Two mirror scanning relay optical system

Abstract

A two-mirror scanning projector is described that employs a collimated laser beam that is directed onto a first mirror that scans in one direction, an optical relay system, and a second mirror that scans perpendicularly from the first mirror, providing a two-dimensional scan of the laser beam. This application discloses an optical projection system that employs a two-mirror scanning configuration in which collimated light is reflected from the first mirror that scans in one direction and recombined onto a second mirror that scans perpendicularly, providing a two-dimensional scan. To achieve this functionality, the geometry and arrangement of the optics and elements used by the disclosed optical scanning system are compact, achromatic, and maintain a high degree of collimation.

Description

[Technical Field]

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 62 / 964,508, filed January 22, 2020, which is incorporated herein by reference in its entirety. [Background technology]

[0002] Digital micromirror devices have been used in image projection systems. For example, U.S. Patent No. 6,856,446 describes a micromirror array in which many individually hinged, controllable micromirror elements can be used to control the direction of reflected light to project an array of digital pixels. These devices often require the use of a color wheel or three individual pixel arrays for different colors to project a full-color image, and generally use large and high-intensity light sources, limiting the compactness of the projection system. Summary of the Invention [Means for solving the problem]

[0003] The present disclosure relates to an optical projection system and its use for image projection. The disclosed optical scanning system includes an optical relay system with multiple mirrors that provides a folded configuration, which can enable optical communication between two scanning mirror devices, such as scanning microelectromechanical systems mirrors, in a compact and space-saving configuration.

[0004] In a first aspect, an optical projection system is described herein. In some embodiments, the optical projection system of this aspect includes a collimated light source; a first microelectromechanical systems mirror positioned to receive the collimated light from the source, the first microelectromechanical systems mirror having a first scan axis and configured or positioned to reflect the collimated light from the source along a first range of propagation directions about the first scan axis; and a first microelectromechanical systems mirror configured or positioned to reflect the collimated light from the source along a first range of propagation directions about the first scan axis. and a second Micro-Electro-Mechanical Systems mirror positioned to receive the collimated light from the optical relay system, the second Micro-Electro-Mechanical Systems mirror having a second scan axis oriented perpendicular to the first scan axis and configured or positioned to reflect the collimated light from the optical relay system in a second range of propagation directions about the second scan axis. Optionally, the optical projection system of this aspect may further include an eyepiece positioned to receive the light reflected from the second Micro-Electro-Mechanical Systems mirror.

[0005] Microelectromechanical systems mirrors, which may also be referred to herein as scanning mirrors, may comprise microfabricated devices with reflective surfaces configured, adapted, or structured to change position over time. The scanning mirrors may oscillate about a scan axis, for example, by adjusting the tilt angle of the reflective surfaces. In some embodiments, the first microelectromechanical systems mirror has a first scan frequency of about 1 kHz to about 10 MHz. In some embodiments, the second microelectromechanical systems mirror has a second scan frequency of about 15 Hz to about 500 Hz. Exemplary microelectromechanical systems mirrors are described, for example, in U.S. Provisional Application No. 62 / 962,168, filed January 16, 2020, and U.S. Provisional Application No. 63 / 058,384, filed July 29, 2020, both of which are incorporated herein by reference in their entireties.

[0006] A variety of different configurations can be used for the optical relays used in the optical projection systems described herein. In some embodiments, the optical relay system comprises one or more flat mirrors, one or more convex mirrors, or one or more concave mirrors. More specifically, the optical relay system may comprise one or more cylindrical mirrors, one or more spherical mirrors, one or more toroidal mirrors, or one or more aspherical mirrors. The mirrors of the optical relay system may be arranged in a configuration to allow three or more reflections, which may in some cases be referred to as a single-pass relay or single-pass configuration. The mirrors of the optical relay system may be arranged in a configuration to allow five or more reflections, which may in some cases be referred to as a double-pass relay or double-pass configuration.

[0007] In some embodiments, the optical relay system comprises a single-pass or double-pass relay having one or more cylindrical mirrors. In some embodiments, the optical relay system comprises a single-pass or double-pass relay having a split cylindrical element comprising a first component, a second component, and a third component. Optionally, the third component has a different radius of curvature or focal length than the first component and the second component. Optionally, the first component and the second component have different radii of curvature or focal lengths. In some embodiments, the optical relay system may exhibit a focusing configuration. In some embodiments, the optical relay system is configured or positioned to receive collimated light, generate uncollimated light, and output collimated light.

[0008] In some embodiments, the optical projection system includes a single-pass or two-pass relay having a cylindrical mirror and a toroidal or aspherical mirror. In some cases, the mirrors of the optical relay may have one axis with cylindrical symmetry and another axis with a toroidal or aspherical configuration.

[0009] In some embodiments, the optical relay system includes a single-pass or double-pass relay with a tilted configuration. Such a configuration can mean that collimated light entering the optical relay can be aligned at an angle relative to the arrangement of mirrors in the optical relay. For example, collimated light can be directed from the first microelectromechanical systems mirror toward the center of the optical relay along an axis perpendicular to the range of propagation angles.

[0010] In some embodiments, the optical relay system comprises a single-pass or double-pass relay that exhibits angular magnification. In other embodiments, the optical relay system comprises a single-pass or double-pass relay without any angular magnification.

