U.S. patent application number 11/789774 was filed with the patent office on 2007-08-30 for ultra low residual reflection, low stress lens coating.
This patent application is currently assigned to Optima, Inc.. Invention is credited to Glen A. Koenig, Nicholas G. Niejelow.
Application Number | 20070202251 11/789774 |
Document ID | / |
Family ID | 33450693 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070202251 |
Kind Code |
A1 |
Koenig; Glen A. ; et
al. |
August 30, 2007 |
Ultra low residual reflection, low stress lens coating
Abstract
A method is provided for coating optical lenses and other
optical articles with anti-reflection (AR) coatings. The lenses
have low reflectivity, provide a substantially white light
reflection and have a low stress AR coating and are ideally suited
for optical lenses made using a molding procedure which provides a
low stress lens substrate. In one aspect the method uses special
coating compositions with one being a high index of refraction
composition and the other being a low index of refraction
composition. In another aspect a method is also disclosed using an
optical monitor in conjunction with a conventional vapor deposition
apparatus whereby an optical reference lens is used and a
particular light frequency of reflected light is measured and this
measurement is then used to determine when the desired optical
coating is achieved. In a still further aspect the method also
preferably calculates the optical thickness of each layer using a
specific ratio of blue to green to red colors in the reflected
light. The stress of the AR coating is also controlled by adjusting
the optical thickness for each layer, if necessary, to minimize the
difference in the tensile stresses and compressive stresses between
low index/high index layers.
Inventors: |
Koenig; Glen A.; (Stratford,
CT) ; Niejelow; Nicholas G.; (Stratford, CT) |
Correspondence
Address: |
LAW OFFICE OF DELIO & PETERSON, LLC.
121 WHITNEY AVENUE
3RD FLLOR
NEW HAVEN
CT
06510
US
|
Assignee: |
Optima, Inc.
Stratford
CT
06497
|
Family ID: |
33450693 |
Appl. No.: |
11/789774 |
Filed: |
April 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11253514 |
Oct 19, 2005 |
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11789774 |
Apr 25, 2007 |
|
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10444582 |
May 23, 2003 |
6972136 |
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11253514 |
Oct 19, 2005 |
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Current U.S.
Class: |
427/164 |
Current CPC
Class: |
C03C 2217/23 20130101;
G02B 1/115 20130101; C23C 14/547 20130101; G02B 1/11 20130101; C03C
17/3417 20130101; C08K 3/36 20130101; C03C 2218/154 20130101; C08K
3/22 20130101; C03C 17/30 20130101; G02B 1/10 20130101; C09D 7/61
20180101; C03C 2217/228 20130101; C03C 2218/15 20130101; C03C
2217/214 20130101; C03C 17/245 20130101; C09D 7/42 20180101 |
Class at
Publication: |
427/164 |
International
Class: |
B05D 5/06 20060101
B05D005/06 |
Claims
1.-10. (canceled)
11. An optical article made by the method comprising the steps of:
supplying one or more optical lens and an optical reference lens:
positioning the lens and the optical reference lens in a vacuum
deposition chamber in the same coating plane, the vacuum deposition
chamber having an optical monitor communicating with the optical
reference lens; providing in the chamber at least one source of a
high index of refraction AR coating composition and at least one
low index of refraction AR coating composition: applying a layer of
the high index of refraction composition on the lens until the
desired optical thickness coating is obtained as determined by the
optical monitor; applying a layer of the low index of refraction
composition on the lens until the desired optical thickness coating
is obtained as determined by the optical monitor; and repeating the
AR application steps until the desired AR coating is applied:
wherein the optical monitor comprises means for directing an on/off
beam of light into the chamber at the optical reference lens,
measuring the reflected light from the reference lens at a
particular frequency and using this measurement to determine when
the desired optical coating thickness is achieved.
