Eyeglass lens with waveguide

Abstract

The present disclosure relates to an augmented reality eyeglass lens having a waveguide and a method of manufacturing such an eyeglass lens having a waveguide. The eyeglass lens comprises a first lens portion and a second lens portion having a cylindrical waveguide therebetween; and the cylindrical waveguide having cylindrical concentric opposing surfaces defining a first cylindrical interface with the first lens portion and a second cylindrical interface with the second lens portion, and wherein the cylindrical waveguide is transparent and comprises a central waveguide core having a transparent medium at the first and second cylindrical interfaces.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a spectacle lens comprising a waveguide for augmented reality display and to a method of manufacturing such a spectacle lens comprising a waveguide. BACKGROUND

[0002] In the field of augmented reality (AR), virtual images superimposed on the real world are displayed to a user using a transparent combiner that redirects images from a projector system to the user's eyes. Current solutions typically employ a transparent planar waveguide formed of a glass material or a plastic material, wherein light from a projector is in-coupled into the waveguide via a diffractive grating, travels through the waveguide along its longitudinal direction by total internal reflection, and is out-coupled to the user's eyes by a further diffractive grating. In such applications, the thickness of the waveguide is typically a few millimeters (mm).

[0003] There exist solutions of transparent combiners based on free-space reflective optics, but these solutions typically have a small area (also referred to as eyebox) in which the user can see an image or an array of such images. Therefore, free-space reflective optics are not suitable for applications in which a large eyebox is required. Due to variations in interpupillary distance (IPD), the small eyebox area requires mechanical adjustments or adaptation of the AR glasses to a specific user, thereby increasing cost and complexity. On the other hand, solutions based on planar waveguides have a large eyebox area, which means that a single variation of the AR glasses design can be adapted to a large population of users and the virtual images can be easily seen by the user.

[0004] It is known to embed a waveguide of the above-mentioned type within a spectacle lens, and this is desirable for a number of reasons. In particular, in AR applications, the in-coupling diffractive grating and the out-coupling diffractive grating can be holographic optical elements (HOEs) having a thickness of less than one millimeter (mm). However, embedding such a waveguide within a lens presents limitations. Typically, the lenses used in spectacles are curved, especially in the case of prescription lenses, while the waveguide is flat. Therefore, embedding the waveguide within a curved lens has the drawback that the thickness of the lens must be greater, and therefore heavier, to accommodate the flat waveguide.

[0005] There exist a number of methods to encapsulate a thin film within a lens or to laminate a thin film on a spectacle. While these methods can be useful for incorporating HOEs having a thickness of less than one millimeter, they are not suitable for use with waveguides having a thickness of a few millimeters encapsulated within a spectacle lens. Moreover, none of the known solutions discuss the problems related to achieving the required refractive index variations within the spectacle lens to ensure that light rays can be efficiently guided from the light source to the user's eyes, thereby replicating the pupil in a continuous manner without the light rays from the same image pixel diverging when projected to infinity. SUMMARY

[0006] An eyeglass lens for augmented reality display is provided, the eyeglass lens comprising: a first lens portion and a second lens portion, with a cylindrical waveguide between the first lens portion and the second lens portion; and a cylindrical waveguide having cylindrical concentric opposing surfaces defining a first cylindrical interface with the first lens portion and a second cylindrical interface with the second lens portion, and wherein the cylindrical waveguide is transparent and comprises a central waveguide core with a transparent medium at the first cylindrical interface and the second cylindrical interface.

[0007] The central core can have a higher refractive index than the transparent medium, and the transparent medium is an adhesive material or an air gap. The first lens portion, the second lens portion, the cylindrical waveguide, and the transparent medium are arranged in an optical stack.

[0008] The eyeglass lens can have a primary axis and a secondary axis, the first cylindrically shaped interface and the second cylindrically shaped interface having a curved profile along the primary axis. The first cylindrically shaped interface and the second cylindrically shaped interface can have a linear profile along the secondary axis. The first lens portion and the second lens portion have a spherical outer profile.

[0009] The eyeglass lens can further comprise an input optic, wherein the input optic is configured and arranged to couple light into the cylindrical waveguide. The input optic can comprise an in-coupling linear diffraction grating with a constant period applied to a surface of the waveguide. The in-coupling linear diffraction grating can be attached to the waveguide at the first cylindrical interface or the second cylindrical interface. The in-coupling linear diffraction grating can be switchable. The in-coupling linear diffraction grating can be formed from a holographic material.

[0010] The input optic can be configured and arranged to receive light rays from an image source and to cause the light rays to enter the cylindrical waveguide such that, at each point of incidence, for a common cylindrical axis, all light rays originating from a same pixel of the image source are incident on a surface of the cylindrical waveguide at a same angle with respect to a surface normal and at a same angle with respect to a plane normal, so that the in-coupled light maintains its direction angle as it propagates along the cylindrical waveguide.