[0011] Optionally, the first microelectromechanical systems mirror includes an actuator controllable to induce movement in the first microelectromechanical systems mirror about a first scan axis, and optionally, the second microelectromechanical systems mirror includes an actuator controllable to induce movement in the second microelectromechanical systems mirror about a second scan axis.

[0012] In another aspect, a method for projecting an image is described. In some embodiments, the method of this aspect includes generating collimated light and directing the collimated light to a first scan mirror, the first scan mirror having a first scan axis and configured or arranged to reflect the collimated light along a first range of propagation directions about the first scan axis; directing the collimated light from the first scan mirror to an optical relay system, the optical relay system configured to receive the collimated light and reflect the collimated light along the first range of propagation directions; and directing the collimated light from the optical relay system to a second scan mirror, the second scan mirror having a second scan axis and configured or arranged to reflect the collimated light along a second range of propagation directions about the second scan axis. In some embodiments, the method of this aspect may further include directing the collimated light from the second scan mirror to an eyepiece. The methods of this aspect may employ any of the optical projection systems described herein, including those described above.

[0013] In another aspect, a head-mounted display system is described herein. In some examples, the head-mounted display system of this aspect comprises any of the optical projection systems described herein and an eyepiece comprising one or more optical components configured or positioned to receive and redirect light reflected by the second microelectromechanical systems mirror to one or two eyes of a user. Optionally, the light produced by the collimated light source comprises light representing virtual content to be presented to the user.

[0014] In some examples, an optical projection system or a head-mounted display system may include a control circuit operably coupled to a collimated light source, a first microelectromechanical systems mirror, and a second microelectromechanical systems mirror. Optionally, the control circuit is configured to display one or more images by synchronously controlling the collimated light source to emit collimated light corresponding to pixels of one or more images, and controlling actuators of the first and second microelectromechanical systems mirrors to induce movement in the first and second microelectromechanical systems mirrors about first and second scan axes, respectively.

[0015] Specific exemplary methods are described below in the detailed description and figures. Furthermore, additional features, advantages, and embodiments are described below in the detailed description, figures, and claims. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 provides a schematic diagram of an exemplary optical projection system.

[0017] [Figure 2] FIG. 2 provides a schematic cross-sectional view of an exemplary optical projection system.

[0018] [Figure 3]FIG. 3 provides a perspective exploded view of an exemplary optical projection system.

[0019] [Figure 4] FIG. 4A provides a perspective exploded view of an exemplary optical projection system, and FIG. 4B provides a perspective assembled view of an exemplary optical projection system.

[0020] [Figure 5] FIG. 5 provides a schematic diagram of a single-pass optical relay with concentric cylindrical mirrors.

[0021] [Figure 6] FIG. 6 provides a schematic diagram of a two-pass optical relay with concentric cylindrical mirrors.

[0022] [Figure 7] FIG. 7 provides a three-dimensional rendering of a single-pass optical relay comprising concentric cylindrical mirrors with an oblique angle of incidence for the input light.

[0023] [Figure 8] FIG. 8 provides a three-dimensional rendering of a two-pass optical relay comprising concentric cylindrical mirrors with an oblique angle of incidence for the input light.

[0024] [Figure 9] 9A and 9B provide a schematic diagram of a two-pass optical relay comprising concentric cylindrical mirrors with one mirror having a splitting configuration.

[0025] [Figure 10] Figure 10A provides a schematic diagram of a single-pass optical relay comprising three concentric cylindrical mirrors, and Figure 10B provides a three-dimensional rendering of the optical relay shown in Figure 10A.

[0026] [Figure 11] 11A and 11B provide a schematic diagram of a single-pass optical relay comprising a toroidal mirror with aspherical components.

[0027] [Figure 12] 12A and 12B provide a schematic diagram of a two-pass optical relay comprising a toroidal mirror with aspherical components.

[0028] [Figure 13] FIG. 13 provides a three-dimensional rendering of a two-pass optical relay comprising a toroidal mirror with aspherical components.

[0029] [Figure 14] FIG. 14 provides an overview of an exemplary image projection method, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0030] Detailed Description This application discloses an optical projection system employing a two-mirror scanning configuration in which collimated light is reflected from a first mirror that scans in one direction and recombined onto a second mirror that scans in the perpendicular direction, providing a two-dimensional scan. To achieve this functionality, the geometry and arrangement of the optics and elements used by the disclosed optical scanning system are compact, achromatic, and maintain a high degree of collimation.

[0031] The disclosed optical projection system is useful for projecting two-dimensional and multi-dimensional images and videos. Methods for projecting light and images using the optical projection system are also disclosed. The disclosed optical projection system can incorporate a collimated light source that emits light onto a first scanning mirror and an optical relay system for receiving the collimated light reflected from the first scanning mirror and directing the relayed collimated light toward a second scanning mirror, which can further reflect the output collimated light to an output plane (which can be, for example, an eyepiece of a head-mounted display system).

[0032] The disclosed optical projection system exhibits features that provide advantages for two-dimensional optical scanning and image projection. For example, the optical projection system can be compact or limited in size by utilizing a folded optical relay or the like, in which incident collimated light is reflected multiple times and, optionally, focused and defocused to generate output collimated light. Furthermore, the optical relay system can accommodate incident light propagating along different directions, such as along a range of directions supported by tilt of a first scanning mirror about a first axis, allowing the output light to remain collimated and be received by a second scanning mirror despite variations in propagation direction due to changes in the orientation of the first scanning mirror about the first axis.