12. An optical article made by the method comprising the steps of:
supplying an optical lens; positioning the lens in a vacuum chamber
of a vacuum deposition apparatus; providing in the vacuum chamber a
source of at least one high index of refraction AR composition and
at least low index of refraction AR composition wherein one of the
high index materials comprises a mixture of cerium and titanium
oxides and one of the low index materials comprises SiO.sub.2:
applying a layer of the high index material on the lens until the
desired optical thickness coating is applied; applying a layer of
the low index material on the lens until the desired optical
thickness coating is applied; and repeating the application steps
until the desired anti-reflection coating is applied.
13.-14. (canceled)
15. An optical article made by the method comprising the steps of:
supplying an optical lens: positioning the lens in a vacuum chamber
of a vacuum deposition apparatus: providing in the vacuum chamber a
source of at least one high index of refraction AR composition and
at least low index of refraction AR composition; applying a layer
of the high index material on the lens until the desired optical
thickness coating is applied; applying a layer of the low index
material on the lens until the desired optical thickness coating is
applied; and repeating the application steps until the desired
anti-reflection coating is applied; with the proviso that the
reflected light off the anti-reflection coating be controlled so
that the ratio of blue light to green light to red light provides a
substantially white reflected light.
16.-18. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to low stress, low residual
reflection multi-layer anti-reflection coatings for optical lenses
and, in particular, to a composition for forming a high refractive
index anti-reflection coating and a composition for forming a low
refractive index anti-reflection coating, methods for making
optical lenses preferably using the composition including using a
conventional vacuum deposition chamber employing an optical monitor
to control the optical properties of the anti-reflection
coating.
[0003] 2. Description of Related Art
[0004] It is well known in the optical arts that a reflection of
light off glass and other surfaces is undesirable or creates visual
sight discomfort. The reflected light makes a user feel dizzy or
causes an image to be blurred, among other such undesirable
effects. For optical lenses this is of particular concern and
compositions and methods have been developed for reducing the
reflection of light off the optical lens surface.
[0005] A considerable number of anti-reflection (AR) coatings have
been suggested in the prior art for a primary design purpose of
ensuring that the residual reflection will be held to a relatively
small value over the entire range of the visual spectrum. Single or
double layer coatings have provided significant improvement but the
residual reflections are still more than desired and to improve the
AR properties, the prior art has resorted to AR coatings having
three or more layers.
[0006] The optical thickness of each deposited AR layer is
typically controlled to optimize or maximize the AR effect and as
well known the optical thickness of a layer is the product of the
real (geometrical) thickness and the refractive index of the
respective layer. The optical thickness is generally described in
fractions of a wavelength of a designated reference light ray for
which the coating is to be used. Frequently, the design wavelength
will be about 510 nanometers (nm) to 550 nm. The optical thickness
of respective AR layers may be defined by the following general
formula where N is the refractive index, d is the geometrical
thickness of the layer and .lamda. is the reference wavelength:
N.sub.ad.sub.a=x.lamda. wherein x is a number, typically a
fraction, indicating the fraction of the wavelength and a is an
integer representing the layer coated with the lowest number being
closer to the eyeglass lens. Typically x will be 0.25 which
represents a quarter wavelength optical thickness.
[0007] As well known in the art today, the optical thickness of the
individual layers can be adjusted to obtain the same results on
substrates of different refractive indices.
[0008] In the formation of each AR layer, the deposited layer
exhibits a maximum value of interference for every one fourth of
the wavelength of light for measurement of the thickness, i.e.,
.lamda./4. Thus, the thickness of an optical AR layer is
conventionally controlled during the formation thereof by utilizing
this phenomenon with the optical thickness being multiples of
0.25.
[0009] While the following description will be directed to
polycarbonate lens for convenience, it will be understood to those
skilled in the art that the invention applies to other lens
materials such as polyurethane, acrylic glass, CR-39, etc. Stress
in a polycarbonate lens causes birefringence and optical
distortion. While not visible under normal circumstances it is
evident when polycarbonate is placed between two polarized
filaments and this is one of the reasons that polycarbonate lenses
are optically inferior to lenses such as glass, CR 39 and other
such materials. The new polycarbonate lens developed by Optima,
trade name Resolution.RTM., is free of this stress and
birefringence and thus the current processing to provide AR
coatings and its inherent stress now becomes more of a concern to
makers of such lenses.
