Device and method

Abstract

To solve the problem in which a light guide of a conventional optical device must be composed of a material high in a refractive index.SOLUTION: An optical device comprises a freeform light guide to direct light from a display toward a region where a user's eye is expected to be positioned. The freeform light guide includes a light guide substrate that has first and second facing surfaces extending between a first end and a second end of the freeform light guide, in which at least the second surface is a freeform surface and overlaid with a partial mirror layer, and the first surface is overlaid with at least a quarter-wave plate layer and a polarization beam splitter layer. The freeform light guide also includes an input-coupling interface close to the first end of the freeform light guide, and for receiving light from the display.SELECTED DRAWING: Figure 4

Description

Background Art

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

[0002] In addition to this, conventional light guides require at least one extraction element embedded or mounted within the light guide itself in order to propagate the reflected light out of the light guide, generally towards the user's eyes, rather than having the reflected light continue to be reflected within the light guide. Such extraction elements include, for example, raised or recessed surface features such as protrusions or indentations, and local material variations or other surface or volume fluctuations in the light guide. These fluctuations can cause a decrease in extraction efficiency (e.g., a decrease in the luminance uniformity of the reflected light), resulting in the possibility of a discontinuous surface being visible to the user or observer.

Summary of the Invention

[0003] Summary of the Invention Embodiments relate to an apparatus comprising a freeform light guide. The freeform light guide includes a light guide substrate including opposing first and second surfaces extending between a first end and a second end of the freeform light guide, at least the second surface being a freeform surface, and the freeform light guide further includes an input coupling interface at least partially formed by the freeform light guide substrate (thus located near the first end of the light guide and forming a part of the first end of the light guide), a quarter-wave plate layer overlapping the first surface of the light guide substrate, a polarization beam splitter layer overlapping the quarter-wave plate layer, and a partial mirror layer overlapping the second surface.

[0004] The apparatus may further comprise a display configured to emit display light towards the input coupling interface of the light guide substrate. The apparatus may further comprise a quarter-wave plate disposed between the display and the input coupling interface. Further, the display may be arranged facing the input coupling interface, and / or the input coupling interface may be oriented with respect to the first or second surface such that the display light from the display incident on the light guide at the input coupling interface is directed towards the first or 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 into light having a first linear polarization state, convert incident light having the first linear polarization state into light having the first circular polarization state, and convert incident light having a second circular polarization state into a second linear polarization state and / or the polarization 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 further comprise an eyeglass frame including eyeglass lenses, and the eyeglass lenses implement the freeform light guide and an output coupling region disposed on or adjacent to the eye side surface of the eyeglass lenses.

[0007] The free-form light guide may further include a linearly polarized layer that overlaps the polarization beam splitter layer and / or an antireflection layer that overlaps the linearly polarized layer. Further, the apparatus may further include a quarter-wave plate for a display configured to be disposed between the display and the input coupling interface and 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 incident light having a reflected first circular polarization state into light having a second circular polarization state and / or to convert incident light having a reflected second circular polarization state into light having a first circular polarization state.

[0009] The apparatus may further include a compensating optical element disposed on the second surface of the light guide. For example, the compensating optical element is composed of a transparent material having a property that allows light to pass through the compensating optical element with minimal diffraction and / or reflection. The surface of the compensating optical element facing the eye may have a free-form curved surface complementary to the (second) surface facing the world of the light guide. The outer width of the compensating optical element may vary such that the surface of the compensating optical element facing the world is parallel or substantially parallel to the (first) surface of the light guide facing the eye. Furthermore, the surface of the compensating optical element facing the world can be a surface that can incorporate the prescription optical correction of the light on the world side for the user.

[0010] Furthermore, an embodiment relates to a method for transmitting display light from a display to a user's eye in a near-eye display system. The method includes providing a freeform light guide, the freeform light guide including a light guide substrate having opposing first and second surfaces, an input coupling interface, a quarter-wave plate layer overlapping the first surface, a polarizing beam splitter layer overlapping the quarter-wave plate layer, and a partial mirror layer overlapping the second surface, at least the second surface including a freeform surface, and the method further includes directing display light emitted by the display to the input coupling interface, transmitting a representation of the display light from the input coupling interface through the light guide to an output coupling region, and transmitting the representation of the display light from the output coupling region toward the eye after the representation of the display light is incident on the second surface.

[0011] Also, embodiments of the above-described apparatus may be used in embodiments of the above method. For example, the freeform light guide may include a linearly polarized layer overlapping the polarizing beam splitter layer.

[0012] Also, transmitting a representation of the display light through the light guide may include causing a first change in the polarization state of the display light such that the display light is reflected by the 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 linearly polarized layer and reaches the output coupling region.