[0033] 1 provides a schematic diagram of an exemplary optical projection system 100. Optical projection system 100 comprises a first scanning micro-mirror device 105 including a first reflector 110, an optical relay 115, and a second scanning micro-mirror device 120 including a second reflector 125. Image projection system 100 also includes a light source 130 arranged in optical communication with first reflector 110 to direct light 135 from light source 130 to first reflector 110, where it is reflected toward optical relay 120, which directs the light to second reflector 125, from where it is output for projection. Movement of first scanning micro-mirror device 105 and second scanning micro-mirror device 120 can be driven in a manner to direct output reflected light 135 to a projection plane 140, which may be, or is in optical communication with, an eyepiece of a head-mounted display device. By using the oscillatory motion of first scanning micromirror device 105 and second scanning micromirror device 120 to control the color, intensity, and timing of light 135 output by light source 130, output light 145 can generate an image at projection plane 140. Using repeated scanning, a sequence of images and / or videos may be projected.

[0034] In some embodiments, the first scanning micromirror device 105 may oscillate about a first axis such that the output light 145 forms a series of horizontal (left-to-right and right-to-left) passes, while the second scanning micromirror device 120 may oscillate about a second axis such that the output reflected light 145 may also oscillate vertically across the projection plane 140, from top to bottom and / or bottom to top. The oscillation frequency along the horizontal direction can be very fast, for example, in the range of 1 kHz to 10 MHz. Some projection systems may use oscillation patterns along the vertical direction that are sawtooth or triangular in shape, which may be useful for creating regularly spaced horizontal passes in one vertical direction (e.g., from top to bottom), although sinusoidal oscillation patterns may also be used. The oscillation frequency along the vertical direction can be slower, for example, in the range of 15 Hz to 2 kHz. If only top-to-bottom repeated projection is desired, a blanking period can be used in which no light is generated by the light source 130 while the second scanning micromirror device 120 oscillates in the upward direction. However, in some cases, both top-to-bottom and bottom-to-top projection can be used. Blanking periods can also be used on the extremes of the horizontal dimension to avoid projection at the side edges of the projection plane 140.

[0035] It should be understood that the references to horizontal (or left-to-right and right-to-left) and vertical (or bottom-to-top and top-to-bottom) directions are merely examples of markings with reference to the orientation of the projection plane 140 shown in FIG. 1 . Other configurations in which the horizontal and vertical markings are switched or other markings are used are also contemplated within the scope of this disclosure. In some cases, the oscillation frequencies of the first scanning micromirror device 105 and the second scanning micromirror device may be opposite; for example, the oscillation frequency of the first scanning micromirror device 105 may be slower, such as in a range of 15 Hz to 2 kHz, while the oscillation frequency of the second scanning micromirror device 120 may be faster, such as in a range of 1 kHz to 10 MHz.

[0036] Optical projection system 100 may be a component of an optical projector, for example, which can be used to project still or video images at a projection plane. In some cases, optical projection system 100 may be a component of a head-mounted display device and / or may be used to couple projected light into an eyepiece, such as an eyepiece of a head-mounted display device. Projection plane 140 may correspond to the eyepiece or a user's retina in some examples. Optical projection system 100 optionally includes other optical elements, such as mirrors, lenses, collimators, filters, gratings, or the like, not shown in FIG. 1 , which may be positioned in the optical path between light source 130 and projection plane 140, for example. Light source 130 may be a monochromatic or polychromatic light source and may include, for example, a light-emitting diode or laser source that can output a switchable or modulatable signal at a high rate, for example, up to 100 MHz. Optionally, light source 130 may comprise or correspond to multiple individually modulatable light sources, such as laser diodes that output different colors (e.g., red, green, blue).

[0037] FIG. 2 provides a schematic diagram of further details of an exemplary optical projection system 200. The optical projection system 200 may comprise various individual components that may be fabricated and assembled independently. As shown, the optical projection system 200 comprises a first MEMS mirror 205, an optical relay system comprising a first mirror 210, a second mirror 215, and a third mirror 220, a second MEMS mirror 225, and a collimated light source 230. A chassis 235 may be used to position the components in the appropriate positions relative to each other. The optical relay system is positioned to receive collimated light output from the source 230 and reflected from the first MEMS mirror 210 and relay the collimated light to the second MEMS mirror 225.

[0038] In the illustrated configuration, the first mirror 210 comprises a flat mirror, the second mirror 215 comprises a concave cylindrical mirror, and the third mirror 220 comprises a convex cylindrical mirror. Optionally, the second mirror 215 comprises a convex cylindrical mirror and the third mirror 220 comprises a concave cylindrical mirror. Other mirror configurations may also be employed, such as the second mirror having concave, flat, and / or convex regions, or the third mirror having concave, flat, and / or convex regions. In some configurations, flat, cylindrical, spherical, toroidal, and / or aspherical mirrors may be used in the optical relay system.

