OPTICAL DISPLAY SYSTEM, METHOD, AND
APPLICATIONS
CROSS-REFERENCE TO RELATED APPLICATIONS
This nonprovisional application claims priority to provisional application No. 62/590,679, entitled Optical Display System, Method, and Applications,” filed 1 1 /27/2017 by the same inventors.
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Funding for the invention was provided by the AFOSR under project number FA9550-14-1 - 0279. The government has certain rights in the invention.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates, generally, to optics. More specifically, it relates to the field of augmented reality devices in which the displayed image is overlaid to the environment with an optical see- through apparatus.
2. Brief Description of the Prior Art
Near-eye displays (NEDs) utilize magnifying optics to magnify and project the display image to a viewable size/distance. See-through type NEDs are also referred to as augmented reality (AR) displays. For these types of NEDs, the viewer can see the displayed image and the environment at the same time. Therefore, in addition to magnifying optics, AR systems require combiners to realize the combination of display images and the real environment. Combiners can be, e.g., simple polarizing/non-polarizing beam splitter cubes, partial reflective concave mirrors, or holographic grating (HG) coupled waveguides. For the former two, a partially reflecting component is placed physically at an angle such that the displayed light can be reflected at an angle toward the viewer without blocking the environment. However, this type of device has a trade-off between form-factor and field of view. An example of this kind of device is Google Glass™ in which a small beam splitter is used as a combiner, resulting in a small form-factor with narrow field of view (FOV). A counterpart to this kind of device is Meta 2™ in which a large, partially reflective, off-axis concave mirror is used, resulting in large form-factor with wide FOV.
For AR devices with HG-coupled waveguides, a thin film HG serves as an in-coupled grating to guide the collimated displayed light into a thin waveguide, and then an out-coupled grating deflects the light toward user’s eye. This allows a slim design and thus is an advantageous approach for AR devices. Common HGs are made of isotropic materials with alternative slanted layers of high and low refractive index. The angular bandwidth for a single HG is determined by the index contrast. HGs based on dichromated gelatin can provide an index contrast as high as 0.15; however, this type of HG is sensitive to humidity, temperature, and other environmental conditions, which makes it extremely unstable and may cause defects in grating structure. Nowadays, most display applications choose photo-polymers as record media with index contrast around 0.035. As a result, the deflection has a high angle/wavelength selectivity. This allows almost 100% transmittance of the environment light; however, this also implies a low efficiency and a low acceptance angle for the display light, resulting in a small field of view (<5°) and a higher energy consumption. To have a larger field of view while maintaining a thin profile, multiple layer HGs are exploited. This not only reduces the transmittance but also greatly increases the cost of one device. HGs based on surface-relief structures are exploited in Microsoft Hololens™. This type of HG is made through imprinting to create a slanted polymer structure. Since the contrast between polymer and air is large, this type of HG has superior performance compared to photo-polymer-based HGs. However, surface-relief HGs are challenging to fabricate and therefore the cost remains very high compared to other solutions.
Another issue with the above-mentioned HGs is their polarization insensitivity. Since the HGs exploited are polarization independent, on-axis reflective mirrors cannot be exploited as magnifying optics as in the case of Google Glass™. This increases the design complexities especially when the target form-factor is small.
Yet another issue with the present AR NEDs is the mismatched distances between the display image the environmental object, preventing the user from simultaneously focusing on both the display and the real environmental object.
Accordingly, what is needed is a system and method that provides NEDs with increased optical efficiency, simple optical magnifying, and the ideal small form-factor, while also controlling the display distance so that the user can focus on both the display image and the real environmental object. However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.
All referenced publications are incorporated herein by reference in their entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. The present invention may address one or more of the problems and deficiencies of the prior art discussed above. However, it is contemplated that the invention may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the claimed invention should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.
BRIEF SUMMARY OF THE INVENTION
The long-standing but heretofore unfulfilled need for improved NEDs is now met by a new, useful, and nonobvious invention.
The novel optical display system includes an image generator, a reflector, and an image output assembly. The image generator is adapted to generate a polarized image and emit the polarized image towards the reflector. In an embodiment, the image generator includes a light source that emits light towards a polarized beam splitter, which in turn directs polarized light to a reflective, preferably liquid, display. The reflective display emits the polarized image towards the reflector. In an embodiment, the image generator is liquid crystal on silicon displays (LCoS), micro liquid crystal display (LCD), micro-organic light emitting diode displays (OLED), digital light processor (DLP), or micro light emitting diode displays (LED). Moreover, the polarized image may be linearly polarized or circularly polarized.
