WO1997048002A1

WO1997048002A1 - Antiglare optical device

Info

Publication number: WO1997048002A1
Application number: PCT/US1996/010154
Authority: WO
Inventors: George S. Levy
Original assignee: Levy George S
Priority date: 1996-06-12
Filing date: 1996-06-12
Publication date: 1997-12-18

Abstract

A device for viewing an object field (8) containing intense light sources (5) which could be disturbing or harmful to the human eye (7). Light (1) from the object field (8) is focused at a focal plane (2) located within a layer of photochromic material. An intense light source (5) produces an opaque mask on the photochromic layer. This mask matches the location and shape of the image of the intense light source at the image plane (9). A lens system permits the viewer to view the image plane (9) to obtain an image of the object field with light from the intense light source dimmed by the opaque mask in the photochromic layer. Dimensionality reduction can be achieved by folding the optical path by means of mirrors or prisms, or arranging a multiplicity of devices in array formation.

Description

ANTIGLARE OPTICAL DEVICE

This application is a continuation-in-part of patent application serial number 08/355,075 filed on 12/13/94, which was a continuation in part of serial number 08/317,137 filed on 9/26/94, now abandonned, which was a continuation in part of serial number 08/01 1 ,743 filed 2/01/93, now patent number 5,351 , 151 . This invention relates to optical instruments and more particularly, to optical instruments such as binoculars, rearview mirrors, welding visors, spacesuit goggles and periscopes for viewing with the human eye .

BACKGROUND OF THE INVENTION

Directing an optical instrument such as binoculars toward an intense light source such as the sun can be very hazardous to the eyes. In astronomical instruments, this problem is sometimes solved by placing in the focal plane inside the instrument, an opaque disk positioned exactly at the focused image of the sun. The disk has the same dimension as the image of the sun and thus blocks out the solar rays. In energy detection devices such as the ones described in US patents 3,020,406 by T. R. Whitney and US patent 3,714,430 by R. C. Finvold, a photochromic Iayer is placed at the focal plane of the device in order to protect sensitive photodetectors. The high energy rays cause the photochromic material to increase in opacity at those points where the rays are most intense. Thus, high intensity rays are attenuated by the same dark spots they generate, and dim rays are left unaffected.

These prior art devices make use of photochromic material sensitive to infrared radiation, such as germanium and gallium arsenide. Furthermore, these devices are specifically designed to protect inanimate energy detectors and transducers.

There is a need to reduce glare in conventional instruments such as rearview mirrors, binoculars, welding visors and periscopes, operating with visible light, and specifically, to protect human vision from high intensity light sources such as the sun, car headlights and welding arcs. In addition, the size of the instruments should be minimized by folding the optical path. As is well known in optics, this can be achieved by the use of prisms and mirrors. The size can also be reduced by using several such instruments arranged in array formation.

SUMMARY OF THE INVENTION

The present invention provides a device for viewing an object field containing intense light sources which could be disturbing or harmful to the human eye. Light from the object field is focused at a focal plane located within a layer of photochromic material. An intense light source in the object field produces an opaque mask in the photochromic Iayer. This mask matches the location and shape of the image of the intense light source at the image plane. A lens system or eyepiece permits a viewer to view the image plane, and obtain an image of the object field in which rays from the intense light source are dimmed by the opaque mask in the photochromic Iayer. The size of the instrument can also be reduced by folding the optical path and by using a multiplicity of devices in array formation. This invention is applicable to the design of instruments for human viewing, such as rearview mirrors, welding visors, binoculars, space goggles, and periscopes.

BRIEF DESCRIPTION OFTHE DRAWINGS

FIG. 1 A is a drawing shows the basic principle of the antiglare device which consists of an inverting telescope equipped with an photochromic Iayer in the focal plane between the two lenses.

FIG. 1 B Illustrates how field lenses can be placed to increase the field of view.

FIG. 1C describes how a compound lens design can reduce the length of the optical path without changing the device magnification.

FIG. 2A illustrates the construction of a photochromic layered system using a liquid crystal. FIG. 2B describes a photochromic system using a liquid crystal and a photoconductor, that operates in the transmission mode, and that relies on controllable light scattering property of the liquid crystal.

FIG. 2C shows a photochromic system using a photoconductor, a liquid crystal and a dielectric mirror, that operates in the reflection mode, and that relies on controllable light scattering property of the liquid crystal.

FIG. 2D illustrates a photochromic system using a photoconductor, a liquid crystal and a semitransparent dielectric mirror, that operates in the reflection mode and that relies on controllable light scattering property of the liquid crystal.

FIG. 2E describes how a video camera combined with a matrix display can operate to provide a photochromic effect.

FIG. 3A shows how an antiglare rearview device for cars can be constructed using prisms.

FIG. 3B provides a variation of the design illustrated in FIG. 3, where the prisms are staggered to improve the driver's field of view.

FIG. 3C illustrates how mirrors can replace prisms in the design describe in FIG. 3. FIG. 3D shows how a side view mirror can be designed by altering the angles in the constituent prisms.

FIG. 3E shows how the basic design of FIG. 3A can be improved by adding a vane screen to stop rays with high angular deviation from the optical axis.

FIG. 3F shows detail of a vane screen stopping rays with high horizontal deviation, and a vane screen stopping rays with high horizontal and vertical deviation.

FIG. 4A describes an overhead rearview device that uses a penta prism and a modified penta prism.

FIG. 4B is the top view of the device shown in FIG. 4A.

FIG. 5A illustrates the use of mirrors in the design of rearview devices.

