Ayee Oe |
`
`
`
`Michael Schaub
`
`
`
` Alan Symmons
`
`Exhibit 2006
`IPR2020-00878
`Page 1 of 26
`
`Exhibit 2006
`IPR2020-00878
`Page 1 of 26
`
`
`
`
`
`Michael Schaub
`
`
`
` Alan Symmons
`
`Exhibit 2006
`IPR2020-00878
`Page 1 of 26
`
`Exhibit 2006
`IPR2020-00878
`Page 1 of 26
`
`
`
`Field Guide to
`
`Molded Optics
`
`Alan Symmons
`Michael Schaub
`
`SPIE Field Guides
`Volume FG37
`
`John E. Greivenkamp,Series Editor
`
`SPIE PRESS
`Bellingham, Washington USA
`
`Exhibit 2006
`IPR2020-00878
`Page 2 of 26
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`Exhibit 2006
`IPR2020-00878
`Page 2 of 26
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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] | © 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
`
`Published by
`
`SPIE
`P.O. Box 10
`Bellingham, Washington 98227-0010 USA
`Phone: 360.676.3290
`Fax: 360.647.1445
`Email: Books@spie.org
`Web: www.spie.org
`
`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://spie.org and type “FG37” in the search
`field.
`
`Exhibit 2006
`IPR2020-00878
`Page 3 of 26
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`
`
`Introduction
`
`1
`
`Molded Optics
`
`Molded optics are conveniently categorized by the base
`material, plastic or glass. Subsequent classification can be
`further subdivided based on the manufacturing process.
`
`Plastic molded optics can be injection molded, cast, or
`compressed/embossed.
`
`Injection molding is the process of
`injecting molten plastic into a mold
`under pressure and then allowing it to
`cool. Injection-compression molding is
`a subset of this process and adds a
`compression step within the molding process.
`
`Cast plastic optics are primarily used for the ophthalmic
`industry. These are made simply by introducing liquid
`plastic resin into a mold and allowing it to solidify.
`
`Molded plastic optics can also be formed using compres-
`sion or embossing.
`
`Glass molded optics are made using several processes:
`blank molding, traditional glass molding, and precision
`glass molding (PGM).
`
`Blank molding is an old method of heating a glass blank
`in a furnace to a near-net shape for further processing.
`
`Glass molding is a non-isothermal
`process in which a molten gob of glass
`is introduced into a mold and is allowed
`to cool.
`
`PGM is typically an isothermal process
`in which a glass preform is formed by
`compression at a set temperature.
`
`A further type of molded optics is glass
`replication, which consists of an ultra-
`violet (UV) monomer cured over a glass
`substrate.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 4 of 26
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`
`
`2
`
`Introduction
`
`Why Use Molded Optics?
`
`Molded optics first come to mind for high-volume applica-
`tions. Why? Because molding is a process that can be
`replicated quickly with high throughput and low cost, two
`very desirable features for high-volume applications.
`
`Molded optics provide many other potential advantages.
`Injection-molded plastic optics (IMPO) can incorporate
`a significant number of
`integrated features,
`thereby
`reducing part count and assembly complexity.
`
`Optical molding processes lend themselves to high repeat-
`ability from component to component. This consistency can
`improve assembly and alignment, resulting in high perfor-
`mance and improved yields, which lead to cost savings.
`
`Molding enables the replication of shapes that might not be
`achievable with conventional manufacturing techniques.
`Steeper slopes, advanced freeforms, and multisurface
`shapes can be achieved.
`
`Molded plastic optics present a significant weight savings
`over their glass counterparts, while molded chalcogen-
`ides are lighter than their diamond-turned germanium
`substitutes.
`
`Regardless of optical molding technology, the reasons for
`selecting a molding process are similar: high-volume
`manufacturing, lower cost, repeatability, integrated fea-
`tures, and design freedoms.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 5 of 26
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`
`
`Introduction
`
`3
`
`Applications of Molded Optics
`
`Molded optics are everywhere.
`
`Injection-molded plastic optics (IPMO) offer a combi-
`nation of high performance and low cost. Their ability to be
`produced at extremely high volumes enabled the cellphone
`camera.
`
`Precision-glass-molded (PGM) aspheres are used in the
`read head of every Blu-ray disc player.
`
`Glass molding is enabling the next generation of auto-
`motive headlights.
`
`State-of-the-art digital still cameras use a combination of
`IMPO and PGM lenses.
`
`The development of cast plastics for eyeglasses revolution-
`ized the eyewear industry due to their lower cost and lower
`weight with improved impact resistance.
