Apparatus, method and near-eye display system

Abstract

The optical device includes a freeform light guide for directing light from a display toward an area where a user's eyes are expected to be located. The freeform light guide includes a light guide substrate having opposing first and second surfaces extending between first and second ends of the freeform light guide, at least the second surface being a freeform surface overlaid with a partial mirror layer. The first surface is overlaid with at least a quarter-wave plate layer and a polarizing beam splitter layer. The freeform light guide also includes an input coupling interface near the first end of the freeform light guide for receiving light from the display.

Description

[Background technology]

[0001] background Conventional head-mounted displays that provide an augmented reality (AR) experience typically use optical systems that allow a user to both see the surrounding environment through the optical system and transmit display light that depicts the AR visual content to one or both of the user's eyes. Such optical systems typically use light guides (also commonly referred to as "waveguides") to transmit display light from the display while also allowing light from the surrounding environment to pass through to the user's eyes. Conventional light guides rely on total internal reflection (TIR) ​​of light provided by the display entirely from input to output, and TIR relies on the light within the light guide reflecting at a critical angle. To achieve TIR with a wide field of view (FOV), such light guides must be constructed from materials with a high refractive index. Also, light guide materials with higher refractive index tend to be heavier and more expensive than materials with lower refractive index, and as a result, conventional TIR-based light guides tend to be more expensive and heavier.

[0002] In addition, conventional light guides require at least one extraction element embedded or implemented within the light guide itself to propagate the reflected light out of the light guide, typically toward the user's eye, rather than continuing to be reflected within the light guide. Such extraction elements include, for example, raised or recessed surface features, such as protrusions or depressions, and localized material variations or other surface or volumetric perturbations in the light guide. These perturbations can cause reduced extraction efficiency (e.g., reduced brightness uniformity of the reflected light) resulting in discontinuous surfaces that may be visible to a user or observer. Summary of the Invention

[0003] Summary of the Invention An embodiment relates to an apparatus comprising a freeform light guide including a light guide substrate having opposing first and second surfaces extending between first and second ends of the freeform light guide, at least the second surface being a freeform surface, the freeform light guide further including an input coupling interface formed at least in part by the freeform light guide substrate (and thus located near and forming part of the first end of the light guide), a quarter wave plate layer overlying the first surface of the light guide substrate, a polarizing beam splitter layer overlying the quarter wave plate layer, and a partial mirror layer overlying the second surface.

[0004] The device may further comprise a display configured to emit display light towards an input coupling interface of the light guide substrate. The device may further comprise a quarter wave plate disposed between the display and the input coupling interface. Furthermore, the display may be positioned relative to the input coupling interface and / or the input coupling interface may be oriented relative to the first surface or the second surface such that display light from the display entering the light guide at the input coupling interface is directed towards the first surface or the second surface.

[0005] Also, the display is configured to emit display light having a first circular polarization state; and / or the quarter-wave plate layer is configured to convert incident light having the first circular polarization state to light having a first linear polarization state, convert incident light having the first linear polarization state to light having the first circular polarization state, and convert incident light having a second circular polarization state to a second linear polarization state; and / or the polarizing beam splitter layer is configured to reflect light having the first linear polarization state and transmit light having the second linear polarization state.

[0006] The apparatus may also further comprise a spectacle frame including a spectacle lens implementing the freeform light guide and an out-coupling region disposed at or adjacent to an eye-side surface of the spectacle lens.

[0007] The freeform light guide may further comprise a linear polarizing layer overlying the polarizing beam splitter layer and / or an anti-reflection layer overlying the linear polarizing layer. The apparatus may also include a display quarter wave plate disposed between the display and the input coupling interface and configured to convert display light emitted from the display from a linearly polarized state to a circularly polarized state.

[0008] The partial mirror layer may be configured to convert reflected incident light having a first circular polarization state to light having a second circular polarization state and / or to convert reflected incident light having the second circular polarization state to light having the first circular polarization state.

[0009] The device may further comprise an adaptive optic disposed on the second surface of the light guide. For example, the adaptive optic is comprised of a transparent material having properties that allow light to pass through the adaptive optic with minimal diffraction and / or reflection. The eye-facing surface of the adaptive optic may have a freeform curved surface that is complementary to the world-facing (second) surface of the light guide. The contour width of the adaptive optic may be varied such that the world-facing surface of the adaptive optic is parallel or nearly parallel to the eye-facing (first) surface of the light guide. Furthermore, the world-facing surface of the adaptive optic may be a surface that can incorporate a prescription optical correction of the world-side light to the user.

[0010] Embodiments also relate to a method for transmitting display light from a display to an eye of a user in a near-eye display system, the method including providing a freeform light guide including a light guide substrate having opposing first and second surfaces, an input coupling interface, a quarter wave plate layer overlying the first surface, a polarizing beam splitter layer overlying the quarter wave plate layer, and a partial mirror layer overlying the second surface, at least the second surface including a freeform surface, the method further including directing display light emitted by the display to the input coupling interface, transmitting a representation of the display light through the light guide from the input coupling interface to an out-coupling region, and transmitting a representation of the display light from the out-coupling region towards the eye after the representation of the display light is incident on the second surface.

[0011] Also, the apparatus embodiments described above may be used in the method embodiments described above.For example, the freeform light guide may include a linear polarizing layer overlying a polarizing beam splitter layer.

[0012] Transmitting a representation of the display light through the light guide may also include causing a first change in a polarization state of the display light such that the display light is reflected at a polarizing beam splitter layer, and / or causing a second change in the polarization state of the reflected display light such that the display light passes through the quarter wave plate layer, the polarizing beam splitter layer, and the linear polarizer layer to reach the output coupling region.

[0013] Additionally, transmitting a representation of the display light through the light guide may include at least one of the following operations: transmitting the display light having a first circular polarization state from the input coupling interface to a quarter-wave plate layer, optionally converting the representation of the display light to a first linear polarization state at the quarter-wave plate layer, optionally reflecting the representation of the display light having the first linear polarization state at a first surface of the freeform light guide towards the quarter-wave plate layer, and optionally converting the reflected representation of the display light from the first linear polarization state to a first circular polarization state at the quarter-wave plate layer.

