Method for design and manufacturing of optics for holographic sight

Abstract

A method for design and fabrication of holographic optical elements for a compact holographic sight is proposed. The method includes use of ray-trace software to design holographic elements having optical power using an intermediate hologram with parameters obtained through minimization of the merit function defining image quality.

Claims

1. An optical device comprising a light guide plate, two holograms secured to the light guide plate, a reticle or microdisplay placed on the light guide plate, a damped least square optimized intermediate holographic element, and at least one LED module in the vicinity of the light guide plate.

2. The optical device of claim 1 further comprising a diffuser.

3. The optical device of claim 1 wherein the light guide plate comprises glass, polycarbonate, acrylic, or mixtures thereof.

4. The optical device of claim 1 wherein the light guide plate comprises a thickness in the range of 3 to 6 mm.

5. The optical device of claim 1 wherein the light guide plate comprises a unitary body or a body comprised of a plurality of bodies.

6. The optical device of claim 1 wherein the light guide plate comprises a single material or a plurality of materials.

7. The optical device of claim 1 wherein the light guide plate comprises a reflective coating on at least one surface.

8. The optical device of claim 7 wherein the coating comprises silver metal.

9. The optical device of claim 1 wherein the light guide plate comprises a tint.

10. The optical device of claim 1 wherein the light guide plate comprises the two holograms on a same surface of the light guide plate or an opposite surface of the light guide plate.

11. The optical device of claim 1 wherein at least one of the holograms comprises a holographic element having optical power.

12. The optical device of claim 1 wherein one of the holograms comprises a holographic lens and the second of the holograms comprises a holographic grating.

13. The optical device of claim 1 wherein the two holograms comprise Bragg holograms.

14. The optical device of claim 1 wherein the two holograms are recorded with lasers of at least three different colors.

15. The optical device of claim 1 wherein the holograms are either reflective or transmissive or a combination thereof.

16. The optical device of claim 1 wherein the at least one LED comprises three LEDs comprising Blue, Green, and Red lighting.

17. The optical device of claim 1 comprising more than one LED and a multiplexed hologram.

18. The optical device of claim 1 further comprising a mirror.

19. The optical device of claim 1 wherein the reticle comprises an image of one color or multiple images of one or multiple colors displayed simultaneously.

20. The optical device of claim 1 wherein at least one hologram is recorded using a divergent spherical wavefront and a collimated wavefront or a collimated wavefront and a wavefront generated by the damped least square optimized intermediate holographic element.

21. The optical device of claim 1 comprising an optical sight, a holographic sight, or a weapon sight.

22. The optical device of claim 1 wherein at least one of the holograms is laminated onto a thin substrate that is attached to the light guide plate.

23. The optical device of claim 1 wherein the thin substrate and the light guide plate are substantially transparent.

24. The optical device of claim 1 wherein the light guide plate comprises a first transparent region spanning the surface of one of the holograms; a second transparent region spanning a surface of the other hologram; a third transparent region spanning a surface opposite to that of the second transparent region corresponding to a field of view; and a transparent volume throughout the light guide plate wherein other surfaces are opaque.

25. The optical device of claim 1 wherein the reticle or microdisplay is placed on either side of the light guide plate.

26. The optical device of claim 1 wherein the LED comprises a light conditioning optic.

27. The optical device of claim 1 wherein a switch is incorporated on the LED to permit switching between colors of light.

28. The optical device of claim 1 wherein the LED comprises a narrow-band emission in the range of about 20-25 nm FWHM.

29. The optical device of claim 1 wherein the reticle or microdisplay is placed on a same side of the light guide plate as a hologram.

30. A method of designing and recording a holographic optical element having optical power comprising using an intermediate hologram and a ray-tracing technique with dampened least squares optimization, which minimizes merit function and optimizes image quality wherein the holographic optical element is recorded with lasers of three different colors.

31. The method of claim 30 wherein a flexible film is used as an index matching material.

32. The method of claim 31 wherein a flexible film comprises a static cling vinyl material.

33. The method of claim 30 further comprising the use of an absorption liner comprising a black polyester or orange dyed polyester material as a top liner.

