HK1237884B - An ergonomic head mounted display device and optical system - Google Patents

Description

Ergonomic head-mounted display device and optical system

This application is a divisional application of the application with application date of December 22, 2011, application number 201180068447.7, and invention name “Ergonomic head-mounted display device and optical system”.

Cross-references

This application claims priority to U.S. Provisional Application Serial No. 61/427,162, filed December 24, 2010, which is hereby incorporated by reference in its entirety.

Technical Field

The present invention generally relates to optical see-through head-mounted display (OST-HMD) devices. More specifically, the present invention relates to an ergonomically designed freeform optical system for use as an optical viewing device in an optical see-through HMD having a glasses-like appearance and a wide see-through field of view (FOV).

Background Art

Long-term applications have proven that head-mounted displays (HMDs) are extremely important for many applications across scientific visualization, medical and military training, engineering design and prototyping, remote operation and telepresence, and personal entertainment systems. In mixed and augmented reality systems, optical see-through HMDs are one of the basic ways to combine computer-generated virtual scenes with real-world scene views. Generally speaking, through an optical combiner, an OST-HMD optically overlays computer-generated images on a real-world view while maintaining a direct, minimally degraded real-world view. OST-HMDs have great potential in creating mobile display solutions that can provide more attractive image quality and screen size than other popular mobile platforms such as smartphones and PDAs.

On the other hand, despite significant advancements in HMD design over the past decade, numerous technical and usability barriers remain, preventing widespread adoption of this technology for demanding applications and everyday use. One of the primary obstacles to HMDs is the unwieldy helmet form factor, which has prevented many demanding and emerging applications from adopting this technology. Few existing optical design approaches have been able to create truly portable, compact, lightweight, and non-invasive HMD designs that can function as eyeglass-style near-eye displays. Excessive weight causes fatigue and discomfort and is considered a major obstacle to HMD-based applications. Furthermore, the ability to provide a wide, see-through field of view with minimal obstruction and quality degradation is crucial for performing everyday tasks. In recent years, freeform surfaces have been introduced into HMD system design [U.S. Patents 5,699,194, 5,701,202, and 5,706,136]. D. Cheng, et al., “Design of an optical see-through head-mounted display with low f-number and large field of view using a freeform prism,” Applied Optics, 48(14), 2009, aims to reduce system weight and create a lightweight HMD. However, in today's market, there is still no solution that can meet both ergonomic and performance requirements. Our work aims to develop a solution with a glasses form factor and a wide see-through FOV while maintaining excellent performance.

Summary of the Invention

The present invention relates to an ergonomic optical see-through head-mounted display (OST-HMD) device having the appearance of glasses and a freeform optical system, wherein the freeform optical system serves as an optical observation device in such a display device. Generally speaking, the optical observation device in an OST-HMD consists of an optical path for observing a displayed virtual display image and a see-through path for directly observing a real-world scene. In the present invention, the virtual image path includes a micro-image display unit for providing display content and an ergonomically designed display observation optical device for a user to observe a magnified display content image. The display observation optical device includes a light guide device (hereinafter referred to as a freeform waveguide prism) comprising multiple freeform refractive and reflective surfaces. The display observation optical device may also include additional coupling optical devices to accurately direct light from the image display device into the waveguide prism. The position and shape of the freeform surfaces and the coupling optical device are designed to enable the observer to see a clear, magnified display content image. The see-through path of the head-mounted display device consists of a waveguide prism and a freeform perspective compensation lens attached to the outer surface of the prism. A perspective compensation lens comprising multiple free-form refractive surfaces allows accurate viewing of the surrounding environment across an extremely wide see-through field of view. The waveguide prism and the perspective compensation lens are appropriately designed to ergonomically fit the ergonomic factors of the human head, thereby achieving a lightweight, compact wrap-around see-through display system design with a glasses-like appearance, a wide see-through field of view, and excellent optical performance.

In one aspect, the present invention provides various embodiments of freeform optical systems for use as optical viewing devices in ergonomic head-mounted display devices. The freeform optical systems of the present invention are optimized to provide viewing optics with an ergonomically designed shape that conforms to the ergonomics of the human head, allowing them to cover the face and provide a glasses-like appearance instead of the helmet-like appearance of prior art HMD designs. The present invention also provides a see-through function, allowing the user to observe the surrounding environment and the displayed content on the image display device through the viewing optics. The present invention provides a see-through field of view (FOV) that is significantly larger than the FOV of the virtual view.

In the present invention, the virtual image path of an OST-HMD device includes a micro-image display unit for providing display content and ergonomically designed display viewing optics for a user to observe the magnified display content image. The display viewing optics include a free-form waveguide prism containing multiple free-form refractive and reflective surfaces and may also include additional coupling optics. The waveguide prism acts as near-eye viewing optics to magnify the image on the micro-image display device. Light emitted from the image display unit enters the waveguide prism through the prism's first refractive surface. The light can be incident on the prism directly from the display device or through a set of coupling lenses. The incident light propagates through the waveguide prism through multiple reflections (typically three or more) and then couples out of the prism through the prism's second refractive surface. The exiting light continues to propagate and reaches the system's exit pupil, where the user can observe the virtual content with their eyes. As light propagates through the waveguide prism, light loss due to reflection is minimized if the total internal reflection (TIR) condition on the reflective surface is met. Therefore, it is best that all reflections meet the TIR condition, but it is not a strict requirement. However, it is also highly desirable to compromise the TIR condition on certain reflective surfaces to achieve a thin waveguide prism design. For reflective surfaces that do not meet the TIR condition and are located within the specified perspective FOV of the device, a translucent coating is applied to these surfaces to ensure that enough light from the micro display unit reaches the exit pupil and produces a bright image, while facilitating the optical see-through function. For reflective surfaces located outside the perspective FOV of the device, if the TIR condition is not met, a highly reflective mirror coating can be applied to the surface to minimize light loss. In the present invention, the micro image display unit can be any type of self-luminous or luminescent pixel array that can act as an image source, including but not limited to a silicon-based liquid crystal (LCoS) display device, a liquid crystal display (LCD) panel, an organic light emitting display (OLED), a ferroelectric silicon-based liquid crystal (FLCoS) device, a digital micromirror device (DMD), or a micro projector constructed according to the above or other types of micro display devices.

In the present invention, the perspective path of the head-mounted display device consists of the free-form waveguide prism and a free-form perspective compensation lens. The compensation lens is attached to the physical outer surface of the waveguide prism to offset the light deviation and distortion caused by the prism and maintain a clear perspective view of the real-world scene. The compensation lens, which contains multiple (typically 2 or more) free-form refractive surfaces, allows accurate observation of the surrounding environment across a very large field of view. When the lens is combined with the prism, the surface of the compensation lens is optimized to minimize the deviation and distortion introduced to the light from the real-world scene. If the reflection on the attached surface of the waveguide prism meets the TIR condition in the virtual image display path, it is necessary to maintain a small air gap between the waveguide prism and the compensation lens.