[0011] The eyeglass lens can further include an output optic configured and arranged to receive propagating light from the cylindrical waveguide and present the light as an image to an eye of a user. The output optic can include an out-coupling linear diffraction grating with a constant period applied to a surface of the waveguide. The out-coupling linear diffraction grating can be attached to the waveguide at the first cylindrical interface or the second cylindrical interface. The out-coupling linear diffraction grating can be switchable. The out-coupling linear diffraction grating can be formed from a holographic material. The out-coupling linear diffraction grating can be attached to the waveguide at the first cylindrical interface or the second cylindrical interface.

[0012] A method of manufacturing an eyeglass lens for an augmented reality display is also provided, the method comprising: forming a first lens portion and a second lens portion, and inserting a cylindrical waveguide between the first lens portion and the second lens portion; forming the cylindrical waveguide having cylindrical concentric opposing surfaces defining a first cylindrical interface with the first lens portion and a second cylindrical interface with the second lens portion, and wherein the cylindrical waveguide is transparent and comprises a central waveguide core having a transparent medium at the first cylindrical interface and the second cylindrical interface.

[0013] The central core can have a higher refractive index than the transparent medium. The transparent medium can be an adhesive material. The transparent medium can be an air gap. The first lens portion, the second lens portion, the cylindrical waveguide, and the transparent medium can be arranged in an optical stack.

[0014] It is therefore advantageous that an eyeglass lens for an augmented reality display is encapsulated within the lens with a curved waveguide that provides an eyebox with significantly reduced aberrations. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order that the features of the disclosure can be understood in detail, a more particular description will be rendered by reference to examples, some of which will be illustrated in the drawings. It is to be noted, however, that the appended drawings are not intended to be exhaustive or limiting of the disclosure, and are not necessarily drawn to scale. The disclosure is intended to cover all alternatives, modifications and equivalents included within the scope of the disclosure, which is set forth in the claims. The drawings are intended to be illustrative only and thus are not necessarily drawn to scale. The principles of the disclosure will be described in connection with the drawings, where like reference numerals will be used to refer to items of like function throughout the various figures and wherein:

[0016] Figure 1a A perspective view of an eyeglass lens with a waveguide according to an embodiment is schematically illustrated;

[0017] Figure 1b An exploded top view of an eyeglass lens with a waveguide according to an embodiment is schematically illustrated;

[0018] Figure 1cA side view of an eyeglass lens with a waveguide according to an embodiment is schematically illustrated;

[0019] Figure 2 A waveguide for an eyeglass lens according to an embodiment is schematically illustrated;

[0020] Figure 3 An in-coupling optic for a waveguide for an eyeglass lens according to an embodiment is schematically illustrated;

[0021] Figure 4 An in-coupling optic and an out-coupling optic for a waveguide for an eyeglass lens according to an embodiment are schematically illustrated;

[0022] Figure 5 A light source, an in-coupling optic, an out-coupling optic, and an eye of a user for a waveguide for an eyeglass lens according to an embodiment are schematically illustrated;

[0023] Figure 6 An out-coupling optic for a waveguide for an eyeglass lens according to an embodiment is schematically illustrated;

[0024] Figure 7a A perspective view of an eyeglass lens with a waveguide according to an embodiment is schematically illustrated;

[0025] Figure 7b An exploded top view of an eyeglass lens with a waveguide according to an embodiment is schematically illustrated; and

[0026] Figure 7c A side view of an eyeglass lens with a waveguide according to an embodiment is schematically illustrated. DETAILED DESCRIPTION

[0027] In general, as Figures 1a to 1cThe eyeglass lens 100 according to embodiments is schematically illustrated as including a first lens portion 102, a second lens portion 104 (also referred to as first and second lens halves, respectively), and a waveguide 106 (also referred to as a light guide) interposed between the first lens portion 102 and the second lens portion 104. In this way, the first lens portion 102, the second lens portion 104, and the waveguide 106 are arranged in an optical stack. The waveguide 106 has first and second opposing surfaces designated as an eye-facing surface and an ambient-facing surface, respectively. Likewise, the first lens portion 102 is designated as an ambient-facing lens, as in use, it is on the ambient-facing side of the waveguide 106. The second lens portion 104 is designated as an eye-facing lens, as in use, it is on the eye-facing side of the waveguide of the user’s eye. The stacked arrangement of the lens portions 102, 104 and the waveguide 106 is transparent to the real world, i.e., the user will be able to see through the eyeglass lens 100 to the ambient.

[0028] In Figure 2 The type of waveguide 106 used in the eyeglass lens 100 is schematically illustrated in FIG. 1, where the lens portions 102, 104 have been omitted for clarity, but their locations are indicated for reference. The waveguide 106 is cylindrical in shape and includes first and second concentric opposing surfaces 108, 110 with a constant thickness t between the opposing surfaces 108, 110. The center of curvature of the waveguide 106 is designated as X. The distances designated as R1 and R2 are the radii of curvature between the center of curvature and the respective opposing concentric surfaces 108, 110. In this way, it can be seen that the concave side of the cylindrical waveguide 106 faces the eye, as discussed in more detail below. Similarly, the distance from the center of curvature X to the inner surface or eye-facing surface 110 of the waveguide 106 is R1, and the distance from the center of curvature X to the outer surface (ambient-facing) 108 of the waveguide 106 is R2. It is clear that R2 = R1 + t, and this applies no matter where the distances R1 and R2 are measured on the cylindrical waveguide 106, due to the constant thickness t. In other words, the waveguide 106 has a common center of curvature X, and the inner and outer surfaces 110, 108 of the waveguide 106 are spaced apart by a thickness t that is constant.

