Patent Description:
Near-eye display systems are becoming more common. Such near-eye display systems attempt to provide a three-dimensional display to the user. In the prior art, displays rendering multiple focal planes utilized mechanical movement such as gears or liquid lenses. Such mechanisms are expensive, slow, and relatively fragile. Another prior art method of displaying multiple focal lengths uses multiple mirrors and lenses.

Such prior art solutions are some combination of large, expensive, and slow. Liquid lenses are expensive and slow, and prior art beam splitters are large. This makes them difficult to use, and not useful for size or cost constrained systems, particularly near-eye display systems.

<CIT> discloses a virtual image display device with a light source unit, a polarized light switching unit an image generating unit, a light path unit, and a projection unit. The polarized switching unit switches the polarization direction of light output by the light source unit between an unaltered first polarization direction and a second polarization direction. The image generating unit generates an image according to the light output by the light source unit. The light path unit has a first light path through which light having the first polarization direction passes and a second light path through which light having the second polarization direction passes and for which the light path is longer than the first light path. A first virtual image is displayed at a first distance from an observer by light passing through the first light path. A second virtual image is displayed at a second distance further from the observer than the first distance by light passing through the second light path. <CIT> discloses a display system that receives from a light source a sequence of images, each representing a different depth plane of a subject, and selectively reflects each image from its corresponding one of plural light direction modulators to synthesize a three-dimensional image of the subject. Each modulator is positioned along an axis at a location that corresponds to a different depth plane. Each modulator reflects the first image incident to it and transmits the succeeding images in the sequence. <CIT> discloses an optical path length adjuster enables electro-optical control of a physical path length between two optical elements, suitable for use in the adjustment of an optical path length within three dimensional display devices that generate a virtual image within a defined imaging volume. The adjuster varies an optical path length between an input optical path and an output optical path. <CIT> discloses a connection board in which multiple external contacts of an electronic component and multiple spiral contacts on a board are arranged to highly accurately face each other, and the external contacts are actively guided to the spiral contacts, so as to reliably provide individual connections therebetween. <CIT> discloses an apparatus and method for displaying images, the apparatus comprising: (i) a display device for displaying an image representing a three-dimensional scene, wherein a depth in said scene is specified as a depth of interest; and (ii) control means for providing a signal for controlling a focal length of lens means for viewing said image, said signal depending on said depth of interest.

A near-eye display system utilizing a modulation stack is described. A modulation stack includes one or more digital light path length modulators, to adjust the path length of light. A digital light path length modulator can be used to create two focal planes. In one embodiment, using a modulation stack with a plurality of digital light path length modulators, the number of focal planes can be increased. Creating a display in which the 3D indicia of overlap, focus, and vergence match provides the capacity to build a system that can meet the physiological requirements of human vision. This produces a better quality 3D display than is currently possible and can prevent the discomfort associated with 3D displays.

The following detailed description of embodiments of the invention makes reference to the accompanying drawings. The drawings show various embodiments of practicing the invention. Description of these embodiments is in sufficient detail to enable those skilled in the art to practice the invention. One skilled in the art understands that other embodiments may be utilized and that logical, mechanical, electrical, functional and other changes may be made without departing from the scope of the present invention. The following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

<FIG> is an illustration of one embodiment of a near-eye display system, in which the present invention may be used. The near-eye display system, in one embodiment includes a head-mounted display, which includes a display for one or both eyes of a user. In one embodiment, the near-eye display system is a display mounted in another device, such as a camera, microscope display, focal assist in a microscope, telescope, digital scope, medical display system, rifle scope, range finder, etc. In one embodiment, the near-eye display system is coupled with a speaker system to enable the playing of audio-visual output such as movies. The near-eye display system may provide an opaque display, partially transparent display, and/or transparent display. The near-eye display system may provide augmented reality and/or virtual reality display.

