Folded optical system with display collimation and angular control

Abstract

A folded optical system includes a display, a lens assembly, and a multilayer beam shaping film disposed between the lens assembly and the display. The folded optical system is configured to display a virtual image for viewing at an exit pupil of the system. The lens assembly includes a first lens disposed in a cavity defined by a partial reflector and a reflective polarizer. The beam shaping film includes lenses arranged on an opaque layer, which defines a plurality of through openings aligned with the lenses. For an emitted cone of image light, the beam shaping film transmits and shapes the emitted cone so that the transmitted shaped cone exits the lens assembly and is incident on the exit pupil as a collimated image light having first energy E1, and passes through the exit pupil, the passed through collimated image light having second energy E2, such that E2 / E1 ≥ 0.2.

Description

[0001] FOLDED OPTICAL SYSTEM WITH DISPLAY COLLIMATION AND ANGULAR CONTROL

[0002] Summary

[0003] In some aspects of the present description, a folded optical system is provided, the folded optical system including a display, an optical lens assembly, and a multilayer beam shaping film disposed between the display and the optical lens assembly. The display is configured to form and emit an image, and the folded optical system is configured to display a virtual image of the emitted image for viewing by an eye disposed at or proximate an exit pupil of the folded optical system. The optical lens assembly includes at least a first optical lens disposed in an optical cavity defined by and between a partial reflector and a reflective polarizer. The multilayer beam shaping film includes an array of optically transparent lenses arranged two-dimensionally on and across an optically opaque layer. The optically opaque layer defines a plurality of through openings aligned with the optically transparent lenses in one-to-one correspondence. For a cone of image light emitted from each location on the image formed by the display, the multilayer beam shaping film transmits and shapes the emitted cone of image light so that the transmitted shaped cone of image light passes through the partial reflector, through the at least the first optical lens, is reflected at least once by the reflective polarizer, and exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy El, and passes through, and substantially fills, the exit pupil. The passed through collimated image light has a second integrated energy E2, such that E2 / E1 is greater than or equal to 0.2.

[0004] In some aspects of the present description, a folded optical system is provided, the folded optical system including an extended illumination source configured to emit light from an extended emission surface thereof, a display panel disposed proximate the extended light source, a multilayer beam shaping film disposed between the display panel and the extended illumination source, and substantially co-extensive in length and width with, the display panel, and an optical lens assembly disposed between the display panel and the viewer. The display panel is configured to receive the emitted light received and transmitted by the multilayer beam shaping film and form an image for viewing by an eye of a viewer located at or proximate an exit pupil of the optical system. The optical lens assembly includes at least a first optical lens disposed in an optical cavity defined by and between a partial reflector and a reflective polarizer. The multilayer beam shaping film is configured to shape and direct the light emitted by the extended illumination source such that, for each cone of image light emitted from each location on the formed image, the transmitted shaped cone of image light passes through the partial reflector, through the at least the first optical lens, is reflected at least once by the reflective polarizer, and exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy El, and passes through, and substantially fills, the exit pupil. The passed through collimated image light has a second integrated energy E2, such that E2 / E1 is greater than or equal to 0.2.

[0005] In some aspects of the present description, an optical system is provided, the optical system including a display, an optical lens assembly including at least one optical lens, and a multilayer beam shaping film disposed between the optical lens assembly and the display. The display is configured to form and emit an image, and the optical system is configured to display a virtual image of the emitted image for viewing by an eye disposed at or proximate an exit pupil of the optical system. The multilayer beam shaping film includes an array of optically transparent lenses arranged two- dimensionally on an optically opaque layer. The optically opaque layer defines a plurality of through openings aligned with the lenses in one-to-one correspondence. For a cone of image light emitted from each location on the image formed by display, the multilayer beam shaping film transmits and shapes the emitted cone of image light so that the transmitted shaped cone of image light exits the optical lens assembly as a substantially collimated image light having a first integrated energy El, and passes through, and substantially fills, the exit pupil. The passed through collimated image light has a second integrated energy E2, such that E2 / E1 is greater than or equal to 0.2.

[0006] In some aspects of the present description, an optical system is provided, the optical system including an extended illumination source configured to emit light from an extended emission surface thereof, a display panel disposed proximate the extended light source, a multilayer beam shaping film disposed between the display panel and the extended illumination source, and an optical lens assembly including at least a first optical lens, the optical lens assembly disposed between the display panel and the viewer. The display panel is configured to receive the emitted light received and transmitted by the multilayer beam shaping film and form an image for viewing by an eye of a viewer located at or proximate an exit pupil of the optical system. The multilayer beam shaping film is substantially co-extensive in length and width with, the display panel, and is configured to shape and direct the light emitted by the extended illumination source such that, for each cone of image light emitted from each location on the formed image, the cone of image light exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy El and passes through, and substantially fills, the exit pupil. The passed through collimated image light has a second integrated energy E2, such that E2 / E1 is greater than or equal to 0.2.

[0007] Brief Description of the Drawings

[0008] FIG. 1 A is a side, cutaway view of a folded optical system including a multilayer beam shaping film disposed between a display and a lens assembly, in accordance with an embodiment of the present description;

[0009] FIG. IB is a schematic view of an exit pupil of a folded optical system, in accordance with an embodiment of the present description; FIG. 2 is a side, cutaway view of a folded optical system including a multilayer beam shaping film disposed between a display and a backlight, in accordance with an embodiment of the present description;

[0010] FIG. 3 is a side, cutaway view of a multilayer beam shaping film, in accordance with an embodiment of the present description;

[0011] FIG. 4 is a side, cutaway view of a non-folded optical system including a multilayer beam shaping film disposed between a display and a lens assembly, in accordance with an embodiment of the present description;

[0012] FIG. 5 is a side, cutaway view of a non-folded optical system including a multilayer beam shaping film disposed between a display and a backlight, in accordance with an embodiment of the present description;

[0013] FIG. 6 is a diagram defining terms for a multilayer beam shaping film, in accordance with an embodiment of the present description;

[0014] FIG. 7 is a side, cutaway view of the structure of a multilayer optical film, in accordance with an embodiment of the present description;

[0015] FIG. 8A is a graph of contrast ratio versus the display half angle for an optical system, in accordance with an embodiment of the present description;

[0016] FIG. 8B is a graph of image irradiance as a function of display half angle for an optical system, in accordance with an embodiment of the present description;

[0017] FIG. 9 is a graph of output angle versus object location for an optical system, in accordance with an embodiment of the present description; and

[0018] FIG. 10 is a graph of changing output angle across a beam shaping film as discussed in the Examples section herein, in accordance with an embodiment of the present description.