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

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

[0015] Also, transmitting the representation of the display light through the light guide may include transmitting the representation of the display light having the second linearly polarized state from the polarizing beam splitter layer to the quarter-wave plate layer, optionally converting the representation of the display light having the second linearly polarized state to a second circularly polarized state in the quarter-wave plate layer, optionally transmitting the representation of the display light having the second circularly polarized state to the second surface, optionally reflecting the representation of the display light having the second circularly polarized state at the partial mirror layer on the second surface such that it is converted to the first circularly polarized state, and optionally transmitting the representation of the display light having the first circularly polarized state through the quarter-wave plate layer, the polarizing beam splitter layer, and the linear polarizer layer to the output coupling region.

[0016] Of course, regarding transmitting the representation of the display light through the light guide, only one of the operations in the above examples can be used. Also, any combination of these operations can be used.

[0017] In another aspect, the present invention relates to a near-eye display system. This near-eye display system includes a free-form light guide having an input coupling interface and an output coupling region facing the assumed position of the wearer's eye. The free-form light guide uses a laminated film disposed on a first main surface facing the assumed position of the wearer's eye and a partial mirror layer disposed on an opposing second main surface, such that when light incident at the input coupling interface traverses the free-form light guide, it causes at least one change in the linearly polarized state of the light and at least one change in the circularly polarized state of the light, thereby transmitting the light to the output coupling region. At least a part of the change in the polarization state causes the light to be reflected within the free-form light guide.

[0018] The near-eye display system may be formed by the device described above. For example, at least a part of the change in the polarization state causes the light to be reflected by a polarization beam splitter layer within the free-form light guide.

[0019] Furthermore, the light guide may include a laminated film including a quarter-wave plate layer and / or a polarization beam splitter layer.

[0020] Also, the laminated film may further include a linear polarization layer and / or an anti-reflection layer. Also, at least a part of the change in the polarization state may be such that the light passes through the laminated film and reaches the output coupling region and heads towards the user's eye.

[0021] Brief Description of the Drawings This disclosure will be understood by those skilled in the art by referring to the accompanying drawings, and many of its features and advantages will become apparent to those skilled in the art. The use of the same reference numerals in different drawings indicates similar or identical items.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0023] Detailed Description Figures 1 through 8 illustrate exemplary embodiments of a freeform polarization light guide for use in a near-eye display system. In at least one embodiment, a near-eye display system uses a freeform polarization light guide (FPLG) to transmit light depicting 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, the FPLG does not rely entirely on TIR. Instead, as light traverses the FPLG, it transmits the representation of the display light from the input coupling interface of the FPLG facing the display to the output coupling region facing the user's eye through multiple changes in the polarization state. Here, at least some of these changes in the polarization state cause reflection of the light within the FPLG. In addition, in some embodiments, some of these changes in the polarization state enable the reflected light to traverse the layer of the FPLG so that the light exits the FPLG from the output coupling region and travels towards the user's eye. The layer of the FPLG functions to reflect the light when the light is in other polarization states.

[0024] By finally manipulating the polarization state of the display light to facilitate reflection within the FPLG until the light is output towards the eye, the FPLG, in contrast to conventional near-eye light guides, can transmit the display light from the input coupling interface to the output coupling region in a way that does not depend on end-to-end TIR or extraction elements. Thus, a light guide substrate of the FPLG that functions as the main conduit for the display light between the input coupling and the output coupling can be implemented using a light-transmissive material with a lower refractive index than the material of the light guide used in conventional TIR-based light guides. At the same time, a higher field of view (FOV) can be provided compared to the FOV typically achievable by such conventional light guides for a material with a given refractive index. Since no special extraction elements or special materials are required, the manufacturing complexity is also reduced. As a result, a lighter FPLG can be manufactured at a lower cost. Also, it does not require end-to-end TIR Therefore, an FPLG having one or more major surfaces with non-precise radius dimensions may be implemented. As an example, the FPLG may be implemented in a form factor where one or both major surfaces are freeform surfaces, and in that way, it can be implemented to provide a refractive power other than zero or can be implemented within an eyeglass lens that fits into an eyeglass frame, thus also providing a lens effect for vision correction.

[0025] FIG. 1 shows an exemplary near-eye display system 100 using a freeform polarization light guide (FPLG) 102 according to at least one embodiment. The system 100 is implemented in a form factor of glasses having a glasses frame 104 with right-eye and left-eye glasses lenses 105, 106 for the wearer, respectively. In the illustrated embodiment, the FPLG 102 is separate from the glasses lenses, but instead, the output coupling region of the FPLG 102 (details will be described later with reference to FIG. 3) overlaps one of the glasses lenses (in this example, glasses lens 105) so as to face the assumed position of the corresponding wearer's eye. The FPLG 102 is attached to the glasses frame 104 via a light guide attachment housing 109. Also, the light guide attachment housing 109 functions to accommodate some or all of the electronic components (not shown in FIG. 1) of the near-eye display system 100, such as a display for generating an augmented reality (AR) image or a virtual reality (VR) image to be displayed to the wearer via the FPLG 102, an input coupling optical element for directing light from the display to the input coupling interface of the FPLG 102, one or more processing devices, one or more wireless interfaces, one or more batteries or other power sources. Details of some of these components will be described later.