In the present invention, multiple reflections are used to extend the optical path length so that the width of the waveguide prism closely matches the width of an average human head. The long optical path facilitates the design of the waveguide prism into an ergonomic shape while maintaining a large perspective FOV. The long optical path of the prism also allows the image display unit to be moved to the side of the display frame, which reduces the front-end weight of the HMD system and improves the ergonomic fit of the system. In addition, the shape of the waveguide prism (and the optical observation device as a whole) can be designed to approximate the natural curve of the human head for optimal ergonomic fit. For example, in some embodiments, the prism shape is curved to approximate the curvature of a pair of 8-base curved glasses, and in some other embodiments, the prism shape approximately follows the form factor of a pair of 4-base curved glasses. Moreover, the combined thickness of the waveguide prism and the compensation lens is specifically controlled to achieve a thin optical device profile (typically less than 30 mm). In summary, the specially controlled prism shape, long optical path, and optical thickness enable a wraparound optical see-through HMD design that ergonomically fits the human head and has an attractive glasses-like appearance.

Another key aspect of the present invention is the ability to provide an extremely large see-through field of view, typically much larger than the FOV of a virtual display. In the present invention, this functionality is achieved through a variety of mechanisms, such as moving the image display device to the side of the head to expand the clear optical aperture of the waveguide prism, specifically controlling the free-form surfaces on the waveguide prism and the compensating lens to correct for light deviation and distortion, and ensuring high see-through performance across a large FOV. In certain embodiments of the present invention, the see-through FOV extends 120 degrees horizontally and 80 degrees vertically. The see-through FOV of the present invention can be expanded to match the field of view of the human eye.

Since a long optical path is required to match the width or curvature of a person's head and to achieve a large perspective FOV, light rays from the same point of the image display device cross at least once within the waveguide prism, which means that an intermediate image of the virtual display is formed inside the waveguide, although the light intersection point may not be well formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a conceptual diagram of an exemplary embodiment of the present invention.

FIG. 2 a illustrates a set of key structural constraints of the design of the present invention in a cross-sectional view in the YZ plane.

FIG. 2 b illustrates further structural limitations of the design of the present invention in a cross-sectional view in the XZ plane.

FIG. 3 illustrates the reference surface 230 in a 3D view.

FIG. 4 shows a preferred embodiment of a waveguide prism with five reflections according to the present invention, wherein the waveguide prism has an inner surface with a wrap-around appearance close to eight base curves.

FIG5 shows another preferred embodiment of the waveguide prism of the present invention with five reflections, wherein the waveguide prism has an inner surface with a cladding-type appearance close to eight base bends.

FIG. 6 shows another preferred embodiment of a waveguide prism of the present invention with five reflections, wherein the waveguide prism has a flat inner arc on the temple side.

FIG. 7 shows another preferred embodiment of a waveguide prism of the present invention with five reflections, which has a shape similar to the previous embodiment in FIG. 6 .

FIG8 shows another preferred embodiment of the waveguide prism of the present invention with five reflections, which has an inner surface with a wraparound appearance close to eight base bends and is based on a reflective microdisplay.

FIG9 shows another preferred embodiment of the present invention that is similar to the previous embodiment in FIG8 , but the waveguide prism has an inner surface that is close to 4 base bends.

FIG10 shows a preferred embodiment of a three-reflection waveguide prism according to the present invention, wherein the waveguide prism has an inner surface with a cladding-type appearance close to 8 base bends.

FIG. 11 shows annotations and component definitions of the fifth embodiment shown in FIG. 8 .

Figures 12-12b show the MTF curves of the selected field of Example 5 for the red wavelength (625nm) in Figure 12, the MTF curve of the selected field of Example 5 for the green wavelength (525nm) in Figure 12a, and the MTF curve of the selected field of Example 5 for the blue wavelength (465nm) in Figure 12b.

FIG. 13 shows annotations and component definitions of the sixth embodiment shown in FIG. 9 .

Figures 14-14b show the MTF curves of the selected field for the red wavelength (625nm) of Example 6 in Figure 14, the MTF curve of the selected field for the green wavelength (525nm) of Example 6 in Figure 14a, and the MTF curve of the selected field for the blue wavelength (465nm) of Example 6 in Figure 14b.

FIG. 15 shows an example of ray tracing of a perspective path in the sixth embodiment.

FIG. 16 shows an exemplary OST-HMD design with a 4-base bend appearance according to Example 6 of the present invention.

FIG. 17 shows annotations and component definitions of Example 7 shown in FIG. 10 .

Figures 18-18b show the MTF curves of the selected field of Example 7 for the red wavelength (625nm) in Figure 18, the MTF curve of the selected field of Example 7 for the green wavelength (525nm) in Figure 18a, and the MTF curve of the selected field of Example 7 for the blue wavelength (465nm) in Figure 18b.

FIG. 19 shows annotations and element definitions of the compensation lens of Example 7 shown in FIG. 10 .

FIG. 20 shows an example of ray tracing of the perspective path of Example 7 shown in FIG. 10 .

21-21 b show multi-color MTF curves of selected fields of the perspective path of Example 7 shown in FIG. 10 .

FIG. 22 shows an unmodified 3D model of Example 7 of the present invention.

FIG. 23 shows an exemplary OST-HMD design having an 8-base bend wraparound appearance according to Example 7 of the present invention.

FIG. 24 shows the mathematical equations that define the shape of a free-form surface.

FIG. 25 shows parameters of the surface of Example 5 of the waveguide shown in FIG. 8 and FIG. 11 .

FIG26 shows the surface parameters of the coupling lens and the objective lens of Example 5 shown in FIG8 and FIG11.

FIG. 27 shows the position and orientation parameters of the optical surface in Example 5 shown in FIG. 8 and FIG. 11 .

FIG28 shows the surface parameters of the waveguide prism of Example 6 shown in FIG9 and FIG13.

FIG29 shows the surface parameters of the coupling lens and the objective lens of Example 6 shown in FIG9 and FIG13.

FIG. 30 shows the position and orientation parameters of the optical surfaces in Example 6 shown in FIG. 9 and FIG. 13 .

FIG31 shows the surface parameters of the waveguide prism of Example 7 shown in FIG10.

FIG32 shows the surface parameters of the coupling lens and the objective lens of Example 7 shown in FIG10 and FIG17.

FIG. 33 shows the position and orientation parameters of the optical surface in Example 7 shown in FIG. 10 and FIG. 17 .

FIG34 shows surface parameters of the compensation lens of Example 7 shown in FIG10 and FIG19.

FIG35 shows the position and orientation parameters of the compensation lens of Example 7 shown in FIG10 and FIG19.

DETAILED DESCRIPTION

Embodiments according to the present invention will be described more fully with reference to the accompanying drawings. This description is provided to provide an understanding of the present invention. However, it will be apparent that the present invention can be practiced without these details. Furthermore, the present invention can be implemented in various forms. However, the embodiments of the present invention described below should not be construed as limited to the embodiments listed herein. Rather, these embodiments, drawings, and examples are intended to be illustrative and to avoid obscuring the present invention.