`
`PGM chalcogenide lens assemblies are the driving
`technology used in the manufacture of low-cost thermal
`imaging systems. Traditional manufacturing methods
`cannot keep pace with the reduction of costs of uncooled
`infrared detectors (microbolometers).
`
`Glass replication enabled the development of wafer-level
`optics and the mass production of very low-cost cellphone
`modules.
`
`Endoscopes, laser pointers, gun sights, machine vision,
`thermal imaging, eyeglasses, automotive headlights, tele-
`communications, all of these use molded optics.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 6 of 26
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`
`
`4
`
`Introduction
`
`Comparison of Molded Optics
`
`Each type of molded optics has its own set of advantages
`and disadvantages. A general comparison is shown below;
`each process can have individual materials or applications
`that can be better or worse.
`
`The costs of the different types of molded optics vary
`greatly based on many criteria but can be generalized.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 7 of 26
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`
`
`Introduction
`
`5
`
`Conventional Manufacturing versus Molded Optics
`
`The traditional method of manufacturing optics is conven-
`tional grind and polish. The number of steps it takes to
`grind and polish a single bi-convex lens is extensive;
`molding presents a significant reduction in process steps.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 8 of 26
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`
`
`6
`
`Introduction
`
`Aspheric Advantage
`
`One of the primary advantages of molded optics has always
`been the use of aspheric surfaces. Aspheric surfaces are
`simply surfaces that are not spherical. Historically, most
`optical surfaces have been spherical (or flat) due to ease of
`fabrication and testing with the exception of molded optics.
`Aspheric surfaces have long been the standard in molded
`optics, regardless of process, again due to ease of manufacture.
`The mold manufacturing process is well suited to aspheric
`manufacturing, and only having to cut a small number of
`molds to make a large quantity of optics made an increase in
`tooling cost trivial when amortized over a molding run.
`
`The most common forms of aspheres are conics. A conic
`surface is described by
`
`x2
`ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
`
`1 ð1 þ kÞð xRÞ2
`
`1R
`
`q
`
`zðxÞ 5
`
`1 þ
`c 5 1
`R
`
`(cid:129) k = 0: sphere
`(cid:129) 1 , k , 0: ellipsoid with
`major axis on the optical
`axis
`(cid:129) k 5 1: paraboloid
`(cid:129) k , 1: hyperboloid
`where z(x) is the sag, R is the radius, c is the curvature, and
`x is the lateral coordinate.
`The addition of even polynomial terms to the conic equation
`results in the most common rotationally symmetric aspheric
`equation used for molded optics:
`
`þ Ax4 þ Bx6 þ Cx8 þ Dx10
`
`x2
`q
`ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
`
`1 ð1 þ kÞð xRÞ2
`1 þ
`þ Ex12 þ Fx14 þ Gx16
`
`1R
`
`zðxÞ 5
`
`The polynomial terms are used to optimize the system and
`reduce aberrations, and typically reduce the number of
`elements in a system. Alternative equations, including the
`Forbes polynomials, can be used, but the above equation is
`the industry standard.
`
`The cost difference between a spherical molded optic and an
`aspherical one is essentially negligible for most applications.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 9 of 26
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`
`
`Precision Glass Molding Design Guidelines
`
`87
`
`PGM Lens Terminology
`
`A precision-glass-molded lens has a number of distinct
`features. These features are shown in the diagram and
`defined on the next page.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 10 of 26
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`
`
`88
`
`Precision Glass Molding Design Guidelines
`
`PGM Lens Terminology (cont.)
`
`➊ Outside diameter (OD)
`
`The diameter of the lens.
`
`➋ Center thickness (CT)
`
`The thickness of the lens at its optical center.
`➌ Clear aperture (CA), or effective diameter (∅c)
`The optical or effective use diameter of the individual lens
`surface.
`➍ Blend radius (Rb)
`The radius transition between the optical surface and the
`flange of the lens.
`➎ Edge radius or corner radius (Rc)
`The radius on the outside diameter due to volumetric
`molding.
`
`➏ Flat or flange
`
`The section of the lens outside of the physical aperture
`leading up to the outside diameter.
`
`➐ Edge thickness (ET)
`
`The thickness of the lens along its edge.
`➑ Physical aperture (PA) or sag diameter (∅s)
`The physical or mechanical diameter of the individual
`optical surface.