[0026] FIG. 2 shows another exemplary near-eye display system 200 using an FPLG202 according to at least one embodiment. Similar to the system 100 of FIG. 1, the system 200 uses the form factor of glasses with a glasses frame 204 having glasses lenses 205, 206. However, in contrast to the system 100, the system 200 implements the FPLG202 using the glasses lens 205. That is, since the FPLG202 is integrated with the glasses lens 205, the appearance of the near-eye display system 200 can be made more like that of conventional glasses. In this embodiment, the display housing (omitted from FIG. 2 for clarity) on the glasses frame 204 above the glasses lens 205 includes a microdisplay or other display for emitting display light depicting an AR image or a VR image, and an input coupling lens for directing the emitted display light to the input coupling interface of the FPLG202 in the lens 205. The display light propagates through the FPLG202 / glasses lens 205 and is sent towards an output coupling region 207 located within the glasses lens 205 / FPLG202 to be aligned with the assumed position (or range of assumed positions) of the corresponding wearer's eye. In some embodiments, the glasses lens 206 also implements a corresponding FPLG202, and the system 200 can similarly use corresponding display components to display an AR image or a VR image to the other eye of the wearer.

[0027] The FPLG 102 of the system 100 in FIG. 1 and the FPLG 202 of the system 200 in FIG. 2 each operate to transmit display light from a proximity display (e.g., a microdisplay) to a user's eye by multiple reflections of the display light within the FPLG body when the display light traverses from one end of the FPLG 202 near the display to the output 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 incident angle may be smaller than the critical angle of the interface between the media at the reflection point. Instead of relying on TIR, the FPLG 202 uses a stacked layer that selectively changes the polarization state of the incident display light or selectively reflects the incident display light based on the polarization state, so that the display light can pass through the surface of the FPLG 202 in the output coupling region 207 facing the wearer's eye. The display light is reflected one or more times within the FPLG 202 until the polarization state of the display light is changed.

[0028] FIG. 3 shows a cross-sectional view 300 of an FPLG 302 that uses this polarization state manipulation to result in internal reflection of the input-coupled display light, according to at least one embodiment. The FPLG 302 represents, for example, the FPLG 202 of the system 200, so the cross-sectional view 300 may represent the cross-section A-A shown in FIG. 2. In other embodiments, the FPLG 302 represents the FPLG 102 of FIG. 1. Note that the illustrated dimensions of the various incident features and angles shown in FIG. 3 are for illustrative purposes of the operating principle and may not reflect the actual dimensions and angles implemented within the FPLG.

[0029] FPLG302 (i.e., the apparatus or system of which FPLG302 forms a part) includes a display 304. The display 304 can be composed of any of a variety of displays suitable for use in a near-eye display system using a light guide, such as an organic light-emitting diode (OLED) or a liquid crystal on silicon (LCOS) microdisplay. In embodiments where the display 304 is configured to emit linearly polarized light, FPLG302 (i.e., the apparatus or system of which FPLG302 forms a part) further includes a quarter-wave plate 306 for the display disposed between the display 304 and the input coupling interface 316 of FPLG302 to convert the polarization of the linearly polarized display light into a circularly polarized state before the display light is incident on FPLG302.

[0030] FPLG302 is composed of a light guide substrate 320 extending from a first end 310 near the display 304 to a second end 312 on the opposite side of FPLG302. Both ends 310, 312 of FPLG302 can be defined by the respective corresponding ends of the substrate 320. Also, FPLG302 includes an input coupling interface 316 near the first end 310 configured to receive display light 318 from the display 304. At least a part of the input coupling interface 316 may be formed by the substrate 320. The light guide substrate 320 is composed of a material that substantially transmits the display light 318, such as glass, optical plastic, etc. The light guide substrate 320 includes two opposing main surfaces 322, 323 extending between the first end 310 and the second end 312 of the light guide substrate 320. The first main surface 322 is the surface facing the direction of the wearer's eye (thus, also referred to as the "eye-facing surface 322" in this specification), and the second main surface 323 is the surface facing the direction opposite to the wearer's eye (thus, also referred to as the "world-facing surface 323" in this specification). Either or both of the eye-facing surface 322 and the world-facing surface 323 can be free-form surfaces. Thus, FLPG302 can be incorporated into the lens of glasses used for vision correction.