[0019] Detailed Description

[0020] In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0021] One of the most important specifications for virtual reality (VR) headsets is image contrast, or the ratio of white to black pixel intensity. This contrast can be limited by the angular output of the display, which is largely Lambertian. To increase the contrast, the angular output of the display must be reduced (e.g., through collimation of the light emitted by the display). However, collimation alone often leads to vignetting, or darkening at the edges of the field of view. Accordingly, collimation and control of the angular direction of the collimated light across the display is necessary to improve both contrast and display uniformity. To reduce vignetting, the central output angle of the display can be changed. When the output angle is optimized as described herein, the vignetting of the display is reduced (and display uniformity is increased).

[0022] According to some aspects of the present description, a folded optical system includes a display configured to form and emit an image, an optical lens assembly having at least one lens, and a multilayer beam shaping film disposed between the optical lens assembly and the display.

[0023] In some embodiments, the folded optical system is configured to display a virtual image of the emitted image for viewing by an eye disposed at or proximate an exit pupil of the folded optical system. In some embodiments, the optical lens assembly further includes a partial reflector and a reflective polarizer, and the at least first optical lens is disposed in an optical cavity which is defined by and disposed between the partial reflector and the reflective polarizer.

[0024] In some embodiments, the multilayer beam shaping film includes an array of optically transparent lenses (e.g., optically transparent beads) arranged two-dimensionally on and across an optically opaque layer. In some embodiments, the optically opaque layer may define a plurality of through openings aligned with the optically transparent lenses in one-to-one correspondence.

[0025] For the purposes of this specification, a ‘through opening’ shall be defined as a substantially optically transmissive region. This may include, but is not limited to, a through-hole (i.e., a physical opening of substantially any appropriate size and / or shape passing through the layer in which it is included) or a chemical composition change to make a material optically transmissive. In some embodiments, ‘optically transmissive’ may be defined as transmitting about 50% or greater of incident light.

[0026] In some embodiments, the optically opaque layer (not including the through openings) may reject light primarily by absorbing the light. In some such embodiments, the optically opaque layer may have an average optical density of greater than about 1, or greater than about 2, or greater than about 2.5, or greater than about 3 in a visible wavelength range extending from about 420 nm to about 680 nm. In some such embodiments, the optically opaque layer may include one or more of a light absorbing pigment, a light absorbing dye and carbon black. In some embodiments, the optically opaque layer may have a black or a dark gray color.

[0027] For the purposes of this specification, optical density (OD) shall be defined by the following:

[0028] OD = -log(T) where T is the amount of transmission of light through the medium and is between 0 (for 0% optical transmission of the light) and 1 (for 100% optical transmission of the light). For example, for 100% transmission, T would be equal to 1 and the optical density would be calculated to be 0.

[0029] In some embodiments, the optically opaque layer may reject light primarily by reflecting the light. In some such embodiments, the optically opaque layer may have an average optical reflectance of greater than about 50%, or greater than about 55%, or greater than about 60%, or greater than about 65%, or greater than about 70%, or greater than about 75%, or greater than about 80%, or greater than about 85%, or greater than about 90%, or greater than about 95% in a visible wavelength range extending from about 420 nm to about 680 nm. In some such embodiments, the optically opaque layer may include a metal. In some such embodiments, the metal may include one or more of silver, copper, gold, aluminum and tungsten.

[0030] In some embodiments, at least some of the optically transparent lenses may include one or more of polymeric beads, glass beads, silicone beads, ceramic beads, and plastic beads. In some embodiments, the optically transparent lenses may be substantially spherical beads. In some embodiments, the multilayer beam shaping film may be a film such as that described in co-pending US Provisional Patent Application 63 / 469968, which is herein incorporated by reference.

[0031] In some embodiments, the optically transparent lenses may be embedded in a binder material. In some embodiments, the binder material may be optically transparent and have an average optical transmittance of greater than about 80%, or greater than about 85%, or greater than about 90%, or greater than about 95% in a visible wavelength range extending from about 420 nm to about 680 nm. In some embodiments, the binder material may be optically light absorbing and have an average optical density of greater than about 0.01, or greater than about 0.03, or greater than about 0.05, or greater than about 0.1 in a visible wavelength range extending from about 420 nm to about 680 nm. In some such embodiments, the optically transparent lenses may be embedded in the light-absorbing material such that at least a portion of the lenses is not occluded by the black binder but such that optical cross-talk between the lenses is minimized.

[0032] In some embodiments, the multilayer beam shaping film may be configured, such that, for a cone of image light emitted from each location on the image formed by the display, the multilayer beam shaping film transmits and shapes the emitted cone of image light so that the transmitted shaped cone of image light passes through the partial reflector, through the at least first optical lens, is reflected at least once by the reflective polarizer, and exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy, El, and passes through, and substantially fills, the exit pupil. In some embodiments, the passed through collimated image light may have a second integrated energy E2, such that E2 / E1 is greater than or equal to about 0.2, or about 0.3, or about 0.4, or about 0.5, or about 0.6, or about 0.7, or about 0.8, or about 0.9.

[0033] Having a E2 / E1 ratio of greater than or equal to about 0.2 (i.e., at least about 20% of the light energy emitted by the optical lens assembly passes through the exit pupil) is a marked improvement over similar optical system configurations in the art. It should be noted, for comparative purposes, that the human eye typically only captures about 3% of the light from a non-collimated source. That is, comparing the integrated energy of a non-collimated source, Enc, to the integrated energy as captured by the human eye, Eh, the ratio of Eh / Enc may only be about 0.03. In other existing display examples, the ratio of E2 / E1 can be around about 0.04 (corresponding to about 4%). In some embodiments, an opening of the exit pupil may have a maximum lateral dimension of greater than about 1 mm and less than about 15 mm, or greater than about 2 mm and less than about 10 mm, or greater than about 4 mm and less than about 8 mm.

[0034] In some embodiments, the optical lens assembly may further include at least a second optical lens. In some embodiments, the at least second optical lens may be disposed outside the optical cavity proximate the reflective polarizer and away from the partial reflector. In some other embodiments, the at least second optical lens may be disposed inside the optical cavity proximate the reflective polarizer and facing the partial reflector. In some embodiments, the folded optical system may further include an absorbing polarizer disposed outside the optical lens assembly proximate the reflective polarizer and away from the partial reflector.

[0035] In some embodiments, the shaping of the emitted cone of image light by the multilayer beam shaping film may include one or more of changing a propagation direction of a central image ray of the emitted cone of image light and changing a cone angle of the emitted cone of image light. For the purposes of this specification, the cone angle shall be defined as the range of angles of light within a cone of light (i.e., the angles of all light rays defining the cone being emitted from a point of the image / display, as they diverge away from a central light ray of the cone). A given cone angle may include light rays with both positive and negative angles relative to a central light ray or local optical axis of the cone of light. As such, it may be convenient to describe the cone of light in terms of the cone’s half angle, which may be defined as the angle between the angle of incidence of the incident beam / cone (i.e., the angle of a central light ray) and the angle of the most oblique marginal ray. See, for example, FIG. 6, for a graphical definition of cone angle and half cone angle.