34. The method of claim 30 wherein the intermediate hologram is recorded by the ray-tracing technique and a final hologram is recorded by a collimated wavefront and a wavefront generated by the intermediate hologram.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram of optical portions of one operative substrate-guided holographic sight;

(2) FIG. 2 is a ray-trace design of substrate-guided holographic sight, holographic lens 214 is recorded using a collimated wavefront and a divergent spherical wavefront, wavelengths: 0.532 m, 0.525 m, 0.510 m;

(3) FIG. 3 is a ray-trace design of a holographic sight using transmissive-type holographic elements.

(4) FIG. 4 is a ray-trace design of a holographic sight using reflective type holographic elements.

(5) FIG. 5 is a spot diagram showing image quality for the ray-trace design of FIG. 2, fields-of-view are: 0 deg, 0.6 deg, +0.6 deg, wavelengths: 0.532 m, 0.525 m, 0.510 m;

(6) FIG. 6 is a collimated wavefront used in recording holographic lens 214;

(7) FIG. 7 is a ray-trace for recording holographic lens 214 using an intermediate hologram; and

(8) FIG. 8 is a spot diagram showing image quality for the ray-trace design of FIGS. 4 and 5, fields-of-view are: 0 deg, 0.6 deg, +0.6 deg, wavelengths: 0.532 m, 0.525 m, 0.510 m.

(9) FIG. 9 is a ray-trace design showing use of a micro display.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) In the following, unless otherwise stated, the term recorded or recording refers to the fabrication of a holographic element.

(11) Although the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described presently preferred embodiments with the understanding that the present disclosure is to be considered as an exemplification of the invention and is not intended to limit the invention to specific embodiments illustrated.

(12) It is to be further understood that the title of this section of the specification, namely, Detailed Description of the Preferred Embodiments relates to a rule of the United States Patent and Trademark Office, and is not intended to, does not imply, nor should be inferred to, limit the subject matter disclosed herein or the scope of the invention.

(13) The method of the subject invention comprises a design for the optics of a see-through holographic weapon sight, with the optical parameters comparable to optical sight based on common optics, with performance in terms of brightness (luminance), contrast, absence of speckle and scattered light that degrades the reticle image, absence of parallax, the number of components used, weight, and cost in a manner that exceeds present optical sights that are based on optics common in the art.

(14) Referring to FIG. 1, a substrate-guided holographic sight 110 of the subject invention has a first hologram 112 and a second hologram 114 either laminated directly to a substrate 116 or, alternatively, laminated onto thin (1 mm) substrates 113 that are attached to the substrate 116. The substrates 113 and 116 are substantially transparent in at least a portion thereof, but may be also entirely transparent in the visible spectrum range (400 nm-700 nm). The substrate 116, or plate, can be made from a number of materials. For example, the transparent portions of the plate 116 can be made of glass, polycarbonate plastic or acrylic plastic. Such a plate 116 is at least operative when having a thickness of the 3-6 mm, but can also be operative at other thicknesses. The external surface of the plate 116 should have a first transparent region 118 (from the reticle side only, the other side can be opaque in the first region) for accepting a transmitted image of the reticle, a second transparent region 120 for transmitting the accepted image, and a third viewing region 122 that permits viewing through the entire plate, and a transparent volume 124 throughout the substrate along with the entire path from where the transmitted image is accepted to where the accepted image is transmitted. All of the transparent regions may overlap with each other, and the substrate is not restricted from having transparent regions or volumes that are larger than mentioned. Substrates 113 can be made from, e.g., optical quality soda-lime glass such as the glass used for manufacturing liquid crystal displays and supplied, e.g., by Corning, and attached to the substrate 116 using a UV-curable optical glue manufactured, e.g., by Norland Products. Alternatively, they can be made of optical quality plastic material known in the art.

(15) The substrate 116 is depicted in the figures as a single, unitary body of a single material. However, the substrate 116 may also comprise a plurality of bodies made of a single or a plurality of materials. A person of ordinary skill in the art will be capable of using ray-tracing software to determine whether the particular configuration of materials and bodies will serve to transmit the accepted image to where it can be transmitted to a viewer.