The present invention relates to an ergonomically designed freeform optical system for use as an optical viewing device in an optical see-through head-mounted display (HMD) having a glasses-like appearance and a wide see-through field of view (FOV). An exemplary embodiment of the present invention, shown in FIG1 , is an image display system that projects a virtual image into the user's pupil via a freeform waveguide prism, thereby allowing the user to see the displayed content overlaid on a real-world scene. The system comprises:

a. A micro image display unit 105, which acts as an image source and projects light into the waveguide;

b. An optional coupling lens group 110, which consists of one or more lenses that direct light from the display unit into the free-form waveguide prism 100 and correct optical aberrations;

c. a transparent freeform optical waveguide prism 100, as described above, which receives light from the image display unit 105 and propagates the light until an image is projected into the user's pupil; wherein the waveguide allows light from a real-world scene to pass through and into the user's pupil; wherein the waveguide has a physical inner surface 115, a physical edge surface 120, and a physical outer surface 125, a first refractive surface 130, a second refractive surface 135, and a plurality of reflective surfaces;

d. a free-form compensating lens 160 mounted on the waveguide's physical outer surface 125 to correct for optical distortion caused by viewing the world through the waveguide prism; wherein the physical inner surface 165 of the compensating lens 160 approximates the shape of the physical outer surface 125 of the waveguide prism 100 and maintains a small air gap 195 between the waveguide 100 and the compensating lens 160 at the surface of the waveguide's physical outer surface 125 that satisfies the TIR condition; wherein the compensating lens 160 is designed to compensate for the light deviation and distortion effects caused by the waveguide 100 so that the user maintains a clear see-through field of view 190;

Thus, the image display unit 105 may be any type of self-luminous or emissive pixel array that can serve as an image source, including but not limited to a liquid crystal on silicon (LCoS) display device, a liquid crystal display (LCD) panel, an organic light emitting display (OLED), a ferroelectric liquid crystal on silicon (LCoS) device, a digital micromirror device (DMD), or a micro-projector constructed based on these or other types of micro-display devices;

Therefore, the image display unit 105 injects light 140 into the optional coupling lens 110 and then passes through the waveguide 100 or directly into the waveguide through the first refractive surface 130;

The light 140 then follows a path 145 along the waveguide that includes multiple reflections from the first refractive surface 130 to the second refractive surface 135;

Then, light rays 140 following paths 145 along the waveguide may intersect and form an intermediate image 155 inside the waveguide 100;

The light 140 then passes through the second refractive surface 135 beyond which the user observes the image with his or her pupil 150;

Light 198 from the real-world scene then passes through the compensating lens 160 and the waveguide 100 before reaching the pupil 150 .

One aspect of the present invention is an ergonomically designed free-form waveguide prism that allows an image to be projected onto a refractive input plane of the prism, where the image is then reflected and refracted until it reaches the user's eyes. The waveguide prism's shape, optical path length, and thickness are specifically optimized to enable a wraparound design for an optical see-through HMD that ergonomically fits the human head and has an attractive, eyeglass-like appearance.

In an exemplary embodiment, the freeform waveguide prism of the present invention comprises at least three physical surfaces, each physical surface comprising a plurality of reflective and refractive optical surfaces disposed on the physical surface, wherein the interior space of the physical surface is filled with a refractive medium having a refractive index (n) greater than 1, the physical and optical surfaces comprising:

a. a physical inner surface 115 disposed toward the user's eyeball, wherein the physical inner surface comprising a plurality of reflective and refractive surfaces adapted to transmit an image to the user's eyeball is limited to fit within the ergonomics of the human head;

b. a physical outer surface 125 positioned toward an external scene, wherein the physical outer surface comprises a plurality of reflective surfaces adapted to reflect an image toward an eye of a user, wherein the physical outer surface is generally within 30 mm of the inner surface at all points, and wherein the physical outer surface comprises at least one refractive surface to allow light from the external scene to pass through the waveguide and reach the eye of the user;

c. Physical edge surface 120, which may include a refractive surface for allowing light from the image display unit to enter the waveguide;

d. a refractive input surface 130 disposed on one of the physical surfaces, which allows light from the image display unit to enter the waveguide;

e. A refractive output surface 135 that allows light to exit the waveguide and is positioned on a physical inner surface, close to the user's pupil, wherein the refractive surface may or may not be covered with a translucent coating;

f. Multiple reflective surfaces placed on the physical inner and outer surfaces, where each reflection is produced by satisfying TIR conditions or by applying a semi-transparent partially reflective coating on the waveguide surface;

Therefore, light 140 from the image display unit 105 enters the waveguide through the first refractive surface 130;

The light 140 then follows a path 145 along the waveguide that includes multiple reflections on multiple reflective surfaces from the first refractive surface 130 to the second refractive surface 135, where each reflection is produced by satisfying a total internal reflection condition or by applying a translucent coating on the surface;

The light 140 then passes through the second refractive surface 135 beyond which the user observes the image with his or her pupil 150;

Thus, light 198 from the real-world scene, after being refracted by the compensating lens 160 , is refracted through the physical outer surface 125 of the waveguide 100 and the physical inner surface 115 of the waveguide before reaching the pupil 150 .

In an exemplary embodiment, the inner and outer surfaces 115, 125 of the waveguide are appropriately designed to produce multiple reflections that direct light into the user's pupil without distorting the image. These multiple reflections extend the optical path length, allowing the width of the waveguide prism to closely match the width of an average head. The long optical path length allows the waveguide prism to be designed with an ergonomic shape. The prism's long optical path further allows the image display unit 105 to be moved to the side of the display frame, thereby reducing the front-end weight of the HMD system and improving the system's ergonomic fit.

In a typical embodiment, inner surface 115 is constrained to a pre-specified curve that approximates the desired eyeglass form factor. Outer surface 125 is further constrained to achieve a thin profile, with the thickness between the inner and outer surfaces typically no greater than 30 mm. In one practice in the art, the total thickness between the inner and outer surfaces is limited to no more than 12 mm. The parameters of the inner and outer surfaces of the waveguide are thus optimized to minimize distortion of the projected image at the waveguide's exit point.

In an exemplary embodiment, the inner surface 115 of the waveguide 100 may comprise a plurality of surface segments; each surface segment is described by a unique set of parameters.

In a typical embodiment, the outer surface 125 of the waveguide 100 may comprise a plurality of surface segments; each surface segment is described by a unique set of parameters.

In some embodiments, a coupling lens 110 may be added between the micro image display unit 105 and the first refractive surface 130 of the waveguide 100 to facilitate injection of light from the display unit 105 into the waveguide. The coupling lens may be used to correct optical aberrations of the waveguide.

Another aspect of the present invention is a free-form perspective compensating lens 160 physically attached to the waveguide prism 100. The compensating lens 160 is designed to counteract the light deviation and distortion caused by the waveguide prism 100 and provide a clear perspective view of the real-world scene across a wide field of view.

In an exemplary embodiment, the free-form compensating lens 160 of the present invention comprises a plurality of (typically two or more) free-form refractive surfaces, wherein the interior spaces of the refractive surfaces are filled with a refractive medium having a refractive index (n) greater than 1, and the optical surfaces include:

a. a refractive outer surface 170 disposed toward the external scene, allowing light 198 from the external scene to enter the compensating lens, wherein the refractive outer surface is typically a continuous single refractive surface and is typically located within 30 mm of the physical inner surface 115 of the waveguide prism 100 at all points;

b. a refractive inner surface 165 disposed toward the outer surface 125 of the waveguide prism 100, which allows light to exit the compensating lens and enter the waveguide prism 100, wherein the refractive inner surface 165, comprising a plurality of refractive surfaces, is generally constrained to approximate or conform to the shape of the outer surface 125 of the waveguide prism 100,

Thus, light 198 from the real-world scene is refracted by the refractive outer surface 170 and the refractive inner surface 165 of the compensating lens 160 , as well as the physical outer surface 125 and the physical inner surface 115 of the waveguide 100 before reaching the pupil 150 .

