WO2025230509A1

WO2025230509A1 - Nonuniform display panel based on waveguide characteristics

Info

Publication number: WO2025230509A1
Application number: PCT/US2024/026832
Authority: WO
Inventors: Jun Yang; Joseph Daniel Lowney; Thomas Leonard HOEKMAN; Ardavan OSKOOI; Dmitriy Churin
Original assignee: Google LLC
Current assignee: Google LLC
Priority date: 2024-04-29
Filing date: 2024-04-29
Publication date: 2025-11-06
Anticipated expiration: 2026-10-29

Abstract

Techniques include using nonuniform fill factors for subpixels across a display panel. When the coupling efficiency for a color channel is a function of angle, then the fill factors of subpixels corresponding to that color channel across pixels of the display panel are related according to the function of angle. In some implementations, there is an inverse relationship between the coupling efficiency and the fill factors of subpixels for a color channel.

Description

NONUNIFORM DISPLAY PANEL BASED ON WAVEGUIDE CHARACTERISTICS

BACKGROUND

[0001] Waveguide-based augmented reality (AR) displays operate by coupling light from a (pLED) display panel into a thin diffractive waveguide, guiding the light within the waveguide, spreading the light over a region larger than the display panel, and then directing the light out of the waveguide and into an eye. At the same time, the waveguided light is combined with the regular see-through image from the world, forming an augmented reality display.

SUMMARY

[0002] The concepts discussed herein are directed to a display panel in a mixed reality system (e.g., an augmented reality (AR) system, a virtual reality (VR) system) that is configured according to characteristics of a waveguide used in the augmented reality system. The display panel has pixels arranged in an array such that a first pixel emits light from a first field of view angle into the waveguide and a second pixel emits light from a second field of view angle into the waveguide. A pixel has subpixels corresponding to color channels, e.g., red, green, or blue. A subpixel has a fill factor defined by how much of the area of the pixel is occupied by the subpixel. Because a coupling efficiency of the waveguide, e.g., the amount of light emitted into the waveguide that is emitted by the waveguide, depends on a field of view angle from which the light is emitted by a subpixel into the waveguide, the light seen by a person using the augmented reality system has nonuniform brightness across the pixels. This nonuniformity in brightness can be corrected by using nonuniform fill factors for the subpixels according to a coupling efficiency of the waveguide.

[0003] Moreover, the peak wavelength emitted by a subpixel depends on a driving current applied to the pixel that includes the subpixel. It is noted that a color channel emits a range of wavelengths rather than a single wavelength. Specifically, an increasing driving current blue-shifts the spectrum of a color channel, e.g., the peak wavelength decreases with increasing driving current. In addition, the peak wavelength emitted by the waveguide depends on the field of view angle from which light is emitted into the waveguide by a pixel. Accordingly, there is a nonuniformity in the gamut of a color channel seen by the person using the augmented reality system. To correct this nonuniformity, the driving current can be applied nonuniformly to the pixels of the display panel according to the peak wavelength of the waveguide.

[0004] In one general aspect, an apparatus includes a first pixel configured to emit light into a waveguide from a first angle and including a subpixel having a first fill fraction of the first pixel, the waveguide having a coupling efficiency that varies as a function of angle. The apparatus also includes a second pixel configured to emit light into the waveguide from a second angle and including a subpixel having a second fill fraction of the second pixel. The first fill fraction and the second fill fraction are related according to the function of angle.

[0005] In another general aspect, an apparatus includes a first pixel, configured to emit light into a waveguide from a first angle, to which a first driving current is applied, the waveguide having a peak wavelength that varies as a function of angle. The apparatus also includes a second pixel, configured to emit light into the waveguide from a second angle, to which a second driving current is applied. The first driving current and the second driving current are related according to the function of angle.

[0006] In another general aspect, a computer program product comprising a nontransitory storage medium, the computer program product including code that, when executed by processing circuitry, causes the processing circuitry to perform a method. The method can include receiving data representing a coupling efficiency of a waveguide, the coupling efficiency varying as a function of angle. The method can also include determining, according to the function of angle, a relation between a first fill fraction of a subpixel of a first pixel and a second fill fraction of a subpixel of a second pixel, the first pixel being configured to emit light into the waveguide from a first angle, the second pixel being configured to emit light into the waveguide from a second angle.

[0007] In another general aspect, a method can include receiving data representing a coupling efficiency of a waveguide, the coupling efficiency varying as a function of angle. The method can also include determining, according to the function of angle, a relation between a first fill fraction of a subpixel of a first pixel and a second fill fraction of a subpixel of a second pixel, the first pixel being configured to emit light into the waveguide from a first angle, the second pixel being configured to emit light into the waveguide from a second angle.

[0008] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. l is a diagram illustrating an example augmented reality system including a display panel and waveguide in accordance with implementations described herein.

[0010] FIG. 2A is a diagram illustrating an example coupling efficiency of a waveguide for red, green, and blue color channels as a function of angle.

[0011] FIG. 2B is a diagram illustrating example pixels with subpixels having fill factors with a nonuniformity according to the dependence of the diffraction efficiency on field of view angle, in accordance with implementations described herein.

