Patent Description:
Some implementations of an HMD provide a see-through display for an augmented reality view in which real-world scenes are visible to a user and additional image information is overlaid thereon. Such an augmented reality view is provided by helmet mounted see-through displays found in military applications and by heads-up displays (HUDs) in windshields of automobiles. In such embodiments, there can be multiple areas for displaying images over the see-through view.

<CIT>, <CIT>, <CIT>, and <CIT> disclose prior art HMDs using polarization optics.

Catadioptric systems employ both refraction and reflection to provide certain benefits including building a lighter head mounted display (HMD). Catadioptric HMDs provide a wide field of view (FOV) for a wearer. Described herein are embodiments of optical devices which may be part of a catadioptric HMDs that combine at least one small electronic display with two optical elements: a polarizing filter and a combiner. The combiner is also known as a reflector. Some embodiments use a freeform partially reflective shell as the reflector, and a reflective circular polarizer as the polarizing filter. The reflector is curved along one or more axes of orientation with respect to an eye of a wearer. A curved reflector shapes or directs a resulting image to an eye pupil. According to certain embodiments, the image is formed from visible light energy. One or more of the elements are freeform where freeform as used herein means at least that a curvature in a surface is without a rotational symmetry or is rotationally asymmetric. For example, a surface of the polarizer or a surface of the reflector does not have a rotational symmetry along one directional axis or along two directional axes. According to some embodiments, the components do not share a same optical axis. For example, a first optical axis of the polarizing filter is offset or not aligned with a second optical axis of the freeform partially reflective reflector.

The reflective circular polarizer eliminates a use of or a need for total internal reflection (TIR). Circular polarization as described herein means at least an electromagnetic wave having a polarization in which, at each point, an electric field of the wave has a constant magnitude and its direction rotates with time in a plane perpendicular to the direction of the wave. This arrangement allows the optical components to be thin shells (e.g., <<NUM>, <<NUM>, and <<NUM>), and does not require a compensating prism for augmented reality (AR) as required in a conventional freeform prism architecture when a see-through outer shell is used to allow ambient light to enter the device. Further, only a single polarizing filter is needed to manage the polarization states throughout the light path. The combination of the elements facilitates virtual reality (VR) and AR vision for the wearer. <FIG> illustrate aspects of the optical architecture further described herein.

Avoiding the use of thick freeform prisms reduces weight, improves aesthetics, and eliminates chromatic aberrations. A result is sleeker and lighter optics for an improved form-factor which is more likely to be adopted by consumers. Some embodiments include use of just two thin shells as opposed to thick prisms of conventional designs. It is possible to use either a single or double reflection from the combiner which can be a freeform combiner.

<FIG> is a simplified diagram of a side view of a catadioptric HMD in accordance with various embodiments. Each of the elements of the HMD <NUM> takes the form of one of various possible embodiments as further described herein. The HMD <NUM> includes a frame <NUM> that supports at least one electronic display <NUM> that produces unpolarized light for one or both user eyes <NUM> of a user <NUM>. The frame <NUM> includes one or more arms that extend from a front of the user <NUM> and rest on one or more ears on a side of the user's head. According to at least some embodiments, a portion of the frame <NUM> rests on a bridge of a nose of the user <NUM>. A combiner or reflector <NUM> is positioned outside of a polarization filter <NUM>. The polarization filter <NUM> is in a light path (within the HMD <NUM>) between the electronic display <NUM> and an expected position of one or both user eyes <NUM> (see, e.g., also <FIG>). As shown, the polarization filter <NUM> is on an eye-ward side of the reflector <NUM> and on a world-facing side of the display <NUM>. An 'eye-ward side' may generally relate to a side which faces an eye of a user wearing a device, such as the HMD <NUM>, including a proposed optical device, whereas a 'world-facing side' may generally relate to a side facing away from an eye of a user. Accordingly, the polarization filter <NUM> may in particular be arranged between the reflector <NUM> and the display <NUM>. The reflector <NUM> reflects at least a portion of light from the electronic display to one or both user eyes <NUM>.

A vision and device coordinate system <NUM> provides a reference for <FIG> and the other figures described herein. According to some embodiments, each of the reflector <NUM> and the polarization filter <NUM> are curved along at least one of a first axis or dimension <NUM> labeled X and along a second axis <NUM> labeled Y, the second axis <NUM> different than the first directional axis <NUM>. A curvature along the first axis <NUM> may be referred to as a horizontal arc along a certain number of degrees of azimuth with respect to the HMD <NUM> and the user <NUM>. A curvature along the second axis <NUM> may be referred to as a vertical arc along a certain number of degrees of altitude with respect to the HMD <NUM> and the user <NUM>. A third axis <NUM> is labeled Z and is an optical axis relative to the user's eyes <NUM> and for the optical elements of the HMD <NUM>.