[0029] Referring to Figure 1a and Figure 1bIn-coupling diffraction gratings 132 can be disposed on the surface of the waveguide 106 to input light from a light source into the waveguide 106. Corresponding out-coupling diffraction gratings 134 can be disposed on the surface of the waveguide to output light from the waveguide to the eye of a user. The in-coupling and out-coupling diffraction gratings 132, 134 can be positioned on the waveguide 106 such that when the first and second lens portions are adhered to the concentric opposing surfaces of the waveguide 106, the waveguide is within the footprint of the first and second lens portions.

[0030] The use of a cylindrical waveguide 106 with this structure can allow light to propagate between curved surfaces without aberration. This is advantageously implemented with input optics (such as lenses, prisms and mirrors, etc.) arranged to receive light from an image source (in particular a pixelated image source or an image source having a light output that can at least theoretically be divided into pixels) and provide the light to the cylindrical waveguide 106. All light rays from the same pixel of the image source are incident on the cylindrical waveguide 106 at the same angle relative to the surface normal at each point of incidence. Thus, all light rays from a central pixel of the image source are incident on the cylindrical waveguide 106 at any point perpendicular to the cylindrical surface. Light rays from non-central pixels are incident at each point of incidence at the same angle relative to the surface normal. Furthermore, at each point of incidence, all light rays from the same pixel of the image source are incident on the cylindrical waveguide 106 at the same angle relative to the plane normal for the cylindrical axis. Thus, the direction of propagation of all light rays remains the same.

[0031] In view of the input optics as demonstrated in Figure 3 and the waveguide structure as described above, light received at the cylindrical waveguide (typically in-coupled to the cylindrical waveguide) maintains its directional angle as it propagates along the cylindrical waveguide. That is, all light rays from a given pixel, no matter how far they propagate, will at the point of incidence of each light ray, approach the output grating at the same angle as measured between the light ray and the surface. Typically, the input optics comprise in-coupling (or injection) optics.

[0032] Unlike conventional collimating optics for planar waveguides, the input optics presented in this disclosure cannot properly be called collimators in classical optical design terminology, because the rays from a pixel are not parallel. Rather, the preferred in-coupling (projector) optics comprise optical equipment arranged to collimate or conform the light in a plane that passes through (i.e. neither parallel nor entirely contained in) and more preferably perpendicular to the cylindrical axis. For example, for eyeglasses and headsets, the cylindrical axis is vertical, and the plane is preferably horizontal. In this way, the rays are incident on the input grating 132 at the same angle in this plane. Wavefront shaping equipment 135, such as cylindrical lenses and / or mirrors, can be used for this task. As is common in optical design best practice, the central pixel ray will advantageously be incident at an angle normal to the surface of the waveguide 106, to make aberration management easier due to symmetry. Other pixels in this plane will yield rays incident on the input grating at other angles, but parallel to other rays from the same pixel.

[0033] However, in a plane orthogonal to the cylindrical axis, such as the horizontal plane, the light can possibly not be collimated but formed in such a way that the rays from the same pixel have the same angle of incidence with respect to the surface normal, considered individually for each different point of incidence. The wavefront shape that satisfies this condition is a cylindrical wavefront that is concentric with the cylindrical shape of the waveguide. Then, the rays from the central pixel will propagate radially from the waveguide cylindrical axis and impinge on the surface at normal incidence. This wavefront is advantageously formed by positioning the image source S (display) with the center of the image source at the waveguide axis. Then, the cylindrical lens 135 or mirror is arranged to have optical focusing power only in the vertical plane.

[0034] Optionally, further or different input optics can be provided, for example to optimize the performance of more or all pixels and / or to minimize the volume of the projector. This can include utilizing optics that focus in the horizontal plane to bring the display closer. In case a concave mirror is used, the image source and / or the in-coupling optics can be arranged such that the light is brought close to the waveguide from the side opposite to the mirror before being reflected and then diffracted.

[0035] The light can propagate through the cylindrical waveguide 106 (e.g. between the in-coupling optics and the out-coupling optics) along a direction parallel to the cylindrical axis (e.g. vertical), or along a direction perpendicular to the cylindrical axis (which can be horizontal, in particular around the circumference of the waveguide), or in a direction between parallel and perpendicular to the cylindrical axis, defined by a vector (typically diagonal).

[0036] As Figure 4As shown, the out-coupling optic generally comprises an out-coupling diffraction grating 134 as described above. In principle, a linear grating could be used. However, the practical use of the waveguide 106 is that the viewer is inside the cylinder. Thus, in this case, a simple linear grating can not be suitable to extract the light, as a simple linear grating would focus the light in a horizontal plane at the axis of the cylinder (producing vertical light rays), rather than far in front of the viewer. Instead, the diverging lens property can cause the light to be collimated in the horizontal direction (it is already collimated in the vertical direction). This can be achieved by adding negative optical power to the output grating along the horizontal direction. By analogy, the grating is the sum of a prismatic function and a cylindrical negative lens function. There are many known examples of how to record such gratings. This grating would not be called "linear" in comparison to the input grating. By adding more focusing power in both planes, the output grating can be chosen to place the digital image at any distance from the viewer.

