Microsoft patent proposes near-eye display with one-dimensional optical pupil expansion using projector arrays and waveguides

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(XR Navigation Network March 25, 2024) Near-eye display systems use a variety of imaging optics to project and redirect the display image to the user's eye. One challenge in the described field is to present the display image in a sufficiently large optical pupil. In display applications, this means a larger viewing window.

One solution is to use multiple projectors to directly provide a larger optical pupil. However, the number of projectors can be prohibitively high depending on the required resolution, field of view, and window of view. The industry has considered Fresnel lenses and Pancake optics, but both methods are relatively bulky and opaque, making them more suited to VR or video MR applications than optical AR applications.ARApplications.

One solution is to utilize a single projector and optical pupil expander to provide a sufficiently large optical pupil. This requires a one-dimensional outgoing optical pupil expander based on a large projector. However, the size and weight of the system may be unacceptable to the user.

More compact solutions use diffractive or reflective structures to provide two-dimensional optical pupil expansion. In real-world display applications, where high color uniformity and a large field of view are required, achieving two-dimensional optical pupil extension is a challenge that requires balancing size, cost, performance and manufacturability.

For example, designing and testing appropriate diffractive structures may involve modeling and simulating the millions of grating interactions that will occur within the waveguide. For waveguides with three separate grating regions, the number of calculations and the difficulty of fabrication lead to an extensive, time-consuming design and testing process.

Another disadvantage of this system is the optical efficiency. More complex grating structures lead to an increase in grating interactions and a decrease in total optical efficiency. Additionally, the propagation and diffraction of light within the waveguide can result in multiple light paths propagating to the same point of the coupler grating, resulting in interference, as evidenced by output intensity variations and color degradation.

鉴于上述观察结果，Microsoft在名为“Near-eye display systems utilizing an array of projectors”的专利申请中，微软提出了利用投影仪阵列和波导进行一维光瞳扩展的近眼显示器。

As shown in FIG. 1, the system 100 includes an array of projectors 102 in communication with the controller 103. Different configurations of projectors may be used depending on the application. For example, a full color application may implement a plurality of monochrome projectors. In one embodiment, projectors implementing scanning elements such as a single two-dimensional scanning mirror or two one-dimensional scanning mirrors may be used to form an image. In other embodiments, a single one-dimensional mirror is used in conjunction with a row of LEDs.

The array of projectors 102 outputs image light 104 to the coupler 106, which couples the image light 104 into a total internal reflection (TIR) path within the waveguide 108. The array of projectors 102 may be arranged along a first dimension to provide image light 104 similar to optical pupil expansion in one dimension.

Accordingly, the waveguide 108 and coupler 106 may be designed to receive image light having an exit pupil extension performed in one dimension. For example, the coupler 106 may be extended or elongated to accommodate the expanded image light. In the described system 100, the projectors 102 are arranged in a row along the y-axis shown in FIG. 1. So the image light 104 is effectively expanded along the y-axis before coupling to the waveguide 108.

The coupler 106 may be implemented using a variety of different optical elements. For example, the coupler 106 may include gratings, prisms, and/or mirrors. The coupler 106 may be designed to have a relatively high efficiency of coupling the imaging light 104 to minimize light loss in the waveguide 108.

The image light 104 is coupled into the waveguide 108 and propagates in the TIR path until it interacts with the coupler 110. The coupler 110 may be implemented using a variety of different optical components. In various embodiments, the coupler 110 may include a grating and/or a partial reflector.

In the described system 100, the coupler 110 includes a series of partial mirrors designed to couple out a portion of the incident light while allowing the remaining portion to pass through. To help avoid significant dimming of the output light along the length of the coupler 110, the efficiency distribution of the coupler 110 may vary in the direction of light propagation. Since the total amount of incident light on the succeeding portion of the reflector decreases due to the coupled out portion of the preceding portion of the reflector, the succeeding portion of the reflector may be sequentially realized and arranged to have an increased efficiency profile so as to couple out a similar amount of light as the preceding portion of the reflector.

For a particular pixel traveling within the waveguide 108, the set of propagating rays will include rays that have complementary angles to each other. As a result, a particular ray may hit the coupler 110 at the wrong angle.Such rays can create noise in the waveguide, so this can be dealt with using a variety of methods, including designing the waveguide 108 and the optics 106, 110 so that the noise remains captured in the waveguide 108 or is absorbed at the end.

In each interaction with the coupler 110, a portion of the image light couples out, effectively replicating the image and expanding the optical pupil in the direction in which the image light 104 is traveling. Said array of projectors 102 and couplers 110 may be oriented to extend said exit pupil in a second dimension transverse to said first dimension.

In one embodiment, the second dimension is orthogonal to the first dimension. In the described system 100, image light 104 projected from the array of projectors 102 is effectively expanded by the array of projectors 102 along the y-axis, and then by the coupler 110 in the x-axis direction. Thus, when pointed at the user's eye 120, the coupler-out light 112 is expanded in two dimensions. The eye position that allows the user to see the image forms the viewport 122. the pupil dilation causes the viewport to increase in size.