[0010] In addition, the current state of AR coatings have a
residual green reflection which varies between 0.75% and 1.5%
residual reflection. This green color is cosmetically unpleasant
and acts as a green filter which decreases the amount of green
light the human eye perceives. A lower residual reflection with no
filtering effect is much more desirable both in the performance of
the coating and in its cosmetic appearance. It is preferred that
only white light be reflected.
[0011] The current design and production of AR coatings are well
understood in the industry today and typically the residual color
is left in the design to make manufacturing much simpler and
cheaper. Current technology uses a Quartz Crystal Monitor to
control the physical thickness of the individual layer required to
produce an AR coating. The current coating standards call for a
4-layer HLHL coating, where H represents a high index dielectric
material chosen for its specific refractive index, and L represents
a low index dielectric material also chosen for its refractive
index. Each layer typically consists of an optical quarter wave of
the high or low index material chosen. Low index materials include
SiO.sub.2 and MgF.sub.2. High index materials include oxide sub
groups of the following materials: Zr, Hf, Ta, Ti, Sb, Y, Ce, and
Yb. While not inclusive, these materials are the most widely used
today.
[0012] Many AR coatings being produced today also include an
adhesion layer, a buffer layer, an abrasion resistance layer, and a
hydrophobic outer layer. These layers are used to enhance the
performance of the coating from a consumer standpoint but have very
little effect on the optical qualities of the AR coating.
[0013] Another concern in the making of AR coatings is that the
high index and low index material induce both compressive as well
as tensile stress in the AR coating film. The current art of
anti-reflection (AR) coatings, however, does not take into account
the amount of stress inherent in the coating itself. This is
because the current lens produced on the market today such as the
polycarbonate lens has so much stress already that the additional
amount of stress caused by the AR coating is not considered
important. This is one of the reasons that current production
techniques try to limit the number of layers used. In general, a
low index material such as silica produces a tensile stress which
is about 5 times the compressive stress produced by a high index
material. If the coating becomes too thick with additional layers,
the differences in stress caused by the low index material and high
index material can cause the AR film to separate and come off the
lens and also cause adverse optical effects.
[0014] Another reason current technology limits the number of
layers is that the quartz crystal monitor is only capable of
measuring the physical thickness of the applied materials. An AR
coating however is designed around optical qualities, which are
very dependent on the refractive indexes of the materials being
used. These indexes will shift as coating conditions such as
available O2, coating rate and deposition temperature change. The
green reflectance left in the coating does an excellent job of
hiding these imperfections during normal production and the high
peak reflectance in the very broad green visible spectrum can shift
during production and be unnoticeable to all except a well trained
professional.
[0015] In order to form an AR coating with no residual color, i.e.
white, and a low overall residual reflection, the manufacturer must
typically add several additional AR layers. The added thickness
created by these layers causes an increase in stress and possible
AR coating delamination and these competing problems must be
addressed by the lens manufacturer.
[0016] Bearing in mind the problems and deficiencies of the prior
art, it is therefore an object of the present invention to provide
a composition for making a high index of refraction AR coating on
an optical lens or other optical article.
[0017] It is another object of the present invention to provide a
composition for making a low index of refraction AR coating on an
optical lens or other optical article.
[0018] It is yet another object of the present invention to provide
a method for making optical lenses or other optical articles having
an AR coating using the above compositions.
[0019] It is still yet another object of the present invention to
provide a method for making optical lenses having an AR coating
using an optical monitor to provide a desired AR optical coating on
the optical lens or other optical articles.
[0020] A further object of the present invention is to provide a
method for coating optical lenses and other optical articles with
an AR coating which has low residual reflection, the reflective
light is essentially white light and the AR coating has low
stress.
[0021] A further object of the present invention is to provide
optical lenses and other optical articles made using the methods of
the invention.
[0022] Still other objects and advantages of the invention will in
part be obvious and will in part be apparent from the
specification.