[0014] Additionally, transmitting a representation of the display light through the light guide may include at least one of transmitting a representation of the display light having a first circular polarization state from the quarter-wave plate layer to the second surface, optionally reflecting the representation of the display light off a partial mirror layer at the second surface such that the first circular polarization state is converted to a second circular polarization state, optionally transmitting the representation of the display light having the second circular polarization state to the quarter-wave plate, optionally converting the representation of the display light having the second circular polarization state to a second linear polarization state at the quarter-wave plate layer, optionally transmitting the representation of the display light having the second linear polarization state to a polarizing beam splitter layer, and optionally reflecting the representation of the display light having the second linear polarization state off the polarizing beam splitter layer.

[0015] Transmitting a representation of the display light through the light guide may also include transmitting a representation of the display light having the second linear polarization state from the polarizing beam splitter layer to a quarter-wave plate layer, optionally converting the representation of the display light having the second linear polarization state to a second circular polarization state at the quarter-wave plate layer, optionally transmitting the representation of the display light having the second circular polarization state to a second surface, optionally reflecting with a partial mirror layer at the second surface such that the representation of the display light having the second circular polarization state is converted to the first circular polarization state, and optionally transmitting the representation of the display light having the first circular polarization state through the quarter-wave plate layer, the polarizing beam splitter layer, and the linear polarizing layer to an output coupling region.

[0016] Of course, only one of the above example operations can be used for transmitting the display light representation through the light guide, or any combination of these operations can be used.

[0017] In another aspect, the invention relates to a near-eye display system comprising a freeform light guide having an in-coupling interface and an out-coupling region facing an assumed location of a wearer's eye, the freeform light guide being configured to transmit light to the out-coupling region by using a laminate film disposed on a first major surface facing the assumed location of the wearer's eye and a partial mirror layer disposed on an opposing second major surface to induce at least one change in a linear polarization state of the light and at least one change in a circular polarization state of the light as the light incident at the in-coupling interface traverses the freeform light guide, at least a portion of the change in polarization state causing the light to be reflected within the freeform light guide.

[0018] A near-eye display system may be formed by the apparatus described above, for example where at least a portion of the change in polarization state causes the light to reflect off a polarizing beam splitter layer within a freeform light guide.

[0019] Additionally, the light guide may include a film stack including a quarter wave plate layer and / or a polarizing beam splitter layer.

[0020] The laminate film may also include a linear polarizing layer and / or an anti-reflective layer, and at least a portion of the change in polarization state may occur as the light passes through the laminate film to the out-coupling region and toward the user's eye.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure can be understood, and its numerous features and advantages made apparent to those skilled in the art by reference to the accompanying drawings, in which: The use of the same reference symbols in different drawings indicates similar or identical items. [Brief description of the drawings]

[0022] [Figure 1]FIG. 1 is a front view of an exemplary form factor for a near-eye display system using a freeform polarizing light guide, according to some embodiments. [Diagram 2] FIG. 1 is a perspective view of another exemplary form factor for a near-eye display system using a freeform polarizing light guide, according to some embodiments. [Diagram 3] FIG. 1 is a cross-sectional view of a freeform polarizing light guide with an associated display according to some embodiments. [Figure 4] 4A-4D are cross-sectional views of the freeform polarizing light guide and associated display representations of FIG. 3 and various close-ups of portions thereof, according to some embodiments. [Diagram 5] FIG. 5 is a flow diagram illustrating a method of using a near-eye display system utilizing the freeform polarizing light guide of FIG. 4 to display images to a user, according to some embodiments. [Figure 6] 1 is a cross-sectional view of another freeform polarizing light guide with an associated display according to some embodiments. [Figure 7] FIG. 7 is a flow diagram illustrating a method of using the near-eye display system with the freeform polarizing light guide of FIG. 6 to display images to a user, according to some embodiments. [Figure 8] 1 is a cross-sectional view of another freeform polarizing light guide and associated adaptive optics according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Detailed Description 1-8 show exemplary implementations of freeform polarizing light guides for use in near-eye display systems. In at least one embodiment, a near-eye display system uses a freeform polarizing light guide (FPLG) to transmit light that represents a display image from a microdisplay or other display to a wearer's eye. However, unlike conventional light guides that rely entirely on total internal reflection (TIR) ​​to transmit light through the light guide, FPLGs do not rely entirely on TIR, but instead transmit a representation of the display light from an input coupling interface of the FPLG facing the display to an output coupling area facing the user's eye through multiple changes in polarization state as the light traverses the FPLG. Here, at least some of these changes in polarization state cause the light to be reflected within the FPLG. In addition, in some embodiments, some of these changes in polarization state allow the reflected light to traverse the layers of the FPLG such that the light exits the FPLG from the output coupling area toward the user's eye. The layers of the FPLG function to reflect the light if it were in any other polarization state.

[0024] By manipulating the polarization state of the display light to facilitate reflections within the FPLG until the light is finally output toward the eye, the FPLG can transmit the display light from the input-coupling interface to the output-coupling region in a manner that does not rely on end-to-end TIR or out-coupling elements, in contrast to conventional near-eye light guides. In this way, the light guide substrate of the FPLG, which serves as the primary conduit for the display light between the input-coupling and the output-coupling, can be implemented using an optically transparent material that has a lower refractive index than the light guide material used in conventional TIR-based light guides, while also providing a higher FOV than can typically be achieved by such conventional light guides for a material with a given refractive index. Since no special out-coupling elements or special materials are required, manufacturing complexity is also reduced. As a result, lighter FPLGs can be manufactured more cheaply. Also, since no end-to-end TIR is required, FPLGs may be implemented that have one or more major surfaces with less strict radial dimensions. As an example, the FPLG may be implemented in a form factor in which one or both major surfaces are freeform surfaces, and as such can be implemented to provide a non-zero refractive power or can be implemented within an eyeglass lens fitted to an eyeglass frame, thereby also providing a vision correcting lens effect.

