Patent Description:
Modem computing and display technologies have facilitated the development of systems for so called "virtual reality" or "augmented reality" experiences, wherein digitally reproduced images or portions thereof are presented to a viewer in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or "VR," scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or "AR," scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the viewer. An example is shown in <CIT> and <CIT> disclosing a projector comprising a scanning light source, a collimating element, a quarter wave plate and a polarizing beam splitter.

Despite the progress made in these display technologies, there is a need in the art for improved methods and systems related to augmented reality systems, particularly, display systems.

The present invention relates generally to methods and systems related to projection display systems including wearable displays. More particularly, embodiments of the present invention provide methods and systems for volumetric displays, also referred to as a light field displays, that create volumetric sculptures of light at more than one depth plane. The invention is applicable to a variety of applications in computer vision and image display systems.

According to an embodiment of the present invention, a projector is provided. The projector comprises the features specified in appended claim <NUM>.

According to an embodiment not according to the claimed invention, a fiber scanning projector is provided. The fiber scanning projector includes a piezoelectric element, a scanning fiber mechanically coupled to the piezoelectric element, and an optical assembly section operable to receive light from the scanning fiber. The optical assembly section includes a prism element, a collimating element coupled to the prism element at an interface, a quarter wave plate, and a polarizing beam splitter disposed at the interface.

According to another embodiment not according to the claimed invention, a fiber scanning projector is provided. The fiber scanning projector includes a piezoelectric element and a scanning fiber passing through and mechanically coupled to the piezoelectric element. The scanning fiber emits light along an optical path. The fiber scanning projector also includes a mirror including an aperture. The scanning fiber passes through the aperture. The fiber scanning projector further includes a collimating mirror disposed along the optical path.

According to an embodiment not according to the claimed invention, a fiber scanning projector is provided. The fiber scanning projector includes a piezoelectric element and a scanning fiber passing through and mechanically coupled to the piezoelectric element. The scanning fiber emits light along an optical path. The fiber scanning projector also includes a first polarization sensitive reflector disposed along the optical path, a quarter wave plate disposed adjacent the first polarization sensitive reflector, and a second polarization sensitive reflector disposed along the optical path.

Numerous benefits are achieved by way of the present invention over conventional techniques. For example, embodiments of the present invention provide methods and systems that can be used to display images to a user in a form factor comparable to standard eyeglasses. In some embodiments, image projectors integrated with a fiber scanning light source can fit within the frames of the eyeglasses. These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.

<FIG> is a simplified perspective view illustrating a fiber scanning projector according to an embodiment of the present invention. The fiber scanning projector <NUM>, which can have dimensions on the order of <NUM> x <NUM> x <NUM>, includes a fiber input <NUM>, a fiber oscillation region <NUM>, and an optical assembly section <NUM>. Driven by piezoelectric actuators (not illustrated), an optical fiber oscillates in the fiber oscillation region <NUM>, for example, in a spiral configuration with an increasing angular deflection during the projection of light for a given frame time. Input light to the fiber scanning projector is provided through fiber input <NUM> and output light from the fiber scanning projector is provided through one or more of the surfaces of optical assembly section <NUM>. The various elements of the fiber scanning projector are described more fully throughout the present specification.

<FIG> is a simplified cutaway perspective view illustrating a fiber scanning projector according to an embodiment of the present invention. In the view illustrated in <FIG>, the fiber scanning projector <NUM> has been rotated horizontally. The fiber input <NUM> is illustrated on the right hand side of the figure, providing an input to the fiber oscillation section <NUM>, which includes a piezoelectric actuator <NUM> supported by a retaining collar <NUM> (and driven by electric signals from wires that are not shown), and a scanning fiber <NUM> is disposed in a mechanical enclosure <NUM>. The optical assembly section <NUM> receives light from the scanning fiber <NUM> as described more fully herein.

During operation, the scanning fiber <NUM>, which is mechanically attached to the piezoelectric actuator <NUM>, oscillates in the fiber oscillation region <NUM>. In an embodiment, the piezoelectric actuator <NUM> includes four electrodes distributed at circumferential positions that are shifted <NUM>° with respect to each other. Accordingly, positive and negative voltages applied to opposing sides of the piezoelectric actuator can flex the actuator, and the scanning fiber, in the plane of the electrodes. By driving all four electrodes in synchronization, oscillation of the fiber can be accomplished. As the light exits the scanning fiber <NUM>, it is coupled into optical assembly section <NUM>, described more fully below.

As described more fully herein, small form factors comparable to standard eyeglasses are enabled by embodiments of the present invention. By utilizing embodiments of the present invention, displays with a desired field of view, depth of resolution, integrated inertial motion units (IMUs), cameras, audio components, and the like are provided. In some embodiments, the fiber scanning projector <NUM> illustrated in <FIG> and <FIG> is mounted in the temple or frame of the eyeglasses and works in combination with an eyepiece disposed in the frame to direct the projected light toward the eye of the user. The size of the fiber scanning projector <NUM> enables the integration of multiple fiber scanning projectors that can direct light toward each eye, increasing the field of view through tiling of the display areas. As an example, if two projectors are used per eye, a diagonal field of view of <NUM>° can be provided using two projectors. Using four projectors per eye, a diagonal field of view of <NUM>° can be achieved. Additionally, in addition to increases in the field of view, additional depth planes can be provided through the use of multiple projectors. Additional description related to tiling of display areas and the use of multiple projectors to increase the field of view is provided in U. Patent Application No. (Attorney Docket No. <NUM>-<NUM>(<NUM>)), filed on March <NUM>, <NUM>.

In an embodiment not according to the claimed invention, the fiber scanning projector <NUM> is fed by fiber input <NUM> and the fiber oscillation region <NUM> and the optical assembly section <NUM> are mounted in the outside edge of the frame as illustrated in <FIG> of U. Patent Application No. (Attorney Docket No. <NUM>-<NUM>(<NUM>)), filed on March <NUM>, <NUM>. The output of the optical assembly section <NUM> is oriented to emit light toward the input coupling elements of the eyepiece mounted in the frame. As an example, light from the output of the optical assembly section could be directed toward the user before it couples into the eyepiece, which can include a world-side cover glass and an eye-side cover glass.

<FIG> illustrates schematically the light paths in a viewing optics assembly (VOA) that may be used to present a digital or virtual image to a viewer, according to an embodiment of the present invention. The VOA includes a projector <NUM> and an eyepiece <NUM> that may be worn around or in front of a viewer's eye. As discussed, herein the VOA can be integrated with the frames of a pair of glasses to present the digital or virtual image to a viewer wearing these glasses.