`➒ Sag depth (ds)
`The depth or thickness associated with the physical
`diameter of the individual optical surface.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 11 of 26
`
`
`
`Precision Glass Molding Design Guidelines
`
`89
`
`PGM Shapes
`
`The most common components manufactured using PGM are
`lenses. PGM lenses come in many shapes and sizes. Five
`potential shapes are shown:
`
`bi-convex, plano-convex, meniscus, plano-concave, bi-concave.
`
`The shape of the lens must be considered when selecting PGM
`lenses.
`
`(cid:129) High-aspect-ratio lenses can be hard to manufacture, as
`are lenses with very small center thickness or thin edges.
`
`The shape of the lens also impacts the preform selection.
`
`(cid:129) Plano-concave and bi-concave lenses cannot be achieved
`with ball or gob preforms.
`(cid:129) Very difficult shapes can be achieved but might require
`expensive near-net shape preforms.
`
`Even with these limitations many different shapes and sizes
`of PGM lenses have been manufactured.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
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`
`
`
`90
`
`Precision Glass Molding Design Guidelines
`
`PGM Optomechanical
`
`design parameters
`straightforward
`of
`A number
`should be implemented into the optomechanical
`design of a PGM component. Many of these parameters
`were defined on pages 87 and 88 and are expanded on
`here.
`
`The outside diameter (OD) of PGM lenses can vary
`anywhere from less than a millimeter up to 150 mm in
`diameter but are commonly in the 3 mm to 15 mm
`diameter range.
`
`There are many reasons for this OD variation, preform
`manufacture being a primary one. It can be very difficult to
`cost-effectively manufacture large preforms regardless of
`their shapes. Demand is another reason. Most high-volume
`applications are size driven; hence, there is less demand for
`large-diameter optics.
`
`Mold manufacture and tooling also become more difficult
`and time consuming with larger ODs. The cosmetic quality
`is more difficult to maintain, resulting in a reduction in
`mold life.
`
`There are also limitations based on the molding machine
`used and the tooling configuration. Large ODs (.30 mm)
`are more suited for fixed-die molding machines.
`
`The center thickness (CT) and edge thickness (ET) of a
`lens are largely dependent on the lens’ overall shape or
`aspect ratio. Very thin CTs down to 0.2 mm can be
`manufactured but might require near-net shape preforms
`to reduce the stress in the glass. CTs greater than 4 mm
`should be avoided in order to minimize thermal gradients
`in the optics. Excessive thermal gradients will lead to
`high stress birefringence, inhomogeneity of the index
`of refraction, and possible fracture due to thermal
`stress.
`
`Very small edge thicknesses (,0.4 mm) should be avoided,
`as these lenses become very difficult to handle and can chip
`easily.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 13 of 26
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`
`
`Precision Glass Molding Design Guidelines
`
`91
`
`PGM Optomechanical (cont.)
`
`The three parameters outside diameter (OD), center
`thickness (CT), and edge thickness (ET) determine the
`relative aspect ratios (ARs) of a PGM lens, where
`
`ARET 5 OD
`ARCT 5 OD
`ET
`CT
`Aspect ratios are highly dependent on the lens shape, so
`general rules of thumb are difficult to provide. Aspect
`ratios (ARCT) for plano-concave lenses can be very large,
`while a typical bi-convex lens should be kept under 5.
`The clear aperture (CA) or effective diameter (∅e) is the
`individual lens surface area that must meet specifications;
`outside of this area, manufacturers do not guarantee that
`the optic will meet the stated specifications. This restric-
`tion also applies to the cosmetic inspection requirements of
`the lens. The CA is a virtual region that does not correlate
`to physical geometry.
`
`The CA should always be smaller than the physical
`aperture in order to allow for a blend radius between the
`optical surface and the flange. How much smaller depends
`on the particular surface and manufacturing method used.
`Transition zones can also be used if necessary.
`
`The convergence of the physical aperture
`of
`the optical surface and the flange
`requires the use of a blend radius Rb.
`This radius is required in order to reduce
`the stress concentration and to provide a
`tool relief for the radius of the cutting tool.
`For concave molds or convex lenses, a sharp edge could
`theoretically be achieved, but this is not good practice as it
`can introduce stress concentrations and restricts the
`manufacturer from post-polishing the molds (post-polish-
`ing inherently adds a small blend radius). Very flat
`surfaces essentially do not have a blend radius.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 14 of 26
`
`
`
`92
`
`Precision Glass Molding Design Guidelines
`
`PGM Optomechanical (cont.)
