Patent Description:
The present disclosure relates to optical scanners and in particular to scanning projectors for near-eye displays.

Head mounted displays (HMD), helmet mounted displays, near-eye displays (NED), and the like are being used increasingly for displaying virtual reality (VR) content, augmented reality (AR) content, mixed reality (MR) content, and they are finding applications in diverse fields including entertainment, education, training and biomedical science, to name just a few examples. The VR / AR / MR content can be three-dimensional (3D) to enhance the experience and to match virtual objects to real objects observed by the user. Eye position and gaze direction, and/or orientation of the user may be tracked in real time, and the displayed imagery may be dynamically adjusted depending on the user's head orientation and gaze direction, to provide a better experience of immersion into a simulated or augmented environment.

Compact display devices are desired for head-mounted displays. Because a display of HMD or NED is usually worn on the head of a user, a large, bulky, unbalanced, and/or heavy display device would be cumbersome and may be uncomfortable for the user to wear.

Scanning projector displays provide images in angular domain, which can be observed by an eye directly, without an intermediate screen or a display panel. The lack of a screen or a display panel in a scanning projector display enables size and weight reduction of the display. Compact and efficient scanners such as tiltable MEMS reflectors may be used to provide a miniature scanning projector suitable for use in a NED and NED-like displays.

<CIT> describes an image display device that includes: a light source which emits light according to an image signal; a high-speed scanning part which scans light relatively in a first scanning direction at a high speed; and a low-speed scanning part which scans the light relatively in a second scanning direction intersecting substantially at a right angle with the first scanning direction at a low speed. The image display device includes: an optical path splitting part which splits the light of a first scanning region and the light of a second scanning region into a first optical path and a second optical path which have optical axes different from each other wherein the first and the second scanning regions substantially divide the scanning region of the low speed scanning part into two regions; an optical path synthesizing part which merges the light of the first scanning region and the light of the second scanning region which are split into the first optical path and the second optical path by the optical path splitting part to an optical path having an identical optical axis; and a control part which allows the light source emit image frame light which is continuously different between the first scanning region and the second scanning region.

<CIT> describes a display system for presenting visual information to a user, that includes a fast scan mirror, a slow scan mirror, and anamorphic relay optics positioned optically between the fast scan mirror and slow scan mirror. The fast scan mirror has a fast scan arc in a scan direction of a display light provided by a light source. The slow scan mirror has a slow scan arc in a cross-scan direction of the display light that is perpendicular to the scan direction. The anamorphic relay optics are configured to magnify the display light in the cross-scan direction.

<CIT> describes an optical system that deploys micro electro mechanical system (MEMS) scanners to contemporaneously generate CG images and to scan a terrain of a real-world environment. An illumination engine emits a first spectral bandwidth and a second spectral bandwidth into an optical assembly along a common optical path. The optical assembly then separates the spectral bandwidth by directing the first spectral bandwidth onto an image-generation optical path and the second spectral bandwidth onto a terrain-mapping optical path. The optical system deploys the MEMS scanners to generate CG images by directing the first spectral bandwidth within the image-generation optical path and also to irradiate a terrain by directing the second spectral bandwidth within the terrain-mapping optical path.

According to an aspect of the invention, there is provided a scanning projector according to claim <NUM>.

In some embodiments, the second scanning reflector may be configured such that the second plane is generally orthogonal to the first plane.

In some embodiments, the beam relay optics may comprise a first polarization beam splitter (PBS) and a first concave reflector coupled to the first PBS, wherein the first PBS is disposed in a triple-pass configuration for routing the light beam sequentially to the first scanning reflector and to the first concave reflector in a first two passes, and toward the second scanning reflector in a third pass.

In some embodiments, there may further comprise a waveplate disposed in an optical path of the light beam for converting a polarization state thereof to an orthogonal polarization state between consecutive passes through the first PBS.

In some embodiments, there may further comprise a lens disposed in an optical path of the light beam upstream of the first scanning reflector.

In some embodiments, the first PBS may be disposed to direct the light beam sequentially to the first scanning reflector in a first pass and to the first concave reflector in a second pass, the beam relay optics further comprising a second PBS and a second concave reflector coupled to the second PBS, wherein the second PBS is disposed in a triple-pass configuration to direct the light beam received from the first PBS sequentially toward the second scanning reflector and toward the second concave reflector in a first two passes through the second PBS, and toward the output pupil in a third pass.

In some embodiments, the beam relay optics may further comprise four quarter-wave plates (QWP) disposed proximate to the first scanning reflector, the second scanning reflector, the first concave reflector, and the second concave reflector, for converting a polarization of the light beam to an orthogonal polarization between consecutive passes through each of the first and second PBS.

In some embodiments, the first PBS may be disposed to direct the light beam reflected from the first scanning reflector toward the first concave reflector, and from the first concave reflector toward the second PBS.

In some embodiments, there may further comprise a first focusing lens disposed upstream of the first PBS, and an output focusing or collimating lens disposed at the output pupil of the scanning projector.

In some embodiments, the first focusing lens may cooperate with the first concave reflector to converge the light beam to a focus at an intermediate location in an optical path between the first and second scanning reflectors.

In some embodiments, there may further comprise second focusing lens proximate to the second scanning reflector.

In some embodiments, the first concave reflector and the second focusing lens may cooperate to relay the first pupil to the second pupil with a magnification.

In some embodiments, the second scanning reflector may be greater in area than the first scanning reflector.

In some embodiments, each of the first and second scanning reflectors may comprise a tiltable MEMS reflector.

According to another aspect of the invention, there is provided a method according to claim <NUM>.

In some embodiments, the method may further comprise using the first PBS and the first concave reflector to direct the light beam from the first scanning reflector to the second scanning reflector, and using a second PBS coupled to a second concave reflector to direct the light beam from the first PBS sequentially toward the second scanning reflector and the output pupil.

In some embodiments, the method may further comprise changing a polarization state of the light beam to an orthogonal polarization state between consecutive passes through each of the first and second PBS.

According to a further aspect of the invention, there is provided a near-eye display device according to claim <NUM>.

In some embodiments, the beam relay optics may comprise a concave reflector and a polarization beam splitter (PBS) disposed in a triple-pass configuration and coupled to the concave reflector.

Exemplary embodiments will now be described in conjunction with the drawings, in which like elements are indicated with like reference numerals, which are not to scale, and in which:.

While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof.

As used herein, the terms "first", "second", and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated.

The terms "pupil relay", "pupil relay system", "pupil relay optics", and the like relate to an optical system that defines one or more optical paths between a first pupil and a second pupil, and which transfers a beam incident at a first pupil to a second pupil located at some distance away from the first pupil. In a pupil relay as understood herein, light beams emanating from the first pupil at different angles substantially overlap at the second pupil. Thus, a pupil relay operating with scanned beams transfers a variable beam angle at the first pupil to a variable beam angle at the second pupil, substantially without lateral shifts in the beam position at the second pupil. Here substantially means with some tolerance that may be related to various inaccuracies in the optical system and components thereof, and may mean for example within +\- <NUM>% of the diameter of the light beam at the second pupil, and preferably within +/-<NUM>% of the diameter of the light beam at the second pupil, depending on system design and tolerances. The tolerance to lateral displacement may depend on the energy profile of the beam. For example, a Gaussian beam profile truncated at the <NUM>/e<NUM> beam diameter may be more tolerant to pupil relay lateral shifts than a flat "top hat" distribution of the beam energy along the same diameter. The first and second pupils may be defined by optical components of the system in which the pupil relay is used, such as reflectors and lenses. The term "pupil relay magnification" refers to an increase in size of the beam from the first to the second pupil. A pupil relay may image the first pupil onto the second pupil.

The term "field of view" (FOV), when used in relation to an optical system, may define an angular range of beam propagation supported by the system. A FOV may be defined by angular ranges in two orthogonal planes coplanar with an optical axis or a portion thereof. For example, a FOV of a NED device may be defined by a vertical FOV, for example +\- <NUM>° relative to a horizontal plane, and a horizontal FOV, for example +\- <NUM>° relative to the vertical plane. With respect to a FOV of a NED, the "vertical" and "horizontal" planes or directions may be defined relative to the head of a standing person wearing the NED. Otherwise the terms "vertical" and "horizontal" may be used in the present specification with reference to two orthogonal planes of an optical system or device being described, without implying any particular relationship to the environment in which the optical system or device is used, or any particular orientation thereof to the environment. The terms "NED" and "HMD" may be used herein interchangeably.

An aspect of the present disclosure relates to a 2D scanning projector comprising: a first scanning stage comprising a first scanning reflector configured to steer an input light beam in a first plane; a second scanning stage comprising a second scanning reflector configured to steer the input light beam received from the first scanning stage in a second plane; and, beam relay optics configured to relay a first pupil defined at the first scanning reflector to a second pupil defined at the second scanning reflector, and to relay the second pupil to an output pupil of the scanning projector.

An aspect of the present disclosure relates to a system and method for scanning a beam of light in two dimensions using two or more sequentially disposed 1D or 2D scanning reflectors.

An aspect of the present disclosure provides a scanning projector for a display apparatus, comprising: a first scanning reflector configured to steer a light beam in at least a first plane; a second scanning reflector configured to steer the light beam received from the first scanning reflector in at least a second plane; and, beam relay optics configured to relay a first pupil defined at the first scanning reflector to a second pupil defined at the second scanning reflector, and to relay the second pupil to an output pupil of the scanning projector. In some implementations the second scanning reflector is configured so that the second plane is generally orthogonal to the first plane.