SUMMARY OF THE INVENTION
[0023] The above and other objects and advantages, which will be
apparent to one of skill in the art, are achieved in the present
invention which is directed to, in a first aspect, a composition
for making a high index of refraction AR coating on an optical lens
comprising a mixture of cerium and titanium oxides wherein the
cerium oxide is less than about 25% by weight of the
composition.
[0024] In a further aspect of the invention, a composition is
provided for making a low index of refraction AR coating on an
optical lens comprising a mixture of silicon and aluminum oxides
wherein the aluminum oxide is less than about 10% by weight of the
composition.
[0025] In still another aspect of the invention a method is
provided for making optical lenses having an anti-reflection (AR)
coating comprising the steps of:
[0026] supplying one or more optical lens and an optical reference
lens;
[0027] positioning the lens and the optical reference lens in a
vacuum deposition chamber in the same coating plane, the vacuum
deposition chamber having an optical monitor communicating with the
optical reference lens;
[0028] providing in the chamber at least one source of a high index
of refraction AR coating composition and at least one low index of
refraction AR coating composition;
[0029] applying a layer of the high index of refraction composition
on the lens until the desired optical thickness coating is obtained
as determined by the optical monitor;
[0030] applying a layer of the low index of refraction composition
on the lens until the desired optical thickness coating is obtained
as determined by the optical monitor; and
[0031] repeating the AR application steps until the desired AR
coating is applied;
[0032] wherein the optical monitor comprises means for directing an
on/off beam of light into the chamber at the optical reference
lens, measuring the reflected light from the reference lens at a
particular frequency and using this measurement to determine when
the desired optical coating thickness is achieved.
[0033] In another aspect of the invention a method is provided for
making optical lenses having an anti-reflection (AR) coating
comprising the steps of:
[0034] supplying an optical lens;
[0035] positioning the lens in a vacuum chamber of a vacuum
deposition apparatus;
[0036] providing in the vacuum chamber a source of at least one
high index of refraction AR composition and at least low index of
refraction AR composition wherein one of the high index materials
comprises a mixture of cerium and titanium oxides and one of the
low index materials comprises SiO.sub.2;
[0037] applying a layer of the high index material on the lens
until the desired optical thickness coating is applied;
[0038] applying a layer of the low index material on the lens until
the desired optical thickness coating is applied; and
[0039] repeating the application steps until the desired
anti-reflection coating is applied.
[0040] In another aspect of the invention a method is provided for
making optical lenses having an anti-reflection (AR) coating
comprising the steps of:
[0041] supplying an optical lens;
[0042] positioning the lens in a vacuum chamber of a vacuum
deposition apparatus;
[0043] providing in the vacuum chamber a source of at least one
high index of refraction AR composition and at least low index of
refraction AR composition;
[0044] applying a layer of the high index material on the lens
until the desired optical thickness coating is applied;
[0045] applying a layer of the low index material on the lens until
the desired optical thickness coating is applied; and
[0046] repeating the application steps until the desired
anti-reflection coating is applied;
[0047] with the proviso that the reflected light off the
anti-reflection coating be controlled so that the ratio of blue
light to green light to red light provides a substantially white
reflected light.
[0048] In a further aspect of the invention, the optical thickness
of the AR coating layers are adjusted, if necessary, to minimize
the difference in tensile stress and compressive stress in the
adjacent layers.
[0049] In another aspect of the invention an optical lens or other
optical article is provided which is made by the above methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] The features of the invention believed to be novel and the
elements characteristic of the invention are set forth with
particularity in the appended claims. The figures are for
illustration purposes only and are not drawn to scale. The
invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed
description which follows taken in conjunction with the
accompanying drawings in which:
[0051] FIG. 1 is a schematic illustration of a conventional vacuum
chamber used to deposit coatings on substrates and the optical
monitor of the invention used in conjunction with the vacuum
chamber.
[0052] FIG. 2 is an illustration of a lens containing an
anti-reflection coating made using the composition and method of
the invention.