(16) The substrate 116 as depicted is an uncoated unitary body. As such, the accepted image is conveyed to the region 120 where the image is transmitted out of the substrate 116. This conveyance may be done directly, without internal reflections by the accepted image being conveyed to the transmission area in a straight line. This conveyance may also be done by internal reflections. One way to achieve internal reflection is to coat the substrate at the locations where reflection is required with a reflective material, many of which are known to those of ordinary skill in the art. An evaporated layer of silver is an example of a coating 126, although the reflective layer may be applied by any means and may be of any composition that is functional.

(17) Another way to achieve internal reflection is by total internal reflection (TIR). In this case, the substrate must either have an index of refraction, relative to the environmental medium, sufficient to internally reflect the light of the accepted image. Total internal reflection is especially preferred for reflections that occur near the portion of the substrate 116 where the accepted image is transmitted out of the substrate 116. For example, for an air-acrylic interface, .sup.TIR=sin.sup.1(1/1.49)=42.2.

(18) Transparent means that the substrate 116 is capable of permitting light through to allow a shooter to receive and interpret the image of the reticle and to see the target. Accordingly, the substrate 116 may be tinted or have other modifications that do not render the device inoperative. For example, any material will have some amount of diffusion from imperfections or inclusions, but the diffusion should not be so great as to prevent the acceptance, conveyance, and transmission of the image by the substrate 116.

(19) Referring further to FIG. 1, the first transparent region 118 (accepting a transmitted image) faces first hologram H1 112; the second transparent region 120 (transmitting the accepted image) faces second hologram H2 114; the third transparent region is at least as large as the field of view 128 and includes the surfaces on both sides of the substrate and the volume in between.

(20) The first and second holograms 112 and 114 can be placed either on the same side of the substrate, or on opposite sides. Holograms H1 and H2 in fact are holographic optical elements (HOE), either or both of them can have optical power. The preferred embodiment has at least one with optical power.

(21) In one embodiment, first hologram H1 112 has optical power. As such, first hologram H1 112 is a holographic lens. In that embodiment, second hologram H2 is a holographic grating 112 with no optical power.

(22) A distinctive feature of these holograms is their capability to couple the light in the substrate at angles larger than or equal to total internal reflection (TIR) angle of the substrate, and to out-couple the light that propagates along the substrate.

(23) Another distinctive feature of these holograms 112, 114 is that they are Bragg holograms. This means that they diffract the light in single diffraction order. Hence their diffraction efficiency can be very high (theoretically 100%). This results in very high light throughput of the optical system. Contrary to this, other see-through sights are based on beam combiners (semitransparent or dichroic mirrors) and have much smaller light throughput.

(24) Another distinctive feature of holograms 112, 114 is that they are recorded with lasers of, e.g., three different colors (e.g., Blue at 457 nm, Green at 532 nm and Red at 647 nm), thus providing a means of generating an image of the reticle in either color, depending on shooter's preference and the color and tint of the background scene.

(25) The substrate-guided holographic see-through sight 110 operates by using substrate-guided wave (SGW) holograms. Some basic information about SGW holograms and theory developed is presented in H. Qiang and J. A. Gilbert, Diffraction Properties of Substrate Guided Wave Holograms, Optical Engineering, col. 34, no. 10, p. 2891, 1995, also on Kogelnik's coupled wave theory. H. Kogelnik, Coupled Wave Theory for Thick Hologram Gratings, The Bell System Technical Journal, vol. 48, no. 9, 1969.

(26) Holographic elements 112 and 114 can be either reflective or transmissive, as shown in FIGS. 3 and 4, or a combination of reflective and transmissive type. The type of the holographic element (reflective or transmissive) is defined by a corresponding experimental/manufacturing recording geometry known to those skilled in the art. These geometries yield better adjustments to the specific weapon, more convenient eye position and higher resolution and wavelength selectivity for a reflection hologram.

(27) The transparent plate 130 with the reticle implemented on it is illuminated by the LED module 140 placed in the vicinity of the plate 130. The LED module 140 comprises, at least, one low power LED (20 mA driving current value) and can have a light conditioning optic. The LED light can be either Blue, Green or Red, or of any other suitable color comprising three LEDs that is appropriate for target aiming. For LEDs of different colors (e.g., Blue, Red and Green), a switch 150 is incorporated on the LED module that allows a shooter to switch between three colors depending on the background scene. E.g., for brown-red backgrounds (desert type scenery) Green illumination can be chosen. For green backgrounds (grass, trees), Red illumination can be chosen, etc. Thus, substrate-guided holographic sight provides a better, improved visibility of the aiming reticle on various backgrounds as compared to the systems known in the prior art. Preferably, an LED(s) with narrow-band emission is used, 20-25 nm FWHM.

