HK1090099B - Ultra low residual reflection, low stress lens coating - Google Patents

Description

low stress lens coating with ultra low residual reflection

Technical Field

The present invention relates to a low stress low residual reflection multilayer anti-reflective coating for lenses, and more particularly to a high refractive index anti-reflective coating forming composition and a low refractive index anti-reflective coating forming composition, preferably a method of making optical lenses using the same, comprising the use of a vacuum deposition chamber equipped with an optical monitor for controlling the optical properties of the anti-reflective coating.

Background

It is well known in the optical arts that the reflection of light from glass and other surfaces is undesirable or creates visual discomfort. In addition to this undesirable effect, the reflected light may also appear dizzy to the user, or produce a blurred image. For optical lenses of particular interest, compositions and methods have been developed for reducing reflections from optical lens surfaces.

To ensure that the residual reflection remains at a relatively small value throughout the visible spectrum, a considerable number of anti-reflection (AR) coatings have been proposed in the prior art. Single or dual layer coatings, have given significant improvements, but the residual reflection is still greater than desired, and to improve the properties of the AR, the prior art has resorted to AR coatings having three or more layers.

The optical thickness of each deposited AR layer is typically controlled to optimize or maximize the AR effect, and as is well known, the optical thickness is the product of the true (geometric) thickness and the refractive index of the respective layer. Optical thickness is generally described in terms of a fraction of a given reference light wavelength using the coating. The design wavelength is often about 510 nanometers (nm) to 550 nm. The optical thickness of the corresponding AR layer can be defined by the following general formula, where N is the refractive index, d is the layer's geometric thickness, and λ is the reference wavelength:

N_ad_a＝xλ。

where x is a number, typically a fraction, indicating a percentage of the wavelength, and a is an integer representing the number of layers that are coated at the lowest number closer to the spectacle lens. Typically x takes 0.25 and represents a quarter wavelength optical thickness.

Today, it is well known in the art that adjusting the optical thickness of individual layers can achieve the same result on substrates of different refractive indices.

In the formation of each AR layer, the deposited layer exhibits an interference maximum at a quarter wavelength of light, i.e., λ/4, measured for each thickness. Therefore, in the formation of the optical AR layer, the thickness of the AR layer can be easily controlled by utilizing the interference maximum phenomenon that the optical thickness is a multiple of 0.25.

Although the following description is directed to polycarbonate lenses for convenience, it will be understood by those skilled in the art that the present invention may be used with other lens materials, such as polyurethane, acrylic glass, CR-39, and the like. Stress in the polycarbonate lens, resulting in birefringence and optical distortion. Although not visible in normal circumstances, birefringence and optical distortion are apparent when polycarbonate is placed between two polarizing filaments, and it is this reason that polycarbonate lenses are not optically comparable to lenses such as glass, CR-39, and other similar materials. Developed by Optima and having a trade name ofWithout such stress and birefringence, the new polycarbonate lenses of (1) thus, the current processing techniques to provide AR coatings and the inherent stress of AR coatings are now becoming more of a concern to such lens manufacturersAnd (5) problems are solved.

In addition, the current state of the AR coating, with residual green reflection, varies between 0.75% and 1.5% residual reflection. This green color is unpleasant in appearance and acts as a green filter, reducing the amount of green light perceived by the human eye. Lower residual reflection without filtering effect is desirable in both coating performance and its appearance. Preferably only white light is reflected.

The current design and production of AR coatings is well understood in the industry today and typically leaves residual color in the design for much simpler and cheaper fabrication. Current technology uses Quartz Crystal monitors to control the physical thickness of the individual layers required to produce AR coatings. Current coating standards require 4 HLHL coatings, where H represents a high index dielectric material selected for its characteristic refractive index and L represents a low index dielectric material also selected for its refractive index. Each layer is typically composed of an optical quarter-wavelength of the selected high or low index material. The low refractive index material comprises SiO₂And MgF₂. The high refractive index material includes the following material oxide subclasses: zr, Hf, Ta, Ti, Sb, Y, Ce, and Yb. Although not all are included, these materials are currently the most widely used.

Many AR coatings currently produced also include an adhesion layer, a buffer layer, an abrasion resistant layer, and a hydrophobic outer layer. From a consumer's point of view, these layers serve to enhance the performance of the coating, but have little effect on the optical quality of the AR coating.