[0053] FIG. 3 is a graph showing the reflectance (percent) as a
function of wavelength for a conventional anti-reflection coating
vs. an anti-reflective coating made using the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0054] In describing the preferred embodiment of the present
invention, reference will be made herein to FIGS. 1-3 of the
drawings in which like numerals refer to like features of the
invention. Features of the invention are not necessarily shown to
scale in the drawings.
[0055] Applicants have invented AR coating compositions in both the
low and high index ranges, which allow control of the AR coating
with regard to residual reflection and the coating stress produced.
This allows the number of AR layers used to be increased
significantly if necessary to achieve the desired lens. Applicants
also use an optical monitor to control the optical thickness and
rate of the materials being coated. The optical monitor uses a
special test glass, which receives the coating material at the same
time as the lens. By measuring the coating optically in-situ, one
can automatically correct for any minor changes in refractive index
and stop the coating of the layer at the precise optical thickness
required. This is extremely important as any error induced in one
layer can cause each subsequent layer to be mismatched. In this
respect, the optical monitor besides being optically correct can
also make minor corrections in subsequent layers if required.
[0056] The end result of Applicants' invention is a cosmetically
pleasing coating, with low residual unwanted color, low reflectance
and low stress.
[0057] Although the present invention has been described with
reference to a specific embodiment, those of skill in the art will
recognize that changes may be made thereto without departing from
the scope and spirit of the invention as set forth in the appended
claims. While the AR coating was developed specifically for
polycarbonate lenses, the techniques described can be used for any
lens materials, organic or inorganic, including glass, CR-39, and
lenses with indexes ranging from 1.40 to >1.90.
[0058] Referring now to FIG. 1, a conventional vacuum chamber is
shown generally as 10 for depositing an anti-reflection coating on
lenses and includes an optical monitor shown generally as numeral
30.
[0059] Any conventional vacuum coating apparatus can be used and
exemplary are those shown in U.S. Pat. Nos. 3,695,910; 5,026,469;
and 5,124,019, which patents are hereby incorporated by
reference.
[0060] The vacuum chamber comprises a chamber 11 having a
transparent section 18 at the top of the chamber. In the vacuum
chamber are positioned containers 12a, 12b, 12c and 12d, which are
used to hold coating materials 13a, 13b, 13c and 13d, respectively.
It will be appreciated by those skilled in the art that the number
of containers and coating materials will vary depending on the
anti-reflection coatings desired to be applied to the lens
substrate.
[0061] An E-gun 14 is shown which is used to provide electrons
which are directed at the various containers to volatilize the
material in the container. Depending on the material to be
volatilized, the container is moved into position so that the E-gun
electrons are directed at the container and material. The material
is vaporized and is spread throughout the chamber as shown by the
arrows. A substrate holder 15 is shown which is curved (typically a
dome) and the volatilized material is applied evenly on all the
substrate surfaces. A distribution shield is typically used to
apply the volatilized materials evenly. Four substrates are shown
as 16a-16d. Typically 75-140 substrates are positioned on a dome. A
reference substrate 17 is positioned in the center of the substrate
holder 15 and, it too will likewise be coated by the volatilized
material at the same rate and with the same composition as the
other substrates 16 on the substrate holder 15. Input 32 is used
typically for gases such as O.sub.2 which is used to form oxides
for some AR layers.
[0062] In operation, the desired container and coating material
will be moved in position in the vacuum chamber and the E-gun
activated to direct electrons at the container to volatize the
coating material. The coating material will be vaporized and the
vapors coat each of the substrates 1 6 held by the substrate holder
15. The reference substrate 17 will likewise be coated. Such a
coating process and vacuum chamber are conventional and well known
in the art as shown in the above patents. Vacuum deposition is
preferred but other methods such as sputtering may be used.
[0063] During the coating operation, it is preferred to use an
optical monitor and a high intensity beam of light 20 is projected
from light source 19. The beam of light 20 passes through a light
chopper 21 which turns the beam on and off providing an on/off beam
22. The sequence of the on/off light is synchronized with the light
detector 29 at the end of the monitor. This is important since
during the off period of the light beam, the light detector 29 will
still receive a large amount of ambient light. Since it is
programmed that the light it is receiving during the off period is
noise, it subtracts it from the amount of light it receives when
the light beam is on. This ensures that only the light which it is
supposed to be measured, is in fact measured.