Referring to <FIG>, a fiber scanning projector <NUM> is illustrated. However, it will be appreciated that other scanned light systems or scanned beam systems, which can be implemented, for example, as a scanned waveguide system, which includes a scanning waveguide source, can be utilized in conjunction with embodiments of the present invention. Thus, although an optical fiber as one implementation for waveguiding light is illustrated in some embodiments, the present invention is not limited to fiber scanning systems and other waveguide scanning systems can be utilized according to other embodiments. Examples of other waveguiding systems include microelectromechanical systems (MEMS) that integrate waveguide features, for example, a silicon waveguide integrated with a cantilevered beam, into light scanning systems. Moreover, a scanning mirror system in which a converging beam of light is scanned by the projector to create a curved object surface, can be utilized with embodiments of the present invention as described herein. Furthermore, a scanning point source, for instance a light emitting diode (LED) or an organic LED (OLED) can be utilized in conjunction with the optics described herein. As an example, one implementation of a MEMS-based waveguide scanner is illustrated in <FIG>.

Although not illustrated in <FIG>, optional projector relay optics can be used to direct light from the fiber scanning projector <NUM> into eyepiece <NUM>. Since these projector relay optics are optional, they are not required by the present invention and other optical configurations can be utilized according to embodiments of the present invention. In the illustrated embodiment, light exits the optical assembly section in a direction generally perpendicular to the longitudinal axis of the mechanical enclosure <NUM> of the fiber scanning projector <NUM> and is collimated, which provides a suitable input for incoupling gratings <NUM>.

During operation, the optical fiber <NUM>, which is mechanically attached to the piezoelectric actuator <NUM>, oscillates in the fiber oscillation region <NUM>. In an embodiment, the piezoelectric actuator <NUM> includes four electrodes distributed at circumferential positions that are shifted <NUM>° with respect to each other. Accordingly, positive and negative voltages applied to opposing sides of the piezoelectric actuator can flex the actuator, and the scanning fiber, in the plane of the electrodes. By driving all four electrodes in synchronization, oscillation of the fiber can be accomplished. As the light exits the optical fiber <NUM> as it scans, it is coupled into optical assembly section <NUM>, which redirects the light toward the eyepiece <NUM>.

The fiber scanning projector <NUM> can provide multiple colors, including the three primary colors, red, green, and blue (RGB) to form a full-color display. Accordingly, the eyepiece <NUM> may include one or more eyepiece layers. In one embodiment, the eyepiece <NUM> includes three eyepiece layers, one eyepiece layer for each of the three primary colors, red, green, and blue. In another embodiment, the eyepiece <NUM> may include six eyepiece layers, i.e., one set of eyepiece layers for each of the three primary colors configured to form a virtual image at one depth plane, and another set of eyepiece layers for each of the three primary colors configured to form a virtual image at another depth plane. In other embodiments, the eyepiece <NUM> may include three or more eyepiece layers for each of the three primary colors for three or more different depth planes. Each eyepiece layer comprises a planar waveguide and may include an incoupling grating <NUM>, an orthogonal pupil expander (OPE) region <NUM>, and an exit pupil expander (EPE) region <NUM>.

Still referring to <FIG>, the projector <NUM> projects image light onto the incoupling grating <NUM> in an eyepiece layer <NUM>. The incoupling grating <NUM> couples the image light from the projector <NUM> into the planar waveguide propagating in a direction toward the OPE region <NUM>. The waveguide propagates the image light in the horizontal direction by total internal reflection (TIR). The OPE region <NUM> of the eyepiece layer <NUM> also includes a diffractive element that couples and redirects a portion of the image light propagating in the waveguide toward the EPE region <NUM>. The EPE region <NUM> includes an diffractive element that couples and directs a portion of the image light propagating in the waveguide in a direction approximately perpendicular to the plane of the eyepiece layer <NUM> toward a viewer's eye <NUM>. In this fashion, an image projected by projector <NUM> may be viewed by the viewer's eye <NUM>.

As described above, image light generated by the projector may include light in the three primary colors, namely blue (B), green (G), and red (R). Such image light can be separated into the constituent colors, for example, temporally or spatially, so that image light in each constituent color may be coupled to a respective waveguide in the eyepiece.

<FIG> shows a partial cross-sectional view of a waveguide scanning system using a silicon-based waveguide according to an embodiment of the present invention. In this embodiment, rather than using a tapered optical fiber as the light scanning element, a MEMS scanner <NUM> incorporating a cantilevered beam including a silicon-based, cantilevered waveguide is utilized.

In the embodiment illustrated in <FIG>, light for display through the eyepiece is provided using an optical fiber (not shown) that is optically coupled to waveguide <NUM> supported by cantilevered beam <NUM>. Cantilevered beam <NUM> extends from support structure <NUM>, which is mechanically attached to mechanical enclosure <NUM>. Accordingly, light from the optical fiber is able to propagate down waveguide <NUM>, be emitted, and received by optical assembly section <NUM>. As described more fully in relation to <FIG>, optical assembly section <NUM> includes a prism element <NUM> and a collimation element <NUM> coupled at an interface, defining beam splitter <NUM>. As illustrated in <FIG>, light emitted from waveguide <NUM> can pass through beam splitter <NUM>, pass through a quarter wave plate (not shown), and impinge on the collimating surface <NUM>. After reflection, the light passes through the quarter wave plate a second time and reflects off of beam splitter <NUM> as illustrated by optical ray <NUM>.

In order to actuate the cantilevered beam <NUM>, the optical scanner illustrated in <FIG> includes a transducer that includes a frame <NUM> and a hub <NUM> driven by piezoelectric strips <NUM>. Piezoelectric strips are coupled to both frame <NUM> and hub <NUM> to cooperatively induce oscillation of cantilevered beam <NUM> in a predefined pattern. Bracket <NUM> can be configured to position cantilevered beam <NUM>, frame <NUM>, and hub <NUM> relative to optical assembly section <NUM>. Moreover, bracket <NUM> can be mechanically coupled to mechanical enclosure <NUM>.

As illustrated in <FIG>, hub <NUM> can be configured to rotate in place to achieve a desired scan pattern of cantilevered beam <NUM>. For example, sequential actuation of piezoelectric strips <NUM> can result in longitudinal extension and contraction of the piezoelectric strips such that the hub is maneuvered in a pattern that oscillates cantilevered beam <NUM>, particularly the waveguide tip, in a spiral scan pattern. In other embodiments, hub <NUM> can be configured to shift laterally and/or vertically to induce the desired scan pattern, for example, a raster scan pattern. While hub <NUM> is depicted having a circular shape, it should be appreciated that many other shapes such as elliptical, rectangular, and other polygonal gap geometries are also possible.

Cantilevered beam <NUM> can be formed from a length of silicon or silicon carbide. The waveguide <NUM>, which can be a single mode waveguide, can be formed using semiconductor processing steps that define an index of refraction difference to support waveguiding. Although cantilevered beam <NUM> is illustrated as including a single waveguide <NUM>, other embodiments can implement multiple waveguides supported by the cantilevered beam. It should be appreciated that cantilevered beam <NUM> could also be utilized in conjunction with other actuators, for example, piezoelectric actuator <NUM> described more fully herein. Thus, the frame and hub implementation illustrated in <FIG> is merely exemplary of structures that can be used to actuate the cantilevered beam.