Another concern in making AR coatings is that the high and low index materials induce compressive and tensile stresses in the AR coating film. However, current techniques for anti-reflective (AR) coatings do not take into account the amount of intrinsic stress in the coating itself. This is because lenses currently produced on the market, such as polycarbonate lenses, already have so much stress that the additional amount of stress induced by the AR coating is considered insignificant. This is one reason why current production techniques attempt to limit the number of layers used. Generally, the tensile stress generated by a low index material, such as silicon dioxide, is about 5 times the compressive stress generated by a high index material. If the coating becomes too thick due to the additional layers, the low and high index materials cause a difference in stress that can cause the AR film to separate and fall off the lens, also resulting in detrimental optical effects.

Another reason that current production technology limits the number of layers is that quartz crystal monitors can only measure the physical thickness of the coated material. However, AR coatings are designed around the optical quality, which is very dependent on the refractive index of the material used. These indices of refraction will shift with changes in coating conditions, such as commercially available O2, coating rate, and deposition temperature. The green reflection left in the coating is indeed a good result of masking these defects during normal production, and the high peak reflection in the very broad green visible spectrum can be shifted during normal production without attracting the attention of all but a trained professional.

In order to form an AR coating without residual color, i.e., the AR coating is white and has a low overall residual reflection, manufacturers typically must add several additional AR layers. The additional thickness created by these layers results in increased stress and possible stripping of the AR coating, and these tradeoffs must be addressed by the lens manufacturer.

With the foregoing problems and deficiencies of the prior art in mind, it is an object of the present invention to provide a composition for making high index AR coatings on optical lenses or other optical articles.

It is another object of the present invention to provide a composition for making a low refractive index AR coating on an optical lens or other optical article.

It is a further object of the present invention to provide a method of making an AR coated optical lens or other optical article using the above composition.

It is yet another object of the present invention to provide a method of making an AR coated optical lens that provides a desired AR optical coating on an optical lens or other optical article with an optical monitor.

It is a further object of the present invention to provide a method of coating an optical lens or other optical article with an AR coating that has low residual reflection, reflected light is substantially white light, and the AR coating has low stress.

It is a further object of the present invention to provide optical lenses and other optical articles made by the method of the present invention.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

Disclosure of Invention

The above and other objects and advantages, which will be apparent to those skilled in the art, are achieved in the present invention which is directed in a first aspect to a composition for forming a high refractive index AR coating on an optical lens, the composition comprising a mixture of cerium and titanium oxides, wherein the cerium oxide is less than about 25% by weight of the composition.

In yet another aspect of the present invention, there is provided a composition for making a low index of refraction AR coating on an optical lens, the composition comprising a mixture of silicon and aluminum oxide, wherein the aluminum oxide is less than about 10% by weight of the composition.

In yet another aspect of the present invention, there is provided a method for making an anti-reflection (AR) coated optical lens, the method comprising the steps of:

providing one or more optical lenses and an optical reference lens;

positioning the lens and the optical reference lens in the same coating plane in a vacuum deposition chamber having an optical monitor in communication with the optical reference lens;

providing a source of at least one high refractive index AR coating composition, and at least one low refractive index AR coating composition in the chamber;

coating a layer of a high refractive index composition on the lens until a coating of a desired optical thickness is obtained as determined by an optical monitor;

coating a low refractive index component layer on the lens until a coating of a desired optical thickness is obtained as determined by an optical monitor; and

repeating the AR coating step until the required AR coating is coated;

wherein the optical monitor includes a means for directing the on/off beam into the chamber onto an optical reference lens; for measuring the reflected light of the reference lens at a specific wavelength; and for using the measurement to determine when the desired optical coating thickness is achieved.

In another aspect of the present invention, there is provided a method for making an anti-reflection (AR) coated optical lens, the method comprising the steps of:

providing an optical lens;

positioning the lens in a vacuum deposition chamber of a vacuum deposition apparatus;

providing a source of at least one high refractive index AR component and at least one low refractive index AR component in a vacuum chamber, wherein one of the high refractive index materials comprises a mixture of cerium and titanium oxides and one of the low refractive index materials comprises SiO₂；

Coating a layer of high refractive index material on the lens until a coating of desired optical thickness is applied;

coating a layer of low refractive index material on the lens until a coating of desired optical thickness is applied; and

the coating steps are repeated until the desired anti-reflective coating is applied.