[0039] The first microelectromechanical systems mirror 205 can have a first scan axis that allows collimated light to be reflected from the source 230 along a first range of propagation directions about the first scan axis. The use of concave and convex cylindrical mirrors for the second mirror 215 and the third mirror 220 can allow collimated light reflected by the first mirror 210, for example, by and between the second mirror 215 and the third mirror 220, to be reflected and focused in such a way that light exiting the third mirror 220 that is directed toward the second microelectromechanical systems mirror 225 is collimated. In some examples, the light reflected from the first microelectromechanical systems mirror 205 can undergo one or multiple reflections in an optical relay before reaching the second microelectromechanical systems mirror 225, such as 2, 3, 4, 5, 6, or more reflections. In some embodiments, light can be reflected between the second mirror 215 and the third mirror 215 multiple times before reaching the second Microelectromechanical Systems mirror 225. As shown, light is reflected between the second mirror 215 and the third mirror 215 multiple times, five times, before reaching the second Microelectromechanical Systems mirror 225.

[0040] The second microelectromechanical systems mirror 225 can have a second scan axis oriented perpendicular to the first scan axis that can direct output light toward the eyepiece 240. In one example, the first scan axis can be aligned in the plane of the illustration shown in Figure 2 so that the reflection of light from the first microelectromechanical systems mirror 205 can vary in a direction out of the plane of the illustration shown in Figure 2, while the second scan axis can be aligned perpendicular to the plane of the illustration shown in Figure 2 so that the reflection of light from the second microelectromechanical systems mirror 225 can vary in a direction in the plane of the illustration shown in Figure 2.

[0041] Figure 3 provides an exploded perspective schematic view of another exemplary optical projection system 300, which may be the same as or different from optical projection system 200 depicted in Figure 2. Optical projection system 300 includes a first Microelectromechanical Systems mirror 305, an optical relay system including a first mirror 310, a second mirror 315, and a third mirror 320, a second Microelectromechanical Systems mirror 325, and a chassis 335. A collimated light source may be included in optical projection system 300, but is not shown in Figure 3 so as not to obscure other details.

[0042] In the illustrated configuration, the first mirror 310 comprises a planar mirror, the second mirror 315 comprises a concave cylindrical mirror, and the third mirror 320 comprises a convex cylindrical mirror. The first mirror 310, the second mirror 315, the third mirror 320, and the second microelectromechanical systems mirror 325 may each be coupled to a chassis 335 using a removable or fixed coupling arrangement, or the like. The chassis 335 may optionally be coupled to a base 340. The first microelectromechanical systems mirror 305 may optionally be coupled to the base 340 or the chassis 335.

[0043] Figure 4A provides an exploded perspective schematic view of another example optical projection system 400, and Figure 4B provides an assembled perspective schematic view of optical projection system 400. Optical projection system 400 may be the same as or different from optical projection system 200 depicted in Figure 2 and / or optical projection system 300 depicted in Figure 3. Optical projection system 400 includes a first Microelectromechanical Systems mirror 405, a second Microelectromechanical Systems mirror 425, a collimated light source 430, and a chassis 435. An optical relay may be included in optical projection system 400 but is not shown in Figure 4A or 4B to avoid obscuring other details.

[0044] In the configuration shown, first microelectromechanical systems mirror 405, second microelectromechanical systems mirror 425, and collimated light source 430 are all coupled to chassis 435 in a configuration that provides suitable optical alignment between the components. The optical relay components may be positioned inside chassis 435 in locations that are not visible from the perspective views shown in Figures 4A or 4B.

[0045] As mentioned above, various mirror configurations may be used in the optical relay system. For example, the optical relay system may include one or more flat, convex, or concave mirrors. The mirrors of the optical relay system may be cylindrical, spherical, toroidal, or aspherical mirrors. The use of such mirrors in the optical relay system may allow the optical relay system to diverge in the input angle of incident light as it is reflected from a first scanning mirror (e.g., a microelectromechanical system mirror) in a compact configuration and relay the incident light to a second scanning mirror via one or more reflections and / or focusing without introducing undesirable optical effects. The incident light to the optical relay may exhibit various input angles depending on the tilt angle of the first scanning mirror; therefore, the optical relay system must exhibit an optical configuration large enough to accommodate the divergence of the light as it passes through the optical relay, while still directing the light to the second scanning mirror.

[0046] A variety of different optical relay system configurations can be useful to achieve such a configuration. For example, in some cases, the optical relay system comprises an afocal, two-pass relay with one or more cylindrical mirrors. In some cases, one or more of the cylindrical mirrors may be split, such as with one or more components having different radii of curvature from each other. The mirrors in the optical relay system may be concentric or non-concentric.

[0047] Optical relays useful with the optical projection systems described herein include those that generate images of objects at shifted positions in space. Offner relay-type configurations may be used, as described in U.S. Pat. No. 3,748,015, incorporated herein by reference. FIG. 5 depicts an exemplary configuration of a two-mirror optical relay 500, including a first mirror 505 and a second mirror 510, which are concentric in the configuration shown, meaning their focuses are aligned, and provides a cross-sectional view. Collimated light 515 is received as input to the optical relay 500. The first mirror 505 reflects and focuses the light 515 toward the second mirror 510, which defocuses the light 515 toward the first mirror 505, which then outputs collimated light 515 once again. In this configuration, three reflections—two on the first mirror 505 and one on the second mirror 510—shift and redirect the collimated light in space. This case may be referred to, for example, as a “single-pass” configuration and may employ a cylindrical mirror. In the case of a cylindrical mirror, the input light 515 may have a distribution of input angles in directions outside the plane of the illustration, based on the scan axis of the scanning micromirror being in the plane of the illustration. In some cases, additional optical components may be included in the optical relay 500 other than those shown in FIG. 5 , such as additional mirrors, lenses, filters, or the like.