[0036] In some embodiments, it may be advantageous to vary either the propagation direction or cone angle of a cone of light such that it contributes to improved contrast, improved uniformity, or an optimal combination of both, and therefore the performance and / or structure of the multilayer beam shaping film may vary across the plane of the multilayer beam shaping film. For example, the output angle of the cone of light (i.e., the propagation direction of the cone of light) may gradually change (e.g., increase in magnitude) for points in the image as the distance of the point increases from a center of the image.

[0037] In some embodiments, for example, for first and second emitted cones of image light emitted from different respective first and second locations on the image formed by the display, central image rays of the first and second transmitted shaped cones may propagate along different respective first and second directions. In some embodiments, for first and second emitted cones of image light emitted from different respective first and second locations on the image formed by the display, the first and second transmitted shaped cones have different respective first and second shapes (e.g., different cone angles).

[0038] In some embodiments, the folded optical system may be substantially centered on a folded optical axis that passes through substantially a center of the exit pupil (that is, the optical axis may be folded through the use of reflection and / or redirection of the light transmitted by the optical system, such as may be necessary in a virtual reality system (e.g., head-worn goggles). In some embodiments, the emitted cone of image light may be substantially centered on a central image ray, and wherein, after being transmitted by the multilayer beam shaping film, exiting the optical lens assembly and being incident on the exit pupil, the central image ray may pass through the exit pupil at, or substantially proximate to, the center of the exit pupil. In some such embodiments, at least a portion of the folded optical axis that is within the optical cavity may be folded on itself. In some embodiments, a first central image ray of a first transmitted shaped cone of image light corresponding to a first location of the image farther from the folded optical axis may make a first angle with the folded optical axis, and a second central image ray of a second transmitted shaped cone of image light corresponding to a second location of the image closer to the folded optical axis makes a second angle with the folded optical axis, wherein a magnitude of the second angle is less than a magnitude of the first angle.

[0039] According to some aspects of the present description, a folded optical system may include an extended illumination source (e.g., a backlight, LED array, etc.) configured to emit light from an extended emission surface thereof, a display panel disposed proximate the extended light source, a multilayer beam shaping film disposed between the display panel and the extended illumination source, and substantially co-extensive in length and width with, the display panel, and an optical lens assembly comprising at least a first optical lens disposed in an optical cavity defined by and between a partial reflector and a reflective polarizer. In some embodiments, the optical lens assembly may be disposed between the display panel and the viewer. In some embodiments, the display panel may be configured to receive the emitted light received and transmitted by the multilayer beam shaping film and form an image for viewing by an eye of a viewer located at or proximate an exit pupil of the optical system.

[0040] In some embodiments, the multilayer beam shaping film may be configured to shape and direct the light emitted by the extended illumination source such that, for each cone of image light emitted from each location on the formed image, the transmitted shaped cone of image light passes through the partial reflector, through the at least the first optical lens, is reflected at least once by the reflective polarizer, and exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy El and passes through, and substantially fills, the exit pupil. In some embodiments, the passed through collimated image light may have a second integrated energy E2, such that E2 / E1 is greater than or equal to 0.03.

[0041] In some embodiments, the extended illumination source may include a lightguide for propagating light therein along a length (e.g., along an x-axis) and width (e.g., along a y-axis) of the lightguide, and at least one light source. In some such embodiments, the lightguide may be disposed between a back reflector and the extended emission surface. In some embodiments, the at least one light source may be disposed proximate an edge surface of the lightguide. In some such embodiments, the back reflector may be configured to reflect light that exits the lightguide toward the back reflector.

[0042] In some embodiments, the extended illumination source may include a reflective layer, an optically diffusive layer, and at least one light source. In some embodiments, the optically diffusive layer may be disposed on the reflective layer and may include the extended emission surface, or may be disposed proximate the extended emission surface. In some embodiments, the optically diffusive layer and the reflective layer may be substantially coextensive with each other in length (e.g., along an x-axis) and width (e.g., along a y-axis) and may define an optical cavity therebetween. In some embodiments, the at least one light source may be disposed in or proximate the optical cavity.

[0043] In some embodiments, the extended illumination source may include a reflective polarizer. In some such embodiments, for a substantially normally incident light and a visible wavelength range extending from about 420 nm to about 680 nm, the reflective polarizer may have an average reflectance of greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90%, or greater than about 95% when the incident light is polarized along a first inplane direction (e.g., along an x-axis) and an average transmittance of greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90%, or greater than about 95% when the incident light is polarized along an orthogonal second in-plane direction (e.g., along a y-axis).

[0044] In some embodiments, the extended illumination source may further include a first prismatic film having a plurality of first prisms extending along a first longitudinal direction (e.g., along a y- axis). In some such embodiments, the extended illumination source may further include a second prismatic film disposed proximate the first prismatic film and having a plurality of second prisms extending along a second longitudinal direction (e.g., an x-axis) different from the first longitudinal direction.

[0045] In some embodiments, an opening of the exit pupil may have a maximum lateral dimension of greater than about 1 mm and less than about 15 mm, or greater than about 2 mm and less than about 10 mm, or greater than about 4 mm and less than about 8 mm. In some embodiments, the folded optical system may be substantially centered on a folded optical axis that passes through substantially a center of the exit pupil, wherein the exit pupil is substantially normal to, and substantially centered on, the folded optical axis.

[0046] In some embodiments, the multilayer beam shaping film comprises an array of optically transparent lenses arranged two-dimensionally on an optically opaque layer, the optically opaque layer defining a plurality of through openings aligned with the lenses in one-to-one correspondence.

[0047] In some embodiments, each corresponding pair of lens and through opening of the multilayer beam shaping film may be centered on a local optical axis, and, wherein the local optical axis for one pair is not parallel to the local optical axis for another pair. In some such embodiments, the local optical axis may make a local angle to a folded optical axis of the optical system, and wherein a magnitude of the local angle increases from a center of the optical system to a periphery (see, e.g., FIG. 9, discussed elsewhere herein).

[0048] In some embodiments, the folded optical system may be substantially centered on a folded optical axis that passes through substantially a center of the exit pupil, wherein the emitted cone of image light is substantially centered on a central image ray, and wherein after being transmitted by the multilayer beam shaping film, exiting the optical lens assembly and being incident on the exit pupil, the central image ray passes through the exit pupil at, or substantially proximate to, the center of the exit pupil. In some such embodiments, at least a portion of the folded optical axis that is within the optical cavity, may be folded on itself.

[0049] According to some aspects of the present description, an optical system may include a display configured to form and emit an image, an optical lens assembly having at least one optical lens, and a multilayer beam shaping film disposed between the optical lens assembly and the display. In some embodiments, the optical system may be configured to display a virtual image of the emitted image for viewing by an eye disposed at or proximate an exit pupil of the optical system.