In some implementations the beam relay optics comprises a first polarization beam splitter (PBS) and a first concave reflector coupled to the first PBS, wherein the first PBS is disposed in a triple-pass configuration for routing the light beam sequentially to the first scanning reflector and to the first concave reflector in a first two passes, and toward the second scanning reflector in a third pass.

In some implementations the scanning projector comprising a waveplate disposed in an optical path of the light beam for converting a polarization state thereof to an orthogonal polarization state between consecutive passes through the first PBS.

In some implementations a lens may be disposed in an optical path of the light beam upstream of the first scanning reflector. In some implementations the lens may comprise an output lens disposed at the output pupil.

In some implementations the first PBS may be disposed to direct the light beam sequentially to the first scanning reflector in the first pass and to the first concave reflector in the second pass. The beam relay optics may further comprise a second PBS and a second concave reflector coupled to the second PBS. The second PBS may be disposed in a triple-pass configuration to direct the light beam received from the first PBS sequentially toward the second scanning reflector and toward the second concave reflector in a first two passes through the second PBS, and toward the output pupil in a third pass.

In some implementations the beam relay optics may further comprise four quarter-wave plates (QWP), one QWP proximate to each of the first scanning reflector, the second scanning reflector, the first concave reflector, and the second concave reflector, for converting a polarization of the light beam between consecutive passes through each of the first and second PBS.

In some implementations the first PBS may be disposed to direct the light beam reflected from the first scanning reflector toward the first concave reflector, and from the first concave reflector toward the second PBS. In some implementations a first focusing lens may be disposed upstream from the first PBS, and an output focusing or collimating lens may be disposed at the output pupil of the scanning projector. In some implementations the first focusing lens may be configured to cooperate with the first concave reflector to converge the light beam to a focus at an intermediate location in an optical path between the first and second scanning reflectors. In some implementations a second focusing lens may be disposed proximate to the second scanning reflector. In some implementations the first concave reflector and the second focusing lens cooperate to relay the first pupil to the second pupil with a magnification. In some implementations the second scanning reflector may be greater in area than the first scanning reflector.

In some implementations each of the first and second scanning reflectors comprises a tiltable MEMS reflector.

An aspect of the present disclosure provides a method for forming an image, the method comprising: providing a light beam to a first scanning reflector; responsive to a first image signal, steering the light beam in a first plane with the first scanning reflector; relaying the light beam from the first scanning reflector onto a second scanning reflector; responsive to a first image signal, steering the light beam with the second scanning reflector in a second plane; and, relaying the light beam from the second scanning reflector to an output pupil at an angle defined by steering angles of the first and second scanning reflectors and substantially without an angle-dependent lateral spatial shift. The relaying the light beam from the first scanning reflector onto a second scanning reflector or from the second scanning reflector to the output pupil may comprise using a first concave reflector and a first PBS in a triple-pass configuration.

In some implementations the method may comprise using the first PBS and the first concave reflector to direct the light beam from the first scanning reflector to the second scanning reflector, and using a second PBS coupled to a second concave reflector to direct the light beam from the first PBS sequentially toward the second scanning reflector and the output pupil.

In some implementations the method may comprise changing a polarization state of the light beam to an orthogonal polarization state between consecutive passes through each of the first and second PBS.

An aspect of the present disclosure provides a near-eye display (NED) device comprising: a support structure for wearing on a user's head; a light source carried by the support structure for providing a light beam; a pupil expander carried by the support structure; and, a scanning projector carried by the support structure. The scanning projector may comprise a first scanning reflector configured to steer the light beam in at least a first plane, a second scanning reflector configured to steer the light beam received from the first scanning reflector in at least a second plane, and beam relay optics configured to relay a first pupil defined at the first scanning reflector to a second pupil defined at the second scanning reflector, and to relay the second pupil to an output pupil of the scanning projector. The pupil expander may be configured to expand the output pupil of the scanning projector in size for directing the light beam toward an eye of the user.

In some implementations the beam relay optics comprises a concave reflector, and a polarization beam splitter (PBS) that is disposed in a triple-pass configuration and is coupled to the concave reflector.

In some implementations one of the first and second scanning reflectors may be operable to scan light in two dimensions to form a two-dimensional (2D) image in a field of view (FOV) defined in an angle space, and the other of the two scanning reflectors may be operable to shift the 2D image in the angle space in response to a control signal.

Referring to <FIG>, a two-stage scanning projector <NUM>, also referred to as projector <NUM>, is configured to receive an input light beam <NUM>, and scan it angularly in two dimensions (2D). The input light beam is scanned using two successive beam scanning stages, a first scanning stage <NUM> and a second scanning stage <NUM>, to produce an output light beam <NUM>. The output light beam <NUM> may be scanned across a particular FOV, generally in 2D. In some embodiments, for example when projector <NUM> is used in a display device, the input light beam <NUM> may be temporally modulated in coordination with the scanning, so that the output light beam <NUM> at the output of projector <NUM> renders a 2D image in an angle space, which may be converted to a spatial image by an observer's eye or by a focusing lens for displaying on a screen.

In some embodiments each of the first and second scanning stages <NUM>, <NUM> may be configured to scan a light beam it receives angularly in a particular plane, and may be referred as a 1D scanning stage. In example embodiments described hereinafter, the first scanning stage <NUM> includes a first scanning reflector (SR) <NUM> configured to steer an input light beam in a first plane, while the second scanning stage <NUM> includes a second SR <NUM> configured to steer the input light beam received from the first scanning stage <NUM> in a second plane. Each of the SRs <NUM> and <NUM> may include, for example, a tiltable mirror or more generally a tiltable reflector (TR). However, embodiments using light steering devices other than tiltable reflectors may also be envisioned, such as those based on controllable refraction and/or diffraction of incident light. In at least some example embodiments described below the planes in which the first and second SRs <NUM>, <NUM> steer the input light beam are substantially orthogonal, which simplifies scanning the output light beam <NUM> in a raster scanning pattern. Here "substantially" means with certain accuracy, for example +\- <NUM>°, or +\-<NUM>° , depending on system design and tolerances. It will be appreciated however that scanning the input beam sequentially in two planes that are neither orthogonal nor parallel can also be used to produce a 2D scanning pattern. Non-parallel planes may mean for example planes that are oriented at an angle of at least <NUM>° relative to each other. Embodiments in which the SRs <NUM>, <NUM> steer their respective input beams in a same plane could also be envisioned, for example to scan the output scanning light beam <NUM> in a wider angular range that may be supported by either of the SRs <NUM> or <NUM>, or to provide coarse and fine scanning separately.

Projector <NUM> may further include beam relay optics <NUM>, <NUM> that relay the input beam from the first SR <NUM> to the second SR <NUM>, and from the second SR <NUM> to an output pupil <NUM> of the scanning projector <NUM>. In the embodiment illustrated in <FIG>, this beam relay optics is represented by a first beam relay <NUM> and a second beam relay <NUM>. The first beam relay <NUM> and the second beam relay <NUM> may be considered as parts of the respective first and second scanning stages <NUM> and <NUM> as shown, but may also be coupled thereto, and/or may share with them one or more optical components. The first beam relay <NUM> may include refractive and/or reflective optics that relays the beam reflected from the first SR <NUM> to the second SR <NUM>, while the second beam relay <NUM> may include refractive and/or reflective optics that relays the beam reflected from the <NUM>nd SR <NUM> to output pupil. The first beam relay <NUM> and the second beam relay <NUM> may share one or more optical components, such as a lens in front of the second SR <NUM> that is double-passed as described below with reference to one or more example embodiments. The optics of the first beam relay <NUM> and the second beam relay <NUM> may function as a pupil relay, relaying a first pupil defined at the first SR <NUM> to a second pupil defined at the second SR <NUM>, and to relay the second pupil to an output pupil <NUM> of the scanning projector. The output pupil <NUM> may be defined, for example, by an output focusing or collimating lens, as described below.

With reference to <FIG>, there is illustrated an embodiment of projector <NUM> in which the first beam relay <NUM> includes first imaging optics <NUM> and first routing optics <NUM>, while the second beam relay <NUM> includes second imaging optics <NUM> and second routing optics <NUM>. Elements that are indicated in <FIG> with the same reference as in <FIG> perform in the embodiment of <FIG> the same function as in the embodiment of <FIG>, and may not be described again. Imaging optics <NUM> and <NUM> may include one or more refractive and/or reflective optical elements having optical power. In some embodiments, imaging optics <NUM> may be configured to image a reflective surface of SR <NUM>, or an operating portion thereof, onto a reflective surface of SR <NUM>, or an operating portion thereof, so that the beam scanned by SR <NUM> impinges upon generally a same area of the second SR <NUM> for a range of scanning angles of SR <NUM>. In some embodiments, imaging optics <NUM> may be configured to image a reflective surface of SR <NUM>, or an operating portion thereof, onto the output pupil <NUM>, so that beam <NUM> incident upon the output pupil <NUM> impinges upon generally a same area thereof for a range of the scanning angles provided by the first and second SRs <NUM>, <NUM>. The routing optics <NUM> and <NUM> may include one or more optical elements that may be without optical power but are configured to rout beams incident thereon in desired directions. The first routing optics <NUM> may rout the input optical beam from the first SR <NUM> to the second SR <NUM>, such as through, or engaging, one or more optical elements of the first imaging optics <NUM>. The second routing optics <NUM> may rout the input optical beam from the second SR <NUM> to the output pupil <NUM>, such as through, or engaging, one or more optical elements of the second imaging optics <NUM>. In some embodiments the routing optics <NUM> and <NUM> may fold the optical path of the input beam to decrease the projector footprint, and may provide polarization-assisted multi-pass routing.