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

[0032] In one embodiment, on the eye-facing surface 322, a plurality of layers of a material configured to change one or more polarization states of light when the light crosses or to transmit light having a different polarization state while reflecting light having a specific polarization state (i.e., selectively transmit light and send it to a subsequent layer or out of the light guide) are stacked. This collection of layers is referred to as a laminated film 330. As will be described later with reference to FIG. 4, in some embodiments, the laminated film 330 is a quarter-wave plate (QW It includes a (P) layer 332, a polarizing beam splitter (PBS) layer 334, and a linear polarizer (LP) layer 336. In order not to unnecessarily reflect the light from the eye side, the laminated film 330 may further include an anti-reflection (AR) layer 338 disposed between the assumed position of the user's eye 314 and the other layers of the laminated film 330. Each layer can be provided as a pre-formed film layer such that a plurality of films are overlapped with each other to form the laminated film. The laminated film is overlapped on the surface of the light guide substrate 320. Alternatively, each layer can be provided as a coating continuously deposited on the surface of the light guide substrate 320. Further, in some embodiments, while implementing one or more of these layers as one pre-formed film layer, one or more other layers are implemented as a coating. In addition to this, the FPLG302 includes a partial mirror layer 328 or a 50 / 50 reflection coating disposed on the surface 323 facing the world. The partial mirror layer 328 functions such that at least a part of the light incident on the surface 323 facing the world is reflected while the remaining part of the light can pass through the surface facing the world and exit from the FPLG302.

[0033] The FPLG302 further includes an output coupling region 326 for outputting the representation of the display light 318 reflected within the light guide substrate 320 towards the wearer's eye. As used herein, the term "output coupling region" may refer to the region of the surface facing the eye and the overlapping region of the laminated film through which the representation of the display light 318 exits the FPLG302 towards the wearer's eye (such as the surface 322 facing the eye and the respective illustrated regions of the laminated film 330).

[0034] FIG. 4 shows a further cross-sectional view 400 of the FPLG 302 including further details of the layers of the stacked film 330 according to at least one embodiment, an example of the transmitted display light 318 through the FPLG 302 based on a selective change in the polarization state of the input combined display light 318, and a selective reflection of the input combined display light 318 based on its polarization state. For ease of explanation, in the operations described below, the display light 318 is shown as a single ray of light. The stacked film 330 is disposed on the eye-facing surface 322 of the FPLG 302 and includes a QWP layer 332 disposed to overlap the eye-facing surface 322. In some embodiments, the PBS layer 334 overlaps 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 to overlap the PBS layer 334 such that the PBS layer 334 is disposed between the QWP layer 332 and the LP layer 336. The AR layer 338 may be overlaid on the LP layer 336 such that the LP layer 336 is disposed between the anti-reflection (AR) layer 338 and the PBS layer 334 to prevent unnecessary reflection of light from the eye side. Each layer can be provided as a pre-formed film layer such that a plurality of films are overlapped with each other to form a stacked film. The stacked film is overlaid on the surface of the light guide substrate 320. Alternatively, each layer can be provided as a coating continuously deposited on the surface of the light guide substrate 320. Further, in some embodiments, one or more of these layers are implemented as a single pre-formed film layer while one or more other layers are implemented as a coating.

[0035] The QWP layer 332 is formed from one material or a 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. Also, the QWP layer 332 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 changes the polarization state of light passing through it without shifting or moving it. In a quarter-wave plate, the phase difference between the polarization components projected along the fast axis and the slow axis is a quarter wavelength. The QWP layer 332 can be implemented, for example, as a multi-order, zero-order, or achromatic QWP layer. Examples of materials for implementing the QWP layer 332 include calcite film or crystal film, polychromatic film, 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, wire grid type PBS layers, dielectric coating type PBS layers, 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, wire grid polarizers, calcite polarizers, or dichroic polarizers. Furthermore, the LP layer 336 can improve image quality by reducing stray light and ghost images by reducing the light reflected to the user's eye on the eye side of the FPLG 302. The AR layer 438 disposed on the LP layer 336 also helps to reduce the light reflected to the user's eye on the surface 322 facing the eye of the FPLG 302, so that the image quality can be further improved.

[0037] The surface 323 facing the world of the FPLG302 is configured as a continuous or smoothed free-form surface, enabling specular reflection of light propagating within the FPLG302 when it hits the surface 323 facing the world. When all or part of the surface 323 facing the world is covered by the partial mirror layer 328, at least a part of the display light propagating within the FPLG302 is reflected by the surface 323 facing the world. Light having a first circular polarization state hitting the partial mirror layer 328 on the surface 323 facing the world is converted to a second circular polarization state, and light having a first linear polarization state hitting the surface 323 facing the world is converted to a second linear polarization state. Similarly, light having a second circular polarization state incident on the partial mirror layer 328 is converted to the first circular polarization state, and light having a second linear polarization state incident on the partial mirror layer 328 is converted to the first linear polarization state.