[0037] In the case where the cylindrical waveguide 106 is embedded inside a head-mounted structure (e.g. a prescription eyeglass) that already corrects the user's vision, the input and output gratings can also be corrected to take that into account. The main factor is to maintain the above-mentioned conditions of the light while it propagates inside the waveguide, no matter how close and far the light gets to the "layer sandwich" of the whole optical stack.

[0038] The waveguide 106 of the above type is placed between the first lens half 102 and the second lens half 104 to form the eyeglass lens 100. Figure 1a The final formed eyeglass lens 100 is shown, while Figure 1b An exploded view of the first lens half 102 and the second lens half 104 with the waveguide 106 in between is shown. The first lens half 102 has a spherical outer front surface or spherical outer outward-facing surface and a cylindrical back surface having a radius of curvature such that it coincides with and is mateable with the radius of curvature R2 of the outward-facing surface 108 of the waveguide 106. The second lens half 106 has a cylindrical outer front surface or outward-facing surface having a radius of curvature such that it coincides with and is mateable with the radius of curvature R1 of the eye-facing surface 108 of the waveguide 106 and the spherical back surface or spherical outer outward-facing surface. It can be seen that the thickness t of the waveguide 106 is equal or constant over its circumference. As such, the skilled person will understand that the waveguide 106, and the associated in-coupler 132 and out-coupler 134, are placed between the first lens half 102 and the second lens half 104. Reference is made to the above description of the waveguide 106 and the in-coupler 132 and out-coupler 134. Figure 1cA side view of the spectacle lens 100 shows the waveguide 106 cooperatively inserted between the first lens portion 102 and the second lens portion 104, and it can be seen that the thickness t of the waveguide 106 along its vertical edges is equal or constant, so that the waveguide is flat in one axis. It can thus be seen that the cylindrical surface of the first lens portion 102 is concentric with the cylindrical surface of the second lens portion 104, so that the remaining surfaces are spherical. The constant thickness of the waveguide on its circumference and along its vertical edges ensures a uniform propagation of the light rays in the waveguide. In this way, the waveguide 106 can be considered as a flat lens from an optical point of view, since the waveguide has zero optical power and does not contribute to the optical power of the spectacle lens.

[0039] In each of the Figures, Figures 1a to 1c The (x-) axis, the (y-) axis and the (z-) axis are indicated for reference purposes in each of the Figures, and these references will be used consistently herein. Reference Figure 1a The spectacle lens 100 according to the embodiments has a main axis along the horizontal (x) direction and secondary axes along the vertical (y) direction and the depth (z) direction. The depth (z) dimension of the spectacle lens is typically significantly smaller, by a factor of about 10, than the dimensions in the (x) or (y) directions.

[0040] In applications such as ready-made sunglasses and ski goggles, simple spherical lenses can be used for zero power lenses. In these applications, the eye-facing surface and the world-facing surface have spherical curvatures, where the curvature of the world-facing surface is referred to as the base curvature, and the two surface profiles curvatures are non-concentric. The base curvature of the lens provides the best optical performance of the lens, while also enabling the best aesthetics and reducing the weight of the lens. For example, based on empirical data, a 6 diopter curve front (world-facing) lens surface corresponding to a radius of curvature of approximately 83 mm is considered to be the optimal form to provide the best peripheral vision for most users. For aesthetic reasons, presbyopic and fashion lenses can have flatter surfaces, with a typical base arc of 4 diopters, and in this case, the first lens portion 102 will have a base arc of +4 diopters, and the second lens portion will have a base arc of -4 diopters (giving a net zero (0) diopters). Typically, the world-facing front surface of the first lens portion 102 is curved so that it provides better visual acuity, especially when compared to a plano-convex lens, and improves the visual acuity over the field of view of the user. To correct for astigmatism, power can be added to the eye-facing surface of the second lens portion 104. In terms of astigmatism, the second lens portion 104 can have a base arc that is selected to correct the astigmatism of the user’s eye and to correct the astigmatism of the cylindrical waveguide 106, where the amount of astigmatism of the cylindrical waveguide 106 will depend on the radii of curvature R1 and R2. Similarly, to correct for myopia or hyperopia, a net power can be added (or subtracted) by changing the optical power of the second lens portion 106.