<FIG> is a partial cross-sectional view illustrating a structure of an eyepiece according to an embodiment of the present invention. The region shown in the cross-sectional view includes the region of the incoupling diffractive optical element (e.g., incoupling grating) of the eyepiece <NUM>. As shown in <FIG>, the eyepiece <NUM> includes a stack of waveguide plates <NUM>, <NUM>, and <NUM> that receive input light from the fiber scanning projector and output image information to the eye <NUM> of a viewer. The eyepiece <NUM> illustrated in <FIG> includes an eye-side cover layer <NUM> positioned on the side of the eyepiece adjacent the viewer's eye, and a world-side cover layer <NUM> positioned on the side of the eyepiece facing toward the world.

In some embodiments, the waveguide plates <NUM>, <NUM>, and <NUM> include respective planar waveguides <NUM>, <NUM>, or <NUM>, for propagating light in the planes of their respective waveguide plates <NUM>, <NUM>, and <NUM>. Each planar waveguide <NUM>, <NUM>, or <NUM> has a back surface facing the viewer's eye, and a front surface facing the world. In the embodiment illustrated in <FIG>, the waveguide plates <NUM>, <NUM>, and <NUM> also include respective gratings <NUM>, <NUM>, or <NUM> disposed on the back surfaces of their respective waveguides <NUM>, <NUM>, or <NUM>, for coupling and redirecting a portion of the light propagating in their respective waveguides <NUM>, <NUM>, or <NUM>.

In the illustrated embodiment, each waveguide <NUM>, <NUM>, or <NUM> , as well as each grating <NUM>, <NUM>, or <NUM>, may be wavelength selective, such that it selectively propagates or redirects light in a given wavelength range. In some embodiments, each of the waveguide plates <NUM>, <NUM>, and <NUM> may be configured for a respective primary color. For example, the waveguide plate <NUM> is configured for red (R) light, the waveguide plate <NUM> is configured for green (G) light, and the waveguide plate <NUM> is configured for blue (B) light. It will be appreciated that the eyepiece <NUM> may include two or more waveguide plates for red light, two or more waveguide plates for green light, and two or more waveguide plates for blue light, for different depth planes, as described above. In some other embodiments, other colors, including magenta and cyan, may be used in addition to or may replace one or more of red, green, or blue.

In order to improve the optical efficiency, some embodiments utilize a reflective surface, for example, metallization of the surface, on one of the surfaces, for example, the front surface, of the eye-side cover layer to provide a highly reflective surface (e.g., ∼<NUM>% reflective coating) that forms a reflective structure behind the input coupling elements (e.g., vertically aligned incoupling gratings) to reflect the input light, which can be RGB light, that passes through the input coupling elements and produce a second pass through the input coupling elements to improve the image brightness. As illustrated in <FIG>, reflector <NUM> reflects input light <NUM> incident from the fiber scanning projector that is not coupled into the waveguides. After reflection from reflector <NUM>, the input light is able to make a second pass through the input coupling elements and increase the amount of light coupled into the waveguides.

In an alternative embodiment, an annular reflector <NUM>, for example, fabricated using <NUM>% reflective metal coatings, can be placed on the world-side cover glass. Although this annular reflector <NUM> is shown on the back side of the world-side cover layer <NUM>, this is not required by the present invention and it may alternatively be mounted on the front side. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. In this alternative embodiment, the input light <NUM> from the fiber scanning projector passes through the center of the annular reflector <NUM> after it is output from the optical assembly section of the fiber scanning projector. Since the input light is diverging, the beam spreads as it passes through the eyepiece and reflects from the reflector <NUM> behind the input coupling elements. This reflected light <NUM> propagates back through the eyepiece, with the cone of light expanding during propagation. In some embodiments, reflected light <NUM> is also coupled into the incoupling gratings during the return path, being characterized by the same orientation as the input beams for display to the viewer since, although reflected light <NUM> is the mirror image of input light <NUM>, entry through the opposing side of the incoupling grating results in the same orientation. A substantial portion, which can be the majority, of the light, reflects from the annular reflector <NUM> on the world-side cover layer as illustrated by doubly reflected light <NUM> and is able to make a third pass through the input coupling elements, resulting in additional coupling of light into the waveguide plates. As will be evident to one of skill in the art, a Hall of Mirrors effect can be achieved that results in increased brightness correlated with the increased number of rays passing through the eyepiece, improving the fill factor and image quality.

A channel can be cut in the temple and the frames to accommodate the fiber and electrical wiring. As the fiber/wires pass over the spring hinge, the design dimensions enable the fiber to not be bent past is minimum bend radius of curvature as the temples are folded.

In addition to reflective structures associated with the input coupling elements discussed in relation to <FIG>, some embodiments utilize a partially reflective (e.g., <NUM>% aluminized) surface on the inside surface of world-side cover glass so that a portion (e.g., half) of the light that is propagating toward the world from the eyepiece is reflected and directed back toward the eye of the user, which increases the overall brightness and increases the beam density as a result of the slight lateral offset to the beams, which contributes to an improved fill factor.

<FIG> is a ray tracing diagram illustrating propagation of light through the optical assembly section according to an embodiment of the present invention. The optical assembly section <NUM> includes a prism element <NUM> and a collimation element <NUM> coupled at an interface. In an embodiment, the prims element and the collimation element are optically bonded at the interface. As described more fully herein, one or more of the surfaces of the optical assembly section <NUM> can include optical power. Thus, although collimation of light in terms of collimating surface <NUM> is discussed herein, it will be appreciated that surfaces other than collimating surface <NUM> can contribute to collimation of light by the system. The scanning fiber <NUM> in the fiber oscillation region <NUM> is illustrated at three scanning positions: on axis <NUM> (solid lines), off axis to the right <NUM> (dashed lines), and off axis to the left <NUM> (dashed lines). As illustrated in <FIG>, the tip of the scanning fiber sweeps through a substantially spherical surface, illustrated by curve <NUM> in <FIG>, as it oscillates, resulting in a convex surface to be imaged, such that curve <NUM> can be referred to as a convex object surface. Conventional lenses are typically designed for flat object planes or concave object surfaces. Embodiments of the present invention utilize designs in which the convex object surface <NUM> associated with the tip of the scanning fiber <NUM> is matched with the concave collimating surface <NUM>, which, at a high level, can be a substantially spherical mirror having twice the radius of curvature of the radius of curvature of the convex object surface <NUM>. Accordingly, in some embodiments, the majority of focusing is achieved using convex collimating surface <NUM>, which can be implemented as a curved mirror with an aspheric correction term. Although refractive and reflective elements are illustrated in <FIG>, embodiments of the present invention are not limited to these implementations and diffractive surfaces, meta-surfaces, and the like can be utilized in accordance with embodiments of the present invention. For example, collimating surface <NUM>, rather than be a reflective surface, could be a diffractive surface, a meta-surface, or the like. One of more of the other surfaces illustrated in <FIG> can also be implemented using diffractive structures or combinations of diffractive and/or refractive structures. An example would be a diffractive structure to compensate for chromatic aberration and a refractive structure to focus/defocus the beam. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

In addition to scanning fibers, other optical systems can be utilized to form the convex object surface <NUM>. Examples of these optical systems include other waveguide scanning systems including MEMS-based scanning systems, a scanning mirror system with a converging beam, a scanning point source, a flat panel display combined with optics to create the curved object surface, or the like.