[0012] FIG. 3 is a diagram illustrating example groups of pixels having the same subpixel fill factors in accordance with implementations described herein.

[0013] FIG. 4A is a diagram illustrating plots of peak wavelength emitted by the waveguide as a function of field of view angle.

[0014] FIG. 4B is a diagram illustrating plots of peak emission wavelength from the display panel as a function of driving current.

[0015] FIG. 5 is a diagram illustrating an example electronic environment in which nonuniformity of fill factor and driving current is configured according to characteristics of the waveguide.

[0016] FIG. 6 is a flow chart illustrating an example process of determining a nonuniform fill factor for subpixels of pixels of a display panel.

[0017] FIG. 7 is a flow chart illustrating an example process of determining a nonuniform drive current to be applied to pixels of a display panel.

DETAILED DESCRIPTION

[0018] Waveguide-based augmented reality (AR) displays operate by coupling light from a (pLED) display panel into a thin diffractive waveguide, guiding the light within the waveguide, spreading the light over a region larger than the display panel, and then directing the light out of the waveguide and into an eye. At the same time, the waveguided light is combined with the regular see-through image from the world, forming an augmented reality display. [0019] The waveguide has characteristics which affect the uniformity of light brightness at the eye as well as color gamut of color channels (e.g., red, green, blue) at the eye. For example, the waveguide has a coupling efficiency, defined to be a ratio of light power output by a waveguide outcoupler to the power input into a waveguide incoupler. The coupling efficiency depends on wavelength and field of view angle from which light is emitted into the waveguide. Field of view angle is defined as a ratio of position on the display panel to the distance from the display panel to the waveguide. The position on the display panel is defined relative to an origin, e.g., the center of the display panel. The distance from the display panel to the waveguide is measured along an axis normal to both the display panel and the waveguide. While there is little appreciable variation in brightness at the eye for a given color channel, the dependence on field of view angle can be significant. This is because pixels at different positions in the display panel emit light at different angles of incidence on the waveguide.

[0020] A pixel has subpixels corresponding to the color channels. For example, a red subpixel emits red light, e.g., light in a range of about 590-640 nm, a green subpixel emits green light, e.g., light in a range of about 530-570 nm, and a blue subpixel emits blue light, e.g., light in a range of about 450-480 nm. A subpixel of a pixel has an associated fill factor. A fill factor is a fraction of the pixel’s area occupied by the subpixel.

[0021] Conventional display panels have pixels with subpixels having uniform fill factors across the display panel. For example, a conventional display panel may have a fill factor of 0.4 for the red channel, 0.3 for the green channel, and 0.3 for the blue channel, for each pixel in the display panel.

[0022] At least one technical problem with the previously described conventional display panels is that an image seen at the eye will have nonuniform brightness, even if the light emitted by a display panel is uniformly distributed. The reason for this is that the coupling efficiency of the waveguide varies as field of view angle and therefore pixel position in the display panel. An effect of the nonuniform brightness of the image at the eye is difficulty in seeing the image and/or a perception of poor image quality.

[0023] The nonuniformity in the brightness of the light at the eye can be understood in more detail as follows. For example, consider a first pixel configured to emit red light into the waveguide from a first angle such that the coupling efficiency at the first angle is 0.6. If the input light has unit brightness, then the brightness of the light from the first pixel emerging from the waveguide is 0.6. For a second pixel configured to emit red light into the waveguide from a second angle such that the coupling efficiency at the second angle is 0.4, the brightness of the light from the second pixel emerging from the waveguide is 0.4. This difference in brightness occurs even when the brightness of the light emitted by the first pixel and the second pixel is the same, and the fill factors of the red subpixels for the first pixel and the second pixel are the same.

[0024] In some implementations, a way to reduce such nonuniformity in brightness, as well a nonuniformity in color, is to perform color and brightness calibration. Calibration is performed by dimming the brighter portion of the display by either reducing the current density for some pixels or by reducing the duration that some pixels are turned on (pulse width modulation). Nevertheless, such calibration has some disadvantages. For example, the brightness is limited by the dimmest pixel and the brightness reduction may be large.

Moreover, in the display image processing pipeline, the calibration consumes digital bits that reduce the dynamic range of the content.

[0025] At least one technical solution to the technical problem includes using nonuniform fdl factors for the subpixels across a display panel. When the coupling efficiency for a color channel is a function of angle, then the fill factors of subpixels corresponding to that color channel across pixels of the display panel are related according to the function of angle. In some implementations, there is an inverse relationship between the coupling efficiency and the fill factors of subpixels for a color channel.

[0026] To see such an inverse relationship, consider the previous example in which the coupling efficiency in the red channel at a first angle is 0.6 and at a second angle is 0.4. The first angle corresponds to a first position in the display panel, at which a first pixel emits light into the waveguide at the first angle, and the second angle corresponds to a second position in the display panel at which a second pixel emits light into the waveguide. If the fill factors of the first pixel and the second pixel are the same, then the brightness of the first pixel at the eye is 0.6, while the brightness of the second pixel at the eye is 0.4. To equalize the brightness from the first pixel and the second pixel, the fill factor of the red subpixel of the second pixel is to be to be increased with respect to the fill factor of the red subpixel of the first pixel.