FIG. 5B shows how curved "field" mirrors can be used to provide more flexibility to the design of the optics.

FIG. 6A describes a ceiling-mounted optical insert that converts an ordinary rearview mirror into an antiglare rearview device.

FIG. 6B provides a detailed functional view of the device shown in FIG. 6A. FIG. 7A illustrates a possible design using a field lens arrangement to improve operational parameters such as field of view and vignetting.

FIG. 7B shows how several devices shown in FIG. 7A can be organized in array formation to provide a wider field of view.

FIG. 7C describes how the optical path in FIG. 7B can be folded by means of a two mirrors at intersecting at 90°.

FIG. 7D illustrates how the optical path can be folded by two mirrors at 45° of each other.

FIG. 7E shows the optical path folded by two mirrors at 60° of each other.

FIG. 7F describes how the optical path can be folded by two mirrors intersecting at a 30° angle.

FIG. 8 illustrates a rearview mirror that uses a photochromic system operating in reflection mode and that employs three reflections.

FIG. 9A describes a rearview mirror that uses a photochromic system operating in reflection mode and that employs five reflections. FIG. 9B shows a rearview mirror that uses a photochromic system operating in reflection mode, that employs five reflections, and that uses some of the internal reflectors as "field lenses."

FIG. 10A illustrates a rearview mirror that uses a photochromic system operating in reflection mode, that employs five reflections, in which the reflections occur at an angle of about 45°, thus allowing the use of prisms.

FIG. 10B is similar to FIG. 10A except that some of the internal surfaces are curved to operate as "field lenses."

FIG. 10C is similar to FIG. 10A except that the shape is elongated to facilitate reflections when prisms are used.

FOG. 10D is similar to FIG. 10A except that the design is elongated to conform to the particular space available in the rearview mirror mounting location.

FIG. 10E is similar to FIG. 10D except that some of the internal surfaces are curved to operate as "field lenses."

FIG. 1 1 A illustrates a rearview mirror that uses a photochromic system operating in reflection mode, that employs seven reflections, in which the reflections occur at an angle of about 27° from the normal to the surfaces. FIG. 11B is similar to FIG. 11 A except that some of the internal surfaces are curved to operate as "field lenses."

FIG. 12A describes a rearview mirror in which the rays are folded in an hexagonal pattern and undergo a total of seven reflections with the reflection angle of about 30° from the normal with the reflecting surfaces.

FIG. 12B describes a rearview mirror in which the rays are folded in an hexagonal pattern and undergo a total of nine reflections, with the reflection angle of about 60° from the normal to the reflecting surfaces.

FIG. 12C describes a rearview mirror in which the rays are folded in an hexagonal pattern and undergo a total of eleven reflections, with the reflection angle of about 60° from the normal to the reflection surfaces, and in which some surfaces are used as "field lenses."

FIG. 12D describes a rearview mirror in which the rays are folded in an hexagonal pattern and undergo a total of thirteen reflections, with the reflection of angle about 60° from the normal to the reflecting surfaces, and in which one of the surfaces is an eccentric Fresnel mirror. FIG. 12E describes a rearview mirror similar to the one in FIG. 12D except that the Fresnel mirror is replaced by a conventional curved surface.

FIG. 13A illustrates a rearview device in which the major portion can be mounted vertically in the vehicle dashboard.

FIG. 13B shows how the device illustrated in FIG. 13A can be converted into an antiglare forward view device.

FIG. 14 provides a three dimensional view of prism binoculars equipped with an antiglare Iayer.

FIG. 15 describes a welding viewing device equipped with an antiglare Iayer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention can be described by reference to the drawings. It comprises two subsystems, the optical system and the photochromic system.

Description of the Optical System

We shall first describe the general principle of an antiglare device. FIG. 1 A describes a simple inverting telescope modified to eliminate glare. Light rays 1 enter the objective lens 2 and are focused on the focal plane 3 which lies within the photochromic Iayer 4. Rays originating from an intense source such as the sun 5 create a dark spot 6 on the photochromic Iayer. This spot, in turn, substantially blocks out the light of the sun, permitting a viewer 7 to see an image of an airplane 8 flying at an angular position near the sun. The rays leave the telescope through the eyepiece or lens system 9. This technology is clearly applicable to focal systems that internally generate a real image such as the Newtonian and Cassegrain non- inverting telescopes.

As indicated in FIG. 1 B, the device field of view can be increased by using the well known technique of imaging the objective lens unto the eyepiece by means of field lenses 101 and 102.

The lenses do not have to be simple lenses as outlined above, but could be compound lenses, curved mirrors or Fresnel lenses or mirrors as needed, to improve the quality of the image, reduce aberrations and decrease the weight of the device.

Compound lenses can also reduce the effective focal length, f , as

shown in FIG. 1 C. This figure shows a telescope system with a magnification of unity in which one of the focal distances has been reduced by means of a compound lens arrangement.

Magnification of the image, other than unity may be desirable. For example, in the case of rearview mirrors, reduction of the image can provide a wider field of view. More generally, intentional distortion of the image can be of possible value as in the case of rearview mirror. In such systems, one area of the image is kept distortion- free. Distortion is applied to the remaining of the image to increase the effective field of view. Magnification and intentional distortion can easily be implemented by adjusting the optical parameters of lenses, mirrors and prisms of the antiglare system.

To reduce the size of the device, the optical path could be folded by means of prisms or mirrors. While prisms can further reduce the length of the optical path because of the high index of refraction of their constituent material and thus allow the construction of more compact devices, mirrors have the advantage of providing low weight design solutions. In the description of specific embodiments, we shall explain how means such as mirrors and prisms can be used to reduce the dimensions of the device. Prisms and/or mirrors have the added function of erecting the image reinverted by the convex lenses or concave mirrors in the device.