<FIG> is a block diagram of one embodiment of a near-eye display system. The near-eye display system <NUM> includes, in one embodiment, a display subsystem <NUM>, an audio subsystem <NUM>, a processor <NUM>, a memory <NUM>, and optionally an auxiliary data system <NUM>. The display subsystem <NUM> generates image data. Memory <NUM> may be a buffer-memory, enabling the near-eye display system <NUM> to stream content. The memory <NUM> may also store image and video data for display. I/O system <NUM> makes image, audio, video, VR, or other content available from other sources (e.g. enables downloading or streaming of content from various sources.

The display subsystem <NUM> includes, in one embodiment, image source <NUM> and projection assembly <NUM>. The image source <NUM> in one embodiment includes a light source <NUM>, which in one embodiment is a spatial light modulator (SLM). The image source <NUM> in one embodiment also includes a digital correction system <NUM>, to correct the output of the light source <NUM>, to account for distortion in the projection assembly <NUM>. In one embodiment, the light source <NUM> may be a real image, in which case the light source <NUM> is external to the system, and there is no digital correction. In one embodiment, the NED <NUM> may be used for one or more of virtual reality (digital image source), augmented reality (a combination of real and digital image source), and reality (real image source.

The projection assembly <NUM> includes a polarizer <NUM> in one embodiment. The polarizer <NUM> passes through light with a particular polarization.

The projection assembly <NUM> includes a modulation stack <NUM>. The modulation stack <NUM> includes one or more digital light path length modulators <NUM>, <NUM>. The digital light path length modulators <NUM>, <NUM> alter the light path length based on the polarization of the light. In one embodiment, polarizer <NUM> may be positioned after modulation stack <NUM>.

Imaging assembly <NUM> is used to display the image to the user. In one embodiment, the display subsystem <NUM> may include additional mechanical and optical elements which can provide correction or alteration of the image.

The system may include a binocular elements display subsystem <NUM>. In one embodiment, the binocular elements display subsystem <NUM> may include only an imaging assembly, while the image source <NUM>, polarizer <NUM>, and modulation stack <NUM> may be shared between the display subsystem <NUM> and the binocular elements display subsystem <NUM>. In another embodiment, the binocular elements display subsystem <NUM> may include more of the elements, including one or more of a separate polarizer, modulation stack, and image source.

In one embodiment, the system may receive data from auxiliary data system <NUM>. The auxiliary data system may provide information for selecting the focal lengths. As noted above, the modulation stack <NUM> can create a perception of an image element at various virtual object distances. The auxiliary data system <NUM> may be used to select a virtual object distance, based on various factors.

One auxiliary data system <NUM> element is an eye tracking mechanism <NUM>. The eye tracking mechanism <NUM> tracks the gaze vector of the user's eyes. In one embodiment, the system may place image elements in one or more selected locations based on where the user's eyes are looking, using the eye tracking mechanism <NUM>. In one embodiment, the eye tracking mechanism <NUM> is an infrared optical sensor or camera to sense light reflected from the eye. Other techniques may be used for eye tracking. Eye tracking mechanism <NUM> may track one or both eyes.

Environmental feedback system <NUM> utilizes sensors to obtain data from the external environment. For example, the environmental feedback system <NUM> may identify the position of a wall, or window, or other targeted location or object, so data displayed by display subsystem <NUM> can have a virtual object distance appropriate for that target location. The environmental feedback system <NUM> may be a range sensor, camera, or other system.

Content data-based focal point selection <NUM> enables the system to selectively choose a virtual object distance, based on what is being displayed. For example, the system may selectively choose a portion of the image for focus.

User input systems <NUM> enable focus selection based on head tracking, gestures, voice control, and other types of feedback or input systems. Such user input systems <NUM> may include video game controllers, microphones, cameras, inertial measurement sensors, and other sensors for detecting user input.

In one embodiment, biometric systems <NUM> may also be used to detect the user's state, including the user's identity, emotional state, etc. In one embodiment, the biometric system <NUM> may be used to detect the user's vision correction, and provide adjustment based on the vision correction.

Other control data <NUM> may also be provided to the system. Any of this data from auxiliary data system <NUM> may be used to adjust the virtual object distance of one or more image elements. In one embodiment, in addition to auxiliary data system <NUM>, the system may additionally accept manual adjustment <NUM>. In one embodiment, the manual adjustment may be used to correct for the user's optical issues, which sets a baseline for the user. In one embodiment, the manual adjustment is stored so that a user may have a customized setting, which may be beneficial if the near-eye display system is shared.

