31295002786381.Pdf (7.347Mb)

A LASER PLOTTER FOR OPTICAL PROCESSING by BAILEY HENRY JONES III, B.S. in E.E. A THESIS IN ELECTRICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN ELECTRICAL ENGINEERING Approved May 1982 ACKNCWLEDGMENTS I would like to thank Dr. Jchn F. Walkup and Dr. mThoma s F. Krile for their g-uidance and patience during the completion of this thesis. I am also indebted to the staff of the Cptical Systems Lab, whose support and friendship made this a particularly enjoyable task. This volume is dedicated to the memory of my mother, who, had she lived to see it, would have been very proud. This work 'vvas supported by AFCSR grant #79-0076 CONTENTS Page ACKNOWLEDGMENTS ii LIST OF TABLES vi LIST OF FIGURES vii CHAPTER 1. INTRODUCTION 1 CHAPTER 2. AN OVERVIEW OF THE SYSTEM 6 CHAPTER 3. SUBSYSTEMS 12 3.1 Image Data Processing 12 3.1.1 Computers 12 3.1.2 Generating the Image Data I3 3.1.3 Data Conversion l4 3.2 Interface Components 19 3.2.1 Purpose of the Interface I9 3.2.2 The Random Access Mode Interface ... 20 The OUT Instruction 24 Address Decoding 26 Buffer Memories 27 D/A Converters 29 3.2.3 The Sequential Access Mode Interface . 30 3.2.4 Shutter Timing Control Circuit .... 33 111 3-3 Laser and Shutter Sutsystems 37 3.3.1 Laser '37 3.3.2 A/O Shutter yj 3.3.3 A/ Shutter Driver 39 3.4 Beam Forming ptics 44 3.4.1 General and 1-D Plotxing 46 3.4.2 Flotting Holograms . • 50 3.. 5 Scanning Mirrors 34 3.6 Software- '^'^ 3.6.1 Software Organiza-cion '^'c 3.6.2 Data Processing Sof-ware 59 NORML 59 TRANS 60 FILZ and FILL 65 HARM 65 CGHI 66 LAEEL 67 3.6.3 Cperating Systems 69 XYPLCT/XYPLT2 73 HGLC/HCLC2 73 lDrLCT/lD?LT2 l^ LSrELL 73 3.6.^ Maintenance Scitware 79 rv^IRALI cC CALBR8 iv FSET 82 CHAPTER 4. APPLICATIONS 83 4.1 General Output Device 83 4.2 Computer Generated Holography 83 4.3 Phase Masks 85 4.4 Plotting Color Images 86 4.3 Laser Plotter as a Scanner 87 CHAPTER 3. RESULTS AND EXAMPLES 92 3.1 Alphanumerics 92 3.2 Gray Scale 92 3.3 Plotting Images 94 3.4 Computer Generated Hologram 94 CHAPTER 6. FUTURE EXPANSION AND CONCLUSICNS . 97 REFERENCES 104 APPENDICES 106 A. Background on CGH's 106 ?. Characteristics of Panatomic-X Film .... 110 C. Wiring Diagrams and Circuit Layout .... II3 D. Program Listings 120 V LIST OF TABLES Table Page 3.1 VAX 11/780 Calling Sequence 18 3.2 Typical BASIC Sequence in Normal Mode ... 24 3.3 Typical BASIC Sequence in Extended Mode . 23 3.4 Set Up Data for General and 1-D Plotting . 48 3.3 Set Up Data for Computer Holography .... 51 3.6 Scanning Mirror Specifications '^'^ 3.7 ASCII Character Set 63 3.8 Format for Input to HARM (^(^ 3.9 Characters Available for LSPELL Routine . 68 3.10 Output Port Designations 70 3.11 BASIC Output Sequence for RAM Plotting ... 71 B.l Characteristic Curve Data for Panatomic-X Film 112 C.l Compucolor II Interface Bus 113 0.2 44 Pin Interface Bus 114 0.3 RS-2^2C Interface Pin Designations II5 0.4 D/A Converter Pin Designations II6 VI LIST OF FIGURES Figure í Page 2-1 Block diagram of the Laser Plotter 7 2-2 Photograph of the Laser Plotting System . 8 3-1 Characteristic curve for Panatomic-X film . 15 3-2 Block diagram of RAM Interface 22 3-3 RAM Address Decoding Circuits 27 3-4 RAM Buffer Memory Circuits 28 3-5 SAM Interface Circuit 31 3-6 Shutter Timing Control Circuit 34 3-7 Shutter circuit timing diagram 35 3-8 A/O Shutter Driver Circuit 40 3-9 A/O Shutter driving signals 42 3-10 Diagram of beam forming optics for (a) General and 1-D Plotting, and (b) CGH Plotting 45 3-11 Photograph of circular pixels 47 3-12 Photograph of rectangular pixels 53 3-13 Coordinate mapping on film plane 55 3-14 Pixel arrangement for CGH plotting 76 4-1 Using the laser plotter as a scanning detectDr 88 4-2 Using the laser plotter to scan a transparency 90 vii 5-1 Demonstration of alphanumeric capability ... 93 5-2 A gray scale made with the laser plotter ... 93 5-3 "Wheel" image plotted in General Plotting Mcde 95 5-4 Computer-generated hologram of "Double T", (a) Plotted CGH 96 (b) Reconstructed Image 96 C-1 Layout of Shutter Timing Board 117 C-2 Layout of RAM Interface Board 118 C-3 Layout of SAM Interface Board 119 VI11 Chapter One Introduction Optical processors are gaining wide acceptance in, and out, of the laboratory because of their potential for high speed parallel processing. Information is processed in these systems in the form of modulation of a laser beam or other optical carrier. This modulation may be either spatial or temporal, or both. Spatial modulation is often accomplished through the use of optical transparencies. A transparency which is