BEAM

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application

S/N 62/863300 entitled“WEARABLE DISPLAY FOR NEAR-TO-EYE VIEWING WITH EXPANDED BEAM” in the names of David Kessler and Adam J. Davis, filed 19 June 2019 and incorporated herein in its entirety. Reference is made to commonly assigned co-pending U.S. Patent Application Publication US2018/0149862 by Kessler et al. and entitled“WEARABLE DISPLAY FOR NEAR-TO-EYE

VIEWING”.

TECHNICAL FIELD

The present disclosure relates generally to near-to-eye displays and more particularly to a display that employs an imaging apparatus that employs a pupil relay configuration having concentric design.

BACKGROUND

There have been a number of solutions proposed for providing image content from wearable devices. Various types of goggles, glasses, and other apparatus have been described for displaying image content to a viewer who is wearing the apparatus. These devices may be completely immersive, so that the viewer sees only images generated by the apparatus and has no ability to see the outside world when wearing the device, thus providing virtual reality (VR) display. Alternately, varying degrees of visibility of the real world are provided with other designs, so that the generated images are superimposed on the real-world image as an augmented reality (AR) or mixed reality (MR) display or, in some way, used to complement the real-world visual content that lies in the viewer's field of view.

Wearable display devices offer considerable promise for providing information and displaying complementary imagery that can improve performance and efficiency in a number of fields and can help to enhance a viewer's understanding of visual content that lies in the field of view. In medicine and dentistry, for example, the capability to view image content that had been previously stored and, optionally, post processed, or is currently being acquired from another vantage point can help the practitioner to more accurately obtain detailed data that would aid diagnosis and treatment. Imaging data that is currently available only from high-cost 3-D imaging systems can be provided in a usable format for viewing on less expensive wearable imaging equipment that allows the practitioner to have this information in an active clinical setting. Stereoscopic imaging, with its enhanced spatial understanding and improved presentation of relevant detail, can be particularly useful for those treating patients using medical imaging guidance or medical data, as well as for those skilled in other fields. In addition, even the presentation of non-stereoscopic 2-D image content, provided by eyewear that allows clear visibility of the primary visual field without obstruction, can be useful for various functions, including uses in patient monitoring as well as tele-medicine and in remote diagnostic or therapeutic guidance, as well as in industrial, consumer electronics, and other applications.

With many of the apparatus that have been proposed for wearable displays, the viewer is encumbered by the device in some way, due to device size, bulkiness and discomfort, component and image positioning, poor image quality, eye fatigue, and other difficulties. Although many clever solutions for providing a more natural viewing experience have been outlined, and a number of advances toward improved image quality have been introduced, the form factors for many of these solutions still make it difficult to win broad-based acceptance for these devices, particularly for long-term use or during work or recreational activity. Their bulky size and appearance are still considered to be significant factors in limiting the appeal of wearable imaging devices for many people.

Despite years of design effort and optimization, including integration of miniaturization and improved imaging technologies, designing wearable display apparatus with acceptable ergonomics and high image quality has proved to be a continuing challenge. Workable solutions for wearable display devices that have a natural "feel" and that can be easily worn and used remain elusive. Thus, it can be appreciated that there is a need for a wearable device for single-eye or bilateral eye 2D or bilateral eye stereoscopic display that provides high image quality and is lightweight, inexpensive, easy to use, and ergonomically less invasive and cumbersome than conventional designs and provides enhanced display opportunities without obstructing or diminishing the primary visual field.

SUMMARY

It is an object of the present disclosure to advance the art of direct, virtual retinal display, more generally known as virtual image presentation for virtual reality viewing from a wearable apparatus. Embodiments of the present disclosure provide a wearable viewing apparatus that provides suitable image quality with little or no impediment to viewer visibility over the field of view. Embodiments of the present disclosure can provide an improved viewing apparatus that reduces a number of optical, physiological, and ergonomic constraints of conventional head-mounted displays (HMDs). Embodiments of the present disclosure can provide a wearable viewing apparatus having increased field of view with versatile arrangements of scanning, beam width adjustment, multi-focal light field, and related optical components in an ultra-near-to-eye imaging arrangement, including embodiments with optical components encroaching within the object focal length of the eye.

These objects are given only by way of illustrative example, and such objects may be exemplary of one or more embodiments of the disclosure.

The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects.

Other desirable objectives and advantages inherently achieved by the disclosure may occur or become apparent to those skilled in the art. The invention is defined by appended claims.

According to one aspect of the present disclosure, there is provided an optical apparatus for near-eye viewing comprising an optical apparatus worn by a viewer and comprising:

a laser light source energizable to direct a modulated beam toward a scan mirror;

an objective lens in the path of the modulated beam directed toward the scan mirror, wherein the objective lens and the scan mirror define a curved focal surface for the scanned, modulated beam, wherein the curved focal surface has a focal surface center of curvature at the scan mirror;

a numerical aperture (NA) expander, with no optical power, having an expansion surface that conforms to the defined curved focal surface in position and in curvature and that increases the NA of the scanned, modulated beam; and

pupil relay optics disposed to relay an entrance pupil at the scan mirror to an exit pupil at an eye lens of the viewer, the pupil relay optics defining an optical path between the entrance and exit pupils, the optical path comprising:

(i) a curved mirror surface disposed to transmit substantially half of the light incident from the modulated beam and that has a first center of curvature at the entrance pupil; and

(ii) a first polarizer disposed in the optical path to receive light from the scan mirror and formed to reflect incident light of a first polarization toward the curved mirror surface and to transmit incident light of a second polarization, orthogonal to the first polarization, wherein the optical path defined by the pupil relay optics directs the modulated light beam twice to the first polarizer, and wherein the modulated light beam incident the second time on the first polarizer is collimated and directed toward the exit pupil.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the disclosure will be apparent from the following more particular description of the embodiments of the disclosure, as illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other.

FIG. 1 A is a schematic top view that shows the horizontal field of view of a viewer.

FIG. IB is a schematic side view that shows the vertical field of view of a standing viewer looking forward, with normal and peripheral fields of view.

FIG. 1C is a schematic side view that shows the vertical field of view of a seated viewer looking forward, with normal and peripheral fields of view.

FIG. ID is a cross section view showing portions of the eye and object and image focal lengths of the eye.

FIG. IE is a schematic diagram that shows components of an image source according to an embodiment of the present disclosure.

FIG. IF is a schematic diagram showing a conventional“pancake” design for an eyepiece of an imaging apparatus.

FIG. 2A is a perspective view that shows components of a pupil relay in an imaging apparatus for near-eye viewing according to an embodiment of the present disclosure.

FIG. 2B is a side view that shows components of an imaging apparatus for near-eye viewing according to a pupil relay embodiment of the present disclosure.

FIG. 2C is a side view of an alternate embodiment of a pupil relay for near-eye viewing.

FIGs. 3 A and 3B are schematic views showing input optics for scanning and prefocusing according to an embodiment of the present disclosure.

FIG. 3C lists surface and lens characteristics for the input optics. FIG. 4A shows a side view of a configuration for an imaging apparatus for near-eye viewing using a pupil relay with a "pancake" optical configuration.

FIG. 4B lists surface and lens characteristics for the refractive configuration of FIG. 4 A.

FIG. 4C shows a perspective view of configuration for an imaging apparatus for near-eye viewing using a pupil relay.

FIG. 4D shows a side view of the configuration of FIG. 4A.

FIG. 4E shows a top view of the configuration of FIG. 4A.

FIG. 4F shows the system with a folded optical path.

FIG. 4G is an exploded side view of the configuration of FIG. 4A.

FIG. 4H is a perspective view of the configuration of FIG. 4 A.

FIG. 5 is a perspective view of the configuration of FIG. 4A.

FIGs. 6 and 7 show side and front views, respectively, of an imaging apparatus on the face of a viewer.

FIG. 8A shows schematic side view of a symmetrical arrangement with a beam splitter used to correct distortion.

FIG. 8B shows a perspective exploded view of the arrangement of

FIG. 8A.

FIG. 8C shows keystone distortion that can occur due to scanning for the embodiment of FIG. 4A if not corrected.

FIG. 8D shows correction achieved for this distortion.

FIG. 9A is a schematic diagram that shows a pupil relay apparatus that utilizes a concentric numerical aperture (NA) expander.