[0050] In some embodiments, multilayer beam shaping film may include an array of optically transparent lenses arranged two-dimensionally on an optically opaque layer. In some embodiments, the optically opaque layer may define a plurality of through openings aligned with the lenses in one- to-one correspondence. In some embodiments, for a cone of image light emitted from each location on the image formed by display, the multilayer beam shaping film may transmit and shape the emitted cone of image light so that the transmitted shaped cone of image light exits the optical lens assembly as a substantially collimated image light having a first integrated energy, El, and passes through, and substantially fills, the exit pupil. In some embodiments, the passed through collimated image light may have a second integrated energy E2, such that E2 / E1 is greater than or equal to about 0.2, or about 0.3, or about 0.4, or about 0.5, or about 0.6, or about 0.7, or about 0.8, or about 0.9.

[0051] In some embodiments, an opening of the exit pupil may have a maximum lateral dimension of greater than about 1 mm and less than about 15 mm, or greater than about 2 mm and less than about 10 mm, or greater than about 4 mm and less than about 8 mm.

[0052] In some embodiments, the shaping of the emitted cone of image light by the multilayer beam shaping film may include one or more of changing a propagation direction of a central image ray of the emitted cone of image light and changing a cone angle of the emitted cone of image light. In some embodiments, for first and second cones of image light emitted from different respective first and second locations on the image formed by the display, central image rays of the first and second cones propagate along different respective first and second directions. In some embodiments, for example, for first and second cones of image light emitted from different respective first and second locations on the image formed by the display, the first and second cones may have different respective first and second shapes. In some embodiments, the optical system may be substantially centered on an optical axis that passes through substantially a center of the exit pupil. In some embodiments, the emitted cone of image light may be substantially centered on a central image ray, and wherein after being transmitted by the multilayer beam shaping film, exiting the optical lens assembly and being incident on the exit pupil, the central image ray passes through the exit pupil at, or substantially proximate to, the center of the exit pupil.

[0053] In some embodiments, the optical system may be substantially centered on an optical axis, wherein a first central image ray of a first transmitted shaped cone of image light corresponding to a first location of the image farther from the optical axis makes a first angle with the optical axis, and a second central image ray of a second transmitted shaped cone of image light corresponding to a second location of the image closer to the optical axis makes a second angle with the optical axis, wherein the second angle is less than the first angle.

[0054] In some embodiments, the optical lens assembly may further include at least one nonpolarizing partial reflector configured to receive and one of transmit and reflect between about 30% to about 70% of image light normally incident to the partial reflector.

[0055] According to some aspects of the present description, an optical system may include an extended illumination source (e.g., a backlight) configured to emit light from an extended emission surface thereof, a display panel disposed proximate the extended light source, a multilayer beam shaping film disposed between the display panel and the extended illumination source, and substantially co-extensive in length and width with, the display panel, and an optical lens assembly including at least a first optical lens and disposed between the display panel and the viewer. In some embodiments, the display panel may be configured to receive the emitted light received and transmitted by the multilayer beam shaping film and form an image for viewing by an eye of a viewer located at or proximate an exit pupil of the optical system.

[0056] In some embodiments, the multilayer beam shaping film may be configured to shape and direct the light emitted by the extended illumination source such that, for each cone of image light emitted from each location on the formed image, the cone of image light exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy, El, and passes through, and substantially fills, the exit pupil. In some embodiments, the passed through collimated image light may have a second integrated energy, E2, such that E2 / E1 is greater than or equal to about 0.2, or about 0.3, or about 0.4, or about 0.5, or about 0.6, or about 0.7, or about 0.8, or about 0.9.

[0057] In some embodiments, an opening of the exit pupil may have a maximum lateral dimension of greater than about 1 mm and less than about 15 mm, or greater than about 2 mm and less than about 10 mm, or greater than about 4 mm and less than about 8 mm. In some embodiments, the optical system may be substantially centered on an optical axis that passes through substantially a center of the exit pupil, wherein the exit pupil is substantially normal to, and substantially centered on, the optical axis.

[0058] In some embodiments, the multilayer beam shaping film may include an array of optically transparent lenses (e.g., self-arranged beads) arranged two-dimensionally on an optically opaque layer. In some embodiments, the optically opaque layer may define a plurality of through openings aligned with the lenses in one-to-one correspondence. In some embodiments, the nature of the one-to- one correspondence may be that each pair of lens and through opening may be aligned along a local optical axis, wherein the local optical axis for one pair is not parallel to the local optical axis for another pair. In some such embodiments, the local optical axis makes a local angle to an optical axis of the optical system, and wherein a magnitude of the local angle increases from a center of the optical system to a periphery.

[0059] In some embodiments, the optical lens assembly may further include at least one nonpolarizing partial reflector configured to receive and one of transmit and reflect between about 30% to about 70% of image light normally incident to the partial reflector.

[0060] Turning now to the figures, FIG. 1A is a side, cutaway view of an embodiment of a folded optical system including a multilayer beam shaping film disposed between a display and a lens assembly, according to the present description. FIG. IB is a schematic view of an embodiment of an exit pupil of the folded optical system of FIG. 1A. FIGS. 1A and IB should be viewed together for the following description.

[0061] In some embodiments, folded optical system 300 (e.g., a virtual reality system, such as a headset) may include a display 10 configured to form and emit an image 11, and the folded optical system may be configured to display a virtual image 12 of emitted image 11 for viewing by an eye 13 disposed at or proximate an exit pupil 20 of the folded optical system.

[0062] In some embodiments, folded optical system 300 may further include an optical lens assembly 30. In some embodiments, optical lens assembly 30 may include at least a first optical lens 31 disposed in an optical cavity 32 defined between a partial reflector 33 and a reflective polarizer 34. In some embodiments, the optical lens assembly may further include at least a second optical lens 34a. In some such embodiments, at least second optical lens 34a may be disposed outside optical cavity 32 proximate reflective polarizer 34 and away from partial reflector 33. In other such embodiments, at least second optical lens 34a may be disposed inside optical cavity 32 proximate reflective polarizer 34 and facing partial reflector 33 (not shown in FIG. 1). In some embodiments, folded optical system may further include an absorbing polarizer 60 disposed outside optical lens assembly 30, proximate reflective polarizer 34 and away from partial reflector 33.

[0063] In some embodiments, folded optical system 300 may further include a multilayer beam shaping film 40 disposed between optical lens assembly 30 and display 10. In some embodiments, multilayer beam shaping film may be configured such that, for a cone of image light 50 emitted from each location 51 on image 11 formed by display 10, the multilayer beam shaping film 40 may transmit and shape emitted cone of image light 50 so that the transmitted shaped cone of image light 52 passes through partial reflector 33, through the at least first optical lens 31, is reflected at least once by reflective polarizer 34, and exits optical lens assembly 30 and is incident on the exit pupil 20 as a substantially collimated image light 53 having a first integrated energy El, and passes through, and substantially fills, exit pupil 20 (i.e., fills opening 22 of exit pupil 20). The passed-through collimated image light having a second integrated energy E2, such that the ratio of E2 / E1 is greater than or equal to about 0.2, or about 0.3, or about 0.4, or about 0.5, or about 0.6, or about 0.7, or about 0.8, or about 0.9.