As we shall describe in the specific embodiment below, these same principles can be used in applications such as rearview mirrors, binoculars and welding helmets. This technology can also be applied to the design of space suit goggles to reduce the high contrast found in space between objects exposed to the sun and those in the shade. Astronauts exposed to high intensity sunlight lose their night adapted vision and can't see objects in the shade. This antiglare technology could benefit them.

Description of the Photochromic System

The photochromic system can comprise a single homogeneous Iayer or several layers which together possess a photochromic property. Multiple Iayer systems may offer better performance in terms of speed and sensitivity, than single Iayer systems.

Photochromies Using Assemblies of Optically Active Materials and Photoconductive Materials

A possible photochromic system shown in FIG. 2A uses optically active materials in conjunction with polarizers. This arrangement bears a certain resemblance to the Hughes Liquid Crystal Light Valve discussed in Fundamentals of Photonics by Saleh and Teich, Wiley Interscience, page 728, except that no mirror and optical isolator is used. An advantage of using a liquid crystal technique is that applied voltage can be used to turn on or off, or otherwise gradually control the photochromic functionality of the device.

My system comprises the following layers arranged in a stack:

1 ) A transparent electrode 210 made of material such as Indium Tin Oxide (ITO), supported by glass plate 213,

2) A photoconductive Iayer 212 made of material such as

Selenium, Zinc Selenide, Selenium doped with Tellurium, Bismuth Silicon Oxide (Bi Si O ) or a transparent organic

photoconductor,

3) An optically active Iayer 214 made of liquid crystal consisting of a "twisted" nematic Iayer with a twist of 90 degrees.

4) A second transparent electrode 216 of ITO supported by glass plate 215.

It is evident to experts versed in optics, that antireflection layers could be used on surfaces to reduce reflections inside the device. It is also known to experts in the field of liquid crystals that the surfaces in contact with the liquid crystal may have to be coated with chemicals such as polyimides, and rubbed if alignment of the liquid crystal molecules in contact with the surfaces is desired. It is also known that the if the liquid crystal is in contact with a material such as a photoconductor and if a chemical reaction can occur between the liquid crystal and the material, then a passivation Iayer such as silicon dioxide can be used to coat the material. Such a Iayer has the added benefit of preventing short circuits across the liquid crystal Iayer. These techniques are well known in the field of liquid crystals.

A controllable electric power source 219 is applied across the electrodes and an electric field develops across the photoconductive and liquid crystal layers. When exposed to light, the photoconductive material becomes conductive in proportion to the intensity of the incident light. As a result, a spatial pattern of conductance is formed in the photoconducting Iayer, and the electric field across the layer is altered in those areas where the conductance is high. In turn, the liquid crystal rotates the plane of polarization of light as an inverse function of the electric field intensity.

If the above system is enclosed between two crossed polarizers 218 and 21 1 , then bright rays which are not rotated in polarization by the liquid crystal, are attenuated by the second polarizer on their path. The polarizers must be located on each side of the aforementioned layers, along the optical axis. They may be in contact with the Iayer assembly as shown in the figure, or, more generally, elsewhere on the optical axis of the instrument. The applied voltage must follow the drive requirements for liquid crystals to avoid electrolysis of the solution. The above example describes how a liquid crystal in conjunction with polarizers can be used to construct a photochromic system. The use of polarizers, however, results in the loss of at least 50% of the light. Other methods explained below do not need polarizers. These techniques are well known and are described in technical literature on optics such as the Handbook of Optics. Volume II, Michael Bass Ed., 1995, Chapter 14, and the periodicals Liquid Crystals, and Molecular Crystals and Liquid Crystals. These methods rely on scattering or absorption of light by liquid crystals. Some of the most interesting approaches include the following:

1 ) Guest-host effect

2) Polymer-dispersed liquid crystals (PDLC)

3) Polymer stabilized liquid crystals (PSLC)

Guest-host systems are formed by dissolving a few percent of dichroic dye or more generally, pleochroic dye in the liquid crystal. Changes in the orientation of the liquid crystal molecules in response to an electric field results in changes in orientation of the dye, and changes in color or opacity. Systems operating in positive mode, that increase in opacity with the electric field, have been constructed (Bahadur et al., 13th International Liquid Crystal Conference, Vancouver, BC, Canada, 22-27, July 1990 and Molecular Crystal and Liquid Crystal, 1991 , Vol. 209, pp 39-61 , and Ivaschenko et al., 13th International Liquid Crystal Conference, Vancouver, BC, Canada, 22-27, July 1990 and Molecular Crystal and Liquid Crystal, 1991 , Vol. 202, pp 13-16). Polymer-dispersed liquid crystals (PDLCs) modulate light by scattering it, as a function of the electric field. They consist of microscopic droplets of liquid crystal dispersed in a transparent polymer. Control of the refractive index of the liquid crystal by means of an electric field allows the material to be switched from clear to scattering mode. The refractive index mismatch between the liquid crystal droplets and the host polymer is the physical mechanism responsible for the scattering effect. PDLCs can be constructed to operate in the positive mode, that is to be clear when no electrical field is present, and to scatter light when the field is turned on (Ma et al., Proceedings of SPIE, 1990, Vol. 1257, pp 46.).