[0038] According to the described configuration, in the embodiment where the display light 318 emitted from the display 304 enters the light guide and travels toward the surface 322 facing the eye, the display light 318 first undergoes TIR, and then, when the display light 318 (or its representation) is reflected or transmitted at the film layer and / or the main surfaces 322, 323 of the laminated film 330, it undergoes multiple changes in polarization state. Referring to the enlarged insert view 406 shown in FIG. 4, the display light 318 having a first circular polarization state propagating within the light guide substrate 320 enters the QWP layer 332 and is converted into light having a first linear polarization state as the converted representation of the display light 318 propagates within the QWP layer 332. The converted light having the first linear polarization state then hits the overlapping PBS layer 334. Since the PBS layer 334 is configured to transmit light having the first linear polarization state, the light is transmitted to the LP layer 336. Since the LP layer 336 is configured to transmit light having the first linear polarization state, the incident light passes through the LP layer 336 at 338 and undergoes TIR at the boundary formed between the eye side of the laminated film 330 and the surrounding medium. Thereafter, the reflected light passes through the LP layer 336 and the PBS layer 334 again and returns to the QWP layer 332. As the transmitted light propagates within the QWP layer 332, the QWP layer 332 converts the polarization state of the light from the first linear polarization state to the first circular polarization state so that the reflected light having the first circular polarization state re-enters the light guide substrate 320. This first reflection is a TIR-based reflection as it depends on the angle at which the display light enters the laminated film 330. However, subsequent reflections of the light within the FPLG 302 occur due to interaction with a specific layer in the laminated film configured to reflect light of a specific polarization and are thus independent of the angle at which the light strikes these layers. Therefore, as will be described in detail later, the FPLG 302 utilizes both TIR and the polarization state-based reflection characteristics of the laminated film 330 to "bounce back" the display light along the length of the light guide substrate 320.

[0039] The representation of the display light that is reflected at the boundary formed between the eye side of the laminated film 330 and the surrounding medium and becomes in the first circular polarization state after passing through the QWP layer 332 is incident again on the light guide substrate 320 and transmitted to the surface 323 facing the world. At the surface 323 facing the world When the reflected light is reflected by the partial mirror layer 328 and transmitted through the light guide substrate 320 again and travels toward the laminated film 330, it is converted from the first circular polarization state to the second circular polarization state. When the reflected light having the second circular polarization state propagates through the QWP layer 332 and reaches the PBS layer 334, it is converted to the second linearly polarized state. Since the PBS layer 334 is configured to reflect the light having the second linearly polarized state, the light transmitted from the QWP layer 332 is reflected by the PBS layer 334 and transmitted through the QWP layer 332 again. 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 propagates toward the surface 323 facing the world. At the surface 323, the reflected light is converted to the first circular polarization state when it is reflected by the partial mirror layer 328 and transmitted through the light guide substrate 320 toward the laminated film 330.

[0040] The light having the first circular polarization state reflected at the surface 323 facing the world then enters the QWP layer 322 and is converted from the first circular polarization state to the first linearly polarized state. Since the PBS layer 334 and the LP layer 336 are configured to transmit the light having the first linearly polarized state, the light transmitted from the QWP layer 332 passes through the PBS layer 334 and the LP layer 336 and reaches the AR layer 338. Since the orientation of the surface 322 facing the eye of the FPLG302 and the surface 323 facing the world is not parallel, the incident angle on the AR layer is smaller than the critical angle of TIR, and at least a part of the transmitted light from the LP layer 336 propagates through the AR layer 338 and reaches the output coupling region 326, exits the FPLG302, and reaches the user's eye. With this configuration, light can exit the FPLG302 even though there is no extraction element used in a conventional light guide.

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

[0042] At block 508, when the display light reaches a boundary between two media such as the boundary between the film layer and air, the display light propagates through the light guide substrate 320 at an angle with respect to the eye-side surface such that the angle at which the light reaches the boundary is greater than or equal to the critical angle at which TIR occurs for these two media. As shown by the enlarged inset 406 of FIG. 4, at block 510, when incident on the QWP layer 332, the representation of the display light 318 resulting in the RCP state is converted into light having linearly polarized y-light 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 linearly polarized y-light, at block 512, the converted light propagates through the PBS layer, the LP layer, and the AR layer and reaches the boundary between the AR layer 338 on the eye-facing surface 322 side of the FPLG 302 and the surrounding medium 362. Since the transmitted light reaches the boundary at an angle 360 greater than or equal to the critical angle between the AR layer 338 material and air, at block 514, the converted light 350 undergoes TIR at the boundary and returns to the QWP layer 332 after passing through the PBS layer 334, the LP layer 336, and the AR 338 layer. When incident on the QWP layer 332, at block 516, the reflected light 351 having a linearly polarized y-light state is converted into light having an RCP state 352 when transmitted toward the surface 323 facing the world of the FPLG 402. It is converted into light having.