[0041] By way of non-limiting example, in the case of a zero power stock lens, the eyeglass lens 100 according to embodiments can have a horizontal dimension (x-axis) of 55 mm and a vertical dimension (y-axis) of 32 mm and a combined thickness (z-axis) of 2 mm of the first lens 102 and the second lens portion 104. The eye-facing surface of the second lens portion 104 can have a radius of curvature of 150 mm (approximately 3.3 diopters). The world-facing surface of the first lens portion 102 can have a radius of curvature of 152 mm. The eye-facing surface of the first lens portion 102 and the world-facing surface of the second lens portion 104 are cylindrically curved in the xz-plane and flat in the yz-plane and flat in the xy-plane. The cylindrically curved surface of the first lens portion 102 has a radius of curvature of 125 mm in the x-axis, and the cylindrically curved surface of the second lens portion has a radius of curvature of 126 mm in the x-axis. The profile of the cylindrically curved surface of the first lens portion 102 and the profile of the cylindrically curved surface of the second lens portion 104 are flat in the y-axis. The difference in radii of curvature takes into account the thickness of the cylindrical waveguide 106 and allows the concentric surfaces of the waveguide 106 to conformally attach to the cylindrically curved surfaces of the first lens portion 102 and the second lens portion 104.

[0042] According to the present disclosure, the waveguide 106 can have a thickness t between 0.1 mm and 10 mm and preferably between 0.5 mm and 2 mm and a radius between 80 mm and 300 mm given a radius of curvature R1 and R2 of the lens curvature between 2 diopters and 6 diopters. The first lens portion 102 and the second lens portion 104 can generally be manufactured separately, but can alternatively be formed by dividing or segmenting a single spectacle lens. The cylindrical surface profile of the first lens portion 102 and the second lens portion 104 can be made by grinding or injection molding or a combination of both. Alternatively, 3D printing can be used to manufacture the lens parts. The lens grinding process and the mold manufacturing process can use diamond grinding to obtain the cylindrical surface.

[0043] With reference to Figure 1a , Figure 1b and Figure 2 , the eye-facing surface of the first lens portion 102 and the world-facing surface of the second lens portion 104 define a cylindrically conformable interface of the waveguide 106. As a non-limiting example of the above, the radii of curvature of the cylindrical surfaces of the first lens portion 102 and the second lens portion 104 can be 126 mm and 125 mm, respectively, defining a waveguide thickness of 1 mm. Since the waveguide is conformable with the cylindrical surfaces of the first lens portion 102 and the second lens portion 104, their respective radii of curvature will be the same as the corresponding surfaces of the waveguide 106. In other words, the eye-facing surface of the first lens portion 102 has a radius of curvature equal to R1 and the world-facing surface of the second lens portion 104 has a radius of curvature equal to R2. The intermediate section of the first lens portion 102 will be thicker than the outer sections, while for a prescription of a hyperopic user, the second lens portion outer sections will be thicker than the intermediate section, or for a prescription of a myopic user, the second lens portion outer sections will be thinner than the intermediate.

[0044] While the preceding discussion refers to pure cylindrical surfaces of the first lens portion 102 and the second lens portion 104 and surfaces of the waveguide 106, the skilled person will understand that those surfaces can be partially spherocylindrical or toric, provided that any deviation from the pure cylindrical shape is negligible and provided that the thickness of the waveguide 106 remains constant.

[0045] The waveguide 106 can be attached to the first lens portion 102 and the second lens portion 104 by any suitable means. For example, the waveguide 106 can be attached by a transparent adhesive applied on each of the cylindrical surfaces of the first lens portion 102 and the second lens portion 104 or the waveguide 106 or both. The transparent adhesive can be a low refractive index material such as, for example, Norland Optical Adhesive 1315 with a refractive index of 1.315. This has the advantage that the adhesive serves to mechanically fix the first lens portion 102 and the second lens portion 104 to the waveguide 106 but also maintains the refractive index difference required to allow total internal reflection in the waveguide. As an example, the thickness of the transparent adhesive would be between 20 pm and 100 pm. The adhesive can also be an adhesive film or tape or a liquid adhesive. Furthermore, the adhesive can be considered as a transparent medium that acts as a cladding material for the waveguide 106 that is necessary to achieve the refractive index difference described above. For example, when the thickness of the adhesive is 0.1 pm and applied on both concentric cylindrical surfaces of the waveguide 106, the radii of the cylindrical surfaces of the first lens portion 102 and the second lens portion 104 can be adjusted appropriately to account for the additional thickness of the transparent adhesive material. It should be noted that the thickness of the transparent adhesive material does not need to be uniform on the cylindrical surfaces of the waveguide 106 from an optical point of view and that any variation will not affect the total internal reflection of the waveguide 106 if the thickness is not zero. In terms of the refractive index difference required to achieve total internal reflection in the waveguide 106, a typical example difference between the waveguide and the transparent adhesive can be 0.5. Taking the example of a refractive index of 1.3 for the transparent adhesive (as described above), the waveguide should have a refractive index of 1.8 and can be formed, for example, of lanthanum glass which will result in a total internal reflection for a field of view (FOV) of 40 degrees. The field of view of the waveguide can be modified by choosing the refractive index of the waveguide appropriately, with higher refractive index waveguide materials allowing for higher fields of view.

[0046] Alternatively, the waveguide can be formed of BK7 glass with a typical refractive index of 1.52 and, taking this example, to achieve a refractive index difference of 0.5, the transparent adhesive should have a refractive index of 1.02. SF11 glass with a refractive index of 1.78 is also available as a waveguide material. Schott AG also offers waveguide materials with a refractive index as high as 2.0 and, by taking a refractive index difference of 0.5, the refractive index of the transparent adhesive should be 1.5.

