Proceedings Volume 7060

Current Developments in Lens Design and Optical Engineering IX

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Proceedings Volume 7060

Current Developments in Lens Design and Optical Engineering IX

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Volume Details

Date Published: 28 August 2008
Contents: 9 Sessions, 27 Papers, 0 Presentations
Conference: Optical Engineering + Applications 2008
Volume Number: 7060

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7060
  • Fabrication
  • Lens Design I
  • Lens Design II
  • Applications
  • Instruments and Techniques
  • Optimization and Testing
  • Theory and Design
  • Poster Session
Front Matter: Volume 7060
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Front Matter: Volume 7060
This PDF file contains the front matter associated with SPIE Proceedings Volume 7060, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Fabrication
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Low-scatter bare aluminum optics via chemical mechanical polishing
Kevin J. Moeggenborg, Carlos Barros, Stanley Lesiak, et al.
Traditionally, aluminum optics have been produced via a combination of machining, lapping, and diamond turning techniques. The surface roughness and diffraction grating effects resultant from diamond turning have largely limited the use of these optics to IR applications. Work arounds for this problem have included nickel coatings which are subsequently polished to a required finish for use in visible and/or ultraviolet spectra. Unfortunately, this introduces additional costs as well as bimetallic effects that can limit the application of such components. We have developed chemical mechanical polishing (CMP) techniques that allow high quality optical surfaces to be produced on bare aluminum alloy such as 6061-T6. Alloy properties such as grain size, inclusions, and voids can impact all types of finishing processes. The CMP method, however, has been very robust in polishing performance over a range of alloy types and properties. Surface roughness <20 Å rms is readily attainable with this process, and values below 10 Å have been produced with proper process conditions and alloy properties. The monolithic mirrors produced via CMP techniques have been compared against other current alternatives such as diamond turned aluminum, nickel coated aluminum, and aluminized glass. Data indicate the aluminum mirrors produced via CMP can provide performance improvements versus the alternatives based on measurements comparing parameters such as surface roughness, surface quality, reflectivity, and bidirectional reflectance distribution function.
Forces acting between polishing tool and workpiece surface in magnetorheological finishing
Magnetorheological finishing is a computer-controlled polishing technique that is used mainly in the field of high-quality optical lens production. The process is based on the use of a magnetorheological polishing fluid that is able, in a reversible manner, to change its viscosity from a liquid state to a solid state under the control of a magnetic field. This outstanding characteristic facilitates rapid control (in milliseconds) of the yield stress, and thus the pressure applied to the workpiece surface to be polished. A three-axis dynamometer was used to measure the forces acting between the magnetorheological fluid and the workpiece surface during determination of the material removal characteristic of the polishing tool (influence function). The results of a testing series using a QED Q22-X MRF polishing machine with a 50 mm wheel assembly show that the normal forces range from about 2 to 20 N. Knowledge of the forces is essential, especially when thin workpieces are to be polished and distortion becomes significant. This paper discusses, and gives examples of, the variation in the parameters experienced during a programme of experiments, and provides examples of the value of this work.
Material removal study at silicon nitride molds for the precision glass molding using MRF process
Andreas Geiss, Rolf Rascher, Juraj Slabeycius, et al.
High-technology applications which are using high precision optic components in high and medium quantities have increased during recent years. One possibility to mass-produce e.g. such lenses is the precision glass molding (PGM) process. Especially for aspheric and free-form elements the PGM process has certain advantages. Premise is to manufacture accurate press molds, which have to feature smaller figure errors as the required lenses and may be made of materials, which are difficult to machine, like silicon nitride ceramics. These work pieces have to be machined in economical and steady process chains. However, due to the complex shapes and the corresponding accuracy an error dependent polishing is required. The Magnetorheological Finishing (MRF) as a high precision computer controlled polishing (CCP) technique is used and will further be presented in this work. To achieve the postulated demands a previous study of the material removal at selected machining parameters is needed. Changing machining parameters modify the removal, which is presented through values like the peak and volume removal rate. The value changes during the controlled variation of process parameters are described and discussed. Magnetorheological Finishing (MRF) provides one of the best methods to finish PGM molds that are relatively inaccurate to high precision in an economical, steady and efficient way. This work indicates the MRF removal selection and removal interference for the correction and finishing of precise silicon nitride molds for the precision glass molding.