In one embodiment, the near-eye display <NUM> may provide depth blending. In one embodiment, the system <NUM> enables depth blending between the focal lengths created using the modulation stack <NUM>. Depth blending uses weighting of pixel values between adjacent planes, in one embodiment. This creates an appearance of continuous depth. In one embodiment, the weighting may be linear weighting. In one embodiment, nonlinear optimization techniques may be used. In one embodiment, the image source <NUM> adjusts the pixel values output, to create such depth blending.

<FIG> is a block diagram of one embodiment of a projection assembly <NUM>. The projection assembly <NUM>, in one embodiment, includes a plurality of digital light path length modulators (<NUM>, <NUM>) as well as a plurality of intermediate optics elements (<NUM>, <NUM>, <NUM>, <NUM>) together forming a greater modulation stack <NUM>. In one embodiment, the projection assembly in a real system may include <NUM>-<NUM> elements which include lenses, mirrors, apertures, and the like, referred to as intermediate optics. In one embodiment, the intermediate optics may be interspersed with the digital light path length modulators. In one embodiment, they may be positioned before and/or after the set of digital light path length modulators. In one embodiment, polarization filter <NUM> may be positioned before 299A or after 299B in the greater modulation stack <NUM>.

In one embodiment, the projection assembly <NUM> may correct for chromatic aberration and other irregularities of optical systems.

<FIG> and <FIG> are diagrams of one embodiment of a near-eye display (NED) system including a modulation stack. The light modulator <NUM> outputs polarized light, both state <NUM> and state <NUM> polarized light, in one embodiment. Polarizing filter <NUM> removes the state <NUM> polarized light, and passes through state <NUM> polarized light only.

The modulation stack <NUM> includes one or more digital light path length modulators <NUM>. For simplicity the illustration here includes a single digital light path length modulator <NUM>. The digital light path modulator <NUM> includes a polarization modulator <NUM>, which can rotate the polarization of light, and an optical light path extender (OPLE) <NUM> which selectively extends the light path length, based on the polarization of the light.

The polarization modulator <NUM> in <FIG> is "off," leaving the state <NUM> polarized light to pass through. In this context, the term "on" refers to a setting in which the polarization modulator <NUM> alters the polarization of light, while the term "off" refers to the setting in which the polarization modulator <NUM> does not alter the polarization of light.

The OPLE <NUM> has a plurality of polarization sensitive reflective elements, which reflect state <NUM> polarized light, while passing through state <NUM> polarized light. Here, state <NUM> polarized light is transmitted straight through. The output in one embodiment is transmitted to near-eye display (NED) projection optics <NUM>. Though it is not shown, additional optical elements may be included in this system, including lenses, correction systems, etc..

<FIG> is a diagram of the near-eye display system of <FIG> with the polarization modulator "on. " Here, again, the polarizing filter passes only state <NUM> polarized light. However, here, the polarization modulator <NUM> modulates the light, and outputs state <NUM> polarized light. The state <NUM> polarized light is reflected by the polarization sensitive reflective elements of OPLE <NUM>. Thus, this light goes through a longer light path than the light with state <NUM> polarization, which is passed through without reflection.

A comparison of <FIG> and <FIG> shows that the state <NUM> polarized light has a longer light path than the state <NUM> polarized light. In this way, a digital light path length modulator <NUM> can change the light path length. While only a single digital light path length modulator <NUM> is shown here, a plurality of digital light path length modulators <NUM> may be stacked to provide a larger number of light path lengths.

<FIG> and <FIG> show a time sequential embodiment, in which all of the light entering the digital light path length modulator <NUM> has one polarization, and is either modulated or not modulated by polarization modulator <NUM>. In this example, the system switches between the states shown in <FIG> and <FIG>, in time. The polarization modulator <NUM> may selectively modulate the polarization of a subset of the light, in one embodiment. In one embodiment, modulation may be based on location, time, color, wavelength, and optionally other differentiable factors.

