Mems laser scanner with enlarged fov

Abstract

A MEMS laser scanner for use in a near-eye display including an increased field of view (FOV) is disclosed. One or more Bragg polarization gratings can be disposed on a scanning element such that one polarization of light is directed to one direction to form a first portion of the FOV, where a second polarization of light is directed to a second, different direction to form a second, different portion of the FOV. Using different polarizations of light, the MEMS laser scanner is able to expand the FOV without increasing the range of mirror oscillation of the scanner.

Description

Background Technology

[0001] Near-eye transparent or semi-transparent displays can be used to realize various types of computing, entertainment, and / or mobile devices. Near-eye displays can include transparent or semi-transparent displays through which users can view their surroundings and also see images (e.g., text, graphics, videos, etc.) generated on the display to make them appear as part of and / or overlaid on the surroundings.

[0002] Near-eye displays typically utilize spatial light modulation (SLM) systems, which include, for example, liquid crystal on silicon (LCoS) display engines and digital light processing (DLP) display engines for generating images. Both LCoS and DLP display systems simultaneously project all pixels of an image to modulate the amplitude, phase, intensity, or polarization of light on the image. Another emerging technology is microelectromechanical systems (MEMS) laser scanners. MEMS laser scanners typically include a laser source comprising, for example, red, green, and blue laser diodes that guide RGB laser light to MEMS mirrors capable of deflecting about two orthogonal axes.

[0003] Compared to LCoS and DLP displays, MEMS laser scanners typically generate two-dimensional raster scan images pixel-by-pixel for each image frame. The laser source is synchronized with a dual-axis MEMS mirror driver, enabling the dual-axis deflection of the MEMS mirror to guide the laser from the source to the corresponding pixel during raster scanning, as the RGB laser of each pixel is modulated to generate the desired light content for each pixel in the image.

[0004] The biaxial range of motion of the MEMS mirror in a near-eye display laser scanner establishes the size of the field of view (FOV) that the laser scanner can generate. However, various factors limit the range of pivoting motion of the MEMS mirror during image frame scanning. These factors include, for example, the mass of the MEMS mirror and the opposing forces exerted by air (or other gases) on the mirror surface as the MEMS mirror pivots. Currently, MEMS mirrors in near-eye display laser scanners typically achieve a range of motion of approximately 30 degrees and an FOV of approximately 35 degrees. Summary of the Invention

[0005] Some embodiments of this technology relate to a MEMS laser scanner for use in near-eye displays that include an increased field of view (FOV). In embodiments, one or more polarization gratings may be applied to the mirror of the MEMS laser scanner, and these polarization gratings may be configured according to a Bragg scheme.

[0006] According to a time-division multiplexing scheme, one or more polarization gratings diffract polarized light from a laser image source in two different directions based on the polarization of the light. The MEMS scanner pivots back and forth about its axis through its range of motion to complete a full stroke. During the first half of the MEMS scanner's pivoting journey, the laser image light can be polarized, for example, as LHC-polarized light. One or more polarization gratings can be tuned to allow the zeroth-order LHC-polarized light to pass directly through the grating without diffraction and be reflected off the MEMS mirror at an angle equal to the angle of incidence. As the MEMS scanner pivots through its first half of the journey, the undiffracted zeroth-order light trajectory forms the first part of the field of view (FOV).

[0007] During the latter half of the MEMS scanner's pivoting motion around its axis through its travel range, the laser can be polarized, for example, as RHC-polarized light. One or more polarization gratings can be tuned to diffract the first-order RHC-polarized light at an angle greater than the mirror angle to reflect it away from the MEMS scanner. As the MEMS scanner pivots through its range of motion, the diffracted first-order light trajectory forms the second part of the FOV. The first and second parts of the FOV can overlap and be combined to provide a magnified overall FOV.

[0008] This "Summary" is provided to introduce some concepts in a simplified form, which will be further described in the "Detailed Description" below. This "Summary" is not intended to identify key or essential features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter. Attached Figure Description

[0009] Figure 1 This is a perspective view of a beam scanning assembly according to an embodiment of the present technology.

[0010] Figure 2 It can be left through reflection. Figure 1 The light generated by the biaxial optics of the beam scanning assembly produces a Lissajous pattern view of the sample.

[0011] Figure 3a and 3b This is a view of a first embodiment of a MEMS laser scanner that receives polarized light at time t1.

[0012] Figure 3c This is a view of a first embodiment of a MEMS laser scanner that receives polarized light at time t2.

[0013] Figure 4a This is a view of a second embodiment of a MEMS laser scanner, showing zero-order reflections from the first and second Bragg polarization gratings.

[0014] Figure 4bThis is a view of a second embodiment of a MEMS laser scanner that receives polarized light at time t1.

[0015] Figure 4c This is a view of a second embodiment of a MEMS laser scanner that receives polarized light at time t2.

[0016] Figure 5 This is an enlarged view showing the orientation of liquid crystal molecules within a Bragg polarization grating used in a first embodiment of this technology.

[0017] Figure 6a This is a view of a third embodiment of a MEMS laser scanner, showing zero-order reflections from the first and second Bragg polarization gratings.

[0018] Figure 6b This is a view of a third embodiment of a MEMS laser scanner that receives polarized light at time t1.

[0019] Figure 6c This is a view of a third embodiment of a MEMS laser scanner that receives polarized light at time t2.

[0020] Figure 7 This is a view of the fourth embodiment of a MEMS laser scanner that receives polarized light at time t1.

[0021] Figure 8 This is a view of the fourth embodiment of a MEMS laser scanner that receives polarized light at time t2.

[0022] Figure 9 This illustrates the formation of a first portion of the field of view when an optical element pivots about one of its axes while receiving polarized light.

[0023] Figure 10 The formation of the second part of the field of view is shown when the optical element pivots about one of its axes while receiving polarized light.

[0024] Figure 11 An alternative embodiment is shown in which a second portion of the field of view is formed when an optical element pivots about one of its axes while receiving polarized light.

[0025] Figure 12 This is a flowchart illustrating the operation of an embodiment of the present technology.

[0026] Figure 13 This is a view of an alternative configuration of a MEMS laser scanner according to an embodiment of the present technology.

[0027] Figure 14 This is a view of an alternative configuration of a MEMS laser scanner according to an embodiment of the present technology. Detailed Implementation

[0028] Certain embodiments of this technology can be used to increase (also referred to as expand) the field of view (FOV) that can be supported by a MEMS laser scanner, for example, used in near-eye displays. In an embodiment, the MEMS laser scanner includes a display engine comprising a plurality of laser diodes, for example, emitting light at red, green, and blue (RGB) wavelengths. Light from the display engine is directed onto optics of a beam scanning assembly. In one embodiment, the optics may be a mirror.