In another aspect of the present invention, there is provided a method for making an anti-reflection (AR) coated optical lens, the method comprising the steps of:

providing an optical lens;

positioning the lens in a vacuum deposition chamber of a vacuum deposition apparatus;

providing a source of at least one high refractive index AR component and at least one low refractive index AR component in a vacuum chamber;

coating a layer of high refractive index material on the lens until a coating of desired optical thickness is applied;

coating a layer of low refractive index material on the lens until a coating of desired optical thickness is applied; and

repeating the coating steps until a desired anti-reflective coating is applied;

the reflected light from the anti-reflective coating must be controlled so that the ratio of blue to green to red light gives a substantially white reflected light.

In yet another aspect of the invention, the optical thickness of the AR coating is adjusted, if necessary, to minimize the difference in tensile and compressive stresses in adjacent layers.

In another aspect of the invention, there is provided an optical lens or other optical article made by the above method.

Drawings

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 illustrative 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 following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration of a conventional vacuum chamber for depositing a coating on a substrate, and an optical monitor of the present invention used in conjunction with the vacuum chamber.

FIG. 2 is an illustration of a lens comprising an anti-reflective coating made using the compositions and methods of the present invention.

FIG. 3 is a graph plotting reflectance (in percent) as a function of wavelength, comparing a conventional anti-reflective coating to an anti-reflective coating made according to the present invention.

Detailed Description

In describing the preferred embodiment of the present invention, reference will be made to FIGS. 1-3 of the drawings in which like numerals refer to like parts of the invention. The components of the present invention are not necessarily drawn to scale in the figures.

Applicants have invented AR coating compositions in the low and high refractive index ranges that enable control of the AR coating in both residual reflection and resulting coating stress. In this way, the number of AR layers used can be significantly increased, if necessary, to obtain the desired lens. Applicants have also used optical monitors to control the optical thickness and the coating rate of the material. The optical monitor uses a special test glass that receives the coating material simultaneously with the lens. By optical measurements on the coating site, one can automatically correct for any small variations in refractive index and stop the application of the layer at the exact optical thickness required. This is extremely important because any error induced in one layer can result in a mismatch for each subsequent layer. In this regard, the optical monitor can make minor corrections in subsequent layers, if necessary, in addition to the optical corrections.

The end result of applicants' invention is an aesthetically pleasing coating with low residual unwanted color, low reflectivity, and low stress.

While the invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes may be made thereto without departing from the scope and spirit of the invention, which is set forth in the following claims. Although the AR coating was developed specifically for polycarbonate lens lenses, the described techniques can be used for any lens material, organic or inorganic, including glass, CR-39, and lenses having refractive indices in the range of 1.40 to > 1.90.

Referring now to FIG. 1, there is illustrated a conventional vacuum chamber, generally indicated at 10, for depositing an anti-reflective coating on a lens, and an optical monitor, generally indicated at 30.

Any conventional vacuum coating apparatus may be used, such as those described in U.S. Pat. Nos. 3,695,910, 5,026,469, and 5,124,019, which are incorporated herein by reference.

The vacuum chamber comprises a chamber 11 with a transparent portion 18 at the top of the chamber. Containers 12a, 12b, 12c, and 12d are placed in the vacuum chamber, respectively containing coating materials 13a, 13b, 13c, and 13 d. It will be apparent to those skilled in the art that the number of containers and the number of coating materials will vary depending on the antireflective coating desired to be coated on the lens substrate.

An electron gun 14 is shown for providing electrons directed to each of the containers to volatilize material in the containers. Depending on the material to be volatilized, the container can be put in place to direct electrons from the electron gun to the container and the material. The material is vaporized and spreads throughout the chamber as indicated by the arrows on the figure. The figure shows a curved substrate holder 15 (usually a dome) so that the vaporized material is uniformly coated on all the surfaces of the substrate. A dispensing baffle is typically used to uniformly coat the volatilized material. There are 4 substrates 16a-16d shown. Typically 75-140 substrates can be placed on the dome. Reference substrate 17 is placed in the center of substrate holder 15 and, like the other substrates 16 on substrate holder 15, is coated with the same volatile material at the same rate and with the same composition. Input 32 typically supplies gasSuch as O₂Used to form oxide for certain AR layers.

In operation, the desired container and coating material are moved into position in the vacuum chamber, and the electron gun is activated to direct electrons toward the container to volatilize the coating material. The coating material will be vaporized and the vaporized vapor coats each substrate 16 held by the substrate holder 15. The reference substrate 17 is also coated. As shown in the above patents, such coating processes and vacuum chambers are conventional and well known in the art. Vacuum deposition is desirable, but other methods may be used, such as sputtering.