[0027] At least one technical benefit of the technical solution is that there may be less digital calibration of the pixels performed. In such a case, the pixels can be turned on to a maximum driving condition, e.g., a largest pulse width modulation. Such a large pulse width modulation allows for a high brightness without increasing the pixel size. Moreover, as less digital calibration is performed, there may be more bits reserved for content display, which enables a higher dynamic range.

[0028] FIG. 1 is a diagram illustrating an example augmented reality system 100 including a display panel 110 and waveguide 130. The pixels of the display panel 130, e.g., pixels 112(1) and 112(2), are co-configured with the waveguide 130 such that fill factors of subpixels of the pixels are distributed according to a function of angle that defines the coupling efficiency of the waveguide.

[0029] The display panel 110 is, in some implementations, a microLED (pLED) panel that includes a plurality of pixels, e.g., pixels 112(1) and 112(2), each of which is configured to emit respective light beams 114(1), 114(2) in the red, green, and/or blue color channels. It is noted that only two pixels 112(1), 112(2) are shown here for simplicity of discussion; in a typical display panel, there are thousands or millions of pixels. Each pixel 112(1), 112(2) has subpixels corresponding to the red, green, and blue channels. Each subpixel has a fill factor defined as a fraction of the area of the pixel 112(1), 112(2) occupied by that subpixel.

[0030] The beams 114(1), 114(2) diverge from the emitting pixels 112(1), 112(2) and are collimated by a projector lens 120. The collimated beams 114(1), 114(2) are incident on the waveguide 130 at respective angles. That is, the angle of incidence on the waveguide 130 varies with pixel position in the display panel 1 10 and therefore field of view angle.

[0031] Once the beams 114(1), 114(2) enter the waveguide 130, the beams 114(1) and 114(2) are coupled in the waveguide by incoupler 132 and propagate through the waveguide 130 to the outcoupler 134. The outcoupler 134 couples the beams 114(1), 114(2) out of the waveguide 130 and toward eye lens 140. Eye lens 140 then focuses the beams 114(1), 114(2) onto retina 150.

[0032] It is desired that the brightness of the beams 114(1), 114(2) at the retina 150 be about equal. In order for the brightness of the beams 114(1), 114(2) to be about equal, the fill factor of a respective subpixel of the pixels 112(1), 112(2) for a color channel are distributed according to the coupling efficiency as a function of field of view angle. This coupling efficiency and function of angle are shown in more detail with regard to FIGs. 2A and 2B.

[0033] FIG. 2A is a diagram illustrating an example coupling efficiency 200 of a waveguide (e.g., waveguide 130) for red, green, and blue color channels as a function of angle. In this context “angle” can refer to a field of view angle of a pixel on the display panel.

[0034] The coupling efficiency shown in FIG. 2A is an example configured to demonstrate a general behavior and is not representative of an actual waveguide. In this example, the coupling efficiency of the red channel 212 is a decreasing function of angle. The coupling efficiency of the green channel 214 is a roughly constant function of angle. The coupling efficiency of the blue channel 216 is an increasing function of angle.

[0035] It is noted that the plots for the example coupling efficiency 200 as a function of field of view angle are simplified for the sake of discussion. In some implementations, the coupling efficiency for the red channel 212, green channel 214, and blue channel 216 are curves. For example, the coupling efficiency for the red channel 212 may be a curve that decreases at a nonuniform rate as a function of field of view angle. The coupling efficiency for the green channel 214 may be a curve that oscillates about an average value. The coupling efficiency for the blue channel 216 may be a curve that increases at a nonuniform rate as a function of field of view angle.

[0036] It is further noted that the field of view angle here is measured with respect to a horizontal axis. In some implementations, the field of view angle can be a two-dimensional angle, corresponding to a two-dimensional position within the display panel. In such a case, the coupling efficiency would be represented as a contour plot, for example. Nevertheless, for simplicity of discussion, the one-dimensional field of view angle will be discussed.

[0037] FIG. 2B is a diagram illustrating example pixels 260(1), 260(2), 260(3) with subpixels having fill factors with a nonuniformity according to the dependence of the coupling efficiency on field of view angle shown in FIG. 2A. The pixels 260(1), 260(2), 260(3) are arranged in increasing field of view angle to reflect the plots in FIG. 2A and correspond to the field of view angles 220(1), 220(2), and 220(3), respectively.

[0038] For example, consider the red subpixels 262(1) in pixel 260(1), 262(2) in pixel 260(2), and 262(3) in pixel 260(3). On the left-hand side of the plot in FIG. 2A, the coupling efficiency of the red channel at field of view angle 220(1) is high and decreases to smaller values as field of view angles 220(2) and 220(3). Accordingly, to make the brightness of the red light at the eye more uniform, the fill factor, or relative width, of the red subpixel should increase with field of view angle across the pixels 260(1), 260(2), and 260(3). The increase in fill factor of the red subpixels 262(1), 262(2), and 262(3) with field of view angle is according to the function of field of view angle that is the coupling efficiency of the red channel 214. For example, if the coupling efficiency of the red channel at field of view angle 220(1) is 0.9, the coupling efficiency of the red channel at field of view angle 220(2) is 0.6, and the coupling efficiency of the red channel at field of view angle 220(3) is 0.3, then the fill factors of the red subpixels 262(1), 262(2), and 262(3) will be in inverse proportion to the coupling efficiencies, or 0.2 for the red subpixel 262(1), 0.3 for the red subpixel 262(2), and 0.6 for the red subpixel 262(3). That is, in response to the coupling efficiency of the red channel at field of view angle 220(1) being greater than the coupling efficiency of the red channel at field of view angle 220(2), the fill factor for the red subpixel 262(1) will be less than the fill factor for the subpixel 262(2).