placed in the optical (light) path of the processor spatially modulates the light passing through it. The transparency may contain data, such as an image to be transformed, or a processing mask which may function as a transforming element in the optical system. Coherent light is a complex-valued quantity which may be represented mathematically by two terms, a real amplitude and a phase factor. Both the amplitude and the phase of a light wave can be affected by passing the light through an optical medium. The amplitude of the light which passes through the medium is dependent on the medium's intensity transmittance. This kind of modulation is easily performed with photographic film, indeed, this is the basis of photography. As a light wave travels through any optical medium, it undergoes a phase shift. The size of the phase shift depends both on the thickness and the index of refraction of the medium. In practice, it is difficult to control the phase shifting properties of a piece of film precisely, or independently of the amplitude. The film base itself is rarely optically flat and the thickness of the emulsion varies with the transmittance of the developed film. The phase shifting characteristics of film are therefore generally undesirable and are often eliminated by mounting the film in a liquid gate.(l) Thus, for most purposes, purely amplitude- modulating transparencies are used in optical processors. When it is necessary to introduce a complex quantity into a system, techniques which allow one to represent these quantities with purely real functions are employed. These techniques are perhaps most commonly used for the realization of holographic filters (e.g. Vander Lugt filters) and computer generated holograms. A popular way of generating optical transparencies is to photograph the output of a computer-driven X-Y plotter. The desired function is generated in the computer and drawn by the X-Y plotter on a sheet of paper. This image is then photoreduced to the required size. The principal disadvantage to this technique is that the ink and paper format of the plotter is best suited to binary images; it is difficult to represent more than two levels of contrast (unless halftone techniques are employed). In another common approach the X-Y plotter is replaced with a CRT (cathode ray tube). The displayed function is photographed directly off of the CRT screen. Using the CRT, .many levels of contrast are available, however pincushion dis-tortion and other CRT-related distortions must be eliminated before satisfactory results can be achieved. ne problem inherent in both of these approaches involves the photoreduction process. Often several transparencies will be cascaded in an optical processor. These transparencies cannot be properly aligned unless they are all exactly the same size. This requires that all photographs be taken at precisely the same distances, etc, or that all of the functions be photographed simultaneously, on a single frame of film. The Laser Plotter This thesis describes a third approach--the computer-controlled laser plotter, which has been shown to be quite effective for generating optical transparencies. (2) Here the generated function is plotted, point-by- point, directly onto a frame of 35mm film with a focused laser beam, thus avoiding photoreduction completely. The position of the beam in the film plane is controlled by a microcomputer, which also determines the length of the exposure at each point. The laser plotter achieves the gray scale capabilities absent in the digital X-Y plotter while avoiding the distortion and complexity of CRT-based systems. The laser plotter developed in this thesis is capable of generating amplitude masks and computer generated holograms in a film plane of 1024x1024 points, with a contrast resolution of 256 gray levels. The system was designed for operation with a minimum of training, and uses interactive operating software to achieve this goal. Two different hardware interfaces and three operating systems were designed, allowing for operation in six different plotting modes, including an It should be noted that while X-Y plotters and some CRT based systems plot "point-to-point" (that is, in line segments), the laser plotter and most modem graphics displays plot "point-by-point", with discrete dots. alphanumeric capability. This is a general purpose system, easily expandable, which can perform in a variety of applications. Thesis Organization Chapter Two of this thesis presents an overview of the laser plotter, outlining its operation and components.

Load more