Referring to <FIG>, there is schematically illustrated a display device <NUM> using an embodiment of projector <NUM> to generate image light. Elements that are indicated in <FIG> with the same reference numerals as in <FIG> perform in the embodiment of <FIG> the same function as in the embodiments of <FIG>, and may not be described here again. As illustrated, the display device <NUM> may be an NED which provides angularly scanned image light to an eye <NUM> of the user. A support structure <NUM>, such as a monocular or binocular frame, may be configured for wearing on the head of a user. The support structure <NUM> may carry a light source <NUM>, projector <NUM>, and a pupil expander <NUM>. In binocular implementation, the support structure <NUM> may carry two instances or these devices, one for each eye <NUM> of the user. In other embodiments the display device <NUM> may be configured to project the angularly scanned image light onto a screen. In some embodiments the pupil expander <NUM> may be absent or may be replaced with an objective or suitable projecting optics configured to form a spatial image on a screen. When implemented as a NED, the display device <NUM> may be configured to form virtual images. The light source <NUM> carried by the frame <NUM> provides the input beam <NUM> to projector <NUM>, also carried by the frame <NUM>. The pupil expander <NUM> expands the output pupil <NUM> of projector <NUM> in area for presenting to the user's eye <NUM>. The light source <NUM> may be configured to modulate the input light in time and spectrum to transmit images, and may be coupled to an image generating processor <NUM> that provides corresponding timing and color selection signals to the light source <NUM>. In RGB displays the light source <NUM> may include, for example, sources of red, green, and blue light, such as red, green, and blue laser diodes (LDs) or light emitting diodes (LEDs), which light may be separately modulated in accordance with signals from processor <NUM>, and optically multiplexed to produce the input light beam <NUM>. From the light source <NUM>, the input light <NUM> may be delivered to projector <NUM> using, for example, a suitable optical waveguide such as an optical fiber, or bulk optical components, or in free space. Projector <NUM> scans the modulated input light beam <NUM> to produce the output light <NUM> beam that is 2D-scanned in the angle space within some 2D FOV, as defined by angle scanning ranges of the SRs <NUM> and <NUM> and, possibly, aperture limitations of the beam routing optics of the projector <NUM>. The pupil expander <NUM> may then be used to expand the output pupil <NUM> of the projector for the viewer. The pupil expander <NUM> may be for example in the form of an optical waveguide with an input and output couplers, with the output couplers generally being greater in area that the input coupler or couplers. In one embodiment, the pupil expander <NUM> is an optical waveguide having one or more input grating as an input coupler and one or more output gratings as the output coupler, with the gratings configured to match the FOV of projector <NUM> to a range of angles of total internal reflection (TIR) provided by the waveguide. Although <FIG> shows a single projector <NUM> coupled to a single optical source <NUM> at its input and a single pupil expander at its output, it will be appreciated that in binocular NEDs a separate projector <NUM> coupled to its own light source <NUM> and its own pupil expander <NUM> may be used for each eye of the user.

The beam relay optics of a scanning projector according to some embodiments of the present disclosure may include, in addition to first and second SRs, a curved reflector, such as a concave mirror, which may cooperate with other optical elements of the projector to provide pupil relay, and at least one polarization beam splitter (PBS) to implement polarization controlled multi-pass beam routing. In some embodiments the PBS may be disposed in a triple-pass configuration to sequentially direct the input light beam toward a selected SR and a concave reflector in a first two passes, and to direct the beam reflected from the concave mirror or the SR toward either the second scanning stage or toward an output pupil in a third pass.

Referring now to <FIG> and <FIG>, there is illustrated an example scanning projector <NUM> that may be viewed as an embodiment of the two-stage scanning projector <NUM> generally described above. The scanning projector <NUM>, which may be referred hereinafter simply as projector <NUM>, implements, among other features, polarization-assisted multi-pass beam routing, providing two-stage pupil relay in a compact footprint. <FIG> illustrates a cross-section of projector <NUM> in a plane of incidence of an input beam <NUM> upon an input pupil <NUM> of the projector, while <FIG> illustrates projector <NUM> in projection on a plane orthogonal to the plane of incidence. In the following description a Cartesian coordinate system (x,y,z) <NUM> may be used, in which the input light beam <NUM> is incident upon the projector in the direction of the y-axis, and the two scanning stages of the projector are aligned generally in the z-axis direction. In the following description the input light beam <NUM>, as it traverses projector <NUM>, may be referred to as the input beam <NUM>, or as beam <NUM>, or simply as "the beam". Similarly to the projector <NUM> as generally described above, the input light beam <NUM> is passed through the two scanning stages in sequence, emerging from an output pupil <NUM> of the projector in the form of an output beam <NUM>. The first scanning stage includes a first SR <NUM>, while the second scanning stage includes a second SR <NUM>. The output beam <NUM>, which may be scanned with SRs <NUM> and <NUM> in sequence to produce an image, may also be referred to as the image beam <NUM>. In the illustrated embodiment the first SR <NUM> is operable to steer the beam in a first plane, while the second SR <NUM> is operable to steer the beam in a second plane that may differ from the first plane. In the illustrated example the first plane may be the plane of the figure, which is also the (z, y) plane of the Cartesian coordinate system <NUM>, while the second plane is generally orthogonal to the first plane, and may be described as an (x,y) plane of the coordinate system <NUM>. The first SR <NUM> may be a tiltable reflector (TR), such as a tiltable mirror, controlled by a first actuator <NUM> to tilt it about an axis <NUM> parallel to the x-axis. The second SR <NUM> may also be a TR controlled by a second actuator <NUM> to tilt it about an axis <NUM> parallel to the z-axis. In other embodiments the tilt axes of SRs <NUM>, <NUM> may have other relative orientations.

In the illustrated embodiment the routing optics of projector <NUM> includes a PBS in each of its two scanning stages, a first PBS <NUM> with a polarization routing surface <NUM> in the first scanning stage, and a second PBS <NUM> with a polarization routing surface <NUM> in the second scanning stage. The PBS <NUM>, <NUM> may be in the form of, or include, PBS cubes or prisms, but may also be embodied using other types of polarizers, for example using wire grid polarizers as the polarization routing surfaces <NUM>, <NUM>. The input pupil <NUM> may be defined by an optional input lens <NUM>. Input lens <NUM> may be disposed at an input of a first scanning stage of the projector, such as at an input face or side of the first PBS <NUM>. The beam relay of the projector may be formed with two curved reflectors, a first concave reflector <NUM> optically coupled to the first SR <NUM> via PBS <NUM>, and a second concave reflector <NUM> optically coupled to SR <NUM> via PBS <NUM>. The concave reflectors <NUM>, <NUM> may be each in the form of a concave mirror configured to fully, or at least partially, reflect incident light. At the first scanning stage, the first PBS <NUM> is disposed in a triple-pass configuration to direct the input light beam <NUM> toward the second scanning stage after sequential reflections from the first SR <NUM> and the first concave reflector <NUM>. At the second scanning stage, the second PBS <NUM> is disposed to receive the beam from the first scanning stage. The second PBS <NUM> is optically coupled to the second SR <NUM> and the second concave reflector <NUM> in a triple-pass configuration to direct the beam received from the first scanning stage, toward the output pupil <NUM> after consecutive reflections from the second SR <NUM> and the second concave reflector <NUM>. In the context of the present disclosure, "direct the beam" may include allowing the beam to propagate therethrough without a change of direction.

In order to provide the desired beam routing by the respective PBS <NUM> or <NUM>, one or more polarization converters, such as one or more waveplates, may be provided to convert the beam to an orthogonal polarization between consecutive passes through each of the PBS. In the illustrated embodiment, a quarter-wave plate (QWP) may be provided proximate to each of the reflectors <NUM>, <NUM>, <NUM> and <NUM>, so as to be passed by the beam both on the way to and from a respective reflector, thereby changing the polarization of the beam to an orthogonal polarization at each consecutive entrance of the PBS <NUM> or PBS <NUM>. More particularly, a first QWP <NUM> may be provided in the optical path between PBS <NUM> and SR <NUM>, a second QWP <NUM> may be provided in the optical path between PBS <NUM> and concave reflector <NUM>, a third QWP <NUM> may be provided in the optical path between PBS <NUM> and SR <NUM>, and a fourth QWP <NUM> may be provided in the optical path between PBS <NUM> and concave reflector <NUM>. In some embodiments QWPs <NUM> and <NUM> may be laminated onto respective PBS faces. In some embodiments QWPs <NUM> and <NUM> may be laminated on the respective concave mirrors.