[0064] The chopped light 22 also passes through a focusing lens 21a
and is then directed towards a high reflectance mirror 23. The
reflectance mirror 23 turns the beam as reflected beam 24 towards
the transparent opening 18 in the chamber at the reference
substrate 1 7 which is disposed inside the chamber. As noted above,
the reference substrate 17 is located in the same curvilinear plane
as the substrates 16 which are to be coated. This ensures that
during the actual AR coating process the reference substrate 1 7
receives the same coating of AR material as each of the substrates
being coated.
[0065] When the reflected beam 24 reaches the reference substrate 1
7, the majority of the light passes through the reference
substrate. Approximately 5% of the light from the back surface and
5% of the light from the front surface are reflected. It is
preferred that the beam of light enters the chamber at a small
incident angle so that the light beam reflected from the front and
back surface of the monitor glass return at a slightly different
angle. This is important because only the light being reflected
from the front surface of the reference substrate is to be
measured. This reflected light from the front surface is shown as
second reflected beam 25. The beam reflected from the back surface
is not shown.
[0066] The 5% of the original light which is being reflected back
from the front surface as beam 25 now passes out of the chamber
through transparent section 18 and hits a second reflection mirror
26 and is turned towards the light detector 29. Before reaching the
detector 29 light beam 25 passes through a light filter 27 which is
a frequency specific filter designed to allow only one frequency of
light to pass through the filter. This specific frequency light is
shown as beam 28 which beam is then passed into light detector
29.
[0067] The method of the invention provides an optical coating
which is accurate at a specific desired light frequency. Because of
this, in order to design and form optical coatings, the AR coating
thickness desired must be designed through a specific light
frequency. The light filter 27 is chosen to pass only the light
frequency chosen by the designer when designing the AR coating.
Typically, the frequency is 480 to 530 nm.
[0068] The specific frequency light continuing into the detector 29
is then measured for the amount of light received and the detector
amplifies the light to a more accurate, readable intensity. Through
the use of high-resolution A/D converters and microprocessors, the
detector is capable of detecting light changes as small as 0.01%.
The light detector 29 sends the light intensity data to the
vaporization control system 31 which uses the information to
determine the optical thickness for each layer of material being
applied and when to stop the vaporization process for the material
to be applied when the desired optical thickness is coated on the
lens. It should be noted that it is because the optical monitor 30
is reading the change in optical performance during the coating
process at the same time as the actual change in optical
performance on the lens surface which makes the monitor so
accurate. The monitor 30 also allows the system to make minor
corrections for shifts in refractive index during the coating
process. It should be appreciated that the monitor 30 relies
strictly on optical performance of the coating and not material
physical thickness which is coated on the substrate surface.
[0069] The AR coating stress can also be controlled as discussed
above to change the design AR coating optical thickness to minimize
the difference between the tensile and compressive forces in the
layers. Changes in optical thicknesses will generally be in steps
of 0.5 .lamda. since this has no significant effect on the optical
properties.
[0070] FIG. 2 is a representation of the AR coating of the
invention on a lens substrate. All coatings begin at the substrate
and are coated sequentially outward, both in design and in the
actual manufacture. The substrate shown is a stress-free
polycarbonate optical lens. This lens was made using a patented
process as shown in U.S. Pat. No. 6,042,754, assigned to the
assignee of the subject invention. Although the process being
described is for this particular lens, it can also be used on any
lens material having refractive indexes of 1.40 through 1.9, or
higher, with modifications to the AR layer thicknesses to
compensate for the different lens materials. All thickness
measurements are in Quarter Wave Optical Thickness (QWOT) (0.25
.lamda.). The frequency of the light used to design the formula and
used during the actual production process is between 470 nm and 580
nm. The AR coating layers were calculated as discussed herein by
controlling the ratio of the amount of blue light to green light to
red light in the light reflected off the coated optical lens. Blue
was controlled to 37.16%, green to 28.57% and red to 34.27%. It
will be appreciated that the calculated optical thicknesses can be
varied somewhat to accommodate manufacturing requirements.