Polymer Stabilized Liquid Crystals can also be used to modulate light by scattering. To prepare these materials, monomers in low concentration are dispersed in a liquid crystal. The monomers are then photopolymerized while the liquid crystal molecules are suitably aligned by a field. The function of the polymer is to hold in place the liquid crystal molecules. The resulting material can operate in the negative mode (clear when the field is present) or in the positive mode (clear when the field is absent). (Yang et al., Applied Physics Letters, Vol. 60 No. 25, June 22, 1992, pp 3102, 3104 and Hikmet et al., Physical Review E, Vol 51 , No. 6, pp 5824- 5831 ).

The Liquid Crystal Dispersed Polymer, also called Liquid Crystal Gels systems contain a small amount of polymer in a matrix of liquid crystal (Jakli et al, Liquid Crystals 1995, Vol 18, No. 4, pages 601 -605, and Hikmet, R.A.M., Liquid Crystals 1991 , Vol 9, No. 3, pages 405-416). These systems can be transparent in the "off" state and translucent in the "on" state.

Many other variations exist for constructing light valves, as is well known by experts versed in this art and as described in the technical literature.

Several photoconducting materials are available, with different spectral sensitivities, transparencies to visible light and manufacturing application processes. For example, silicon is sensitive to infrared but opaque to visible radiation. Selenium is sensitive to blue and green light thus allowing only orange and red visible light to pass. Selenium's sensitivity van be pushed toward the blue by alloying it with zinc or adding tellurium as a dopant. The tendency of selenium to crystallize can be mitigated by the addition of arsenic. Organic semiconductors can also be used. For example, titanylphthalocyanine have a peak transparency around 485 nm (Fujikake et al., Japanese Journal of Applied Physics, 1995, Vol 34, Part 1 , No. 8A, pp. 4067-4073. )

As is well known in the art, many other methods of constructing light valves have been developed. It is a purpose of this patent to utilize the functionality of light valves when these light valves are positioned at the focal plane of an optical system. FIG. 2B illustrates the principle of such a light valve adapted for the purpose of this invention to operate in the transmissive mode. It comprises a stack of the following materials:

1) A glass plate 221

2) A transparent electrode 222 consisting of Indium Tin Oxide (ITO)

3) A photoconductive material 223 transparent to visible light, consisting for example of selenium or zinc selenide or an organic photoconductor.

4) A liquid crystal Iayer 224 operating in positive mode using one of the scattering or absorption methods discussed above.

5) A second ITO transparent electrode 225

6) A second glass plate 226

Light enters the system through the transparent electrode 222 and traverses the photoconductive material 223 where it generates charge carriers. As these carriers migrate they create space charges on the surface of the liquid crystal system 224. This generates an electric field that changes the optical properties of the liquid crystal Iayer. As a result, the liquid crystal absorbs or scatters high intensity rays, but is transparent to low intensity light.

FIG. 2C describes a scattering system operating in the reflective mode. It consists of the following elements:

1) A glass plate 231 2) A transparent electrode consisting of Indium Tin Oxide (ITO) 232

3) A photoconductive material transparent to visible light, consisting for example of selenium or zinc selenide 233

4) A liquid crystal Iayer 234 operating in positive mode by varying the amount of scattering or absorption of light

5) A dielectric mirror 237 consisting of, for example, multiple lay ^Jers of HfO 2 /SiO 2

6) An electrode 235

7) A substrate 236 made of plastic, metal or ceramic.

This system operates as the one above, except that, in this case, light is reflected by the dielectric mirror 237 and undergoes a second pass through the system.

A variation on the above design, shown in FIG 2D, involves the following components:

1) A glass plate 241

2) A transparent electrode 242 consisting of Indium Tin Oxide (ITO)

3) A liquid crystal Iayer 244 operating in positive mode by scattering or absorbing light.

4) A semitransparent dielectric mirror 247 consisting of, for example, multiple layers of HfO /SiO .

5) A photoconductive Iayer 243 consisting of hydrogenated silicon. 6) An electrode 245

7) A substrate 246 made of plastic, metal or ceramic.

In this case the photoconductive material 243 is located behind the mirror 247 and can be made of a material such as silicon opaque to visible light. Light enters the system through the transparent electrode 241 and traverses the liquid crystal Iayer. As the light reaches the semitransparent mirror 247, most of it is reflected. Some light, however traverse the mirror and is captured by the photoconductive material 243 where it generates charge carriers. As these carriers migrate, they create space charges on the surface of the polymer-dispersed liquid crystal. The resulting electric field changes the optical properties of the liquid crystal. In turn the liquid crystal absorbs or scatters high intensity rays but is transparent to low intensity light. The semitransparent mirror can be made mostly reflective in the visible portion of the spectrum, and mostly transparent in the infrared portion. This design provides an optimum allocation of the spectrum. The silicon photoconductor receives the infrared rays to which it is sensitive. The remaining rays which are visible, are reflected toward the human viewer.

Protection of Sensitive Materials Against Ultraviolet Radiation

If the materials used in the photochromic or optical systems can be damaged by certain radiations such as UV, it is possible to place in front of the optical system, a filter to prevent these radiations to enter the optical system.

Photochromic Effect Implemented with Video Camera and Matrix Display Layer

The photochromic function can also be performed by a video camera used in combination with a liquid crystal transparent display as shown in FIG. 2E. The matrix display Iayer 252 is a conventional black and white liquid crystal display operating as a controllable transparency, consisting of a matrix of electrodes arranged in rows and columns and used, to control liquid crystal pixels. A twisted nematic liquid crystal could be used, with a 90 degree twist and enclosed between two plates. On the first plate, electrodes are arranged in rows. On the second plate, electrodes are arranged in columns. This whole assembly is enclosed between two polarizers with parallel polarizarion axes. The resulting assembly is identical to conventional liquid crystal transparency displays.

