SPIE PRESS | Tutorial Text
`
`SPIE
`
`The Design of
`
`Plastic
`Optlcal
`Systems
`
`
`
`Michael P. Schaub
`
`APPL-1031 /Page 1 of 153
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`APPL-1031 /Page 2 of 153
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`The Design of
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`Plastic
`Optical
`Systems
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`Tutorial Texts Series
`
`• Optical Design: Applying the Fundamentals, Max J. Riedl, Vol. TT84
`• Infrared Optics and Zoom Lenses, Second Edition, Allen Mann, Vol. TT83
`• Optical Engineering Fundamentals, Second Edition, Bruce H. Walker, Vol. TT82
`• Fundamentals of Polarimetric Remote Sensing, John Schott, Vol. TTSI
`• The Design of Plastic Optical Systems, Michael P. Schaub, Vol. TTSO
`• Radiation Thermometry: Fundamentals and Applications in the Petrochemical Industry, Peter Saunders, Vol.
`TT78
`• Matrix Methods/or Optical Layout, Gerhard Kloos, Vol. TT77
`• Fundamentals of Infrared Detector Materials, Michael A. Kinch, Vol. TT76
`• Practical Applications of Infrared Thermal Sensing and Imaging Equipment, Third Edition, Herbert Kaplan,
`Vol. TT75
`• Bioluminescencefor Food and Environmental Microbiological Safety, Lubov Y. Brovko, Vol. TT74
`• Introduction to Image Stabilization, Scott W. Teare, Sergio R. Restaino, Vol. TT73
`• Logic-based Nonlinear Image Processing, Stephen Marshall, Vol. TT72
`• The Physics and Engineering a/Solid State Lasers, Yehoshua Kalisky, Vol. TT71
`• Thermal Infrared Characterization of Ground Targets and Backgrounds, Second Edition, Pieter A. Jacobs,
`Vol. TT70
`• Introduction to Confocal Fluorescence Microscopy, Michie! Millier, Vol. TT69
`• Artificial Neural Networks: An Introduction, Kevin L. Priddy and Paul E. Keller, Vol. TT68
`• Basics a/Code Division Multiple Access (CDMA), Raghuveer Rao and Sohail Dianat, Vol. TT67
`• Optical Imaging in Projection Microlithography, Alfred Kwok-Kit Wong, Vol. TT66
`• Metrics/or High-Quality Specular Surfaces, Lionel R. Baker, Vol. TT65
`• Field Mathematics for Electromagnetics, Photonics, and Materials Science, Bernard Maxum, Vol. TT64
`• High-Fidelity Medical Imaging Displays, Aldo Badano, Michael J. Flynn, and Jerzy Kanicki, Vol. TT63
`• Dif.fractive Optics-Design, Fabrication, and Test, Donald C. O'Shea, Thomas J. Suleski, Alan D. Kathman,
`and Dennis W. Prather, Vol. TT62
`• Fourier-Transform Spectroscopy Instrumentation Engineering, Vidi Saptari, Vol. TT61
`• The Power- and Energy-Handling Capability of Optical Materials, Components, and Systems, Roger M.