FIG. 1 depicts a specific example near-eye display system for providing two-dimensional exit pupil extension, and various other configurations can be implemented depending on a given application. For example, the near-eye display may be designed to have a viewing window on the side of the waveguide opposite the projector array.

In the near-eye display system 200 shown in FIG. 2, the viewport 222 is located on one side of the waveguide 108 opposite the array of projectors 102. As shown, the waveguide 108 includes a coupler 210, the coupler 210 being designed and oriented to couple image light 104 output from the waveguide 108 on the side opposite the array of projectors 102.

As mentioned above, the coupler in and coupler out can be realized using different optical elements. In FIGS. 1 and 2, the coupler is a reflector and the coupler is a periodic structure with a partially reflecting mirror. In other embodiments, the coupler and/or coupler are realized as diffractive elements, such as surface relief gratings and holographic gratings.

FIGS. 3A-3C show waveguides with different types of optical elements as couplers in and couplers out. FIG. 3A shows an example waveguide 300 with a reflector implemented as a coupler 302 and a series of partial mirrors implemented as couplers 304. FIG. 3B shows an example waveguide 310 with a surface undulation grating implemented as an input 312 and output 314 coupler. FIG. 3C shows an example waveguide 320 with a holographic grating implemented as an input 322 and output 324 coupler.

In one embodiment, the couplers and couplers are different optical elements. For example, a waveguide may be realized with mirrors as couplers and surface relief gratings as couplers. Depending on the application, the different configurations will have their own advantages and disadvantages. For example, depending on the type of projector, dispersion introduced by the coupler and coupler may be an issue.

In one embodiment, the couplers and couplers are matched to correct for dispersion such that angular errors introduced by one coupler are canceled by the other coupler. The couplers may be matched using similar structures and/or grating vectors. In other embodiments, one or more additional optical elements are implemented to correct for dispersion.

The system described above can provide two-dimensional outgoing optical pupil expansion by designing waveguides for only one-dimensional outgoing optical pupil expansion. This design reduces the complexity of the waveguide, thereby reducing manufacturing difficulty and yield.

Systems for two-dimensional exit pupil expansion generally utilize a waveguide with three optical elements (a first diffractive element for coupling light into the waveguide, a second diffractive element for exit pupil expansion in the first dimension, and a third diffractive element for exit pupil expansion in the second dimension) while coupling light out of the waveguide.

Instead, the invention describes a waveguide designed to have a coupler for coupling in light expanded in the first dimension and a coupler for expanding light in the second dimension and for coupling the light out of the waveguide. Since the waveguide is designed to receive light that is efficiently expanded in the first dimension, intermediate optical elements for exit pupil expansion are not required for two-dimensional exit pupil expansion.

FIG. 4 shows a waveguide 400 for light expanded in one dimension.As shown in plan view, the waveguide 400 includes a coupler 402 and a coupler 404.Said coupler 402 is elongated to receive the image light expanded in the first dimension. In the waveguide 400 depicted in FIG. 4, the inputs and couplers 402, 404 are realized using diffraction gratings. Other optical elements such as prisms, mirrors, partial mirrors and reflection gratings may be used as appropriate for the application.

Microsoft notes that the invention describes near-eye display systems that provide architectures that advantageously allow for different manufacturing processes than other systems. For example, the projector used by the invention may be simpler and easier to manufacture than the individual high-specification projectors typically used in other near-eye displays.

For example, the projector array may include a single stack of lens arrays and a single display device. Alternatively, the one-dimensional out-of-pupil extension waveguide includes only two diffractive optical elements for two-dimensional out-of-pupil extension. This shortens the propagation path of the light and reduces the number of reflections within the waveguide. This allows for simpler fabrication and lower tolerances. Waveguides can be made of plastic rather than glass, which reduces material costs and allows for different manufacturing processes. For example, waveguides can be injection molded, allowing for a low-cost, high-volume manufacturing process. Plastic waveguides allow for different waveguide designs and functions at the same time.

Another advantage of using waveguides is that the optics are simpler, including achieving full color displays. In near-eye displays using diffraction gratings, full color can be achieved by utilizing a different grating layer for each individual RGB color. To reduce the number of grating layers, solutions based on multiplexing two or more gratings have been proposed in the industry. However, manufacturability and design complexity become a bigger issue.

This simplifies the design of optics by realizing one-dimensional optical pupil extension waveguides. For example, full color can be achieved in near-eye displays using multiple monochrome projectors. Using three monochrome projectors instead of one full-color projector increases the cost and complexity of the device. However, the optics of each projector are relatively simple. This avoids the need to correct for chromatic aberration compared to other methods.