This display is driven by a signal originating from a video camera 251 , such that a negative black and white image is generated: points of high intensity light in the image generate opaque pixels. A negative image could be obtained, either by electronic means such as reversing the polarity of the video signal, or by optical means, using crossed polarizers instead of parallel polarizers. The matrix display is inserted in the focal plane of an optical system, and the negative video image on the liquid crystal is aligned with the real image produced by the optical system. In this arrangement, the negative video image behaves like a mask that selectively blocks off high intensity rays passing through the optical system. This arrangement has clear advantages over a simple video display used to eliminate glare:

1 ) The resulting image is three dimensional.

2) The resolution of the antiglare mask depends on the pixel size of the video system. However, the resolution of the image depends on the optical system. Clearly, image resolution is more important than mask resolution.

Alternatively other liquid crystal techniques could be used that do not need polarizers. These systems include those that absorb light such as the guest/host systems or that scatters light such as the PLCD or polymer stabilized liquid crystals.

Photochromic Systems Using Combinations Of Absorbing Dyes

Many organic chemicals such as 3,4,9,10, perylenetetracarboxylic dianhydride (PTCDA) exhibit large nonlinear optical effects. These materials are very fast (in the nano or femtosecond range). Using techniques of molecular engineering, various molecular assemblies and mixtures may be created, with properties of light sensitivity and control, tailored to the specific application. [A. Ersen, "Laser recrystallized Si/PLZT smart spatial light modulators for optoelectronics computing," Dissertation, UCSD 1992, page 19]

Photochromies Using Photoinduced Electron Transfer Chemicals

The technique described in US patent 5,062,693 by Beratan and Perry, can be used for generating phototropic chemicals, based on an electron transfer mechanism between donor molecules and acceptor molecules. These chemical pairs can be designed with customized optical properties such as photochromism and optical activity and can be used as dopants in a matrix comprising the photochromic Iayer. When excited by light, the molecular system changes state temporarily and reversibly. The optical properties of the excited state differ from those of the ground state. The molecular system then decays back to its ground state thus restoring the system back to its original optical properties. The number of chemical pairs capable of this behavior is significant. Well studied donor molecules include ruthenium trisbipyridyl and phthallocyanine. Acceptor molecules include methyl viologen. These chemicals would typically be embedded in some transparent matrix material. Methods of forming these chemicals in thin sheets or films are discussed in the Beratan patent.

Use of Materials or Systems with Properties Other than Photochromic

While a photochromic system Iayer at the focal plane can be used in many optical instruments, material with other properties can also be used. We shall refer to this widening in functionality by using the term "photoactive Iayer" to name the material at the focal plane. Thus, by photoactive we mean photochromic as well as other functions such as fluorescent and phosphorescent. Interestingly, materials or systems that reflect, detract, retard or scatter light or rotate its plane of polarization as a function of the input light intensity can be used in place of photochromic systems.

Fluorescent And Phosphorescent Materials

The photoactive Iayer can also be built of material such as zinc sulphide that emits visible light when illuminated by an invisible radiation fFundamental of Photonics by Saleh and Teich, Wiley- Interscience, 1991 , Page 456]. Zinc sulphide fluoresces with visible light when irradiated with ultraviolet light. This technique allows the construction of goggles capable of seeing invisible radiation such as ultraviolet light while providing the viewer with a stereoscopic perspective.

Description of Specific Embodiments

Among the several embodiments of the concept described in this invention, I shall describe rearview mirrors, binoculars and welding goggles.

Rearview mirrors

I shall describe a few of the many design alternatives available for constructing rearview mirrors in accordance with this invention. Such devices can be made to be mounted above the windshield, in front of the driver, or on the ceiling in the center of the car, or outside to provide a side view. They could rely on several optics technologies such as refractive optics, reflective optics, Fresnel optics and microlens optics.

FIG. 3A illustrates a rearview device that could be placed in front of the driver. It consists of two rectangular convex lenses 31 and 32, a 90 degree reflection prism 33 and a 90 degree reflection ftat edge, roof prism 34 for image reinversion. It also includes a photochromic Iayer system 35 in the focal plane located between the prisms. Light rays 36 enter the device through the lens 31 , and are reflected by prism 33. They come in focus at the photochromic Iayer 35. They then are reflected and inverted by the prism 34. After traversing the lens 32 they exit the device and provide an upright image to a viewer 37. Lenses 31 and 32 can be simple as shown in the figure, or can be compound to reduce aberrations. Since the two prisms 33 and 34 are different, the optical path is asymmetrical. If the photochromic Iayer is placed in the exact center of the device, the power of the input lens 31 and output lens 32 must be adjusted to insure that the focal plane coincides with the photochromic material. If the input and output lenses are selected to be identical, then the focal plane does not fall exactly in the center of the device and the position of the photochromic Iayer must be adjusted to coincide with the focal plane.

FIG. 3B describes an almost identical device as FIG. 3A except that the lenses 321 and 322 are staggered in height. Lens 321 is lower and lens 322 is raised to provide to the driver a better view of the front road. This approach has the additional advantage that the line 38 in FIG. 3A which corresponds to the tip of the roof peak in prism 34 is not visible to the viewer.

The device described in FIG. 3C is identical to the one in FIG. 3A except that mirrors are replacing prisms.