[0025] FIG. 1 illustrates an exemplary near-eye display system 100 using a freeform polarizing light guide (FPLG) 102, according to at least one embodiment. The system 100 is implemented in an eyeglass form factor with an eyeglass frame 104 having eyeglass lenses 105, 106 for the right and left eyes of a wearer, respectively. In the illustrated embodiment, the FPLG 102 is separate from the eyeglass lenses, but instead overlies one of the eyeglass lenses (in this example, eyeglass lens 105) such that an output coupling area of ​​the FPLG 102 (described in more detail below in FIG. 3) faces the corresponding intended location of the wearer's eye. The FPLG 102 is attached to the eyeglass frame 104 via a light guide mounting housing 109. The light guide mounting housing 109 also serves to house some or all of the electronic components of the near-eye display system 100 (not shown in FIG. 1 ), such as a display for generating augmented reality (AR) or virtual reality (VR) images for display to the wearer via the FPLG 102, input coupling optics for directing light from the display to the input coupling interface of the FPLG 102, one or more processing units, one or more wireless interfaces, one or more batteries or other power sources, etc. More details on some of these components are provided below.

[0026] 2 illustrates another exemplary near-eye display system 200 using an FPLG 202, according to at least one embodiment. Similar to system 100 of FIG. 1, system 200 uses an eyeglass form factor using an eyeglass frame 204 having eyeglass lenses 205, 206. However, in contrast to system 100, system 200 implements FPLG 202 using eyeglass lenses 205. That is, FPLG 202 is integrated with eyeglass lenses 205, allowing the appearance of near-eye display system 200 to have a more conventional eyeglass appearance. In this embodiment, a display housing (omitted from FIG. 2 for clarity) on the eyeglass frame 204 above the eyeglass lens 205 includes a microdisplay or other display for emitting display light depicting an AR or VR image, and an input coupling lens for directing the emitted display light to an input coupling interface of the FPLG 202 in the lens 205, where the display light propagates through the FPLG 202 / eyeglass lens 205 and is directed towards an output coupling area 207 located in the eyeglass lens 205 / FPLG 202 to be aligned with the assumed position (or assumed range of positions) of the corresponding wearer's eye. In some embodiments, the eyeglass lens 206 also implements a corresponding FPLG 202 in a similar manner, and the system 200 also enables the display of an AR or VR image to the other eye of the wearer using a corresponding display component in a similar manner.

[0027] The FPLG 102 of the system 100 of FIG. 1 and the FPLG 202 of the system 200 of FIG. 2 each operate to transmit display light from a nearby display (e.g., a microdisplay) to the user's eye by multiple reflections of the display light within the body of the FPLG as the display light traverses from one end of the FPLG 202 proximal to the display to an out-coupling region of the FPLG 202 facing the wearer's eye. However, unlike conventional light guides, some or all of these reflections do not rely on TIR. That is, the angle of incidence may be less than the critical angle of the interface between the media at the reflection point. Rather than relying on TIR, the FPLG 202 instead uses stacked layers that selectively change the polarization state of the incident display light or selectively reflect the incident display light based on its polarization state, thereby reflecting the display light one or more times within the FPLG 202 until the polarization state of the display light is changed such that the display light can be transmitted through the face of the FPLG 202 at the out-coupling region 207 facing the wearer's eye.

[0028] Figure 3 illustrates a cross-sectional view 300 of an FPLG 302 that uses this manipulation of polarization state to provide internal reflection of in-coupled display light, according to at least one embodiment. FPLG 302 may represent, for example, FPLG 202 of system 200, such that cross-sectional view 300 may represent cross-section AA shown in Figure 2. In other embodiments, FPLG 302 represents FPLG 102 of Figure 1. It is noted that the illustrated dimensions of the various incidence features and angles shown in Figure 3 are for purposes of explaining the principles of operation and may not reflect the actual dimensions and angles implemented within the FPLG.

[0029] The FPLG 302 (i.e., the device or system of which the FPLG 302 forms a part) comprises a display 304. The display 304 may be comprised of any of a variety of displays suitable for use in light guide based near eye display systems, such as an organic light emitting diode (OLED) or liquid crystal on silicon (LCOS) microdisplay. In embodiments in which the display 304 is configured to emit linearly polarized light, the FPLG 302 (i.e., the device or system of which the FPLG 302 forms a part) further comprises a display quarter wave plate 306 disposed between the display 304 and the input coupling interface 316 of the FPLG 302 for converting the polarization of the linearly polarized display light to a circular polarization state before the display light is incident on the FPLG 302.

[0030] The FPLG 302 is comprised of a light guide substrate 320 that extends from a first end 310 near the display 304 to a second end 312 opposite the FPLG 302. The two ends 310, 312 of the FPLG 302 may be defined by respective corresponding ends of the substrate 320. The FPLG 302 also includes an input coupling interface 316 near the first end 310 that is configured to receive display light 318 from the display 304. At least a portion of the input coupling interface 316 may be formed by the substrate 320. The light guide substrate 320 is comprised of a material that is substantially transparent to the display light 318, such as glass, optical plastic, or the like. The light guide substrate 320 includes two opposing major surfaces 322, 323 that extend between the first end 310 and the second end 312 of the light guide substrate 320. The first major surface 322 is a surface that faces toward the wearer's eyes (and thus is also referred to herein as "eye-facing surface 322"), and the second major surface 323 is a surface that faces away from the wearer's eyes (and thus is also referred to herein as "world-facing surface 323"). Either or both of the eye-facing surface 322 and the world-facing surface 323 may be freeform surfaces. Thus, the FLPG 302 may be incorporated into a lens of a pair of glasses used for vision correction.