[0029] The optical element is supported by a curved portion to pivot about two axes, referred to herein as the x and y axes, which in embodiments may be coplanar and orthogonal to each other. The beam scanning assembly also includes a dual-axis driver that pivots the optical element about the axes. The dual-axis driver and the laser diode may be coupled to a controller that coordinates the emission of the respective RGB laser with the x and y positioning of the optical element via the dual-axis driver to trace the pixels of the image within the field of view.

[0030] When an optical element pivots through the first half of its cycle about one of its axes (e.g., the x-axis), it can receive light from the display engine that is polarized in a first direction, such as left-hand circular (LHC) polarization. When an optical element pivots through the second half of its cycle about an axis, it can receive light from the display engine that is polarized in a second direction, such as right-hand circular (RHC) polarization.

[0031] According to various aspects of this technology, one or more polarization gratings may be mounted on or above an optical element, and these polarization gratings may be configured according to the Bragg scheme. Such gratings are referred to herein as Bragg polarization gratings, or more simply as BPGs. One or more BPGs on the optical element cause the maximum order of light with different polarizations to diffract in different directions or otherwise propagate through one or more BPGs.

[0032] Therefore, light from a first portion of the entire image can be directed to one or more BPGs on the optical element having a first polarization (e.g., LHC polarization). This light will exit the optical element along a first direction to trace a path forming the first portion of the entire FOV. Light from a second portion of the entire image can be directed to one or more BPGs on the optical element having a second polarization (e.g., RHC polarization). This light will exit the optical element along a second direction to trace a path forming the second portion of the entire FOV. By time-division multiplexing the image light between LHC and RHC polarized light to synchronize with the optical element as it pivots, the first and second portions of the FOV can be combined to provide a magnified entire FOV.

[0033] In embodiments, the MEMS laser scanner described herein can be used in near-eye displays, such as head-mounted display (HMD) devices used in augmented and virtual reality environments. However, it should be understood that this technology can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make this disclosure thorough and complete, and to fully convey the invention to those skilled in the art. Indeed, the invention is intended to cover alternatives, modifications, and equivalents to these embodiments that are included within the scope and spirit of the invention as defined by the appended claims. Furthermore, numerous specific details are set forth in the following detailed description of the invention to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without these specific details.

[0034] The terms “top” and “bottom,” “upper” and “lower,” “vertical” and “horizontal,” “left” and “right,” and their forms, as may be used herein, are for illustrative purposes only and are not intended to limit the description of the invention, as the referenced items may be interchanged in position and orientation. Furthermore, as used herein, the terms “substantially” and / or “about” mean that a specified dimension or parameter may vary within acceptable manufacturing tolerances for a given application. In one embodiment, the acceptable manufacturing tolerance is ±0.25%.

[0035] Figure 1 A general diagram of a beam scanning assembly 100 for use in a MEMS laser scanner, according to various aspects of the present invention, is shown. The beam scanning assembly 100 includes an optical element 102, which, in embodiments, may be a mirror formed from any suitable specular reflector for reflecting light. The reflective surface of the optical element may be planar, but it is conceivable that in other embodiments it may have a raised or recessed profile. In some further embodiments described below, the optical element 102 may instead include a transmissive substrate for transmitting light. Whether reflective or transmissive, the optical element may also have one or more BPGs on one of its surfaces, according to various aspects of the present invention described below.

[0036] As shown in the figure, structures for supporting and driving optical element 102 to pivot about the x-axis and y-axis are known in the art. Such structures are illustrated and described, by way of example only, in U.S. Patent No. 7,515,329 entitled "Driving a MEMS Scanner with a Combined Actuator Drive Signal" and U.S. Patent Application Publication No. 2007 / 0053044 entitled "Electrostatic Drive Type MEMS Mirror Scanner".

[0037] However, typically, the beam scanning assembly 100 can be photolithographically formed in silicon using MEMS micromachining and semiconductor fabrication techniques known in the art. The silicon can be fabricated to include an outer frame 104 having electrical contacts 106. The number and arrangement of the electrical contacts 106 are shown as examples only and may vary in other embodiments. The silicon can be etched or otherwise photolithographically developed to define a first pair of bends 108 such that the inner frame 110 is pivotable relative to the outer frame 104 about the y-axis. The silicon can also be etched or otherwise photolithographically developed to define a second pair of bends 114 such that the optical element 102 is pivotable relative to the inner frame 110 about the x-axis. The bends 108, 114 are shown as examples only and may have different structures in other embodiments.

[0038] Figure 1 A first drive actuator 120 and a second drive actuator 122 operably coupled to a controller 124 are also shown. Figure 1 (Symbolically shown in the image). The controller 124 may be integrated into the beam scanning assembly 100 or may be electrically connected to the beam scanning assembly 100. Figure 1 The controller 124 is shown schematically connected via some contacts 106, but it should be understood that in other embodiments, the beam scanning assembly 100 may be electrically coupled to the controller 124 in various other ways.

[0039] The first drive actuator 120 and the second drive actuator 122 are configured to deflect the optical element 102 about the y and x rotation axes, respectively. In the embodiment shown herein, a single optical element 102 located on a biaxial mount deflects about orthogonal rotation axes. In other embodiments, the same effect can be achieved using two optical elements 102 arranged in series, wherein each optical element 102 is located on a uniaxial mount.

[0040] The first drive actuator 120 and the second drive actuator 122 can operate according to various techniques to cause the optical element 102 to pivot at the bends 108, 114. For example, drive actuators 120 and / or 122 can be, for example, piezoelectric, electromagnetic, or electrostatic transducers. The first and second drive actuators can be driven by the same or different techniques, respectively. Controller 124 is configured to apply a drive signal (voltage or current) to each drive actuator to provide the desired deflection of the optical element 102 about the x-axis and y-axis. In one embodiment, one or both drive actuators can be electrostatic transducers that apply a deflection force to the optical element 102 when a voltage is applied to closely spaced plates or combs. Electrostatic transducers can be fabricated using standard MEMS processes.

[0041] As described in more detail below, the MEMS laser scanner also includes a display engine 140, which includes, for example, red, green, and blue laser diodes for emitting image lasers toward the optical element 102. The projected image FOV is generated by modulating the three lasers in synchronization with the position of the scanning beam. Specifically, one of the driving actuators (e.g., driving actuator 120) can be driven at a high frequency, while another driving actuator (e.g., driving actuator 122) can be driven at a lower frequency. As a result, light can be reflected away from the oscillating optical element in a Lissajous pattern 134, an example of which is shown in… Figure 2 As shown in the diagram. Pattern 134 is conceptually illustrative, and the oscillating optical element 102 can trace to form a Lissajous pattern of a much higher order to obtain a suitable high resolution.