[0039] The green channel has a roughly constant coupling efficiency as a function of field of view angle. Accordingly, the fill factors for the green subpixels 264(1), 264(2), and 264(3) can be roughly the same. In this case, the coupling efficiencies at the field of view angle 220(2) for the red, green, and blue channels are roughly equal. Thus, the fill factor for the green subpixel 264(2) is about 0.3. Because the coupling efficiency for the green channel 214 is roughly constant, the fill factors for the green subpixels 264(1), 264(2), and 264(3) can be about equal, or in this case about 0.3.

[0040] The blue channel has a coupling efficiency 216 that increases with field of view angle. Hence, the fill factors of the blue subpixels 266(1), 266(2), and 266(3) decrease with field of view angle, or across pixels 260(1), 260(2), 260(3). Alternatively, the fill factors of the blue subpixels 266(1), 266(2), 266(3) may be found from other considerations. For example, the width of the blue subpixel 266(1) may be found by subtracting the fill factors for the red subpixel 262(1) and the green subpixel 264(1) from unity; that is, a constraint for the fill factors is that the fill factors for red, green, and blue subpixels add up to at most one. In this case, the fill factor for the blue subpixel 266(1) would be 0.5 and the fill factor for the clue subpixel 266(3) would be 0.1. The fill factor for the blue subpixel 266(3) is the same as that for the red subpixel 262(2) and the blue subpixel 266(2) because the coupling efficiency is roughly the same for the red, green, and blue channels.

[0041] The result of configuring the pixels 260(1), 260(2), 260(3) with nonuniform fill factors is more uniform brightness at the eye than if the pixels had uniform fill factors. For example, a rough measure of brightness at the eye is obtained if the coupling efficiency is multiplied by the fill factor. Thus, the brightness at the eye from red subpixel 262(1) is (0.9)(0.2)=0.18; the brightness from red subpixel 262(2) is (0.6)(0.3) = 0.18; and the brightness from red subpixel 262(3) is (0.3)(0.6) = 0.18. This calculation carries over to the green and blue subpixels. The sum of the brightnesses from the red, green, and blue, e g., the brightness of white light from the pixels 260(1), 260(2), 260(3), is also made more uniform.

[0042] It is noted that this increasing of the uniformity of the brightness at the eye is performed without dimming the brighter portions of the display. Rather, the uniformity was increased by changing the fill factors of the subpixels of the pixels of the display panel.

[0043] The configuration of pixels in a display panel does not need to be in exact accordance with the coupling efficiency curves. For example, the resolution of the subpixels is limited by the manufacturing process used in creating the subpixels, e.g., a semiconductor lithographic process. For ease of manufacture, it may be advantageous to have as little variation in fill factor as possible. Such a scenario is shown with regard to FIG. 3.

[0044] FIG. 3 is a diagram illustrating example groups 330(1), 330(2), 330(3) of pixels having the same subpixel fill factors. The pixels 310(1) and 320(1) are disposed within group 330(1), pixel 310(2) is disposed within group 330(2), and pixels 310(3) and 320(3) are disposed within group 330(3). The fill factors of the subpixels vary across the groups 330(1), 330(2), 330(3).

[0045] Group 330(1) is defined by the pixels 310(1) and 320(1) having the same fill factors across their respective subpixels. Thus, if the red subpixel 312(1) has a fill factor of 0.2, then red subpixel 322(1) also has a fill factor of 0.2. Similarly, if the green subpixel 314(1) has a fill factor of 0.3, then the green subpixel 324(1) has a fill factor of 0.3, and if blue subpixel 316(1) has a fill factor of 0.5, then the blue subpixel 326(1) has a fill factor of 0.5. These fill factors are the same even though the pixels 310(1) and 320(1) are at different field of view angles.

[0046] Group 330(2) is defined by a single pixel, 310(2). Group 330(3) is defined by the pixels 310(3) and 320(3) having the same fill factors across their respective subpixels. Thus, if the red subpixel 312(3) has a fill factor of 0.5, then red subpixel 322(3) also has a fill factor of 0.5. Similarly, if the green subpixel 314(3) has a fill factor of 0.3, then the green subpixel 324(3) has a fill factor of 0.3, and if blue subpixel 316(3) has a fill factor of 0.2, then the blue subpixel 326(3) has a fill factor of 0.2. These fill factors are the same even though the pixels 310(3) and 320(3) are at different field of view angles.