FIG. 9B is a schematic diagram showing how the NA expander changes the angular characteristics of the scanned imaging beam.

FIGs. 10A and 10B show curvature, thickness, and materials data for a pupil relay apparatus according to an embodiment.

FIG. 11 is a schematic diagram that shows an improved input beam shaper to the scanning system. FIG. 12 is a schematic diagram that shows a pupil imaging apparatus having an improved scanning system.

FIG. 13 is a perspective view that shows an image generator with an NA expander concentric with a scan mirror.

FIG. 14 is a perspective view showing an embodiment having a cylindrically curved circular polarizer disposed in the optical path.

FIG. 15 is a side view diagram that shows an optional actuator that provides mechanical motion to the NA expander.

FIG. 16 shows a progression, in simplified form, using light field imaging to change the apparent location of the virtual image that is formed by pancake imaging optics.

FIG. 17 is a side view diagram that shows functional components of an imaging apparatus that uses a virtual retinal display with multiple focal lengths to provide light field imaging.

DETAILED DESCRIPTION

Figures provided herein are given in order to illustrate principles of operation and component relationships along their respective optical paths according to the present disclosure and are not drawn with intent to show actual size or scale. Some exaggeration may be necessary in order to emphasize basic structural relationships or principles of operation. Some conventional components that would be needed for implementation of the described embodiments, such as support components used for providing power, for packaging, and for mounting, for example, are not shown in the drawings in order to simplify description. In the drawings and text that follow, like components are designated with like reference numerals, and similar descriptions concerning components and arrangement, or interaction of components already described may be omitted.

Where they are used, the terms“first”,“second”, and so on, do not necessarily denote any ordinal or priority relation, but may be used for more clearly distinguishing one element or time interval from another. The term“plurality” means at least two.

In the context of the present disclosure, the term“energizable” describes a component or device that is enabled to perform a function upon receiving power and, optionally, upon also receiving an enabling signal.

In the context of the present disclosure, positional terms such as“top” and“bottom”,“upward” and“downward”, and similar expressions are used descriptively, to differentiate different surfaces or views of an assembly or structure and do not describe any necessary orientation of the assembly in an optical apparatus. The terms "upstream" and "downstream" as used herein have their conventional usage and refer to relative positions of light or light-conditioning or redirecting components as the light proceeds along an optical path.

In the context of the present disclosure, the term“coupled” is intended to indicate a mechanical association, connection, relation, or linking, between two or more components, such that the disposition of one component affects the spatial disposition of a component to which it is coupled. For mechanical coupling, two components need not be in direct contact, but can be linked through one or more intermediary components.

In the context of the present disclosure, the term "left eye image" describes a virtual image that is formed in the left eye of the viewer and a "right eye image" describes a corresponding virtual image that is formed in the right eye of the viewer. The phrases "left eye" and "right eye" may be used as adjectives to distinguish imaging components for forming each image of a stereoscopic image pair, as the concept is widely understood by those skilled in the stereoscopic imaging arts.

An optical pupil relay system defines an optical axis and an optical path that transfers a beam incident at a first pupil at a first position to a second pupil position. That is, the scanned beams coming out of the aperture at the first position are all directed to overlap at the second position, either at a 1 : 1 size ratio or with possible magnification. In embodiments of the present disclosure, no pupil magnification is required; pupil relay optics described herein can be 1:1 relays.

Additional magnification can be provided, however. The beams are not identical at the respective first and second pupil positions; at the entrance pupil to the relay system, beams are divergent and at the exit pupil, beams are collimated. In a pupil relay system, the input and exit pupils are clearly defined by the optical components.

It is well known that optical systems have two sets of major conjugate surfaces. A first set of conjugate surfaces comprises the object and image surfaces of the optical system; a second set of conjugate surfaces comprises the entrance pupil and the exit pupil. By default, when imaging is discussed, it is understood that the conjugate surfaces are the object and the image surface.

The term“pupil relay”, as used in the optical arts and in the instant disclosure, is used to emphasize that the main function of the optical system is to image the entrance pupil to the exit pupil. Imaging can be achieved with a system using pupil relay optics; however, the principles of operation are based on relay of a first pupil to a second pupil, as is familiar to those skilled in the optical design arts. The requirements for aberration correction for an optical system differ, depending on whether the system is an object-to-image imager or a pupil relay. Since an imaging system is commonly used with incoherent light, phase differences between object points is of little or no interest. In a pupil relay, however, the phase at the entrance pupil is a consideration. Typically, a pupil relay accepts a collimated beam centered at the entrance pupil at some field angle, and provides an output beam, usually collimated and centered at the exit pupil, and with no degradation of the phase of the input beam.

Two sets of aberrations may need to be corrected, corresponding to the two sets of conjugates, as is well known to those skilled in optical design. Among those skilled in optics, the set of aberrations associated with the conjugation of the entrance pupil to the exit pupil are termed“pupil aberrations”. For example, a well- known imaging system is the“Offner system” disclosed in U.S. Patent No. 3,748,015 to Offner entitled“Unit Power Imaging Catoptric Anastigmat”. The Offner system is designed to be corrected over an arc at the image plane. It is not corrected, however, as a relay, and an incoming collimated beam, even if on axis, will be strongly degraded. US 8,274,720 by Kessler, entitled“Concentric Afocal Beam Relay,” discusses the steps and significant modifications needed for conversion of the Offner imager to an afocal pupil relay.

It is noteworthy that most pupil relays are afocal. That is, for pupil relays, both the input beam and the output beam are collimated. The system typically has no power but is usually composed of two groups, both with optical power, wherein each of the groups of optics is focal. The combination of the two groups results in an afocal relay in the same way that an afocal Keplerian telescope is composed of two positive groups with an intermediate focal plane, where the two groups are significantly separated by their two focal distances.

Pupil relays for embodiments of the present disclosure are focal. A focal pupil relay defines an optical path that accepts a focused input beam and outputs a collimated beam. In general, the focal pupil relay includes multiple lens elements and related optical components that can be formed into a small number of groups, with grouped elements cemented together or clustered together in close proximity. This characteristic makes the focal pupil relay compact, when compared to afocal relays that use separated groups, such as mirrors. An example of an afocal relay is given in US Patent Application Publication No. 2011/0242635 by Oka. It should be noted that the optical path tracks the optical axis but is not necessarily collinear with the optical axis at each point. The optical axis can be a single, undeviated line that connects the two pupils or may be folded and have a number of line segments having different directions, such as using mirrors or reflective polarizer optics, as described in subsequent embodiments.

A characteristic of the pupil relay, as compared with imaging optics in general, is that the input and exit pupils are clearly defined by the optical system geometry. The focal pupil relay optics of the present disclosure performs two functions of particular significance to the imaging task: (i) conjugates the entrance pupil, at which a scanner mirror is positioned, with the exit pupil, at the position of the iris or lens of the viewer's eye; and (ii) collimates the curved input focal surface.

By comparison with the focal pupil relay, an afocal relay provides only the first function (i), conjugation of entrance and exit pupils. Collimation is not provided with the afocal relay, since the input beam is already collimated, and the relay system has no optical power.

The term“oblique”, where used in the present disclosure, describes an angular relationship that is not parallel or normal, that is, other than an integer multiple of 90 degrees. In practice, two optical surfaces are considered to be oblique with respect to each other if they are offset from parallel or normal by at least about +/- 2 degrees or more. Similarly, a line and a plane are considered to be oblique to each other if they are offset from parallel or normal by at least about +1- 2 degrees or more. Substantially parallel planes are parallel to within +/- 2 degrees. Likewise, substantially parallel beams are parallel to within about +/- 2 degrees. In the context of the present disclosure, the term "about", when used with reference to a measurement, means within expected tolerances for measurement error and inaccuracy that are accepted in practice. Some reasonable tolerance must be allowed, for example, for measurement differences in determining the extent of a particular viewer's visual field, as it would vary from the measurement of one practitioner to another.

Microelectromechanical systems (MEMS) devices include a number of mechanical components that provide systems of miniaturized mechanical and electro-mechanical elements (that is, devices and structures) that are made using microfabrication techniques analogous to those used for forming semiconductor devices. MEMS devices can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics. In a MEMS device, at least some of the elements have a mechanical function, whether or not the elements are themselves movable. MEMS devices can alternately be termed "micro-machined devices" or devices formed and operating using microsystems technologies. Physical dimensions of individual MEMS elements can range from well below one micron to several millimeters. In the context of the present disclosure, MEMS devices provide mechanically movable elements, such as reflectors, that are energizable to temporally and spatially modulate light in order to provide a virtual image using a raster scan pattern.