`
`If a PGM lens is manufactured
`using volumetric molding, it
`will have an edge radius (Rc) or
`corner radius. This area is the
`relief area in the molding pro-
`cess;
`it compensates for the
`variations in the volume of the
`preform. This means that the
`edge radii will vary slightly from
`part to part. The radius at the bottom corner relative to the
`direction of molding will commonly have a smaller radius
`than the top corner.
`
`Mounting features can be molded directly
`into a PGM component. Flanges or flats are
`typical on most PGM lenses and allow for
`easy mounting of lens stacks and assemblies.
`
`Flanges must take into consideration both the blend
`radius and the edge radius. In order to have sufficient
`landing for assembly, they may need to be extended to
`account for these radii.
`
`It is always preferred to include flanges because it is
`difficult or nearly impossible to extend the optical surface
`to the edge of the part. Lens surfaces without flanges create
`a sharp tooling condition and also leave no room for an
`edge radius. A strict limitation on the lens radius would
`require very accurate preform volume control, leaving no
`volumetric relief.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 15 of 26
`
`
`
`Precision Glass Molding Design Guidelines
`
`93
`
`PGM Optomechanical (cont.)
`
`The physical aperture (PA) or sag diameter (∅s) of an
`optical surface is the diameter at which the optical surface
`ends. The PA should extend beyond the clear aperture,
`which means that there are portions of the surface that are
`not optically active. The physical aperture should always
`be larger than the clear aperture.
`
`The PA can also be obscured by a blend radius and might
`not be explicitly measurable. Transition zones can
`extend the physical aperture.
`The sag depth or sag height (ds) is the height of optical
`surface from the flat plane of the physical aperture to the
`highest or lowest point of the surface. Sag depth can also be
`extended by transition zones (see PGM Slope).
`
`Sag depth is the equivalent depth of the physical aperture
`based on the optical prescription. Therefore, any change in
`the physical aperture results in a change in sag depth or
`height.
`
`The tolerance on one dimension drives the tolerance on the
`other. The tolerance dependency on sag height is related to
`the localized slope of the surface at the physical aperture.
`The sag depth is driven directly by the mold manufacture.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 16 of 26
`
`
`
`94
`
`Precision Glass Molding Design Guidelines
`
`PGM Slope
`
`The slope of a lens surface should be kept less than
`55 deg for PGM. High slopes create difficultly in mold
`manufacture and testing. Very steep surfaces can be
`difficult to manufacture and difficult to measure. Precision
`diamond grinding is limited to just under
`55 deg, but the maximum angle varies
`based on final geometry and manufac-
`turer. Many surface profilometers can-
`not measure surfaces this steep and begin
`to lose accuracy at high angles. Stitching
`profilometers can be used to measure steep slopes.
`
`Best practice:
`f , 55 deg
`
`Steep geometries also can lead to gas
`entrapment and might require vac-
`uum molding. High slopes can be
`driven by severe aspheric departure
`outside of the clear aperture.
`
`One method to allevi-
`ate steep slopes is the
`use
`of
`transition
`zones. Once the clear
`aperture is exceeded,
`a tangent transition
`zone can be added.
`The tangent angle is
`equivalent to the slope
`of the localized surface at the end of the optical surface. The
`slope at a specific point along an aspheric surface can be
`determined by taking the first derivative z0(x) of the
`aspheric equation:
`
`z 0ðxÞ 5
`
`p
`ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
`2x=R
`1 ð1 þ KÞðx=RÞ2
`ð1 þ KÞðx=RÞ3
`p
`ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffip
`
`ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
`1 ð1 þ KÞðx=RÞ2
`1 ð1 þ KÞðx=RÞ2
`2nA2nx2n 1
`
`1 þ
`X∞
`
`1 þ
`þ
`
`þ
`
`n51
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 17 of 26
`
`
`
`Precision Glass Molding Design Guidelines
`
`95
`
`PGM Tolerances
`
`Tolerances on PGM lenses can vary greatly based on
`different lens sizes and geometries. Smaller lenses are
`typically held to tighter tolerances, whereas larger lenses
`are held to looser ones.