[0031] The light guide substrate 320 further includes opposing minor surfaces 324, 325. The first minor surface 324 is located at the first end 310 and is disposed at an acute angle to the eye-facing surface 322 so as to form an input coupling interface 316 whose optical axis is not parallel to the major surfaces 322, 323. The second minor surface 325 is located at the second end 312 and can be disposed perpendicular to the major surfaces 322, 323 as shown, or at a non-perpendicular angle to the major surfaces 322, 323.

[0032] In one embodiment, the eye-facing surface 322 is overlaid with multiple layers of materials configured to change one or more polarization states of light as it traverses the surface or to reflect light having a particular polarization state while transmitting light having a different polarization state (i.e., selectively transmitting light to a subsequent layer or out of the light guide). This collection of multiple layers is referred to as a laminate film 330. As will be described below with reference to FIG. 4, in some embodiments, the laminate film 330 includes a quarter wave plate (QWP) layer 332, a polarizing beam splitter (PBS) layer 334, and a linear polarizer (LP) layer 336. To prevent unwanted reflection of light from the eye side, the laminate film 330 may further include an anti-reflection (AR) layer 338 disposed between the intended location of the user's eye 314 and the other layers of the laminate film 330. Each layer may be provided as a preformed film layer, such that multiple films are laminated together to form the laminate film. The laminate film is laminated onto the surface of the light guide substrate 320. Alternatively, each layer can be provided as a coating deposited in succession on the surface of the light guide substrate 320. Furthermore, in some embodiments, one or more of the layers are implemented as a preformed film layer while one or more other layers are implemented as coatings. Additionally, the FPLG 302 includes a partial mirror layer 328 or a 50 / 50 reflective coating disposed on the world-facing surface 323. The partial mirror layer 328 functions to reflect at least a portion of the light incident on the world-facing surface 323 while allowing the remaining portion of the light to exit the FPLG 302 through the world-facing surface.

[0033] FPLG 302 further includes an out-coupling region 326 for outputting a representation of the display light 318 reflected within light guide substrate 320 toward the wearer's eye. As used herein, the term "out-coupling region" may refer to an area of ​​the eye-facing surface and overlapping area of ​​the laminate film (such as the illustrated respective areas of eye-facing surface 322 and laminate film 330) where a representation of the display light 318 exits FPLG 302 toward the wearer's eye.

[0034] 4 illustrates another cross-sectional view 400 of the FPLG 302 including further details about the layers of the laminate film 330, as well as an example of transmission of the display light through the FPLG 302 based on selective changes in the polarization state of the coupled-in display light 318, and selective reflection of the coupled-in display light 318 based on its polarization state, according to at least one embodiment. For ease of illustration, the display light 318 is shown as a single beam in the operations described below. The laminate film 330 is disposed on the eye-facing surface 322 of the FPLG 302 and includes a QWP layer 332 disposed overlying the eye-facing surface 322. In some embodiments, a PBS layer 334 is disposed overlying the QWP layer 332 such that the QWP layer 332 is adjacent to the eye-facing surface 322 and is disposed between the PBS layer 334 and the eye-facing surface 322. The FPLG 302 further includes an LP layer 336 disposed over the PBS layer 334 such that the PBS layer 334 is disposed between the QWP layer 332 and the LP layer 336. An anti-reflective (AR) layer 338 may be overlaid on the LP layer 336 such that the LP layer 336 is disposed between the AR layer 338 and the PBS layer 334 to prevent unwanted reflection of light from the eye side. Each layer may be provided as a preformed film layer such that multiple films are overlaid on each other to form a laminated film. The laminated film is overlaid on the surface of the light guide substrate 320. Alternatively, each layer may be provided as successively deposited coatings on the surface of the light guide substrate 320. Furthermore, in some embodiments, one or more of these layers are implemented as a preformed film layer while one or more other layers are implemented as coatings.

[0035] The QWP layer 332 is formed from a material or combination of materials that act to convert light having a first circular polarization state to light having a first linear polarization state and vice versa. The QWP layer 332 also acts to convert light having a second circular polarization state to light having a second linear polarization state and vice versa. More generally, a quarter-wave plate such as the QWP layer 332 transmits light and changes its polarization state without shifting or displacing it. In a quarter-wave plate, the phase difference between the polarization components projected along the fast and slow axes is a quarter-wave. The QWP layer 332 may be implemented, for example, as a multi-order, zero-order, or achromatic QWP layer. Materials for implementing the QWP layer 332 include calcite or crystal films, polychromatic films, and the like.

[0036] The PBS layer 334 is implemented using a material that acts to transmit light having a first linear polarization state and reflect light having a second linear polarization state. Examples include, but are not limited to, a wire grid type PBS layer, a dielectric coating type PBS layer, and the like. The LP layer 336 acts to reduce unwanted light transmitted by the PBS layer 334. The LP layer 336 is implemented using a material that acts to transmit light having a second linear polarization state. Examples include, but are not limited to, a wire grid polarizer, a calcite polarizer, or a dichroic polarizer, and the like. Furthermore, the LP layer 336 can improve image quality since it reduces stray light and ghost images by reducing light reflected at the eye side of the FPLG 302 to the user's eye. The AR layer 438 disposed on the LP layer 336 can also further improve image quality since it helps to reduce light reflected at the eye-facing surface 322 of the FPLG 302 to the user's eye.

[0037] The world-facing surface 323 of the FPLG 302 is configured as a continuous or smoothed freeform surface, allowing specular reflection of light propagating within the FPLG 302 when it encounters the world-facing surface 323. When all or a portion of the world-facing surface 323 is covered by the partial mirror layer 328, at least a portion of the display light propagating within the FPLG 302 is reflected at the world-facing surface 323. Light having a first circular polarization state that encounters the partial mirror layer 328 at the world-facing surface 323 is converted to a second circular polarization state, and light having a first linear polarization state that encounters the world-facing surface 323 is converted to a second linear polarization state. Similarly, light having a second circular polarization state that is incident on the partial mirror layer 328 is converted to the first circular polarization state, and light having a second linear polarization state that is incident on the partial mirror layer 328 is converted to the first linear polarization state.