(28) If more than one LED is used, multiplexed holograms are used as known by those skilled in the art. Holograms are recorded with a larger angle between recording beams (preferably reflection holograms) to avoid crosstalk between reticle images retrieved with different holograms. The condition of avoiding crosstalk is to satisfy the difference in angles of beams diffracted on wrong holograms so they do not intersect in the image area, as known by those skilled in the hologram multiplexing art.

(29) FIG. 2 shows an example of the actual ray-trace for substrate-guided holographic sight. The rays are traced from the position of the shooter's eye towards the reticle, field-of-view 1.2 deg. The reticle can be placed on either side of the substrate-guided holographic sight substrate. For instance, on FIG. 2 it is placed on the same side as the viewing holographic element. For achieving a more compact packaging, it can be placed on the side of the substrate which is opposite to the one where a viewing holographic element is placed.

(30) A flat fold mirror can be placed in between the reticle 230 and holographic lens 214 to provide a better over-all compactness of the weapon sight.

(31) FIG. 5 shows the image quality (geometrical spot size) for the ray-trace of FIG. 5. A rather substantial amount of spherical aberration is visible on the spot diagram. For the design shown on FIG. 2, the holographic lens 214 is recorded with ray-tracing software using a divergent spherical wavefront and a collimated wavefront. These wavefronts are not shown on FIG. 2, instead, a resultant ray-trace through existing HOEs is shown.

(32) To improve the image quality, a method is developed that comprises recording an intermediate holographic element in a ray-trace software (e.g., in Zemax or in Code V), so that a final holographic lens 214 is recorded by a collimated wavefront and a wavefront generated by the intermediate holographic element. Such procedure offers such advantages as it is more robust (always converges to a solution) and more flexible (i.e., applicable to a variety of holographic element design tasks) compared to a traditional analytical recursive technique proposed, e.g., in [13Ya. Amitai, A. Friesem, I. Shariv, Planar Holographic Optical Device for Beam Expansion and Display, U.S. Pat. No. 6,169,613 B1 (2001)].

(33) FIGS. 6 and 7 show wavefronts that are used for recording with ray-trace software the HOE 214: FIG. 6a collimated wavefront and FIG. 5a wavefront generated by an intermediate hologram 515. Coordinates of the two points that are used in recording hologram 515 with ray-trace software are variables for the merit function that also includes surface tilts and decenters as variables as well. Point 449 is a point source, surface 444 represents a paraxial surface that can be implemented in practice, e.g., using a high-quality achromatic doublet of the same focal length as the paraxial lens manufactured, e.g., by JML Optical; element 414 is a plane for recording of the hologram 214. Intermediate hologram 515 is recorded with ray-trace software using a point source 550 and a point at infinity (not shown); paraxial lens 545 represents, e.g., a high-quality achromatic doublet which is of the same focal length as the paraxial lens. FIG. 8 shows spot diagram for substrate-guided holographic sight that includes hologram 214 recorded using the described method.

(34) A sight with a single reticle can further be improved with a dynamic overlay image by replacing the reticle with a micro display 217, as shown in FIG. 9.

(35) The described embodiments of the method for design and fabrication of the holographic optics for the weapon sight refer to methods and techniques to make master holograms. The master holograms need to be replicated. This can be done, e.g., using contact copying of volume (thick) holographic optical elements by means of a single laser beam illumination, known by those skilled in the art, with roll-to-roll web process. A flexible film such as static cling vinyl as an index matching material can be used. The advantage of this material is that it will suppress the recording of spurious holograms and will allow dry contact copying.

(36) Another important factor in copying is that the photopolymer material requires an absorption liner such as black polyester or orange dyed polyester (available, e.g., from CPFilms) as a top liner to avoid recording spurious holograms.

(37) The foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present inventions. It is to be understood that no limitation with respect to the specific embodiment illustrated or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims. All of the references that follow are incorporated by reference as if set forth fully herein.