`Wood, Vol. TT60
`• Hands-on Morphological Image Processing, Edward R. Dougherty, Roberto A. Lotufo, Vol. TT59
`• Integrated Optomechanical Analysis, Keith B. Doyle, Victor L. Genberg, Gregory J. Michels, Vol. TT58
`• Thin-Film Design: Modulated Thickness and Other Stopband Design Methods, Bruce Perilloux, Vol. TT57
`• Optische Grundlagenfor Infrarotsysteme, Max J. Riedl, Vol. TT56
`• An Engineering Introduction to Biotechnology, J. Patrick Fitch, Vol. TTSS
`•Image Performance in CRT Displays, Kenneth Compton, Vol. TT54
`• Introduction to Laser Diode-Pumped Solid State Lasers, Richard Scheps, Vol. TT53
`• Modulation Transfer Function in Optical and Electro-Optical Systems, Glenn D. Boreman, Vol. TT52
`• Uncooled Thermal Imaging Arrays, Systems, and Applications, Paul W. Kruse, Vol. TTSl
`• Fundamentals of Antennas, Christos G. Christodoulou and Parveen Wahid, Vol. TTSO
`• Basics a/Spectroscopy, David W. Ball, Vol. TT49
`• Optical Design Fundamentals/or Infi·ared Systems, Second Edition, Max J. Riedl, Vol. TT48
`• Resolution Enhancement Techniques in Optical Lithography, Alfred Kwok-Kit Wong, Vol. TT47
`• Copper Interconnect Technology, Christoph Steinbriichel and Barry L. Chin, Vol. TT46
`
`For a complete listing of Tutorial Texts, visit http://spie.org/tutorialtexts.xml
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`The Design of
`
`Plastic
`Optical
`Systellls
`
`Michael P. Schaub
`
`Tutorial Texts in Optical Engineering
`Volume TT80
`
`SPIE
`PRESS
`Bellingham, Washington USA
`
`APPL-1031 / Page 5 of 153
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`Library of Congress Cataloging-in-Publication Data
`
`Schaub, Michael P.
`The design of plastic optical systems I Michael P. Schaub.
`p. cm. -- (Tutorial texts series ; TT 80)
`Includes bibliographical references and index.
`ISBN 978-0-8194-7240-3
`1. Plastic lenses. 2. Optical instruments--Design and construction. 3. Plastics--Optical
`properties. 4. Optical materials. I. Title.
`TS517.5.P5S33 2009
`68 l '.4--dc22
`
`2009028012
`
`Published by
`
`SPIE
`P.O. Box 10
`Bellingham, Washington 98227-0010 USA
`Phone: 360.676.3290
`Fax: 360.647.1445
`E-mail: Books@spie.org
`www.spie.org
`
`Copyright© 2009 Society of Photo-Optical Instrumentation Engineers
`
`All rights reserved. No part of this publication may be reproduced or distributed
`in any form or by any means without written permission of the publisher.
`
`The content of this book reflects the thought of the author(s). Every effort has been made
`to publish reliable and accurate information herein, but the publisher is not responsible
`for the validity of the information or for any outcomes resulting from reliance thereon.
`
`Printed in the United States of America.
`
`SPIE
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`Introduction to the Series
`
`Since its inception in 1989, the Tutorial Texts (TT) series has grown to more than 80
`titles covering many diverse fields of science and engineering. The initial idea for the
`series was to make material presented in SPIE short courses available to those who
`could not attend and to provide a reference text for those who could. Thus, many of
`the texts in this series are generated by augmenting course notes with descriptive text
`that further illuminates the subject. In this way, the TT becomes an excellent stand(cid:173)
`alone reference that finds a much wider audience than only short course attendees.
`Tutorial Texts have grown in popularity and in the scope of material covered
`since 1989. They no longer necessarily stem from short courses; rather, they are
`often generated by experts in the field. They are popular because they provide a
`ready reference to those wishing to learn about emerging technologies or the latest
`information within their field. The topics within the series have grown from the
`initial areas of geometrical optics, optical detectors, and image processing to include
`the emerging fields of nanotechnology, biomedical optics, fiber optics, and laser
`technologies. Authors contributing to the TT series are instructed to provide
`introductory material so that those new to the field may use the book as a. starting
`point to get a basic grasp of the material. It is hoped that some readers may develop
`sufficient interest to take a short course by the author or pursue further research in
`more advanced books to delve deeper into the subject.
`The books in this series are distinguished from other technical monographs and
`textbooks in the way in which the material is presented. In keeping with the tutorial
`nature of the series, there is an emphasis on the use of graphical and illustrative
`material to better elucidate basic and advanced concepts. There is also heavy use of
`tabular reference data and numerous examples to further explain the concepts
`presented. The publishing time for the books is kept to a minimum so that the books
`will be as timely and up-to-date as possible. Furthermore, these introductory books
`are competitively priced compared to more traditional books on the same subject.