[0038] According to the described configuration, in an embodiment where display light 318 exiting the display 304 enters the light guide towards the eye-facing surface 322, the display light 318 first undergoes TIR and then undergoes multiple changes in polarization state as the display light 318 (or a representation thereof) is reflected or transmitted by the film layers and / or major surfaces 322, 323 of the laminate film 330. Referring to the close-up inset 406 shown in FIG. 4, the display light 318 having a first circular polarization state propagating through the light guide substrate 320 enters the QWP layer 332 and is converted to light having a first linear polarization state as the converted representation of the display light 318 propagates through the QWP layer 332. The converted light having the first linear polarization state then encounters an overlying PBS layer 334. The PBS layer 334 is configured to transmit light having the first linear polarization state, and therefore transmits the light to the LP layer 336. Since the LP layer 336 is configured to transmit light having a first linear polarization state, the incident light is transmitted through the LP layer 336 338 and undergoes TIR at the boundary formed between the eye-side of the laminate film 330 and the surrounding medium. The reflected light then transmits back through the LP layer 336 and the PBS layer 334 to the QWP layer 332. As the transmitted light propagates through the QWP layer 332, the QWP layer 332 converts the polarization state of the light from the first linear polarization state to a first circular polarization state such that the reflected light having a first circular polarization state re-enters the light guide substrate 320. It will be appreciated that this initial reflection is a TIR-based reflection since it depends on the angle at which the display light is incident on the laminate film 330. However, subsequent reflections of the light within the FPLG 302 are independent of the angle at which the light is incident on these layers since they occur due to interaction with specific layers in the laminate film configured to reflect light of specific polarizations. Thus, as will be described in more detail below, the FPLG 302 utilizes both TIR and the polarization state-based reflective properties of the laminate film 330 to “bounce” the display light along the length of the light guide substrate 320 .

[0039] The representation of the display light reflected at the boundary formed between the eye side of the laminate film 330 and the surrounding medium and having a first circular polarization state after passing through the QWP layer 332 reenters the light guide substrate 320 and is transmitted to the world-facing surface 323. At the world-facing surface 323, the reflected light is converted from the first circular polarization state to a second circular polarization state as it is reflected at the partial mirror layer 328 and transmitted again through the light guide substrate 320 toward the laminate film 330. The reflected light having the second circular polarization state is converted to a second linear polarization state as it propagates through the QWP layer 332 to the PBS layer 334. Since the PBS layer 334 is configured to reflect light having the second linear polarization state, the light transmitted from the QWP layer 332 is reflected at the PBS layer 334 and transmitted again through the QWP layer 332. In the QWP layer 332, the light is converted to the second circular polarization state when the resulting representation of the display light 318 is incident on the light guide substrate 320. The reflected light having the second circular polarization state is propagated towards the world-facing surface 323. At surface 323, the reflected light is converted to the first circular polarization state when it reflects off the partial mirror layer 328 and transmits through the light guide substrate 320 towards the laminate film 330.

[0040] The light having the first circular polarization state reflected from the world-facing surface 323 then enters the QWP layer 332 and is converted from the first circular polarization state to a first linear polarization state. Since the PBS layer 334 and the LP layer 336 are configured to transmit the light having the first linear polarization state, the light transmitted from the QWP layer 332 is transmitted through the PBS layer 334 and the LP layer 336 to the AR layer 338. Because the eye-facing surface 322 and the world-facing surface 323 of the FPLG 302 are not oriented parallel, the angle of incidence on the AR layer is less than the critical angle for TIR, and at least a portion of the transmitted light from the LP layer 336 propagates through the AR layer 338 to the out-coupling region 326 and exits the FPLG 302 to the user's eye. This configuration allows light to exit the FPLG 302 despite the absence of an extraction element as used in conventional light guides.

[0041] FIG. 5 is a flow diagram illustrating a method 500 of using a near-eye display system with the freeform light guide of FIG. 3 (further shown in FIG. 4) to display an image to a user, according to at least one embodiment. The method 500 begins at block 502. In block 502, the display 304 emits display light 318. The display is oriented with respect to the input coupling interface 316 such that the emitted display light 318 is directed to a laminate film 330 disposed on an eye-facing surface 322 (i.e., a first major surface) of the FPLG 302. If the provided display is configured to emit light having a left-handed circular polarization state, in block 504, a QWP layer may be provided between the display and the input coupling interface to convert the display light to an RCP state before it is incident on the light guide substrate 320. The light having the RCP state is then incident on the light guide substrate 320 of the FPLG 302 via the input coupling interface 316 in block 506.

[0042] In block 508, the display light propagates in the light guide substrate 320 at an angle to the eye-side surface such that when it encounters an interface between two media, such as a film layer and air interface, the angle at which the light encounters the interface is equal to or greater than the critical angle at which TIR occurs for the two media. As shown by the close-up inset 406 in FIG. 4, in block 510, upon incidence on the QWP layer 332, the resulting representation of the display light 318 in the RCP state is converted to light having linear y-polarization 350. Since the PBS layer 334, the LP layer 336, and the AR layer 338 of the laminated film 330 are configured to transmit light having linear y-polarization, in block 512, the converted light propagates in the PBS layer, the LP layer, and the AR layer to the interface between the AR layer 338 and the surrounding medium 362 on the eye-facing surface 322 of the FPLG 302. Because the transmitted light encounters a boundary at an angle 360 ​​that is greater than or equal to the critical angle of the AR layer 338 material and air, in block 514 the converted light 350 undergoes TIR at the boundary and travels back through the PBS layer 334, the LP layer 336, and the AR 338 layer back to the QWP layer 332. Upon entering the QWP layer 332, in block 516 the reflected light 351 having a linear y polarization state is converted to light having an RCP state 352 as it is transmitted towards the world-facing surface 323 of the FPLG 402.