[0047] Groups do not have to be defined along a horizontal axis as shown in FIG. 3. Rather, groups can be defined by pixels in either or both the horizontal and vertical direction. In some implementations, groups do not need to have contiguous pixels.

[0048] Nonuniformity at the eye can take the form not only of brightness of color channels or white light, but also in the color gamut within a color channel. For example, within the red color channel there is a range of wavelengths, e.g., about 590-640 nm. Within this range there is a peak wavelength representing a wavelength at which the highest brightness occurs. This peak wavelength, however, can vary with field of view angle. This is shown in FIG. 4A.

[0049] FIG. 4A is a diagram illustrating plots 410, 420, 430 of peak wavelength emitted by the waveguide as a function of field of view angle for the red, green, and blue color channels. For simplicity of discussion, the plots are shown in one dimension although the peak wavelength may vary with field of view angle in two dimensions.

[0050] Given a constant peak wavelength emitted by the pixels of the display panel, the effect of the waveguide is to shift the peak wavelength of the spectrum of each color channel. Even if the peak emission wavelength is the same for the pixels of the display panel, the peak wavelength as seen by a person using the AR system will vary with field of view angle, e.g., across the image.

[0051] The effect of the phenomena represented in plots 410, 420, 430 is that the color gamut for a color channel varies over the display panel. Accordingly, in a center eyebox for a person using the AR system, the colors may vary across the image. For example, what might be red may be red-orange or red-yellow depending on the place in the image. Such an effect may be seen in plot 410 for the variation of peak wavelength, where the deeper reds come from one end of the display panel and the red-yellows come from the other end of the display panel.

[0052] Similar phenomena may be seen in plot 420 for the green channel and plot 430 for the blue channel. For example, one end of the display panel, according to plot 420, produces yellow-greens while the other end of the display panel produces blue-greens.

According to plot 430, one of end the display panel produces violet-blues while the other end of the display panel produces green blues.

[0053] There is a nonuniform color gamut in each color channel observed by a person using the AR system. Nevertheless, the color gamut in each channel can be made roughly constant by introducing a nonuniform driving current to the pixels of the display panel. This is shown with regard to FIG. 4B.

[0054] FIG. 4B is a diagram illustrating plots 460, 470, 480 of peak emission wavelength from the display panel as a function of driving current. The plots 460, 470, 480 are semi-log plots of the peak emission wavelength vs. a logarithm of the current density applied to a pixel of the display panel. In an LED, the driving current affects the spectrum emitted.

[0055] According to plot 460, increasing the driving current applied to a pixel blueshifts the peak emission wavelength emitted by that pixel. That is, the peak emission wavelength - the wavelength at which the brightness of the wavelength spectrum peaks - decreases with increasing applied driving current.

[0056] In some implementations, the driving current may be applied to individual subpixels of a pixel when the subpixels correspond to the color channels. For example, a pixel may have three subpixels corresponding to the red, green, and blue color channels. In this case, the driving current may be applied to a subpixel to control the peak emission wavelength for a color channel.

[0057] Accordingly, by using information such as the plots 410, 420, 430 of how the peak wavelength shifts according to field of view angle in a color channel, the color gamut in that color channel can be made roughly constant by varying the driving current applied to the pixels of the display panel. For example, at a pixel whose peak emission wavelength is red- shifted by the waveguide, a larger driving current may be applied to that pixel to blue-shift the peak emission wavelength. At a pixel whose peak emission wavelength is blue-shifted by the waveguide, a smaller driving current may be applied to that pixel to red-shift the peak emission wavelength.

[0058] In some implementations, a pixel can have both subpixel fdl factors and applied driving current co-configured with the waveguide according to the coupling efficiency. Such a co-configuration of both fill factors and driving current can help achieve brightness uniformity and constant color gamut at the same time.

[0059] FIG. 5 is a diagram that illustrates example processing circuitry 520 of a computing device configured to determine a co-configuration of a display panel with a waveguide. The processing circuitry 520 is configured to determine fill factors of subpixels of pixels and determine driving currents applied to pixels such that illumination at an eye has a uniform brightness and a constant color gamut.

[0060] The processing circuitry 520 includes a network interface 522, one or more processing units 524, and nontransitory memory 526. The network interface 522 includes, for example, Ethernet adaptors, Bluetooth adaptors, and the like, for converting electronic and/or optical signals received from the network to electronic form for use by the processing circuitry 320. The set of processing units 524 include one or more processing chips and/or assemblies. The memory 526 is a storage medium and includes both volatile memory (e.g., RAM) and nonvolatile memory, such as one or more read only memories (ROMs), disk drives, solid state drives, and the like. The set of processing units 524 and the memory 526 together form part of the processing circuitry 520, which is configured to perform various methods and functions as described herein as a computer program product.

[0061] In some implementations, one or more of the components of the processing circuitry 520 can be, or can include processors (e.g., processing units 524) configured to process instructions stored in the memory 526. Examples of such instructions as depicted in FIG. 5 include an coupling efficiency manager 530, a fill factor manager 540, a peak wavelength manager 550, and a driving current manager 560. Further, as illustrated in FIG. 5, the memory 526 is configured to store various data, which is described with respect to the respective managers that use such data.