[0048] 6 depicts an example configuration of a two-mirror optical relay 600, including a first mirror 605 and a second mirror 610 that are concentric in the configuration shown, meaning their focuses are aligned, providing a slightly perspective view. Collimated light 615 is received as input to the optical relay 600. In this configuration, five reflections—three at the first mirror 605 and two at the second mirror 610—shift, focus, defocus, and redirect the collimated light in space. This case may be referred to as a “two-pass” configuration, and again may employ, for example, a cylindrical mirror.

[0049] In the configurations shown in Figures 5-6, the collimated light is parallel to the axis passing through the focal point of the mirror. In other cases, tilted arrangements may be used where the collimated light is arranged in a configuration that is not parallel to the axis passing through the focal point of the mirror.

[0050] FIG. 7 depicts an example three-dimensional rendering of a two-mirror optical relay 700, similar to the optical relay 500 shown in FIG. 5 , using a cylindrical mirror to illustrate the different paths that input light 715 can take based on the spread of input angles for a single-pass configuration. Optical relay 700 includes a first mirror 705 and a second mirror 710 that are concentric in the configuration shown, meaning their foci are aligned. FIG. 7 illustrates how light 715 can become a line focus at the second mirror 715. In the case shown in FIG. 7 , the input light 715 has a tilted configuration in which it does not propagate directly horizontally toward the first mirror 705, but propagates at an angle of approximately 15 degrees from horizontal, which may be due to a tilt in the scan axis of the scanning mirror providing the input light 715. Such a configuration may advantageously ensure overlap of the exit pupils.

[0051] FIG. 8 depicts an example three-dimensional rendering of a two-mirror optical relay 800, similar to the optical relay 800 shown in FIG. 6 , using a cylindrical mirror to illustrate the different paths that input light 815 can take based on the input angle spread for a two-pass configuration. Optical relay 800 includes a first mirror 805 and a second mirror 810, which are concentric in the configuration shown. In the case shown in FIG. 8 , input light 815 has a tilted configuration in which it does not propagate directly horizontally toward first mirror 805, but may propagate at an angle of approximately 15 degrees from horizontal, which may be due to a tilt in the scan axis of the scanning mirror providing input light 815. Such a configuration may advantageously ensure overlap of the exit pupils. Advantageously, cylindrical mirror systems such as those shown in FIGS. 5-8 are useful for reimaging a beam in the plane of the scan angle spread while leaving the beam vertically unaffected, as shown by the apparent line focus in FIGS. 7 and 8 .

[0052] In the two-pass configuration shown in FIG. 6 , light 615 is focused at the center of the first mirror 605. This can provide an opportunity to control the angle of the light by splitting the first mirror 605 into multiple components and adjusting the angle at which the light is focused. As an example, FIGS. 9A and 9B depict an optical relay 900 with a configuration in which the first mirror is split into multiple components 905, 906, and 907. FIG. 9A shows a slightly perspective view of the optical relay 900 with the scanning axis of the first scanning mirror device oriented in the plane of the illustration, and FIG. 9B shows a top view at approximately 90 degrees to the view shown in FIG. 9A . Collimated light 915 first interacts with the first mirror component 905, where it is reflected to the second mirror 910, which in turn reflects the light 915 to the first mirror component 906. From there, light 915 is reflected to second mirror 910, which in turn reflects light 915 to first mirror component 907. The size of first mirror components 905, 906, and 907 needs to be sufficient to contain all input angles for light 915 to provide overlapping outputs. An advantage of this configuration is that by inserting first mirror component 906 between components 905 and 906, the angles of different input beams of light 915 can be easily changed so that they overlap, while second mirror 910 and first mirror components 905 and 906 can be used to maintain good collimation. Advantageously, optical relay 900 can limit or minimize chromatic aberrations. Because first mirror component 906 interacts with light 915 at a focal point, first mirror component 906 can be a flat, aspherical, or cylindrical mirror without loss of performance.

[0053] In the configurations shown in FIGS. 5-9B, the collimated light may exhibit little or no angular magnification (e.g., an angular magnification of about 1.0). In some cases, the first mirror may be completely split into two separate mirrors with asymmetric positions, which may allow for angular magnification, for example. FIG. 10A shows an optical relay 1000 in which the first mirror is split into separate components. Collimated light 1015 initially interacts with the first mirror 1005, approaching it at an oblique angle. The first mirror 1005 directs the light to the second mirror 1010, which further directs the light to the third mirror 1006. FIG. 10B shows a three-dimensional rendering of the optical relay 1010. By using different radii of curvature for the first mirror 1005, second mirror 1010, and third mirror 1006, angular magnification can be greater than or less than 1.