`
`Parameter
`
`Standard
`
`Precision
`
`Radius
`
`Center Thickness, mm
`
`Diameter, mm
`
`Surface Figure, fringes
`
`Surface Irregularity, fringes
`
`0.5%
`
`±0.050
`
`±0.025
`
`5
`
`2
`
`Surface Quality Scratch/Dig
`
`60/40
`
`Surface Roughness, nm
`
`20
`
`S1 to S2 Displacement (mm)
`
`0.020
`
`Wedge, arcmin
`
`±5
`
`0.25%
`
`±0.020
`
`±0.005
`
`3
`
`1
`
`40/20
`
`5
`
`0.003
`
`±3
`
`Improvements in surface form and surface figure might
`require multiple iterations of mold compensation. The
`greater the number of compensations the tighter the
`performance can be held, up to a limit. This limit is
`dependent on the materials and shape of the surface. High-
`slope surfaces can be particularly difficult to manufacture
`and measure at very tight tolerances.
`
`Outside diameter and other mechanical tolerances are
`driven by the precision level of the tooling. Wear of tooling
`is greater in PGM than IMPO due to higher processing
`temperature, the hardness of the glass, and the loads
`involved. This wear can result in larger mechanical
`tolerances.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 18 of 26
`
`
`
`96
`
`Precision Glass Molding Design Guidelines
`
`Insert Precision Glass Molding
`
`Insert precision glass molding (iPGM) is the process of
`molding an optical glass component inserted within a
`holder. It is a volumetric molding process. Therefore, the
`preform must fit within the insert—a simple but funda-
`mentally important concept.
`
`The insert design should take tooling into consideration.
`Sharp edges should be avoided in order to extend mold life.
`
`The stress in the glass should also be minimized. The
`interface diameter and the differential
`thermal
`expansion coefficients between the glass and the insert
`should be kept to a minimum in order to keep the interface
`pressure low.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 19 of 26
`
`
`
`Injection-Molded Plastic Optics Design Guidelines
`
`97
`
`IMPO Shape
`
`The shapes of injection-molded plastic optics can be quite
`different from those of conventionally fabricated glass
`elements. These shape differences arise for multiple
`reasons, including the fact that shapes that are difficult
`to fabricate by traditional grind and polish techniques are
`straightforward to mold.
`
`The limited material choices along with the minimized
`number of elements to keep cost lower can result in each
`element “working as hard as possible,” which can result in
`unusual shapes. Examples of such shapes are gull-wing
`correctors (often seen in cellphone camera lens designs)
`and extremely deep concave aspheric meniscus elements,
`both shown below.
`
`While the full range of spheres, aspheres, and diffractive
`surfaces are available in plastic, shallow or flat surfaces
`are more difficult to accurately produce. This is because
`shallow surfaces have less “self-support” than more steeply
`curved surfaces (similar to an arch).
`
`The rule in plastic optic design is to push a flat or shallow
`surface to have more curvature, if possible.
`
`Flats, if needed, might end up being produced by injection
`compression molding.
`
`In addition to unusual single-element shapes, it is also
`possible for multiple optical surfaces to be put on each side
`of the part, including combinations of reflective, refractive,
`and diffusing surfaces.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 20 of 26
`
`
`
`98
`
`Injection-Molded Plastic Optics Design Guidelines
`
`IMPO Flanges
`
`One of the advantages of IMPO is the ability to mold
`alignment or mounting features into the elements. Most
`often, a flange is formed around the outside of the
`element.
`
`Flanges can be used for several purposes, such as to set the
`spacing between lenses in a multi-element system. If the
`flanges are tapered, they can be used to provide alignment
`between elements.
`
`If possible, the length of the flanges should extend beyond
`the vertex of convex optical surfaces. The flange then
`provides protection to the surface if the lens is placed in a
`tray or other packaging.
`
`The flange length should not be excessively large, as this
`will be difficult to fill during molding. If very long flanges
`are needed to stack two widely spaced lenses, it is better to
`keep the flanges a more reasonable length and use a
`spacer. Alternatively, the spacing could rely on positioning
`features within the assembly housing.
`
`For noncircular elements, such as rectangular lenses for
`head-mounted displays, the corners of the element and its
`flanges should be rounded, not sharp. Sharp corners will
`create stress areas and are more difficult to mold.
`
`Any sharp features on parts should be rounded
`whenever possible.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 21 of 26
`
`
`
`Injection-Molded Plastic Optics Design Guidelines
`
`99
`
`IMPO Draft
`
`Draft is the tapering of parts in order to help them be
`removed from the mold. The draft is arranged such that the
`larger diameter of the draft cone is near or at the parting
`line of the mold. The amount of draft depends on the
`material and part design, but about 1 deg is preferred.
`
`Drafting the part on the fixed half of the mold allows it to
`be pulled from the fixed half when the mold opens. The
`part remains in the moving half until it is pushed out of
`that half by the ejection mechanism. The draft of the part
`on the moving half of the mold allows it to be easily ejected.