Embodiments of the present invention enable the optical prescriptions of the various optical surfaces to be varied to optimize size, exit pupil diameter, combined optical power, linear magnification, angular magnification, distance between the exit pupil and the output surface, and the like. Control of the curvature of the input surface <NUM>, collimating surface <NUM> and output surface <NUM> enables various properties of the output beam to be controlled, including beam diameter, angular magnification of the angle associated with the fiber deflection (i.e., angle between scanning positions <NUM> and <NUM>), and the like. It should be noted that in some implementations, beam splitter <NUM> can include curvature such that it is not a planar surface, thereby providing additional design freedom. This non-planar shape (i.e., non-planar curvature) can include curvature (e.g., concave or convex) to introduce optical power, compensate for aberrations, or the like. Additionally, the index of refraction of the materials used to fabricate optical assembly section <NUM> can be adjusted to modify the optical properties discussed above. Moreover, the beam splitter <NUM> can be a partially reflective (<NUM>/<NUM> split) surface, polarizing beam splitter, a wavelength selective beam splitter, or the like.

Referring to <FIG>, a multiplexing functionality could be implemented if the polarizing beam splitter <NUM> has varying polarization, for example, as a function of time, alternately passing and reflecting incident light. Shutters integrated into the optical path between the partially reflective surface/polarizing beam splitter and the collimating surface <NUM>/surface <NUM> could be utilized to multiplex between the two optical paths. Accordingly, some embodiments provide a multiplexed display with a high resolution, narrow field of view image surrounded by a lower resolution, wide field of view image. In some embodiments, surface <NUM> could be absorbing, providing a shutter effect when light is reflected from the polarizing beam splitter <NUM> toward surface <NUM>. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

Referring once again to <FIG>, the scanning fiber <NUM> acts as a point source of light, emitting a cone of light. These cones of light as illustrated as they propagate from the convex object surface <NUM> through the optical assembly section <NUM>. As the scanning fiber sweeps through the oscillatory pattern, different pixels are illuminated to form the desired image. In the embodiment illustrated in <FIG>, the light from the scanning fiber is polarized so that after it enters the optical assembly section <NUM> though input surface <NUM>, it will pass through the polarizing beam splitter <NUM> with little reflection, passes through quarter wave plate <NUM>, and impinges on the collimating surface <NUM>. After reflection, the light passes through quarter wave plate <NUM> a second time and reflects off of polarizing beam splitter <NUM> toward output surface <NUM>. Exit pupil <NUM> is formed outside the optical assembly section <NUM> for delivery to the eyepiece. As will be evident to one of skill in the art, for many optical systems, alignment between the exit pupil and the input plane of another optical system is preferable. Accordingly, the working distance between output surface <NUM> and exit pupil <NUM> enables embodiments of the present invention to be utilized in conjunction with a wide variety of optical systems. As an example, if the light emitted by the fiber scanning projector is utilized by a waveguide-based optical system, the input coupling element of the waveguide-based optical system could be placed coincident, for example, coplanar, with the exit pupil <NUM>. In an embodiment, the exit pupil <NUM>, which provides a location at which a small diameter beam is formed, can enable efficient coupling into a small input coupling element, which can be matched in size to the exit pupil, thereby efficiently utilizing the area of the waveguide-based optical system. As illustrated in <FIG>, the three cones of light emitted at each of the three illustrated positions <NUM>, <NUM>, and <NUM> of the scanning fiber <NUM>, are collimated as they exit the optical assembly section as shown, for example, by collimated rays <NUM> and <NUM>, which define the edges of the cone of light emitted at on axis position <NUM>.

In another particular embodiment, the polarizing beam splitter can be replaced with a wavelength selective beam splitter such that one or more colors would pass through the beam splitter while other color(s) are reflected toward surface <NUM>, which can be implemented as a surface with optical power. This wavelength selectivity will enable focusing through the use of diffractive elements or meta-surfaces as diffractive optics are used as an alternative to refractive optics. Thus, embodiments of the present invention can integrate meta-surfaces on one or more of the input surface <NUM>, collimating surface <NUM>, surface <NUM>, and/or output surface <NUM> to encode multiple lens functions into a meta-surface for wavelength selective optical processing, other diffractive optical functions, dispersion compensation, or the like. In some designs, dispersion correction is provided by the various surfaces, for example, dispersion compensation can be implemented by correcting aberrations occurring at the input surface by aberration correction provided on the output surface.

As discussed in additional detail in relation to <FIG>, the quarter wave plate can also be fabricated by vacuum forming on the collimated surface <NUM>. In this implementation, after formation of the quarter wave plate on the curved surface, a metallized or other suitable reflective surface could be formed to complete the fabrication of collimating surface.

In an embodiment, the input surface <NUM>, the collimating surface <NUM>, and the output surface <NUM> of the optical assembly section <NUM> can have optical power to compensate for spherical aberration as well as to provide for magnification of the field of view in some embodiments. Accordingly, using a smaller deflection of optical fiber in the fiber oscillation region leads to larger field of view. As an example, the input surface <NUM> can be convex with respect to the input light to provide positive optical power, the collimating surface <NUM> can be concave with respect to the light from the input surface to provide negative optical power, and the output surface can be convex with respect to light from the beam splitter to provide negative optical power. The collimating surface <NUM> is substantially spherical, but includes an aspheric curvature in some implementations. The aspherical curvature can correct spherical aberration and the overall curvature can result in collimation of the light by the collimating surface. The collimating surface <NUM> can be fabricated as a reflective element through the deposition of one or more reflective coatings, a metalized coating, or the like.

It should be noted that although collimating surface <NUM> can have approximately twice the radius of curvature of convex object surface <NUM>, which can also be referred to as a curved object surface, in some embodiments, this is not required by the present invention and the input surface <NUM> and the output surface <NUM> can incorporate optical power in addition to the optical power present in collimating surface <NUM>. Thus, as additional optical power is implemented through input surface <NUM> and output surface <NUM>, the curvature of collimating surface <NUM> can deviate from twice the curvature of convex object surface <NUM>. Additionally, as discussed herein, aspherical components can be integrated into the optical surfaces including input surface <NUM>, collimating surface <NUM>, and output surface <NUM>.