[0047] Alternatively, and taking into account the requirement for a refractive index difference, there can be an air gap at the interface between the first and second lens portions 102, 104 and the cylindrical surface of the waveguide 106. Those skilled in the art will appreciate that the refractive index of air is 1.0, whereas, as discussed above, the refractive index of the waveguide 106 should be 1.5. Thus, the air gap can be considered as a cladding material necessary to achieve the required refractive index difference. In this case, in order to mechanically secure the first and second lens portions 102, 104 to the waveguide 106, a small amount of adhesive will be required around the periphery of the lens portions. This small amount of adhesive material will also serve to environmentally seal the air gap from contaminants such as moisture ingress. As an alternative to adhesive, the air gap can be sealed and the respective portions of the waveguide 106 that are secured to the respective portions of the first and second lens portions 102, 104 can be heat sealed. In the case of an air gap, an anti-reflective coating can be applied to the spherical surfaces of the lens portions and / or the waveguide to prevent back reflection and ghost images. In the case of an air gap, the first and second lens portions 102, 104 should ideally be formed from a relatively rigid material such as, for example, glass, rather than a relatively flexible polycarbonate. This reduces the chance of any bending in the lens causing the above-mentioned material to contact the waveguide, which would result in light leaking from the waveguide 106.

[0048] Alternatively, the first and second lens portions 102, 104 can be formed from a low refractive index material and the waveguide 106 can be formed from a high refractive index material, such that the first and second lens portions 102, 104 can be considered as cladding materials for the waveguide that are necessary to achieve the refractive index difference. In this case, ophthalmic lenses typically require high refractive index materials to reduce weight. Plastic lenses typically have a refractive index between 1.3 and 1.8. Typically, polycarbonate lenses are 1.5 to 1.6, whereas Trivex (RTM) material is 1.53 or CR39 (RTM) is 1.49. High refractive index plastics with a refractive index of 1.8 are available. Thus, from the above discussion, the skilled person will see that by adopting a refractive index range of 1.3 to 1.8, there is a requirement for a waveguide material with a refractive index of 1.8 to 2.3. The use of a waveguide material with a refractive index of 2.0 from Schott AG in combination with Trivex (RTM) or CR39 material will provide the necessary minimum refractive index difference of 0.5. As a further alternative, the waveguide 106 can comprise a transparent cladding material to provide the refractive index difference required for total internal reflection. As yet a further alternative to adhesive, the first and second lens portions 102, 104 and the waveguide can be heat sealed directly to the waveguide, provided that one of the above options can be used to maintain the refractive index difference.

[0049] Referring to the above regarding the radius of curvature Rl And the discussion of R2, in practice, when using adhesive material to attach the first and second lens portions 102, 104 to the waveguide, or in the case of utilizing an air gap, one skilled in the art will appreciate that due to the thickness of the adhesive or air gap, the radii of curvature Rl and R2 of the waveguide will not be exactly identical to the radii of curvature of the cylindrical surface of the first and second lens portions 102, 104. However, the thickness of the adhesive or air gap will be negligible.

[0050] Figure 3 is a schematic illustration of a cylindrical waveguide 106 exhibiting optical properties, and as Figure 2 is the case, the lens portions have been omitted for clarity. In addition to the waveguide 106, an in-coupler 132 is also illustrated. Collimated light rays can be coupled into the waveguide 106 (in-coupled) by the in-coupler 132 at an angle β. Light rays incident on the in-coupler 132 are normal to the surface at each point on the surface of the in-coupler 132, and the angle β is such that the angle between the normal and the internal ray in the waveguide 106 is less than the critical angle of the waveguide 106. For example, the angle β will typically be less than 48 degrees. More preferably, the angle β will be at least 30 degrees and up to 40 degrees. Light rays other than the central ray will be coupled into the waveguide 106 at a slightly different angle (e.g. β + 1), however, this angle will be consistent at each point along the surface of the in-coupler 132. The in-coupler 132 can be a diffractive grating or a holographic grating.

[0051] One skilled in the art will appreciate that the light rays can originate from an image source S located at the center of the radius of curvature X of the concentric surface of the waveguide 106. Light rays from a central pixel of the image source S can be collimated in a plane by a collimating lens 135. This collimation of light rays is a form of wavefront shaping to couple the collimated light rays into the waveguide, as described above.

[0052] When the opposing surfaces 108, 110 of the waveguide 106 are concentric, as Figure 2 and Figure 3 illustrated, the angle of incidence of the light rays on the outer surface 108 is the same after reflection on the inner surface opposing surface 110, and thus the light rays will maintain their directional angle as they propagate through the waveguide 106, which is not the case for arrangements of curved waveguides without concentric surfaces. As Figure 3As shown, if the angle of incidence of the outward-facing surface 108 is α, then the angle of incidence of the eye-facing surface 110 will be β, and subsequently, the angle of reflection from the outward-facing surface 108 will also be α. In other words, the angle of incidence inside the waveguide is the same for each alternating reflection from the respective surfaces of the waveguide 106. Light rays incident on the left, center, or right side of the inner coupler 132 from a pixel will approach the inner surface at the same angle throughout the waveguide after reflection from the outward-facing surface 108. Pixels other than the center pixel will have different α and β values, but the incident and reflection relationship described above still applies.