[0043] At the world-facing surface 323, the transmitted light 352 is converted from an RCP state to light having an LCP state 354 when reflected off the partial mirror layer 328 (block 518). The resulting representation of the display light having an LCP state is returned from the world-facing surface 323 towards the QWP layer 332 of the laminate film 330 disposed on the eye-facing surface 322. As shown in the close-up inset 408 of FIG. 4, at block 520, the reflected light propagates through the QWP layer 332 and is converted to a linear x-polarization state 356. The resulting modified light 356 then encounters the PBS layer 334. Because the PBS layer 334 is configured to reflect light having a linear x-polarization state, the PBS layer 334 reflects the modified light 356 back to the QWP layer 332 (block 522).

[0044] As the reflected light 358 propagates within the QWP layer 332, the QWP layer 332 converts the reflected light 358 from a linear x-polarization state back to light having an LCP state 359 (block 524) before the light 359 enters the light guide substrate 320. As represented by block 526, the reflected light having an LCP state 358 is converted back to an RCP state when it enters the world-facing surface 323 and is reflected off the partial mirror layer 328 and directed into the light guide substrate 320 towards the eye-facing surface 322. In block 528, the reflected light having an RCP state is converted to a linear y-polarization state when it enters the QWP layer 332. Because the PBS layer 334, the LP layer 336, and the AR layer 338 are configured to transmit light having linear y-polarization, in block 530 the converted light is transmitted through the PBS layer 334, the LP layer 336, and the AR layer 338 toward a boundary between the AR layer 338 and air on the eye-side of the FPLG 302. However, because the transmitted light is not incident on the boundary at an angle equal to or greater than the critical angle, the transmitted linear y-polarized light is not reflected at the boundary, but instead is transmitted toward a region of the FPLG 302 corresponding to the out-coupling region 326 for transmission toward the user's eye. This method can be repeated for each image projected by the display.

[0045] The internal reflections within the FPLG 302, represented by blocks 518 through 526, occur by manipulating the polarization state of the representation of the transmitted display light 318 in view of the polarization state specific reflections and transmission properties of the stacked material layers overlying the major surfaces 322, 323 of the light guide substrate 320, and do not rely on TIR. Thus, to achieve a given FOV, the light guide substrate 320 can be constructed from a material, such as optical plastic, that has a lower refractive index than the light guide materials (e.g., relatively heavy and expensive optical glasses) traditionally used in TIR-based light guides. Alternatively, a larger FOV can be achieved by the FPLG 302 by using a material with the same refractive index as the corresponding TIR-based light guide. Also, because no TIR is required, the light guide substrate can use at least one freeform major surface that is typically impractical to implement in a traditional TIR-based light guide.

[0046] 6 illustrates a cross-sectional view 600 of another embodiment of an FPLG 602, according to some embodiments. The FPLG 602, formed from (or including) a light guide substrate 620, includes a display 604 oriented to direct display light 606 emitted from the display 604 to an input coupling interface 616. The FPLG 602 (i.e., the device or system of which the FPLG 602 forms a part) may also include a display quarter-wave plate 608 disposed between the display and the input coupling interface 616 to convert display light having a linear polarization state to light having a circular polarization state. The input coupling interface 616 is disposed at an acute angle with respect to the world-facing surface 619 of the FPLG 602, such that the display light 606 from the display 604 entering the FPLG 602 at the input coupling interface 616 is directed to the world-facing surface 619. A partial mirror layer 624 or a 50 / 50 reflective coating is disposed on the world-facing surface 619. Partial mirror layer 624 functions to reflect at least a portion of the light incident on world-facing surface 619 while allowing the remaining portion of the light to pass through world-facing surface 619 and exit FPLG 602 .

[0047] Opposite the world-facing surface 619 is an eye-facing surface 618 located on the eye-facing side of the FPLG 602. The laminate film 610 includes a QWP layer 612 and a PBS layer 614 on the eye-facing surface 618 of the FPLG 602. Either or both of the eye-facing surface 618 and the world-facing surface 619 can be freeform surfaces that can incorporate a prescription optical correction for world-side light as it passes through the FPLG 602 to the user's eye. Thus, the FLPG 602 can be incorporated into a lens of eyeglasses that a user uses for vision correction.

[0048] Light directed into the FPLG 602 undergoes multiple reflections and exits the out-coupling area 62 on the eye-facing side of the FPLG 602. 2 toThe output coupling region 622 is typically located in a region of the FPLG 602 where the user's eye is expected to be located, such that light exiting the FPLG 602 from the output coupling region 622 is directed toward the user's eye.

[0049] According to the described configuration, light 606 emitted from the display 604 is first directed to the world-facing surface 619 of the FPLG 602 and then undergoes a change in polarization state as it is reflected or transmitted by layers and / or major surfaces 618, 619 of the laminate film 610. If the display 604 is configured to emit light having a first linear polarization state, the display quarter-wave plate 608 converts the display light 606 to a first circular polarization state before it enters the FPLG 602 at the input coupling interface 616. A representation of the display light 606 resulting from propagating through the light guide substrate 620 with the first circular polarization state is then converted to a second circular polarization state as it enters the world-facing surface 619 and is reflected off the partial mirror layer 624 towards the laminate film 610.

[0050] The representation of the display light having the second circular polarization state reflected at the world-facing surface 619 is converted to a second linear polarization state as it propagates through the QWP layer 612 to the PBS layer 614. Because the PBS layer 614 is configured to reflect light having the second linear polarization state, the transmitted light from the QWP layer 612 is reflected at the PBS layer 614 and transmitted back through the QWP layer 612. At the QWP layer 612, the light is converted to a second circular polarization state as it enters the light guide substrate 620. The reflected light having the second circular polarization state propagates towards the world-facing surface 619. At the world-facing surface 619, the reflected light is converted to the first circular polarization state as it is reflected and transmitted through the light guide substrate 620 back to the laminate film 610.