[0064] In some embodiments, folded optical system 300 may be substantially centered on a folded optical axis 301 that passes through substantially a center X of exit pupil 20 (see FIG. IB). In some such embodiments, emitted cone of image light 50 may be substantially centered on a central image ray 50a of the cone, being transmitted by multilayer beam shaping film 40, exiting optical lens assembly 30 and being incident on exit pupil 20, the central image ray 53a passes through exit pupil 20 at, or substantially proximate to, center X of exit pupil 20. In some embodiments, at least a portion 302 of folded optical axis 301 that is within optical cavity 32, is folded on itself.

[0065] In other embodiments, the multilayer beam shaping film 40 may be disposed behind display 10, between display 10 and an extended light source such as a backlight. FIG. 2 is a side, cutaway view of an embodiment of a folded optical system 305 including multilayer beam shaping film 40 disposed between display 10 and a backlight (extended light source) 25, according to the present description. It should be noted that the elements of the embodiment of FIG. 2 which share reference numbers with the embodiment of FIG. 1A shall be assumed to have the same functionality as the like- numbered elements of FIG. 1A unless specifically stated otherwise herein. Therefore, only the elements of the embodiment of FIG. 2 which have a unique purpose or function shall be discussed in the following description.

[0066] In the embodiment of folded optical system 305 of FIG. 2, multilayer beam shaping film 40 is located inside of the backlight of display 10 (i.e., it is disposed between display 10 and extended light source 25). In some embodiments, extended light source 25 may include one or more light sources 17 (e.g., light emitting diodes) and a back reflector 14. Eight emitted by light sources 17 may be transmitted toward multilayer beam shaping film 40, either directly or after reflection from one or more surfaces within extended light source 25, including back reflector 14. This emitted light may then be shaped by multilayer beam shaping film 40 before being emitted toward and transmitted by display 10. Accordingly, a shaped light cone 52a transmitted by display 10 from location 51a may have a different propagation direction and / or cone angle than a light cone 50a that was not first shaped by multilayer beam shaping film 40. (Note: Light cone 50a is shown as dashed lines to indicate how the light might be transmitted if not shaped first by beam shaping film 40.) Stated another way, wither multilayer beam shaping film 40 is disposed between display 10 and optical lens assembly 30 (as shown in the embodiment of FIG. 1 A) or disposed between display 10 and extended light source 25 (as shown in the embodiment of FIG. 2), the purpose of the multilayer beam shaping film is essentially the same (i.e., shaping and transmitting light to produce an optimal image for the optical system). The multilayer beam shaping film may be configured to find an acceptable balance between display image contrast and uniformity.

[0067] FIG. 3 is a side, cutaway view of an embodiment of a multilayer beam shaping film, according to the present description. In some embodiments, multilayer beam shaping film 40 includes an array of optically transparent lenses 80 arranged two-dimensionally on and across an optically opaque layer 70. In some embodiments, optically opaque layer 70 defines a plurality of through openings 71 aligned with optically transparent lenses 80 in one-to-one correspondence. In some embodiments, each of through openings 71 may extend between major top surface 72 and opposite bottom surface 73 of optically opaque layer 70.

[0068] In some embodiments, optically transparent lenses 80 may be at least partially embedded in a first layer 81. In some embodiments, first layer 81 may be substantially optically opaque. In some such embodiments, at least a portion of optically transparent lenses 80 may extend through first layer 81 toward optically opaque layer 70 such that light may enter optically transparent lenses 80 and be transmitted by multilayer beam shaping film 40.

[0069] In some embodiments, a spacer layer 50 may be disposed between first layer 81 and optically opaque layer 70. For example, a spacer layer 50 may be used to adjust a focal length relative to the location of the through openings 71. In some embodiments, a thickness tl of spacer layer 50 may be such that when a substantially collimated light 54 is substantially normally incident on optical assembly 300, then each of optically transparent lenses 80 focuses the incident light 54 to a focal spot 56 disposed within, or adjacent to, the through opening 71 corresponding to the optically transparent lens 80 to which it is aligned.

[0070] In some embodiments, multilayer beam shaping film 40 may further include a substrate layer 90 disposed on optically opaque layer 70 opposite first layer 81. In some such embodiments, a bonding layer 120 may bond optically opaque layer 70 to substrate layer 90.

[0071] In some embodiments, each corresponding pair of lens 80 and through opening 71 may be centered on a local optical axis 305. In some embodiments, the local optical axis 305a for one pair may not be parallel to the local optical axis 305b for another pair. In some embodiments, the local optical axis 305 / 305a / 305b (collectively, 305) may make a local angle 91 / 92 to a folded optical axis 301 of the optical system (see, e.g., optical system 300 of FIG. 1A). Please note that a small vertical dashed line is shown for local angles 91 / 92, representing the direction of folded optical axis 305. In some embodiments, a magnitude of the local angle increases from a center of the optical system 300 (e.g., a point on multilayer beam shaping film closest to folded optical axis 301) to a periphery (e.g., the magnitude of 92, being farther away from folded optical axis 301, may be greater than the magnitude of 91, closer to folded optical axis 301). Because of the possibly different angles of the local optical axes 305, the location of the through holes 71 may be adjusted as needed such that the through holes 71 and lenses 80 in each pair of through hole and lens are aligned along that pair’s local optical axis 305. Note in FIG. 3 that focal spot 56a for light 54a is still disposed within, or adjacent to, a through opening 71.

[0072] FIG. 4 is a side, cutaway view of an embodiment of a non-folded optical system including a multilayer beam shaping film disposed between a display and a lens assembly, and FIG. 5 is a side, cutaway view of an embodiment of a non-folded optical system including a multilayer beam shaping film disposed between a display and a backlight. Stated another way, the embodiment of the optical system 310 shown in FIG. 4 is a version of the embodiment of the folded optical system 300 of FIG. 1A except that the optical axis 301 of embodiment 310 of FIG. 4 is a non-folded optical axis. Similarly, the embodiment of the optical system 315 shown in FIG. 5 is a non-folded version of the embodiment of the folded optical system 305 of FIG. 2. Unless specifically stated otherwise, the like- numbered elements of FIGS. 4 and 5 common to their corresponding elements in FIGS. 1 A and 2 shall be assumed to have similar functionality, and these common elements may not be further explained in the following discussion.

[0073] A primary difference between the non-folded embodiment of optical system 310 of FIG. 4 and the folded embodiment of optical system 300 of FIG. 1 A is in optical lens assembly 30. In some embodiments, optical lens assembly 30 includes at least one optical lens 31, but it may not have the partial reflector 33 and reflective polarizer 34 of embodiment 300 of FIG. 1A, and optical axis 301 will not have folded section 302, as shown in FIG. 1 A. Similarly, the embodiment of optical system 315 of FIG. 5 includes the non-folded version of optical lens assembly 30. In all embodiments of the optical systems described herein, the multilayer beam shaping film 40 is configured such that the image as seen at the exit pupil of the system (by the viewer) has an optimal balance of image contrast and image uniformity.