`When a proposal for a text is received, each proposal is evaluated to determine
`the relevance of the proposed topic. This initial reviewing process has been very
`helpful to authors in identifying, early in the writing process, the need for additional
`material or other changes in approach that would serve to strengthen the text. Once a
`manuscript is completed, it is peer reviewed to ensure that chapters communicate
`accurately the essential ingredients of the science and technologies under discussion.
`It is my goal to maintain the style and quality of books in the series and to
`further expand the topic areas to include new emerging fields as they become of
`interest to our reading audience.
`
`James A. Harrington
`Rutgers University
`
`v
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`Contents
`
`Preface .................................................................................................... ix
`
`Acknowledgments .................................................................................. xi
`
`Chapter 1
`
`Introduction ...................................................................... 1
`
`1.1 Background ........................................................................... 1
`1.2 When Are Plastic Optics Appropriate? ................................. 5
`
`Chapter 2
`
`Optical Plastics .............................................................. 15
`
`2.1 Plastic Versus Glass Maps ..................................... :: ........... 15
`2.2 Material Properties .............................................................. 19
`2.3 Material Selection ............................................................... 28
`2.4 Material Specification ......................................................... 29
`
`Chapter 3
`
`Manufacturing Methods ................................................ 31
`
`3.1 Casting ................................................................................. 31
`3.2 Embossing and Compression Molding ................................ 35
`3.3 Machining ............................................................................ 36
`3.4 Injection Molding ................................................................ 39
`
`Chapter 4
`
`Design Guidelines ......................................................... 65
`
`4.1 Design Basics ...................................................................... 65
`4.2 Tolerances ........................................................................... 81
`4.3 Plastic Versus Glass ............................................................ 87
`4.4 Shape and Thickness ........................................................... 90
`4.5 Aspheric Surfaces ................................................................ 94
`4.6 Diffractive Surfaces ........................................................... 100
`4.7 Athermalization ................................................................. 105
`4.8 Coatings ............................................................................. 110
`4.9 Optomechanical Design .................................................... 113
`4.10 Stray Light ....................................................................... 118
`4.11 Special Considerations for Small and Large Parts .......... 128
`4.12 Drawings ......................................................................... 132
`4.13 Vendors and Vendor Interaction ..................................... 140
`
`Vll
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`Chapter 5
`
`Design Examples ......................................................... 143
`
`5.1 Singlet Lens ....................................................................... 143
`5.2 Webcams ........................................................................... 151
`5.3 Cell Phone Camera ............................................................ 164
`5.4 Infrared Multiorder or Harmonic Diffractive Lens ........... 167
`
`Chapter 6
`
`Testing .......................................................................... 177
`
`6.1 Parameters, Equipment, and Techniques ........................... 177
`6.2 Making Testing Easier ...................................................... 189
`
`Chapter 7
`
`Prototyping ................................................................... 193
`
`7.1 Optics ................................................................................ 193
`7 .2 Mechanical Parts ............................................................... 197
`7.3 Assembly and Test ............................................................ 198
`
`Chapter 8
`
`Production .................................................................... 201
`
`8.1 Transition to Production .................................................... 201
`8.2 Steady-State Production .................................................... 206
`
`References ........................................................................................... 207
`
`Index ..................................................................................................... 213
`
`viii
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`Preface
`
`We routinely come into contact with and utilize plastic optical systems in our
`daily lives. As an illustration of this, consider the following events that may
`occur during a typical weekday. Traveling to work in our car, traffic signals
`change color to regulate the flow of vehicles. Arriving at work, as we enter the
`building, motion sensors turn on the hallway lights. At our desk, a fingerprint
`reader grants us access to our laptop computer. In the lab, we take and send
`pictures of the latest prototype, using the camera in our cell phone, enabling
`others to see the hardware. After work, stopping at the store, the bar code reader
`brings up the prices of our items. Back at home, we enjoy the latest movie
`released on DVD.