In an exemplary fabrication process, the optical assembly section <NUM> is fabricated by bonding three elements together. In this process, the first element is a prism element <NUM> and the second element is a collimating optic section <NUM> that is bonded to the prism element. The prism element <NUM> receives light through input surface <NUM>. A polarizing beam splitter <NUM> is formed at the interface of the prism element <NUM> and the collimating optic section <NUM>. In some embodiments, a polarization selective coating is applied to the longest surface of the prism prior to bonding to form the polarizing beam splitter. A quarter wave plate <NUM> is formed on the back surface of the collimating optic section <NUM> and a third element comprising a curved reflective optic <NUM> is bonded to the quarter wave plate. As described herein, the curved reflective optic <NUM> includes collimating surface <NUM>, which can be metalized or otherwise coated to provide high reflectivity.

During operation, using polarized light at the input, the majority of the polarized input light will pass through polarizing beam splitter <NUM> on a first pass, pass through a quarter wave plate <NUM>, reflect and be collimated by the collimating surface <NUM>, pass a second time through the quarter wave plate <NUM> (now with an orthogonal polarization state) and substantially reflect from the polarizing beam splitter toward the output surface <NUM>.

<FIG> is a side view of an alternative optical assembly section according to an alternative embodiment of the present invention. Referring to <FIG> and <FIG>, collimating optic section <NUM> and curved reflective optic <NUM> illustrated in <FIG> have been combined into a single (i.e., monolithic) collimating reflector <NUM> to form alternative optical section <NUM>. Reflective surface <NUM> includes a wave plate that introduces a half wave of phase shift upon reflection. In one implementation, a quarter wave plate is formed on the right edge of the collimating reflector <NUM> before reflective surface <NUM> is formed, for example, by depositing a metal film, a dielectric film, or the like. In other embodiments, a microstructure can be utilized to introduce the half wave of phase shift upon reflection. Thus, the alternative optical section <NUM> is not limited to a specific manner of implementing phase retardation and reflection. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

<FIG> side view of a beam splitter cube based optical assembly section according to an embodiment of the present invention. Beam splitter cube <NUM> is utilized as the basis of the beam splitter cube based optical assembly section <NUM> and additional optical elements <NUM>, <NUM>, and <NUM> are cast onto the outer surfaces of the beam splitter cube <NUM> to form the input surface, the collimating surface, and the output surface, respectively. In this embodiment, a quarter wave plate can be implemented at the intersection of the beam splitter cube <NUM> and the optical element <NUM> forming the collimating surface. In an alternative embodiment, a surface <NUM> can be used to define the collimating surface of the optical element <NUM>, resulting in alignment between the edge of optical element <NUM> and the surface <NUM> of optical element <NUM>. In this alternative embodiment, it can be noted that the optical element <NUM> can be trimmed at the periphery to form elements with non-circular plan views, including rectangular plan views. Accordingly, optical element <NUM> has a trimmed surface or edge that is aligned with surface <NUM> of beam splitter cube <NUM>. This alignment between edges of the various elements can facilitate registration during manufacturing, including bonding of the various elements. The use of a glass beam splitter cube <NUM> provides advantages including the selection of the polarization selective coatings used to fabricate the beam splitter surface <NUM>. Additionally, manufacturability is enhanced by this design due to the wide availability of glass beam splitter cubes, including small beam splitters. In other embodiments, beam splitters of materials other than glass, including plastic, are utilized. In addition to formation of the optical elements (e.g., refractive and reflective optical elements) through casting, other techniques can be utilized to achieve optical effects, including molded elements, traditionally fabricated optics, the use of diffractive surfaces, and/or meta-surfaces, and the like.

<FIG> is a side view of another alternative optical assembly section according to an alternative embodiment of the present invention. In the alternative embodiment of the optical assembly section <NUM> illustrated in <FIG>, the polarization selective coating utilized for the polarizing beam splitter is removed along with the quarter wave plate. In this alternative embodiment, a partially reflective surface <NUM> (e.g., <NUM>/<NUM> reflector) joins the prism element <NUM> to the collimating element <NUM>. Half of the light incident from input surface <NUM> passes to collimating surface <NUM> and reflects back toward the partially reflective surface <NUM> joining the prism element <NUM> and the collimating element <NUM>. The other half of the light is reflected toward reflective surface <NUM>, which can have the same curvature as collimating surface <NUM> in this alternative embodiment. As a result, light reflected from collimating surface, as well as light reflected from reflective surface <NUM> is collimated (given the optical power of output surface <NUM>). The embodiment illustrated in <FIG> can improve optical efficiency since light that is reflected from reflective surface <NUM> is available for output from the optical assembly section. In an embodiment, a single exit pupil is shared by the light reflecting from collimating surface <NUM> as well as the light reflecting from reflective surface <NUM>, discussed as superimposed exit pupils in relation to <FIG>.

Utilizing this design, different optical power can be achieved using the collimating surface <NUM> and reflective surface <NUM>, which can have different curvatures, resulting in a zoomed in/out view, wide/narrow field of view, and the like as light is directed to each of these surfaces in a multiplexed manner. As an example, the reflectivity of the partially reflective surface <NUM> could be varied to provide time-base multiplexing.

A multiplexing functionality could be implemented since the partially reflective surface <NUM> could have varying reflectivity, alternately passing and reflecting incident light. Shutters integrated into the optical path between the partially reflective surface <NUM> and the collimating surface <NUM>/reflective surface <NUM> could be utilized to multiplex between the two optical paths. Accordingly, some embodiments provide a multiplexed display with a high resolution, narrow field of view image surrounded by a lower resolution, wide field of view image. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

In another implementation, a tiled image can be formed by tilting partially reflective surface <NUM> at an angle other than <NUM>° with respect to the incoming light. Light passing through the partially reflective surface <NUM> will reflect from collimating surface <NUM> and be directed in a first direction after passing through output surface <NUM>. Light reflecting from the partially reflective surface <NUM> will reflect from reflecting surface <NUM> and be directed in a second direction after passing through output surface <NUM>. Accordingly, light reflected from collimating surface <NUM> could be tilted to the left after passing through output surface <NUM> and light reflected from reflecting surface <NUM> could be tilted to the right after passing through output surface <NUM>, thus providing inputs directed to different portions of the image field for tiled display implementations.

<FIG> is a side view of a multi-polarization tilted reflector optical assembly section according to an alternative embodiment of the present invention. In this implementation in which a polarization sensitive material forms a polarizing beam splitter <NUM> at the interface of the prism element <NUM> and the collimating element <NUM>, similar to polarizing beam splitter <NUM> in <FIG>, the input light from the fiber scanning projector could have two signals encoded with different polarizations. A first input beam <NUM> encoded with a first polarization could pass through the polarization sensitive material of the polarizing beam splitter <NUM> to reflect off of collimating surface <NUM>. This beam will form an exit pupil <NUM>. The second input beam <NUM> encoded with the second polarization will reflect from the polarization sensitive material of the polarizing beam splitter <NUM> to reflect off of reflecting surface <NUM>. This beam will form an exit pupil <NUM>. Because the interface of the prism element <NUM> and the collimating element <NUM> are tilted at an angle other than <NUM>° with respect to the input beams, the exit pupils <NUM> and <NUM> can be spatially offset. As an example if polarizing beam splitter <NUM> is color selective, an exit pupil associated with a first color (e.g., green) can be positioned adjacent an exit pupil associated with a second color (e.g., red) so that the exit pupils can provide spatially separated beams for input to the eyepiece. In addition to the spatial separation in the z-direction as illustrated in <FIG>, the exit pupils can be spatially separated in the x-direction or the y-direction.