During the coating process, an optical monitor is preferably used and projects a high intensity beam 20 from a light source 19. The high intensity beam 20 passes through a photointerrupter 21, which photointerrupter 21 switches the beam on and off to give an on/off beam 22. The sequence of on/off light is synchronized with the light detector 29 at the end of the monitor. This is important because during the off period of the light beam, the light detector 29 still receives a significant amount of ambient light. Because the photodetector is programmed such that the light received by the photodetector during the off period is noise, the photodetector subtracts the noise from the amount of light received by the photodetector when the beam is on. This ensures that only the light which is supposed to be measured is actually measured.

The chopped light 22 also passes through a focusing lens 21a and is then directed to a high reflectivity mirror 23. The mirror 23 deflects the beam into a reflected beam 24 towards the transparent opening 18 in the chamber, which falls on the reference substrate 17 placed in the chamber. As indicated above, the reference substrate 17 is positioned in the same bending plane as the substrate 16 to be coated. This ensures that during the actual processing of the AR coating, the reference substrate 17 receives the same coating of AR material as each substrate being coated.

When the reflected beam 24 reaches the reference substrate 17, a large portion of the light passes through the reference substrate. About 5% of the light is reflected from the back surface and about 5% of the light is reflected from the front surface. Preferably, the light beams are directed into the chamber at a small angle of incidence, so that the light beams reflected from the front and rear surfaces of the monitor glass return at slightly different angles. This is important because only light reflected from the front surface of the reference substrate is measured. The light beam reflected from the front surface is indicated in the figure as a second reflected light beam 25. The light beam reflected from the rear surface is not shown.

5% of the original light reflected from the front surface, as beam 25, now exits the chamber through the transparent portion 18, falls on the second mirror 26, and is deflected towards the light detector 29. Before reaching the detector 29, the light beam 25 passes through an optical filter 27, which is a frequency-specific filter that passes only one frequency of light. The light of this particular frequency is represented on the graph by a beam 28 which then enters a photodetector 29.

The method of the present invention provides an optical coating that is accurate at the particular desired light frequencies. Because of this, in order to design and form an optical coating, the required AR coating thickness must be designed by a specific light frequency. When designing an AR coating, the optical filter 27 is chosen to pass only the light frequencies chosen by the designer. Typically, the frequency is 480 to 530 nm.

Then, for light of a specific frequency continuing into the photodetector 29, the amount of light received is measured, and the detector also amplifies the light to a readable intensity with higher accuracy. By using a high resolution a/D converter and microprocessor, the detector can detect changes as small as 0.01%. The light detector 29 sends light intensity data to a vaporization control system 31 which uses this information to determine the optical thickness of each layer of the coated material and to stop the vaporization of the coating material when the desired optical thickness is applied to the lens. It should be noted that this is so accurate because the optical monitor reads the change in optical properties of the lens surface simultaneously with the actual change in optical properties during the coating process. Monitor 30 also enables the system to make minor corrections for refractive index shifts during the coating process. It is apparent that monitor 30 is strictly dependent on the optical properties of the coating, not the physical thickness of the coating material on the substrate surface.

The optical thickness of the AR coating can also be designed to vary, as discussed above, to control the stress of the AR coating to minimize the difference between the tensile and compressive forces in the layer. The optical thickness is typically varied in steps of 0.5 λ, since the step size has no significant effect on the optical performance.

Figure 2 represents an AR coating of the invention on a lens substrate. All coatings start from the substrate and are applied out in sequence as designed and fabricated. The substrate in the figure is a stress-free polycarbonate lens. The lens is made using the process shown in U.S. patent No.6,042,754, which is assigned to the assignee of the subject invention. Although the process described is for this particular lens, modifying the AR layer thickness to compensate for different lens materials may also be used for any lens material having a refractive index of 1.40 to 1.90, or higher. All Thickness measurements were made as Quarter Wave Optical Thickness (QWOT) (0.25 λ). In the actual production process, the frequency of light used to design the formulation and use is between 470nm and 580 nm. From the light reflected from the coated optical lens, the AR coating is calculated by controlling the ratio of the amount of blue light to the amount of green light to the amount of red light, as discussed herein. Blue was controlled at 37.16%, green at 28.57%, and red at 34.27%. Obviously, the calculated optical thickness can be varied to some extent in order to adapt to manufacturing requirements.