`All of these devices-the traffic signals, motion sensors, fingerprint readers,
`cell phone cameras, bar code scanners, and DVD players-rely upon plastic
`optical systems to perform their function. As a result, there is a growing need for
`individuals who are knowledgeable in the design, development, and production
`of such systems. This tutorial text is written with this need in mind. The book is
`an elaboration upon the material covered in the SPIE short course "The Design of
`Plastic Optical Systems." It is meant to provide an overview of the design of
`plastic optical systems and is structured along the lines of a typical development
`project. Following a brief background discussion,
`the advantages and
`disadvantages of plastic optics are considered. Next, the available materials and
`their properties are described, as well as the issues of material selection and
`specification. Various manufacturing methods are reviewed, followed by a
`chapter on design guidelines, leading into several design examples. Following the
`examples, the prototyping and testing of a design is covered. Finally, bringing the
`design to production is discussed.
`There are several groups that should be able to benefit from the material
`presented. The first group is optical engineers, who often have received training
`in optical system design, particularly with glass optics, but who are unfamiliar
`with the special design characteristics of plastic optics. The second group is
`technical management, who need to understand the advantages and limitations of
`plastic optical systems. The third, and by far the largest group, is engineers of
`other disciplines who find they need to design and develop plastic optical
`systems but lack the knowledge or training to do so.
`The text is written at an introductory level. No familiarity with plastic optical
`parts or their design is assumed. Any background knowledge of optics and
`optical design will be useful, but not required, to understand most of the subjects
`covered. Discussions of many of the subjects covered in this text can be found
`distributed amongst various publicly and/or commercially available sources.
`There is a wealth of information on plastic optics available in articles, conference
`proceedings, trade journals, books, the Internet, and various patent databases. We
`reference many of these throughout the text and encourage the reader to utilize
`
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`Chapter 1
`Introduction
`In this chapter, we provide some background information on plastic optics,
`including a brief history of their development, as well as recent advances in
`materials, machining, and manufacturing processes. We also discuss issues that
`may determine if plastic optics should be used for a particular application, as well
`as their potential advantages and disadvantages.
`
`1.1 Background
`Plastic optics have existed for longer than most currently practicing engineers. In
`1936, after several years of development, the Rohm and Haas Company
`announced the commercial availability of polymethylmethacrylate (PMMA),
`now commonly referred to as acrylic, under the trade name Plexiglas.9 In the
`same year, DuPont began commercial production of its acrylic material, known
`as Lucite. 10 In Britain, the Imperial Chemical Industries PLC introduced its
`version, which was called Perspex. 11 The following year, Dow Chemical
`introduced polystyrene in the United States under the name STYRON. 12
`Plastic lenses appeared around the same time, along with colorful marketing
`campaigns and disagreements over their invention. In London, on March 20,
`1934, the KGK Syndicate Ltd. was formed between Peter Maurice Koch de
`Gooreynd and Arthur Kingston; just under four years later, in February 1938, the
`partnership was dissolved. The Wellcome Library, also in London, houses copies
`of documents concerning the partnership, as well as a copy of a letter from
`Kingston's lawyer regarding a dispute between the partners over who deserved
`credit for inventing the plastic optical lens. 13 It seems that a BBC radio broadcast
`stated that Koch de Gooreynd was the inventor of the plastic lens, a claim that
`Kingston disagreed with.