[0062] The coupling efficiency manager 530 is configured to cause the processing circuitry 520 to receive coupling efficiency data 532 representing a coupling efficiency of a waveguide. The coupling efficiency of the waveguide, in some implementations, is in the form of a function of angle for a color channel.

[0063] Accordingly, the coupling efficiency data 532, in some implementations, is in the form of an array of coupling efficiency values over a grid of field of view angles. In some implementations, the grid of field of view angles corresponds to the field of view angles of the pixels of the display panel. In some implementations, the grid of field of view angles has a fixed stepsize, e.g., 0.1 degrees, 0.5 degrees, 1 degree, or the like. In some implementations, the grid is two-dimensional, e.g., coupling efficiency depends on a horizontal angle and a vertical angle. In some implementations, the value at a field of view angle is a triplet of values corresponding to red, green, and blue color channels. In some implementations, the coupling efficiency data 532 has a separate field of view grid of values for each color channel.

[0064] In some implementations, the coupling efficiency manager 530 receives the coupling efficiency data 532 over a network, e.g., via network interface 522. In some implementations, the coupling efficiency manager 520 receives the coupling efficiency data 532 via a disk drive, e.g., a flash drive connected to the computing device.

[0065] The fill factor manager 540 is configured to cause the processing circuitry 520 to derive fill factors for the subpixels of the pixels of the display panel (e.g., fill factor data 542) based on the coupling efficiency data 532. In some implementations, the fill factors data 542 takes the form of an array of triplets of values, a triplet corresponding to a fill factor of a red subpixel of a pixel, a fill factor of a green subpixel of the pixel, and a fill factor of a red subpixel of the pixel. In some implementations, the three values of a triplet add to one. In some implementations, the three values of a triplet add to a number less than one.

[0066] In some implementations, the fill factor manager 540 derives the fill factor data 542 by considering the reciprocals of the coupling efficiencies for each color channel and scaling the results such that the sum of the fill factors for a pixel is one or less than one. For example, it is assumed that the coupling efficiency for the red channel at a pixel corresponding to a field of view angle is 0.9, the coupling efficiency for the green channel at the pixel corresponding to the field of view angle is 0.6, and the coupling efficiency for the blue channel at the pixel corresponding to the field of view angle is 0.3. The fill factor manager 540 may compute a = — - ^7 — u — ~ 0.164 and then compute, as the red fill factor, — « 0.182, as

/0 9⁺ /0.6⁺ /0.3 ^{0 9} the green fill factor — « 0.273, and as the blue fill factor — « 0.545, which sum to one.

[0067] In some implementations, the coupling efficiency data 532 identifies those pixels that are to be a part of a group of pixels having the same fill factors. In this case the coupling efficiency data 532 includes a group identifier for each pixel, e.g., a numeral identifying a group. If a new group identifier is encountered, the fill factor manager computes the fill factors for that pixel as usual. If, however, the pixel is determined to be part of a group, the fill factors computed for that group is used as the fill factors for the pixel.

[0068] The peak wavelength manager 550 is configured to cause the processing circuitry 520 to receive peak wavelength data 552 representing a peak wavelength as a function of field of view angle for a waveguide and emission wavelength data 554 representing a peak emission wavelength for a color channel as a function of current density applied to a pixel. The peak wavelength for the waveguide represented by the peak wavelength data 552, in some implementations, is in the form of a function of angle for a color channel.

[0069] Accordingly, the peak wavelength data 552, in some implementations, is in the form of an array of wavelength values over a grid of field of view angles. In some implementations, the grid of field of view angles corresponds to the field of view angles of the pixels of the display panel. In some implementations, the grid of field of view angles has a fixed stepsize, e.g., 0.1 degrees, 0.5 degrees, 1 degree, or the like. In some implementations, the grid is two-dimensional, e.g., peak wavelength depends on a horizontal angle and a vertical angle. In some implementations, the value at a field of view angle is a triplet of values corresponding to red, green, and blue color channels. In some implementations, the peak wavelength data 552 has a separate field of view grid of values for each color channel.

[0070] In some implementations, the peak wavelength manager 550 receives the peak wavelength data 552 and emission wavelength data 554 over a network, e.g., via network interface 522. In some implementations, the peak wavelength manager 550 receives the peak wavelength data 552 and emission wavelength data 554 via a disk drive, e.g., a flash drive connected to the computing device.

[0071] The driving current manager 560 is configured to cause the processing circuitry 520 to derive driving currents for the pixels of the display panel based on emission wavelength data 554 and peak wavelength data 552. Emission wavelength data 554 is, in some implementations, a grid of values of peak emission wavelengths for the red, green, and blue color channels as a function of current density or logarithm of current density. The driving current applied to a pixel is equal to the current density times the area of a pixel. The result is driving current data 562, which represents the driving current to be applied to the pixels of the display panel.