<FIG> illustrates one embodiment of a simple optical system to show a relationship between a focal length and conjugate ratio. The conjugate ratio is the ratio of object distance o to image distance I, along the principal axis of a lens or mirror. For an object at the focal point of a lens, the conjugate ratio is infinite. A combination of the focal length and conjugate ratio determines the virtual object distance of an image.

<FIG> illustrates one embodiment of a modulation stack <NUM> including three digital light path length modulators. Each of the digital light path length modulators <NUM>, <NUM>, <NUM> includes a polarization modulator and an OPLE. In this example, two of the OPLEs <NUM>, <NUM> are self-aligned OPLEs.

Self-aligned OPLEs include two plates that adjust the spatial shift of the reflected light. The self-aligned OPLE <NUM> can be used to spatially realign the reflected and passed-through light. In one embodiment, the two plates are matched. In one embodiment, they may be matched by having the same thickness, t2, and mirror image polarization sensitive reflective elements. In one embodiment, two plates may be matched by having the spatial shift created by one of the plates with a particular thickness, and angle of the polarization sensitive reflective elements be matched by a second plate with a different thickness and/or angles, which is designed to provide a matching spatial shift. In one embodiment, the base material of the OPLE may change as well, with the materials having a different index of refraction, bifringence, and other properties.

In various embodiments, one or more of the following variations may be made: the material used to make the OPLE, effective thickness of the OPLEs may vary, as may the angles of the polarization sensitive reflective elements. The effective thickness of the OPLE is defined as the cumulative thickness of the one or more plates which make up the OPLE. Thus the effective thickness of OPLE <NUM> is different than the thickness of OPLE <NUM>, even though the individual plates in the two OPLEs <NUM>, <NUM> are identical.

With the shown set of three different OPLEs, the system can create up to eight (<NUM><NUM>) virtual object distances by selectively modulating the polarization, as follows:.

<FIG> illustrates one embodiment of the effect of using an OPLE <NUM>, with a light source for non-reflected light. The light source is real source <NUM>. As can be seen, in this example, for state <NUM> polarized light which is not reflected by the polarization sensitive reflective elements, the real light source <NUM> and the "virtual" or perceived light source are in the same position. This figure additionally shows that for a real light source <NUM>, light travels in a cone, rather than a straight light as is usually illustrated for simplicity.

<FIG> illustrates one embodiment of the effect of using the OPLE <NUM> of <FIG>, with a light source for reflected light. In this illustration, state <NUM> polarized light is reflected. Thus, the user's perceived "virtual light source" <NUM> is spatially shifted from the real light source <NUM>. The lengthening of the light path shifts the virtual source vertically, while the movement of the light caused by the bounce shifts the apparent light source horizontally. In the example shown, the virtual light source is shifted to the right and back. The virtual rays show that the user's perception tracks back the light, to perceive the virtual source.

<FIG> illustrates one embodiment of the effect of using a self-aligned OPLE <NUM>, with a light source, for reflected light. As can be seen, by using the self-aligned OPLE <NUM>, the virtual light source <NUM> appears to be further away (e.g. lengthening the virtual object distance) from the real source <NUM>, but not shifted in position. Although the self-aligned OPLE <NUM> shown in <FIG> has no gap between the plates, a gap, including a gap with additional optical elements, could continue to provide this self-alignment feature. Furthermore, while the two plates in the shown self-aligned OPLE <NUM> are matched, they need not have an identical thickness or angle for the polarization sensitive reflective elements, as discussed above.

<FIG> shows the effect of light extension, on a perceived image. The illustration shows three degrees of light extension side by side, for comparison. The first one passes the light without any lengthening, so the image is perceived at the focal plane of the display. The second one lengthens the light path, which causes the user to perceive the image at a different focal plane. The third one lengthens the light path further, which causes the user to perceive a virtual image at a third focal plane. Thus, by controlling the length of the light extension, a system can create virtual images and image elements at various focal points. Using the digital light path length modulator, the system can adjust the light path digitally, and selectively position virtual images at various virtual object distances.