[0053] It has been recognized that a high-performance and compact optical system can be achieved by directing all light rays originating from the same point on the image surface onto the cylindrical waveguide 106 at the same angle. For example, with a brightness of 100,000 nits (cd / m²), 2 Taking a display as an example, the output brightness at the output end (from the user's perspective) will be in the 10,000 nits range, which corresponds to 10% system efficiency, and the loss here can be mainly attributed to the losses in the inner coupling diffraction grating 132 and the outer coupling diffraction grating 134.

[0054] While the central ray angle has been discussed in this disclosure, other ray angles may exist, generated by the image source S (such as, for example, a microdisplay or a laser beam scanning projector). These other ray angles can be extended and collimated for use in the waveguide and, in use, can generate the field of view of the image to be viewed by the user. These other ray angles propagate through the waveguide 106 in the same manner as the central ray, except that there will be some image quality loss or ray aberration at the edges of the field of view or image. However, if these aberrations can be kept below 1 arcminute (the limit of human acuity), the user will not notice them substantially. In any case, aberrations can be compensated for by optical devices (such as multi-element, large, high-quality, aspherical, long-focal-length collimating optics) to reduce aberrations at the edges of the field of view. Advantageously, aberrations do not accumulate with the number of internal reflections within the waveguide 106. For example, if light rays from a given pixel are coupled into waveguide 106 at an angle of 60 ± 0.1 degrees, then after any number of reflections and pupil replications, regardless of how the light rays change position or are shuffled, the angular resolution of waveguide 106 and the internally coupled optics will still support a resolution of ± 0.1 degrees. This contrasts with waveguides that accumulate aberrations along their transmission length.

[0055] Figure 4 Demonstrated as Figure 2 and Figure 3A schematic top view of the waveguide is shown, with the difference that an out-coupler 134 is included. The out-coupler 134 can be a diffractive or holographic grating applied on the surface of the waveguide 106, and the out-coupler 134 is preferably matched to the in-coupler 132. That is, the central guide angle of the waveguide for the in-coupler and the out-coupler (in other words, the TIR angle for the central pixel, central light ray) is the same, and the wavelength is the same. For reference only, in Figure 4 In the present case, the plane of the page (and any plane parallel thereto) is considered to be a horizontal plane. Likewise, a vertical plane (and any plane parallel thereto) outside the page is considered to be a vertical plane. In this way, a cylindrical waveguide can be considered to be a cylindrical pair of goggles on a flat surface, etc. As discussed previously, the image source S can be located at the centre of the radius of curvature of the concentric surface of the waveguide 106 and collimated in one plane (in this example, the vertical plane) by a collimating lens 135. As discussed above, the light rays entering the waveguide 106 from the in-coupler 132 will propagate along the waveguide with rotational symmetry. In other words, as Figure 4 The waveguide shown can be rotated about the cylindrical axis, and the light rays from a given pixel will maintain the same angle with respect to the cylindrical surface of the waveguide. This rotational symmetry makes the waveguide invariant to the placement position of the out-coupler 134 on the waveguide 106, thus eliminating the need for precise alignment of the out-coupler 134 on the waveguide 106. Thus, the light collimated in one plane by the collimating lens 135 enters the waveguide 106 at the in-coupler 132 and propagates through the waveguide 106, and then exits the waveguide 106 at the out-coupler 134 to provide light to the eye of the user.

[0056] The waveguide 106 allows the spherical wavefront from the light source S to itself conform to the curvature of the waveguide 106 in the horizontal plane, and adds power in the vertical plane by the cylindrical lens 135. This means that the light rays map back onto themselves after two reflections in the waveguide 106 and this repeats indefinitely. Thus, the pupil can be replicated and expanded to expand the eyebox in one dimension (in this case, the horizontal). The collimating lens 135 can be incorporated into an augmented reality eyeglass lens system, as discussed below, or it can be provided externally (such as in a display projector system). The size of the vertical eyebox is set by the vertical dimension of the cylindrical lens 135. Because the position of the out-coupler relative to the input pupil is not important to the choice of waveguide thickness and central light ray guide angle, the size of the vertical eyebox also relaxes the alignment tolerance. If vertical replication is required, a so-called "spin grating" can be used to expand the eyebox vertically.