[0043] On the surface 323 facing the world, when the transmitted light 352 is reflected by the partial mirror layer 328, it is converted into light having an LCP state 354 from the RCP state (block 518). The resulting representation of the display light having an LCP state is returned from the surface 323 facing the world toward the QWP layer 332 of the laminated film 330 disposed on the surface 322 facing the eye. As shown in the enlarged inset 408 of FIG. 4, at block 520, the reflected light propagates through the QWP layer 332 and is converted into a linearly polarized x-light state 356. The resulting changed light 356 then hits the PBS layer 334. Since the PBS layer 334 is configured to reflect light having a linearly polarized x-light state, the PBS layer 334 reflects the changed light 356 and returns it to the QWP layer 332 (block 522).

[0044] When the reflected light 358 propagates within the QWP layer 332, the QWP layer 332 converts the reflected light 358 from the linearly x-polarized state back to light having the LCP state 359 before the light 359 is incident on the light guide substrate 320 (block 524). As represented by block 526, the reflected light having the LCP state 358 is incident on the world-facing surface 323, reflected by the partial mirror layer 328, incident on the light guide substrate 320, and converted back to the original RCP state when sent toward the eye-facing surface 322. In block 528, the reflected light having the RCP state is converted to the linearly y-polarized state when incident on the QWP layer 332. Since the PBS layer 334, LP layer 336, and AR layer 338 are configured to transmit light having the linearly y-polarized state, in block 530, the converted light propagates through the PBS layer 334, LP layer 336, and AR layer 338 and is sent toward the boundary between the AR layer 338 on the eye side of the FPLG 302 and air. However, since the transmitted light does not enter the boundary at an angle greater than the critical angle, the sent linearly y-polarized light is not reflected at the boundary. Instead, it is sent toward the region corresponding to the output coupling region 326 of the FPLG 302 and transmitted toward the user's eye. This method can be repeated for each image projected by the display.

[0045] The internal reflection within the FPLG 302 represented by blocks 518 to 526 occurs by manipulating the polarization state representation of the transmitted display light 318 in view of the polarization state-specific reflection and the transmission characteristics of the laminated material layers overlapping the main surfaces 322, 323 of the light guide substrate 320, and does not rely on TIR. Thus, the light guide substrate 320 can be composed of a material such as an optical plastic having a lower refractive index than the materials of the light guides conventionally used in TIR-based light guides (e.g., relatively heavy and expensive optical glass) to achieve a given FOV. Alternatively, by using a material having the same refractive index as the corresponding TIR-based light guide, a larger FOV can be achieved by the FPLG 302. Also, since TIR is not required, the light guide substrate can use at least one freeform main surface that is not usually practical to implement in conventional TIR-based light guides.

[0046] FIG. 6 shows a cross-sectional view 600 of another embodiment of FPLG602 according to some embodiments. FPLG602 formed from (or including) the light guide substrate 620 includes a display 604 directed to direct the display light 606 emitted from the display 604 towards the input coupling interface 616. FPLG602 (i.e., the device or system of which FPLG602 forms a part) also includes a quarter-wave plate 608 for the display disposed between the display and the input coupling interface 616, which can convert the display light having a linearly polarized state into light having a circularly polarized state. The input coupling interface 616 is disposed at an acute angle with respect to the world-facing surface 619 of FPLG602 such that the display light 606 from the display 604 incident on FPLG602 at the input coupling interface 616 is directed towards the surface 619 facing the world. A partial mirror layer 624 or a 50 / 50 reflective coating is disposed on the world-facing surface 619. The partial mirror layer 624 functions such that at least a part of the light incident on the world-facing surface 619 is reflected while the remaining part of the light can pass through the world-facing surface 619 and exit from FPLG602.

[0047] The surface on the opposite side of the world-facing surface 619 is the eye-facing surface 618 located on the side facing the eye of FPLG602. The laminated film 610 includes a QWP layer 612 and a PBS layer 614 on the eye-facing surface 618 of FPLG602. Either or both of the eye-facing surface 618 and the world-facing surface 619 can be made into a freeform surface that can incorporate the prescription optical correction of the light on the world side when passing through FPLG602 and reaching the user's eye. Thus, FLPG602 can be incorporated into the lens of glasses used by the user for vision correction.

[0048] The light directed into the FPLG602 undergoes multiple reflections and has its polarization state changed before being directed to the output coupling region 622 on the side of the FPLG602 facing the eye. The output coupling region 622 is generally arranged in the region of the FPLG602 where the user's eye is assumed to be located, whereby the light emitted from the output coupling region 622 and exiting the FPLG602 is directed towards the user's eye.

[0049] According to the described configuration, the light 606 emitted from the display 604 is first directed to the surface 619 of the FPLG602 facing the world and then undergoes a change in polarization state when reflected or transmitted by the layers of the laminated film 610 and / or the main surfaces 618, 619. If the display 604 is configured to emit light having a first linearly polarized state, the quarter-wave plate 608 for the display converts the display light 606 to a first circularly polarized state before the display light 606 enters the FPLG602 at the input coupling interface 616. As a result of propagating within the light guide substrate 620 having the first circularly polarized state, the representation of the display light 606 is then incident on the surface 619 facing the world and is converted to a second circularly polarized state when reflected by the partial mirror layer 624 and directed towards the laminated film 610.