`In 193 7, TIME magazine published an article describing competition
`between U.S., British, and German firms to substitute glass lenses with plastic
`lenses in cameras, eyeglasses, and binoculars. It is noted that shortly before the
`article's printing, Gooreynd (of the KGK Syndicate) appears in New York and
`bounces lenses on the table to show their fracture resistance. A few weeks later,
`in Los Angeles, a Rohm and Haas customer named E. G. Lloyd goes even
`further, putting on a dramatic exhibition for the press by taking a hammer to his
`lenses. 14 Despite the impressive displays, these early lenses suffered from several
`problems, such as low scratch resistance and discoloration. Nevertheless, the
`field of plastic optics had begun in earnest.
`With materials available, the manufacturers searched for markets to buy
`them. For instance, Rohm and Haas produced a few acrylic musical instruments,
`including a flute and a violin. The flute reportedly had good tone, while the violin
`
`1
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`2
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`Chapter 1
`
`did not.9 Most early successful uses of optical plastic were either for eyeglasses
`or window applications. There were various attempts to create the equivalent of
`modem laminated windows, commonly known as "safety" glass, where a plastic
`film is sandwiched between glass plates to keep glass shards from flying when
`the window is broken.
`The use of plastic windows in airplanes provided an initial market for the
`acrylic manufacturers and allowed them to continue development of the material.
`Acrylic initially was used for small windows, and as the material became more
`accepted and understood, larger windows; ultimately, even cockpit canopies were
`produced. With the beginning of World War II, the use of acrylic for military
`aircraft skyrocketed. Other war-time uses of plastic optics included antitank gun
`sights and experimental aerial cameras. 15
`Demand was high throughout the war period but abruptly declined with the
`end of the war and cancellation of government contracts. Manufacturers worked
`to replace the lost sales, putting acrylic into everyday items. Consumers,
`however, were not particularly interested in plastic products, due to the return of
`other materials that were not available during the war. In 1947, jukeboxes were
`the largest market for Plexiglas. 9 Plastic optical elements began to appear in the
`auto industry, with acrylic replacing elements previously made of glass, such as
`tail lights. This association with the auto industry turned into a sig nificant market
`for plastic optics and remains so today. Another application that developed
`shortly after the war, which remains with us today, is the illuminated sig n .
`Polycarbonate was introduced in the 1950s, with GE Plastics developing
`LEXAN16 and Bayer developing Makrolon. 17 However, these early versions of
`polycarbonate·were not suitable for most optical uses due to the "golden" tint of
`the material, as it was described by Bayer's advertising. 17 Also in the 1950s,
`Kodak began producing cameras with acrylic viewfinders and objective lenses. 18
`Cameras continued to be a large market for plastic lenses in the 1960s, with over
`50 million Kodak INSTAMATIC cameras made during the decade. 19 Acrylic and
`polystyrene lenses were often used together to achieve color correction in these
`types of systems. Polycarbonate elements were still being used more often in
`nonimaging applications, such as car tail lights and traffic sig n als. In 1965, ICI
`developed polymethylpentene, often known by the trade name TPX. It is used
`today in some specialty plastic optical applications. In the 1970s, continued
`development of polycarbonate removed most of its tint, not necessarily enough
`for imaging applications, but enough to enable it to be used for automotive
`headlamps.
`Significant progress in the use of polycarbonate elements occurred in the
`early 1980s with the introduction of optical-grade polycarbonate. The optical
`grade material was used for a variety of applications, such as eyeglass lenses and
`safety visors, as well as for canopies on fighter jets such as the F-14. Encouraged
`by the demand for optical data storage discs, optical-grade polycarbonate was
`used for CDs, first introduced in 1982, as well as for lenses to read them. This
`provided, in the view of the chemical companies producing the material, an
`optical application with significant plastic material usage. Having similar optical
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`Introduction
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`3
`
`properties to polystyrene, optical-grade polycarbonate could be used as an
`alternative in color-correcting optical systems.
`increase in available optical plastics. Two newly
`The 1990s saw an
`developed materials to emerge were cyclic olefin copolymers (COCs), commonly
`known by the trade name Zeonex/ and cyclic olefin polymers (COPs), known by
`the names Apelii and Topas. iii These materials are probably the first plastics
`designed specifically with optical products in mind. They have similar optical
`lower water
`properties to acrylic but have higher thermal capability and
`absorption. We will discuss these materials in more detail in the next chapter.