[0072] The components (e.g., modules, processing units 324) of processing circuitry 320 can be configured to operate based on one or more platforms (e.g., one or more similar or different platforms) that can include one or more types of hardware, software, firmware, operating systems, runtime libraries, and/or so forth. In some implementations, the components of the processing circuitry 320 can be configured to operate within a cluster of devices (e.g., a server farm). In such an implementation, the functionality and processing of the components of the processing circuitry 320 can be distributed to several devices of the cluster of devices. [0073] The components of the processing circuitry 520 can be, or can include, any type of hardware and/or software configured to process attributes. In some implementations, one or more portions of the components shown in the components of the processing circuitry 520 in FIG. 5 can be, or can include, a hardware-based module (e.g., a digital signal processor (DSP), a field programmable gate array (FPGA), a memory), a firmware module, and/or a software-based module (e.g., a module of computer code, a set of computer-readable instructions that can be executed at a computer). For example, in some implementations, one or more portions of the components of the processing circuitry 520 can be, or can include, a software module configured for execution by at least one processor (not shown). In some implementations, the functionality of the components can be included in different modules and/or different components than those shown in FIG. 5, including combining functionality illustrated as two components into a single component.

[0074] Although not shown, in some implementations, the components of the processing circuitry 520 (or portions thereof) can be configured to operate within, for example, a data center (e.g., a cloud computing environment), a computer system, one or more server/host devices, and/or so forth. In some implementations, the components of the processing circuitry 520 (or portions thereof) can be configured to operate within a network. Thus, the components of the processing circuitry 520 (or portions thereof) can be configured to function within various types of network environments that can include one or more devices and/or one or more server devices. For example, the network can be, or can include, a local area network (LAN), a wide area network (WAN), and/or so forth. The network can be, or can include, a wireless network and/or wireless network implemented using, for example, gateway devices, bridges, switches, and/or so forth. The network can include one or more segments and/or can have portions based on various protocols such as Internet Protocol (IP) and/or a proprietary protocol. The network can include at least a portion of the Internet.

[0075] In some implementations, one or more of the components of the search system can be, or can include, processors configured to process instructions stored in a memory. For example, coupling efficiency manager 530 (and/or a portion thereof), fill factor manager 540 (and/or a portion thereof), peak wavelength manager 550 (and/or a portion thereof), and driving current manager 560 (and/or a portion thereof) are examples of such instructions.

[0076] In some implementations, the memory 526 can be any type of memory such as a random-access memory, a disk drive memory, flash memory, and/or so forth. In some implementations, the memory 526 can be implemented as more than one memory component (e.g., more than one RAM component or disk drive memory) associated with the components of the processing circuitry 520. In some implementations, the memory 526 can be a database memory. In some implementations, the memory 526 can be, or can include, a non-local memory. For example, the memory 526 can be, or can include, a memory shared by multiple devices (not shown). In some implementations, the memory 526 can be associated with a server device (not shown) within a network and configured to serve the components of the processing circuitry 520. As illustrated in FIG. 5, the memory 526 is configured to store various data, including coupling efficiency data 532 and fill factor data 542.

[0077] FIG. 6 is a flow chart illustrating a method 600 of determining a fill factor for a subpixel of a pixel of a display panel based on a coupling efficiency of a waveguide. The method 600 may be performed with processing circuitry, e.g., processing circuitry 520 as shown in FIG. 5.

[0078] At 602, a coupling efficiency manager (e.g., coupling efficiency manager 530) receives data (e.g., coupling efficiency data 532) representing a coupling efficiency of a waveguide, the coupling efficiency varying as a function of angle (e.g., field of view angle). [0079] At 604, a fill factor manager (e.g., fill factor manager 540) determines, according to the function of angle, a relation between a first fill fraction (e.g., fill fraction data 542) of a subpixel of a first pixel and a second fill fraction (e g., fill fraction data 542) of a subpixel of a second pixel. The first pixel is configured to emit light into the waveguide from a first angle, and the second pixel is configured to emit light into the waveguide from a second angle.

[0080] FIG. 7 is a flow chart illustrating a method 700 of determining a driving current applied to a pixel of a display panel based on a coupling efficiency of a waveguide. The method 700 may be performed with processing circuitry, e.g., processing circuitry 520 as shown in FIG. 5.

[0081] At 702, a peak wavelength manager (e.g., peak wavelength manager 550) receives data (e.g., peak wavelength data 552) representing a peak wavelength of a waveguide, the peak wavelength varying as a function of angle (e.g., field of view angle).

[0082] At 704, a driving current manager (e.g., driving current manager 560) determines, according to the function of angle, a relation between a first driving current of a first pixel (e g., driving current data 562) and a second driving current of a second pixel e.g., driving current data 562). The first pixel is configured to emit light into the waveguide from a first angle, and the second pixel is configured to emit light into the waveguide from a second angle.

[0083] Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments, however, may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

[0084] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including," when used in this specification, specify the presence of the stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

[0085] It will be understood that when an element is referred to as being "coupled," "connected," or "responsive" to, or "on," another element, it can be directly coupled, connected, or responsive to, or on, the other element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly coupled," "directly connected," or "directly responsive" to, or "directly on," another element, there are no intervening elements present. As used herein the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0086] Spatially relative terms, such as "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature in relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 70 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.

[0087] Example embodiments of the concepts are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments of the described concepts should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Accordingly, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments.