[0050] The representation of the display light having the second circularly polarized state and reflected by the surface 619 facing the world is converted to a second linearly polarized state when propagating through the QWP layer 612 to the PBS layer 614. Since the PBS layer 614 is configured to reflect light having the second linearly polarized state, the transmitted light from the QWP layer 612 is reflected by the PBS layer 614 and passes through the QWP layer 612 again. In the QWP layer 612, this light is converted to a second circularly polarized state when incident on the light guide substrate 620. The reflected light having the second circularly polarized state is propagated towards the surface 619 facing the world. At the surface 619 facing the world, this reflected light is converted to a first circularly polarized state when reflected and transmitted through the light guide substrate 620 and returned to the laminated film 610.

[0051] The light having the first circular polarization state, which is reflected by the partial mirror layer 624 disposed on the surface 619 facing the world, is incident on the QWP layer 612 of the laminated film 610 and is converted from the first circular polarization state to the first linear polarization state. Since the PBS layer 614 is configured to transmit the light having the first linear polarization state, the transmitted light from the QWP layer 612 passes through the PBS layer 614, reaches the output coupling region 622, exits the light guide, and heads towards the user's eyes.

[0052] FIG. 7 is a flowchart showing a method 700 of using a near-eye display system having the freeform light guide of FIG. 6 to display an image to a user, according to at least one embodiment. The method 700 starts at block 702. At block 702, the display 604 emits display light 606 that represents a display image that may include AR content or VR content. For the sake of convenience of explanation, the first circular polarization state is the 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 can be provided between the display 604 and the input coupling interface 616 to convert the emitted light to the RCP state before it is incident on the light guide substrate at block 704. At 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] The representation of the display light having an RCP state propagates through the light guide substrate 620 at a specific angle and thus impinges on the surface 619 facing the world (i.e., the second major surface). At the surface 619 facing the world, 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 sent from the surface 619 facing the world toward the QWP layer 612 of the laminated film 610 disposed on the surface 618 facing the eye (i.e., the surface facing the eye). When the reflected light propagates through the QWP layer 612, the QWP layer 612 changes the polarization state of the light to a second linearly polarized state (block 710). As an example, in this specification, the second linearly polarized state is described as a linearly polarized state in the x direction. Since the PBS layer 614 is configured to reflect the light having a linearly polarized state in the x direction, the PBS layer 614 reflects the changed light and returns it to the QWP layer 612 (block 712).

[0054] When the changed light propagates within the QWP layer 612, the QWP layer 612 converts the light to return it from the linearly polarized state in the x direction to the LCP state so that the changed light is incident on the light guide substrate 620 again as the reflected light having an LCP state (block 714). As represented by block 716, the reflected light having an LCP state is incident on the surface 619 facing the world. Then, when reflected by the partial mirror layer 624 and incident on the light guide substrate 620 and sent toward the surface 618 facing the eye, it is converted to the original RCP state. In block 718, when the reflected light having an RCP state is incident on the QWP layer 612, it is converted to the first linearly polarized state. As an example, in this specification, the first linearly polarized state is described as a linearly polarized state in the y direction. Since the PBS layer 414 is configured to transmit the light having a linearly polarized state in the y direction, in block 720, the changed light propagates through the PBS layer 614, exits from the FPLG 602, and is sent toward the user's eye. This method can be repeated for each image projected by the display.

[0055] Internal reflections within the FPLG602 represented by block 708 to block 716 occur by manipulating the polarization state of the representation of the display light 606 in view of the reflection specific to the polarization state and the transmission characteristics of the laminated material layers overlapping the main surfaces 618, 619 of the light guide substrate 620, and do not rely on TIR. Thus, the light guide substrate 620 can be composed of a material such as an optical plastic having a refractive index lower than that of the material of the light guide conventionally used in a TIR-based light guide. In addition, by using a material having the same refractive index as the corresponding TIR-based light guide, a larger FOV can be realized by the FPLG602. Also, since TIR is not required, the light guide substrate can use at least one free-form main surface.