[0051] Light having a first circular polarization state reflected from partial mirror layer 624, located on world-facing surface 619, enters QWP layer 612 of laminate film 610 and is converted from the first circular polarization state to a first linear polarization state. Because PBS layer 614 is configured to transmit light having the first linear polarization state, the transmitted light from QWP layer 612 passes through PBS layer 614 to out-coupling region 622 and exits the light guide toward the user's eye.

[0052] FIG. 7 is a flow diagram illustrating a method 700 of using the near-eye display system with the freeform light guide of FIG. 6 to display an image to a user, according to at least one embodiment. The method 700 begins at block 702. In block 702, a display 604 emits a display light 606 representing a display image, which may include AR or VR content. For ease of explanation, the first circular polarization state is a right-handed circular polarization (RCP) state. However, if the provided display 604 is configured to emit light having a left-handed circular polarization (LCP) state, a quarter-wave plate may be provided between the display 604 and the input coupling interface 616 to convert the emitted light to the RCP state before being incident on the light guide substrate in block 704. In block 706, the display light 606 having the RCP state is incident on the light guide substrate 620 of the FPLG 602 via the input coupling interface 616.

[0053] A representation of the display light having an RCP state propagates through the light guide substrate 620 at a certain angle, thus encountering the world-facing surface 619 (i.e., the second major surface). At the world-facing surface 619, the transmitted light is converted to an LCP state when reflected by the partial mirror layer 624 (block 708). The light having an LCP state is directed from the world-facing surface 619 toward the QWP layer 612 of the laminate film 610 disposed on the eye-facing surface 618 (i.e., the surface facing the eye). As the reflected light propagates through the QWP layer 612, the QWP layer 612 changes the polarization state of the light to a second linear polarization state (block 710). As an example, the second linear polarization state is described herein as a linear x-polarization state. The changed light having a linear x-polarization state then encounters the PBS layer 614. Because the PBS layer 614 is configured to reflect light having a linear x-polarization state, the PBS layer 614 reflects the modified light back to the QWP layer 612 (block 712).

[0054] As the modified light propagates through the QWP layer 612, the QWP layer 612 converts the light from the linear x-polarization state back to the LCP state (block 714) such that the modified light re-enters the light guide substrate 620 as reflected light having the LCP state. As represented by block 716, the reflected light having the LCP state is incident on the world-facing surface 619 and is converted back to the RCP state when it is reflected off the partial mirror layer 624 and enters the light guide substrate 620 and is directed towards the eye-facing surface 618. In block 718, the reflected light having the RCP state is converted to a first linear polarization state upon entering the QWP layer 612. By way of example, the first linear polarization state is described herein as a linear y-polarization state. Because the PBS layer 414 is configured to transmit light having a linear y polarization state, the modified light is transmitted through the PBS layer 614 and out of the FPLG 602 toward the user's eye in block 720. This method can be repeated for each image the display projects.

[0055] The internal reflections within the FPLG 602, represented by blocks 708 through 716, occur by manipulating the polarization state of the representation of the display light 606 in view of the polarization state specific reflection and transmission properties of the stacked material layers overlying the major surfaces 618, 619 of the light guide substrate 620, and do not rely on TIR. Thus, the light guide substrate 620 can be constructed from a material, such as an optical plastic, that has a lower refractive index than light guide materials traditionally used in TIR-based light guides. In addition, a larger FOV can be achieved by the FPLG 602 by using a material with the same refractive index as the corresponding TIR-based light guide. Also, since no TIR is required, the light guide substrate can use at least one freeform major surface.

[0056] 8 illustrates a cross-sectional view 800 of an FPLG 802 employing a transparent adaptive optic 804, according to at least one embodiment. The FPLG 802 may represent, for example, the FPLG 302 shown in FIGS. 3 and 4, or in other embodiments, the FPLG 802 may represent the FPLG 602 of FIG. 6. The adaptive optic 804 is comprised of a transparent material that has properties that allow world light 806 to pass through the adaptive optic 804 with minimal diffraction and / or reflection. This allows a user wearing a near-eye display system, such as, for example, the near-eye display system 200 shown in FIG. 2 implementing the FPLG 802, to view the user's environment in addition to a representation of the display light 808 emitted by the display 810. The eye-facing surface 812 of the adaptive optic 804 has a freeform curve that is complementary to the world-facing surface 814 of the FPLG 802, and the contour width 818 of the adaptive optic can be varied such that the world-facing surface 816 of the adaptive optic is parallel or nearly parallel to the eye-facing surface of the FPLG 802. This allows the combination of the FPLG 802 and adaptive optic 804 to be fixed within an eyeglass frame, such as eyeglass frame 204 of Figure 2. Furthermore, the world-facing surface 816 of the adaptive optic can be a surface that can incorporate a prescriptive optical correction of world-side light for a user.

[0057] It should be noted that not all of the above operations or components are required in the overall description. Particular operations or parts of the device may not be required. In addition to those described, one or more additional operations may be performed and one or more additional components may be included. Furthermore, the order in which the operations are listed is not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, those skilled in the art will recognize that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the appended claims. Thus, the specification and drawings should be regarded as illustrative rather than strict, and all such modifications are intended to be within the scope of the present disclosure.

[0058] Benefits, other advantages, and solutions to problems have been described for specific embodiments. However, these benefits, advantages, solutions to problems, and any feature(s) that may give rise to or make the benefits, advantages, or solutions more apparent should not be construed as key, necessary, or essential features of any or all claims. Furthermore, the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein, and the particular embodiments disclosed above are illustrative only. The present invention is not limited to the contents of the construction or design shown herein, but rather as set forth in the appended claims. Thus, it is apparent that the particular embodiments disclosed above may be modified and varied, and all such variations are considered to be within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the appended claims.