In contrast to methods for forming a real image, a virtual image is not formed on a display surface. That is, if a display surface were positioned at the perceived location of a virtual image, no image would be formed on that surface. A virtual image is formed by an optical system that also determines viewing parameters such as far point, apparent angular width, and other characteristics. Virtual image display has a number of inherent advantages for augmented reality and virtual reality viewing. For example, the size of a virtual image is not limited by the size or location of a display surface. Additionally, the source object for a virtual image may be small; a magnifying glass, as a simple example, provides a virtual image of its object. It is known that, in comparison with systems that project a real image, a more realistic viewing experience can be provided by forming a virtual image that is disposed to appear some distance away. Providing a virtual image using only modulated light also obviates any need to compensate for screen or other display artifacts, as may be necessary when forming a real image.

In conventional use, the term "field of view" (FOV) broadly relates to the overall visual field that is available to a viewer with relatively normal eyesight under daylight viewing conditions. Field of view is typically measured in orthogonal horizontal and vertical directions. FIG. 1 A shows how angular portions of the horizontal field of view are defined according to the present disclosure. Horizontal monocular visual limits are generally considered to be slightly in excess of 120 degrees, centered about a central horizontal line of sight SI, as bounded between lines 16 and 18. Symbol recognition in the horizontal FOV is generally considered to be in the area about +/- 30 degrees from horizontal line of sight SI, as bounded between lines 56 and 58.

The vertical field of view, as this measurement is referred to herein, is shown schematically in FIG. IB. A horizontal line of sight SI is defined, extending generally at about 0 degrees to horizontal for a viewer who is standing, varying from true horizontal by no more than about +/- 2 degrees. The horizontal line of sight has been defined as the primary position of the eyes with the retinal plane co-planar with the transverse visual head plane (TVHP). This TVHP is the center of rotation of the eye, the oculomolar nucleus, and the calcarine cortex. It is defined as having a constant relationship to the canthomeatal line and is perpendicular to Listing's plane.

It is known to those skilled in human anatomical studies that, for the alert human being of normal build, the primary position of the eyes is a natural constant position that is anatomically defined and is not dependent on factors such as gravity, fixation, fusion reflex, or head position. For a human subject, the principal horizontal retinal plane is coplanar with the TVHP. This defines the primary position of the eyes, and by extension the primary horizontal plane of vision and it is well described in the medical literature (Jampel and Shi,“The Primary Position of the Eyes, The Resetting Saccade and the Transverse Visual Head Plane”, Investigative Ophthalmology and Visual Science, Vol 33, No.8, July 1992, page 2501). It is defined within The Dictionary of Optometry and Visual Science, 8 ^th Edition, Michel Milodot, Elsevier 2019.

The lull vertical FOV for an adult viewer having normal vision generally extends from about 60 degrees above (expressed as +60 degrees) to about 75 degrees below horizontal (expressed as -75 degrees); the normal "usable" vertical field of view (FOV) FI for display of a virtual image is typically considered to be defined within the range of angles from + 25 degrees above to -30 degrees below the horizontal line of sight SI.

Different portions of the field of view can be distinguished from each other. Foveal vision, having the highest visual acuity due to the greatest retinal cone density, encompasses the central portion of the human visual field. This region uses approximately 50% of our optical pathway. Parafoveal vision, providing high quality acuity and color vision as well, due to a high retinal cone concentration, is thus generally considered to be at an angle a that is within no more than about +/- 5 degrees of the line of sight. The approximately ten-degree parafoveal visual field is generally circular about the line of sight with about a four-inch diameter at a distance of 22 inches. As an approximation for an adult viewer, this region would be slightly smaller than the surface of a standard compact disc (CD) or digital video disc (DVD) held out at arm's length. Outside of this region, the visual field is considered to be peripheral and provides increasingly less visual information. Due to the retinal rod distribution of the human eye, the bulk of peripheral visual information lies within about the first 20 degrees beyond the parafoveal field of view.

For the embodiments described herein, a normal usable vertical FOV FI is larger than the parafoveal FOV and is defined as being within the range from about + 25 to -30 degrees of the line of sight. FOV FI is considered generally to be within the limits of color discrimination, which degrades substantially for vision angles increasingly outside this region. FIGs. IB and 1C show the lower portion of the normal vertical FOV FI, below forward horizontal line of sight SI, as bound within an angle Q of horizontal line of sight SI. The region that lies within the +60 to -75 degree vertical visual limits of the viewer but in the regions above or below the normal vertical FOV FI is considered to be the "vertical peripheral vision" field or, simply, a peripheral vertical field with upper and lower portions F2A, F2B, respectively.

FIG. IB shows the two portions of the peripheral vertical field, an upper portion F2A above the line of sight SI and a corresponding lower portion F2B below horizontal line of sight SI . Upper portion F2A lies between about 60 degrees from line of sight SI, shown by a line 12, and the upper definition of FOV FI which is about 25-30 degrees above line of sight SI . A lower portion F2B of the peripheral vertical field lies below FOV FI which extends down to about -30 degrees; portion F2B is bounded by about -75 degrees from line of sight SI, shown by a line 14.

Thus, lower portion F2B of the peripheral vertical FOV lies between about -30 and - 75 degrees relative to horizontal light of sight SI.

Line of sight SI generally tracks head position. For a seated viewer, for example, the reference line of sight SI tends to shift downwards to about 15 degrees from horizontal. All of the other vertical coordinates and angles that define parafoveal and peripheral fields shift accordingly, as is shown schematically in FIG. 1C. In the context of the present disclosure, the reference line of sight SI for vertical fields is considered to correspond to the horizontal for a standing viewer, tilted to about 15 degrees from horizontal for a seated viewer. This line of sight is termed a horizontal line of sight in the description that follows.

As shown in the cross-sectional side view of FIG. ID, the optics system of the human eye E, considered as an optical component primarily with lens 24 and cornea 28, has focal lengths that are determined by the geometry of the lens 24, cornea 28, and the surrounding medium. For an adult with normal, uncorrected vision, the eye E has a front focal length F ₀ of about 16.7mm. The normal, uncorrected adult human eye E has a rear focal length Fi of about 22.3mm. The front focal length F ₀ is in air; the rear focal length Fi is within the refractive liquid medium of the eye E, which effectively shortens the actual optical distance dimensions as shown in FIG. ID. The iris, which forms the pupil of the eye as an imaging system and limits the aperture to less than about 7mm, is not shown for clarity in FIG. ID. Under bright light conditions, the pupil diameter controlled by the iris averages only about 2.5mm. A "normal" eye can focus parallel light rays from a distant object onto the retina 26, with the parallel rays considered to be at infinity, to a point on the retina 26 at the back of the eye E, where processing of the visual information begins. As an object is brought close to the eye E, however, the muscles change the shape of the lens 24 so that rays form an inverted real image on the retina 26. The theoretical region of focus in front of the lens at 16.7mm is the object image zone, generally at the lower limit of normal physiologic focus.

The schematic block diagram of FIG. IE shows components of an image generator 212 for forming a modulated beam according to an embodiment of the present disclosure. A control logic processor 20 obtains image data, either from a memory or from some other image source, such as via wireless transmission (e.g. Bluetooth), and provides the necessary timing and control signals for forming the image in each eye of the viewer. Control logic processor 20 is in signal

communication with a light module 30 and modulates the light from module 30 in order to provide color image content. Frequency, duration, intensity and color modulation is provided. According to an embodiment, light module 30 provides modulated light from red, green, and blue laser diodes 32r, 32g, and 32b,

respectively, coupled along an optical path and through an optional objective lens LI 0 to a light guide, such as an optical fiber 40. The modulated beam is

characterized by pulses of laser light of variable color, duration and intensity. This light must be raster-scanned in order to form a recognizable image. Optical fiber 40 directs the source light to a MEMS scanner apparatus 50, such as through an optional collimator lens L12. The optional collimator lens L12 can alter focus in addition to beam size. Optional beam expanders can alternately be used. When energized, the MEMS scanner apparatus 50 scans by reflecting the light from optical fiber 40 through input lens 240, described in more detail subsequently, in a raster scanning pattern. Power is provided by a power source 22, such as a battery.