FIG. 3D describes a modification to the basic design in FIG. 3A, which allows the driver to position the rearview device on the side of the vehicle. The figure shows a top view of the device. The angle between the surface 343 and the roof 348 has been increased such that the driver can observe the rearview image at an angle of 45 degrees from the forward direction. Rays with a high angular deviation from the optical axis can interact with the photochromic Iayer without being properly processed by the prisms. These rays could add unwanted components to the antiglare mask, corresponding to secondary images. It may be desirable to stop these rays. FIG. 3E is a modification on the basic design of FIG. 3A, in which vanes 351 and 352 have been inserted behind each lens to stop rays those rays with a high angular deviation. Two kinds of vanes are illustrated in FIG. 3F. Vanes 361 filter out rays only with high horizontal deviation. Vanes 362 filter out rays with both high horizontal and vertical deviations. These vanes could be placed either in front or behind the lenses. They comprise thin layers of opaque and non reflective material arranged in parallel strips, with the plane of each Iayer parallel to the optical axis. These strips could be arranged vertically or horizontally or both. More conventional baffles and stops are also possible as is well known in the art of optics. Design details on baffles, vanes and stops can be found in the Handbook of Optics. Michael Bass Ed., McGraw Hill, 1995. We use here the term baffles to refer to baffles, vanes and stops.

The device shown in FIG. 4A is identical to the one in FIG. 3A except that the prisms have been modified to achieve a longer optical path and thus avoid using lenses with low f numbers. Prism 43 is a penta prism and prism 44 is a modified penta prism which includes a roof configuration 48 to invert the image. This prism combination provides a longer optical path for light rays, at the cost of two additional reflections. The longer path is advantageous since it allows the construction of a more compact device. FIG. 4B is a top view of the device showing the penta prism 43 on top, the modified penta prism 44 on the bottom, with its roof edge 48.

FIG. 5A describes a rearview mirror using reflective optics. The device is enclosed in a box 51 equipped with a transparent panel 52 at the bottom. Light rays entering the device through this window, are reflected by a concave reflector 53. The rays are then focused on a photochromic layer 54 and immediately reflected by a flat mirror 55 located behind the photochromic Iayer. After passing through the photochromic Iayer a second time the rays are reflected by a second concave mirror 56 that has approximately double the curvature of mirror 53. The rays are then focused on, and reflected by, a flat mirror 57. They are sent back to mirror 53, and exit the device through the window 52 at the bottom of the enclosure. The image provided by this device is upright.

The device in FIG. 5B is identical to the one in FIG. 5A except that the flat mirrors 55 and 57 have been replaced by concave mirrors 58 and 59. These allows greater flexibility to the optical design for reducing aberrations and providing a wider field of view. The photochromic Iayer must also conform to the concave shape of the mirror behind it and follows more closely the focal locus.

Ceiling Mounted Rearview Mirror FIG. 6A illustrates the construction of a ceiling mounted rearview mirror and its placement in a car. The optical components are enclosed in a box 61 equipped with a pop up/down mechanism to allow the device to be either inserted in the optical path of the light rays reaching the conventional rearview mirror, or stored out of the way when not in use. FIG. 6B describes in more detail the operation of the device. The device comprises mainly two concave mirrors 60 and 66 and two corner reflectors 67 and 69 which cancel out the image inversion produced by the concave mirrors. The device also contains a photochromic Iayer 68 located at the optical focal plane. The surfaces 62, 612, 63 and 613 are transparent and function as windows to allow rays to enter and leave the device. Light rays 64 originating from behind the driver, are reflected by the concave surface 66. The rays are then reflected and inverted by the corner reflector 67. The rays reach a focus in the center of the device which holds the photochromic material 68 where the brightest rays are attenuated. The rays are then reflected and reverted by the second corner reflector 69. They reflect from the second concave reflector 60. The rays continue on their path to a standard rearview mirror 65 where they are reflected toward the driver. Thus, this device intercepts, modulates and retransmits rays going through to a conventional rearview mirror.

Use of Field Lenses to Decrease Vignetting FIG 7A illustrates how field lenses can be introduced in an optical system to reduce vignetting. The light rays 75 pass through a first lens 71 , and a second lens 72 and reach their focal plane at 73 where the photochromic system is located. They continue and are reflected by a concave mirror 74. The rays then traverse for a second time, the focal plane 73, lens 72 and lens 71 . The rays emerging from the device appear to be reflected form a mirror that attenuates the most intense rays and leaves the dim rays unaffected. This basic device can be used singly or in array configuration as shown in FIG. 7B.

To reduce the size of the device, the light rays in the basic device shown in FIG. 7A can be folded by means of mirrors. As shown in FIG. 7C, the mirrors 736 can be at a 90° angle, or as in FIG. 7D, the mirrors 746 can be at a 45° angle, or as in FIG. 7E, the mirrors 756 can be at a 60° angle, or as in FIG. 7F, the mirrors 766 can be at a 30° angle. Obviously many other intermediate angles are also possible.

Rear View Mirrors Using Reflecting Photochromic Systems

Reflecting photochromic systems can fold the optical path and thus contribute in reducing the size of the device. FIG. 8 illustrates such a system in which the rays undergo three reflections. Light rays 85 are focused by lens 81 onto focal plane 82 which contains the photochromic system. The rays are attenuated selectively, and reflected toward a concave mirror 83 which sends them back through the optical system.

FIG. 9A shows a system in which the rays are reflected five times. This system can be implemented by means mirrors or, if the reflection angles are below the critical angle which is slightly larger than 45° for glass, by means of prisms. The reflecting surface 93 is concave and consists of a metallized surface. The reflecting surface 91 could be the face of a prism if the system is designed as a prism. Otherwise it could be a metallized surface.