[0054] While cylindrical mirrors can be used as described above, mirrors with toroidal configurations can be used, such as toroidal mirrors with aspherical components. Such mirrors can have one axis with cylindrical symmetry and one axis that is toroidal / aspherical in nature. Such mirrors may perform additional focusing along the toroidal axis, which may be present in the case of cylindrical mirrors. FIGS. 11A and 11B show an example optical relay 1100, with FIG. 11A showing a view along the toroidal axis and FIG. 11B showing a view at approximately 90 degrees relative to that shown in FIG. 11A (along the axis of cylindrical symmetry), showing a single-pass configuration. A first mirror 1105 focuses light 1115 onto a second mirror 1110 in the configuration shown, which can allow the second mirror 1110 not only to have a toroidal / cylindrical configuration as described, but also for such mirrors to have reverse curvatures.

[0055] 12A and 12B show an example optical relay 1200 employing a toroidal mirror with aspherical components, similar to the optical relay 1100 shown in FIGS. 11A and 11B, with a two-pass configuration. FIG. 12A shows a slightly perspective view along the toroidal axis, and FIG. 12B shows a view at approximately 90 degrees to that shown in FIG. 12A, along the axis of cylindrical symmetry. The optical relay 1200 includes a first mirror 1205 and a second mirror 1210, which may be split into two separate components 1210 and 1211, if desired. Collimated light 1215 reflects from the first mirror 1205 to the second mirror component 1210, where it is reflected for output, back to the first mirror 1205, to the second mirror component 1211, and back to the first mirror 1205.

[0056] 13 depicts an example three-dimensional rendering of an optical relay 1300 similar to optical relay 1200, employing a toroidal mirror with a two-pass configuration, aspherical components, and a second mirror 1310. Optical relay 1300 includes a first mirror 1305 and a second mirror 1310, showing paths along which collimated light 1315 can take various input angles. In the configuration shown in FIG. 13, the second mirror 1310 has a toroidal axis aligned opposite to the toroidal axis of the first mirror 1305, while the cylindrical axes of the first mirror 1305 and the second mirror 1310 are concentric.

[0057] 14 provides an overview of an exemplary method 1400 for projecting an image. The image may comprise a raster-scan image, for example, as described above with respect to FIG. 1. The image may, in some cases, comprise a frame within a video image, where multiple images may be displayed in sequence by repeating method 1400 one or more times in sequence. To generate the image, a light source may be modulated in time using modulation of tilt angles on two scanning mirrors to display a sequence of pixels that create the raster-scan image.

[0058] In block 1405, collimated light is generated. The collimated light may comprise light from a laser or a light emitting diode, for example. In some cases, multiple light sources may be used to generate the collimated light, such as light sources that emit different colors. For example, in some embodiments, a green light source, a blue light source, and a red light source may be used and combined to enable the projection of any specific color by mixing the modulation of the intensity of each color.

[0059] In block 1410, the collimated light is directed to a first scan mirror. In some cases, the collimated light is emitted directly from the light source onto the first scan mirror. However, in other cases, one or more intervening optical elements, such as lenses, mirrors, waveguides, or the like, may be used. In some cases, multiple light sources may be combined using a combining element. The first scan axis may allow the first scan mirror to be tilted along a first range of angles to allow the collimated light to reflect along a first range of propagation directions about the first scan axis.

[0060] In block 1415, the collimated light from the first scan mirror is directed from the first scan mirror to an optical relay system. The optical relay system may be configured, sized, and / or arranged to receive the collimated light from the first scan mirror along a first range of propagation directions. The optical relay system may include a plurality of flat, concave, and / or convex mirrors arranged relative to each other to relay the collimated light from the first scan mirror to the second scan mirror.

[0061] In block 1420, the collimated light from the optical relay system is directed to a second scan mirror. The second scan mirror may have a second scan axis that is aligned perpendicular to the first scan axis. The second scan mirror may be tilted along a second range of angles about the first scan axis to allow the collimated light to be reflected along a second range of propagation directions. By using the perpendicularly aligned scan axes, a raster image may be projected by appropriately scanning the first and second scan mirrors.

[0062] In block 1425, the collimated light from the second scanning mirror is directed, for example, to an eyepiece of a head mounted display device or an input aperture or structure for an eyepiece of a head mounted display device for projection.

[0063] Aspects of method 1400, such as the modulation of the collimated light and the control over the scanning of the first and second scanning mirrors, may be controlled by a computing device. In some cases, the computing device may execute processor-executable instructions, as described in further detail below, to control aspects or components of the optical projection system to project an image. Computing Device Components

[0064] A computing device may be incorporated as part of the systems described above, such as image projection systems, head-mounted display systems, and two-dimensional scanning systems. The computing device may be useful for implementing aspects of the methods and systems described above. For example, the computing device may be useful for controlling the modulation of a light beam. The computing device may also be useful for controlling the orientation and / or oscillation of a scanning mirror. The computing device may also be useful for controlling the application of voltage or current. An exemplary computing device comprises hardware elements that may be electrically coupled (or otherwise communicate) via a bus. The hardware elements may include one or more processors, including but not limited to one or more general purpose processors and / or one or more special purpose processors (such as digital signal processing chips, graphics acceleration processors, video decoders, and / or the like); one or more input devices, which may include but are not limited to a mouse, touch screen, keyboard, remote control, voice input, and / or the like; and one or more output devices, which may include but are not limited to a display device, printer, speaker, servo, linear actuator, rotary actuator, etc.