In embodiments that provide stereoscopic imaging, an optical fiber 40 and scanner apparatus 50 can be provided for each eye E. (Only the system for a single eye E is shown in FIG. IE for clarity.) The same light module 30 can be used to generate images for both eyes, such as synchronously generating left- and right-eye modulated light; alternately, each eye E can have a separate light module 30, with appropriate image processing logic, provided by control logic processor 20 and appropriate light handling components for the optical path that forms each left-eye and right-eye image.

Light module 30 can be a commercially available modular component for generating a modulated beam of light according to input image data, such as a pico-projector device from Microvision, Inc., Redmond, WA for example. By way of example only, this device forms an image using light from three primary color laser diodes, at 638 nm (Red), 517 nm (Green), and 450 nm (Blue). Other wavelengths can be used for primary colors. The lasers can be low-power Class 1 devices, whose light can be directed toward the eye of a viewer without concern for energy levels that are considered to be harmful. Light from each of the primary color lasers can be provided separately, so that red, green, and blue beams are provided in rapid sequence. Alternately beams of the different primary wavelengths are combined for forming the color image. Techniques for beam combination include the use of multilayered dichroic combiners, for example. Spot sizes for the light beams can be varied from each other, such as for improved efficiency. The light beams can be collimated to provide the smallest optimal size or enlarged to overfill a small or large MEMS scanning mirror, as described in more detail subsequently. Beams can be converted from a generally Gaussian profile to a flat-top profile for improved beam homogeneity.

An exemplary optical fiber 40 can be a single-mode optical fiber. This type of light guide can be easily fitted into the band that is used for fitting the scanner apparatus 50 against the viewer's face, as described subsequently. The optical fiber can have an angled or otherwise shaped termination, such as to help prevent back reflection. A single fiber can be used for guiding light from all of the laser diodes 32r, 32g, 32b. Alternately, three fibers can be used, spliced together to form a single fiber at the light output at scanner apparatus 50.

The optical components of scanner apparatus 50 used in a particular wearable imaging apparatus can vary and may include, in addition to a MEMS scanner device, alternate types of reflective and refractive relay optics, folding optics that may or may not provide optical power, and other components that are used to scan image content into eye E. Alternate components that may be part of scanner apparatus 50 are described with reference to subsequent embodiments of the present disclosure.

The schematic diagram of FIG. IF shows an exploded view of a conventional "pancake" optical system 90 of an eyepiece intended for forming an image for a viewer. The catadioptric pancake optical system uses polarization for folding the light path of the modulated beam back upon itself and employs reflective focusing optics with a curved mirror Ml. Curved mirror Ml defines an optical axis OA. The conventional image source 60 is a cathode-ray tube or other planar emissive surface that provides a two-dimensional (2-D) image field. In any implementation of this optic arrangement, Image source 60 is positioned to form an image at the front focal surface of a curved mirror Ml . A collimated beam is provided to the eye E from every field point. For the conventional pancake optics design, magnification is very large and can be considered to be effectively infinity.

The pancake system 90 shown in FIG. IF works as follows:

unpolarized light of a modulated beam from the CRT or other image source 60 is linearly polarized by polarizer POL1 and converted to a left-hand circularly polarized light by quarter wave plate QWP1. The light goes through semi-transparent curved mirror Ml; half of the light is reflected and lost. Mirror Ml is considered to be "partially transmissive" or "semi-transmissive" or "semi-transparent", so that it transmits at least about 35% of the incident light from QWP1, preferably transmitting 50% of the incident light and reflecting 50% for peak efficiency. For embodiments of the present disclosure, a curved mirror can be considered "partially transmissive" or "semi-transparent" if the mirror does not transmit more than 65% of the incident light.

The transmitted circularly polarized light goes through another QWP2 to become vertically linearly polarized light and is directed to a reflective polarizer, polarization beam splitter PBS1, which reflects most of the light back towards the curved mirror Ml . Reflected light from PBS1 transits QWP2 again to become right- hand circularly polarized. The curved mirror Ml again reflects about half of the light and loses the other half from transmission. The reflected polarized light from mirror Ml is now left-hand circularly polarized and is converted by quarter wave plate QWP2 into horizontally polarized light, passing through the reflective polarizer or polarization beam splitter PBS1 and through an optional cleaning polarizer POL3 into the eye E of the viewer. Each transit of the light through a quarter wave plate (QWP) retards the phase by a 90 degree phase shift, changing polarization state.

In spite of seemingly complex polarization and light-directing mechanisms, pancake optics function well, but with the penalty of considerable loss of more than 75% of the light originally generated from the light source 60. This inefficiency and substantial loss of light makes the pancake optical configuration unusable for many applications with conventional sources of modulated light. The Applicants, however, have recognized that this optical configuration can be useful given the high levels of light attenuation using lasers with MEMs modulation, in which it is desirable to limit the light energy provided to the viewer eye box. Advantageously, this configuration uses the mirror on axis, without the need to provide other means for separating the input beams into the mirror from the output beams. Folding of the optical path is optional, rather than a requirement.

Unlike earlier optical systems that employ pancake optics as a type of objective lens for a flat-panel image source, embodiments of the present disclosure use the pancake optical approach to form a pupil relay. Embodiments described following apply a number of approaches to render the pancake design as a more suitable platform for near-to-eye imaging, different from the flat imaging optics of earlier pancake optical systems, designed to use scanned, collimated light and hence surmounting problems related to low light efficiency and high parts count. Expansion of the numerical aperture, as described in detail subsequently, allows wider entrance and exit pupils than other imaging apparatus using collimated laser light with a MEMS device, thereby allowing the advantages provided by a flat image field.

The embodiments that follow further enable the pancake optics design to have the advantage of higher resolution over a larger field of view (FOV) as compared to a tilted mirror system. The pancake optical design of the present disclosure is smaller, and, while ultra near-to-eye in position, provides improved eye relief as compared to single mirror system using a splitter and provides a number of advantages not available with the conventional flat-panel imaging design shown in FIG. IF.

Embodiment #1

The perspective view of FIG. 2A and side view of FIG. 2B show components of an imaging apparatus 200 for near-eye viewing using a 1 : 1 pupil relay apparatus 250 arrangement according to an embodiment of the present disclosure.

This embodiment employs an optical "pancake" configuration as an optical relay system, using reflective components for beam shaping and focus, that defines an optical axis and relays the entrance pupil to the exit pupil. With the arrangement shown in FIGs. 2A and 2B, imaging apparatus 200 relays an entrance pupil PI at image generator 212 to an exit pupil P2 at the eye E of the viewer. Alternately stated, imaging apparatus 200 conveys a curved image at a focal surface 214 (wherein the generated image at focal surface 214 occupies the "object" position relative to the optics) to an image field at retina R. That is, in addition to its role as pupil relay optics, apparatus 200 also images, to retina R, a curved aerial "object", the light pattern or“image” that is generated by the focused, scanned modulated beam from image generator 212, formed at focal surface 214.

An image generator 212 is provided by a scan mirror at an entrance pupil PI that directs a focused modulated beam of light to form curved aerial image at focal surface 214 as the optical "object" for subsequent imaging by imaging apparatus 200. The modulated light at the aerial image is linearly polarized and is directed to a polarizer 210 that transmits light of a first polarization and reflects light of a second polarization that is orthogonal to the first polarization. The transmitted modulated light is directed through a quarter wave plate 216 which provides the corresponding phase retardance and to a curved mirror 220 that is partially reflective (nominally 50% reflective), partially transmissive (nominally 50% transmissive) and that serves as a type of beam splitter, focusing the modulated beam of light. Reflection of a portion of the light from mirror 220 reverses the circular polarization of the light, which transmits through the quarter wave plate 216 when traveling in the opposite direction. Light transmitted through mirror 220 polarizes, absorbed by circular polarizer 230. Light reflected from mirror 220 has changed circular polarization and is reflected from polarizer 210 and back through quarter wave plate 216. A portion of this light travels through curved mirror 220 and transmits through for cleaning by optional circular polarizer 230. This cleaning helps to remove any leaked light having the orthogonal polarization that could cause image ghosting. The collimated light from imaging apparatus 200 is directed through the eye E of the viewer and to an exit pupil P2 and, ultimately, to the retina R of the viewer, forming an image as shown. The pancake optical system of FIG. 2B is a pupil relay apparatus 250 having elements 210, 216, 220, and 230 similar to the FIG. 2A arrangement. In this first embodiment there is air space between the components, thus the term“air pancake” can be applied to this optical arrangement.