[0074] FIG. 6 is a diagram defining terms for an embodiment of a multilayer beam shaping film, according to the present description. The embodiment shown in FIG. 6 corresponds to the embodiment of folded optical system 300, but the terms defined can be applied equally to any of the embodiments discussed herein. Display 70 is configured to emit an image 11. Each point 51 in image 11 will emit an emitted cone of image light 50 (Note: a “cone” of light is shown in these figures defined by three rays of light, a central image ray and two outer rays defining the extent of the cones. A true “cone” of light would include a large number of light rays forming a three-dimensional cone shape, similar to an ice cream cone.)

[0075] The emitted cone of image light 50 has a cone angle, al , which defines the amount of divergence of the cone as it travels away from display 70. The propagation direction, Pl, of the emitted cone of image light 50 is defined by the central image ray which follows a local optical axis (305) as shown in FIG. 3. Once the emitted cone of image light 50 passes through and is transmitted and shaped by the multilayer beam shaping film 40, the transmitted shaped cone of image light 52 may have a different cone angle, a2, and / or a different propagation direction, P2. The “shape” of a cone of image light is therefore defined by both the propagation direction and the cone angle, as defined in FIG. 6.

[0076] Practically, the propagation direction (e.g., Pl, P2) can be expressed as an “output angle”, which is the magnitude of the angle of the central light ray from the optical axis 301 of the optical system. For example, looking at FIG. 6, propagation direction Pl of cone of image light 50 is nearly parallel to the optical axis 301. Propagation direction P2, on the other hand, diverges away from optical axis 301 by an “output angle” of Opj. For the purposes of this specification, the terms “propagation direction” and “output angle” shall be considered to be synonymous.

[0077] It should be noted that it may be advantageous to describe the shape of a cone of image light by the cone’s half angle, oii / 2, which assumes the cone of light is symmetrical around the central image ray and avoids having to refer to the sign of the angle (positive or negative angle off of the central image ray). For example, the charts shown in FIGS. 8A and 8B refer to the “half angle” of the display (which can have an effect on the contrast ratio, for example, as shown in FIG. 8A).

[0078] FIG. 7 is a schematic, side view showing the structure of an embodiment of a multilayer optical film, such as substrate layer 90 of FIG. 3. As discussed elsewhere herein, in some embodiments, a substrate layer 90 may be disposed on the optically opaque layer 70 opposite the first layer 81. In some such embodiments, the substrate layer 90 may have a multilayer structure and include a plurality of polymeric layers 91, 92 as shown in FIG. 7, the polymeric layers numbering at least 10, or at least 20, or at least 50, or at least 100, or at least 200, or at least 300, or at least 400 in total. In some embodiments, an average thickness of each of the polymeric layers may be less than about 500 nm, or less than about 450 nm, or less than about 400 nm, or less than about 350 nm, or less than about 300 nm, or less than about 250 nm, or less than about 200 nm. In some embodiments, substrate layer 60 may further include at least one skin layer 93 having an average thickness of greater than about 500 nm, or greater than about 750 nm, or greater than about 1000 nm, or greater than about 1250 nm, or greater than about 1500 nm.

[0079] In some embodiments, the indices of refraction of alternating polymeric layers 91, 92 may have different indices of refraction from each other. In some embodiments, the indices of refraction of at least one of the alternating polymeric layers 91, 92 may vary across a profile of layers in the z- direction, as shown by the coordinate system in FIG. 7. In some embodiments, a profile plotting various physical and optical characteristics of alternating polymeric layers 91, 92 such as index of refraction, thickness, etc. may vary (e.g., may show a changing gradient of one or more of the characteristics, may vary randomly, continuously, non-continuously, etc.). In this way, optical transmission characteristics of the substrate layer may be modified to meet a specific requirement. For example, in some embodiments, for a substantially normally incident light and a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of polymeric layers 91, 92 may have an average reflectance of greater than about 50%, or greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90%, or greater than about 95% when the incident light is polarized along a first in-plane direction (e.g., along the x-axis) and an average transmittance of greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90%, or greater than about 95% when the incident light is polarized along an orthogonal second in-plane direction (x-axis).

[0080] FIGS. 8A, 8B, and 9 provide charts detailing characteristics of an embodiment of a multilayer beam shaping film, such as any of the embodiments included herein. FIG. 8 A is a graph of contrast ratio versus the display half angle for an optical system, according to the present description.

[0081] FIG. 8A illustrates that the contrast ratio of a display can be affected by the cone angle (i.e., the cone half angle, used in FIG. 8A). As shown in the figure, as the output angle (half angle) of the display is decreased from 20 degrees down to 5 degrees, there is a significant increase in the contrast ratio. When the half angle is 20 degrees, for example, the contrast ratio is about 43. When the half angle is reduced to 5 degrees (i.e., the cone is narrower, the light more collimated), the contrast ratio increases to about 68. The data shown in FIG. 8A is for an object located 6 mm off the center of the display, but the trend is similar for other object locations.

[0082] The plot of FIG. 8A suggests that collimating the output of the display to 5 degrees can significantly increase contrast over a standard system. However, contrast is not the only consideration for these devices. Display uniformity is also very important.

[0083] FIG. 8B is a graph of image irradiance as a function of display half angle for an optical system, according to the present description. FIG. 8B illustrates the intensity of the image for objects 6 mm and 12 mm from the center of the display as the angular output (half angle) is decreased from 20 to 5 degrees. It can be seen that the display intensity drops as the half angle is decreased. So, while there is an improvement in contrast, the uniformity is also decreased across the display, leading to vignetting (dimming of intensity near the outer edges of the display).

[0084] To reduce the vignetting and further improve signal to noise, the central output angle of the display can be changed. FIG. 9 is a graph of output angle versus object location for an embodiment of an optical system, according to the present description. Specifically, FIG. 9 shows the optimal output angle as the object location is changed to 6 mm, 12 mm, and 16 mm from the center of the display. This figure indicates that there is an optimal central output angle to maximize the contrast across the display. In this embodiment, the optimal output angle increases as the image object location moves away from the center of the display.

[0085] Examples

[0086] All parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight, unless noted otherwise.

[0087] Table 1: Materials Used in the Examples

[0088] General description

[0089] The order of operations to prepare these examples begins with coating of the desired light blocking layer onto the substrate, followed by coating of the spacer layer, followed by coating of the beaded microlens array layer.

