the Collision Rate 76 5.6 Thermal Dependence of the ZnPc 80 5.7 Conclusion 83 Appendix A Power Dependence of Photopatterning in C‐18 RG dye 85 A.1 Introduction 85 2 A.2 Reading from Subdiffraction Systems 89 A.3 Sample Preparation 90 A.4 Photopatterning at the TPA Wavelength 90 A.5 Photopatterning with Linear Absorption 94 A.6 Appendix Conclusion 97 Bibliography 98 3 List of Tables Table 5.1 71 4 List of Figures Chapter 2 Two‐Photon Induced Aggregate Switching of Excimer‐Forming Dyes 25 Figure 2.1 27 Figure 2.2 28 Figure 2.3 29 Figure 2.4 29 Figure 2.5 33 Figure 2.6 33 Chapter 3 High Density Optical Data Storage in Multilayer Polymer Films 36 Figure 3.1 40 Figure 3.2 42 Figure 3.3 42 Figure 3.4 44 Figure 3.5 47 Figure 3.6 48 Chapter 4 The effect of Multilayering on the Contrast of 3D Data Storage Media 53 Figure 4.1 55 Figure 4.2 57 Figure 4.3 60 Figure 4.4 60 Figure 4.5 62 Figure 4.6 64 Figure 4.7 65 5 Figure 4.8 66 Figure 4.9 67 Chapter 5 Thermal Influence on Biexciton Annihilation in Zinc Phthalocyanine 69 Figure 5.1 71 Figure 5.2 74 Figure 5.3 74 Figure 5.4 82 Figure 5.5 83 Figure 5.6 83 Appendix A Power Dependence of Photopatterning in C‐18 RG dye 85 Figure A.1 91 Figure A.2 92 Figure A.3 93 Figure A.4 95 Figure A.5 96 6 Acknowledgements A broad range of techniques, skills, and principles are required to create and refine new ideas as related to these multidisciplinary projects. My contributions to the field exist only as enabled by my interactions. Throughout the course of these experiments and inventions, I collaborated with many individuals from the various departments at CWRU. Here is presented a list of those individuals whose contributions were palpable: Dr. Jie Shan, Brent Valle, Anuj Siani, Dr. Cory Christenson, Dr. Jack Johnson, Dr. Joseph Lott, Dr. Kenneth Singer, Dr. Eric Baer, Dr. Anne Hiltner, Dr. David Schiraldi, and Dr. Christoph Weder. 7 Three Dimensional Optical Data Storage in Polymeric Systems Abstract by CHRISTOPHER J. RYAN Since the late 1980s optical data storage has been a staple for the circulation of digital information. Through the years the storage capacity of these devices has grown to match new demands and applications. However, fundamental optical limitations exist which inhibit the growth of the current paradigm of devices. This work is comprised of experiments and demonstrations related to new optical data storage techniques. Various results are presented to augment and optimize future iterations of such devices. Most notably, a 64 layer disk is fabricated and used to store data. This device is fashioned using a polymer coextrusion technique and stores information at a high density on 23 of its 64 fluorescent layers. To understand the significance of such devices, a simulation is used to quantify the benefits of multilayered storage disks over monolithic devices. Noise is shown to be drastically reduced in multilayered structures, while the signal contrast grows under the influence of confinement effects. In the process of making this device, an aggregrochromic dye was chosen as a candidate material. Further experiments characterize how the dye changes phases as a response to photopatterning. As presented, these projects cite specific issues with optical data storage technology and offer options for complexity and growth within the field. 8 Chapter 1: Introduction to Optical Data Storage 1.1 Motivation Since the late 1980s, three‐dimensional (3D) optical data storage has become a significant area of interest to the scientific and engineering communities. As formats progressed from Laserdisc to Compact Disc to Digital Video Device to Blue Ray Disc, 2D storage devices have remained a standard for cheap, stable data storage. With each new generation of devices came in increase in overall storage density. [1] However, the wave nature of light has imposed fundamental limits to the storage density of such optical devices. There are new methodologies to circumvent these bottlenecks. Expanding storage into the third dimension has produced devices that push density of optical media over a terabyte per disk[2, 3]. 1.2 Features of Optical Data Storage The general operating principles of 2D optical storage formats rely upon modulated reflection patterns. Most commercial disks store information on a thin aluminum film that is housed within a transparent plastic disk. Information is stored on such a device during the fabrication process as the aluminum films are stamped with a pattern. The 9 information is later read by reflecting a focused laser beam at the surface. The disk is spun about its axis, which translates the pattern relative to the laser. The resultant reflection from the disk is modulated with the information from the pattern, and the reflection is captured by a photodiode. As a result the photodiode produces a modulated electrical signal which conveys the information to the next step in the process [3]. These aluminum based disks are the most prevalent kind of write‐once‐read‐many (WORM) disk. Other materials have been used for variations of this concept. Cyanine, phthalocyanine, and azo based dyes have been layered adjacent to the aluminum or even used as a replacement for it. In this kind of disk, there is no stamping, and the disk is manufactured without a pattern. Instead, writing is done by modulating a laser beam that is focused on this material. Absorption of the modulated light causes heating, and as a result there is a spatial modulation created in the phase of the disk (typically polycrystalline or amorphous). There is a difference in the refractive index of the two phases, so the result is that the disk is patterned with a modulated reflection coefficient. This type of disk is read in the same way as its stamped counterparts. The benefit is that the disk is writable post fabrication[3, 4]. For later versions of this device, the disk is also erasable. In such disks, the active material is typically a semimetal alloy such as GeSbTe. The basic principles are the same, 10 but by further exploitation of the material’s phase behavior, the disks are made rewritable. When heated above the material’s crystallization temperature (~ 150 C), an amorphous region becomes polycrystalline and more reflective. By taking any region, polycrystalline or amorphous, above its melting temperature (~600 C), it melts and cools rapidly to an amorphous solid. During photopatterning, the laser power is controlled to utilize these properties. A low power mode is used to write data on a blank region of the disk, and a high power setting is used to erase written regions. The resultant photopattern is later read with reflection based methods[5]. The wave nature of light has imposed a fundamental limit to the data storage density (DSD) of all optical storage formats thus far[6]. The radius of the narrowest part of the beam is called the beam waist (0). Diffraction limits the minimum size of 0 based upon the wavelength () of the light being focused and the numerical aperture(NA) of the lens that is used to focus it . There exists a simple proportionality relation between them (Eq1) (1) The beam waist also defines the resolution of a typical reading system. Features with separation smaller than 0 cannot be easily discriminated with linear microscopy methods.