The reflector is optically arranged to reflect light from the polarized image back towards the image generator. In an embodiment, the reflector is a concave reflector.
The image output assembly includes a polarization volume grating, a waveguide, and an output grating. The polarization volume grating is disposed between the image generator and the reflector, wherein the polarization volume grating is adapted to selectively deflect the light reflected from the reflector. The waveguide is disposed to receive light deflected by the polarization volume grating, wherein the waveguide internally reflects the received light to an output grating. The output grating is adapted to deflect the internally reflected light towards an output side of the optical display system, producing an output image to be viewed by a user.
In an embodiment, the waveguide and output grating are transparent to allow background light to reach the user. Moreover, the waveguide may be a total internal reflector. An embodiment further includes a tunable lens disposed between the image generator and the reflector. The tunable lens includes electrically-controllable optical power to control magnification and display distance.
An embodiment also includes a polarization film disposed between a user and the output grating. The polarization film adjusts a polarization state of the output image to result in uniform light output. In an embodiment, the output grating is either a holographic grating, a surface- relief grating or a polarization volume grating.
An embodiment of the present invention includes a secondary image output assembly, wherein the secondary image output assembly includes: a secondary polarization volume grating disposed between the image generator and the reflector, wherein the secondary polarization volume grating is adapted to selectively deflect a specific spectrum of the light that is reflected from the reflector; a secondary waveguide disposed to receive light deflected by the secondary polarization volume grating, wherein the waveguide internally reflects the received light to a secondary output grating; and the secondary output grating adapted to deflect the internally reflected light towards the output side of the optical display system.
An embodiment also includes a quarter-wave-plate disposed before the reflector. A quarter- wave-plate disposed before the reflector can convert the polarization of light, and so it will be promoted to the correct polarization state, and the majority of the light will be accepted by the polarization volume grating.
An embodiment of the present invention includes a symmetric setup is disposed for a user’s second eye to provide a binocular display.
An aspect of the invention is an optical display system. In an exemplary, non-limiting embodiment the optical display system includes a display panel whose polarization is defined by a polarizer (e.g., left-handed circularly polarized). The display light passes through polarization-dependent reflective polarization volume grating (e.g., deflects only right-handed circular polarization) in the first passage. Upon reflection and collimation by a concave mirror disposed optically on-axis with respect to the display, it changes polarization and is then deflected by the reflective polarization volume grating into the waveguide. The display light is guided toward the user’s eye and then deflected again by the output grating to emit the image out of the waveguide and enter the user’s eye.
These and other important objects, advantages, and features of the invention will become clear as this disclosure proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the disclosure set forth hereinafter and the scope of the invention will be indicated in the claims. BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
Fig. 1 is a top schematic plan view of an optical display system according to an exemplary augmented reality application embodiment of the invention.
Fig. 2 is a top schematic plan view of an optical display system according to an exemplary augmented reality application embodiment of the invention.
Fig. 3 is a top schematic plan view of an optical display system according to an exemplary augmented reality application embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part thereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.
As used in this specification and the appended claims, the singular forms“a,”“an,” and“the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term“or” is generally employed in its sense including “and/or” unless the context clearly dictates otherwise.
The present invention includes a system and method that provides NEDs with increased optical efficiency and simple optical magnifying in an ideal small form-factor. An embodiment of the present invention is also adapted to control the display distance so that the user can focus on both the display image and the real environmental object. An embodiment utilizes reflective polarization volume gratings (PVGs) as a waveguide-coupler which allows for high optical efficiency, simple optical magnification, and an ideal small form-factor. By utilizing a lens with electrically-controllable focus, the system can control the display distance so that the user can focus on both the display image and the real environmental object.
Referring to Fig. 1 , an embodiment of the invention includes an image generation module, which is comprises light source 1 , beam splitter 2, and reflective display 3. Light source 1 emits light 12 towards beam splitter 2 and beam splitter 2 deflects light 13 towards reflective display 3. Reflective display 3 then outputs light 14 back in the opposite direction where it eventually passes through reflective polarization volume grating (PVG) 4 (also known as a“polarization selective grating”) when moving away from reflective display 3. Reflective display 3 is preferably a programmable/controllable (virtual) image-generating component adapted to generate a display image that is preferably polarized.