In an exemplary embodiment, the compensating lens 160 and the waveguide prism 100 are specifically co-optimized to allow accurate viewing of the surrounding environment across an extremely wide field of view 190. When the compensating lens 160 is combined with the waveguide prism 100, the inner and outer surfaces 165, 170 of the compensating lens 160 are optimized to minimize the offset and distortion introduced to light rays from the real-world scene. The inner surface 165 of the compensating lens 160 can be identical to the outer surface 125 of the waveguide prism 100, with only a slight offset along the z-axis. If reflections from the attached outer surface 125 of the waveguide prism 100 meet TIR conditions in the virtual image display path, it is necessary to maintain a small air gap 195 between the waveguide prism 100 and the compensating lens 160. If there is no TIR requirement for the outer surface 125 of the waveguide prism 100, the air gap 195 can be filled with an index-matching adhesive to bond the compensating lens 160 to the waveguide 100. The inner surface 165 of the compensating lens 160 can also be redesigned along with the outer surface 170 of the compensating lens 160 to achieve better see-through performance. For this case, the air gap 195 between the waveguide prism 100 and the compensating lens 160 can be limited to less than 6 mm at any point along the surface. The outer surface 170 is further limited to limit the total thickness of the waveguide prism 100 and the compensating lens 160 to typically no more than 30 mm. In one practice in the art, we limit the total thickness of the prism and lens to no more than 15 mm. For a given see-through FOV 190, the inner surface 165 and the outer surface 170 of the compensating lens 160 should be large enough. The shape and thickness of the compensating lens are specifically optimized to achieve a wraparound design for an optical see-through HMD that ergonomically fits on a person's head and has an attractive glasses-like appearance.

In an exemplary embodiment, the inner and outer surfaces on the compensating lens 160 and the waveguide prism 100 are large enough to achieve a wide see-through field of view 190 that is as large as the field of view of the human eye, for example, up to 90° temple-side, up to 60° nose-side, and up to 60° vertically superior and inferior relative to the center of the field of view. The free-form surfaces on the waveguide prism 100 and the compensating lens 160 are optimized to correct for light deviation and distortion to ensure high see-through performance across a large FOV.

All of the above surfaces are free-form surfaces, including but not limited to spherical surfaces, aspherical surfaces, deformed aspherical surfaces, XYP polynomials, or other types of mathematical specifications. The surfaces are asymmetric in the YZ plane of the global coordinate system shown in FIG1 , wherein the origin of the coordinate system is located at the center of the exit pupil 150, wherein the Z axis 175 points to the external scene, the Y axis 180 points to the temple side, and the X axis 185 points vertically along the head. Throughout the present invention, unless otherwise specified, the same coordinate system is used for all drawings and descriptions.

A primary goal of the present invention is to design a free-form optical system for use as an optical viewing device in an optical see-through HMD, thereby achieving a glasses-shaped appearance and a wide see-through field of view (FOV). Therefore, designing a waveguide prism requires optimizing the parameters of each individual surface to minimize an appropriate optical error function, such as wavefront error or system modulation transfer function (MTF). The waveguide prism shown in Figure 1 includes multiple free-form surfaces that provide more design freedom compared to traditional rotationally symmetric optical surfaces. Therefore, the free-form design approach provides the ability to design an optical viewing device with better optical performance and ergonomic fit, while using fewer surfaces than an optical viewing device of similar specifications using traditional rotationally symmetric optical surfaces. However, appropriate constraints must be imposed on all surfaces in order to produce an efficient waveguide prism design that achieves the primary goal of maintaining the desired form factor and providing a large see-through FOV.

Figures 2 and 3 illustrate the structural constraints used in our design process. These control methods embed structural signatures into our designs.

Figure 2 illustrates a set of key structural constraints for waveguide prism design. Figures 2a and 2b show cross-sectional views in the YZ and XZ planes, respectively. In the figures, the exit pupil 250 of waveguide 200 is aligned with the pupil of the human eye; dashed line 230 is a reference surface used to constrain the shape of the inner surface 215 of waveguide 200 and the position of the micro-image display unit 205. Reference surface 230 is a cylindrical surface in 3D space (as shown in Figure 3), approximating the natural curvature of the human head from the nose to the ears. The radius of reference surface 230 in the horizontal YZ plane can vary from 40 mm to as large as 100 mm, depending on the head size of the target user population. The radius of reference surface 230 in the vertical XZ plane can be straight or curved, as long as the inner surface of the prism does not obstruct the user's face. In one practice in the field, a horizontal radius of 65 mm is chosen, which is similar to the radius of 8-base curved glasses. The center of the reference arc 232 is defined by reference dimensions Y _ref1 234, Z _ref1 236, and Y _HIPD 238, where Y _HIPD 238 is half the user's interpupillary distance (IPD), which typically falls between 40 mm and 80 mm for over 95% of the population. Reference dimensions 234, 236, and 238 are selected based on specific design goals. In one embodiment of the present invention, dimensions 234, 236, and 238 are selected to be 10 mm, 50 mm, and 32 mm, respectively, for an example of 8 base curves and an IPD of 64 mm. The dashed line 240, defined by dimension Z _ref2 242, is another reference surface used to constrain the shape of the inner surface 215. Reference surface 240, which can be flat or curved with a desired shape, ensures that the compensation lens 260 is not positioned too far from the user's face, which would otherwise result in a poorly designed optical design. Dashed lines 290a and 290b mark the boundaries of the specified see-through FOV 290 in the horizontal dimension from temple to nose, while dashed lines 290c and 290d mark the boundaries of the specified see-through FOV 290 in the vertical dimension.

To meet our ergonomic design goals and the required see-through FOV, the following constraints are imposed on the inner surface 215 of the waveguide 200:

a. The entire inner surface 215 is limited to being located outside the reference surface 230 to ensure that the prism does not obstruct the user's head;

b. The inner surface 215 may deviate from the reference surface 230 but is restricted from passing through the reference surface 240;

c. When it is necessary to divide the inner surface 215 from a single surface description into multiple surface segments, each surface segment has its own mathematical formula to increase design freedom. The breakpoints must be located outside the upper boundary 290a of the perspective FOV 290, or the broken segments must abut the intermediate segments to maintain first-order continuity. In other words, the surface segments 215a of the inner surface 215 located within the perspective FOV 290 must be continuous and smooth optical surfaces. The local radius of curvature of the surface segments 215a should be no less than 20 mm to maintain acceptable perspective distortion.

d. Surface segment 215a is constrained to a curvature close to the design. The shape of inner surface segment 215a determines the appearance of the waveguide prism, because the outer surface 270 of compensation lens 260 is similar in shape to inner surface segment 215. In one practice in the art, surface segment 215a is designed to follow an 8-base bend located 10 mm outside reference surface 230, thereby achieving an 8-base bend wraparound design.

The outer surface 225 of the waveguide prism 200 has greater degrees of freedom than the inner surface 215. The outer surface can be divided into multiple surface segments as needed. The breakpoints can be located inside or outside the see-through FOV 290. When the breakpoints are located inside the see-through FOV 290, a clear gap of at least 1 mm is required around the intersection of two adjacent surface segments to ensure a smooth transition between the two segments. The outer surface 225 must be sufficiently wide in both the X and Y directions for the given see-through FOV 290. The maximum distance between the outer surface 225 and the inner surface 215 is typically limited to less than 30 mm to ensure the waveguide prism is not too thick. In many practical applications, the maximum distance is limited to less than 15 mm. While low light loss is desirable, reflections on the outer surface 225 do not need to meet TIR conditions. If TIR conditions are not met, surface segments within the see-through FOV 290 require a translucent, semi-reflective coating. For surface segments outside the see-through FOV 290, if TIR conditions are not met, a highly reflective mirror coating is recommended.