<FIG> is an overhead cross-sectional view along line <NUM>-<NUM> of the catadioptric HMD <NUM> shown in <FIG>. Ambient light <NUM> passes through a front surface <NUM> of the reflector <NUM> and through the polarization filter <NUM> to reach the eyes of the user <NUM>. The frame <NUM> supports the electronic display <NUM>, the reflector <NUM>, and the polarization filter <NUM>. The polarization filter <NUM> includes a front surface <NUM> and a back surface <NUM>. According to the embodiment shown, each of the reflector <NUM> and the polarization filter <NUM> is substantially planar along a first axis <NUM>.

<FIG> is a diagram of a side view of an arrangement <NUM> of elements of a catadioptric HMD not in accordance with the present invention. Support elements are omitted for clarity of illustration and are present in assembled HMDs as understood by those in the art. A pupil <NUM> of a user eye <NUM> is behind a partially reflective reflector <NUM> and a partially reflective polarization filter <NUM>.

The reflector <NUM> includes a first interior or eye-facing surface <NUM> and an exterior or world-facing surface <NUM>. While the reflector <NUM> is shown as a single material, the reflector <NUM> comprises one or more layers of one or more various materials. For example, the reflector <NUM> takes the form of a freeform thin shell that includes a partial mirror coating on a substrate such as on the eye-facing surface <NUM> and an anti-reflecting coating on the substrate on the world-facing surface <NUM>. The polarization filter <NUM> also is shown as a single material. However, the polarization filter <NUM> comprises one or more layers of one or more various materials according to various embodiments. For example, the filter <NUM> includes a planar substrate, a linear polarizer, a linearly polarizing reflective film, and a quarter-wave retarder film.

The eye <NUM> receives light emitted from an electronic display <NUM> after it has traveled along a light path within the HMD. The filter <NUM> generates circular polarized light from the display <NUM>. The filter <NUM> reflects orthogonal circular polarized light after the light reflects a first time from the reflector <NUM>. The filter <NUM> transmits circular polarized light after the light reflects a second time from the reflector <NUM>.

According to some embodiments, the eye <NUM> also receives light from an ambient outside of the catadioptric HMD. According to some embodiments, the display <NUM> is oriented at an angle <NUM> relative to an axis of the substantially planar partially reflective polarization filter <NUM>. In other embodiments, the display <NUM> is placed parallel or contiguous with a proximate surface of the partially reflective polarization filter <NUM>. Preferably, light <NUM> emanates from a front or first side or surface <NUM> of the electronic display <NUM> and not from a back or second side <NUM> of the electronic display <NUM>.

The display <NUM> is shown as substantially planar at least along a first surface <NUM>. The display <NUM> includes a second or back surface <NUM>. The display <NUM> is either substantially planar, or contoured or curved, depending on the particular embodiment. The display <NUM> is shown and assembled in the HMD a distance <NUM> from an interior surface of the polarization filter <NUM>. However, the display <NUM> may be mounted to or formed directly contiguous with the polarization filter <NUM>. An actual construction of the display <NUM> uses organic light emitting diodes (OLED), light emitting diodes (LED), or any other suitable material or combination of elements to produce a plurality of light emitting sources which are arranged on a substantially locally continuous surface such as an edge-illuminated element and a liquid crystal display (LCD). According to some embodiments, the display <NUM> provides a rectangular array of light emitting elements. According to some embodiments, the display <NUM> is transparent or semi-transparent and that transparency can be either an overall general passing of light or take a form of a dot type beam splitter where there are small non-transparent elements on a largely transparent substrate so that the overall effect is that the display allows light to pass through it.