Light 12 emitted from light source 1 is adapted to be linearly or circularly polarized through polarizing beam splitter 2. Light source 1 emits light 12 through a reflective polarizer for higher optical efficiency. Most of light 12 from light source 1 is reflected toward the reflective display 3, which produces the display content. The light output 14 from reflective display 3 has an opposite polarization as that of light 13 so that, on the second pass through polarizing beam splitter 2, a relatively larger amount of the display light 14 passes through beam splitter 2.
In an embodiment, reflective display 3 is a liquid crystal display, such as a liquid crystal on silicon display (LCoS) display. It is also considered that reflective display 3 may be a micro liquid crystal display (LCD), a micro-organic light emitting diode displays (OLED), a digital light processor (DLP), a micro light emitting diode display (LED), or any other type of display known in the art. An embodiment may use a backlit type display or immersive display rather than the reflective display, which may not require light source 1 and beam splitter 2. These alternative displays would direct the display content light 14 towards reflective polarization volume grating (PVG) 4.
Light 13 is specifically polarized by reflective display 3 such that light 14 has a specific polarization state and PVG 4 is designed to ensure that a majority of light 14 passes through reflective PVG 4 on the first pass towards reflector 5. To explain further, PVG 4 (e.g. a liquid crystal grating) can deflect certain polarizing light while light of the opposite polarization will transmit through PVG 4 with minimal defection. For example, an embodiment of PVG 4 is designed to redirect/deflect right handed circular polarized light. In this case, light 14 is characterized by left-handed circular polarization and thus a majority (about 90%) of light 14 will pass through PVG 4 when headed towards reflector 5. Light 14 is reflected by, a preferably concave, reflector 5 producing light 15 which is circularly polarized in the right-hand direction. Thus, PVG 4 redirects/deflects the right handed circularly polarized light 15.
While the provided example characterizes light 14 as being circularly polarized in a left-hand direction and PVG 4 being designed to redirect/deflect right handed circular polarized light, an embodiment may be designed such that light 14 is circularly polarized in a right-hand direction and PVG 4 is designed to redirect/deflect left-handed circular polarized light. In addition, an embodiment may use linearly polarized light with a PVG designed to deflect linearly polarized light reflected from reflector 5.
In an embodiment, reflective PVG 4 enables simple optical magnification with a concave mirror. Reflective PVG 4 can be made to selectively deflect linear polarized light as explained in US6567573 B1 (also known as holographic polymer-dispersed liquid crystal or H-PDLC) or to selectively deflect circularly polarized light, as reported in Y. Weng, D. Xu, Y. Zhang, X. Li, and S. T. Wu,“A polarization volume grating with high efficiency and large diffraction angle,” Opt. Express 24(16), 17746-17759 (2016).
As previously explained light 14 is reflected by concave reflector 5 and the polarization state is flipped such that the reflected light from concave reflector 5 will be deflected by reflective PVG 4. While it is considered that any reflector may be used, reflector 5 is preferably concave and preferably collimates light 14 to produce reflective light 15.
Upon deflection by the reflective PVG 4, light 16 enters waveguide 6 and is guided to the viewing region. Waveguide 6 may be comprised of any type of transparent material, e.g. glass or plastic material, and is preferable a total internal reflection waveguide. Transparent material causes total internal reflection which is determined by the material’s total refractive index. Preferably waveguide 6 will comprise of a material having a higher refractive index, e.g. a range of refractive index may be between 1 .5 and 1 .8.
The viewing region is established by reflective grating 8, which is intended to reside in front of user’s eye 9. Grating 8 is adapted to deflect and distribute light 1 6 into a wider region as depicted by light 17. Preferably the grating angle of grating 8 is equivalent to the grating angle in PVG 4, but equivalent grating angles are not necessary for the device to operate.
As depicted, grating 8 produces four light rays 16. The number of output light rays 17, however, may be adjusted as deemed necessary. Grating 8 is also designed to allow transmission of background light 1 1 , which also passes through waveguide 6 and film 7 to be seen by a user. For example, grating 8 may be designed to be low efficiency for circularly polarized light in the right-handed direction and have zero efficiency for circularly polarized light in the left-handed direction. As such, about 80% of background light 1 1 passes through the system to be seen by the user.
Upon deflection of light 16 by grating 8, light 17 passes through polarization film 7. Film 7 helps manage the polarization of light 17. When light 16 enters waveguide 6, the polarization is defined, but that polarization can change as light 16 travels though waveguide 6. In addition, the deflection of light 16 by grating 8 weakens the light and produces several reflections with nonuniform intensity. Film 7 controls the polarization to produced uniform output light 17, which is viewed by user’s eye 9. In an embodiment, polarization film 7 is a liquid crystal film. The specific characteristics and type of polarization film may be adjusted based on the specific polarization of the light employed by the system.