In addition to the constraints imposed on the inner and outer surfaces of the waveguide prism, the width 244 of the waveguide prism 200 (the distance measured from the pupil 250 to the temple in the Y direction) is limited by a lower boundary so that the width of the waveguide prism at the temple is sufficient to provide the desired see-through FOV 290. The width 244 is further limited by an upper boundary to ensure that the resulting waveguide prism does not protrude too much at the temple of a person's head for ergonomic fit and an attractive appearance. In one practice in the art, the width 244 is set by an upper boundary of 50 mm from the exit pupil 250 in the Y direction.

The width 246 of the waveguide prism (measured in the Y direction from the pupil 250 to the side of the nose) is limited by a lower boundary so that the width of the waveguide prism 200 on the side of the nose is sufficient to provide the desired see-through FOV 290. The width 246 is further limited by an upper boundary to ensure that the resulting waveguide prism does not interfere with the bridge of the nose on a person's head. In one practice in the art, the width 246 is set by an upper boundary of 30 mm from the exit pupil 250 in the Y direction.

The heights 252 and 254 of the waveguide prism (measured in the X direction from the pupil 250 to the forehead and cheek) are limited by a lower boundary so that the height of the waveguide prism 200 is sufficient to provide the desired see-through FOV 290 above and below in the vertical direction.

Two positional constraints are imposed on the micro-image display unit 205: (1) any part of the display unit should be outside the reference surface 230; and (2) the display unit should not be too far from the exit pupil 250 in the Y direction.

The compensating lens 260 is designed to offset the light deviation and distortion caused by the waveguide prism 200 and is physically attached to the waveguide prism 200. When the compensating lens 260 is combined with the waveguide prism 200, the inner surface 265 and outer surface 270 of the compensating lens 260 are optimized to minimize the deviation and distortion introduced to the light from the real-world scene. The inner surface 265 of the compensating lens 260 can be identical to the outer surface 225 of the waveguide prism 200, with a slight offset along the z-axis. If the reflection from the attached outer surface 225 of the waveguide prism 200 meets the TIR condition in the virtual image display path, it is necessary to maintain a small air gap 295 between the waveguide prism 200 and the compensating lens 260. If there is no TIR requirement for the outer surface 225 of the waveguide prism 200, the air gap 295 can be filled with a refractive index matching adhesive to bond the compensating lens to the waveguide prism. The inner surface 265 of the compensating lens 260 can also be redesigned along with the outer surface 270 of the compensating lens 260 to achieve better see-through performance. For this scenario, the air gap 295 between the waveguide prism 200 and the compensating lens 260 can be limited to less than 6 mm at any point along the surface. The outer surface is further limited to limit the total thickness of the waveguide prism 200 and the compensating lens 260 to typically no more than 30 mm. In one practice in the art, we limit the total thickness of the prism and lens to no more than 15 mm. The inner surface 265 and outer surface 270 of the compensating lens 260 should be large enough for a given see-through FOV 290.

FIG3 shows a 3D view of reference surface 230. Reference arc 230 in FIG2 sweeps along the X-axis to become cylindrical surface 330. The entire inner surface 325 of waveguide prism 300 should lie outside cylindrical surface 330 to ensure that the prism does not physically obstruct the user's face. Circle 350 marks the exit pupil location of waveguide 300.

The following figures illustrate example embodiments of the present invention that implement some or all of the above limitations and result in different design structures for different base bend styles.

FIG4 illustrates a preferred embodiment of a five-bounce waveguide prism of the present invention, having an inner surface with a nearly 8-base bend wraparound appearance. This embodiment can be used to implement an HMD system with an 8-base bend wraparound glasses form factor. In this embodiment, the physical inner surface 415 and the physical outer surface 425 of the waveguide prism 400 are two continuous smooth surfaces, each described by a freeform surface parameter set. The refractive surface 430 of the waveguide prism 400 is not part of the inner surface 415 and is described by a different surface parameter set. In this figure, light beams 440a, 440b, and 440c originate from three different pixels on a micro-image display unit 405. A coupling lens 410 is used between the display unit 405 and the waveguide prism 400 to help correct optical aberrations and improve image quality. In this embodiment, light beams 440a, 440b, and 440c enter the waveguide prism 400 through the refractive surface 430, are reflected five times (R1 to R5) by the outer surface 425 and the inner surface 415, are emitted through the refractive surface 435, and finally reach the exit pupil 450. Among the five reflections, the reflection R1 on the outer surface 425 and the reflection R2 on the inner surface 415 meet the TIR condition, while the reflection R4 on the inner surface 415 and the reflections R3 and R5 on the outer surface 425 do not meet the TIR condition. In order to increase the reflection efficiency of the reflections R3, R4, and R5, it is necessary to apply a translucent coating to both the inner surface 415 and the outer surface 425. In order to maintain the TIR condition for the reflections R1 and R2, a dielectric coating is preferably used. To ensure the 8-base bend envelope form factor, the inner surface 415 is constrained to be close to the predefined 8 base bends in the horizontal dimension. Inside waveguide prism 400, light ray bundles 440a, 440b, and 440c are refocused and form intermediate images 455a, 455b, and 455c, respectively.

FIG5 illustrates another preferred embodiment of a waveguide prism of the present invention with five reflections, having an inner surface approaching eight base bends. In this embodiment, the physical inner surface 515 of the waveguide prism 500 is divided into two surface segments 515a and 515b, each of which is a smooth surface described by a different set of freeform surface parameters. The physical outer surface 525 of the waveguide prism 500 is a continuous smooth surface described by a set of freeform surface parameters. The refractive surface 530 and the reflective surface 515a are described by the same set of freeform surface parameters and are therefore a single smooth surface; the reflective surface 515b and the refractive surface 535 are described by the same set of freeform surface parameters and are therefore a single smooth surface. Surface segments 515a and 515b are connected by surface segment 515c. Surface segment 515c is designed to maintain first-order continuity at the intersection between surfaces 515b and 515c, provided that the intersection lies within the upper boundary 590a of the perspective FOV 590. Similarly, if the intersection between surfaces 515a and 515c is located within the upper boundary 590a of the see-through FOV 590, it is also necessary to maintain first-order continuity at the intersection between surfaces 515a and 515c. Of the five reflections, reflections R2, R3, and R4 satisfy the TIR condition, while reflections R1 and R5 do not satisfy the TIR condition. To increase reflection efficiency, a translucent coating is applied to the outer surface 525. To maintain the TIR condition for reflection R3 on surface 525, a dielectric coating is preferably used. If segment 525a is located outside the upper boundary 590a of the see-through FOV 590, a mirror coating can be applied to the upper surface segment 525a. A coupling lens 510 is used between the image display unit 505 and the refractive surface 530 of the waveguide prism 500 to help correct optical aberrations and improve image quality. Surface segment 515b is constrained to move close to the 8-base bend, while surface segment 515a is constrained to move close to the outer surface 525, thereby facilitating a reduction in the overall weight of the waveguide prism 500.