The beam routing in projector <NUM> may be understood by considering the propagation of the input beam <NUM>, which is illustrated in the figure by its central ray shown with a dotted line. The input beam <NUM> enters the first stage of the projector through an input pupil <NUM> as polarized light of a first polarization state, which may be denoted as LP1. A polarization state orthogonal to LP1 may be denoted as LP2. In some embodiments, the polarization state LP1 may correspond to a linear p-polarization, as defined relative to its incidence upon the first polarization routing surface <NUM>, with the LP2 corresponding to the linear s-polarization. In some embodiments, the input light beam <NUM> may be provided in the desired LP1 polarization by a light source (not shown in <FIG>, <FIG>). In some embodiments an optional polarizer <NUM> may be provided at the input pupil <NUM> of projector <NUM> to output the input beam <NUM> that is LP1-polarized. The input pupil <NUM> may be defined at a first, or input, face or side of PBS <NUM>. The first PBS <NUM> may be configured to optically couple the input pupil <NUM> to SR <NUM> in LP1 polarization, and optically couple SR <NUM> to the concave reflector <NUM> in LP2 polarization. The second PBS <NUM> may be configured to optically couple SR <NUM> to the second concave reflector <NUM> in one of LP1 or LP2 polarization, and to optically couple the second concave reflector <NUM> to the output pupil <NUM> in the other of the LP1 or LP2 polarization. An LP1 to LP2 polarization converter <NUM>, such as a suitably oriented half-wave plate (HWP), may be optionally provided between an output face or side <NUM> of PBS <NUM> and an input face or side <NUM> of PBS <NUM>.

In the embodiment illustrated in <FIG> and <FIG>, the input light beam <NUM> is p-polarized at the input pupil <NUM>, and is transmitted toward SR <NUM> in a first pass through PBS <NUM>. After passing through QWP <NUM>, which is oriented to change the polarization of the beam to circular, the beam is reflected off the first SR <NUM>, which is shown for illustration in a tilted state. SR <NUM> steers the beam away from an input axis C1 by twice the first tilt angle θ<NUM> of SR <NUM> about an x-directed axis <NUM> (<FIG>) in accordance with the laws of reflection. The input beam <NUM> steered by SR <NUM> may be referred as the first steered beam 401A. The reflection off SR <NUM> directs the beam generally back toward the first PBS <NUM> for a second pass therethrough. Passing through QWP <NUM> for a second time changes the beam to s-polarization (or LP2).

The second pass through PBS <NUM> re-directs the beam, now in s-polarization, toward the first concave mirror <NUM> via the second QWP <NUM>. A reflection off the first concave mirror <NUM> directs the beam generally back toward PBS <NUM> via a second pass through QWP <NUM>, which changes the beam back to the p-polarization (LP1), which PBS <NUM> transmits through. Thus the third pass through the first PBS <NUM> directs the beam toward an output side or face <NUM> of PBS <NUM>. An input side <NUM> of the second PBS <NUM> may be located proximate to the output side or face <NUM> of PBS <NUM> to receive the beam therefrom. A half-wave plate <NUM> may be disposed between the output face or side <NUM> of PBS <NUM> and the input face or side <NUM> of PBS <NUM> to convert the beam to an orthogonal polarization.

In the illustrated embodiment, the beam reflected from the concave mirror <NUM> passes through PBS <NUM> as p-polarized light, is converted by the HWP <NUM> to s-polarized light, and is directed toward SR <NUM> by reflection off the polarization routing surface <NUM> in a first pass through PBS <NUM>. After passing through the third QWP <NUM>, which is oriented to change the polarization of the beam to circular, the beam is reflected off the second SR <NUM>, which steers the beam in accordance with its tilt angle θ<NUM> about a z-directed axis <NUM> (<FIG>). After being steered by the second SR <NUM>, the first steered beam 401A may be referred as the image beam 401B.

The reflection off SR <NUM> directs the beam generally back toward PBS <NUM> through the third QWP <NUM>, which changes the beam to p-polarization. The second pass through PBS <NUM> directs the beam through the polarization routing surface <NUM> and the fourth QWP <NUM> toward the second concave mirror <NUM>. A reflection off the second concave mirror <NUM> directs the beam generally back toward PBS <NUM> passing again through QWP <NUM>, which changes the beam to the s-polarization. The third pass through PBS <NUM> re-directs the s-polarized image beam 401B toward an output lens <NUM> and the output pupil <NUM> by reflection upon the polarization routing surface <NUM>.

Referring to <FIG>, the operation of pupil replication or pupil imaging optics of projector <NUM> in one embodiment thereof is illustrated. An input beam <NUM>, as it propagates through projector <NUM>, is schematically outlined with dotted lines, which in this figure indicate the beam "edges". Note that input beams that are narrower than illustrated could be used. The beam propagation is illustrated for nominal, i.e. not tilted, positions of SR <NUM> and <NUM> by way of example; in these SR positions, the beam may have a substantially normal incidence at each of the SRs <NUM> and <NUM>, and may also have on-axis incidence on the concave reflectors <NUM> and <NUM>. Here substantially normal means accounting for fabrication tolerance, generally within +\- <NUM>°, or in some embodiments within +\- <NUM>°. In the illustrated embodiment the pupil replication is focal, i.e. the input beam <NUM> is not collimated at the input pupil <NUM> of the projector, but converges at some location on a focal surface <NUM>, which may be within the projector's first stage or between the stages. Embodiments with a virtual focus surface <NUM> located behind the concave reflector <NUM> may also be envisioned. In the illustrated embodiment an input focusing lens <NUM> may be provided at the input facet or side of PBS <NUM> to provide a convergent beam that has a size S<NUM> at the light reflecting face of SR <NUM> in its nominal, not-tilted state. The input pupil <NUM> may be defined by a light-accepting face of lens <NUM>, or a central portion thereof. Si may represent, for example, the beam diameter at SR <NUM>. The light reflecting face of SR <NUM> defines a first pupil <NUM>, which size may be substantially S<NUM>/cos(θ1max) to avoid clipping the beam when the SR is tilted, or slightly large to account for tolerances, for example <NUM>% larger. Here, θ1max represents a maximum tilt angle of SR <NUM> expected during projector operation. In some embodiments the reflecting face of SR <NUM> may be elliptical.

The pupil replicating optics of projector <NUM> operates so as to make the location illuminated by beam <NUM> at the output pupil <NUM> substantially independent on the tilt angle θ<NUM> of the first SR <NUM> and the tilt angle θ<NUM> of the second SR <NUM> within their respective angular ranges of operation. It provides an image beam <NUM> emanating from the output pupil <NUM> that is capable of scanning in the angle space within the projector's FOV substantially without lateral spatial displacement of the beam at the output pupil <NUM>. Here substantially means accounting for system tolerances, generally with a lateral displacement less than <NUM>% of the diameter of image beam <NUM> and preferably less than <NUM>% of the diameter of the image beam in some embodiments.

In the illustrated embodiment the pupil replicating optics of projector <NUM> includes the input focusing lens <NUM>, two concave mirrors <NUM> and <NUM>, a second focusing lens <NUM> that may be disposed at the second SR <NUM>, and an output lens <NUM> disposed at the output pupil <NUM>. In some embodiments the output pupil <NUM> may be at a distance from lens <NUM>. The first concave mirror <NUM> and the second focusing lens <NUM>, which may be referred to as the first pupil replicating optics or the first pupil relay, cooperate to replicate or relay the first pupil <NUM> defined at SR <NUM> onto a second pupil <NUM> defined at SR <NUM>, so that the input beam <NUM> hits the light reflecting face of SR <NUM> for any tilt angle θ<NUM> of SR <NUM> within an operating range thereof, e.g. from -θ1max to + θ1max. By way of example, θ1max can be in the range from <NUM> to <NUM> degrees. The input lens <NUM> may cooperate with the concave mirror <NUM> to define the focal surface <NUM> where beam <NUM> converges after reflecting off the concave mirror <NUM>. Lens <NUM> may be configured to cooperate with the concave mirror <NUM> to image the first pupil <NUM> onto the second pupil <NUM> with a magnification X, in which case the second SR <NUM> may be greater in size than the first SR <NUM> by a factor of X (linear). The magnification factor X depends on the optical distance between SRs <NUM> and <NUM>, the radius of curvature of concave mirror <NUM>, and to some extent on the optical power of lens <NUM>, and may be suitably adjusted by varying one or more of these parameters. The magnification factor X may be greater than <NUM> when the optical path between SR <NUM> and the concave mirror <NUM> is shorter than the optical path between the concave mirror <NUM> and SR <NUM>. In some embodiments the optical power of the concave mirror <NUM> may be selected to image SR <NUM> to SR <NUM> with the magnification factor X. In embodiments in which the beam is relayed from the first SR <NUM> to the second SR <NUM> with magnification, the second SR <NUM> may be proportionally greater in size than the first SR <NUM>. By way of example, in a projector with the pupil magnification X between the first and second SRs <NUM> and <NUM>, the light reflecting face of SR <NUM>, which defines the second pupil <NUM>, may have a size of substantially X·S<NUM>/cos(θ2max), or slightly large to account for tolerances, for example <NUM>% larger. Here, θ2max represents a maximum tilt angle of SR <NUM> expected during projector operation. By way of example, θ2max can be in the range from <NUM> to <NUM> degrees. By way of a non-limiting example, X may be equal to <NUM> +-<NUM>%.

The second concave mirror <NUM> and the output lens <NUM> cooperate with the second focusing lens <NUM> to relay the second pupil <NUM> onto the output pupil <NUM>, and may be referred to as the second pupil relaying optics or the second pupil relay. The second focusing lens <NUM>, which may be shared with the first pupil relay, may cooperate with the second concave mirror <NUM> and the output lens <NUM> to image the second pupil <NUM> onto the output pupil <NUM>. In embodiments where lenses <NUM> and <NUM> are close to respective pupil planes, SR <NUM> may be imaged onto the output pupil <NUM> primarily by the optical power of the concave mirror <NUM>. The second pupil relaying optics may replicate or relay the second pupil <NUM> to the output pupil <NUM> either with or without magnification.