The details of the lens 50 shown in fig. 2 are as follows:

substrate 51-a polycarbonate lens with an index of refraction of about 1.59.

Primer 52-primer is applied to the lens to make it easier to adhere the final hard coat. The thickness is about 0.5 to 1.0 microns. A refractive index of 1.50.

Hard coat layer 53-a silicone based thermoset material, with a thickness of between 3.5 and 5.0 microns. A refractive index of 1.49.

L154-Low refractive index materials, e.g. SiO₂. And a thickness of about 1.70 to 1.9 QWOT. The refractive index is about 1.45-1.5.

H155-high index material designed by the present invention with lower stress and increased index of refraction. About 0.10-0.25 QWOT thick. The refractive index is about 2.04-2.30.

L256-is the same material as L1. About 0.10-0.25 QWOT thick.

H257-is the same material as H1. And a thickness of about 1.00 to 1.25 QWOT.

L358-is the same material as L1. About 0.01 to 0.1 QWOT in thickness.

H359-is the same material as H1. And a thickness of about 1.25 to 1.50 QWOT.

M160-medium index material to help increase adhesion and improve rub resistance. About 0.01 to 0.1 QWOT in thickness.

L461-is the same material as L1. About 1.75 to 2.00 QWOT in thickness.

Hydro 62-a polysiloxane material coated on the outer surface to form a smooth, satin surface. It improves the cleanability of the lens. And a thickness of about 0.01 to 0.25 QWOT. The refractive index is about 1.40-1.50.

It has been found that the lens has low stress, low reflection, and low residual colour, i.e. the reflected light is substantially white. The final lens has a curve similar to curve 71 of fig. 3.

Figure 3 plots the difference between the AR coating of the present invention and a typical lens currently available on the market. The curve only shows the optical advantage of the coating and not the ability of the coating to reduce stress. Curve 70 represents the residual reflection obtained on the AR coating currently produced on the market and plots the peak 70a, which is in the green spectrum and produces the residual green reflection of a conventional lens. It should also be noted that the minimum points 70b and 70c represent the reflection of blue and green light, respectively.

As discussed previously, conventional lenses are commercially acceptable, thus masking fluctuations in coating thickness during production. By moving the entire curve to the right or to the left, the peak reflection 70a (the highest point on the curve) can be adjusted to move to the right or to the left. The result is that the residual color of green becomes more blue or yellow to look. In addition, AR coating companies can rotate the curve to bring the minima to the right of the curve up to about 0.75% reflection. The consequence is that the total amount of residual reflections rises very significantly. As a further consequence, the residual colour appears noticeably yellowish green.

Curve 71 represents the AR coating of the inventive lens shown in figure 2. It is noted here that the total residual reflection is much lower than the conventional curve 70. Note also that the curve also extends (wider) to both the infrared and ultraviolet regions of the visible spectrum. This is a significant factor because the AR coating on all lenses has a tendency to change color as the angle of incident light (the angle at which the light falls on the surface) gradually deviates from direct illumination. This change in color appearance is due to the curve shifting to the left as the angle of incidence increases. The whole curve is narrower and its color changes faster. This is quite apparent because the green color suddenly changes to yellow, orange, or red. The curve 71 has a much wider width and is colorless. As the angle of incidence increases, the curve starts to move to the left, but the color remains unchanged until the angle is extremely large, for example up to 45 °.

Applicants' invention, in one aspect, is directed to a modification of the conventional curve, as indicated by numeral 70, to a white light curve, as indicated by numeral 71. The color combination of the white light curve 71 produces a white light reflection without the dominant green reflection presented by the conventional curve 70.

Applicants have discovered that adjusting the ratio of blue, green, and red light in the reflected light from the anti-reflective coating to each other can produce a curve, as shown by numeral 71, that produces substantially white light. It is known to calculate the thickness of a film by specifying some optical parameters using computer software which will use these parameters to calculate the AR coating and give the thickness of the film. Specifying that, for example, the blue, green, and red colors are of equal concentration alone does not produce white light, but rather gives a curve such as curve 70 with a peak green and a residual green reflection.