[0071] Details of the lens shown in FIG. 2 are as follows:
[0072] Substrate 51--Polycarbonate lens with a refractive index of
approximately 1.59.
[0073] Primer 52--A primer is applied to the lens so that the final
hard coat will adhere more readily. Approximate thickness is 0.5 to
1.0 microns. Refractive index of 1.50.
[0074] Hard Coat 53--A polysiloxane based thermal cure material
with a thickness of between 3.5 to 5.0 microns. Refractive index of
1.49.
[0075] L1 54--A low index material such as SiO.sub.2. The thickness
is approximately 1.70-1.9 QWOT. The refractive index is
approximately 1.45-1.5.
[0076] H1 55--A high index material of the invention designed to
have lower stress and increased refractive index. The thickness is
approximately 0.10-0.25 QWOT. The refractive index is approximately
2.04-2.30.
[0077] L2 56--Same material as L1. Thickness is approximately
0.10-0.25 QWOT.
[0078] H2 57--Same material as H1. Thickness is approximately
1.00-1.25 QWOT.
[0079] L3 58--Same material as L1. Thickness is approximately
0.01-0.1 QWOT.
[0080] H3 59--Same material as H1. Thickness is approximately
1.25-1.50 QWOT.
[0081] M1 60--A middle index material used to help increase
adhesion and improve scratch resistance. The thickness is
approximately 0.01-0.1 QWOT.
[0082] L4 61--Same material as L1. Thickness is approximately
1.75-2.00 QWOT.
[0083] Hydro 62--A polysiloxane material applied to the outer
surface to form a smooth slick surface. It improves the
cleanability of the lens. The approximate thickness is 0.01-0.25
QWOT. The refractive index is approximately 1.40-1.50.
[0084] The lens was found to have low stress, low reflection and
low residual color, i.e., the reflected light was essentially
white. The final lens has a curve similar to curve 70 in FIG.
3.
[0085] FIG. 3 shows graphically the difference between the AR
coating of the invention and a typical AR coated lens currently
available on the market. This graph only shows the optical
superiority, and not the decreased stress capability of the
coating. Curve 70 represents the residual reflection found on AR
coatings being produced for the market today and shows peak 70a
which is in the green spectrum and produces the residual green
reflectance of conventional lenses. It should also be noted that
minima points 70b and 70c represent blue light and red light
reflectance, respectively.
[0086] As discussed previously, this is commercially acceptable
since it hides the fluctuations in coating thickness during the
production process. The peak reflection 70a (highest point on
curve) can be adjusted to the right or left by moving the entire
curve right or left. The result is to change the green residual
color to a more bluer appearance or a yellower appearance. In
addition, an AR coating company can rotate the curve so that the
minimum on the right side of the curve comes up to around 0.75%
reflection. The result is that the total amount of residual
reflection rises quite significantly. The other result is that the
residual color has a definite greenish yellowish appearance.
[0087] Curve 71 represents the AR coating of the invention as shown
in the lens of FIG. 2. Notice that the total residual reflection is
much lower than the conventional curve 70. Also notice that the
curve extends further into both the infrared and ultraviolet
regions of the visible light spectrum (wider). This is a
significant factor since all AR coatings on lenses will have a
tendency to change color as the angle of the incident light (angle
of light hitting the surface) becomes less and less direct. This
apparent change in color is caused by the curve shifting to the
left as the angle of incidence increases. The narrower the total
curve, the quicker it changes color. It is very noticeable because
suddenly green becomes yellow, orange or red. Curve 71 has a much
broader width and also has no color. As the angle of incidence
increases, the curve will begin to shift left, but the color will
remain unchanged until the angle is extremely steep such as up to
45.degree..
[0088] Applicants' invention is directed in one aspect to modifying
the conventional curve shown as numeral 70 to a white light curve
such as shown as numeral 71. The white light curve 71 has a
combination of colors that produces a white light reflection and
does not have a predominant green reflection as shown in the
conventional curve 70.