[0042] In the example shown, the high-frequency drive actuator 120 causes the optical element to oscillate faster in the y-direction compared to the low-frequency drive actuator 122 causing the optical element to oscillate in the x-direction. Therefore, the optical element generates a raster-like image such that each virtual pixel of the image is hit at least once within the time of one image frame. In one embodiment, the optical element may complete a frame 60 times per second (e.g., the entire oscillation cycle in both the x and y directions). In other embodiments, the frame rate may be higher or lower than 60 frames per second.

[0043] Under the control and coordination of controller 124, the position of optical element 102 is synchronized with the modulation of red, green, and blue lasers, so that each pixel receives the appropriate color combination within the image, and each image frame creates the desired image. If one of the colors is not needed due to the image content, its associated laser can be down-modulated, which minimizes power consumption.

[0044] When the MEMS laser scanner of this technology is used, for example, in a near-eye display device, the image light reflected or transmitted by the oscillating optical element 102 presents an image with a specific field of view (FOV) to the user's eye at the scanner's output pupil. Reference Figure 2 In conventional MEMS laser scanners, the degree of oscillation of the optical element about the x-axis and y-axis defines the length L and width W components of the FOV 136 at the output pupil 138. The FOV can be measured as a diagonal or region of the scanned image, but in other embodiments it can be measured in other ways. As explained below, for a given x-axis and y-axis oscillation of the optical element 102, or even a smaller x-axis and / or y-axis oscillation of the optical element 102, this technique provides a larger total FOV 136 at the output pupil.

[0045] Now refer to Figure 3- Figure 11 , Figures 13-14 The view and Figure 12The flowchart describes an embodiment of the present technology using the beam scanning component 100 described above. Figure 3a , 3b Figures 3 and 3c illustrate the structure and operation of a first embodiment of a MEMS laser scanner 200 according to the present technology. Figure 3a The image light incident on optical element 102 at two different times is shown. This figure illustrates zero-order diffraction light present because the diffraction grating is not 100% effective. This light contributes nothing to the final image and will appear as ghosting; therefore, mechanisms such as blocking apertures will be used to block the light from reaching subsequent components in the optical system. Figure 3b and 3c The figures illustrate image light incident on optical element 102 at two different times. These figures show two separate fields of view formed by diffracting the display light onto MEMS mirror 168 via two separate Bragg polarization gratings 170 and 171, as described below. The image light is generated by display engine 140, which emits the image light in step 300, and the image light is modulated pixel-by-pixel by controller 124. In embodiments, display engine 140 may be a commercially available component, such as the PicoP from Microvision Corporation of Redmond, Washington. TM Display engine.

[0046] However, typically, display engine 140 may include three laser diodes: a red laser diode 142, a green laser diode 144, and a blue laser diode 146, although more or fewer laser diodes may be present in other embodiments. Additionally, in another embodiment, one or more laser diodes may emit light in the invisible spectrum, such as infrared light. Each of the RGB laser diodes 142, 144, and 146 may be operatively coupled to controller 124. The controller may be configured to modulate the intensity of the illumination beam from each RGB laser diode for each pixel by controlling the current or voltage applied to the respective laser diode. In another embodiment, the laser intensity of the respective diode may be modulated in other ways. The light from the three laser diodes may be combined using dichroism or other optics to form a single white beam emitted by display engine 140.

[0047] Laser emitted from display engine 140 can pass through optical polarization assembly 150. According to a time-division multiplexing scheme, polarization engine 150 is provided to polarize light from display engine into light with different first and second polarizations. Optical polarization assembly 150 may include a fast polarization modulator (FPM) 152 and a color quarter-wave plate 154. FPM 152 may be an LC-based polarization modulator / rotator whose polarization is controlled by an externally applied drive voltage. Therefore, in step 302, light from display engine 140 can be linearly polarized without moving parts, without vibration, and in a device with a small footprint. The FPM 152 used for this technology is available from, for example, LC-TEC Displays AB in Borgeng, Sweden.

[0048] The FPM 152 also enables time-division multiplexing switching between two orthogonal linear polarization states at a desired switching rate. As described below, the switching rate is synchronized by the controller 134 with the oscillation of the optical element 102 about the x-axis or y-axis. In an embodiment, the FPM may switch the polarization state of the received light once per frame, although it can be more or less frequent. As noted, in an embodiment, the display engine 140 may generate frames at a rate of 60 frames per second, but in other embodiments it may be faster or slower.

[0049] In step 306, the quarter-wave plate 154 converts the linear polarization from the FPM 152 into circular polarization of its corresponding helicity, i.e., left-hand circular (LHC) or right-hand circular (RHC). Based on the linear polarization received from the FPM 152, the quarter-wave plate cycles between generating RHC-polarized light and LHC-polarized light. The quarter-wave plate 154 used for this technique is available from, for example, Thorlabs Corporation of Newton, New Jersey. It should be understood that the polarization assembly 150 may include other or alternative components for generating time-division multiplexing switching between LHC and RHC-polarized image light.

[0050] Then, the polarized image light from the polarization engine 150 is directed onto the optical element 102 of the beam scanning assembly 100 to form a field of view (FOV) at the output pupil in steps 310-316 described below. Figures 3a-3c 4a-4c and 6a-c show the optical element 102, and other components of the beam scanning assembly 100 are omitted for clarity. Figures 3a-3c Figures 4a-4c and 6a-c also show side views of an optical element rotated about the x-axis at different times (the x-axis is aligned with the page of the figure as it enters and exits). Rotation about the y-axis is discussed below, but not in [the figure]. Figures 3a-3c As shown in 4a-4c and 6a-c.

[0051] Figures 3a-3cA pair of optical elements 160, 162 are shown for guiding polarized image light onto optical element 102. The optical elements may be mirrors. However, it should be understood that various optical components can be used to guide polarized image light from display engine 140 onto optical element 102, including, for example, beam splitters, prisms, and folding mirrors, which may include diffraction gratings. For example, optical element 162 deflects image light from display engine downwards onto optical element 102. However, if optical element 102 is perpendicular to the incoming image light, the light will be reflected back towards optical element 162. Such reflected image light should pass directly through optical element 162 unaffected so as not to disrupt the image light forming the field of view (FOV) at the output pupil.