Lens Design I
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Design and fabrication of low-cost thermal imaging optics using precision chalcogenide glass molding
Aspheric and diffractive surfaces in infrared materials are traditionally fabricated by single point diamond turning, which is a high-cost, low-throughput process, not suitable for low-cost, high-volume applications. Precision molding of chalcogenide glasses is a novel process we developed to allow the efficient fabrication of quality infrared optics in large volumes. In this paper we present the advantages and particularities of designing thermal imaging lenses for high-volume applications using precision molded chalcogenide glasses. As an example, we present a compact 19 mm F/1.1 infrared lens design for a 320 × 240 uncooled detector array operating from 8 to 14 microns. The excellent image quality and transmission of tested prototypes prove that precision molding of chalcogenide glasses is an ideal optical fabrication technology for the high-volume production of infrared optics.
Day and night security camera
Milton Laikin, Gyeong-il Kweon, Young-ho Choi
We have designed a fisheye lens with a field of view of 190° and F# of 2.8 The diameter of the circular image plane is designed to fit within the width of the image sensor plane, so that a 190° horizontal field of view can be obtained. It is composed of 8 spherical lens elements and the overall length is 35mm from the first lens surface to the image sensor plane. This fisheye lens operates simultaneously in the visible and the near infrared wavelength regions.
High-resolution UV relay lens for particle size distribution measurements using holography
Robert M. Malone, Gene A. Capelle, Brian C. Cox, et al.
Shock waves passing through a metal sample can produce ejecta particulates at a metal-vacuum interface. Holography records particle size distributions by using a high-power, short-pulse laser to freeze particle motion. The sizes of the ejecta particles are recorded using an in-line Fraunhofer holography technique. Because the holographic plate would be destroyed in an energetic environment, a high-resolution lens has been designed to relay the scattered and unscattered light to a safe environment where the interference fringes are recorded on film. These interference fringes allow particles to be reconstructed within a 12-mm-diameter, 5-mm-thick volume. To achieve resolution down to 0.5 μm, both a high-resolution optical relay lens and ultraviolet laser (UV) light were implemented. The design and assembly of a nine-element lens that achieves >2000 lp/mm resolution and operates at f/0.89 will be described. To set up this lens system, a doublet lens is temporarily attached that enables operation with 532-nm laser light and 1100 lp/mm resolution. Thus, the setup and alignment are performed with green light, but the dynamic recording is done with UV light. During setup, the 532-nm beam provides enough focus shift to accommodate the placement of a resolution target outside the ejecta volume; this resolution target does not interfere with the calibrated wires and pegs surrounding the ejecta volume. A television microscope archives images of resolution patterns that prove that the calibration wires, interference filter, holographic plate, and relay lenses are in their correct positions. Part of this lens is under vacuum, at the point where the laser illumination passes through a focus. Alignment and tolerancing of this high-resolution lens will be presented, and resolution variation through the 5-mm depth of field will be discussed.
New tools for the lens designer
Several common impediments to successful lens design can be removed by application of new techniques. These involve using information that has long been calculated during the design process, but then discarded. Problems so addressed include the nuisance of discovering ray failures in the starting configuration, and that of tolerance desensitization, among others.
Lens Design II
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Optical design of reflective wide-field cameras
This paper discusses some methodologies that apply to the optical design of reflective wide-field cameras. Among the methods considered are off-axis and eccentric pupil systems, concatenation of systems, tilted component systems, aberration theory, and confocal systems. The goal of the paper is to review design methods. In particular some systems are shown to illustrate two methodologies.
Five-lens corrector for Cassegrain-form telescopes
Mark R. Ackermann, John T. McGraw, Peter C. Zimmer
Refractive elements are commonly used on Cassegrain-form telescopes to correct off-axis aberrations and both widen and flatten the field. Early correctors used two lenses with spherical surfaces, but their performance was somewhat limited. More recent correctors have three or four lenses with some including at least one aspheric surface. These systems produce high resolution images over relatively wide fields but often require the corrector and mirrors to be optimized together. Here we present a new corrector design using five spherical lenses. This approach produces high image quality with low distortion over wide fields and has sufficient degrees of freedom to allow corrector to be optimized independent of the mirrors if necessary.
Material selection for color correction in the short-wave infrared
With the increasing availability of InGaAs detectors for imaging applications in the short wave infrared (SWIR, 0.9 - 1.7 μm), the need for diffraction limited lenses optimized for this spectrum is rising as well. With an abundance of commercially available optical glasses that are transparent in the SWIR, correcting chromatic aberration over the broader SWIR waveband might seem only a moderately difficult task for the optical designer. As it turns out, it is considerably more difficult because the dispersive nature of most of the common glass flints is decreased in the SWIR, limiting the availability of strong flints for achromatization. Fortunately, a limited selection of highly dispersive SWIR transparent materials can be found among materials used for mid-wave and long wave infrared (IR) optics. However, some of these IR materials have a strong absorption edge in close proximity to the SWIR waveband which presents the optical designer with a different challenge. This paper examines challenges and tradeoffs specific to material selection for color correction in the design of diffraction limited lenses for the SWIR. Solutions are proposed for achromatic and apochromatic lenses. A discussion of material properties and the SWIR glass map is included.