Polarizer 210, disposed in the path of light from the scan mirror is formed to transmit incident light of a first polarization, incident at a first angle that is divergent with respect to optical axis OA, toward the curved mirror 220 surface. Polarizer 210 then reflects incident light from mirror 220 of a second polarization that is orthogonal to the first polarization of the transmitted incident light and at a second angle with respect to a normal to the polarizer surface. The polarizer 210 and curved mirror 220 are disposed along the optical path to cooperate, directing the modulated beam to polarizer 210 twice. Polarizer 210 is thus in the path of light to and from the curved mirror 220 and folds the optical path back toward curved mirror 220. The light that exits the polarizer the second time is collimated and directed toward pupil P2 and convergent with respect to an optical axis OA.

Unlike conventional arrangements wherein the pancake configuration forms an eyepiece to collimate the flat-panel source, embodiments of the present disclosure use the pancake optics to relay the scanning mirror 212 in FIG.2B to the iris 232 of the observer. The pancake optics form a pupil relay, wherein the entrance pupil PI on FIG. 2 A is at the scanning mirror and P2 is the exit pupil at the eye. The pancake pupil magnification here is finite, preferably about -1 (minus one), for example.

The curved image at focal surface 214 and mirror 220 are substantially concentric with respect to pupil PI, defined by curved mirror 220, with the image at focal surface 214 and mirror 220 sharing a center or axis of curvature at image generator 212. The axis of rotation of the scan mirror of the image generator 212 and the center of curvature of the curved mirror 220 lie along the same line.

In the context of the present disclosure, two features are considered "substantially concentric" with respect to a pupil PI or P2 when they share the same common axis of, and center of curvature to within 20% of the larger radial distance of the two curved features, so that any slight difference in distance between their respective centers of curvature is less than 20% of the larger radial distance from that axis or center.

Polarizers 210 and 230 can be, for example, wire grid polarizers, such as devices from Moxtek Inc., Orem, UT. Alternately, conventional polarizers could be employed.

The design of the optical path that is defined by the pupil relay optics of the embodiments of the present disclosure is essentially aberration-free. The off- axis beams encounter exactly the same optics as the on-axis beam and thus there are no off-axis aberrations such as coma, astigmatism, and distortion which commonly limit the performance of optical systems. Thus, this display system is capable of providing large FOV. According to an embodiment, the system shown in FIGs.2A and 2B has a FOV of 43 degrees horizontally by 25 degrees vertically. It is emphasized that this is one example only. Larger or smaller FOV could be created using oscillating MEMS mirrors and lenses having different specifications and performance.

Note that in both FIGs. 2A and 2B, the retina R is represented ideally as a flat surface, since the eye lens in this model is represented as an ideal paraxial lens. When the eye is represented using a more realistic eye model, the retina is represented as a curved retina.

The embodiment shown in FIGs.2A and 2B can also be used with the one to one pupil relay with the curvature of mirror 220 reversed along the optical axis OA as shown in FIG. 2C. In pupil relay apparatus 260, the aerial image formed at focal surface 214 is of circularly polarized light. Nominally half of the light is rejected by the semi-transparent curved mirror 220 and half is transmitted. The transmitted portion passes through QWP 216 to become linearly polarized and is thus reflected from reflective polarizer 210 back to the curved mirror 220. This light is collimated and directed back to pupil P2 through polarizer 210, in the orthogonal polarization which transmits through the polarizer 210 towards iris 232. An optional cleaning polarizer 236 can be used to eliminate light of the wrong polarization that may have leaked through the reflective polarizer. Curved mirror 220 has its radius of curvature centered at or centric with pupil P2. As with the FIG. 2A embodiment, the light first incident on polarizer 210 is divergent with respect to optical axis OA. The light incident on polarizer 210 the second time is collimated and directed along optical axis OA.

According to alternate embodiments using the FIGs. 2A-2C arrangement, curved mirror 220 is not a 50-50 semi-transparent mirror, but acts as a curved reflective polarizer, transmitting light of a first polarization and reflecting light of the orthogonal polarization state. Flat reflective polarizer 210 is replaced with a semitransparent mirror. One skilled in the imaging arts can appreciate that additional variations are possible using the curved mirror 220 as reflective polarizer and using a flat, semi-transparent mirror.

Input optics

The side schematic view of FIG. 3 A and unfolded view of FIG. 3B show input optics 240 that pre-focus the light that is directed through polarizer 210 and other components of the pupil relay in various embodiments of the present disclosure. An objective lens 244 is positioned in the path of the generated modulated light beam that is directed to scan mirror 242. Lens 244 conditions the modulated light by expanding the input beam and focusing it to a position between the scan mirror 242 and the pupil relay, defining and forming focal surface 214 (FIGs. 2 A, 2B) according to the scanning pattern. Objective lens 244 can consist of two elements, in the form of a cemented doublet or spaced apart, as shown subsequently. An off-the-shelf doublet can be used to correct for the axial color of the relay, assuming that three laser beams or more at different wavelengths are used. Since the rest of the system is symmetrical and reflective, and with the axial color corrected by the input optics, there are no axial or lateral color aberrations in FIG. 3A and 3B embodiments. Enhanced embodiments described subsequently add a low power cylindrical lens prior to the doublet which compensates for astigmatism that is induced by the use of a tilted polarizing beam splitter with an angle of inclination with respect to the optical axis OA.

With respect to the embodiments shown in FIGs. 2A, 2B, 2C and following, input optics 240 focus the light to form the curved aerial image at focal surface 214.

A scanning mirror 242 can be used to fold the optical path and to form a 2-D image from the directed light beam.

By way of example only, FIG. 3C lists surface and lens characteristics for input optics 240 according to an embodiment of the present disclosure.

The light source can be a scanned laser or other solid-state light source.

Embodiment #2

FIGs. 4A through 4H and FIG. 5 show different views of an all-glass pancake configuration for a pupil relay apparatus 450 in an imaging apparatus 400 for near-eye viewing according to an embodiment of the present disclosure. As with the previous embodiment of FIGs. 2A and 2B, apparatus 450 is a finite conjugate pupil relay working at a magnification of about -1. Focal surface 414 and curved input surface 92 of lens LI are substantially concentric with respect to pupil PI . The output surface 420 of lens LI and output surface 94 of lens L3 are substantially concentric with respect to pupil P2. In the optical path defined by pupil relay apparatus 450, polarizer 430 receives light of a first polarization that is at a divergent angle with respect to optical axis OA and reflects this light back toward partially reflective curved surface 420 formed on lens L2, which focuses the light. Two transits through QWP 424 change the polarization of the light beam to a second polarization state, orthogonal to the first polarization state at polarizer 430. Polarizer 430 transmits the returned light, now collimated and directed toward pupil P2.

Some or all portions of pupil relay apparatus 450 can be positioned within the object focal length of the eye, 16.7mm. This capability applies for other pupil relay apparatus embodiments described subsequently. This ultra near-to-eye position provides important advantages for reducing size and“footprint” of the device while maintaining large FOV and avoiding obstruction of the usable field of view.

FIG. 4B lists exemplary lens and polarizer surfaces for imaging apparatus 400 according to an embodiment of the present disclosure.

FIG. 4C is a perspective view showing imaging apparatus 400 with input optics 240 disposed at one side of scanning mirror 242.

Lenses LI, L2, and L3 may not be spherical in an embodiment of the present disclosure. FIG. 4D shows a vertical view of imaging apparatus 400.

Scanning is in the direction orthogonal to the plane of the page.

FIG. 4E shows a horizontal view of imaging apparatus 400. Scanning is in the horizontal direction, in the plane parallel to the page.

As shown in FIG. 4F, the optical path can be folded in order to reduce the overall length and device footprint. Folding mirrors 454, 456 are shown by way of example.

