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Library of Congress Cataloging-in-Publication Data

Names: Symmons, Alan, author. | Schaub, Michael P., author.

Title: Field guide to molded optics / Alan Symmons and Michael Schaub.

Other titles: Molded optics

Description: Bellingham, Washington USA : SPIE Press, [2016] | copyright 2016 | Series: SPIE field guides | Includes bibliographical references and index.

Identifiers: LCCN 2015047156| ISBN 9781510601246 (spiral ; alk. paper) | ISBN 1510601244 (spiral ; alk. paper) | ISBN 9781510601253 (PDF) | ISBN 1510601252 (PDF) | ISBN 9781510601260 (epub) | ISBN 1510601260 (epub) | ISBN 9781510601277 (Kindle) | ISBN 1510601279 (Kindle)

Subjects: LCSH: Optical instruments-Design and construction-Handbooks, manuals, etc. | Optical materials-Handbooks, manuals, etc. | Plastics-Optical properties-Handbooks, manuals, etc.

Classification: LCC TS513 .S96 2016 | DDC 620.1/1295-dc23

LC record available at http://lccn.loc.gov/2015047156

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SPIE

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Copyright © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

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 authors. 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.

First printing.

For updates to this book, visit http://www.spie.org and type “FG37” in the search field.

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Introduction to the Series

Welcome to the SPIE Field Guides—a series of publications written directly for the practicing engineer or scientist. Many textbooks and professional reference books cover optical principles and techniques in depth. The aim of the SPIE Field Guides is to distill this information, providing readers with a handy desk or briefcase reference that provides basic, essential information about optical principles, techniques, or phenomena, including definitions and descriptions, key equations, illustrations, application examples, design considerations, and additional resources. A significant effort will be made to provide a consistent notation and style between volumes in the series.

Each SPIE Field Guide addresses a major field of optical science and technology. The concept of these Field Guides is a format-intensive presentation based on figures and equations supplemented by concise explanations. In most cases, this modular approach places a single topic on a page, and provides full coverage of that topic on that page. Highlights, insights, and rules of thumb are displayed in sidebars to the main text. The appendices at the end of each Field Guide provide additional information such as related material outside the main scope of the volume, key mathematical relationships, and alternative methods. While complete in their coverage, the concise presentation may not be appropriate for those new to the field.

The SPIE Field Guides are intended to be living documents. The modular page-based presentation format allows them to be updated and expanded. We are interested in your suggestions for new Field Guide topics as well as what material should be added to an individual volume to make these Field Guides more useful to you. Please contact us at fieldguides@SPIE.org.

John E. Greivenkamp, Series Editor

College of Optical Sciences

The University of Arizona

The Field Guide Series

Keep information at your fingertips with the SPIE Field Guides:

Adaptive Optics, Second Edition, Robert K. Tyson and Benjamin W. Frazier

Astronomical Instrumentation, Christoph U. Keller, Ramon Navarro, and Bernhard R. Brandl

Atmospheric Optics, Larry C. Andrews

Binoculars and Scopes, Paul R. Yoder, Jr. and Daniel Vukobratovich

Diffractive Optics, Yakov G. Soskind

Digital Micro-Optics, Bernard Kress

Displacement Measuring Interferometry, Jonathan D. Ellis

Fiber Optic Sensors, William Spillman, Jr. and Eric Udd

Geometrical Optics, John E. Greivenkamp

Holography, Pierre-Alexandre Blanche

Illumination, Angelo Arecchi, Tahar Messadi, and R. John Koshel

Image Processing, Khan M. Iftekharuddin and Abdul Awwal

Infrared Systems, Detectors, and FPAs, Second Edition, Arnold Daniels

Interferometric Optical Testing, Eric P. Goodwin and James C. Wyant

Laser Pulse Generation, Rüdiger Paschotta

Lasers, Rüdiger Paschotta

Lens Design, Julie Bentley and Craig Olson

Lidar, Paul McManamon

Linear Systems in Optics, J. Scott Tyo and Andrey S. Alenin

Microscopy, Tomasz S. Tkaczyk

Nonlinear Optics, Peter E. Powers

Optical Fabrication, Ray Williamson

Optical Fiber Technology, Rüdiger Paschotta

Optical Lithography, Chris A. Mack

Optical Thin Films, Ronald R. Willey

Optomechanical Design and Analysis, Katie Schwertz and James H. Burge

Physical Optics, Daniel G. Smith

Polarization, Edward Collett

Probability, Random Processes, and Random Data Analysis, Larry. C. Andrews and Ronald L. Phillips

Radiometry, Barbara G. Grant

Special Functions for Engineers, Larry C. Andrews

Spectroscopy, David W. Ball

Terahertz Sources, Detectors, and Optics, Créidhe M. O’Sullivan and J. Anthony Murphy

Visual and Ophthalmic Optics, Jim Schwiegerling

Field Guide to Molded Optics

In the last few decades, molding has become the dominant optical manufacturing process around the world, although one could hardly tell in the United States. It is the authors’ hope that the concept of a Field Guide to provide a convenient and concise source of knowledge on optical molding technologies will be a valuable reference for any optical engineer.