Accordingly, two overlapping images could be produced or, using a tilted surface at the interface of the prism element <NUM> and the collimating element <NUM> as illustrated in <FIG>, two spatially separated images could be formed in the image field. Thus, two laterally separated exit pupils could be provided, which could provide input for two input coupling elements on waveguide displays. As discussed herein, the curvatures of collimating surface <NUM> and reflecting surface <NUM> can be different. For example, in a wavelength selective implementation, a wavelength selective beam splitter could be used that would pass a first color to reflect from collimating surface <NUM>. A second color would reflect from the polarizing beam splitter and then reflect from reflective surface <NUM>, thereby producing a beam having the second color that either diverges or converges after reflection from reflective surface <NUM>. This could allow, for example for spatial separation between two different color channels for subsequent coupling into two different incoupling gratings, each associated with a different waveguide layer of the eyepiece. Additionally, these designs can be extended to multi-depth plane implementations in which multiple beams at each color are utilized to provide, for example, M beams at N colors for coupling into MxN waveguides. The integration of quarter wave plates can be implemented in polarization sensitive implementations. As a result, polarization selective reflectors can be implemented in conjunction with spatial separation of the pupils to enable routing of one color to a first depth plane and routing of a second color to a second depth plane. Thus, both wavelength separation as well as polarization separation are included within the scope of the present invention.

In other embodiments, the exit pupils can be disposed at the same location (i.e., superimposed). Thus, the illustration of the spatially separated pupils in <FIG> is merely one example and should not be understood to limit embodiments of the present invention. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

One of more of the optical surface discussed in relation to <FIG> can be variable focus and their focus can be controlled in conjunction with the input from the fiber scanning projector. Accordingly, rays injected into the optical assembly section at different angles can experience different optical powers. In this embodiment, a multi-focal display can be implemented as a function of field angle. Moreover, additional optical elements can be integrated with the structures described herein, for example, between the output surface and the one or more exit pupils or optically downstream of the one or more exit pupils. These additional optical elements, which can include relay optics, can have variable optical power, for example, a variable focus lens positioned between the output surface and the one or more exit pupils. Accordingly, collimated beams can be focused, aberration can be corrected, other optical effects can be implemented, or the like. In some embodiments, the shape of convex object surface <NUM> can vary from spherical and variable focus surfaces or additional optical elements can be utilized as appropriate for the curvature of the convex object surface. Various materials can be utilized to fabricate the structures illustrated herein, including materials that vary their index of refraction as a function of an applied bias, including liquid crystal lenses, electro-optic polymers, lithium niobate, and the like. Since the fiber scanning projector can be scanned at high frequencies, optical materials that can vary their optical properties at high frequencies are suitable for use in various embodiments. As an example, an optical structure that can modulate focal length rapidly can work with a fiber scanning projector to vary the focus on a line-by-line basis or on a pixel-by-pixel basis. These materials can be utilized in conjunction with the input surface and/or the output surface of the optical assembly section as well as in conjunction with collimating surface <NUM>. As an example, a deformable mirror could be integrated as an element of collimating surface <NUM> or as a replacement for reflective surface <NUM>. Such a deformable mirror, operating at kilohertz rates and above, can provide variable focus operation on a line-by-line basis or on a pixel-by-pixel basis as appropriate to the particular application.

The maximum distance to which prism element <NUM> extends in the z-direction, marked at point A in <FIG>, can vary according to the particular implementation. As illustrated in <FIG>, point A is the intersection of the right side of the collimating element <NUM> and the bottom of the prism element <NUM>. The design illustrated in <FIG> enables a wide field of view as the tip of the scanning fiber sweeps through the substantially spherical surface, illustrated by curve <NUM> in <FIG>. In other embodiments, the surface of prism element <NUM> forming the right upper side of the prism element is tilted such that point A is moved to a reduced value in the z-direction. In a similar manner, point B can be moved to larger values in the x-direction as the left side of the prism element <NUM> is extended and the left side of the collimating element <NUM> is reduced. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

<FIG> is a side view of an optical assembly including a Mangin mirror according to an embodiment of the present invention. Similar to one or more of the designs discussed above, beam splitter cube <NUM> is utilized as the basis of the beam splitter cube based optical assembly section <NUM>. Quarter wave plate <NUM> is implemented at the intersection of the beam splitter cube <NUM> and the Mangin mirror <NUM>, which provides for collimation of the input beam. In the illustrated embodiment, output lens <NUM> is implemented as an achromatic doublet, although other lens configurations can be utilized according to embodiments of the present invention.

<FIG> is a side view of an optical assembly including a Mangin mirror according to an alternative embodiment of the present invention. In the embodiment illustrated in <FIG>, beam splitter cube <NUM> is utilized as the basis of the beam splitter cube based optical assembly section <NUM>. Quarter wave plate <NUM> is implemented at the intersection of the beam splitter cube <NUM> and the Mangin mirror <NUM>, which provides for collimation of the input beam. In the illustrated embodiment, output lens <NUM> is implemented as a molded glass lens, although other lens configurations can be utilized according to embodiments of the present invention.

<FIG> is a side view of an optical assembly including a 3D printed lens according to an embodiment of the present invention. Similar to one or more of the designs discussed above, beam splitter cube <NUM> and quarter wave plate <NUM> are utilized in optical assembly section <NUM>. An input lens <NUM> and an output lens <NUM>, which can be molded glass lenses, are utilized in this embodiment. The collimating optic, also referred to as a printed lens, is formed using 3D printing, also referred to as additive manufacturing. This collimating optic includes a substrate <NUM> that supports printed lens <NUM>, for example, a polymer lens formed with curvatures associated with a Mangin lens. The substrate <NUM> is joined to quarter wave plate <NUM>, for example, using an optical adhesive.

It should be noted that any of the characteristics of any of the elements and surfaces discussed or illustrated in reference to <FIG> are applicable to the implementations provided in any of the other implementations illustrated in <FIG> as appropriate. Merely by way of example, curvatures of surfaces, reflective or diffractive properties of surfaces, polarization properties, and the like are applicable to any of the implementations as appropriate.