Advantageously, in embodiments where the SRs <NUM> and <NUM> are orthogonally oriented 1D scanners, the FOV of projector <NUM> may be adjusted independently in two orthogonal planes, which may correspond for example to the vertical and horizontal dimensions when used in a NED. When image beam 401B is steered by one of the first and second SRs <NUM>, <NUM>, the image beam 401B may scan across an input face of the output focusing lens <NUM>, changing the location of its incidence upon the lens. The output focusing lens <NUM> is configured to convert this change of location to a change in angle of the output beam <NUM>. This is schematically illustrated in <FIG>, which shows image beams 501B1 and 502B2, outlined by dotted and dashed lines, respectively, that are incident upon the output focusing lens <NUM>. The two image beams 501B1 and 501B2 may correspond to two different tilt angles of, for example, SR <NUM>, and may be spatially shifted relative to each other as they enter the output lens <NUM>. These two image beams are converted by lens <NUM> into output scanning beams 503a and 503b which substantially overlap at the output pupil <NUM> generally without a lateral shift therebetween, and emerge from it at different angles.

Referring to <FIG>, each of the SRs <NUM> and <NUM> may be for example in the form of a uni-axial MEMS scanner <NUM>, where "MEMS" stands for a micro electro-mechanical system. It includes a scanning reflector <NUM>, e.g. a mirror, supported by a pair of torsional hinges <NUM> allowing tilting the scanning reflector <NUM> about an "X" axis. The torsional hinges <NUM> extend from the scanning reflector <NUM> to a fixed base <NUM>, for tilting the scanning reflector <NUM> about "X" axis. Note that the "X" axis of <FIG> may represent either the x-axis or the z-axis of the Cartesian coordinate system <NUM> of <FIG> and <FIG>. Actuators may be disposed underneath the scanning reflector <NUM> for providing a force for actuating the tilt of the scanning reflector <NUM> about the "X" axis. The actuators may be electrostatic, electro-magnetic, piezoelectric, etc. For electrostatic mirror actuation, a comb drive may be located on the torsional hinge members. For example, in the embodiment shown in <FIG>, an actuator <NUM> may be disposed under an edge of reflector <NUM> to tilt the scanning reflector <NUM> about X-axis. In some embodiments a biaxial scanning reflector may be used, in which torsional hinges <NUM> extend from the scanning reflector <NUM> to a gimbal ring (not shown), which is supported by a second pair of torsional hinges (not shown) extending from the gimbal ring to the fixed base <NUM>, for tilting the gimbal ring and the scanning reflector <NUM> as a whole about "Y" axis.

A feedback circuit <NUM> may be provided for providing feedback information about the angles of tilt of the scanning reflector <NUM>. The feedback circuit <NUM> may for example measure electric capacitance between the electrostatic actuator <NUM> and the scanning reflector <NUM> to determine the tilt angle θ. Separate electrodes may also be provided specifically for the feedback circuit <NUM>. The capacitance may be measured via voltage measurements, and/or via a radio-frequency (RF) reflection from portion(s) of the scanning reflector <NUM> and a phase detector using, for example, a frequency mixer and low-pass filter. In some embodiments, a small magnet may be placed on the scanning reflector <NUM>, and a nearby pickup coil e.g. fixed to the base <NUM> may be used to pick oscillations of the scanning reflector <NUM>. Furthermore in some embodiments, an optical signal may be reflected from the scanning reflector <NUM> and a photodetector may be used to detect the reflected beam. The photodetector may or may not have spatial resolution. For spatial resolution detectors, a detector array or a quadrant detector may be used. Sync pulses or signals may be generated at specific angles of tilt of the scanning reflector <NUM>, e.g. when crossing a zero tilt angle.

In some embodiments, the first and second SRs <NUM> and <NUM> may be implemented using two 1D MEMS tiltable reflectors <NUM> supported by two different bases <NUM>. In some embodiments, the first and second SRs <NUM> and <NUM> may be implemented using two MEMS tiltable reflectors <NUM> supported by the same base <NUM>. In some embodiments, raster scan signals may be provided to each actuator <NUM> of the two tiltable reflectors <NUM> with non-parallel, e.g. orthogonal, tilt axes to implement a 2D raster scan pattern of the image beam. In some embodiments one or more tiltable reflectors <NUM> may be operated in a resonant mode for speed and energy efficiency. In the resonant mode of operation, a tiltable reflector <NUM> oscillates about its tilt axis at a near-resonance frequency, and the beam is pulse-modulated in time in accordance with an image pattern. In a pair of tiltable reflectors such as 1D MEMS scanners coupled via a pupil relay and oscillating about non-parallel axes, the oscillations are decoupled from one another, which simplifies the overall trajectory prediction.

It is noted that the 1D MEMS scanner <NUM> is only an example of a scanner implementation. Many other implementations are possible, including refractive and diffractive beam scanners. When implemented with MEMS, various comb structures may be used to provide an increased electrostatic attraction force between electrodes. Comb and/or honeycomb structures may be used to stiffen the tiltable reflector <NUM>. The tiltable reflector <NUM> may include a mirror surface, a multilayer dielectric reflector, etc. The tiltable reflector <NUM> may be located at the center of the 1D MEMS scanner <NUM>, or may be offset from the center if required. Two or more of 1D MEMS scanners with parallel and/or non-parallel, including orthogonal, tilt axes may be supported by the same base <NUM>.

Referring back to <FIG>, <FIG>, and <FIG>, the PBS <NUM> and <NUM> may be in the form of, or include, polarization splitting cubes or prisms with one of their optical axes aligned along a common optical axis C2, which may be parallel to the z-axis in <FIG>, <FIG>, with an output face <NUM> of PBS <NUM> proximate to an input face <NUM> of PBS <NUM> and parallel thereto. The polarization routing surfaces <NUM> and <NUM> may be oriented at <NUM> degrees to the common optical axis C2 of the two PBS. The PBS cubes or prisms embodying PBS <NUM> and <NUM> may be of the same size or of differing sizes. <FIG> and <FIG> illustrate an embodiment with optical magnification from SR <NUM> to SR <NUM>, as described above; in such embodiments, PBS <NUM> may be physically smaller than PBS <NUM> in at least one dimension as it routs a smaller-diameter beam.

Furthermore, in the example embodiment described above, SR <NUM> of the first steering stage is aligned with the input pupil <NUM> of the projector, and is coupled therewith in transmission for p-polarization, while being coupled to the first concave mirror <NUM> in reflection for s-polarization. The optical axis of the concave reflector <NUM>, defined by a vortex and a center of curvature thereof, may be generally perpendicular to the direction of the first pass of the input beam <NUM> through PBS <NUM>. However, in other embodiments the input pupil <NUM>, the first SR <NUM>, and the concave mirror <NUM> may be positioned differently relative to the output face <NUM> of PBS <NUM>. For example, in one embodiment the locations of SR <NUM> and concave mirror <NUM> may be switched, in which case the input light beam <NUM> may be s-polarized at the input pupil <NUM>. In another embodiment, the locations of the input pupil <NUM> and the first concave reflector <NUM> may be switched, with the input light beam <NUM> again in the s-polarization state as it enters PBS <NUM> for the first pass. Similarly, the positioning of SR <NUM>, output pupil <NUM>, and the second concave mirror <NUM> relative to PBS <NUM> in the second stage may be different from the example embodiment illustrated in <FIG>, <FIG>, and <FIG>.

Furthermore, in the example embodiment described above the respective polarization routing surfaces <NUM>, <NUM> of PBS <NUM> and <NUM> transmit p-polarized light and reflect s-polarized light. However, embodiments may be envisioned in which the polarization routing surfaces <NUM>, <NUM> of PBS <NUM> and <NUM> are configured to operate with other orthogonal pairs of polarization states. Furthermore, in some embodiments the respective polarization routing surfaces <NUM>, <NUM> of PBS <NUM> and <NUM> may not be parallel to each other.

Generally, the second SR <NUM> and the second concave mirror <NUM> may be positioned at any of five remaining "free" faces of PBS <NUM>, with the polarization routing surface <NUM> of the second PBS <NUM> suitably oriented to couple SR <NUM> to the input face <NUM> for one polarization state and to couple SR <NUM> to the second concave reflector <NUM> in the orthogonal polarization state. In some embodiments, the polarization routing surfaces <NUM>, <NUM> of PBS <NUM> and <NUM> may incline in different planes.

<FIG> illustrates an example embodiment 400A of projector <NUM> where the configuration of the second stage generally repeats that of the first stage with a <NUM> degree counter-clockwise rotation. In this example configuration, SR <NUM> is disposed at a PBS face <NUM> of PBS <NUM> across from the input PBS face <NUM> and is thus coupled thereto in transmission for p-polarized light. In this configuration, a HWP between PBS <NUM> and <NUM> is not needed. The second concave mirror <NUM> is disposed with its optical axis at <NUM> degrees from the common optical axis C2 of PBS <NUM> and <NUM>, and across from the output pupil <NUM>, so as to receive s-polarized image light steered by SR <NUM> after it is reflected by the polarization routing surface <NUM>. In the illustrated embodiment the input pupil <NUM> and the output pupil <NUM> are on the same side of the projector. In another embodiment PBS <NUM> may be rotated by <NUM> degrees about the C2 axis, so that the polarization routing surfaces <NUM>, <NUM> are parallel and the input pupil <NUM> and the output pupil <NUM> are on opposite sides of the projector.