[0056] FIG. 8 shows a cross-sectional view 800 of an FPLG802 using a transparent compensating optical element 804 according to at least one embodiment. The FPLG802 represents, for example, the FPLG302 shown in FIGS. 3 and 4, or in other embodiments, the FPLG802 represents the FPLG602 of FIG. 6. The compensating optical element 804 is composed of a transparent material having the property of allowing world light 806 to pass through the compensating optical element 804 with minimal diffraction and / or reflection. Thereby, for example, a user wearing a near-eye display system such as the near-eye display system 200 shown in FIG. 2 in which the FPLG802 is mounted can view the user's environment in addition to the representation of the display light 808 emitted from the display 810. The surface 812 of the compensating optical element facing the eye has a free-form curved surface complementary to the surface 814 facing the world of the FPLG802, and the outer width 818 of the compensating optical element can vary such that the surface 816 of the compensating optical element facing the world is parallel or substantially parallel to the surface of the FPLG802 facing the eye. Thereby, a combination of the FPLG802 and the compensating optical element 804 can be fixed within an eyeglass frame such as the eyeglass frame 204 of FIG. 2. Furthermore, the surface 816 of the compensating optical element facing the world can be made a surface that can incorporate the prescription optical correction of the light on the world side for the user. The surface 812 of the compensating optical element facing the eye has a free-form curved surface complementary to the surface 814 facing the world of the FPLG802, and the outer width 818 of the compensating optical element can vary such that the surface 816 of the compensating optical element facing the world is parallel or substantially parallel to the surface of the FPLG802 facing the eye. Thereby, a combination of the FPLG802 and the compensating optical element 804 can be fixed within an eyeglass frame such as the eyeglass frame 204 of FIG. 2. Furthermore, the surface 816 of the compensating optical element facing the world can be made a surface that can incorporate the prescription optical correction of the light on the world side for the user.

[0057] Note that not all of the operations or components described above in the overall description are necessary. It may not be necessary to require a specific operation or a part of the device. In addition to what is described, one or more additional operations may be performed, and one or more additional components may be included. Further, the order in which the operations are listed is not necessarily the order in which they are executed. Also, the concept has been described by taking a specific embodiment as an example. However, those skilled in the art will understand that various modifications and changes can be made without departing from the scope of the present disclosure described in the appended claims. Therefore, the specification and the drawings should be regarded as illustrative rather than strict, and all such modifications are intended to be included within the scope of the present disclosure.

[0058] The advantages, other advantages, and solutions to problems of the specific embodiments have been described. However, none of these advantages, advantages, problem solutions, and any feature(s) that can give rise to or make more apparent these advantages, advantages, or solutions should be construed as an important feature, a necessary feature, or an essential feature of any or all of the claims. Also, since those skilled in the art who have the advantages of the teachings herein may modify and implement the disclosed subject matter in different but equivalent ways, the specific embodiments disclosed above are merely illustrative. It is not limited to the content of the configuration or design shown in this specification, but is limited as described in the appended patent claims. Therefore, it is clear that the specific embodiments disclosed above may be changed or modified, and all such modifications are considered to be included within the scope of the disclosed subject matter. Therefore, the protection sought in this specification is as described in the appended patent 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 said freeform 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 display is configured to emit the display light having a first circular polarization state; and / or 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; and / or 4. The apparatus of claim 3, 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 eyeglasses further include an eyeglass frame including eyeglass lenses; 10. The apparatus according to any of the preceding claims, 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.

6. The freeform light guide may include a linear polarizing layer overlying the polarizing beam splitter layer; and / or 13. The device of any preceding claim, further comprising an anti-reflection layer overlying the linear polarizing layer.

7. 13. The apparatus of any preceding claim, further comprising a display quarter-wave plate disposed between the display and an input coupling interface and configured to convert the display light emitted from the display from a linear polarization state to a circular polarization state.

8. the partial mirror layer converts reflected incident light having a first circular polarization state into light having a second circular polarization state; and / or 2. An apparatus according to any preceding claim, configured to convert reflected incident light having the second circular polarization state into light having the first circular polarization state.

9. 10. The apparatus of any preceding claim, further comprising an adaptive optics element disposed on the second surface of the light guide.

10. A method for transmitting display light from a display to a user's eye in a near-eye display system, in particular using the device according to one of the preceding claims, comprising: 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; The method further comprises: Directing display light emitted by a display to the input coupling interface; transmitting the display light representation from the input-coupling interface through the light guide to an output-coupling area; 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.

11. The method of claim 10 , wherein the freeform light guide further comprises a linear polarizing layer overlying the polarizing beamsplitter layer.

12. Transmitting the representation of the display light through the light guide includes: 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 / or 12. The method of claim 11, 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.

13. Transmitting the representation of the display light through the light guide includes: 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; 13. The method of claim 11 or claim 12, 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.

14. Transmitting the representation of the display light through the light guide includes: 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 wave plate; 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; 14. The method of claim 13, 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.

15. Transmitting the representation of the display light through the light guide includes: 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; 15. The method of claim 14, further comprising at least one of 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 polarizer layer to the output coupling region.

16. 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; A near-eye display system, wherein at least a portion of the change in polarization state causes the light to reflect within the freeform light guide.

17. 17. The near-eye display system of claim 16, wherein at least a portion of the change in polarization state causes the light to reflect off a polarizing beam splitter layer in the freeform light guide.

18. 18. The near-eye display system of claim 16 or claim 17, wherein the light guide comprises a laminate film including a quarter wave plate layer and / or a polarizing beam splitter layer.

19. The near-eye display system of any one of claims 16 to 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 16 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