[0065] A computing device may further include (and / or be in communication with) one or more non-transitory storage devices, which may comprise, but are not limited to, local and / or network-accessible storage devices, and / or may include, but are not limited to, disk drives, drive arrays, optical storage devices, solid-state storage devices such as solid-state drives ("SSDs"), random access memory ("RAM"), and / or read-only memory ("ROM"), etc., which may be programmable, flash-updateable, and / or the like. Such storage devices may be configured to implement any suitable data storage, including, but not limited to, various file systems, database structures, and / or the like.

[0066] The computing device may also include a communications subsystem, which may include, but is not limited to, a modem, a network card (wireless or wired), an infrared communications device, a wireless communications device, a wireless communications device, and / or a chipset (Bluetooth® device, Bluetooth® Low Energy or BLE device, 802.11 device, 802.15.4 device, WiFi device, WiMax device, cellular communications device, etc.), a G.hn device, and / or the like. The communications subsystem may enable data to be exchanged with networks, other computer systems, and / or any other devices described herein. In many embodiments, the computing device will further comprise working memory, which may include RAM or ROM devices as described above.

[0067] A computing device may also include software elements shown as currently residing in working memory, including an operating system, device drivers, executable libraries, and / or other code, such as one or more application programs, that may be equipped with computer programs provided by various embodiments and / or that may be designed to implement methods and / or configure systems provided by other embodiments as described herein. By way of example only, one or more procedures described for the methods discussed above may be implemented as code and / or instructions executable by a computer (and / or a processor within a computer), and in certain aspects, such code and / or instructions may then be used to configure and / or adapt a computer (or other device) to perform one or more operations in accordance with the described methods or for operation of the described devices and systems.

[0068] A set of these instructions and / or code may be stored on a non-transitory computer-readable storage medium, such as the non-transitory storage devices described above. In some cases, the storage medium may be incorporated into a computer system, such as the computing device described above. In other embodiments, the storage medium may be separate from the computer system (e.g., removable media such as a compact disc, or a cloud or network-based storage system) and / or provided within an installation package, such that the storage medium may be used to program, configure, and / or adapt a computer with the instructions / code stored thereon. These instructions may take the form of executable code that is executable by a computing device or a component thereof, and / or may take the form of source and / or installable code, which then takes the form of executable code, upon compilation and / or installation on the computing device (e.g., using any of various commonly available compilers, installation programs, compression / decompression utilities, etc.).

[0069] It will be apparent to those skilled in the art that substantial variations may be made according to particular requirements. For example, customized hardware may also be used, and / or particular elements may be implemented in hardware, software (including portable software such as applets), or both. Furthermore, connection to other computing devices, such as network input / output devices, may also be employed.

[0070] As described above, in one aspect, some embodiments may employ a computing device to perform methods according to various embodiments. According to one set of embodiments, some or all of the procedures of such methods are performed by the computing device in response to a processor executing one or more sequences of one or more instructions contained in working memory (which may be embedded in an operating system and / or other code, such as an application program). Such instructions may be read into the working memory from another computer-readable medium, such as one or more non-transitory storage devices. By way of example only, execution of a sequence of instructions contained in working memory may cause the processor to perform one or more procedures of the methods described herein.

[0071] The terms “machine-readable medium,” “computer-readable storage medium,” and “computer-readable medium,” as used herein, refer to any medium that participates in providing data that causes a machine to operate in a tangible manner. These media may be non-transitory. In an embodiment implemented using a computing device, various computer-readable media may participate in providing instructions / code to a processor for execution and / or may be used to store and / or carry such instructions / code. In many implementations, computer-readable media are physical and / or tangible storage media. Such media may take the form of non-volatile media or volatile media. Non-volatile media include, for example, optical and / or magnetic disks, such as non-transitory storage devices. Volatile media include dynamic memory, such as, but not limited to, working memory.

[0072] Common forms of physical and / or tangible computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tape or any other magnetic medium, CD-ROMs, any other optical medium, any other physical medium with a pattern of marks, RAM, PROM, EPROM, FLASH-EPROM, any other memory chip or cartridge, or any other medium from which a computer can read instructions and / or code. Network-based and cloud-based storage systems can also be useful forms of computer-readable media.

[0073] Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution. By way of example only, the instructions may initially be carried on a magnetic and / or optical disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions as signals over a transmission medium to be received and / or executed by a computing device.

[0074] The communications subsystem (and / or its components) generally receives signals, and a bus may then carry the signals (and / or the data, instructions, etc. carried by the signals) to working memory, from which the processor retrieves and executes the instructions. The instructions received by the working memory may optionally be stored on a non-transitory storage device either before or after execution by the processor.

[0075] Furthermore, it should be understood that components of a computing device may be distributed. For example, some processing may be performed in one location using a first processor, while other processing may be performed by another processor remote from the first processor. Optionally, the systems described herein may include multiple independent processors that may exchange instructions, issue commands, or provide data to one another. Other components of a computing device may be distributed as well. Thus, a computing device may be interpreted as a distributed computing system that performs processing at multiple locations. In some instances, a computing device may be interpreted as a single computing device, such as a distinct laptop, desktop computer, or the like, depending on the context.