Correctly making panoramic imagery and the meaning of optical center
The production and viewing of panoramic scenes have fascinated people for over a millennium beginning with the camera obscura. With the advent of photography in the mid-1800s, techniques were developed to create panoramic scenes far larger than could be realized by a single camera. Making a panoramic scene from two or more images taken using a film camera was found to be challenging. Various advanced techniques for making panoramic images were developed during the 20th century and required specialized cameras and film processing. In recent years, digital cameras and powerful software programs have become readily available to aid in making panoramic imagery although often strange artifacts appears in the composite image. This is generally due to improperly locating the rotation axis of the camera. Interestingly, there is significant argument about where the axis of rotation should be for making proper panoramic imagery. The most common "answer" is the rotation axis should be about the second or rear nodal point, which will be shown in this paper to be incorrect. A second "answer" is to rotate the camera about its optical center. This is also incorrect; however, what actually constitutes the optical center of a lens and its applications will be briefly discussed. Examples of correctly and incorrectly produced panoramic image will be presented.
Applications
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Automated design and fabrication of ocular optics
Automated computer-aided procedure for component selection, optical design, and optimization was developed and used to produce prototype ocular optics of a head-mounted display for biomedical imaging, with the field of view and resolution approaching those of normal human vision. The new display has the potential to dramatically increase the amount and fidelity of real-time visual information presented to the user. The selected approach was based on a tiled configuration and "optically stitched" virtual image, resulting in seamless imagery generated by multiple micro-displays. Several optical configurations were studied in the design stage, to arrive at the optimal optical layout. The automated procedure provided for extensive search of the best candidate stock components out of thousands of candidate lenses offered by different vendors. At each iteration, the candidate lens was "digitally inserted" in the optical layout, its position was optimized, and the achieved merit function characterizing the quality of the stitched image was stored, along with the design prescription. A few best designs were then closely evaluated in a traditional "manual" procedure. The design effort was followed by experimental demonstration and tests of a limited prototype optical system.
Instruments and Techniques
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3D imaging from theory to practice: the Mona Lisa story
Francois Blais, Luc Cournoyer, J.-Angelo Beraldin, et al.
The warped poplar panel and the technique developed by Leonardo to paint the Mona Lisa present a unique research and engineering challenge for the design of a complete optical 3D imaging system. This paper discusses the solution developed to precisely measure in 3D the world's most famous painting despite its highly contrasted paint surface and reflective varnish. The discussion focuses on the opto-mechanical design and the complete portable 3D imaging system used for this unique occasion. The challenges associated with obtaining 3D color images at a resolution of 0.05 mm and a depth precision of 0.01 mm are illustrated by exploring the virtual 3D model of the Mona Lisa.
Design of a discrete scan laser focusing system with a ring grating scan element
An optical system application required a high speed laser scanning subsystem that produced high quality extended images focused at 32 discrete separated positions along a line, rather than continuously varying positions along the line as in more familiar scanning systems. This paper describes the optical design trades and selection of a grating-based scan element that produces this unusual type of scan, and the optical design methods that corrected aberrations produced by the scan element. A variety of different grating-based scan element designs were explored, in a flat disk geometry, but these produced excessive aberrations, both in the absolute level and in the magnitude of variation with scan. A ring-shaped scan element geometry was identified, which greatly minimized the scan-varying aberrations and brought them to near acceptable levels. Additional cylindrical corrector elements were added near the ring scan element to reduce the astigmatism of the ring substrate, and cylindrical lenslets were placed near the focus to provide further independent correction of astigmatism in each scan position. The resulting design achieved diffraction limited wavefront quality across the scan range.