Referring to <FIG>, the projector <NUM> may be used in an NED device <NUM>, referred to as NED <NUM> in the following, to generate a scanning image beam <NUM> that may be relayed to an eye <NUM> of a user to form an image for the user. In the illustrated embodiment the output pupil <NUM> of projector <NUM> is coupled to in input coupler <NUM> of a waveguide <NUM>, which also has one or more output couplers <NUM> which may be configured to expand the scanning image beam in size to provide an expanded image beam <NUM>. In this embodiment, the waveguide <NUM> operates as a pupil expander or pupil replicator. The input coupler <NUM> may be in the form of, or include, one or two diffraction gratings or one or two coupling prisms. It may be sized to match the output pupil <NUM> of projector <NUM>. The output coupler or couplers <NUM> may be for example in the form of one or more diffraction gratings, which in some embodiments may be holographically defined. By way of example, in one embodiment the input coupler <NUM> may be in the form, or include, a diffraction grating, such as a relief grating, with a grating vector g<NUM>, and the output coupler <NUM> may be in the form, or include, a first output diffraction grating with a grating vector g<NUM> and a second output diffraction grating with a grating vector g<NUM>, so that g<NUM>+g<NUM>+g<NUM>=<NUM>. In such embodiments, an output angle of the expanded output image beam <NUM> is equal to an angle at which the scanning image beam <NUM> from projector <NUM> impinges the input coupler <NUM>, so that the waveguide <NUM> relays the output FOV of projector <NUM> to the user's eye <NUM> one to one. NED <NUM> may include an image signal generating processor <NUM> that provides electrical images signals V1 and V2 to the first and second SRs <NUM> and <NUM>, respectively. These signals may define the beam steering angles of an output beam <NUM> of the projector in two orthogonal planes, which may correspond to the vertical and horizontal scanning directions of an output beam <NUM> of the NED. The electrical images signals V1 and V2 may be synchronized with color and intensity modulation of the input beam <NUM> so that the NED output beam <NUM> draws a 2D image in the angle space to be converted in a spatial image in the eye <NUM> of the user. Advantageously, performing the vertical and horizontal scanning of the image beam using two 1D scanners enables independent adjustment of their characteristics, such as pixel density, scan frequency, raster size, etc, and produce a more predictable raster scan pattern than that available from biaxial scanners operating at near-resonance.

Referring to <FIG>, there is illustrated a method <NUM> for scanning a light beam according to an embodiment of the present disclosure. In the flowchart, each box represents a step or operation that may be performed by a scanning projector example embodiment of which have been described above, or one or more elements thereof, and may be referred to generally as a step. The method may include providing an input light beam to a first SR at step <NUM>, steering the input light beam in at least a first plane with the first SR at step <NUM>, relaying the input light beam from the first SR onto a second SR at step <NUM>, steering the input light beam with the second SR in a second plane at step <NUM>, and at step <NUM> relaying the input light beam from the second scanning reflector upon an output pupil at an angle defined by tilt angles of the first and second scanning reflectors. In some embodiments, step <NUM> may include using a first PBS coupled to a first concave reflector. In some embodiments, step <NUM> may include using a second PBS coupled to a second concave reflector. Step or operation <NUM> may include providing a first electrical image signal to an actuator of the first SR, with the first SR steering the beam in the first plane by a first angle defined by the first electrical image signal. Step or operation <NUM> may include providing a second electrical image signal to an actuator of the second SR, with the first to steer the beam in a second plane by a second angle defined by the second electrical image signal. Step or operation <NUM> may be performed so that a position of the image beam at the output pupil is generally independent on tilt angles of the first and second scanning reflectors within operating tilt angle ranges thereof. In some embodiments the first plane may be orthogonal to the second plane. In some embodiments the first plane may correspond to a vertical plane of a two-dimensional FOV supported by the projector, and the second plane may correspond to a horizontal plane of the 2D FOV supported by the projector.

In some embodiments, at least one of the two SRs <NUM>, <NUM> may be configured as a 2D scanning reflector to scan the light beam it receives in two different, for example orthogonal, planes. A 2D SR may be implemented for example with a 2D tiltable reflector, such as a 2D MEMS reflector that is configured to tilt about two orthogonal axes. In one embodiment the first SR <NUM> may be implemented with a 2D TR that is operable to form a 2D image within an FOV defined in the angle space, and the second SR <NUM> as a 1D TR or a 2D TR operable to shift the FOV in the angle space, for example in response to a user-related or image-related signal. In some embodiments, these functions of the SR <NUM> and <NUM> may be switched.

Turning to <FIG>, a NED <NUM> includes a light source <NUM>, a scanning projector <NUM> coupled to an image light source <NUM>, and a pupil-replicating waveguide assembly <NUM> coupled to the scanning projector <NUM>. NED <NUM> may be an embodiment of NED <NUM> described above. The scanning projector <NUM> may be embodied as described above with reference to the scanning projectors of <FIG>, <FIG>, and <FIG>. In the embodiment shown in <FIG>, the scanning projector <NUM> includes first <NUM> and second <NUM> tiltable reflectors, e.g. MEMS reflectors tiltable about one or two axes. The tiltable reflectors <NUM> and <NUM> may represent the SRs <NUM> and <NUM> of the scanning projector <NUM> describe above. A controller <NUM> is operably coupled to the light source <NUM>, the first <NUM> and second <NUM> tiltable reflectors, and to an optional eye tracker <NUM>. The function of the eye tracker <NUM> is to determine at least one of position or orientation of a user's eye <NUM> in an eyebox <NUM>, from which a gaze direction of the user may be determined in real time.

In operation, the controller <NUM> operates the first <NUM> and second <NUM> tiltable reflectors to cause a light beam <NUM> at the exit pupil of the scanning projector <NUM> to have a beam angle corresponding to a pixel of an image to be displayed. The controller <NUM> operates the image light source <NUM> in coordination with the tiltable reflectors <NUM>, <NUM> to form an image in angular domain for displaying to the user. The pupil-replicating waveguide assembly <NUM> ensures that the image may be observed by the user's eye <NUM> at any position of the user's eye <NUM> in the eyebox <NUM>. In some embodiments, the eye tracker <NUM> is operated to determine the gaze direction of the user.

In embodiments where each tiltable reflector <NUM> and <NUM> is a 2D tiltable reflector, one of them, e.g. the first tiltable reflector <NUM>, may be operated to scan the light beam <NUM> in two non-parallel directions to form the image in the angular domain while the other, i.e. the second tiltable reflector <NUM>, may be operated to shift the entire image, i.e. to shift a FOV of the near-eye display <NUM>, towards the gaze direction of the user. The image being rendered by the controller <NUM> may be updated accordingly, i.e. shifted in opposite direction by the same amount, to make sure that the virtual image is steady as the FOV is shifted. The resulting effect of "floating" FOV is similar to viewing a dark scenery by using a flashlight, where the flashlight is automatically turned in a direction of user's gaze, illuminating different parts of a surrounding scenery depending where the user is looking at the moment. As the rate of FOV shift is determined by the eye mobility which is generally slower than speed of scanning, the first tiltable reflector <NUM> may be made smaller and faster, while the second tiltable reflector <NUM> may be made larger and slower. In some embodiment the second tiltable reflector <NUM> may be operable to shift the image in one dimension only, for example along a horizontal axis of the NED.

Embodiments of the present disclosure may include, or be implemented in conjunction with, an artificial reality system. An artificial reality system adjusts sensory information about outside world obtained through the senses such as visual information, audio, touch (somatosensation) information, acceleration, balance, etc., in some manner before presentation to a user. By way of non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include entirely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, somatic or haptic feedback, or some combination thereof. Any of this content may be presented in a single channel or in multiple channels, such as in a stereo video that produces a three-dimensional effect to the viewer. Furthermore, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, for example, create content in artificial reality and/or are otherwise used in (e.g., perform activities in) artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a wearable display such as an HMD connected to a host computer system, a standalone HMD, a near-eye display having a form factor of eyeglasses, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

Referring to <FIG>, an HMD <NUM> is an example of an AR/VR wearable display system which encloses the user's face, for a greater degree of immersion into the AR/VR environment. The function of the HMD <NUM> is to augment views of a physical, real-world environment with computer-generated imagery, and/or to generate the entirely virtual 3D imagery. The HMD <NUM> may include a front body <NUM> and a band <NUM>. The front body <NUM> is configured for placement in front of eyes of a user in a reliable and comfortable manner, and the band <NUM> may be stretched to secure the front body <NUM> on the user's head. A display system <NUM> may be disposed in the front body <NUM> for presenting AR/VR imagery to the user. The display system <NUM> may for example include two optical waveguides for relaying scanning image beams to the eyes of the user from scanning projectors <NUM>. Sides <NUM> of the front body <NUM> may be opaque or transparent.

In some embodiments, the front body <NUM> includes locators <NUM> and an inertial measurement unit (IMU) <NUM> for tracking acceleration of the HMD <NUM>, and position sensors <NUM> for tracking position of the HMD <NUM>. The IMU <NUM> is an electronic device that generates data indicating a position of the HMD <NUM> based on measurement signals received from one or more of position sensors <NUM>, which generate one or more measurement signals in response to motion of the HMD <NUM>. Examples of position sensors <NUM> include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU <NUM>, or some combination thereof. The position sensors <NUM> may be located external to the IMU <NUM>, internal to the IMU <NUM>, or some combination thereof.