Claims

1. Equipped with a freeform light guide, The freeform light guide comprises: a light guide substrate including opposing first and second surfaces extending between first and second ends of the freeform light guide, at least the second surface being a freeform surface, the freeform light guide further comprising: an input coupling interface formed at least in part by the light guide substrate; a quarter-wave plate layer overlying the first surface of the light guide substrate; a polarizing beam splitter layer overlying the quarter wave plate layer; a partial mirror layer overlying the second surface.

2. The apparatus of claim 1 , further comprising a display configured to emit display light towards the input coupling interface of the light guide substrate.

3. The apparatus of claim 2 , further comprising a quarter wave plate disposed between the display and the input coupling interface.

4. the quarter-wave plate layer is configured to convert incident light having a first circular polarization state to light having a first linear polarization state, convert incident light having the first linear polarization state to light having the first circular polarization state, and convert incident light having a second circular polarization state to a second linear polarization state; 3. The apparatus of claim 2, wherein the polarizing beam splitter layer is configured to reflect light having the first linear polarization state and transmit light having the second linear polarization state.

5. The apparatus of claim 3 , wherein the quarter-wave plate is configured to convert the display light emitted from the display from a linear polarization state to a circular polarization state.

6. The eyeglasses further include an eyeglass frame including eyeglass lenses; 6. The apparatus of claim 1, wherein the spectacle lens implements the freeform light guide and an out-coupling region arranged at or adjacent to an eye-side surface of the spectacle lens.

7. 7. The apparatus of claim 1, wherein the freeform light guide further comprises a linear polarizing layer overlying the polarizing beam splitter layer.

8. The apparatus of claim 7 , wherein the freeform light guide further comprises an anti-reflective layer overlying the linear polarizing layer.

9. the partial mirror layer converts reflected incident light having a first circular polarization state into light having a second circular polarization state; 4. An apparatus according to claim 1, configured to convert reflected incident light having the second circular polarization state into light having the first circular polarization state.

10. The apparatus of claim 1 , further comprising a adaptive optical element disposed on the second surface of the light guide substrate.

11. providing a freeform light guide comprising: a light guide substrate having opposing first and second surfaces; an input coupling interface; a quarter wave plate layer overlying the first surface; a polarizing beam splitter layer overlying the quarter wave plate layer; and a partial mirror layer overlying the second surface, at least the second surface comprising a freeform surface; Directing display light emitted by a display to the input coupling interface; transmitting the representation of the display light from the in-coupling interface through the freeform light guide to an out-coupling region; transmitting the representation of the display light from the out-coupling region toward an eye after the representation of the display light is incident on the second surface.

12. The method of claim 11 , wherein the freeform light guide further comprises a linear polarizing layer overlying the polarizing beamsplitter layer.

13. Transmitting the representation of the display light through the freeform light guide comprises: causing a first change in the polarization state of the display light such that the display light is reflected at the polarizing beam splitter layer; and 13. The method of claim 12, further comprising: creating a second change in the polarization state of the reflected display light such that the display light passes through the quarter wave plate layer, the polarizing beam splitter layer, and the linear polarizer layer to reach the output coupling area.

14. Transmitting the representation of the display light through the freeform light guide comprises: transmitting the display light having a first circular polarization state from the input coupling interface to the quarter waveplate layer; converting the representation of the display light to a first linear polarization state at the quarter waveplate layer; reflecting the representation of the display light having the first linear polarization state off the first surface of the freeform light guide towards the quarter waveplate layer; 14. The method of claim 12 or claim 13, comprising at least one step of converting the representation of the reflected display light from the first linear polarization state to the first circular polarization state at the quarter waveplate layer.

15. Transmitting the representation of the display light through the freeform light guide comprises: transmitting the representation of the display light having the first circular polarization state from the quarter waveplate layer to the second surface; reflecting the representation of the display light off the partial mirror layer at the second surface such that the first circular polarization state is converted to a second circular polarization state; transmitting the representation of the display light having the second circular polarization state to the quarter waveplate layer; converting the representation of the display light having the second circular polarization state at the quarter waveplate layer to a second linear polarization state; transmitting the representation of the display light having the second linear polarization state to the polarizing beam splitter layer; 15. The method of claim 14, further comprising at least one of the steps of reflecting the representation of the display light having the second linear polarization state off of the polarizing beam splitter layer.

16. Transmitting the representation of the display light through the freeform light guide comprises: transmitting the representation of the display light having the second linear polarization state from the polarizing beam splitter layer to the quarter waveplate layer; converting the representation of the display light having the second linear polarization state to the second circular polarization state at the quarter waveplate layer; transmitting the representation of the display light having the second circular polarization state to the second surface; reflecting the representation of the display light having the second circular polarization state off the partial mirror layer at the second surface such that the display light is converted to the first circular polarization state; 16. The method of claim 15, further comprising at least one of transmitting the representation of the display light having the first circular polarization state through the quarter waveplate layer, the polarizing beam splitter layer, and the linear polarizer layer to the output coupling region.

17. 1. A near-eye display system, comprising: a freeform light guide having an input coupling interface and an output coupling area facing the expected location of a wearer's eye; the freeform light guide is configured to transmit the light to the out-coupling region by using a laminate film arranged on a first major surface facing the intended position of the wearer's eye and a partial mirror layer arranged on an opposing second major surface to induce at least one change in the linear polarization state of the light and at least one change in the circular polarization state of the light as the light incident at the in-coupling interface traverses the freeform light guide; at least a portion of the change in polarization state causes the light to reflect within the freeform light guide; The laminate film includes a quarter-wave plate layer overlying the first major surface, and a polarizing beam splitter layer overlying the quarter-wave plate layer.

18. 20. The near-eye display system of claim 17, wherein at least a portion of the change in polarization state causes the light to reflect off the polarizing beam splitter layer in the freeform light guide.

19. The near-eye display system of claim 17 or claim 18, wherein the laminate film further comprises a linear polarizing layer and / or an anti-reflection layer.

20. 20. A near-eye display system as described in any of claims 17 to 19, wherein at least a portion of the change in polarization state causes the light to pass through the laminate film and reach the output coupling area toward a user's eye.

Images