<FIG> illustrates one embodiment of the capability of displaying a single frame including image elements at a plurality of virtual object distances. In this example, the stick figure in focal plane <NUM>599A and the tree in focal plane <NUM>599B are perceived at different virtual object distances, though they are part of the same image frame. This can be done on a time sequential basis or on a per pixel basis, as will be discussed in more detail below.

<FIG> is a flowchart of one embodiment of using the near-eye display system including multiple focal planes. The process starts at block <NUM>.

At block <NUM>, a plurality of image elements are identified. In one embodiment, the image includes at least two elements. In another embodiment, any particular frame or image may include only a single image element.

At block <NUM>, the preferred virtual object distance is determined for each of the plurality of image elements. The virtual object distance is the perceived focal length of the image element to the user. The virtual object distance is defined by the focal length and conjugate ratio.

At block <NUM>, one or more of the image elements are associated with one or more target virtual object distances.

At block <NUM>, the appropriate light path lengths are created, using the modulation stack, as described above, for the selected virtual object distance. In one embodiment, the modulation may be time-based and/or pixel-based.

At block <NUM>, the input is adjusted to correct for any artifacts created by the modulation stack. As noted above, the modulation stack may create lateral movement that is not intended. The digital correction system may adjust the light source to correct for such effects.

At block <NUM>, the NED display system is used to display the image elements at a plurality of positions. The process then ends. In a real system, the process is continuous, as long as the NED is being used, with each frame, or sub-portion of a frame processed as described above.

<FIG> is a flowchart of one embodiment of using the near-eye display system with spatial adjustments of light path length. Spatial adjustment in this context means that the virtual object distances are adjusted on a per pixel basis. Though the term "per pixel" is used, this does not necessarily refer to a pixel being a particular size, and the modulation may be on a per "zone" basis, where the zone is a portion of the frame being displayed. For some frames, the zone may be the entire frame. The size of the zone that is adjusted may range from a <NUM> pixel by <NUM> pixel area to a much larger area, including the entirety of a frame. However, within a single frame passed through, the system may create multiple virtual object distances. The process starts at block <NUM>.

At block <NUM>, polarized light with both types of polarization is received. In one embodiment, this is S-type polarization and P-type polarization.

At block <NUM>, polarization is set on a per pixel basis, using the polarization modulator. This means, utilizing the OPLE discussed above, that on a per-pixel basis the light takes the longer or shorter path.

At block <NUM>, the light is passed through the modulation stack. As noted above, the polarization of some or all of the light may change multiple times as it passes through the modulation stack. This adjusts the light path length for the light, on a per pixel basis.

At block <NUM>, the NED display system displays the image at the plurality of virtual object distances. The process then ends at block <NUM>. As noted above, in a real system, the process is continuous, as long as the NED is being used, with each frame processed as described above.

<FIG> is a flowchart of one embodiment of using the near-eye display system with time sequential adjustments of light path length. Time sequential adjustment utilizes the rapid display of a plurality of subframes, each subframe including one or more image elements at a particular virtual object distance. The plurality of subframes create a single perceived frame, with a plurality of image elements at a plurality of virtual distances. The process starts at block <NUM>.

At block <NUM>, a subframe is selected, with a particular polarization. In one embodiment, a subframe defines the image elements at a particular virtual object distance. In one embodiment, a polarization filter is used. In one embodiment, a single visual frame is made up of one or more subframes, where each subframe represents a virtual object distance.

At block <NUM>, polarization is modulated for the subframe. Polarization is modulated for the entire subframe, using the polarization modulator.

At block <NUM>, the subframe is passed through the modulation stack. The length of the light path can be set by altering the polarization using the polarization modulators between the OPLEs for the whole subframe, as it passes through the modulation stack.

At block <NUM>, the subframe is displayed at a particular virtual object distance, based on the passage of the light through the modulation stack.

At block <NUM>, the process determines whether there are any more subframes that are part of this frame. If so, the process returns to block <NUM> to select the next subframe to add to the image. The subframes are displayed in a way that enables the perception of the sequence of subframes as a single frame, including multiple virtual object distances. The process then ends at block <NUM>. As noted above, in a real system, the process is continuous, as long as the NED is being used, with each subframe processed as described above.