The locators <NUM> are traced by an external imaging device of a virtual reality system, such that the virtual reality system can track the location and orientation of the entire HMD <NUM>. Information generated by the IMU <NUM> and the position sensors <NUM> may be compared with the position and orientation obtained by tracking the locators <NUM>, for improved tracking accuracy of position and orientation of the HMD <NUM>. Accurate position and orientation is important for presenting appropriate virtual scenery to the user as the latter moves and turns in 3D space.

The HMD <NUM> may further include a depth camera assembly (DCA) <NUM>, which captures data describing depth information of a local area surrounding some or all of the HMD <NUM>. To that end, the DCA <NUM> may include a laser radar (LIDAR), or a similar device. The depth information may be compared with the information from the IMU <NUM>, for better accuracy of determination of position and orientation of the HMD <NUM> in 3D space.

The HMD <NUM> may further include an eye tracking system for determining orientation and position of user's eyes in real time. The obtained position and orientation of the eyes also allows the HMD <NUM> to determine the gaze direction of the user and to adjust the image generated by the display system <NUM> accordingly. In one embodiment, the vergence, that is, the convergence angle of the user's eyes gaze, is determined. The determined gaze direction and vergence angle may also be used for real-time compensation of visual artifacts dependent on the angle of view and eye position. Furthermore, the determined vergence and gaze angles may be used for interaction with the user, highlighting objects, bringing objects to the foreground, creating additional objects or pointers, etc. An audio system may also be provided including e.g. a set of small speakers built into the front body <NUM>.

Referring to <FIG>, an AR/VR system <NUM> includes the HMD <NUM> of FIG. 11A, an external console <NUM> storing various AR/VR applications, setup and calibration procedures, 3D videos, etc., and an input/output (I/O) interface <NUM> for operating the console <NUM> and/or interacting with the AR/VR environment. The HMD <NUM> may be "tethered" to the console <NUM> with a physical cable, or connected to the console <NUM> via a wireless communication link such as Bluetooth®, Wi-Fi, etc. There may be multiple HMDs <NUM>, each having an associated I/O interface <NUM>, with each HMD <NUM> and I/O interface(s) <NUM> communicating with the console <NUM>. In alternative configurations, different and/or additional components may be included in the AR/VR system <NUM>. Additionally, functionality described in conjunction with one or more of the components shown in <FIG> and <FIG> may be distributed among the components in a different manner than described in conjunction with <FIG> and <FIG> in some embodiments. For example, some or all of the functionality of the console <NUM> may be provided by the HMD <NUM>, and vice versa. The HMD <NUM> may be provided with a processing module capable of achieving such functionality.

As described above with reference to <FIG>, the HMD <NUM> may include the eye tracking system <NUM> for tracking eye position and orientation, determining gaze angle and convergence angle, etc., the IMU <NUM> for determining position and orientation of the HMD <NUM> in 3D space, the DCA <NUM> for capturing the outside environment, the position sensor <NUM> for independently determining the position of the HMD <NUM>, and the display system <NUM> for displaying AR/VR content to the user. In some embodiments the display system <NUM> includes (<FIG>) a scanning projector <NUM>. The display system <NUM> may further include an optics block <NUM>, whose function may be to convey the images generated by the scanning projector <NUM> to the user's eye. The optics block may include various lenses, e.g. a refractive lens, a Fresnel lens, a diffractive lens, an active or passive Pancharatnam-Berry phase (PBP) lens, a liquid lens, a liquid crystal lens, etc., a pupil-replicating waveguide, grating structures, coatings, etc. The display system <NUM> may further include a varifocal module <NUM>, which may be a part of the optics block <NUM>.

The I/O interface <NUM> is a device that allows a user to send action requests and receive responses from the console <NUM>. An action request is a request to perform a particular action. For example, an action request may be an instruction to start or end capture of image or video data or an instruction to perform a particular action within an application. The I/O interface <NUM> may include one or more input devices, such as a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the action requests to the console <NUM>. An action request received by the I/O interface <NUM> is communicated to the console <NUM>, which performs an action corresponding to the action request. In some embodiments, the I/O interface <NUM> includes an IMU that captures calibration data indicating an estimated position of the I/O interface <NUM> relative to an initial position of the I/O interface <NUM>. In some embodiments, the I/O interface <NUM> may provide haptic feedback to the user in accordance with instructions received from the console <NUM>. For example, haptic feedback can be provided when an action request is received, or the console <NUM> communicates instructions to the I/O interface <NUM> causing the I/O interface <NUM> to generate haptic feedback when the console <NUM> performs an action.

The console <NUM> may provide content to the HMD <NUM> for processing in accordance with information received from one or more of: the IMU <NUM>, the DCA <NUM>, and the I/O interface <NUM>. In the example shown in <FIG>, the console <NUM> includes an application store <NUM>, a tracking module <NUM>, and a processing module <NUM>. Some embodiments of the console <NUM> may have different modules or components than those described in conjunction with <FIG>. Similarly, the functions further described below may be distributed among components of the console <NUM> in a different manner than described in conjunction with <FIG> and <FIG>.

The application store <NUM> may store one or more applications for execution by the console <NUM>. An application is a group of instructions that, when executed by a processor, generates content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the HMD <NUM> or the I/O interface <NUM>. Examples of applications include: gaming applications, presentation and conferencing applications, video playback applications, or other suitable applications.

The tracking module <NUM> may calibrate the AR/VR system <NUM> using one or more calibration parameters and may adjust one or more calibration parameters to reduce error in determination of the position of the HMD <NUM> or the I/O interface <NUM>. Calibration performed by the tracking module <NUM> also accounts for information received from the IMU <NUM> in the HMD <NUM> and/or an IMU included in the I/O interface <NUM>, if any. Additionally, if tracking of the HMD <NUM> is lost, the tracking module <NUM> may re-calibrate some or all of the AR/VR system <NUM>.

The tracking module <NUM> may track movements of the HMD <NUM> or of the I/O interface <NUM>, the IMU <NUM>, or some combination thereof. For example, the tracking module <NUM> may determine a position of a reference point of the HMD <NUM> in a mapping of a local area based on information from the HMD <NUM>. The tracking module <NUM> may also determine positions of the reference point of the HMD <NUM> or a reference point of the I/O interface <NUM> using data indicating a position of the HMD <NUM> from the IMU <NUM> or using data indicating a position of the I/O interface <NUM> from an IMU included in the I/O interface <NUM>, respectively. Furthermore, in some embodiments, the tracking module <NUM> may use portions of data indicating a position or the HMD <NUM> from the IMU <NUM> as well as representations of the local area from the DCA <NUM> to predict a future location of the HMD <NUM>. The tracking module <NUM> provides the estimated or predicted future position of the HMD <NUM> or the I/O interface <NUM> to the processing module <NUM>.

The processing module <NUM> may generate a 3D mapping of the area surrounding some or all of the HMD <NUM> ("local area") based on information received from the HMD <NUM>. In some embodiments, the processing module <NUM> determines depth information for the 3D mapping of the local area based on information received from the DCA <NUM> that is relevant for techniques used in computing depth. In various embodiments, the processing module <NUM> may use the depth information to update a model of the local area and generate content based in part on the updated model.

The processing module <NUM> executes applications within the AR/VR system <NUM> and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof, of the HMD <NUM> from the tracking module <NUM>. Based on the received information, the processing module <NUM> determines content to provide to the HMD <NUM> for presentation to the user. For example, if the received information indicates that the user has looked to the left, the processing module <NUM> generates content for the HMD <NUM> that mirrors the user's movement in a virtual environment or in an environment augmenting the local area with additional content. Additionally, the processing module <NUM> performs an action within an application executing on the console <NUM> in response to an action request received from the I/O interface <NUM> and provides feedback to the user that the action was performed. The provided feedback may be visual or audible feedback via the HMD <NUM> or haptic feedback via the I/O interface <NUM>.

In some embodiments, based on the eye tracking information (e.g., orientation of the user's eyes) received from the eye tracking system, the processing module <NUM> determines resolution of the content provided to the HMD <NUM> for presentation to the user using the scanning projector <NUM>. In some embodiments, the processing module <NUM> can further use the eye tracking information to adjust the image presented with the scanning projector1125 to prevent vergence-accommodation conflict and/or to offset optical distortions and aberrations.

Referring to <FIG>, a simplified block diagram of an example electronic system <NUM> is an example of a wearable display system for implementing some of the embodiments disclosed herein. The electronic system <NUM> may include one or more processors <NUM> and a memory <NUM>. Processor(s) <NUM> may be configured to execute instructions for performing operations and methods disclosed herein and can be, for example, a general-purpose processor or a microprocessor suitable for implementation within a portable electronic device. Processor(s) <NUM> may be communicatively coupled to a plurality of components within the electronic system <NUM>. To implement this communicative coupling, the processor(s) <NUM> may communicate with other illustrated components across a bus <NUM>. The bus <NUM> may be any subsystem adapted to transfer data within electronic system <NUM>. The bus <NUM> may include a plurality of computer buses and additional circuitry to transfer data.