The most common optical molding technologies are injection molding of optical plastics and precision glass molding. This guide primarily focuses on these two technologies but also covers the full spectrum of optical molding. Molding processes continue to innovate and push the boundaries of optical systems, not only for state-of-the-art, high-volume consumer products, but also touching on almost every application where optics are used, from automotive headlights and medical endoscopes to thermal weapon sights.

This work would not have been possible without the support of the team at LightPath Technologies Inc., who the author (A.S.) wholeheartedly believes are the world’s experts in precision glass molding. The authors would like to thank SPIE and specifically Tim Lamkins and Dara Burrows for the opportunity to write this guide and for their support along the way.

This book is dedicated to: my family—Lauren, Carter, Cooper, and Holden—for their support; my parents for making me who I am today; and Yanggiong ‘Alvin’ Lai, a good friend and a great engineer, who was taken from us way too soon. A.S.

This Field Guide is dedicated to Elsa, Shadow, Shira, and Patinhas. M.S.

Alan Symmons

Michael Schaub

May 2016

Table of Contents

Glossary of Symbols and Acronyms xi

Introduction 1

Molded Optics 1

Why Use Molded Optics? 2

Applications of Molded Optics 3

Comparison of Molded Optics 4

Conventional Manufacturing versus Molded Optics 5

Aspheric Advantage 6

Material Properties 7

Index of Refraction 7

Dispersion 8

Abbe Diagram 9

Birefringence 10

Transmission 11

Plastic Optic Transmission 12

Thermal Properties 13

Heat Expansion 14

Glass Viscosity 15

Materials 16

Moldable Glass 16

Moldable Glasses for Precision Glass Molding 17

Chalcogenide Glass 18

Glass Datasheets 19

Plastic Optic Materials 21

Plastic Optic Materials Summary 22

Plastic Optic Glass Map 23

Infrared Plastic Optics 24

Plastic Materials Data Sources 25

Thermal Characteristics 26

Glass versus Plastic 27

Molded Glass versus Molded Plastics 28

Environmental Regulations 29

Optical Plastics: Material Selection Criteria 30

Optical Plastic Material Specification 31

Manufacturing 32

Glass Replication 32

Wafer-Level Glass Replication 33

Blank Molding 34

Glass Molding 35

Plastic Optics Manufacturing Methods 36

Precision Glass Molding (PGM) 37

Precision Glass Molding (PGM) 37

PGM Configurations 38

Preforms for PGM 39

Spherical or Ball Preforms 40

Gob Preforms 41

PGM Processing 42

The PGM Zone 43

Process Simulation 44

Annealing Rates 45

Annealing Coefficient 46

Index Drop 47

Index Tolerances 48

Tooling Configurations 49

PGM Machine Diagram 50

PGM Machine Description 51

Transfer Molding 52

PGM Cavitation 53

Vacuum Molding 54

Volumetric Molding 55

Nonvolumetric Molding 56

Very Low-Tg PGM 57

Low-Tg PGM 58

High-Tg PGM 59

Array and Wafer-Level Molding 60

Insert Precision Glass Molding 61

Cost of PGM 62

Injection-Molded Plastic Optics (IMPO) 63

Injection Molding Process 63

Injection Molding Machine Diagram 64

Injection Molding Machine Description 65

Injection Mold Diagrams 66

Injection Mold Description 67

Undercuts, Slides, and Threads 69

Injection Mold Materials 70

Mold Cavitation 71

Family Molds 72

Mold Processing 73

Molding Capacity 74

Optical Molds 75

Optical Molds 75

Mold Materials 76

PGM Mold Design 77

IMPO Mold Compensation 78

Single-Point Diamond Turning 79

Ultraprecision Grinding 80

Vertical Grinding 81

Other Grinding Methods 82

Mold Coatings 83

Mold Metrology 84

Diffractive Surfaces 85

Precision Glass Molding Design Guidelines 86

PGM Glass Selection 86

PGM Lens Terminology 87

PGM Shapes 89

PGM Optomechanical 90

PGM Slope 94

PGM Tolerances 95

Insert Precision Glass Molding 96

Injection-Molded Plastic Optics Design Guidelines 97

IMPO Shape 97

IMPO Flanges 98

IMPO Draft 99

IMPO Gate Flats and Vestige 100

IMPO Center Thickness 101

IMPO Edge Thickness 102

IMPO Clear Aperture 103

IMPO Achromatization 104

IMPO Athermalization 105

IMPO Stray Light 106

IMPO Tolerances 107

IMPO Cost Considerations 108

IMPO Assembly 109

Drawings and Post-processing 110

ISO 10110 110

Geometrical Dimensioning and Tolerancing 111

PGM Drawing Sample 112

PGM Drawings 113

IMPO Drawing Sample 114

IMPO Drawings 116

Antireflection Coatings 117

IMPO Coatings 118

IMPO Secondary Operations 119