For the color uniformity problem in diffractive waveguides, two-dimensional out-of-pupil expansion results in light taking multiple paths, which then produces interference. In a one-dimensional out-of-pupil extended waveguide, the light travels along a single path, which avoids interference and so produces better color uniformity.

Alternatively, a two-dimensional optical pupil expansion waveguide near-eye display would use two or even three separate waveguides to accommodate the red, green, and blue channels. A simple one-dimensional optical pupil expansion waveguide avoids the increase in size, cost, complexity, and weight.

FIG. 6 shows an example near-eye display system 600 that implements full color using monochrome projectors 602R, 602G, and 602B. As shown, the near-eye display system 600 includes monochrome projectors 602R, 602G, and 602B for projecting red light 604R, green light 604G, and blue light 604B, respectively, to the coupler.

In the described system 600, a set of dichroic mirrors 606R, 606G, and 606B are implemented as couplers. each of the dichroic mirrors 606R, 606G, and 606B is designed to couple light from a respective monochrome projector. For example, dichroic mirror 606G is designed to couple green light 604G from monochromatic projector 602G. green light 604G then propagates in a TIR path within waveguide 608 until it is coupled out of waveguide 608 via coupler 610. other color configurations may be implemented as appropriate depending on the specific application.

In one embodiment, a first projector is used to output light in the wavelength range of 600 nm-770 nm, a second projector is used to output light in the wavelength range of 495 nm-600 nm, and a third projector is used to output light in the wavelength range of 430 nm- 495 nm. In such an embodiment, the coupler is accordingly designed to efficiently couple the light from the projector.

In addition to using different optics for the coupler, different configurations in the placement of the optics can be realized at the same time. For example, implementing full color in a near-eye display system may include using multiple sets of monochrome projectors. In a particular configuration, each set of monochrome projectors may be placed at a different location relative to the waveguide.

FIG. 8 illustrates a near-eye display system 800 that implements full color using two sets of 802, 804 monochrome projectors located at opposite ends of a waveguide 806. The waveguide 806 includes two corresponding couplers 808, 810. in the depicted system 800, each of the two couplers 808, 810 includes a set of three surface relief gratings. The couplers 808, 810 couple light from the respective monochrome projector set to the same coupler 812, which couples the light out of the waveguide 806.

In one embodiment, a plurality of sets of monochrome projectors may be implemented as appropriate for the application. A first set of projectors is used to output light in the wavelength range of 600 nm-770 nm, a second set of projectors is used to output light in the wavelength range of 495 nm-600 nm, and a third set of projectors is used to output light in the wavelength range of 430 nm-495 nm.

In such an embodiment, the coupler is accordingly designed to efficiently couple light from the projectors. FIG. 9 illustrates the use of a plurality of monochrome projectors 900. As shown, the array of projectors 900 includes five sets of monochrome projectors. Each group of projectors is located in a different column to form a 5 x 3 projector array. As shown in FIG. 9, the projected image light is effectively spread out in the horizontal direction.

Figures 10A-10D show different arrangements of projector arrays. In systems using projector arrays, gaps between the projectors can create gaps within the viewport that can introduce intensity variations. In such cases, different arrangements may be used to minimize the gap between the projectors. FIG. 10A shows a looser arrangement. FIG. 10B shows a tighter arrangement.

FIG. 10C shows a packing arrangement in which the columns of the projector are offset from neighboring columns. Such a structure is unlikely to create gaps in the viewport. FIG. 10D shows another packing arrangement in which two rows of monochrome projectors are used to eliminate gaps between them. Two monochrome projectors stacked on top of each other will create nearly identical fields of view.

FIG. 11A illustrates a gap in the field of view 1100 produced by the looser packing arrangement 1102. FIG. 11B illustrates how offset rows 1104 of the projector minimize the gap in the viewport 1100. FIG. 11C illustrates how diffractive optics 1106 can be used to minimize the gap in the viewport 1 produced by the arrangement of the projector 1108.

FIG. 11C shows light paths from projectors 1110 and 1112. When light from projector 1110 or projector 1112 interacts with diffractive optics 1106, it is partially redirected. The exit pupil dilates and the gap between the projectors fills. Since the optical pupil expansion only requires filling the gap between the projectors, the optics of the diffractive optical element 1106 allow for simpler two-dimensional optical pupil expansion than diffractive optics in other waveguides.

FIG. 17 illustrates an example method 1700 for providing a two-dimensional pupil extension.

In step 1702, the image light is projected using an array of projectors arranged in the first dimension.

In step 1704, a coupler is used to redirect the projected image light to a coupler within the waveguide in the TIR path.

In step 1706, said redirected image light in the second dimension is expanded laterally into said first dimension using said coupler.

In step 1708, the expanded image light is coupled out of the waveguide using a coupler. As described above, the two-dimensional expansion and out-coupling occur in the same process.

名为“Near-eye display systems utilizing an array of projectors”的Microsoft patent申请最初在2022年9月提交，并在日前由美国专利商标局公布。