FIG6 illustrates another preferred embodiment of a waveguide prism of the present invention with five reflections, featuring a gentle inner curvature on the temple side. In this embodiment, the refractive surface 630 of the waveguide prism 600 is not part of the inner surface 615 and is described by a different surface parameter set, while the inner surface 615 is a continuous smooth surface. The refractive surface 635 shares the same surface parameter set as the surface 615. The physical outer surface 625 of the waveguide prism 600 is a continuous smooth surface and is described by a freeform surface parameter set. Of the five reflections, reflections R2, R3, and R4 satisfy the TIR condition, while reflections R1 and R5 do not. To increase reflection efficiency, a translucent coating is applied to the outer surface 625. To maintain the TIR condition for reflection R3 on the surface 625, a dielectric coating is preferably used. If the surface segment 625a is located outside the upper boundary 690a of the perspective FOV 690, a mirror coating can be applied to the upper surface segment 625a. The inner surface 615 is not restricted to any predetermined curvature, but the surface position is restricted to ensure that the prism is not too far from the face. A coupling lens 610 is used between the image display unit 605 and the refractive surface 630 of the waveguide prism 600 to help correct optical aberrations and improve image quality.

FIG7 shows another preferred embodiment of a waveguide prism of the present invention with five reflections, which is similar to the embodiment shown in FIG6 . In this embodiment, the refractive surface 730 of the waveguide prism 700 is not part of the inner surface 715 and is described by a different surface parameter set, while the inner surface 715 is a continuous smooth surface. The refractive surface 735 shares the same surface parameter set as the surface 715. The physical outer surface 725 of the waveguide prism 700 is divided into two segments 725a and 725b, each of which is a smooth surface described by a different free-form surface parameter set. Surface segments 725a and 725b are connected by surface segment 725c. Surface segment 725c is designed to maintain first-order continuity at the intersection between surfaces 725b and 725c, provided that the intersection is within the upper boundary 790a of the perspective FOV 790. Similarly, it is also necessary to maintain first-order continuity at the intersection between surfaces 725a and 725c if the intersection between surfaces 725a and 725c is located within the upper boundary 790a of the perspective FOV 790. In addition, this embodiment does not require the use of a coupling lens between the waveguide prism 700 and the micro image display unit 705 because the prism itself is sufficient to correct optical aberrations.

FIG8 illustrates a preferred embodiment of a five-reflection waveguide prism of the present invention, having an inner surface approaching eight base bends, and specifically designed for reflective light-emitting pixel arrays such as LCoS or FLCoS microdisplay panels. In this embodiment, the physical inner surface 815 of the waveguide prism 800 is divided into two planar segments 815a and 815b, each of which is a smooth surface described by a different set of freeform surface parameters. The refractive surface 830 and the reflective surface 815a are a single smooth surface described by the same set of planar parameters; the reflective surface 815b and the refractive surface 835 are a single smooth surface described by the same set of planar parameters. Surface segments 815a and 815b are connected by surface segment 815c. Surface segment 815c is designed to maintain first-order continuity at the intersection between surfaces 815b and 815c, provided that the intersection lies within the upper boundary 890a of the perspective FOV 890. Similarly, if the intersection between surfaces 815a and 815c lies within the upper boundary 890a of the perspective FOV 890, it is also necessary to maintain first-order continuity at the intersection between surfaces 815a and 815c. The physical outer surface 825 of the waveguide prism 800 is divided into two segments 825a and 825b, each of which is a smooth surface described by a different set of freeform surface parameters. Surface segments 825a and 825b are connected by surface segment 825c. Surface segment 825c is designed to maintain first-order continuity at the intersection between surfaces 825b and 825c, provided that the intersection lies within the upper boundary 890a of the perspective FOV 890. Similarly, if the intersection between surfaces 825a and 825c lies within the upper boundary 890a of the perspective FOV 890, it is also necessary to maintain first-order continuity at the intersection between surfaces 825a and 825c. Surface segment 815b is limited to near the 8-base bend, while surface segment 815a is limited to near the outer surface 825a to help reduce the overall weight of the prism. Of the five reflections, reflections R2, R3, and R4 meet the TIR condition, while reflections R1 and R5 do not. Therefore, to increase reflection efficiency, a translucent coating is required on the outer surface 825. To maintain the TIR condition for reflection R3 on surface 825b, a dielectric coating is preferably used. If surface segment 825a is located outside the upper boundary 890a of the perspective FOV 890, a mirror coating can be applied to the upper surface segment 825a. A coupling lens 810 is used between the micro-image display unit 805 and the refractive surface 830 of the waveguide prism 800 to help correct optical aberrations and improve image quality. In this embodiment, the micro-image display unit 805 includes a reflective micro-display panel 805a (e.g., an LCoS display panel), an objective lens 805b, and a polarization beam splitter 805c. Objective lens 805b is used to perform telecentric focusing of light on the micro display surface. Polarization beam splitter 805c acts as a beam combiner to merge the display illumination path (not shown) and the display imaging path. Polarization beam splitter 805c also acts as a polarizer and an analyzer for the incident and outgoing light of micro display panel 805a. The component definitions of this embodiment are shown in Figure 11, and the parameters are given in Figures 25-27 (Tables 2-4).

FIG9 shows another preferred embodiment of the present invention that is similar to the embodiment shown in FIG8 , except that the physical inner surface 915 of the waveguide prism 900 is optimized to approximate 4 base curves rather than 8 base curves. In this embodiment, the waveguide prism 900 has similar structural characteristics to the embodiment in FIG8 . However, the inner surface segment 915b is limited to approximate 4 base curves. Therefore, this embodiment can be used to implement an HMD system with a flat appearance similar to a pair of 4 base curve glasses and with the form factor of 4 base curve glasses. Similar to the embodiment shown in FIG8 , this embodiment is specifically designed for reflective light-emitting pixel arrays such as LCoS or FLCoS type microdisplay panels. The component definitions of this embodiment are shown in FIG13 , and the parameters are given in FIG28-30 (Tables 5-7).

FIG10 shows a preferred embodiment of a three-reflection waveguide prism of the present invention, which has an inner surface close to an 8-base bend wrap-around appearance. This embodiment can be used to implement an HMD system with an 8-base bend wrap-around form factor. In this embodiment, the physical inner surface 1015 and the physical outer surface 1025 of the waveguide prism 1000 are two continuous smooth surfaces, each of which is described by a free-form surface parameter set. The refractive surface 1030 of the waveguide prism 1000 is not part of the inner surface 1015 and is described by a different surface parameter set. The micro-image display unit 1005 includes a micro-display panel 1005a and an objective lens 1005b for achieving telecentric focusing of light on the micro-display surface. The micro-display panel 1005a can be a reflective micro-display (e.g., an LCoS, FLCoS, or DMD panel) or a transmissive micro-display (e.g., an LCD panel) or a self-luminous micro-display (e.g., an OLED panel). In the example of a reflective microdisplay panel, a beam splitter (not shown) needs to be installed after the objective lens 1005b to introduce an illumination path (not shown). A coupling lens 1010 is used between the image display unit 1005 and the waveguide prism 1000 to help correct optical aberrations and improve image quality. In this design example, light beams 1040a, 1040b, and 1040c from three different pixels on the microdisplay 1005a enter the waveguide prism 1000 through the refractive surface 1030, are reflected three times by the inner surface 1015 and the outer surface 1025, then exit through the refractive surface 1035 and finally reach the exit pupil 1050. In this example, among the three reflections, reflection R1 and reflection R2 meet the TIR condition, while reflection R3 on the outer surface 1025 does not meet the TIR condition. In order to increase the reflection efficiency of reflection R3, it is necessary to apply a translucent coating on the outer surface 1025. In order to maintain the TIR condition for reflection R1, a dielectric coating is preferably used. To ensure an 8-base bend eyeglass form factor, the inner surface 1015 is constrained to approximate the predefined 8-base bend. Inside the waveguide prism 1000, the light bundles 1040a, 1040b, and 1040c are refocused and form intermediate images 1055a, 1055b, and 1055c, respectively. The component definitions for this embodiment are shown in FIG17 , and the parameters are given in FIG31-33 (Tables 8-10).