<FIG> is a flowchart of one embodiment of using the near-eye display system with variable adjustment of light path length, based on auxiliary data. The process starts at block <NUM>.

At block <NUM>, auxiliary data is received. Auxiliary data may include eye tracking data (showing the user's current gaze vector), environmental sensors (identifying a position of a wall or other surface for the image), key object identification (selecting a key object to be in the focal plane for the user), user input, and other external factors which may alter the selection of the virtual object distance for an image element or subframe.

At block <NUM>, the virtual object distance for one or more image elements is identified, based on the auxiliary data. This may be where the user is looking, or where the system wants the user to look, for example the location of an external object which is a proper focus for an image for an augmented reality type display.

At block <NUM>, the image element is displayed at the designated virtual object distance. This is done by passing the image elements through the modulation stack, and adjusting the light path length to place the image element at the desired virtual object distance.

The process then ends at block <NUM>. As noted above, in a real system, the process is continuous, as long as the NED is being used.

<FIG> is a flowchart of one embodiment of using dynamic focal planes using eye tracking for feedback. The process starts at block <NUM>.

At block <NUM>, a plurality of image elements are displayed at various focal planes. At block <NUM>, the user's gaze vector is identified. Gaze vector is the direction and angle of the gaze of the user. This is one type of output of an eye tracking system.

At block <NUM>, the process determines whether the display needs diopter adjustment. In one embodiment, this may be done based on user input, or calibration with the user. If so, at block <NUM>, the virtual object distances are adjusted, using the modulation stack, without the use of moving parts. In one embodiment, the process may use controlled diopter steps for adjustment.

At block <NUM>, the process determines whether the user's gaze vector is directed at the "wrong" location. Wrong in this context means that the gaze vector indicates that the user's point of focus is not on the portion of the frame that he or she is meant to be focused on. This may be determined based on eye tracking, or other auxiliary information. If so, at block <NUM> the virtual object distances, and locations optionally, of one or more image elements are adjusted. As noted above, this may be done by adjusting the modulation stack, so that those image elements are placed in a different focal plane.

At block <NUM>, the process determines whether the focal point is to be altered, based on auxiliary information. If so, at block <NUM>, the system selectively focuses or blurs image portions. This may be done by actually blurring, or by placing the "blurred" portions into a different image plane, which is further from the user's focus to effectively blur the element.

The process then ends at block <NUM>. As noted above, in a real system, the process is continuous, as long as the NED is being used. Additionally, while a flowchart format is used for this Figure, the individual elements need not be in any particular order, and the system can function equally well with a subset of these potential adjustments.

In this way, a near-eye display system provides a highly adjustable multi-focus display, using a modulation stack. Because the light path length is digitally controlled using the polarization modulator, the change in the virtual object distance may be accomplished extremely quickly. This also enables the system to use time-based alteration of the focal plane, through the same modulation stack. Alternatively, the system may use pixel-based selection of focal length, or variable focal length. This system may be used in near-eye display systems ranging from the headphone configured display system shown in <FIG>, to camera view finders, rifle scopes, binoculars, and any other near-eye display type systems.

Claim 1:
A near-eye display system (<NUM>) to display an image to a user comprising:
an image source (<NUM>) to provide light;
a modulation stack (<NUM>,<NUM>) comprising one or more digital light path length modulators (<NUM>,<NUM>,<NUM>), a digital light path length modulator (<NUM>) comprising:
a polarization modulator (<NUM>) to receive light and to selectively modulate a polarization of the light; and
an optical path length extender (OPLE) (<NUM>) to direct the light having a first polarization through a first light path through the OPLE, and to direct the light having a second polarization through a second light path through the OPLE, the first and second light paths having different light path lengths; and
the modulation stack to output light via a first light path and a second light path, the first light path and the second light path having different light path lengths, the light path lengths altered on a time sequential basis; and
an imaging assembly (<NUM>) to display a plurality of subframes from the modulation stack received on the time sequential basis to create a perceived single frame having depth.