[0076] While preferred embodiments of the present invention have been shown and described, it will be apparent that the present invention is not limited to these embodiments. Numerous modifications, changes, variations, substitutions, and equivalents will become apparent to those skilled in the art without departing from the spirit and scope of the present invention, as set forth in the claims.

Claims

1. 1. An optical projection system comprising: a collimated light source; a first microelectromechanical systems mirror positioned to receive collimated light from the light source, the first microelectromechanical systems mirror having a first scan axis, the first microelectromechanical systems mirror configured to reflect the collimated light from the light source along a first range of propagation directions about the first scan axis; an optical relay system positioned to receive collimated light from the first microelectromechanical systems mirror and direct reflected collimated light along the first range of propagation directions about the first scan axis, the optical relay system comprising a two-pass relay having concentric first and second mirrors, the first mirror comprising a split cylindrical element comprising a first component, a second component, and a third component, the third component having a different radius of curvature than the first and second components, the first mirror comprising a first reflective surface that directs and focuses the collimated light from the first microelectromechanical systems mirror onto a second reflective surface of the second mirror, the second reflective surface directing the focused light onto the first reflective surface that reflects and collimates the directed light; a second microelectromechanical systems mirror positioned to receive collimated light from the optical relay system, the second microelectromechanical systems mirror having a second scan axis oriented perpendicular to the first scan axis, the second microelectromechanical systems mirror configured to reflect the collimated light from the optical relay system about the second scan axis in a second range of propagation directions; An optical projection system comprising:

2. The optical projection system of claim 1 , further comprising an eyepiece positioned to receive light reflected from the second micro-electro-mechanical systems mirror.

3. The optical projection system of claim 1 , wherein the optical relay system comprises one or more flat mirrors, one or more convex mirrors, or one or more concave mirrors.

4. 10. The optical projection system of claim 1, wherein the optical relay system comprises one or more cylindrical mirrors, one or more spherical mirrors, one or more toroidal mirrors, or one or more aspherical mirrors.

5. The optical projection system of claim 1 , wherein the optical relay system comprises a two-pass relay having one or more cylindrical mirrors.

6. The optical projection system of claim 1 , wherein the optical relay system comprises a two-pass relay having a cylindrical mirror and a toroidal or aspherical mirror.

7. The optical projection system of claim 1 , wherein the optical relay system comprises a two-pass relay with a tilt configuration.

8. The optical projection system of claim 1 , wherein the optical relay system comprises a two-pass relay that exhibits angular magnification.

9. 2. The optical projection system of claim 1, wherein the collimated light reflected from the first microelectromechanical system mirror undergoes at least three reflections in the optical relay system before reaching the second microelectromechanical system mirror.

10. 10. The optical projection system of claim 1, wherein the collimated light reflected from the first microelectromechanical system mirror undergoes at least five reflections in the optical relay system before reaching the second microelectromechanical system mirror.

11. 1. A method for projecting an image, the method comprising: generating collimated light; directing the collimated light to a first scan mirror, the first scan mirror having a first scan axis and configured to reflect the collimated light along a first range of propagation directions about the first scan axis; directing collimated light from the first scanning mirror to an optical relay system configured to receive the collimated light and reflect the collimated light along the first range of propagation directions, the optical relay system including a first component, a second component, a third component, and a wherein the third component has a different radius of curvature than the first and second components; directing collimated light from the optical relay system to a second scan mirror, the second scan mirror having a second scan axis and configured to reflect the collimated light along a second range of propagation directions about the second scan axis; A method comprising:

12. The method of claim 11 , further comprising directing collimated light from the second scanning mirror to an eyepiece.

13. 12. The method of claim 11 , wherein the optical relay system includes one or more flat mirrors, one or more convex mirrors, one or more concave mirrors, one or more cylindrical mirrors, one or more spherical mirrors, one or more toroidal mirrors, or one or more aspherical mirrors.

14. The method of claim 11 , wherein the optical relay system includes a two-pass relay having one or more cylindrical mirrors.

15. The method of claim 11 , wherein the optical relay system includes a two-pass relay having a cylindrical mirror and a toroidal or aspherical mirror.

16. The method of claim 11 , wherein the optical relay system includes a two-pass relay with a tilt configuration.

17. The method of claim 11 , wherein the optical relay system includes a two-pass relay that exhibits angular magnification.

18. 1. A head mounted display system, comprising:

1. An optical projection system, comprising: a collimated light source; a first microelectromechanical systems mirror positioned to receive collimated light from the light source, the first microelectromechanical systems mirror having a first scan axis, the first microelectromechanical systems mirror configured to reflect the collimated light from the light source along a first range of propagation directions about the first scan axis; an optical relay system positioned to receive collimated light from the first micro-electro-mechanical systems mirror and direct reflected collimated light along the first range of propagation directions about the first scan axis; a second microelectromechanical systems mirror positioned to receive collimated light from the optical relay system, the second microelectromechanical systems mirror having a second scan axis oriented perpendicular to the first scan axis, the second microelectromechanical systems mirror configured to reflect the collimated light from the optical relay system about the second scan axis in a second range of propagation directions; an optical projection system comprising: an eyepiece comprising one or more optical components configured to receive and redirect light reflected by the second microelectromechanical systems mirror to one or two eyes of a user; A head-mounted display system comprising:

Images