[0089] Applicants have discovered that adjusting the ratios of blue
light, green light and red light to each other in the reflected
light from the anti-reflection coating will produce a curve shown
as numeral 71 which produces a substantially white light. It is
known to use computer software to calculate thin film thicknesses
for optical lenses by specifying certain optical parameters which
the computer software will use to calculate and provide thin film
thicknesses for the AR coating. Merely specifying, for example,
that the blue, green and red levels are the same will not produce a
white light but will provide a curve such as curve 70 which has a
green peak and a residual green reflection.
[0090] It is an important feature of Applicants' invention that the
ratio of blue peak, green peak and red peak in the reflected light
be controlled to provide a white light reflection. The three colors
are controlled within a particular ratio to produce a white light
reflection. In general, in color peak percent, the blue peak will
range from about 34 to 40%, preferably 36-38%, e.g., 37%, the green
about 24 to 32%, preferably 26-30%, e.g., 29%, and the red about 30
to 38%, preferably 32-36%, e.g., 34%. When these ratios are
supplied to the computer software along with other optical
properties such as the refractive indices of the materials being
used and a table of the refractive indices over a range of optical
thicknesses, the software will calculate the AR layers needed to
produce the specified blue, green and red peaks. A typical computer
software program is called "Essential MacLeod", Optical Coating
Design Program, Copyright Thin Film Center, Inc. 1995-2003, Version
V 8.6, which program is distributed by the Thin Film Center, Inc.
Other similar known software programs can be used to calculate thin
film thicknesses which meet the above ratios. It should also be
appreciated that the optical thicknesses needed to meet the above
ratios can be calculated manually as is known in the art. A typical
calculation method is shown in U.S. Pat. No. 4,609,267, which
patent is hereby incorporated by reference, but other known methods
for calculating optical thicknesses can be used.
[0091] In another aspect of the invention it is important that the
AR coating have low stress since high stress causes optical
distortion and the AR coating may delaminate. It has been found
that the high index material and the low index material have
different stresses when formed as thin films and it is a feature of
the invention to minimize the difference in the stresses in the
layers to produce an AR coating having low stress.
[0092] For example, it has been found that silicon dioxide which is
a typical low index material provides a tensile stress when coated.
On the other hand, high index materials typically provide a
compressive stress when coated. It has been found, however, that
the compressive stress is usually less than the tensile stress of
the low index material. Accordingly, this provides a difference in
tensile and compressive stresses between layers and could lead to
delamination and optical distortion.
[0093] It is thus an important feature of Applicants' invention to
adjust, if necessary, each adjacent layer of the optical coating to
balance the tensile stress and compressive stress. This is
accomplished by first calculating the optical thicknesses for the
various layers as described above specifying the desired reflective
peaks (ratios) for blue, green and red light. Once the optical
thickness and number of AR layers are determined by the computer
calculations, the optical thickness of each layer may be modified
in 0.5 .lamda. steps to balance (equilibrate) the stress between
layers. For example, if a low index layer has an optical thickness
of 0.25 .lamda. and provides a tensile stress of 5 and the adjacent
high index layer having also a 0.25 .lamda. optical thickness
produces a compressive stress of only 1, the optical thickness of
the high index layer is preferably increased to increase the
compressive force to balance or minimize the higher tensile stress
of the preceding low index layer. In this example, the optical
thickness of the high index layer could be adjusted to 0.75 .lamda.
or even 1.25 .lamda. to increase the compressive stress to be
closer to the low index layer tensile stress. Increasing the
optical thickness of one layer vs. the adjacent layer will have no
significant effect on the white light reflection of the coated lens
because the optical thickness will be typically increased in 0.5
.lamda. steps.
[0094] While the present invention has been particularly described,
in conjunction with a specific preferred embodiment, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. It is therefore contemplated that the appended claims
will embrace any such alternatives, modifications and variations as
falling within the true scope and spirit of the present
invention.
[0095] Thus, having described the invention, what is claimed
is:
* * * * *