`Besides these new polymers, optical grades of polyetherimide (PEI), best
`known by the trade name ULTEM/v and polyethersulfone (PES), known by the
`trade name RADEL/ also became available. These materials have excellent
`temperature capability, beyond the other optical plastics, as well as relatively
`high refractive indices. Their potential downside is a deep amber color, which
`limits their use for many visible applications.
`Another fairly recently introduced material is optical polyester. One example
`is OKP4,vi which is produced by the Osaka Gas Chemicals Co., Ltd. This new
`material has a refractive index over 1.6, birefringence properties similar to
`acrylic, and a low Abbe number.
`In addition to improvements in plastic optical materials, there have also been
`significant advances in areas that affect the production of plastic optics. In
`particular, there have been improvements in injection molding machines, as well
`as
`in machining
`technologies,
`such as
`single-point diamond
`turning.
`Improvements in molding machines have been driven by both product and
`process innovation. 20 Product innovation refers to changes such as reducing the
`number of components in a system by making the components perform multiple
`functions. This often results in more complex parts, pushing the capability of the
`molding machines and spurring their advance. Process innovation refers to
`optimizing a production process to make it as efficient and capable as possible.
`There has been a big push for process control and improvement across many
`industries, driven by the acceptance of manufacturing philosophies such as
`statistical process control and "lean" and ''just-in-time" manufacturing. These
`philosophies have created demand for injection molding machines with greater
`process control and feedback.
`Probably the largest change in injection molding equipment, particularly for
`use in the production of plastic optics, has been the switch from hydraulic-
`operated machines to hybrid or electric machines. Hybrid machines, as the name
`suggests, use a combination of hydraulic and electrical drives. Electric machines,
`sometimes referred to as "all electric" machines, completely eliminate the use of
`
`i ZEONEX is a registered trademark of ZEON Corporation.
`ii Apel is a registered trademark of Mitsui Chemicals.
`iii Topas is a registered trademark ofTopas Advanced Polymers.
`iv Ultem is a registered trademark of SABIC Innovative Plastics.
`v RADEL is a registered trademark of Solvay Advanced Polymers, LLC.
`vi OKP4 is a product of Osaka Gas Chemicals.
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`4
`
`Chapter 1
`
`hydraulics, relying on electrical motors and drives. The transition to electric
`machines has occurred for several reasons. The primary reason is repeatability.
`The repeatability of an electric machine ( or its potential for repeatability) is
`inherently higher than for a hydraulic machine. 2 1 Given the precision required in
`optical elements, repeatability of a manufacturing process is a highly desired
`characteristic. In addition to this, moving from a hydraulic to an electric machine
`eliminates the use of hydraulic oil in the machine clamp mechanism. Hydraulic
`oil is associated with several problems. It can cause environmental issues,
`particularly ground contamination from leaking oil. It creates health and safety
`concerns such as oil vapors, falls, and fire hazards. There is also a cost associated
`with its storage and disposal. This argument can only be pressed so far though,
`for as we shall see, although switching to electric machines eliminates hydraulic
`oil in the molding machine, oil is still often required for temperature regulation of
`the mold itself. It can fairly be said that the use of electric machines does not
`completely remove the use of oil, but it does reduce the total quantity of oil used
`on the molding floor. In addition, electric machines tend to use less power than
`hydraulic machines, resulting in energy cost savings.
`The general advances in processors and computing, which have also had
`great influence on the process of optical desig n , have influenced the development
`and use of injection molding machines. Most machines are now fully computer
`controlled, with a flat screen on the side of the machine displaying the current
`process parameters, as well as time-based graphs of pressure and other
`parameters for each injection cycle. Multiple sensors provide feedback, for
`display as well as for closed-loop control. The molding machine can be
`connected to a personal computer to continuously send process and sensor data
`for analysis and tracking, and the data can be stored for later download and
`further evaluation.