[0052] According to various aspects of this technology, two or more Bragg polarization gratings 170 and 171 (also referred to herein as BPG 170 and 171) may be disposed on or above the main flat surface 168 of the optical element 102. For example Figures 3a-3c The thicknesses of BPGs 170 and 171, as shown in 4a-4c, 6-7, and 9-12, and optical element 102, may not be drawn to scale relative to each other. Details of the fabrication and operation of different embodiments of one or more Bragg polarization gratings 170 and 171 are described, for example, in various embodiments of U.S. Patent Publication No. 2016 / 0033698 entitled “Bragg Liquid Crystal Polarization Gratings” by Escuti et al. However, generally, in the field of diffraction gratings, the dimensionless parameter Q can be used to define schemes for defining the optical behavior of a particular grating configuration such that:

[0053] Q=2λd / Λ2n, (1)

[0054] Where λ is the vacuum wavelength of light, d is the grating thickness, Λ is the grating period (i.e., the spacing) of the optical element, and n is the average refractive index of the medium through which the light travels. Within this framework, the Bragg scheme can be defined as Q>1, the Ramanus scheme can be defined as Q<1, and Q=1 can refer to a hybrid scheme possessing the properties of both.

[0055] In embodiments of this technology, one or more polarization gratings used on optical element 102 may be formed, for example, of a liquid crystal material having a grating period Λ, thickness d, and / or average refractive index n selected such that the wavelength of light used by the system satisfies the Bragg condition (Q>1). Each of the above parameters can be selected to tune BPG 170 and 171 to provide light propagation according to various aspects of this technology, including but not limited to high diffraction efficiency, finite diffraction order, and / or polarization selectivity. These features are explained in more detail below.

[0056] Figure 5 These are enlarged views of examples of BPGs 170 and 171 including multiple sublayers 172 having liquid crystal molecules 174 (one of which is numbered). As indicated in Escuti's published patent No. 2016 / 0033698, the sublayer 172 can be multiple stacked polymeric nematic liquid crystal sublayers formed by patterning a thin film having optical anisotropy. In particular, the liquid crystal sublayer 172 can have local optical axes that can be defined by the orientation of the liquid crystal molecules 174, these orientations extending through the thickness of the sublayer and aligning across the interfaces between the sublayers.

[0057] Some Bragg polarization gratings possess the characteristic of high coupling efficiency for light with preferred polarization orientation. Figure 5 In one embodiment, BPG 170 can have high coupling efficiency for the negative first order of light with first polarization (e.g., LHC), and BPG 172 can have high coupling efficiency for the positive first order of light with second polarization (e.g., RHC).

[0058] For example, in Figure 5 In this configuration, liquid crystal molecules can be formed with a right-hand twisted helix 180. This allows RHC-polarized light to couple within sublayer 172 and diffract in first-order diffraction, as described below, where other orders of RHC polarization are minimized. Conversely, LHC-polarized light can pass directly through sublayer 172 unaffected. Figure 5 The specific molecular orientation shown is merely an example and can be varied in other embodiments. In another example explained below, the liquid crystal molecules can alternatively be formed with a left-handed twisted helix. Such a configuration will diffract first-order LHC polarized light while allowing RHC polarized light to pass directly through BPG170 unaffected.

[0059] The embodiments described herein include Bragg polarization gratings on optical elements for maximizing the order of light to be guided in two different directions according to the polarization of the light. However, it should be understood that other gratings exhibiting high coupling efficiency for light with preferred polarization orientation can be used. One such additional grating that can be used is a switchable Bragg grating. Such switchable Bragg gratings are known and are described, for example, in U.S. Patent No. 7,265,882 entitled “Switchable Polymer-Dispersed Liquid Crystal Optical Elements”.

[0060] Figure 3aThe diagram illustrates polarized light striking optical element 102 as LHC or RHC light when the optical element pivots about the x-axis. In this figure, two BPGs 170, 171 are mounted between optical element 102 and element 162, such that light from display engine 140 passes through stationary BPGs 170, 172. For a specific portion of the light, the forward beam passes through the BPGs unaffected. This is a zero-order diffraction mode and exists because the diffraction efficiency of the BPGs is not 100%. Refraction at the air-glass interface of 170 is ignored for simplification. Light is incident at an arbitrary angle with respect to a vector (referred to herein as the normal vector) perpendicular to the surface of BPG 170 and the surface of optical element 102. Light is incident on BPG 170 and optical element 102. The light travels at an angle relative to the normal vector, the same as the angle of incidence. Specular reflection exits the optical element 102. Since the direction of the light is outside the angular range of the BPG, the reflected light passes through the BPG 170 unaffected. This light represents a potential ghosting path of unwanted light and should be collected, for example, by using an aperture that blocks the path, allowing the displayed light to pass through.

[0061] Figure 3b The diagram illustrates polarized light striking optical element 102 at a certain time t1 as the optical element pivots about the x-axis, acting as RHC light. In this embodiment, BPG 170 is sensitive to RHC polarized light, such that the first-order RHC polarized light is diffracted as it passes through BPG 170. The light is incident at the same arbitrary angle relative to the normal vector. Incident at BPG 170, and diffracted relative to the normal vector to an angle. Light travels at the same angle as the diffraction angle. The mirror reflects light away from the optical element 102. As described below, the reflected light passes through the BPG 170 to form the first part of the image at the output pupil.

[0062] Figure 3c The diagram illustrates polarized light striking optical element 102 as LPS light at a certain time t2 when the optical element pivots about the x-axis. In this embodiment, BPG 170 is sensitive to LHC polarized light, such that the first order of LHC polarized light is diffracted as it passes through BPG 170. The light is incident at the same arbitrary angle relative to the normal vector. Incident at BPG 170, and diffracted relative to the normal vector to an angle. Light travels at the same angle as the diffraction angle. The specular reflection exits the optical element 102. As described below, the reflected light passes through the BPG 170 to form a second portion of the image at the output pupil.

[0063] In an embodiment, Figure 3bThe expected diffraction angle of the +1st order diffracted light shown. This can be achieved through controlled selection of the grating thickness of one or more BPGs, the BPG period, and the refractive index of one or more BPGs. In another embodiment, the properties of the light diffracted by one or more BPGs 170 can be advantageously controlled by providing a chiral tilt to the liquid crystal molecules 174 through the thickness of the sublayers and the interfaces between the sublayers. The chiral tilt of the liquid crystal molecules is discussed in Escuti's aforementioned patent publication No. 2016 / 0033698.

[0064] In the above embodiments, one or more BPG 170s allow for the maximization of the negative first order of LHC polarized light in the first time diffraction of the first order, and the maximization of the positive first order of RHC polarized light in the second time diffraction.