Development and optical testing of the camera, hand lens, and microscope probe with scannable laser spectroscopy (CHAMP-SLS)
Conducting high resolution field microscopy with coupled laser spectroscopy that can be used to selectively analyze the surface chemistry of individual pixels in a scene is an enabling capability for next generation robotic and manned spaceflight missions, civil, and military applications. In the laboratory, we use a range of imaging and surface preparation tools that provide us with in-focus images, context imaging for identifying features that we want to investigate at high magnification, and surface-optical coupling that allows us to apply optical spectroscopic analysis techniques for analyzing surface chemistry particularly at high magnifications. The camera, handlens, and microscope probe with scannable laser spectroscopy (CHAMP-SLS) is an imaging/spectroscopy instrument capable of imaging continuously from infinity down to high resolution microscopy (resolution of ~1 micron/pixel in a final camera format), the closer CHAMP-SLS is placed to a feature, the higher the resultant magnification. At hand lens to microscopic magnifications, the imaged scene can be selectively interrogated with point spectroscopic techniques such as Raman spectroscopy, microscopic Laser Induced Breakdown Spectroscopy (micro-LIBS), laser ablation mass-spectrometry, Fluorescence spectroscopy, and/or Reflectance spectroscopy. This paper summarizes the optical design, development, and testing of the CHAMP-SLS optics.
Lens design and system optimization for foveated imaging
Foveated imaging addresses the need for compact wide-angle imagers capable of high-resolution and compressed data transmission. The principle behind foveated imaging is to cover a wide field-of-view (FOV) with a relatively simple and compact low-resolution lens, and use a liquid crystal spatial light modulator (SLM) to correct wavefront aberrations at any selected field point. The SLM correction provides a high-resolution fovea that can be actively moved anywhere within the FOV. While most research has focused so far mainly on SLM performance, the general trend being to increase SLM resolution and modulation depth, the actual lens design and system optimization aspects were often neglected. In this paper, we propose a wide-angle lens design intended for foveated imaging applications, and discuss typical tradeoffs. Taking this design as an example, we present a method to estimate the smallest SLM resolution required to correct the wavefront error effectively, showing that with the appropriate design, this resolution can be reduced up to 10 times compared to current designs. Increasing the SLM resolution beyond this point and increasing the modulation depth above one wavelength is not necessary, and will actually reduce the performance of the imaging system. We also demonstrate the importance of fabrication tolerances, and we propose a method to calibrate the SLM in order to cancel out all additional wavefront aberrations introduced by fabrication and assembly errors.
Optimization and Testing
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Advanced techniques for computer-controlled polishing
Markus Schinhaerl, Richard Stamp, Elmar Pitschke, et al.
Computer-controlled polishing has introduced determinism into the finishing of high-quality surfaces, for example those used as optical interfaces. Computer-controlled polishing may overcome many of the disadvantages of traditional polishing techniques. The polishing procedure is computed in terms of the surface error-profile and the material removal characteristic of the polishing tool, the influence function. Determinism and predictability not only enable more economical manufacture but also facilitate considerably increased processing accuracy. However, there are several disadvantages that serve to limit the capabilities of computer-controlled polishing, many of these are considered to be issues associated with determination of the influence function. Magnetorheological finishing has been investigated and various new techniques and approaches that dramatically enhance the potential as well as the economics of computer-controlled polishing have been developed and verified experimentally. Recent developments and advancements in computer-controlled polishing are discussed. The generic results of this research may be used in a wide variety of alternative applications in which controlled material removal is employed to achieve a desired surface specification, ranging from surface treatment processes in technical disciplines, to manipulation of biological surface textures in medical technologies.
Design efficiency of 3188 optical designs
Ozan Cakmakci, Jannick P. Rolland, Kevin P. Thompson, et al.
In this study, we take a data-driven approach to study the design efficiency of a variety of optical designs. Efficiency is defined to be the number of resolvable spots across the image per lens element. 3188 designs were selected from a commercially available lens database. Each design was imported into a raytrace code, briefly optimized, and the number of resolvable spots was computed. Examples of efficient designs within this dataset are shown. Four design efficiency groupings are created and discussed separately: 1) all-spherical, monochromatic designs, 2) monochromatic designs with some aspheres, 3) all-spherical, polychromatic designs, and 4) polychromatic designs with some aspheres. Zoom lens systems were excluded from the dataset. The results of the analysis are intended to answer the question of "how many elements does it take, as a minimum, to deliver a certain number of resolved spots?"
High resolution wavefront measurement of aspheric optics
With the recently emerged large volume production of miniature aspheric lenses for a wide range of applications, a new fast fully automatic high resolution wavefront measurement instrument has been developed. The Shack-Hartmann based system with reproducibility better than 0.05 waves is able to measure highly aspheric optics and allows for real time comparison with design data. Integrated advanced analysis tools such as calculation of Zernike coefficients, 2D-Modulation Transfer Function (MTF), Point Spread Function (PSF), Strehl-Ratio and the measurement of effective focal length (EFL) as well as flange focal length (FFL) allow for the direct verification of lens properties and can be used in a development as well as in a production environment.