FIG. 9B describes a system in which the rays undergo five reflections. The concave mirror 94 acts as a field lens and is used to improve the vignetting and field of view of the system.

FIG. 10A through FIG. 10D illustrate a systems using seven reflections.

FIG. 10A provide the basic concept for this class of design. All reflections occur at an angle of approximately 45°, which makes it possible to construct the system using prisms (assuming a critical angle for glass larger than 45°). The first 1011 and third 1013 reflections occur on a glass/air prism face, and therefore no metallized coating is necessary provided the light ray angles remain close to the paraxial rays. The second reflection 1012 takes place at the photochromic Iayer. Because the index of refraction of the material composing the photochromic system is close to the index of refraction of glass, light rays can penetrate and be modulated by the photochromic system.

FIG. 10B describes a system similar to the one in FIG. 10A except that the flat reflecting surfaces in 10A are replaced by curved surfaces 1021 and 1023 in 10B. If rays intersect the reflecting surfaces at an angle greater than the critical angle metallized surfaces should be used.

The rearview mirror in FIG. 10C is similar to the one in FIG 10A except that the proportions have been elongated in the horizontal direction to flatten ray angles at 1031 and 1033 and sharpen them at 1032. This is done to ensure that, if a prism approach is used, reflection occurs at 1031 and 1033 and penetration of the photochromic system occurs at 1032, even with rays far from the paraxial region.

The systems illustrated in FIGs. 10D and 10E are similar to those in FIGs. 10A and 10B respectively except that the horizontal light rays paths have been elongated to provide more flexibility in the optical design and conform better to the available space in cars where rearview mirrors are mounted.

FIG. 1 1 A illustrates a rearview mirror design using seven reflections. This design is more compact than the ones shown in FIG. 10A through 10E, but does not allow the use of prisms to reflect light because the angle of incidence of the rays is significantly larger than the critical angle for glass. Reflecting surfaces must be coated with metallized surfaces.

FIG. 11B describes a system similar to the one shown in 11A except that the flat reflecting surfaces in 11A have been replaced by concave surfaces 1121 and 1123 in 11B to act as field lenses and provide better optics and reduce vignetting.

FIG. 12A illustrates a rearview mirror using an hexagonal arrangement of reflectors, that includes seven reflections. Light rays 1219 enters the system through lens 1211 and e reflected by a flat metallized surface 1212. The rays are then reflected again at 1213 and reach their focus at the photochromic system 1214. The rays are reflected selectively by the photochromic system and reach the concave reflector 1215. The rays are then reflected by the metallized Iayer 1212, and undergo two more reflections at 1216 and 1217. The rays 1218 then leave the optical system at an angle approximately 60° from the incoming rays 1219.

FIG. 12B shows a rearview mirror using a hexagonal arrangement of reflectors. In this system the rays undergo a total of nine reflections. All reflection angles are below the critical air/glass critical angle, which make possible the utilization of a prism architecture. The rays can still penetrate the photochromic system because of the index of refraction of the material composing the photochromic system is close to that of glass. FIG. 12C illustrates an hexagonal arrangement of reflectors in which the rays undergo eleven reflections. The concave reflectors 1231 and 1232 operate as field lenses. The photochromic system 1233 is placed radially from the center of the polygon to one of the corners. Rays must go twice through the photochromic system. This system cannot be implemented with prisms, but its advantage over the systems in 12A and 12B is its efficiency in folding the optical path.

FIG. 12D shows a rearview mirror with an hexagonal arrangement of reflectors. In this system, the light rays are reflected thirteen times. Reflector 1241 is an eccentric Fresnel lens mirror which reflects the rays back at an angle and focuses them on the photochromic system.

FIG. 12E illustrates a system similar to the one in 12D except that the Fresnel lens has been replaced by a conventional concave mirror 1251. The resulting design is not as compact but can provide better quality images.

Rearview/Forward View Device

The device shown in FIG. 13A is almost identical to the basic device shown in FIG. 3A, except that it is mounted vertically in the vehicle dashboard. In addition, two prisms have been added, prism 1311 which is a penta prism, and prism 1313 which is a reflection prism. The incoming rays 1312 enter the penta prism which deflects them down by 90 degrees without reversing the image. The rays then enter the basic device where the most intense rays are attenuated as already described in FIG. 3A. The rays then leave the basic device and are deflected backward by prism 1313. Prisms 131 1 and 1313 could be mounted above and in front of the driver. The basic device could be mounted vertically in the vehicle dashboard.

FIG. 13B describes a small modification to the device in FIG. 13A. The penta prism 1311 is replaced by a reflection prism 1321 which allows the device to convert from a rearview mirror to a forward view device. The conversion process could be implemented simply by rotating one prism out of the way and substituting the other in the optical path in order to achieve two modes of operation for this device.

Binoculars

FIG. 14 describes how to incorporate antiglare technology in binoculars. Light rays 141 enter the binocular objective lens 142 and are reinverted by prisms 143 and 144. The rays reach the photochromic Iayer 146 which is placed at the focal plane. There, bright rays are selectively attenuated. Finally the rays leave the device through the eyepiece lens 148. The image provided to the viewer is erect since the reinversion produced by the lenses is cancelled by the reinversion produced by the prisms. Welding Goggles

FIG. 15 describes welding goggles equipped with the antiglare technology. The design resembles the one for binoculars, except that the photochromic Iayer 156 is placed between the prisms 150 and 152 since this is where the focal plane is, given the unity optical gain of the device. The rays 154 exit the optical system erect and available for viewing by the user. The prisms could be replaced by reflecting mirrors to achieve a lighter weight device.