[0090] Preparation of light blocking layers

[0091] Light blocking layers were made on polyethylene terephthalate (PET) substrates by vacuum deposition of a thin aluminum layer on the surface the PET. Optical density of the PET substrates with light blocking layer were measured with a Gretag-Macbeth AG D200-II with light source incident on the substrate. Our examples include light blocking layers with optical density 3.0. An organic polymer planarization layers is coated before the aluminum layer on the PET substrate, at a thickness of 100- 1000 nm. In this example, we used SR833s from Sartomer deposited by evaporation and cured by electron beam radiation. A protective layer is coated on top of the light blocking layer by reactively sputtering silicon aluminum oxide at a thickness of about 10 nm. Optionally, an interlayer adhesion layer (or tie layer) is deposited before the light blocking layer is deposited to improve adhesion to underlying layers. The tie layer can be a layer of metal like titanium or nickel -chromium or other metals known to those skilled in the art. The thickness of this layer depends on the desired adhesion level and optical properties at the interface but can be as little as 1 nm or as much as 20 nm.

[0092] Preparation of coating solutions for spacer layers Spacer layer was prepared using SR833S monomer / CN147 oligomer / Klun90 in a ratio of 29.3:3: 1, Irgacure 184 at 0.99 wt% solids in solvents l-methoxy-2-propanol / IPA in ratio of 5.66:1. The wt% solids for spacer is 30%.

[0093] Preparation of coating solutions for beaded microlens array layer

[0094] The beaded microlens coating solution is shown in table 2. The monomers, solvents (1- methoxy-2-propanol / IPA at 5.67: 1 solvent ratio), ESACURE ONE photoinitiator (1.0wt% solids) and TEGORAD 2250 surfactant were mixed together to form a homogenous solution.

[0095] Optically transparent beads SSX-108 with bead diameter of 8um were then added to the solution and further mixed to again form a homogenous solution with the optically transparent beads. The bead to monomer ratio in this solutions was 2.57: 1 weight ratio.

[0096] The carbon black based light absorbing monomer mixture was made in the following manner. The carbon black based light absorbing monomer mixture was a carbon black - IBOA slurry which was made through a media milling process. A dispersant and IBOA were first mixed using a Dispermat CN- 10 laboratory high-shear disperser (BYK-Gardner USA, Columbia MD) until fully dissolved, and then carbon black powder was slowly added under mixing. The slurry was composed of 30% wt carbon black, 55% IBOA, and 15% dispersant. The fully mixed slurry was milled using a LabStar laboratory media mill (Netzsch, Exton PA) with 0.5 mm yttria stabilized zirconia milling media. Small amounts of samples were taken out periodically to monitor the milling progress. The fineness of grind of the final slurry was 7.5 - 8 Hegman unit (or less than 6.5 microns) measured by a Grindometer 100 (BYK Instrument, Columbia MD) as disclosed in ASTM D1210.

[0097] For the purpose of quantifying the optical density of resin systems for bead-free finished coating regions, we made a range of calibration samples of differing thickness using a bead coating solution A but without the addition of beads.

[0098] TABLE 2: Beaded coating solution

[0099] General coating process

[0100] A range of bead-free coatings were coated dried and cured on a clear PET substrate at several thicknesses to measure optical density versus thickness. Optical density was measured with a Gretag- Macbeth AG D200-II on the dry / cured coating on PET with the light incident from the PET side. The coating process was as follows: Solution was supplied at a range of specified rates (cc / min) as specified in the table below to a 4 inch (10.2cm) wide slot type coating die and coated on PET. After the solution was coated on the substrate, the coated web travelled a 10 ft (3m) span in the room environment, and passed through two 5 ft (1.5m) long zones of small gap drying with plate temperatures set at 190 F (88C). The substrate was moving at a speed 10 ft / min (304.8 cm / min) specified in the table below to achieve the wet coating thickness specified in Table 3 below. Finally, the dried coating entered a UV chamber equipped with a Fusion System Model I300P where an H-bulb was used. The UV chamber was purged by nitrogen at a flow rate of 11 scfm (310 liters / min) which resulted in an oxygen concentration of approximately 50 ppm.

[0101] TABLE 3: Light absorbing monomer mixture optical density - coating process for calibration solution

[0102] The measured optical density of the coated dried and cured light absorbing monomer mixture versus dried and cured coating thicknesses between 0.5 microns and 2 microns thick resulted in a linear fit with OD = 0.797 x Thickness [microns] + 0.02.

[0103] Spacer layer coating:

[0104] Clear spacer layer coatings were coated, dried, cured on the aluminum deposited surface of light blocking substrate described above. The spacer layer coatings were made to target of 2.7 micron thickness after coating, drying, and curing. The coating solution was supplied to an 8 inch (20.3 cm) wide slot type coating die, onto a 0.00114 inch (29 micron) thick Al metalized PET film web moving at a speed of 60 ft / min (18.3 m / min). The metalized film had an OD 3. The rate of application of the coating solution was 38.7 g / min. After coating, the web travelled approximately 13 ft (3.9 m) before entering a 30 ft (9.1 m) conventional air floatation drier with three 10ft (3 m) zones set at 38, 49, and 71 °C, respectively. After drying and before winding, the coating was transported through a UV curing systems (Model VPS / I600 from Fusion Systems Inc., Gaithersburg, MD). The Fusion system was configured with an H-bulb and was operated 100 % power. The UV chamber was purged by nitrogen at a flow rate of 16 scfm (450 liters / min) resulting in less than 50 ppm oxygen in the cure zone.

[0105] Beaded microlens array layer coating process

[0106] Beaded microlens solution was coated, dried and cured on the Spacer Layer coating. The solution was supplied to an 8 inch (20.3 cm) wide slot type coating die, onto the surface of solidified first coating at a speed of 40 ft / min (12.2 m / min). The rate of application of the coating solution was 44.1 cm3 / min. After coating, the web travelled approximately 13 ft (3.9 m) before entering a 30 ft (9.1 m) conventional air floatation drier with three 10 ft (3 m) zones set at 104, 60, and 71 °C, respectively. After drying and before winding, the coating was transported through a UV curing systems (Model VPS / I600 from Fusion Systems Inc., Gaithersburg, MD). The Fusion system was configured with an H-bulb and was operated 100 % power at less than 50 ppm oxygen in the cure zone.

[0107] The coating, drying, curing of the beaded microlens solutions generated closely packed monolayer bead coatings on the substrates with near full hemisphere bead protrusions. Given approximately half of the top portions of the monolayer beads are protruding, it can be estimated that the bottom half of the beads are embedded in the cured monomer layer component with the bottom most tip of the beads in near contact with the substrate. An estimate of the optical density through the nonbead areas in the monolayer coating itself in the direction perpendicular to the plane of the substrate can then be calculated for monolayer bead coatings with light absorbing monomer mixtures using the optical density vs. caliper relationship, where film OD = 0.797 x Thickness [microns] + 0.02.