<FIG> is a simplified perspective view of an optical assembly section of a fiber scanning projector according to an embodiment of the present invention. The optical assembly section <NUM> includes prism element <NUM> to the collimating element <NUM>. Light is incident on the input surface (not shown, but facing the back left) and propagates toward polarizing beam splitter <NUM>. The edge of quarter wave plate <NUM>, collimating surface <NUM>, and output surface <NUM> are also illustrated in this view.

In some embodiments, the fiber scanning projector can achieve a <NUM> arcminute angular resolution and a <NUM> x <NUM> aspect ratio with a <NUM>° diagonal field of view although these particular parameters are not required by the present invention. In some implementations, a <NUM>° x <NUM>° elliptical field of view is achieved. In another embodiment, the fiber scanning projector can achieve a <NUM> arcminute angular resolution and a <NUM> x <NUM> aspect ratio with a <NUM>° diagonal field of view. In yet another embodiment, the fiber scanning projector can achieve a <NUM> arcminute angular resolution or less. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

In order to reduce the size and weight of the fiber scanning projector, portions which do not support light can be trimmed, forming a wedge shaped structure that also increasing packaging flexibility, particularly for integration with eyeglasses with curved frames.

<FIG> is a simplified perspective view of elements of the optical assembly section during fabrication according to an embodiment of the present invention. As illustrated in <FIG>, first element <NUM> of the optical assembly section includes a collimating optic section <NUM> that includes the propagation path of light after passing through the beam splitter, the collimating surface <NUM>, and the output surface <NUM>. Second element <NUM> of the optical assembly section includes the surface <NUM> of the prism on which the polarizing beam splitter can be formed. In this perspective view, the input surface not shown as it is facing to the back left. Alignment features <NUM> are integrated into the materials and are designed to match corresponding alignment features (not shown) on the bottom left surface of the first element.

In some embodiments, the second element <NUM> is fabricated from glass materials to facilitate the formation of the polarizing beam splitter at the interface of the first element and the second element since glass materials can be more suitable for deposition of polarization selective coatings than some plastic materials.

<FIG> is a simplified schematic diagram illustrating a fiber scanning projector <NUM> according to an alternative embodiment not according to the claimed invention. As illustrated in <FIG>, a scanning fiber <NUM> passes through an aperture <NUM> in mirror <NUM>. The scanning fiber is illustrated at the ends of the range of motion. A collimating mirror <NUM> reflects light emitted by the scanning fiber, which is then reflected from mirror <NUM> to provide output beam <NUM>. In some embodiments, the radius of curvature of collimating mirror <NUM> is twice the radius of curvature of spherical object surface <NUM>.

As discussed in relation to the fiber scanning projector, as the scanning fiber <NUM> is actuated by piezoelectric element <NUM>, it sweeps out a substantially spherical surface <NUM>, also referred to as a spherical object surface. Accordingly, after reflection off of a substantially spherical reflector having twice the radius of curvature of the surface swept out by the scanning fiber, light emitted from any point along the surface swept out by the scanning fiber will be well collimated after reflection from the substantially spherical reflector.

Because the base of the fiber scanner is adjacent piezoelectric element <NUM>, the deflection of the scanning fiber <NUM> at aperture <NUM> is small although the deflection at the tip of the scanning fiber is large (e.g., on the order of <NUM> degrees). As the beam is emitted from the tip of the scanning fiber, it fans out to form cone <NUM> of light as illustrated in <FIG>. The collimation of the cone by substantially spherical reflector <NUM> provides a beam with a much larger diameter than the diameter of the scanning fiber so that the majority of the reflected light is reflected from mirror <NUM> with little light passing through aperture <NUM> in the return path.

In some implementations, the field of view of the fiber scanning projector <NUM> is a function of the section of arc that scanning fiber <NUM> subtends during oscillation. As an example, if the scanning fiber sweeps through <NUM> degrees, the field of view of the projector is on the order of <NUM> degrees. Increases in the field of view can be accomplished by increasing the range of fiber oscillation. In other embodiments, magnification of the effective field of view is available to increase the field of view independent of the range of fiber oscillation. Comparing the fiber scanning projectors in <FIG> and <FIG>, whereas the field of view associated with fiber scanning projector <NUM> is maintained as a result of the collimation resulting from reflection from reflector <NUM>, optical assembly section <NUM> provides the illustrated optical surfaces that can be used to introduce magnification that can increase the field of view produced by the projector. As an example, modification of the curvature of output surface <NUM> can be utilized to magnify the field of view.

As illustrated herein, embodiments utilize designs that are related through the use of a spherical object plane and a corresponding reflector having a curvature on the order of twice the curvature of the spherical object plane.

<FIG> illustrates a fiber scanning projector according to an embodiment not according to the claimed invention. The fiber scanning projector <NUM> in <FIG> includes a scanning fiber <NUM> passing through and mechanically coupled to a piezoelectric element <NUM>, a first polarization sensitive reflector <NUM>, and a second polarization sensitive reflector <NUM>. A quarter wave plate <NUM> is integrated with the first polarization sensitive reflector.

In operation, light emitted by the scanning fiber <NUM> has a polarization that passes through the first polarization sensitive reflector <NUM> and the quarter wave plate <NUM>. The second polarization sensitive reflector <NUM> reflects the incident light, which makes a second pass through the quarter wave plate <NUM> and, as a result, is reflected from the first polarization sensitive reflector <NUM> since the polarization of the light is now oriented in the orthogonal direction. After reflection from the first polarization sensitive reflector <NUM>, the light passes through second polarization sensitive reflector <NUM> as an output beam <NUM>. As illustrated in <FIG>, the second polarization sensitive reflector <NUM> is curved with a curvature that collimates the light emitted by the scanning fiber <NUM>. As a result, the input beam, which was diverging, is converted to an output beam that is collimated.

Although the optical elements illustrated in <FIG> are illustrated as separated by air gaps, for example, the first polarization sensitive reflector <NUM> and the second polarization sensitive reflector <NUM> separated by air gap G, this is not required. As an example, a solid laminated component can be utilized that includes the first polarization selective reflector, the quarter wave plate, and the second polarization selective reflector and receives light from the scanning fiber, transmits the light to a laminated curved reflector, performs polarization rotation, and then reflects light from the first polarization selective reflector. Thus, solid elements that can also include optical power can be utilized to provide for focusing/defocusing of light as well as aberration correction.

<FIG> is an alternative fiber scanning projector according to an embodiment not according to the claimed invention. The fiber scanning projector <NUM> illustrated in <FIG> shares some similarities with the fiber scanning projector <NUM> illustrated in <FIG> and the description provided in relation to <FIG> is applicable to the fiber scanning projector <NUM> illustrated in <FIG> as appropriate.

Referring to <FIG>, the fiber scanning projector <NUM> includes a scanning fiber <NUM>, a first polarization sensitive reflector <NUM> that is curved to provide for collimation and a second polarization sensitive reflector <NUM> that is substantially planar. A quarter wave plate is integrated with the first polarization sensitive reflector.