Recent advances in the modulation transfer function testing of detector arrays
The increased complexity of imaging sensors and total number of discrete detector sites has challenged traditional testing methods. The importance of reliable modulation transfer function testing of imaging sensors with high uncertainty has consequently grown more difficult. In this paper we demonstrate the design of an aperture for the generation of laser speckle with a flat power spectrum covering a wide-band of the measurement spatial frequency range. This aperture allows for the measurement of modulation transfer function (MTF) from zero to twice the Nyquist frequency of a twodimensional detector array. This design mitigates many of the measurement issues inherent in other aperture designs. The MTF measurement of a charge-coupled device (CCD) detector array is used to demonstrate the measurement technique and illustrate the advantages of the new aperture design.
Theory and Design
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Wavefront generated by reflection of a plane wave from a conic section
We use the general solution of the eikonal equation due to Stavroudis to analyze the light propagation of an incident plane wave that is reflected off-axis from a surface of revolution generated by a conic section. Specifically, a general, explicit expression for the k-function associated with reflection of a plane wave is evaluated for the geometry of the off-axis conic mirror and the resulting k-function is used, following Stavroudis and coworkers, to evaluate the reflected wavefronts and caustic surfaces. This paper presents a new application of the k-function formalism to a practical configuration, without any simplifying rotational or translational symmetry, where the wavefronts and caustics in the focal region will be analyzed.
Display system analysis with critical polarization elements in a non-sequential ray tracing environment
J. A. Herlocker, J. Jiang, K. J. Garcia
Common digital display systems have evolved into sophisticated optical devices. The rapid market growth in liquid crystal displays makes the simulation of full systems attractive, promoting virtual prototyping with decreased development times and improved manufacturability. Realistic simulation using commercial non-sequential ray tracing tools has been instrumental in this process, but the need to accurately model polarization devices has become critical in many designs. As display systems seek more efficient use of light and more accurate color representation, the proper simulation of polarization devices with large acceptance angles is essential. This paper examines non-uniform polarization effects in the simulation of modern display devices using realistic polarizer and retarder models in the ASAP® non-sequential ray-tracing environment.
Poster Session
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An optically passive athermal infrared optical system
Hua Li, Mangzuo Shen
An optically passive athermal infrared optical system working in the 8 - 12 micron long wavelength infrared band was designed by using a special infrared optical material AMTIR (amorphous material transmitting infrared radiation). The design principle, design results are described in this paper. In addition, the optical system was incorporated with an infrared focal plane array forming an infrared camera. The thermal test of imaging quality of this camera is also presented.
Aspherical optics design for minimal spherical aberration in vision correction of human eyes
Using raytracing method (ZEMAX program), the reduction of SA of the whole human eye may be reduced via the combined effects of asphericity (Q) and the ratio of the front and back surface of an IOL. The overall SA for best image quality may be defined by Q* when the image position off axis is reduced to that of the paraxial. Our calculations show the following general features: (1) For a give Q value, the influence on the SA is proportional to the surface power; (2) for minimal whole eye SA, negative Q is needed in IOL; (3) for a given IOL power, the Q* is smaller when the front surface has a smaller power. All above features derived from numerical raytracing method are consistent with analytic formulas.
Modeling diffractive optical elements in hybrid systems with the effect of the material dispersion
The diffractive optical element (DOE) is always modeled as an ideal pure diffractive element which neglects the refractive dispersion of the element's material. In this paper, a new model of the diffractive optical element is proposed, in which the effect of the refractive dispersion of the DOE's material is considered. The new model is explained and compared with standard diffraction-order expansion with the help of a hybrid system example. The analytical results show that the new model has an important meaning for the exact analysis of the hybrid refractive-diffractive optical system.
The design, construction and characterization of a solid elastic lens
Recent times have seen the production of normal and micro liquid lenses with variable focal length. These have been specially made with transparent elastic materials and liquid medium between them, or with a dielectric liquid medium inside the cavity. Change in the volume of the liquid medium, in the first case, or the application of an electric field as in the second, produced a change in the optical parameters of the lens. The present study offers the opto-mechanical design, manufacture and characterization of a solid elastic lens made of Polydimethylsiloxane (PDMS). To do so, we have prepared a mechanical support frame to hold all of the components of the lens and also allow for the application of radial stress on its periphery. In order to ensure a well-finished lens surface a high quality optical glass mold has also been constructed. Finally, we will present an analysis of the properties of this type of lens when it undergoes variations of radial stress. The experimental results are presented.