In other embodiments, the image display unit can be positioned toward the inner surface, outer surface, or edge surface, depending on the lens shape, number of reflections, and desired eyeglass form factor. In a specific embodiment, for an 8-base bend eyeglass form factor, the image display device is typically positioned toward the edge surface of the waveguide, while for a 4-base bend eyeglass form factor, the image display device is typically positioned toward the inner surface.

Although 8-base and 4-base eyeglass designs are described herein, any other eyeglass shape may be designed using the concepts of the present invention, such as industry standard eyeglass form factors including, but not limited to, 2-base, 3-base, 4-base, 5-base, 6-base, 7-base, 8-base, and 9-base.

A feature of the present invention is that the extended optical path length requires that the surfaces be designed so that the light bundle is refocused at an intermediate point through the prism. This refocusing of the light creates an intermediate image halfway through the prism, so the light rays are slightly deflected at the exiting refractive surface. This has the advantage that the overall thickness of the waveguide does not increase rapidly as the field of view of the virtual image path increases in an OST-HMD.

According to the present invention, seven embodiments are provided (Figures 4-10). Hereinafter, numerical data (Figures 8-10) of embodiments 5-7 are provided. Three types of free-form surfaces are used in the embodiments, and the mathematical equations for each type of surface are listed in Figure 24 (Table 1). The equations in Figure 24 (Table 1) are given by a local coordinate system, with its origin being the surface vertex. The position and orientation of the surface are either directly defined in a global coordinate system or defined by a reference coordinate system. As described in the detailed description of Figure 1, the global coordinates are located at the center of the exit pupil, with the x-axis pointing to the inside of the paper, the y-axis pointing upward, and the z-axis pointing to the external scene.

Numerical data of Example 5 (depicted in FIG8 )

FIG11 shows the annotations and component definitions for Example 5 ( FIG8 ). This embodiment is designed for a 0.37” reflective display (e.g., LCoS or FLCoS), resulting in a virtual FOV of 26.5° in the Y direction, 15° in the X direction, and 30° in the diagonal direction. The system focal number (F/number) is 2. FIG25 (Table 2) lists the surface parameters of the waveguide prism 800, and FIG26 (Table 3) lists the surface parameters of the coupling lens 810 and the objective lens 805b. The positions and orientations of all optical surfaces and the optical materials of each optical element are listed in FIG27 (Table 4).

MTF curves for selected fields of red (625 nm), green (525 nm), and blue (465 nm) wavelengths are shown in Figures 12-12b. The MTF performance was evaluated for a centered 3 mm pupil with a cutoff spatial frequency of 80 cycles/mm, which corresponds to an equivalent pixel size of 6.25 μm.

Numerical data of Example 6 (depicted in FIG8 )

FIG13 shows the annotations and component definitions for Example 6 ( FIG9 ). This embodiment is designed for a 0.37” reflective display (e.g., LCoS or FLCoS), resulting in a virtual FOV of 26.5° in the Y direction, 15° in the X direction, and 30° in the diagonal direction. The system focal length is 2. FIG28 (Table 5) lists the surface parameters of the waveguide prism 900, and FIG29 (Table 6) lists the surface parameters of the coupling lens 910 and the objective lens 905b. The positions and orientations of all optical surfaces and the optical materials of each optical component are listed in FIG30 (Table 7).

MTF curves for selected fields of red (625 nm), green (525 nm), and blue (465 nm) wavelengths are shown in Figures 14-14b. The MTF performance was evaluated for a centered 3 mm pupil with a cutoff spatial frequency of 80 cycles/mm, which corresponds to an equivalent pixel size of 6.25 μm.

Figure 15 shows an example of ray tracing of the perspective path of Example 6. The total corrected perspective FOV is 75° horizontally and 70° vertically.

FIG16 illustrates an exemplary OST-HMD design with a four-base bend design according to Example 6 of the present invention. The OST-HMD device comprises a pair of optical components of Example 6: a spectacle frame 1602 and an electronics unit 1604. Each optical component comprises a free-waveguide prism 1600, a compensation lens 1660, a coupling lens 1610, a beam splitter 1605c, an objective lens 1605b, and a microdisplay panel 1605a. The electronics unit 1604, located within the temples of the spectacle frame 1602, can be used to integrate necessary electronic components, including but not limited to circuit boards for the microdisplay unit and display lighting unit, an image and video receiving and processing unit, an audio input and output unit, a graphics processing unit, a positioning unit, a wireless communication unit, and a computational processing unit. The specified see-through FOV 1690 of this embodiment is 45° on the temple side, 30° on the nose side in the horizontal dimension, and ±35° in the vertical dimension (not shown).

Numerical data of Example 7 (depicted in FIG10 )

FIG17 shows the annotations and component definitions for Example 7 ( FIG10 ). This embodiment is designed for a 0.37” reflective display (e.g., LCoS or FLCoS), resulting in a virtual FOV of 26.5° in the Y direction, 15° in the X direction, and 30° in the diagonal direction. The system focal length is 2. FIG31 (Table 8) lists the surface parameters of the waveguide prism 1000, and FIG32 (Table 9) lists the surface parameters of the coupling lens 1010 and the objective lens 1005b. The positions and orientations of all optical surfaces and the optical materials of each optical component are listed in FIG33 (Table 10).

MTF curves for selected fields of red (625 nm), green (525 nm), and blue (465 nm) wavelengths are shown in Figures 18-18b. The MTF performance was evaluated for a centered 3 mm pupil with a cutoff spatial frequency of 80 cycles/mm, which corresponds to an equivalent pixel size of 6.25 μm.

FIG. 19 shows annotations and element definitions of the compensation lens of Example 7 ( FIG. 10 ).

Figure 20 shows an example of ray tracing of the perspective path of Example 6. The total corrected perspective FOV is 80° horizontally and 70° vertically.

Polychromatic MTF curves for selected fields with variable diffraction limits for the perspective path are shown in Figures 21-21b. The MTF performance was evaluated for a centered 3 mm pupil with a cutoff spatial frequency of 60 cycles/mm.

FIG22 shows an unmodified 3D model of Example 7. The model includes a waveguide prism, a compensation lens, a coupling lens, and an objective lens. The model also includes a beam splitter space to provide space for inserting a beam splitter to introduce the illumination path of the reflective microdisplay. The model further includes a cover glass for the microdisplay.