An embodiment further includes tunable lens 10. Lens 10 is not limited to a specific shape and is preferably electrically-controllable for adjusting the optical power. An embodiment specifically uses a liquid lens. The liquid crystal axis can be rotated to adjust the focus of the lens. Lens 10 is preferably disposed after polarizing beam splitter 2 such that the display image distance can be electrically controlled. An embodiment of the present invention is a binocular display. Essentially, the device in Fig. 1 is symmetrically setup for the user’s other eye.
Referring now to Figs. 2 and 3, the device may include more than one image output assembly. The image output assembly includes a waveguide, a PVG, and an output grating. As depicted in Figs. 2 and 3, a plurality of waveguides 6, PVGs 4, and output gratings 8 are used to improve the device’s color coverage. The color is based on polarization or grating. So, one waveguide, PVG, and output grating will not output light 17 in the full color spectrum. Additional waveguides, PVGs, and output gratings provide greater color coverage. Fig. 3, for example includes three image output assemblies, resulting in three waveguides, PVGs, and output gratings to cover the RGB color spectrum. Flowever, more than three image output assemblies may be used.
Referring now specifically to Fig. 2, an embodiment includes two waveguides for two different spectral regions, indicated with suffixes‘A’ and Έ’. By capturing and outputting light with different spectral regions, the device is able to output light 17 having a greater color spectrum. The depicted embodiment includes the image generation module, which comprises light source 1 , beam splitter 2, and reflective display 3. The image generation module emits light 14 towards reflector 5. The image generation module, however, may be an immersive display or backlit display that emits light image 14.
Light 14 has a specific polarization state such that a majority of the light passes through input reflective PVGs 4A, 4B on the first pass. Light 14 is collimated with concave reflector 5 and the polarization state is flipped such that reflected light 15 from concave reflector 5 will be deflected by input reflective PVGs 4A, 4B.
PVGs 4 A, 4B are each designed to deflect a specific spectrum of light 15. For example, PVG 4A may deflect green light into waveguide 6A, and PVG 4B may deflect red and blue light into waveguide 6B. As depicted, PVGs 4A, 4B respectively deflect light 16A, 16B (each of a different spectral region) into waveguides 6A, 6B. Waveguides 6A, 6B guide light 16A, 16B to the viewing region.
Films 7A, 7B, which are preferably liquid crystal films, are disposed at the exit surface of waveguides 6A, 6B, respectively to manage the polarization state and output uniform light 17 when deflected by the output gratings 8A, 8B and received by the viewer’s eye 9.
A multi-waveguide system preferably also includes tunable lens 10 with electrically-controllable optical power. Lens 10 is preferably disposed after the polarizing beam splitter 2, but before the PVGs 4A, 4B such that the display image distance can be electrically controlled. To allow binocular display, a symmetric setup of the depicted device is advantageously utilized for the other eye. Referring now to Fig. 3, an embodiment of the present invention includes three waveguides, PVGs, and output gratings for three different spectral regions, indicated with suffixes‘A’, Έ’ and‘C. As previously explained, light 14 has a specific polarization state such that a majority of the light passes through input reflective PVG 4A, 4B and 4C on the first pass. The light is collimated with concave reflector 5 and the polarization state is flipped such that the reflected light 15 from concave reflector 5 will be deflected by the input reflective PVG 4A, 4B and 4C. Upon deflection by the input reflective PVGs 4A, 4B and 4C, different spectral regions of light 16A, 16B, 16C (for example, red, green and blue light) enter waveguides 6A, 6B and 6C and are guided to the viewing region. Liquid crystal films 7A, 7B, and 7C are disposed to manage the polarization state to producer uniform light output 17 when deflected by the output gratings 8A, 8B and 8C and received by viewer’s eye 9. Advantageously, tunable lens 10 with electrically-controllable optical power can be disposed after the polarizing beam splitter such that the display image distance can be electrically controlled. To allow binocular display, a symmetric setup is advantageously utilized for the other eye.
An embodiment of the present invention may also include a quarter-wave-plate disposed before reflector 5. A quarter-wave-plate disposed before reflector 5 can convert the polarization of light 14 to the correct polarization state resulting in a majority of the light 15 being accepted and deflected by PVG 4.
The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.