[0065] Figure 4a The diagram illustrates polarized light striking optical element 102 as LHC or RHC light when the optical element pivots about the x-axis. In this figure, BPGs 170 and 172 are mounted on and pivot together with a flat surface 168 of optical element 102. For a specific portion of the light, the forward beam is reflected away from the BPG without being affected by diffraction. This is a zero-order diffraction mode and exists because the diffraction efficiency of the BPG is not 100%. Refraction at the air-glass interface of 170 is ignored in the diagram for simplicity. Light is incident at an arbitrary angle with respect to a vector (referred to herein as the normal vector) perpendicular to the surface of BPG 170 and the surface 168 of optical element 102. The light is incident on BPG 170 and optical element 102. In this embodiment, surface 168 is a beam collector because it is coated with a light-absorbing material. Since the direction of the light is outside the angular range of the BPG, zero-order reflected light passes through BPG 170 unaffected. This light represents a potential ghosting path of unwanted light and should be collected, for example, by using an aperture that blocks this path and allows the displayed light to pass through.

[0066] Figure 4b The diagram illustrates polarized light striking optical element 102 at a certain time t1 as the optical element pivots about the x-axis, acting as RHC light. In this embodiment, BPG 170 is sensitive to RHC polarized light, causing the first-order diffraction of the RHC polarized light. The light is incident at the same arbitrary angle relative to the normal vector. Incident at BPG 170, and diffracted relative to the normal vector to an angle. As described below, the diffracted light will form the first part of the image at the output pupil.

[0067] Figure 4cThe diagram illustrates polarized light striking optical element 102 as LPS light at a certain time t2 when the optical element pivots about the x-axis. In this embodiment, the BPG 170 is sensitive to LHC polarized light, causing the first order of LHC polarized light to be diffracted. The light is incident at the same arbitrary angle relative to the normal vector. Incident at BPG 170, and diffracted relative to the normal vector to an angle. As described below, the diffracted light will form the second part of the image at the output pupil.

[0068] In an embodiment, Figures 3b-4c The expected diffraction angle of the ±1st order diffracted light shown. and This can be achieved through controlled selection of the grating thickness of one or more BPGs, the BPG period, and the refractive index of one or more BPGs. In another embodiment, the properties of the light diffracted by one or more BPGs 170 can be advantageously controlled by providing a chiral tilt to the liquid crystal molecules 174 through the thickness of the sublayers and the interfaces between the sublayers. The chiral tilt of the liquid crystal molecules is discussed in Escuti's aforementioned patent publication No. 2016 / 0033698.

[0069] In the above embodiments, one or more BPG 170s allow the incident light of LHC polarized light to diffract to the maximum negative first order and the incident light of RHC polarized light to diffract to the maximum positive first order.

[0070] In the above Figures 3a-3c In one embodiment, the optical element 102 is a reflector having one or more BPGs 170 above surface 168. In embodiments 4a-4c described above, the optical element 102 has one or more BPGs 170 as a reflective diffraction grating. However, in another embodiment, the optical element may be a transmissive substrate having one or more BPGs 170 on surface 168. Reference will now be made to... Figures 6a-6c The side view illustrates such an embodiment. In other embodiments using a transmissive substrate, one or more BPGs 170 may alternatively or additionally be disposed on a second main flat surface 166 of the optical element 102 that is opposite to and parallel to the first main flat surface 168.

[0071] In the transmission embodiment, the optical element 102 may be a substrate made of glass or optical plastic, but is not limited thereto. In the embodiment, the substrate may be a bulk substrate, but is not required. A bulk substrate is an optical substrate in which the thickness of the substrate (between its main surfaces) is at least ten times (i.e., 10 times) the wavelength of the light through which the substrate is used as a light transmission medium. For example, if the light (through which the substrate is used as a light transmission medium) is red light with a wavelength of 620 nm, then the substrate would be considered a bulk substrate with a substrate thickness (between its main surfaces) of at least 6200 nm, i.e., at least 6.2 μm.

[0072] According to some embodiments, the substrate used as optical element 102 has a thickness of at least 25 μm between its main flat surfaces 168 and 166. In specific embodiments, the thickness of the substrate (between its main surfaces) ranges from 100 μm to 1500 μm, with a possible thickness of about 1000 μm. The substrate may be transparent, meaning it allows visible light to pass through it.

[0073] exist Figure 6a In the embodiment of -c, the RGB laser can be generated by the display engine 140, polarized according to the time-division multiplexing scheme of the polarization engine 150, and guided to the optical element through the optical components, as described above.

[0074] Figure 6a The diagram illustrates polarized light striking optical element 102 as LHC or RHC light when the optical element pivots about the x-axis. In this figure, BPGs 170 and 172 are mounted on and pivot together with the flat surface 168 of optical element 102, which, as described above, is a transmission substrate. For a specific portion of the light, the forward beam propagates through the BPGs without being affected by diffraction. This is a zero-order diffraction mode and exists because the diffraction efficiency of the BPGs is not 100%. Refraction at the air-glass interface of 170 is ignored in the diagram for simplicity. Light is incident at an arbitrary angle with respect to the normal vectors of the surfaces of BPG 170 and the surface 168 of optical element 102. The light is incident on BPG 170 and optical element 102. In this embodiment, surface 168 is a beam collector because it is coated with a light-absorbing material. Since the direction of the light is outside the angular range of BPG, the zero-order light passes through BPG 170 unaffected. This light represents a potential ghosting path of unwanted light and should be collected, for example, by using an aperture that blocks this path and allows the displayed light to pass through.

[0075] Figure 6b The diagram illustrates polarized light striking optical element 102 at a certain time t1 as the optical element pivots about the x-axis, acting as RHC light. In this embodiment, BPG 170 is sensitive to RHC polarized light, causing the first-order diffraction of the RHC polarized light. The light is incident at the same arbitrary angle relative to the normal vector. Incident at BPG 170, and diffracted relative to the normal vector to an angle. As described below, the diffracted light will form the first part of the image at the output pupil.

[0076] Figure 6c The diagram illustrates polarized light striking optical element 102 at a certain time t2 as the optical element pivots about the x-axis, representing LHC light. In this embodiment, the BPG 170 is sensitive to LHC polarized light, causing the first order of LHC polarization to be diffracted. The light is incident at the same arbitrary angle relative to the normal vector. Incident at BPG 170, and diffracted relative to the normal vector to an angle. As described below, the diffracted light will form the second part of the image at the output pupil.

[0077] In an embodiment, Figures 6a-6c The expected diffraction angle of the ±1st order diffracted light shown. and This can be achieved through controlled selection of the grating thickness of one or more BPGs, the BPG period, and the refractive index of one or more BPGs. In another embodiment, the properties of the light diffracted by one or more BPGs 170 can be advantageously controlled by providing a chiral tilt to the liquid crystal molecules 174 through the thickness of the sublayers and the interfaces between the sublayers. The chiral tilt of the liquid crystal molecules is discussed in Escuti's aforementioned patent publication No. 2016 / 0033698.