[0108] Laser Processing

[0109] Laser processing was subsequently performed to create an array of openings in the thin aluminum light blocking layer using a laser system comparable to the system described in PCT Publication No. WO 2020 / 035768 to Biyiki et al. and entitled OPTICAL ELEMENT INCLUDING MICROLENS ARRAY. This process included using a pulsed 1064 fiber laser (Trumpf TruNano) coupled to a polygon scanner (NextScan Technology). A linear stage (Aerotech) was used to feed the samples through the scanning laser. The laser pulse rate was set between 1 and 2 MHz with a spot size of approximately 450 micron. The pulse width was set between 10 and 30 ns and the laser power was set between 100 and 200 W. The feed rate of the linear stage was set to about 20 mm / s. A 100 mm diameter lens was placed above the sample to change the incident angle of the light on the sample with azimuthal symmetry. The incident laser direction becomes the output direction from the film when used in its defined case. The experimental output across the film is shown in Figure Fig. 10 showing both a narrow half angle output (a> / 2) and spatially dependent propagation direction P2.

[0110] Optical Characterization

[0111] Optical characterization was carried out using an Eldim conometer. The samples were illuminated using a backlit PTFE slab that acts as a sufficiently Lambertian light source.

[0112] TABLE 4: Summary angular transmission data and descriptions of Examples

[0113]

[0114] Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

[0115] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially equal” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially equal” will mean about equal where about is as described above. If the use of “substantially parallel” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially parallel” will mean within 30 degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees of parallel, or may be parallel or nominally parallel. If the use of “substantially aligned” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially aligned” will mean aligned to within 20% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within 10% or to within 5% of a width of the objects being aligned.

[0116] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0117] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed:

1. A folded optical system comprising: a display configured to form and emit an image, the folded optical system configured to display a virtual image of the emitted image for viewing by an eye disposed at or proximate an exit pupil of the folded optical system; an optical lens assembly comprising at least a first optical lens disposed in an optical cavity defined between a partial reflector and a reflective polarizer; and a multilayer beam shaping film comprising an array of optically transparent lenses arranged two-dimensionally on and across an optically opaque layer, the optically opaque layer defining a plurality of through openings aligned with the optically transparent lenses in one-to-one correspondence, the multilayer beam shaping film disposed between the optical lens assembly and the display, such for a cone of image light emitted from each location on the image formed by the display, the multilayer beam shaping film transmits and shapes the emitted cone of image light so that the transmitted shaped cone of image light passes through the partial reflector, through the at least the first optical lens, is reflected at least once by the reflective polarizer, and exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy El and passes through, and substantially fills, the exit pupil, the passed through collimated image light having a second integrated energy E2, E2 / E1 > 0.2.

2. The folded optical system of claim 1, wherein an opening of the exit pupil has a maximum lateral dimension of greater than about 1 mm and less than about 15 mm.

3. The folded optical system of claim 1, wherein the optical lens assembly further comprises at least a second optical lens disposed outside the optical cavity proximate the reflective polarizer and away from the partial reflector.

4. The folded optical system of claim 1, wherein the optical lens assembly further comprises at least a second optical lens disposed inside the optical cavity proximate the reflective polarizer and facing the partial reflector.

5. The folded optical system of claim 1 further comprising an absorbing polarizer disposed outside the optical lens assembly proximate the reflective polarizer and away from the partial reflector.

6. The folded optical system of claim 1, wherein the shaping of the emitted cone of image light by the multilayer beam shaping film comprises one or more of changing a propagation direction of a central image ray of the emitted cone of image light and changing a cone angle of the emitted cone of image light.

7. The folded optical system of claim 1, wherein for first and second emitted cones of image light emitted from different respective first and second locations on the image formed by the display, central image rays of the first and second transmitted shaped cones propagate along different respective first and second directions.

8. The folded optical system of claim 1, wherein for first and second emitted cones of image light emitted from different respective first and second locations on the image formed by the display, the first and second transmitted shaped cones have different respective first and second shapes.

9. The folded optical system of claim 1 substantially centered on a folded optical axis that passes through substantially a center of the exit pupil, wherein the emitted cone of image light is substantially centered on a central image ray, and wherein after being transmitted by the multilayer beam shaping film, exiting the optical lens assembly and being incident on the exit pupil, the central image ray passes through the exit pupil at, or substantially proximate to, the center of the exit pupil.

10. The folded optical system of claim 9, wherein at least a portion of the folded optical axis that is within the optical cavity, is folded on itself.

11. The folded optical system of claim 1, substantially centered on a folded optical axis, wherein a first central image ray of a first transmitted shaped cone of image light corresponding to a first location of the image farther from the folded optical axis makes a first angle with the folded optical axis, and a second central image ray of a second transmitted shaped cone of image light corresponding to a second location of the image closer to the folded optical axis makes a second angle with the folded optical axis, wherein a magnitude of the second angle is less than a magnitude of the first angle.

12. A folded optical system comprising: an extended illumination source configured to emit light from an extended emission surface thereof; a display panel disposed proximate the extended light source; a multilayer beam shaping film disposed between the display panel and the extended illumination source, and substantially co-extensive in length and width with, the display panel, the display panel configured to receive the emitted light received and transmitted by the multilayer beam shaping film and form an image for viewing by an eye of a viewer located at or proximate an exit pupil of the optical system; andan optical lens assembly comprising at least a first optical lens disposed in an optical cavity defined between a partial reflector and a reflective polarizer, the optical lens assembly disposed between the display panel and the viewer; wherein the multilayer beam shaping film is configured to shape and direct the light emitted by the extended illumination source such that, for each cone of image light emitted from each location on the formed image, the transmitted shaped cone of image light passes through the partial reflector, through the at least the first optical lens, is reflected at least once by the reflective polarizer, and exits the optical lens assembly and is incident on the exit pupil as a substantially collimated image light having a first integrated energy El and passes through, and substantially fills, the exit pupil, the passed through collimated image light having a second integrated energy E2, E2 / E1 > 0.2.

13. The folded optical system of claim 12, wherein an opening of the exit pupil has a maximum lateral dimension of greater than about 1 mm and less than about 15 mm.

14. The folded optical system of claim 12, substantially centered on a folded optical axis that passes through substantially a center of the exit pupil, wherein the exit pupil is substantially normal to, and substantially centered on, the folded optical axis.

15. The folded optical system of claim 12, wherein the multilayer beam shaping film comprises an array of optically transparent lenses arranged two-dimensionally on an optically opaque layer, the optically opaque layer defining a plurality of through openings aligned with the lenses in one-to-one correspondence.

16. The folded optical system of claim 15, wherein each corresponding pair of lens and through opening is centered on a local optical axis, and, wherein the local optical axis for one pair is not parallel to the local optical axis for another pair.

17. The optical system of claim 16, wherein the local optical axis makes a local angle to a folded optical axis of the optical system, and wherein a magnitude of the local angle increases from a center of the optical system to a periphery.

18. The folded optical system of claim 12 substantially centered on a folded optical axis that passes through substantially a center of the exit pupil, wherein the emitted cone of image light is substantially centered on a central image ray, and wherein after being transmitted by the multilayer beam shaping film, exiting the optical lens assembly and being incident on the exit pupil, the central image ray passes through the exit pupil at, or substantially proximate to, the center of the exit pupil.

19. The folded optical system of claim 18, wherein at least a portion of the folded optical axis that is within the optical cavity, is folded on itself.

Images