FIG. 4G shows an exploded view of the pancake arrangement of pupil relay apparatus 450 of FIG.4A, showing polarization states along the optical path that is defined by this optical system. Scanning mirror 412 at entrance pupil PI directs light to form the curved aerial object at focal surface 414. The light is circularly polarized, either being circularly polarized at the input beam or entering as linearly polarized light and rendered to circular polarization by an optional quarter wave plate (QWP) after the scanner mirror 412 (not shown). This light is refracted through first lens LI and through a partially reflective surface 420 to a second lens L2. The light then goes through quarter waveplate QWP 424 and becomes linearly polarized (shown as vertically polarized in FIG. 4G). This light encounters reflective polarizer 430 and reflects back towards surface 420 passing again through QWP 424. About half of the light is then reflected by the semi-transparent surface 420. The reflection off the curved 420 surface of lens L2 collimates the beam which originated from its focused location as the aerial light pattern formed at focal surface 414. The collimated light then goes through QWP 424 the third time and becomes linearly polarized (shown as horizontally polarized light in FIG. 4G.) This light passes through polarizer 430 and a third lens L3. This output light is directed from surface 420 to an iris 440 at exit pupil P2. Optionally a cleaning linear absorptive polarizer (not shown) can be placed between lens L3 and the iris at pupil P2. Focal surface 414 and input surface 96 of lens LI are substantially concentric with entrance pupil PI. Output surfaces 98 and 100 and mirror surface 420 are substantially concentric with pupil P2. Iris 440 is at pupil P2. Focal surface 414 is at the front focal surface of mirror 420, reflected through polarizer 430.

FIGs. 4H and 5 show perspective views of pupil relay apparatus 450.

FIGs. 6 and 7 show side and front views, respectively, of imaging apparatus 400 on the face of a viewer. A conventional mount, such as an eyeglass frame, band, or other structure (not shown) can be provided for positioning imaging apparatus 400 very near to the viewer's eye, so that optical components of the imaging apparatus lie within the object focal length of the eye lens, within 8-16 mm from the cornea. The housing that contains the scanning mirror and optical apparatus lies predominantly outside the usable vertical field of the wearer, substantially within the peripheral visual field, as these fields are described in detail previously. The housing can lie against the face of the viewer, along the cheek, stabilized along the inferior orbital rim and supported by the maxillary bone, nasion, and zygoma.

Symmetrical embodiment

The schematic side view of FIG. 8 A and perspective view of FIG. 8B show a symmetrical arrangement modification of the imaging system of 4A, with a beam splitter 110. Beam splitter 110, which can be a polarization beam splitter, helps to correct keystone distortion. When the input beam approaches the scan mirror 242 at an angle, as in Fig 4C, keystone distortion can be induced, as shown for an outline of the image field in FIG. 8C. FIG. 8C shows uncorrected keystone distortion with a 43 by 25-degree field of view when the incidence angle is 25 degrees from the axis. The dashed line indicates a distortion free field. This distortion can be corrected by electronically modifying the image data sent to the imaging system or by adding a slight aspheric distortion correcting element (not shown) between scan mirror 242 and relay 450 optics. Beam splitter 110 defines a light path with zero angle incidence into scanning mirror 242 and the distortion shown on Fig. 8C is then reduced and made more symmetrical, as shown on Fig. 8D. Objective lens 244 has two lens elements, spaced apart by an air gap. An optional quarter wave plate 246 helps to reduce losses from beam splitter 110 when provided as a polarization beam splitter PBS. A second quarter wave plate 248 changes the light from beam splitter 110 back to circularly polarized light. Mirror 220 can be a semi-transmissive mirror, as mirror surface 420 on Fig. 4A, followed by another quarter wave plate 252. Reflected on- axis light from mirror 220 is reflected from beamsplitter 110 and discarded. Elements LI, mirror 220, quarter wave plate 252, and polarizer 230 may be a single cemented unit. There may be an air gap between the cemented unit and lens L2.

According to an embodiment shown in FIGs. 8A and 8B, the incoming modulated beam from the light module 30 is S-polarized. In the optical path defined by pupil relay apparatus 450, this light is reflected from polarization beam splitter 110 and directed to scan mirror 242 through quarter wave plate (QWP) 246, becoming circularly polarized. The scan mirror 242 reflects the modulated beam back through QWP 246, changing the polarization of the modulated beam to the P-polarization state. P-polarized light is then transmitted through beam splitter 110 and through QWP 248, which changes the polarization state to circularly polarized. This light is conveyed through lens LI . A portion of the light is reflected back along the optical axis OA from semi-transmissive mirror 220. This reflected light again transits QWP 248 and becomes S-polarized, so that it is reflected from beam splitter 110 and discarded. The portion of the modulated beam that transmits through semi transmissive mirror 220, meanwhile, goes through another QWP 252, which changes its polarization to S-polarization state. This divergent light is reflected by polarizer 230 and is then reflected from mirror 220, now collimated and directed toward pupil P2. The collimated, modulated light, upon transiting QWP 252 a second time, is changed to P-polarization and transmits through polarizer 230 and to output lens L2. The apparatus of the present disclosure provides an optical apparatus that is suited for virtual reality (VR) or augmented reality (AR) viewing, as well as for mixed reality (MR) and smart glass“reference display” viewing. AR and MR viewing can be achieved by using a“pass-through” technique that superimposes video content from the real world (optionally acquired by video capture equipment included in the eyewear product) upon the computer-generated data, for example images, icons, and text. Thus, two different alternative views of real-world scene content can be provided.

The imaging arrangement is essentially aberration free due to its optical symmetry. The apparatus is distinct from AR or VR optical configurations based on the use of an eyepiece, such as using catoptric optics, as well as from refractive optics systems that collimate and magnify a flat-panel image source such as an LCOS (Liquid crystal on silicon) display or a device that forms an image using an array of micromirror devices or an array of LEDs or other emitters.

An embodiment of the present disclosure provides an FOV of at least about 40 degrees along the horizontal axis, with a beam of light that is enlarged in width over a scanned light embodiment. Eye tracking could be used to detect and to compensate for viewer eye movement as well as an indicator or sensor for turning the power on and off, for example, if the view is not looking at the device.

According to an embodiment of the present disclosure, there is provided an optical apparatus for near-to-eye viewing or ultra near-to-eye viewing comprising: a laser light source energizable to direct a beam to a scan mirror; a curved mirror surface optically concentric with the scan mirror and partially transmissive; a first polarizer disposed between the scan mirror and the curved mirror surface, the first polarizer having a first polarization axis; a quarter wave plate disposed between the polarizer and the curved mirror surface; and a second polarizer disposed downstream from the curved mirror and having a second polarization axis that is orthogonal to the first polarization axis. The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects.

The hybrid catadioptric approach provided by the“pancake” optical design, further described in detail in commonly assigned U.S. Patent Application

Publication No. 2018/0149862, entitled“Wearable Display for Near-to-Eye Viewing” by Kessler and Davis affords a number of advantages for reducing the size of the device, improving ergonomics, allowing for positioning that is not obstructive to the usable field of view as well as improving image quality, and eliminating or

wearable optics. However, for optical apparatus based on the pancake design there are some inherent shortcomings that can make it difficult to improve the overall usability for the wearer. Among these drawbacks inherent to the pancake model are the following:

(i) Small eye box or exit pupil size. The system optics define a small eye box region over which the viewer’s eye can perceive the full image field. The use of a small scanning mirror at the entrance pupil, wherein the mirror is small enough to have sufficient speed to refresh the display multiple times a second, limits the size of its conjugate exit pupil at the eye box. A larger eye box is beneficial, allowing more latitude for positioning the viewer’s eye and compensating for normal eye saccadic movement. Height and width dimensions of the eye box are primarily a factor of the exit pupil; the larger the exit pupil, the larger the corresponding height and width of the eye box.

(ii) Size of the optical system. Improved performance comes at the cost of increased size and complexity. A goal is to keep the optical system small and lightweight to allow positioning against the face with minimal support.

(iii) Requirements imposed by polarized light. The light that is input to the system optics must be circularly polarized. Ideally, the light source itself provides circularly polarized light. Alternately, additional polarizers and quarter wave plate(s) can be added to the optical path, but with potential disadvantages of increased size, weight, cost, and complexity.

(iv) Accommodation constraints. A fixed accommodation distance is available for existing designs using the conventional pancake model. It would be advantageous to provide an improved measure of depth of focus that allows variable vergence and accommodation that could allow variable focus for plenoptic or light field display.

An embodiment of the present disclosure is directed to providing an optical apparatus that improves optical performance and usability of the imaging system with respect to the above considerations. In addition, the optical apparatus can be designed to provide non-obstructive near-to-eye imaging using the catadioptric system described.