Use of Arrays of Antiglare Elements

It is, of course, possible to organize in array formation, a number of antiglare device. US patent number 5,351 ,151 discusses this possibility when microlens optics is used. With conventional optics, this approach can also be used. A rearview mirror could be broken up, for example, into several segments. The basic idea for this is provided by FIG. 7B, but is generally applicable to designs in which the optical path is folded as shown from FIG. 7C to FIG. 15. Using arrays and folding of the optical path can reduce the dimensionality of the instrument.

Other Embodiments

While the above description contains many specificities, the reader should not construe these as limitations on the scope of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations within its scope. Accordingly the reader is requested to determine the scope of the invention by the appended claims and their legal equivalents, and not by the examples which have been given.

Claims

I Claim:

1. An antiglare optical device for human viewing of an object field containing an intense light source said device comprising:

a) an objective means for focusing an image of said object field onto a focal plane,

b) an eyepiece means for viewing said image focused onto said focal plane,

c) a moderating photoactive Iayer means located at said focal plane for moderating light from said intense light source,

wherein said light passing through said optical device defines an optical path, and further comprising a folding means for folding said optical path.

2. A device as in Claim 1 wherein said photoactive Iayer means comprises photochromic material.

3. A device as in Claim 1 wherein said photoactive Iayer comprises a heterogeneous photoactive assembly.

4. A device as in Claim 1 wherein said photoactive Iayer comprises a liquid crystal Iayer.

5. A device as in Claim 1 wherein said photoactive Iayer comprises a guest/host liquid crystal Iayer.

6. A device as in Claim 1 wherein said photoactive material comprises absorbing dyes.

7. A device as in Claim 1 wherein said photoactive Iayer comprises electron transfer chemicals.

8. A device as in Claim 1 wherein said photoactive Iayer comprises a liquid crystal display operating in a transparency mode, said display being controlled by a video signal generation means to provide images in said display.

9. A device as in Claim 8 wherein the video image generated is aligned with, and is the negative of, the image focused by said objective means.

10. A device as in Claim 1 comprising at least one field lens near said focal plane in order to increase the field of view of said device.

11. A device as in Claim 1 wherein said objective means and said eyepiece means together comprise at least one compound lens.

12. A device as in Claim 1 wherein said objective means and said eyepiece means together comprise at least one mirror.

13. A device as in Claim 1 wherein said objective means and said eyepiece means together comprise at least one Fresnel optical component.

14. A device as in Claim 1 wherein said folding means comprise at least one prism.

15. A device as in Claim 1 wherein said folding means comprise at least one mirror.

16. A device as in Claim 1 and further comprising a deflecting means for deflecting input rays, said deflecting means having two modes of operation such that optionally, either rays coming from the forward direction, or rays coming from the backward direction, are deflected toward the device.

17. A device as in Claim 1 and further comprising a mounting means for mounting said device into the ceiling of a vehicle, wherein said device intercepts, modulates and retransmits rays going through to a conventional rearview mirror.

18. A device as in Claim 1 wherein said device is fabricated in the shape of binoculars.

19. A device as in Claim 1 wherein said device is fabricated in the shape of a welding visor.

20. A device as in Claim 1 wherein said device is fabricated in the shape of space suit goggles.

21. A device as in Claim 1 and further comprising an adjusting means for adjusting the operation of said photoactive Iayer by means of an electrical input.

22. A device as in Claim 1 and further comprising baffles for stopping rays with high angular deviation from the optical axis

23. A rearview mirror comprising : a) an objective means for focusing light, from an object field rearward of a vehicle onto a focal plane, b) an eyepiece means for viewing said image at said focal plane, c) a photochromic Iayer means located at said focal plane for moderating intense light from said object field,

wherein said light passing through said rearview mirror defines and optical path, and further comprising a folding means for folding said optical path.

24. An optical device for human viewing of an object field, said device comprising: a) an optical means for focusing an image of said object field onto a focal plane, b) an eyepiece means for viewing said image focused onto said focal plane, c) a fluorescent Iayer located at said focal plane for converting invisible light from said object field into visible light.

25. A device as in Claim 1 wherein said photoactive Iayer means comprises a material means for scattering light as a function of said light input intensity.

26. A device as in Claim 25 wherein said light scattering material means comprises a polymer stabilized liquid crystal.

27. A device as in Claim 25 wherein said light scattering material means comprises a polymer-dispersed liquid crystal.

28. A device as in Claim 25 wherein said light scattering material means comprises a liquid crystal dispersed polymer also called liquid crystal gel.

29. A device as in Claim 1 wherein said photoactive Iayer means comprises a material means for reflecting light as a function of said light input intensity

30. A device as in Claim 29 wherein said reflective Iayer comprises a transparent electrode Iayer a liquid crystal a photoconducting material an electrode Iayer.

31. A device as in Claim 30 wherein said photoactive Iayer comprises a dielectric mirror.

32. A device as in Claim 30 wherein said dielectric mirror is semitransparent.

33 A device as in Claim 1 wherein the magnification is other than unity.

34. A device as in Claim 1 wherein said image is intentionally distorted.

35. A device as in Claim 1 wherein said photoactive Iayer comprises a photoconductor material.

36. A device as in Claim 1 , a multiplicity of which arranged in array formation.

37. A device as in Claim 1 wherein said device comprises an optical filter for preventing harmful radiation from damaging sensitive materials in the antiglare device.

38. A device as in Claim 5 and further comprising at least one pleochroic dye.