[0078] In the above embodiments, one or more BPG 170s allow for the maximization of the negative first order of incident light diffraction for LHC polarized light and the maximization of the positive first order of diffraction for RHC polarized light.

[0079] Figure 7 and 8 Transmitting BPGs 170a and 170b and reflecting optical element 102 are shown. Now refer to... Figure 7 At the first moment t1, RHC-polarized light from polarization component 150 can be guided to optical element 102. The optical element may include a single BPG, comprising the aforementioned regions 170a and 170b. Alternatively, BPG 170 may comprise separately stacked BPGs 170a and 170b. Part 170a is sensitive to RHC-polarized light. Thus, +1 order polarized light diffracts at an angle of... Diffracting occurs in the first direction. Then the light passes through section 170°b unaffected and at the angle of reflection (also...). The reflection leaves the surface of the optical element and propagates back through sections 170b and 170a to form the first part of the FOV.

[0080] Now for reference Figure 8 At the second time t2, LHC-polarized light from polarization component 150 can be guided to optical element 102. Part 170b is sensitive to LHC-polarized light. Thus, LHC-polarized light passes through part 170a unaffected, and the -1st order polarized light diffracts at an angle... It is diffracted in the second direction. Then the light is reflected at the angle (also) The reflection leaves the surface of the optical element and propagates back through sections 170b and 170a to form the second part of the FOV.

[0081] In one embodiment, the desired diffraction angles of +1 and -1 orders can be achieved through controlled selection of the grating thickness of one or more BPGs, the BPG period, and the refractive index of one or more BPGs. In another embodiment, the properties of the light diffracted by one or more BPGs 170a, 170b can be advantageously controlled by providing chiral tilt to the liquid crystal molecules through the thickness of the sublayers and the interfaces between the sublayers. As mentioned above, the chiral tilt of the liquid crystal molecules is discussed in Escuti's aforementioned patent publication No. 2016 / 0033698.

[0082] Figure 3a-8 The operation of an optical element 102, comprising one or more BPG 170s, guiding differently polarized light in different directions at discontinuous moments is illustrated. The following will now be described. Figure 9-11 as well as Figure 12 The flowchart illustrates how this feature can be used in a time-division multiplexing scheme to form two separate portions of the FOV at the output pupil during a single oscillation cycle of the optical element 102 about one of its axes (e.g., the x-axis). These two FOVs can be combined to provide an expanded overall FOV, as described below.

[0083] Figure 9 An example is shown where the trajectory at the output pupil 138 forms the first portion of the entire FOV, FOV1, during the time interval between time t1 and t2. At time t1, light with a first polarization (e.g., LHC polarization) is guided onto an optical element 102 comprising one or more BPGs 170 (step 310). The display engine 140, polarization assembly 150, and optical assembly used to guide the light onto the optical element 102 are... Figure 9-11 The text is omitted for ease of understanding.

[0084] In this example, BPG 170 is insensitive to LHC polarized light, therefore the zeroth order of polarized light, relative to other order-maximized polarized light, passes directly through one or more BPG 170s at an angle relative to the angle of incidence of the light on optical element 102 (in this example, ). The same angle of reflection.

[0085] While optical element 102 oscillates in step 312 between times t1 and t2, controller 124 maintains the light polarized to LHC polarization. At time t1, optical element 102 is shown pivoting to its maximum extent about the x-axis in one direction, and at time t2, optical element 102 is shown pivoting to its maximum extent about the x-axis in the opposite direction. The optical element may pivot within a range of approximately 30-35 degrees between its maximum extent at times t1 and t2, but in other embodiments it may be within other angular ranges.

[0086] As the optical element pivots from one degree at time t1 to the opposite degree at time t2, where the light is polarized to LHC, the trajectory of the light at the output pupil 138 forms the first part of the entire FOV, FOV1. The pivot trajectory about the x-axis forms the length L of FOV1. High-frequency pivoting about the y-axis (…) Figure 9 (Not shown) The trajectory forms the width W of FOV1. That is, as the oscillation about the x-axis moves along the length of FOV1, the oscillation trajectory about the y-axis forms each column of pixels in FOV1. The specific shape of FOV1 is only an example, and in other embodiments, the aspect ratio of length L to width W can vary.

[0087] Figure 10 Showing with Figure 9 The same configuration is used, however, to form the second part of the entire FOV, FOV2, at the output pupil 138 during the time interval between times t3 and t4. At time t3, which is later than time t2, the optical element 102 has not moved from its maximum position (relative to the x-axis) at time t2. Time t3 can be, for example, a moment immediately following time t2. However, at time t3, the controller 124 switches the polarization of the light from the polarization component 150 so that the light at time t3 is RHC polarized light (step 314).

[0088] As mentioned above, RHC polarized light diffracts in a different direction than LHC polarized light. This is achieved at an incident angle relative to the normal. The incoming light at an angle Diffraction and reflection leave the optical element, in this embodiment It can be greater than Therefore, even if the position of the optical element does not change relative to the x-axis from time t2 to time t3, the light is reflected away from the optical element 102 at time t3 in a different direction than at time t2.

[0089] At time t3, optical element 102 is shown pivoting to its maximum extent about the x-axis in one direction, and at time t4, optical element 102 is shown pivoting to its maximum extent about the x-axis in the opposite direction. Figure 9The time t1 is the same. Since the optical element pivots from one degree at time t3 to the opposite degree at time t4 in step 316, the controller 124 maintains the light as RHC polarized, and the light trajectory forms the second part of the entire FOV, FOV2. The pivot trajectory about the x-axis forms the length L of FOV2. High-frequency pivoting about the y-axis (… Figure 10 (Not shown in the image) The trajectory forms the width W of FOV2. The specific shape of FOV2 is only an example, and in other embodiments, the aspect ratio of length L to width W can vary.

[0090] The depiction at time t4 shows that optical elements, including one or more BPG 170s, have been traced to form FOV1 and FOV2, which combine to provide the entire FOV. (The above is an interpretation of the description.) Figure 9 and 10 The operation can be performed once per image frame. After time t4, the controller 124 can switch the polarization of the light back to LHC polarization, and this process can be repeated to generate the next frame of the image. As shown, in other embodiments, FOV1 and FOV2 may overlap, but they may overlap to a greater or lesser extent, or not overlap at all.

[0091] A key feature of this technology is that the overall FOV size can be significantly increased compared to the same oscillation of the mirrors in a conventional MEMS laser scanner. Specifically, by including one or more BPG 170s and time-division multiplexing the polarization of light to the optical elements, light can be reflected away from the optical elements over a wider angular range, and the overall FOV size can be significantly increased. This increase can be approximately 70 degrees, but in other embodiments it can be larger or smaller than this.