Enhancing eve box size

As noted earlier, the optical system outlined in FIG. 2A defines two different sets of conjugates:

(i) Pupil conjugates. The optics provide a pupil relay that relays the entrance pupil PI at the scanning mirror of image generator 212 to exit pupil P2 at the iris; and

(ii) Image conjugates. The optics provide an image relay that relays focal surface 214 to retina R.

As noted previously, the eye box dimensions are a function of the exit pupil size. With respect to the FIG. 2A embodiment and its variants described previously, a simple way to increase the exit pupil size is simply to increase the diameter of its optical conjugate, the scan mirror at image generator 212. This solution, however, is undesirable since increasing the size and mass of the scan mirror makes it more difficult to maintain the needed oscillation speeds for suitable image refresh. Increasing the mirror diameter is also disadvantaged because it can allow increased deformation during movement, introducing beam aberrations. Furthermore, such large and rapid oscillating bi-axial mirrors are not commercially available.

The Applicants’ solution takes an alternate approach to the problem of exit pupil expansion. With no change to the actual size of the entrance pupil scanning mirror that is conjugate to the exit pupil, an embodiment of the present disclosure expands the numerical aperture (NA) of the source image that is formed at the curved focal plane by light scanned from the entrance pupil. In the context of FIG.2A, this expansion increases the NA of light that forms curved focal surface 214. From the perspective of image-forming optics 940 (FIG. 9A), embodiments of the present disclosure effectively change the entrance pupil size by changing the angular spread of input light that is presented to image-forming optics 940.

Referring to FIG. 9A, there is shown an embodiment of a pupil relay apparatus 950 that utilizes a concentric numerical aperture (NA) expander 960 for conditioning the input light that forms an optical object to the image-forming optics 940 that comprise lenses LI, L2, and L3 and the polarizer 410 and QWP that are sandwiched within these lenses.

Concentric NA expander 960 is disposed at the curved focal surface 914 that is formed within the optical apparatus 950. In order to enjoy the aberration- free benefits of the optical design, concentric NA expander 960 retains the spherical curvature of focal surface 914 and provides an output surface that is optically concentric with respect to pupil PI at the scanning mirror 912.

In standard practice, when an optical system forms an intermediate image such as at the position of NA expander 960, a field lens having optical power is used at the proximity of this image, effectively changing the angles of light handled by subsequent components in the optical path. However, according to an embodiment of the present disclosure, NA expander 960 has zero optical power. For example, a curved sheet of a surface diffuser on a substrate with uniform thickness does not have optical power. Thus, addition of NA expander 960 to the optical assembly does not impose further requirements on the overall optical system or require changes to lens curvature or other optical aspects of the design except for possible resizing of optical elements downstream from expander 960 in order to accommodate the larger NA.

The symmetry of the optical system is maintained with the addition of NA expander 960.

According to an embodiment of the present disclosure that uses the pupil relay configuration of FIG. 9 A, NA expander 960 affects light angles with respect to both the image conjugates and pupil conjugates, as defined previously.

With respect to the pupil conjugates, NA expander 960 effectively appears to increase the size of the scanning mirror 412 at the location of entrance pupil PI, forming an enlarged virtual image 912 of the scanning mirror 412. However, as shown in FIG.

9 A, there is no change needed in the magnification that is provided by the combined lenses of image-forming optics 940. Further, there is no change in the overall length of the optical apparatus 950 due to addition of NA expander 960, allowing for a reduced footprint over other near-to-eye imaging solutions, advantaged for VR, AR, MR imaging as well as reference display. It should also be noted that there is no need for providing the added optics that form an“intermediate image” in order to relay this NA expander 960 image to the image-forming optics 940. Additional relay optics are not required for forming spherically curved focal surface 914 as the optical“object” or for directing the image formed as the optical object at surface 914 to imaging optics 940. That is, with respect to the imaging geometry (excepting polarization), introduction of NA expander 960 modifies light angles but has no impact on the optical configuration, other than making the apertures of optical elements larger, such as by increasing apertures by a few mm in order to accommodate the expanded beam widths that result.

FIG. 9B shows how NA expander 960 changes the angular characteristics of the scanned imaging beam. The unbroken lines indicate the angle of the scanned beam as it moves through focal surface 914 to form the aerial image. The dashed lines indicate the changed angular characteristics using NA expander 960. With respect to FIG. 9A, the etendue of the input light to lenses of optics 940 increases accordingly.

NA expander 960 can be any of a number of types of component, including a diffractive or diffusive optical element, one or more microlens arrays with component lenses of various sizes and patterns, an arrangement of aspherical lenses, one or more holographic optical elements, or other suitable devices.

By way of example, FIGs. 10A and 10B show curvature, thickness, and materials data for pupil relay apparatus 950 according to an embodiment.

Surface assignments for a number of the optical elements are shown. OBJ is the optical object at the curved focal surface 914. The aperture stop STO is at the scanner surface. Surface Surf3 is the first lens surface of a cemented assembly 1010. The mirrored surface is listed twice due to reflection in the optical path, as surfaces Surf5 - Surfl5. Surface SurflO is the reflective polarizer. Surface Surf23 is at the iris.

Lateral chromatic aberration and distortion are eliminated due to concentric design of image-forming optics 940. Notably, all of the lens materials upstream of the scanner mirror, that is, lenses LI, L2, L3 of image-forming optics 940, can be formed from a single optical material, such as from glass or from PMMA. The use of the same polymer lens substrate has advantages for reduced weight and cost. Where available, reflective polarizers of the same polymer can also be used.

By way of example, and not limitation, the particular arrangement shown in FIGs. 10A, 10B can increase the nominal exit pupil size from 1mm to a range from 2mm to about 8mm without changing the overall form factor of the optical apparatus. NOA61 is an optical adhesive, in layers of nominally 0.025 thickness.

It should further be noted that an embodiment of the present disclosure can utilize a combination of approaches for expansion of the eye box, with both an increased size of the actual scanning mirror 912 and an increase in the apparent size of the scanning mirror by the added NA expander 960. The perspective view of FIG. 13 shows image generator 212 with the curved surface of NA expander 960 concentric with a scan mirror 1214.

Improved input/scanner configuration

The Applicants have identified an improvement over conventional scanner design that further reduces size by folding the light path with a reflective polarizer beam splitter that is necessarily tilted in relation to the path of the beam (Fig, 11, 12 13). This improved embodiment corrects for a small amount of aberration that can result from directing a focused beam through a tilted plate.

Referring to FIGs. 11, 12 and 13, there is shown, in simplified schematic form, image generator 212 having a light source 1210 that directs light through a double concave lens LI 23, and a scanning objective 1220 that has a an aspheric plano-convex lens LI 22, and a cylindrical lens L121. Cylindrical lens L121 has very low power and helps to compensate for astigmatism that is induced by the tilted polarizing beam splitter plate 208 that has an angle of inclination Q1 with respect to the optical axis OA.

Providing a tilted polarizing beam splitter (PBS) 208 that is oblique to the optical axis OA as shown in FIG. 11 can be particularly advantageous for reducing the overall size of the system optics, simplifying the task of packaging the optical system for near-to-eye viewing. The oblique angle can be, for example, in a range from 5 to 30 degrees relative to an optical axis extending between the objective lens and the scan mirror. PBS 208 transmits, toward scan mirror 1214, light of one polarization state from light source 1210; PBS 208 reflects light of the orthogonal polarization state that is directed back through scan mirror 1214. One or more QWPs (not shown in FIG. 12; shown in FIG. 14) can be disposed in the light path to and from scan mirror 1214 for changing the polarization state of light from the scanner.

Optical axis OA can be folded at the scanning mirror 1214 as shown in FIG. 12; FIG. 11 shows the OA in schematic, unfolded arrangement. Longitudinal color is eliminated by the doublet LI 22 and LI 23 in the FIG. 11 input optics.

Polarization options

The imaging optics of the disclosed apparatus require circularly polarized light input. This input can be provided by the light source itself or, alternately, by adding a polarizer and a quarter wave plate QWP in the optical path of the scanned light.

NA expander 960 can be a polarization-preserving element, such as a lenslet array, for example. The light must be circularly polarized before it is incident on the QWP (FIG 9A). For linearly polarized light, coming into the expander 960, circular polarization is provided using a QWP between the NA expander 960 and lens LI.