The memory <NUM> may be operably coupled to the processor(s) <NUM>. In some embodiments, the memory <NUM> may be configured for short-term and/or long-term storage, and may be divided into several units. The memory <NUM> may be volatile, such as static random access memory (SRAM) and/or dynamic random access memory (DRAM) and/or non-volatile, such as read-only memory (ROM), flash memory, and the like. Furthermore, the memory <NUM> may include removable storage devices, such as secure digital (SD) cards. The memory <NUM> may provide storage of computer-readable instructions, data structures, program modules, and other data for the electronic system <NUM>. In some embodiments, the memory <NUM> may be distributed in different hardware modules. A set of instructions and/or code might be stored on the memory <NUM>. The instructions might take the form of executable code that may be executable by the electronic system <NUM>, and/or might take the form of source and/or installable code, which, upon compilation and/or installation on the electronic system <NUM> (e.g., using any of a variety of generally available compilers, installation programs, compression/decompression utilities, etc.), may take the form of executable code.

In some embodiments, the memory <NUM> may store a plurality of application modules <NUM> to <NUM>, which may include any number of applications. Examples of applications may include gaming applications, presentation or conferencing applications, video playback applications, or other suitable applications. The applications may include a depth sensing function and/or an eye tracking function. The application modules <NUM> to <NUM> may include particular instructions to be executed by processor(s) <NUM>. In some embodiments, certain applications or parts of the application modules <NUM> to <NUM> may be executable by other hardware modules <NUM>. In certain embodiments, the memory <NUM> may additionally include secure memory, which may include additional security controls to prevent copying or other unauthorized access to secure information.

In some embodiments, the memory <NUM> may include an operating system <NUM> loaded therein. The operating system <NUM> may be operable to initiate the execution of the instructions provided by the application modules <NUM> to <NUM> and/or manage the other hardware modules <NUM>, as well as interfaces with a wireless communication subsystem <NUM>, which may include one or more wireless transceivers. The operating system <NUM> may be adapted to perform other operations across the components of the electronic system <NUM> including threading, resource management, data storage control, and other similar functionality.

The wireless communication subsystem <NUM> may include, for example, an infrared communication device, a wireless communication device and/or a chipset (such as a Bluetooth® device, an IEEE <NUM> device, a Wi-Fi device, a WiMax device, cellular communication facilities, etc.), and/or similar communication interfaces. The electronic system <NUM> may include one or more antennas <NUM> for wireless communication as part of the wireless communication subsystem <NUM> or as a separate component coupled to any portion of the electronic system <NUM>. Depending on the desired functionality, the wireless communication subsystem <NUM> may include separate transceivers to communicate with base transceiver stations and other wireless devices and access points, which may include communicating with different data networks and/or network types, such as wireless wide-area networks (WWANs), wireless local area networks (WLANs), or wireless personal area networks (WPANs). A WWAN may be, for example, a WiMax (IEEE <NUM>) network. A WLAN may be, for example, an IEEE <NUM>. 11x network. A WPAN may be, for example, a Bluetooth network, an IEEE <NUM>. 15x, or some other types of network. The techniques described herein may also be used for any combination of WWAN, WLAN, and/or WPAN. The wireless communications subsystem <NUM> may permit data to be exchanged with a network, other computer systems, and/or any other devices described herein. The wireless communication subsystem <NUM> may include a means for transmitting or receiving data, such as identifiers of HMD devices, position data, a geographic map, a heat map, photos, or videos, using the antenna(s) <NUM> and wireless link(s) <NUM>. The wireless communication subsystem <NUM>, the processor(s) <NUM>, and the memory <NUM> may together comprise at least a part of one or more of a means for performing some functions disclosed herein.

In some embodiments, the electronic system <NUM> includes one or more sensors <NUM>. The sensor(s) <NUM> may include, for example, an image sensor, an accelerometer, a pressure sensor, a temperature sensor, a proximity sensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a module that combines an accelerometer and a gyroscope), an ambient light sensor, or any other similar module operable to provide sensory output and/or receive sensory input, such as a depth sensor or a position sensor. For example, in some implementations, the sensor(s) <NUM> may include one or more inertial measurement units (IMUs) and/or one or more position sensors. An IMU may generate calibration data indicating an estimated position of the HMD device relative to an initial position of the HMD device, based on measurement signals received from one or more of the position sensors. A position sensor may generate one or more measurement signals in response to motion of the HMD device. Examples of the position sensors may include, but are not limited to, one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU, or some combination thereof. The position sensors may be located external to the IMU, internal to the IMU, or some combination thereof. At least some sensors may use a structured light pattern for sensing.

The electronic system <NUM> may further include a display module <NUM>. The display module <NUM> may be a near-eye display, and may graphically present information such as images, videos, and various instructions, from the electronic system <NUM> to a user. Such information may be derived from one or more of the application modules <NUM> to <NUM>, a virtual reality engine <NUM>, the one or more other hardware modules <NUM>, a combination thereof, or any other suitable means for resolving graphical content for the user (e.g., by the operating system <NUM>). The display module <NUM> may include scanning display technology, for example using a two-stage scanning projector as described above.

The electronic system <NUM> may further include a user input/output module <NUM> allowing a user to send action requests to the electronic system <NUM>. An action request may be a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application. The user input/output module <NUM> may include one or more input devices. Example input devices may include a touchscreen, a touch pad, microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the received action requests to the electronic system <NUM>. In some embodiments, the user input/output module <NUM> may provide haptic feedback to the user in accordance with instructions received from the electronic system <NUM>. For example, the haptic feedback may be provided when an action request is received or has been performed.

The electronic system <NUM> may include a camera <NUM> that may be used to take photos or videos of a user, for example, for tracking the user's eye position. The camera <NUM> may also be used to take photos or videos of the environment, for example, for VR, AR, or MR applications. The camera <NUM> may include, for example, a complementary metal-oxide-semiconductor (CMOS) image sensor, e.g. a silicon sensor, with a few millions or tens of millions of pixels. In some implementations, the camera <NUM> may include two or more cameras that may be used to capture 3D images.

In some embodiments, the electronic system <NUM> may include a plurality of other hardware modules <NUM>. Each of other the hardware modules <NUM> may be a physical module within the electronic system <NUM>. While each of the other hardware modules <NUM> may be permanently configured as a structure, some of other hardware modules <NUM> may be temporarily configured to perform specific functions or temporarily activated. Examples of the other hardware modules <NUM> may include, for example, an audio output and/or input module (e.g., a microphone or speaker), a near field communication (NFC) module, a rechargeable battery, a battery management system, a wired/wireless battery charging system, etc. In some embodiments, one or more functions of the other hardware modules <NUM> may be implemented in software.

In some embodiments, the memory <NUM> of the electronic system <NUM> may also store the virtual reality engine <NUM>. The virtual reality engine <NUM> may include an executable code of applications within the electronic system <NUM>. The virtual reality engine <NUM> may receive position information, acceleration information, velocity information, predicted future positions, or some combination thereof of the HMD device from the various sensors. In some embodiments, the information received by the virtual reality engine <NUM> may be used for producing a signal to the display module <NUM>. For example, if the received information indicates that the user has looked to the left, the virtual reality engine <NUM> may generate content for the wearable display device that mirrors the user's movement in a virtual environment. Additionally, the virtual reality engine <NUM> may perform an action within an application in response to an action request received from user input/output module <NUM> and provide feedback to the user. The provided feedback may be visual, audible, or haptic feedback. In some implementations, the processor(s) <NUM> may include one or more GPUs that may execute the virtual reality engine <NUM>.

The above-described hardware and modules may be implemented on a single device or on multiple devices that can communicate with one another using wired or wireless connections. For example, in some implementations, some components or modules, such as GPUs, the virtual reality engine <NUM>, and applications such as, for example, a headset calibration application and/or eye-tracking application, may be implemented on a console separate from the head-mounted display device. In some implementations, one console may be connected to or support more than one wearable display device.

In some implementations, different and/or additional components may be included in the electronic system <NUM>. Similarly, functionality of one or more of the components can be distributed among the components in a manner different from the manner described above. For example, in some embodiments, the electronic system <NUM> may be modified to include other system environments, such as an AR system environment and/or an MR environment.

Claim 1:
A scanning projector (<NUM>, <NUM>) for a display apparatus, the scanning projector comprising:
a first scanning reflector (<NUM>, <NUM>) configured to steer a light beam in at least a first plane;
a second scanning reflector (<NUM>, <NUM>) configured to steer the light beam received from the first scanning reflector in at least a second plane; and
beam relay optics (<NUM>, <NUM>) configured to relay a first pupil (<NUM>, <NUM>) defined at the first scanning reflector to a second pupil (<NUM>) defined at the second scanning reflector, and to relay the second pupil to an output pupil (<NUM>, <NUM>) of the scanning projector,
wherein the beam relay optics comprises a first polarization beam splitter, PBS, (<NUM>) and a first concave reflector (<NUM>) coupled to the first PBS, wherein the first PBS is disposed in a triple-pass configuration for routing the light beam sequentially to the first scanning reflector and to the first concave reflector in a first two passes, and toward the second scanning reflector in a third pass, and
wherein the first PBS is disposed to direct the light beam sequentially to the first scanning reflector in a first pass and to the first concave reflector in a second pass, the beam relay optics further comprising a second PBS (<NUM>) and a second concave reflector (<NUM>) coupled to the second PBS, wherein the second PBS is disposed in a triple-pass configuration to direct the light beam received from the first PBS sequentially toward the second scanning reflector and toward the second concave reflector in a first two passes through the second PBS, and toward the output pupil in a third pass.