An important feature of applicants' invention is that the ratio of blue, green, and red peaks in the reflected light is controlled to produce a reflection of white light. The three colors are controlled within a specific ratio to produce a reflection of white light. Generally, the blue peak is in the range of about 34 to 40%, preferably 36-38%, e.g., 37%, the green is in the range of about 24 to 32%, e.g., 29%, and the red is in the range of about 30 to 38%, preferably 32-36%, e.g., 34%, as a percentage of the color peaks. When these ratios are provided to computer software along with other optical properties, such as the refractive indices of the materials used, and refractive index tables over a range of optical thicknesses, the software will calculate the AR layers required to produce the specified blue, green, and red peaks. A typical computer software Program, entitled "Essential MacLeod," Optical coding design Program, copy Thin Film Center, Inc.1995-2003, Version V8.6, is distributed by Thin Film Center, Inc. Other well known software programs can be used to calculate film thickness that satisfies the above ratios. It is also apparent that the optical thickness necessary to meet the above ratios, as is well known in the art, can also be calculated manually. A typical calculation method is described in U.S. patent No.4,609,267, which is incorporated herein by reference, but other well known methods of calculating optical thickness may be used.

In other aspects of the invention, it is important that the AR coating have low stress, since high stress causes optical distortion and the AR coating may peel off. It has been found that high index materials and low index materials have different stresses when formed into thin films, and one feature of the present invention is to minimize stress differences in the layers, resulting in AR coatings with low stress.

For example, it has been found that the typical low index material, silica, produces tensile stress when coated. In contrast, high index materials create compressive stress when coated. It has been found that compressive stress is often less than the tensile stress of the low index material. Therefore, such a difference between tensile stress and compressive stress between layers occurs during coating, which may cause peeling and optical distortion.

Thus, an important feature of applicants' invention is to adjust each adjacent layer of the optical coating as necessary to balance tensile and compressive stresses. This is done by first specifying the desired reflection peaks (ratios) for blue, green, and red light, as described above, and calculating the optical thickness of each layer. Once the computer calculation determines the optical thickness and the number of AR layers, the optical thickness of each layer can be modified in steps of 0.5 λ to balance (equalize) the stress between the layers. For example, if the low index layer has an optical thickness of 0.25 λ and gives a tensile stress of 5, while an adjacent high index layer, also having an optical thickness of 0.25 λ, only produces a compressive stress of 1, then it is preferable to increase the optical thickness of the high index layer to increase the pressure to balance or minimize the higher tensile stress of the low index layer. In this example, the optical thickness of the high index layer should be adjusted to 0.75 λ or even 1.25 λ to increase the compressive stress to be closer to the tensile stress of the low index layer. Increasing the optical thickness of one layer relative to an adjacent layer has no significant effect on the white light reflection of the coated lens, since the optical thickness typically increases in steps of 0.5 λ.

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.

Thus, after describing the invention, our claims are:

Claims (7)

1. A method for making an anti-reflective coated optical lens comprising the steps of:

providing one or more optical lenses and an optical reference lens;

positioning an optical lens and an optical reference lens in the same coating plane in a vacuum deposition chamber having an optical monitor in communication with the optical reference lens;

providing at least one source of a high index anti-reflective coating composition and at least one low index anti-reflective coating composition in the vacuum deposition chamber;

applying a high refractive index composition layer on the lens until the optical monitor determines that a coating of a desired optical thickness is obtained;

applying a low refractive index component layer on the lens until the optical monitor determines that a coating of a desired optical thickness is obtained; and

repeating the high refractive index layer coating step and the low refractive index layer coating step alternately until a desired antireflection coating is coated;

wherein the optical monitor comprises a means for directing an on/off beam of light into the vacuum deposition chamber to fall on an optical reference lens and a photodetector programmed to: such that the light beam received by the light detector during the off period is noise which the light detector subtracts from the amount of light the light detector receives when the light beam is on to ensure that only light which it is assumed is actually being measured, the apparatus being arranged to measure the reflected light from the reference lens at a particular frequency and to use that measurement to determine when the required optical coating thickness is achieved.

2. The method of claim 1, wherein the source of the high index anti-reflective coating composition is a mixture of cerium oxide and titanium oxide.

3. The method of claim 1, wherein the low index anti-reflective coating composition is a mixture of silicon oxide and aluminum oxide.

4. The method of claim 1, wherein the refractive index of the optical lens is 1.40 to 1.90.

5. The method of claim 1, wherein said coating plane is curved.

6. The method of claim 1, wherein the on/off light beam is provided by a photointerrupter that turns the light beam on and off.

7. The method of claim 1, wherein the lens is a polycarbonate lens.