PGM Secondary Operations 120

Vendor Input and Review 121

Prototyping Injection-Molded Plastic Optics 122

Prototyping Injection-Molded Plastic Optics 122

Plastic Optics: Additive Manufacturing 123

Prototype Machining 124

Prototype Molding 125

Prototype Assembly 126

Prototype Testing 127

Applications of Molded Optics 128

Glass Mold Applications: Condenser Lenses 128

PGM Applications: Diode Collimation 129

PGM Applications: Fiber Coupling 130

PGM Applications: Camera Lenses 131

PGM Applications: Thermal Imaging 132

IMPO Applications: Cellphone Cameras 133

Appendices 134

Appendix A: Moldable Glasses 134

Appendix B: Chalcogenide Glasses 142

Appendix C: Optical Plastic Properties 144

Equation Summary 145

Bibliography 149

Index 151

Glossary of Symbols and Acronyms

Ap

Annealing point temperature

At

Yield point or dilatometric softening point temperature, also Ts

AOI

Angle of incidence

AR

Antireflection

AR

Aspect ratio

BD

Beam diameter

BFS

Best fit sphere

BRC

Blend radius cracking

c

Surface curvature

CA

Clear aperture

CC

Center of curvature

CCM

Cellphone camera module

CGH

Computer-generated hologram

ChG

Chalcogenide glass

CMOS

Complementary metal-oxide semiconductor

CNC

Computerized numerical control

COC

Cyclic olefin copolymer

COP

Cyclic olefin polymer

CT

Center thickness

CTE

Coefficient of thermal expansion

dn/dT

Thermo-optic coefficient

DOE

Diffractive optical element

dPa

Decipascal

DPW

Die per wafer

DSC

Digital still camera

ECHA

European Chemicals Agency

EFL

Effective focal length

ET

Edge thickness

FEA

Finite element analysis

Fr

Fringes

GMP

Glass molding press

iPGM

Insert precision glass molding

IR

Infrared

k

Conic constant

kgf

Kilogram force

LDT

Laser damage threshold

LVDT

Linear variable displacement transducer

LWIR

Longwave infrared

mnd

Annealing coefficient for index of refraction

mνd

Annealing coefficient for Abbe number

MTF

Modulation transfer function

MWIR

Midwave infrared

NA

Numerical aperture

NAS®

A transparent styrene acrylic copolymer from INEOS Styrolution Group GmbH

nC

Index of refraction at 656.27 nm (red hydrogen line)

nd

Index of refraction at 587.56 nm (yellow helium line)

ne

Index of refraction at 546.07 nm (green mercury line)

nF

Index of refraction at 486.13 nm (blue hydrogen line)

Nirreg

Number of fringes, irregularity

Npower

Number of fringes, power

NIR

Near infrared

O-PET

Optical polyethylene terephthalate

OD

Outside diameter

OG

Optical grade

P

Partial dispersion

Pa

Pascal

PA

Physical aperture

PC

Polycarbonate

PEI

Polyetherimide

PES

Polyethersulfone

PGM

Precision glass molding

PMMA

Poly(methyl methacrylate)

PS

Polystyrene

PSU

Polysulfone

P/V

Peak-to-valley ratio

Q

Heat flux per unit area

R

Radius of curvature

RMS

Root mean square

RoHS

Restrictions on Hazardous Substances

SA

Spherical aberration

SAN

Styrene acrylonitrile

SG

Specific gravity

SPDT

Single point diamond turning

Sp

Littleton softening point temperature

Stp

Strain point temperature

SWIR

Shortwave infrared

T

Temperature

T7.6

Temperature at which glass has a viscosity of 7.6 poise or dPa·s

T10

Temperature at which glass has a viscosity of 10 poise or dPa·s

T13

Temperature at which glass has a viscosity of 13 poise or dPa·s

T14.5

Temperature at which glass has a viscosity of 14.5 poise or dPa·s

Tg

Glass transition temperature

Tm

Molding temperature

Ts

Yield point or dilatometric softening point temperature, also At

TIR

Total indicated runout

TVG

Tilted vertical grinding (or 45-deg vertical grinding)

UV

Ultraviolet

VG

Vertical grinding (or cross-axis grinding)

VGA

Video graphics array

VIS

Visible

VLT

Very low Tg

WD

Working distance

WL

Wafer level

WLC

Wafer-level camera

WLGR

Wafer-level glass replication

WLO

Wafer-level optics

WLP

Wafer-level packaging

WLPGM

Wafer-level precision glass molding

WNG

Wheel normal grinding

α

Coefficient of thermal expansion, also CTE

αg

CTE, glass

αL

CTE, liquidus

αm

CTE, mold

αS

CTE, solidus

β

Annealing coefficient

λ

Wavelength

φ

Power of an optical surface

σPV

Wavefront error, peak-to-valley

σRMS

Wavefront error, root mean square

νd

Abbe number at 587.56 nm (yellow helium line)

νe

Abbe number at 546.07 nm (green mercury line)

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