`
`Optical elements are often centered in assemblies by their
`outer diameter. The use of a no draft zone can provide a
`centering feature. The length of the no draft zone should
`be kept as short as possible to facilitate ejection of
`the part.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 22 of 26
`
`
`
`100
`
`Injection-Molded Plastic Optics Design Guidelines
`
`IMPO Gate Flats and Vestige
`
`The gate on most plastic optics is on the edge of the
`element. When the part is ejected from the mold, it is still
`attached to the runner system. It is then cut from the
`runner/gate system in a process known as degating. The
`degating process is not perfect and results in residual
`material being left on the edge of the part. This remaining
`plastic is called gate vestige.
`
`In order to prevent the vestige from interfering with
`insertion of the part into a barrel or other holder, a gate
`flat is often designed into the part. The gate flat is a small
`flat zone cut out of the diameter of the part. It is
`sufficiently deep such that the vestige height does not
`protrude outside the diameter of the part.
`
`If vestige will not create any issues for the part, a gate flat
`is not necessarily required. However, gate flats also provide
`additional width for the size of the gate on parts that come
`to a thin or sharp edge, which can be useful for mold
`processing.
`
`If vestige is an issue and a gate flat cannot be designed into
`the part, it may be necessary to perform machining to
`completely remove the vestige. This secondary opera-
`tion will increase the cost and potentially reduce the yield
`of the part.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 23 of 26
`
`
`
`Injection-Molded Plastic Optics Design Guidelines
`
`101
`
`IMPO Center Thickness
`
`The center thickness of plastic elements needs to be
`large enough to provide an adequate path for the molten
`material to flow through.
`
`When injected, plastic will flow along the path of least
`resistance. For bi-concave or negative meniscus lenses, the
`plastic will flow around the outer edge of the part. If the
`flow travels first around the outside of the lens, then meets
`up at the center, a defect called a flow line will be created
`along the center of the part.
`
`To prevent flow lines, the center thickness might need to be
`increased beyond that required solely for the optical
`performance of the element. This additional thickness
`allows the injected plastic to flow smoothly across the lens
`with a uniform flow front.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 24 of 26
`
`
`
`102
`
`Injection-Molded Plastic Optics Design Guidelines
`
`IMPO Edge Thickness
`
`On most injection molded optical elements, the plastic is
`injected from the edge of the part. The edge therefore needs
`to be large enough to provide an adequate gate size for the
`material to flow in and fill out the part.
`
`If the part has flanges around it, the gate can be placed
`onto the flange instead of into the edge of the optical
`surfaces. However, if the flange thickness is greater than
`the edge thickness of the optical surfaces, it is the latter
`that must be controlled. That is, the minimum cross-
`sectional thickness through the part is the critical
`thickness. Inadequate thickness will restrict the flow of
`the plastic and result in difficulty filling out the part.
`
`The minimum thickness required will depend on the size
`and shape of the part, as well as the material it is made
`from. Small lenses such as those used for cellphone cameras
`can have extremely small minimum cross sections, on the
`order of a few hundred microns. Larger parts will typically
`require correspondingly larger minimum thicknesses.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 25 of 26
`
`
`
`Injection-Molded Plastic Optics Design Guidelines
`
`103
`
`IMPO Clear Aperture
`
`The clear aperture (CA) is the region over which the
`optical surfaces must meet their specification for surface
`shape or performance. While desirable for packaging
`purposes, the clear aperture typically cannot be specified
`all the way out to the edge of the optical surface or part.
`
`The reason for limited specification is the nonuniform
`shrinkage that occurs at transition zones of the part,
`such as where the optical surface joins the flange. This
`shrinkage effect is known as edge break.
`
`Because of the impact of edge break, molders will require
`the CA size to be smaller than the full optical surface that
`is molded. The amount of edge relief will depend on the
`part size, but one millimeter or more in the radial direction
`is desired for parts of approximately 10 to 25 mm in
`diameter.
`
`This much relief is often impractical for smaller parts,
`where it would be a substantial portion of their diameter.
`In this case, the edge break relief zone will need to scale
`down with the part size.
`
`In many designs, only a small portion of the optical beams
`passes through the lens near the edge of the CA. In these
`cases it might be possible to have the surface specification
`broken into two zones: one for most of the surface and the
`other for an annulus near the edge of the CA.
`
`Field Guide to Molded Optics
`
`Exhibit 2006
`IPR2020-00878
`Page 26 of 26
`
`
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