[0088] It will be understood that although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, a "first" element could be termed a "second" element without departing from the teachings of the present embodiments. [0089] Unless otherwise defined, the terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these concepts belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0090] While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover such modifications and changes as fall within the scope of the implementations. It should be understood that they have been presented by way of example only, not limitation, and various changes in form and details may be made. Any portion of the apparatus and/or methods described herein may be combined in any combination, except mutually exclusive combinations. The implementations described herein can include various combinations and/or sub-combinations of the functions, components, and/or features of the different implementations described.

Claims

WHAT IS CLAIMED IS:

1. An apparatus, comprising: a first pixel configured to emit light into a waveguide from a first angle and including a subpixel having a first fill fraction of the first pixel, the waveguide having a coupling efficiency that varies as a function of angle; and a second pixel configured to emit light into the waveguide from a second angle and including a subpixel having a second fill fraction of the second pixel, the first fill fraction and the second fill fraction being related according to the function of angle.

2. The apparatus as in claim 1, wherein the coupling efficiency varies as the function of angle for a color channel.

3. The apparatus as in claim 2, wherein the subpixel of the first pixel is configured to emit light in the color channel, and the subpixel of the second pixel is configured to emit light in the color channel.

4. The apparatus as in any of the preceding claims, wherein the first fill fraction is different from the second fill fraction.

5. The apparatus as in any of the preceding claims, wherein in response to the coupling efficiency of the waveguide at the first angle being greater than the coupling efficiency of the waveguide at the second angle, the first fill fraction is less than the second fill fraction.

6. The apparatus as in any of the preceding claims, wherein the first fill fraction and the second fill fraction are inversely related to the coupling efficiency at the first angle and the coupling efficiency at the second angle.

7. The apparatus as in any of the preceding claims, wherein the first pixel is disposed within a first group of pixels and the second pixel is disposed within a second group of pixels, the first group of pixels corresponding to a first range of angles, the second group of pixels corresponding to a second range of angles, the first group of pixels having a subpixel having the first fill fraction, the second group of pixels having a subpixel having the second fill fraction.

8. An apparatus, comprising: a first pixel, configured to emit light into a waveguide from a first angle, to which a first driving current is applied, the waveguide having a peak wavelength that varies as a function of angle; and a second pixel, configured to emit light into the waveguide from a second angle, to which a second driving current is applied, the first driving current and the second driving current being related according to the function of angle.

9. The apparatus as in claim 8, wherein a subpixel of the first pixel has a first fill fraction of the first pixel, wherein a subpixel of the second pixel has a second fill fraction of the second pixel, and wherein the first fill fraction and the second fill fraction are related according to the function of angle.

10. A method, comprising: receiving data representing a coupling efficiency of a waveguide, the coupling efficiency varying as a function of angle; and determining, according to the function of angle, a relation between a first fill fraction of a subpixel of a first pixel and a second fill fraction of a subpixel of a second pixel, the first pixel being configured to emit light into the waveguide from a first angle, the second pixel being configured to emit light into the waveguide from a second angle.

11. The method as in claim 10, wherein the coupling efficiency varies as the function of angle for a color channel.

12. The method as in claim 11, wherein the subpixel of the first pixel is configured to emit light in the color channel, and the subpixel of the second pixel is configured to emit light in the color channel.

13. The method as in any of claims 10 to 12, wherein the first fill fraction is different from the second fill fraction.

14. The method as in any of claims 10 to 13, wherein in response to the coupling efficiency of the waveguide at the first angle being greater than the coupling efficiency of the waveguide at the second angle, the first fill fraction is less than the second fill fraction.

15. The method as in any of claims 10 to 14, wherein the first fill fraction and the second fill fraction are inversely related to the coupling efficiency at the first angle and the coupling efficiency at the second angle.

16. The method as in any of claims 10 to 15, wherein the first pixel is disposed within a first group of pixels and the second pixel is disposed within a second group of pixels, the first group of pixels corresponding to a first range of angles, the second group of pixels corresponding to a second range of angles, the first group of pixels having a subpixel having the first fill fraction, the second group of pixels having a subpixel having the second fill fraction.

17. A computer program product comprising a nontransitory storage medium, the computer program product including code that, when executed by processing circuitry, causes the processing circuitry to perform a method, the method comprising: receiving data representing a coupling efficiency of a waveguide, the coupling efficiency varying as a function of angle; and determining, according to the function of angle, a relation between a first fill fraction of a subpixel of a first pixel and a second fill fraction of a subpixel of a second pixel, the first pixel being configured to emit light into the waveguide from a first angle, the second pixel being configured to emit light into the waveguide from a second angle.

18. The computer program product as in claim 17, wherein the coupling efficiency varies as the function of angle for a color channel.

19. The computer program product as in claim 18, wherein the subpixel of the first pixel is configured to emit light in the color channel, and the subpixel of the second pixel is configured to emit light in the color channel.

20. The computer program product as in any of claims 17 to 19, wherein the first pixel is disposed within a first group of pixels and the second pixel is disposed within a second group of pixels, the first group of pixels corresponding to a first range of angles, the second group of pixels corresponding to a second range of angles, the first group of pixels having a subpixel having the first fill fraction, the second group of pixels having a subpixel having the second fill fraction.