FIG23 illustrates an exemplary OST-HMD design with an 8-base bend design according to Example 7 of the present invention. The OST-HMD device comprises a pair of optical components of Example 7: a spectacle frame 2302 and an electronics unit 2304. Each optical component comprises a free-waveguide prism 2300, a compensation lens 2360, a coupling lens 2310, an objective lens 2305b, and a microdisplay panel 2305a. The electronics unit 2304, located within the temples of the spectacle frame 2302, can be used to integrate necessary electronic components, including but not limited to circuit boards for the microdisplay unit and display lighting unit, an image and video receiving and processing unit, an audio input and output unit, a graphics processing unit, a positioning unit, a wireless communication unit, and a computational processing unit. The specified see-through FOV 2390 of this embodiment is 65° on the temple side, 35° on the nose side in the horizontal dimension, and ±35° in the vertical dimension (not shown).

From the foregoing description, various modifications of the present invention, in addition to those described herein, will be apparent to those skilled in the art. Such modifications are also intended to be within the scope of the appended claims. Each reference cited in this application is hereby incorporated by reference in its entirety.

While the preferred embodiments of the present invention have been shown and described, it will be readily apparent to those skilled in the art that modifications may be made to the preferred embodiments without departing from the scope of the appended claims. Accordingly, the scope of the present invention is limited solely by the following claims.

The reference numerals listed in the following claims are merely for facilitating the examination of this patent application and are exemplary and are not intended in any way to limit the scope of the claims to the specific features having the corresponding reference numerals in the drawings.

Claims (12)

1. A free-form waveguide prism comprising at least three physical surfaces, each physical surface including a plurality of reflective and refractive free-form optical surfaces disposed thereon, wherein an internal space defined by said physical surfaces is filled with a refractive medium having a refractive index (n) greater than 1, wherein said plurality of reflective and refractive surfaces fold and extend the optical path length to allow the waveguide to conform to the shape of eyeglasses, enabling an image display unit to be positioned to the side of the head and achieving a wide field of view of up to 90° relative to the front in the temple direction, up to 60° relative to the front in the nose direction, and up to 60° relative to the front above and below, wherein its inner and outer surfaces are designed under constraints of eyeglass shape factors and maximum thickness to direct light to the user's pupil without causing image distortion, said physical and optical surfaces comprising: a. A physical inner surface (115) positioned toward the user's pupil, wherein the physical inner surface is constrained to be a pre-specified surface approximating the shape factor of the eyeglasses, wherein the inner surface is configured to reflect an image to the user's eyeball with minimal distortion; b. A physical outer surface (125) facing an external scene, wherein the physical outer surface is configured to reflect an image to the user's pupil with minimal distortion, wherein the physical outer surface is located within the maximum distance of the inner surface at all points, wherein the physical outer surface includes at least one refractive surface to allow light from the external scene to pass through the waveguide and reach the user's eyeball. c. Physical edge surface (120) comprising a refractive surface that allows light from the image display unit to enter the waveguide; d. A refractive incident surface (130) disposed on one of the physical surfaces, which allows light from the image display unit to enter the waveguide; e. A refractive exit surface (135) disposed on the physical inner surface, close to the user's pupil, and allowing light to exit the waveguide; and f. Three or more free-form reflective surfaces are disposed on the physical inner and outer surfaces, wherein each reflection is generated by satisfying a total internal reflection condition or by applying a semi-transparent partially reflective coating to the surface of the waveguide; wherein these reflections are optimized to guide the light along the interior of the waveguide with minimal distortion, wherein multiple reflections extend the optical path length to enable the waveguide to achieve a wide field of view and a size suitable for human head size; thus, light (140) from the image display unit (105) enters the waveguide through the refractive incident surface (130); g. A first reference surface (230) that approximates the shape of a normal person's head, wherein the inner surface is constrained to be located outside the first reference surface, the first reference surface being defined by Y _ref1 , Z _ref1 and Y _HIPD , wherein Y _ref1 is the distance in the Y direction between the midline of the head and the center of the first reference surface, Z _ref1 is the distance in the Z direction between the pupil and the center of the first reference surface, and Y _HIPD is the distance in the Y direction from the pupil to the midpoint of the head; h. A second reference surface (240) that limits the extent to which the waveguide projects outward from the user's face, wherein the inner surface is constrained to be located within the second reference surface; i. The maximum distance between the physical inner surface (115) and the physical outer surface (125); j. The upper and lower limits of the width (244) of the waveguide in the horizontal dimension from the pupil to the temple, so that the waveguide reaches the side of the head and is wide enough to produce a specified perspective field of view set through its upper boundary (290a). k. The upper and lower limits of the width (246) of the waveguide in the horizontal dimension from the pupil to the nose, so that the waveguide is wide enough to produce a specified perspective field of view set through its lower boundary (290b), but without interfering with the bridge of the nose; l. A lower limit of the height of the waveguide in the vertical dimension, starting from the pupil, so that the waveguide is wide enough to produce a specified perspective field of view defined by its upper boundary (290c) or lower boundary (290d). m. Surface segment (215a), wherein the inner surface is constrained to fit the eyeglass shape factor, wherein the width of the surface segment is bounded by the upper boundary (290a) and lower boundary (290b) of the specified perspective field of view projected on the inner surface in the horizontal direction, and the height of the surface segment is bounded by the upper boundary (290c) and lower boundary (290d) of the specified perspective field of view projected on the inner surface in the vertical direction, wherein the local radius of curvature of the surface segment is bounded by a range depending on the eyeglass shape factor; Then, the light (140) travels along the waveguide path (145), which includes multiple reflections on the plurality of reflective surfaces from the refracting incident surface (130) to the refracting exit surface (135), wherein each reflection is generated by satisfying the total internal reflection condition or by a translucent coating applied to the surface. Then, light (140) passes through the refracting exit surface (135) and extends beyond the surface, allowing the user to observe the image through the pupil (150); Then, the light (198) from the external scene is refracted by the physical outer surface (125) and the physical inner surface (115) of the waveguide before reaching the pupil (150), wherein the perspective field of view through the waveguide reaches a maximum of 90° in the direction of the temple, a maximum of 60° in the direction of the nose, and a maximum of 60° above and below directly in front. Therefore, the shapes of the inner and outer surfaces of the waveguide are optimized within these constraints to minimize optical distortion from the incident point to the exit point of the waveguide. 2. The free-form waveguide prism according to claim 1, wherein Y _ref1 is between 0 and 40 mm. 3. The free-form waveguide prism according to claim 1, wherein Z _ref1 is between 30 and 90 mm. 4. The freeform waveguide prism of claim 1, wherein the Y _HIPD is between 20 and 40 mm. 5. The freeform waveguide prism of claim 1, wherein the radius of curvature of the first reference surface is between 40 and 100 mm in the horizontal dimension. 6. The free-form waveguide prism of claim 1, wherein the second reference surface is defined by a reference dimension Z _ref2 , wherein Z _ref2 is the distance between the pupil and the second reference surface. 7. The free-form waveguide prism according to claim 6, wherein Z _ref2 is less than 40 mm. 8. The free-form waveguide prism of claim 1, wherein the maximum distance between the physical inner surface and the physical outer surface is less than 40 mm. 9. The freeform waveguide prism of claim 1, wherein the upper limit of the width (244) of the prism in the direction from the pupil toward the temple is 80 mm. 10. The free-form waveguide prism of claim 1, wherein the lower limit of the width (244) of the prism in the direction from the pupil toward the temple is 15 mm. 11. The freeform waveguide prism of claim 1, wherein the upper limit of the width (246) of the prism from the pupil toward the nose is 40 mm. 12. The free-form waveguide prism of claim 1, wherein the lower limit of the width (246) of the prism from the pupil toward the nose is 8 mm.