[0092] In the above embodiments, one or more BPGs are oriented to diffract light in the length direction of the FOV corresponding to the oscillation about the x-axis, and the time-division multiplexed polarization of the light is synchronized with the oscillation about the x-axis by the controller 124. However, in another embodiment, it should be understood that one or more BPGs may be oriented to diffract light in the width direction of the FOV corresponding to the oscillation about the y-axis, and the controller 124 may synchronize the time-division multiplexed polarized light with the oscillation about the y-axis.

[0093] It should be further understood that controller 124 can synchronize the time-division multiplexing of polarized light with other periodic oscillations of optical element 102 about axes such as the x-axis. For example, Figure 11 It shows Figure 10 Alternatives to the operations shown. In Figure 11 In this embodiment, the optical elements can be traced to form the first part FOV1 of the entire FOV, as referenced above. Figure 9 As shown and described.

[0094] However, in Figure 11 In one embodiment, after time t2, the optical element 102 oscillates back to the same position it had at time t1 (its original position). During this oscillation back to its original position, the controller 124 can downmodulate (turn off) the light from the display engine 140. Once in its original position at time t3, the display engine can emit image light polarized to RHC. The optical element 102 can then pivot from time t3 to time t4 to its opposite extent to trace a second portion of the entire FOV, FOV2. Typically, Figure 10 The embodiment forms FOV2 from right to left. Figure 11 The embodiments can form the same FOV2 from left to right.

[0095] The above embodiments illustrate the switching of polarization of light incident on an optical element as the optical element pivots at its extreme degrees. However, it should be understood that the controller 124 can synchronize the time-division multiplexing scheme of the polarization assembly 150 with the oscillation of the optical element 102 to switch polarization at a point between the extreme degrees of the optical element. This can, for example, occur twice for each complete oscillation of the optical element (e.g., ...). Figure 9 and 10 (as shown) or each complete oscillation of the optical element occurs once (e.g. Figure 9 and 11 (As shown).

[0096] In the above embodiments, each RGB laser is considered to propagate through one or more BPG 170s in the same manner and along a parallel path. However, it is possible that one or more BPG 170s propagate in different manners and / or diffract light of different wavelengths. Figure 13 and 14 Two embodiments are shown for ensuring that the RGB laser components are reflected away from the optical element in a parallel path.

[0097] exist Figure 13 The display engine 140 provides RGB laser diodes 142, 144, 146 and / or optical components such that each RGB laser emitted from the display engine 140 is slightly off-axis relative to each other. The degree of off-axis displacement of the lasers relative to each other is controlled such that once an RGB laser passes through one or more BPGs 170, each will propagate and / or diffract at a slightly different angle, and the RGB lasers will reflect together and in parallel away from the optical element 102. Although Figure 13 The image shows three lasers being reflected along different parallel paths, but this is for illustrative purposes, and the three lasers can be combined together as they leave optical element 102.

[0098] Figure 13An example is shown in which the zeroth order of an LHC-polarized RGB laser passes through one or more BPG 170s. It should be understood that... Figure 13 The embodiment similarly reflects the first-order diffraction of the RHC-polarized RGB laser along a parallel path. Additionally, Figure 13 The off-axis embodiment shown can also be used when the optical element 102 is a transmissive substrate, such as the one described above. Figure 6a -c is shown.

[0099] Figure 14 Another embodiment for compensating for different propagation and / or diffraction at different wavelengths in an RGB laser is shown. Figure 14 In this configuration, one or more BPGs 170 include three distinct BPGs 170a, 170b, and 170c. Each BPG 170a, 170b, and 170c is tuned to one of the RGB lasers, while allowing the other two RGB lasers to pass unaffected. Each BPG 170a, 170b, and 170c is tuned to propagate and / or diffract the wavelength of its sensitive light, such that the RGB lasers are reflected together and in parallel from the surface of the optical element 102.

[0100] Figure 14 Examples of zero-order LHC-polarized RGB lasers passing through BPG 170a, 170b, and 170c are shown. It should be understood that... Figure 14 The embodiment similarly reflects the first-order diffraction of the RHC-polarized RGB laser along a parallel path. Additionally, Figure 14 The illustrated embodiment can also be used when the optical element 102 is a transmissive substrate, such as the one described above. Figure 6a -c is shown.

[0101] In the above embodiments, according to the time-division multiplexing scheme, the polarization of light from a single display engine switches between different first and second polarizations. In another embodiment, the first display engine can provide first polarized light, and the second display engine can provide second polarized light orthogonal to the first polarization. In such an embodiment, light from two different display engines can simultaneously be incident on BPGs 170 and 171, as... Figure 3a , 4a As shown in Figure 6a, the two different polarizations of light will cause the trajectory to form two different parts of the field of view (FOV).

[0102] In summary, examples of this technology relate to a microelectromechanical (MEMS) scanner comprising: an optical element capable of operating on either transmitted or reflected light, the optical element being supported to pivot about an axis between a first position and a second position; and one or more Bragg polarization gratings (BPGs) disposed on a portion of the optical element, the one or more BPGs receiving light from one or more display engines, the light being polarized into a first polarization and a second polarization, the one or more BPGs transmitting first polarized light in a first direction and second polarized light in a second direction, the first polarized light transmitted in the first direction forming a first portion of the field of view (FOV) of an image as the optical element pivots about the axis, and the second polarized light transmitted in the second direction forming a second portion of the FOV of the image as the optical element pivots about the axis, the second portion of the FOV being different from the first portion of the FOV.

[0103] In another example, the technology relates to a microelectromechanical (MEMS) scanner comprising: an optical element capable of transmitting and reflecting light, the optical element being supported to pivot about an axis between a first position and a second position; and one or more Bragg polarization gratings (BPGs) fixed to a portion of the optical element, the one or more BPGs receiving light from one or more display engines, the light being polarized into left-hand circular (LHC) and right-hand circular (RHC) polarizations, the one or more BPGs transmitting LHC-polarized light in a first direction and RHC-polarized light in a second direction, the LHC-polarized light transmitted in the first direction forming a first portion of the field of view (FOV) of an image as the optical element pivots about the axis, and the RHC-polarized light transmitted in the second direction forming a second portion of the FOV of the image as the optical element pivots about the axis, the second portion of the FOV being different from the first portion of the FOV.