Where NA expander 960 does not preserve polarization, a QWP plus a polarizer, that in combination form a circular polarizer, can be added following the NA expander 960. The circular polarizer can be spherically curved or can be cylindrically curved, that is, curved with respect to a single axis.

The perspective view of FIG. 14 shows an embodiment having a cylindrically curved circular polarizer 1410 disposed in the optical path.

A polarized reflecting lens can fold the path of the modulated beam in the path from the objective to the scan mirror to the numerical aperture (NA) expander.

According to an alternate embodiment, scanner light is first incident on a reflective polarizer, instead of on the partially reflective curved surface. This arrangement can eliminate the need for a QWP between the scanning mirror and the optics that follow.

Dithering options

With respect to any object at the curved focal surface 914 (FIG. 9A), the optical system can perform in a similar manner to a magnifying glass. One drawback of this characteristic behavior is that any structure on the surface of NA expander 960 (e.g. a material defect or structural pattern) can tend to be magnified to the viewer. Depending on the composition of the NA expander 960 surface, this can cause graininess or other undesirable effects within the perceived image.

According to an embodiment, mechanical dithering is used to help reduce viewer perception of structure at the focal plane. The side view of FIG. 15 shows an actuator 1512 that provides mechanical motion to NA expander 960.

Actuator 1512 can be a piezoelectric actuator that causes rapid vibration of the expander. Rotation, wobbling, vibration, or other displacement movement could alternately be imparted, while maintaining the shape and center of curvature of NA expander 960. Translation for dithering can be provided in the direction along the optical axis or at any angle relative to the optical axis. Dithering using movement that maintains the center of curvature means that the center of curvature at the scanning mirror remains the same, even with periodic displacement of the NA adapter 960 with respect to optical axis OA. With respect to any point on the spherically curved surface, dithering movement causes displacement that is essentially perpendicular to the radius of curvature at that point. Displacement due to dithering can thus maintain the NA expander surface shape and center of curvature, in conformance with the scanned region of defined focal surface 914.

Light field imaging

To address limitations of the scanned pancake design relative to accommodation constraints, an embodiment of the present disclosure can provide light field imaging.

There may be instances wherein forming the virtual image at infinity focus is not optimal and it would be useful to be able to form the virtual image at a finite optical distance or at a progressively changing sequence of optical distances.

To achieve this effect, light field imaging techniques can be employed, modifying the optical apparatus described herein to change focus in a controlled manner. By way of illustration, the schematic diagram of FIG. 16 shows a progression, in simplified form, using light field imaging to change the apparent location of the virtual image that is formed by pancake imaging optics 940. As is shown in this sequence, translation of NA adapter 960 along the optical axis OA changes the apparent location of the virtual image that is formed by changing the angles of light that reach the viewer at pupil P2.

For embodiments that do not employ NA expander 960, such as the embodiment shown and described with reference to FIGs. 2A, 2B, light field imaging can be implemented by changing the focus of objective lens 244 (FIGs. 3A, 8A) that, using the light from the scanning pattern, forms focal surface 214. This change of focus effectively shifts the position of focal surface 214 forward or backward along the optical axis OA. The optical system then correspondingly changes the focal position of the image that is formed for the viewer.

Light field imaging is feasible using the narrow beam provided by the scanned laser beam without NA expansion. However, light field imaging using a very small input pupil without NA expansion can only change focal distance and is thus of limited value; the image is observed with a relatively low NA, which means a relatively large depth of focus. When using the scanned laser beam itself, light field methods are disadvantaged for depth perception and offer poor solutions for the viewer with respect to vergence and accommodation. In effect, there would be little or no perceptible benefit to light field imaging with the optical arrangement shown in FIGs. 2A, 2B.

With the addition of NA expander 960, light field imaging shows more promise for providing advantages such as improved representation of depth. An embodiment of the present disclosure can provide the capability for light field imaging by changing the longitudinal position of the NA expander 960 along the optical axis, along with a corresponding change to axial position of the objective lens 1220. The side view schematic diagram of FIG. 17 shows functional components of an imaging apparatus 1600 that provides light field imaging based on the pancake optical system, image-forming optics 940, with the added NA expander 960 described in FIGs. 9 A and following. One or more actuators 1622, 1624 are used to adjust the position of focal surface 914 by synchronous displacement of scanning objective 1220 and NA expander 960 along the folded optical axis OA. Processor 20 coordinates actuation of the one or more actuators 1622, 1624 for simultaneous movement that provides the desired angle of light at the exit pupil and consequent distance of the object as perceived in the virtual image that is formed.

Calculation of the focal shift needed to effect a particular shift in image distance is straightforward. For example, given an optical system with lenses L1-L3 defining an effective focal length / of 11mm, the focus shift d’ needed to form an image at a distance d of 0.5 m (500mm) can be computed using:

d’d =f

Then:

d’ = (11 ² / 500) mm = 0.242mm

This is a relatively small displacement in comparison to the length of the light path and is within the operational limits of commercially available actuators, making this a practical solution for light field display.

Light field display allows a number of useful image-forming techniques to be available, including depth animation, in which the display content appears at a sequential progression of angles or distance from the viewer, or is coordinated with eye tracking and sensing of the viewer’s attention from eye movement. Light field display allows system optics to adapt to feedback from eye tracking measurements, allowing the optical system to form virtual images at finite focus, with focus position determined according to viewer eye tracking for example.

According to an embodiment of the present disclosure, at least a portion of the pancake optics lie within the object focal length of the eye, as described hereinabove. The optical apparatus having an NA expander can be configured to lie against the face of the viewer, stabilized along the inferior orbital rim and the nasion and zygoma and not blocking the primary field of view.

According to an aspect of the present disclosure, an optical apparatus worn by a viewer comprises: a laser light source energizable to direct a modulated beam toward a scan mirror; and an objective lens in the path of the modulated beam directed toward the scan mirror. The objective lens and the scan mirror define a curved focal surface for the scanned, modulated beam, wherein the curved focal surface has a focal surface center of curvature at the scan mirror. A numerical aperture (NA) expander, with zero optical power, has an expansion surface that conforms to the defined curved focal surface in position and in curvature and that increases the NA of the scanned, modulated beam. Pupil relay optics are disposed to relay an entrance pupil at the scan mirror to an exit pupil at an eye lens of the viewer, the pupil relay optics defining an optical path between the entrance and exit pupils, the optical path comprising: (i) a curved mirror surface disposed to transmit substantially half of the light incident from the modulated beam and that has a first center of curvature at the exit pupil; and (ii) a first polarizer disposed in the optical path to receive light from the scan mirror and formed to reflect incident light of a first polarization toward the curved mirror surface and to transmit incident light of a second polarization, orthogonal to the first polarization, wherein the optical path defined by the pupil relay optics directs the modulated light beam twice to the first polarizer, and wherein the modulated light beam incident the second time on the first polarizer is collimated and directed toward the exit pupil. The NA expander can be a lenslet array, a diffusive optical element, or a holographic optical element. The curved mirror surface can have a center of curvature at the entrance pupil or, alternately, at the exit pupil. There can be one or more quarter wave plates along the optical path. A circular polarizer can be disposed between the NA expander and a concave lens surface. The pupil relay optics can further relay an image formed at the NA expander to a retina of a viewer. The optical apparatus can have a second polarizing beam splitter disposed in the path of focused light between the objective lens and the scan mirror and oriented at an oblique angle relative to an optical axis extending between the objective lens and the scan mirror. The NA expander can preserve the polarization state of incident light that is circularly polarized. An actuator can be configured to impart vibration or motion to the NA expander and maintain concentricity of the NA expander surface to the scanning mirror. One or more actuators can be configured to provide synchronous movement of the objective lens and the NA expander to provide multiple focal lengths of the laser beam for depth animation in the projected image. A polarized reflecting lens can fold the path of the modulated beam in the path from the objective to the scan mirror to the numerical aperture (NA) expander.

The disclosure has made particular reference to a presently preferred embodiment, but it will be understood that variations and modifications can be effected within the spirit and scope of the disclosure. For example, although the above description concentrates on forming an image for one eye, it can be readily understood that corresponding elements and logic are used for forming the stereoscopic images needed to form and coordinate image content for both right- and left-eye images, using methods familiar to those skilled in the stereoscopic imaging arts. The images that are formed can be stereoscopic or biocular, that is, with the same image content provided to both eyes for monoscopic display.

The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.