In operation, light emitted by the scanning fiber <NUM> has a polarization that passes through the first polarization sensitive reflector <NUM> and the quarter wave plate. The second polarization sensitive reflector <NUM> reflects the incident light, which makes a second pass through the quarter wave plate and, as a result, is reflected from the first polarization sensitive reflector <NUM> since the polarization of the light is now oriented in the orthogonal direction. After reflection from the first polarization sensitive reflector <NUM>, which collimates the light during reflection, the light passes through second polarization sensitive reflector <NUM> as an output beam <NUM>. Comparing <FIG>, the folded optical path illustrated in <FIG> can be replaced with a potentially shorter optical path as illustrated in <FIG>, but with common features of collimation.

<FIG> is another alternative fiber scanning projector according to an embodiment not according to the claimed invention. The fiber scanning projector <NUM> illustrated in <FIG> shares some similarities with the fiber scanning projector <NUM> illustrated in <FIG> and the fiber scanning projector illustrated <NUM> in <FIG> and the description provided in relation to <FIG> and <FIG> is applicable to the fiber scanning projector <NUM> illustrated in <FIG> as appropriate.

In the embodiment illustrated in <FIG>, scanning fiber <NUM> passes through an aperture <NUM> in curved mirror <NUM>. A polarization selective reflector <NUM> reflects light during a first pass toward the curved mirror <NUM>. By integrating a quarter wave plate in the optical path, light, after reflection and collimation from curved mirror <NUM> passes through the polarization selective reflector <NUM> during the second pass. The embodiment illustrated in <FIG> enables a compact configuration in a hybrid design.

As illustrated by optional lens <NUM>, embodiments enable additional optical elements to be placed a significant distance from the elements making up the fiber scanning projector. In this example, the distance D between the surface of the polarization selective reflector <NUM> and the lens <NUM> provides a working distance that is suitable, for example, to insert a field of view magnifier. In addition, a spherical aberration corrector could be inserted given the suitable, extended working distance provided by this embodiment.

<FIG> is yet another alternative fiber scanning projector according to an embodiment not according to the claimed invention. The fiber scanning projector illustrated in <FIG> shares some similarities with the fiber scanning projector <NUM> illustrated in <FIG> and the fiber scanning projector illustrated in <FIG> and the description provided in relation to <FIG> and <FIG> is applicable to the fiber scanning projector <NUM> illustrated in <FIG> as appropriate.

Referring to <FIG>, scanning fiber <NUM> passes through an aperture <NUM> in a planar mirror <NUM>. A curved polarization selective reflector <NUM> reflects light during a first pass toward the planar mirror <NUM>. By integrating a quarter wave plate in the optical path, light, after reflection from and collimation by the curved polarization selective reflector <NUM> and planar mirror <NUM>, passes through curved polarization selective reflector <NUM> during the second pass. The embodiment illustrated in <FIG> also enables a compact configuration in a hybrid design.

<FIG> is a schematic diagram illustrating a lensed fiber tip according to an embodiment of the present invention. As illustrated in <FIG>, the optical fiber <NUM> includes cladding <NUM> and fiber core <NUM>. The optical fiber can be considered as a point light source emitting rays along an emission cone <NUM>. In the embodiment illustrated in <FIG>, the point light source is illustrated as recessed within the core in the longitudinal direction. A shallow lens surface <NUM> can be applied to the end of optical fiber as illustrated. The lens surface <NUM> can be fabricated in a variety of different manners. As an example, a process utilizing focused ion beam (FIB) milling can be used to make a low stroke lens that provides for aberration correction as illustrated in <FIG>. In some embodiments, the lens surface <NUM> is formed directly on the fiber tip, whereas, in other embodiments, a mold is fabricated and the lens is formed separately from the fiber tip and then bonded to the fiber tip. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

The curvature of the lens surface <NUM> can be selected to remove spherical aberration resulting from optical surfaces in the system, including spherical aberration associated with collimating surface <NUM> illustrated in <FIG>, as well as with other surfaces. Accordingly, through the combination of aberration correction provided by lens surface <NUM> and other surfaces, high image quality is provided by embodiments of the present invention. Utilizing scanning fiber designs as discussed herein, it is possible to perform optical correction on per pixel basis in addition to performing optical correction on a display wide scale.

<FIG> is a schematic diagram illustrating a lensed fiber tip according to another embodiment of the present invention. In addition to aberration correction, embodiments of the present invention enable focusing of light emitted from the fiber tip as illustrated through the use of positive lens <NUM> illustrated in <FIG>. Lens <NUM> can be fabricated directly on the fiber tip, for example, using an FIB milling process or can be molded separately from the fiber tip and then bonded to the fiber tip. Emission cone <NUM> is focused by lens <NUM> to form focused cone <NUM> in this example. The strength of lens <NUM> may be such that light is not focused, but the spread of the rays associated with emission cone <NUM> is reduced.

<FIG> is a schematic diagram illustrating a lensed fiber tip according to an alternative embodiment of the present invention. In addition to aberration correction and focusing, embodiments of the present invention enable defocusing of light emitted from the fiber tip as illustrated through the use of negative lens <NUM> illustrated in <FIG>. Lens <NUM> can be fabricated directly on the fiber tip, for example, using an FIB milling process or can be molded separately from the fiber tip and then bonded to the fiber tip. Emission cone <NUM> is defocused by lens <NUM> to form diverging cone <NUM> in this example. Thus, some embodiments enable the numerical aperture to be increased via the use of a diverging lens on the fiber tip.

In contrast with conventional optical systems, for example, imaging an LCD into an image plane, which are constrained by the Lagrange invariant that maintains the optical invariant as a constant throughout the system, fiber scanning systems can modify the characteristics of the pixel and change the spot size emitted by the fiber. By use of the lenses illustrated in <FIG>, modification of the pixel size can be accomplished, for example, effectively reducing the mode field diameter by increasing the numerical aperture, decreasing the pixel size, and decreasing the imaged spot size.

The optical effects illustrated in <FIG> can be combined, for example, to provide a lens tip that corrects spherical aberration and focuses emitted light, corrects spherical aberration and defocuses emitted light, corrects spherical aberration while providing a lens with a convex region near the fiber core and a concave region near the periphery of the fiber, and the like. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

Claim 1:
A projector (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a scanning light source (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) operable to sweep through a convex surface defining a convex object surface to be imaged (<NUM>, <NUM>), and
an optical assembly section (<NUM>) operable to receive light from the scanning light source (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), wherein the optical assembly section (<NUM>) comprises:
a prism element (<NUM>, <NUM>, <NUM>);
a collimating element (<NUM>, <NUM>, <NUM>) coupled to the prism element (<NUM>, <NUM>, <NUM>) at an interface, wherein the collimating element is configured to collimate a cone of light emitted by the scanning light source at on axis position;
a quarter wave plate (<NUM>, <NUM>, <NUM>); and
a polarizing beam splitter (<NUM>, <NUM>, <NUM>) disposed at the interface.