`Besides the injection molding machines themselves, improvements have also
`taken place in the ancillary equipment associated with them. This includes
`improvements in material dryers, thermal conditioning equipment, and automated
`robotic pickers and <legating systems. Improvements in automation have reduced
`the need for human intervention during steady-state production, which results in
`reduced cost, as well as less chance of human error or safety incidents. It is no
`longer necessary to have a person standing by each machine during production.
`In addition to the advances in molding machine technology, there have also
`been sig n ificant advances in machining technologies. This affects the precision
`and complexity of molds that can be built and allows the direct machining of
`plastic optical parts, either as prototypes or for actual production. Advances in
`computing and computer control, as well as in other areas, have pushed
`machining capabilities to previously unthinkable levels. Nowhere is this more
`evident than in the process of single-point diamond turning, often simply referred
`to as diamond turning.
`Diamond turning is a machining process combining the use of gem-quality
`diamond tools with precision computer numerically controlled (CNC) equipment.
`According to Schaefer, advances that hav<:; been made over the last 30 years
`
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`Introduction
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`5
`
`include going from air bearing to oil hydrostatic slide ways, changing from belt
`drive to direct brushless DC spindle drives, changing from laser positioning to
`glass scale positioning systems, using PC DSP instead of tape CNC controllers,
`using epoxy granite instead of granite machine bases, and switching from ball
`lead screws to linear motor drive axis drives. 22
`The result of these advances has been a factor of eight improvement in
`surface finish and a factor of four improvement in surface form. In addition, the
`achievable spindle speeds have increased ten fold and the cost of the diamond-
`turning machines has dropped by about half. The machines are commercially
`available with a number of options, including machines with multiple axes.
`These macliining improvements have enabled the creation of high-precision
`complex parts. Off axis, nonsymmetric, and microfeatured surfaces can all be
`produced using modem diamond-turning equipment. For the optical designer,
`this allows additional freedom in selecting surface forms or in the integration of
`features such as multizonal surfaces. Proper machine setup, processing, and
`fixturing can eliminate the need for postpolishing. This means that plastic optical
`prototypes can be directly machined and that optical mold inserts can be built to
`high optical surface accuracy and surface roughness requirements. Combining
`this precision machining with advances in testing, mold compensation is readily
`performed.
`Designers can, and should, take advantage of the improvements that have
`been made in plastic optical materials, injection molding machines, and
`machining technologies such as diamond turning. Conversations with vendors
`and/or suppliers, who need to stay current with these technologies, is usually the
`best way to be aware of the current state of capability, as well as ongoing
`development.
`
`1.2 When Are Plastic Optics Appropriate?
`As with all optical technologies, plastic optics are not the solution to every
`problem. When deciding whether to use plastic optics, the first question that
`needs to be answered is "Are plastic optics appropriate for my application?"
`There are a number of considerations in determining the answer to this question.
`Finances, project schedule, and supply chain issues can all play a role.
`Production volumes, along with cost and weight, are the top reasons that people
`decide to use plastic optics, while thermal issues such as storage temperature
`limits or temperature-dependant focus shift are the main reason that they are not
`chosen. Other considerations, such as the spectral band used, product lifetime, or
`even biological compatibility, may contribute to the decision whether or not they
`are appropriate. These issues, along with advantages, disadvantages, and
`application examples, are briefly discussed in the following paragraphs.
`If there is a large anticipated production volume, that is, when many systems
`are expected to be manufactured, plastic optics may be appropriate. "What's the
`volume?" is a question typically heard early in discussions with plastic optics
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`6
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`Chapter 1
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`manufacturers. Certain plastic optics manufacturing methods are suitable for
`producing large quantities of parts. In certain consumer applications it is not
`unusual for millions of lenses and lens assemblies to be produced