In line with to the present invention, a surface of the display <NUM> is shaped to fit a contour of at least a portion of the interior surface of the partially reflective polarization filter <NUM>. According to certain embodiments, the angle <NUM> of the orientation of the display <NUM> is coordinated with a contour or curvature of the reflector <NUM> so as to shape a size and orientation of an image reaching the pupil <NUM> when reflected from one or more surfaces of the reflector <NUM> and from one or more surfaces of the polarization filter <NUM>. Any curvature in the display <NUM>, along one or two axes of orientation is coordinated with curvature in one or more axes of curvature of the reflector <NUM> and coordinated with curvature in one or more surfaces of the polarization filter <NUM>. The polarization filter <NUM> is shown substantially planar in <FIG>. According to various embodiments, the curvature in one or more of the reflector <NUM> and the polarization filter <NUM> is any suitable curved element that has a spherical or aspherical or compound shape and a uniform or non-uniform thickness as needed to shape the image of light reaching the pupil <NUM> of the eye <NUM> from the display <NUM>. However, according to the present invention, the reflector and the polarization filter are formed as specified in the appended set of claims.

A portion <NUM> of the ambient light <NUM> passes through the partially reflective reflector <NUM> and the partially reflective polarization filter <NUM> to reach the user eye <NUM>. Light <NUM> emanating from the display <NUM> is unpolarized. According to some embodiments, light <NUM> that first passes through the partially reflective polarization filter <NUM> is left-handed circular-polarized light <NUM>. Upon reflection from the partially reflective reflector <NUM>, the light become right-handed circular polarized light <NUM>. Light <NUM> that has been reflected a first time from the partially reflective polarization filter <NUM> remains right-handed circular-polarized. Upon a second reflection from the partially reflective reflector <NUM>, light <NUM> again becomes left-handed circular polarized light <NUM> and is converted to linearly polarized light <NUM> after passing through the partially reflective polarization filter <NUM>. At each element <NUM>, <NUM>, a portion of the light <NUM> is either reflected or transmitted. Consequently, not all light leaving the electronic display <NUM> reaches the eye <NUM> of the user.

<FIG> is a diagram of a side view of an arrangement <NUM> of elements of a catadioptric HMD in accordance with additional embodiments. A pupil <NUM> of a user eye <NUM> is behind a curved partially reflective reflector <NUM> and a curved partially reflective polarization filter <NUM>. The reflective polarization filter <NUM> includes a first inner surface <NUM> that is concave in contour along at least one directional axis and a second outer surface <NUM> that is convex. The filter <NUM> is of a first thickness <NUM> at a first position and of a second thickness <NUM> at a second position. According to some embodiments, the filter <NUM> is a uniform thickness along the body of the filter <NUM> at least at positions along the light path of light provided by a display <NUM>. The light path extends between the display <NUM> and the user eye <NUM>. According to some embodiments, light <NUM> leaves the display <NUM> in a non-polarized state and, after passing through the filter <NUM>, becomes polarized light <NUM>. Only a fraction of the light <NUM> leaving the display <NUM> arrives at the pupil <NUM> of the user eye <NUM> due to the elements of the HMD.

The reflector <NUM> includes a first interior concave surface <NUM> and an exterior convex surface <NUM>. According to some embodiments, the eye <NUM> also receives ambient light from an ambient outside of the catadioptric HMD but is not shown for sake of simplicity in illustration. In the arrangement <NUM> shown, light from the display <NUM> is reflected at least two times from the partially reflective reflector <NUM> and at least one time from the filter <NUM> before reaching the user eye <NUM>. An outer surface <NUM> of the filter <NUM> is positioned relative to the inner surface <NUM> of the reflector <NUM> in the assembled HMD to provide light from the display <NUM> to the user eye <NUM>. An orientation, a position, or both an orientation and a position of the display <NUM>, relative to the other elements, are selected for the HMD. A shape, a position, or both a shape and an orientation of the filter <NUM>, relative to the other elements, are selected for the HMD. Also, a shape, a position, or both a shape and an orientation of the reflector <NUM>, relative to the other elements, are selected for the HMD. These features are arranged together to shape a resulting image generated by the light originating from the display <NUM> to the user eye <NUM>.

While the reflector <NUM> is shown as a single material in <FIG>, the reflector <NUM> comprises one or more layers of one or more various materials. For example, the combiner or reflector <NUM> takes the form of a freeform thin shell that includes a partial mirror coating on a substrate such as on the eye-facing surface <NUM> of the substrate and an anti-reflection coating on the world-facing surface <NUM> of the substrate. Freeform for the reflector <NUM> refers to a curvature or contour along a first axis or orientation, a curvature or contour along a second axis or orientation, or along both the first and the second axes.