[0104] In yet another example, the technology relates to a microelectromechanical (MEMS) scanner comprising: an optical element capable of operating on either transmitted or reflected light, the optical element being supported to pivot about a first axis between a first position and a second position and a second axis orthogonal to the first axis; a first actuator for pivoting the optical element about the first axis; a second actuator for pivoting the optical element about the second axis; and one or more Bragg polarization gratings (BPGs) fixed to a portion of the optical element, the one or more BPGs receiving an image from an image source, light from the image being polarized into left-hand circular (LHC) polarization and right-hand circular (RHC) polarization, the one or more BPGs allowing the zeroth order of one of the LHC polarization and RHC polarization to pass through in a first direction, and the one or more BPGs diffracting the first order of the other polarization of LHC polarization and RHC polarization in a second direction, wherein when the optical element pivots between the first position and the second position, the light passing through in the first direction forms a first portion of the field of view (FOV) of the image, and when the optical element pivots between the first position and the second position, the light diffracted in the second direction forms a second portion of the FOV of the image, the second portion of the FOV being different from the first portion of the FOV.

[0105] Although the subject matter has been described using language specific to structural features and / or methodological actions, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are disclosed as exemplary forms for implementing the claims.

Claims

1. A microelectromechanical, MEMS, scanner, comprising: a single display engine configured to emit light; a polarizer comprising a fast polarization modulator configured to polarize the light according to a time-division multiplexing scheme; an optical element configured to pivot about an axis between a first position and a second position; and one or more Bragg polarization gratings, BPGs, disposed on a portion of the optical element, the one or more BPGs configured to: receive polarized light from the polarizer, wherein the polarized light comprises a first portion of light having a first polarization and a second portion of light having a second polarization; and transmit the first portion of the light in a first direction and the second portion of the light in a second direction, wherein the first portion of the light transmitted in the first direction forms a first portion of a field of view, FOV, of an image when the optical element is pivoted about the axis between the first position and the second position, and wherein the second portion of the polarized light transmitted in the second direction forms a second portion of the FOV of the image when the optical element is pivoted about the axis, the second portion of the FOV being different than the first portion of the FOV, wherein the first portion of the light and the second portion of the light are repeatedly time-division multiplexed with each other at least once in an image frame.

2. The MEMS scanner of claim 1, wherein the one or more BPGs comprise a first BPG configured to allow zeroth order passage of the first portion of the light and diffract first order of the second portion of the light.

3. The MEMS scanner of claim 1, wherein the one or more BPGs are further configured to transmit the first portion of the light by diffracting positive first order of the first portion of the light in the first direction, and wherein the one or more BPGs are further configured to transmit the second portion of the light by diffracting negative first order of the second portion of the light in the second direction.

4. The MEMS scanner of claim 1, wherein the one or more BPGs are physically separated from the optical element and in a fixed position and orientation.

5. The MEMS scanner of claim 1, wherein the one or more BPGs are disposed on a surface of the optical element.

6. The MEMS scanner of claim 1, wherein the optical element and the one or more BPGs form the first portion of the FOV when the optical element is pivoted from a first position to a second position, and wherein the optical element and the one or more BPGs form the second portion of the FOV when the optical element is pivoted from the second position to the first position. ​ 7. The MEMS scanner of claim 1, wherein the optical element and the one or more BPGs form the first portion of the FOV when the optical element is pivoted from a first position to a second position, and wherein the optical element and the one or more BPGs form the second portion of the FOV when the optical element is pivoted from the first position to the second position.

8. The MEMS scanner of claim 1, wherein the first portion of light and the second portion of light are left circularly polarized light and right circularly polarized light, respectively.

9. A microelectromechanical (MEMS) scanner, comprising: a single display engine configured to emit light; a polarizer comprising a fast polarization modulator configured to polarize the light according to a time-division multiplexing scheme; an optical element configured to pivot about an axis between a first position and a second position; and one or more Bragg polarization gratings (BPGs) disposed on a portion of the optical element, the one or more BPGs configured to: receive polarized light from the polarizer, wherein the polarized light comprises a first portion of light having a left-hand circular (LHC) polarization and a second portion of light having a right-hand circular (RHC) polarization; and transmit the first portion of light in a first direction and the second portion of light in a second direction, the first portion of light transmitted in the first direction forming a first portion of a field of view (FOV) of an image when the optical element is pivoted about the axis between the first position and the second position, and the second portion of light transmitted in the second direction forming a second portion of the FOV of the image that is different than the first portion of the FOV when the optical element is pivoted about the axis between the first position and the second position, wherein the LHC polarized light and the RHC polarized light are generated from the display engine according to a time-division multiplexing scheme.

10. The MEMS scanner of claim 9, wherein the one or more BPGs are further configured to transmit the first portion of light in the first direction in zeroth order, and to transmit the second portion of light in the second direction by diffracting a first order of the second portion of light.

11. The MEMS scanner of claim 9, wherein the one or more BPGs are further configured to transmit the first portion of light in the first direction by diffracting a positive first order of the first portion of light, and to transmit the second portion of light in the second direction by diffracting a negative first order of the second portion of light.

12. The MEMS scanner of claim 9, wherein the optical element comprises a substrate for transmitting light or a mirror for reflecting light.

13. The MEMS scanner of claim 9, wherein the optical element comprises a substrate for transmitting the light by propagating the light through the substrate.

14. A microelectromechanical (MEMS) scanner, comprising: an image source configured to provide image light; ​ a polarizer, including a fast polarization modulator, configured to polarize light from the image light into a first portion of light having a left-handed circular LHC polarization and a second portion of light having a right-handed circular RHC polarization according to a time-division multiplexing scheme; an optical element configured to pivot about a first axis between a first position and a second position and a second axis orthogonal to the first axis; a first actuator to cause the optical element to pivot about the first axis; a second actuator to cause the optical element to pivot about the second axis; and one or more Bragg polarization gratings BPGs disposed on a portion of the optical element, the one or more BPGs configured to: receive the first portion of light and the second portion of light from the polarizer; allow a zeroth order of one of the first portion of light or the second portion of light to pass in a first direction; and diffract a first order of the other of the first portion of light or the second portion of light in a second direction, the light passing in the first direction forming a first portion of a field of view FOV of the image when the optical element is pivoted between the first position and the second position, and the light diffracted in the second direction forming a second portion of the FOV of the image different from the first portion of the FOV when the optical element is pivoted between the first position and the second position, wherein the fast polarization modulator implements back-and-forth time-division multiplexing switching between two orthogonal linear polarization states at a predetermined switching rate.

15. The MEMS scanner of claim 14, wherein the MEMS scanner is part of a head-mounted display for providing an augmented reality environment.

16. The MEMS scanner of claim 14, wherein the optical element includes a substrate for transmitting light or a mirror for reflecting light.

17. The MEMS scanner of claim 14, wherein the optical element includes the substrate for transmitting the light by propagating the light through the substrate. ​ ​

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