The polarization filter <NUM> also is shown as a single material in <FIG>. However, the polarization filter <NUM> comprises one or more layers of one or more various materials according to various embodiments. For example, the filter <NUM> includes a curved or contoured base substrate such as a plastic or glass layer, a linear polarizer, a linearly polarizing reflective film, and a quarter-wave retarder film. The filter <NUM> generates circular polarized light from the display <NUM>. The filter <NUM> reflects orthogonal circular polarized light after a first reflection from the reflector <NUM> and transmits circular polarized light after a second reflection from the reflector <NUM>. The filter <NUM> is shown curved along a first directional axis. The filter <NUM> may be curved along a second directional axis to conform with the shape of a user's head. The filter <NUM> is a freeform surface. Freeform for the filter <NUM> as used herein includes a curved or contoured surface without a rotational symmetry along at least one or first axis or orientation of the filter <NUM> surface. The curvature also may be along a second axis or orientation of the filter <NUM>.

<FIG> is an exploded diagram of elements of portions of a catadioptric device in accordance with various embodiments. A display such as display <NUM> emits unpolarized light <NUM> toward a linear polarizer (LP) <NUM>. The display <NUM> may be rectangular in shape and may have a first dimension and a second dimension which is orthogonal to the first dimension. For example, the first dimension is approximately <NUM> and the second dimension is approximately <NUM>. Linearly polarized light <NUM> passes to and through a reflective polarizer (RP) <NUM>.

Linearly polarized light <NUM> from the RP <NUM> passes to and through a quarter-wave plate (QWP) <NUM> and a glass substrate <NUM> thereby becoming circularly polarized (CP) light <NUM>. The CP light <NUM> is reflected from a curved partially reflective reflector <NUM> which changes its handedness. For example, for left-handed circularized light <NUM>, the first reflected light <NUM> becomes right-handed circularized light. The first reflected light <NUM> passes through the glass substrate <NUM> and the QWP <NUM> and thereby becomes phase-shifted light <NUM>. Such light is linear and orthogonal to the linear transmission polarization state such as that of a reflective polarizer such as polarizer <NUM> and with respect to a linear polarizer such as LP <NUM>. The phase-shifted light <NUM> then is reflected by the RP <NUM> back through the QWP <NUM> and the glass substrate <NUM>. At this point, the light is right-handed circularized light <NUM>. The light <NUM> is reflected a second time by the curved partially reflective reflector <NUM>. The handedness is again reversed back to left-handed circularized light <NUM>. The third-reflected light passes through the glass substrate <NUM>, the QWP <NUM>, the RP <NUM>, and the LP <NUM> and is thereby shaped light <NUM> capable of being observed by or directed into a pupil of a human eye (not shown) as part of an image made by light <NUM> emitted from the display <NUM>. The arrangement <NUM> can take many forms including an HMD or other form of headgear, a head mounted device, a head mounted screen, a wearable device, a VR headset, an AR or VR visor, a set of virtual reality glasses, or electronically enhanced eyewear. Alternatively, the arrangement can be part of a heads-up display (HUD). The display <NUM> can take one of several forms including an electronic image source, an electronic screen, an LED panel, an OLED panel, and an LCD panel.

<FIG> is a flowchart illustrating a method of providing light to a user by way of a catadioptric device in accordance with certain illustrative embodiments. At <NUM>, image light is provided by an image source. At <NUM>, a first portion of the image light is transmitted through a partially reflective circular polarizing filter. The partially reflective circular polarizing filter may be a combination of elements. At <NUM>, a second portion of the first portion of image light is reflected from a partially reflective reflector or combiner such as reflector <NUM>. At <NUM>, at least a portion of the second portion of light is reflected from the partially reflective circular polarizing filter or polarizer. At <NUM>, image light is reflected a second time by the partially reflective reflector or combiner. At <NUM>, a third portion of image light is transmitted through the partially reflective circular polarizer to reach a user eye. For example, such light is the linearly polarized light <NUM> of <FIG>.

In some embodiments, certain aspects of the techniques described above may implemented by one or more processors of a processing system executing software such as to provide power to and control of elements in an electronic display for producing light to reach one or more user's eyes.

Claim 1:
An optical device comprising:
a reflector (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) being curved along a first directional axis (<NUM>) and being rotationally asymmetric along the first directional axis;
a partially reflective circular polarizer (<NUM>, <NUM>, <NUM>), for selecting polarized light, positioned between the reflector and an expected position of a first user eye (<NUM>) and curved along the first directional axis; and
an electronic display (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), configured to provide light to the first user eye, positioned at an eye-ward side of the partially reflective circular polarizer and curved to fit a contour of the eye-ward side of the partially reflective circular polarizer.