[0057] Referring to Figure 5Figure 6B, for example, shows a perspective view of a curved waveguide 106 of an eyeglass lens 100 according to an embodiment. Again, the first and second lens portions are omitted for clarity. Light rays from an image source S (which in this case can be a microdisplay) are collimated in one plane by a collimating lens 135 and coupled into the waveguide 106 by an in-coupler 132. The light rays propagate through the waveguide 106 and are coupled out to the user's eye by an out-coupler 134. The image source S is at a distance from the waveguide 106 that is the same as the radius of curvature of the waveguide on which the in-coupler 132 is applied (Rl in this example), and this distance is achieved by physically locating the image source S at that distance or by placing the image source virtually at that distance using optical means (e.g., using a lens). The image is collimated in one plane by the collimating lens 135 onto the in-coupler 132 located on the concave inner surface of the waveguide 106, which can be a cylindrical plano-convex lens, for example. The collimating lens 135 is oriented so that its focusing power is in the opposite plane compared to the waveguide 106. If the waveguide 106 is oriented horizontally (as shown), it has power in the vertical plane and would reflect light from a point source at the radius of curvature into a vertical line. The collimating lens 135 is then oriented in the opposite vertical plane and has power in the vertical plane to focus light from a point source at the radius of curvature into a horizontal line. Thus, the light rays carrying the image information are collimated in only one plane (horizontal) before entering the waveguide 106, and the curvature of the waveguide 106 is consistent with the light in the perpendicular (vertical) plane. This allows the entire pupil of the light entering the waveguide to propagate along the waveguide 106 and thus allows the pupil to expand from the out-coupler 134 at the output end to the user's eye.

[0058] The focal length of the collimating lens 135 determines the magnification of the object, and the lens 135 is placed at a distance of one focal length from the source S. If a cylindrical lens 135 is placed next to a cylindrical waveguide 106, it will have a focal length approximately equal to the radius of curvature of the waveguide. For example, a typical radius of curvature of a 200 mm eyewear-shaped waveguide means that the object is 200 mm away, and the cylindrical lens has a focal length of 200 mm. To be compact, the distance of 200 mm from the waveguide to the object can be shortened by folding the optical path using a mirror or by virtually setting the object distance using a lens.

[0059] The choice of collimating lens 135 (diameter and / or focal length) determines the size of the vertical eyebox (determined by the diameter of the lens), and the focal length determines the magnification of the source S and thus the field of view (FOV) of the image (and the size of the display). Typically, a multi-element lens is used for the collimating lens 135 (such as is used in cameras), which provides good image quality (small spot size RMS over the entire field of view) over the entire FOV. This is especially desirable for pupil replication systems to precisely stack the pupils and provide a high resolution image. Although a monochrome solution is possible, for a full color microdisplay, the lens system is ideally achromatic. The FOV of the curved waveguide 106 can be determined largely by similar factors, but the FOV will be expanded compared to a planar waveguide due to the curved nature of the user's surroundings.

[0060] The in-coupler 132 can be a diffraction grating that is a linear grating and has equal surface spacing (pitch) between grating lines (or equivalently, equal fringe spacing in a volume holographic grating). The grating can be fabricated by lithography or interferometrically. All light rays collimated in one plane typically impinge across the width of the grating surface (at 90 degrees to the surface), and then diffract at the same angle within the waveguide, which allows for pupil replication.

[0061] A grating on a curved waveguide typically means that collimated light will not typically impinge across the grating width due to the curvature of the waveguide. Typical solutions to this include varying the pitch of the grating to compensate for this, or recording a hologram directly on the curved surface, or lithographically etching on the curved surface, which is complex and expensive. In a preferred embodiment according to the present disclosure, the in-coupler grating 132 is fabricated as a planar linear grating on a flat substrate (as is well known in the art, and is relatively inexpensive and simple to fabricate compared to a variable grating). The in-coupler grating 132 can be made in any flexible holographic material (e.g. photopolymer (e.g. Bayfol (RTM) sold by Covestro AG or silver halide film)), and then attached (laminated) to the cylindrical surface of the waveguide, conforming to the cylindrical surface. The in-coupler grating 132 is preferably index matched by lamination (or another index matching glue or liquid) so that it conforms to the shape of the cylindrical surface, and desirably so that there is no air gap. Recording a hologram on a flat substrate, and then removing the flexible holographic material and laminating on a planar or cylindrical substrate (curved in only one dimension) is simple and inexpensive, whereas recording on a curved surface or laminating on a spherical surface (curved in two dimensions) is more difficult. It is also possible to etch a slanted grating and use embossing techniques or UV-cured resin techniques. The grating can then be transferred to the cylindrical waveguide.

[0062] The pitch of the incoupler grating 132 is designed to diffract the center wavelength of the source S. Since the incoupler grating 132 is nominally designed to diffract normally incident light at an angle, the incoupler grating 132 has a tilt angle, and the pitch is typically specified as the spacing between gratings measured along the planar surface of the grating. For the incoupler grating 132, this is constant, i.e. a linear grating.

[0063] For known planar waveguides, both couplers are typically linear and identical. The system then behaves like a periscope, and presents the viewer with a magnified image of the layering of the microdisplay onto the real world. The design of the entire system means that the positional pixel information of the display is converted to angular information by collimation, and then back to positional information to the human retina. As with the incoupler 132, the outcoupler 134 can also be a diffractive grating with a variable period along the waveguide, and where the source S is a broadband source, and the outcoupler does not eliminate chromatic aberration for each position. However, the period of the grating at the center can be chosen to be the same as the input grating period to minimize this aberration.

[0064] Alternatively, narrowband sources such as laser sources, superluminescent diodes (SLEDs), or notch filtered narrowband LEDs can be used. Narrowband sources can help minimize chromatic aberration. They can also limit the FOV of the output image, but this can be mitigated using a thin volume holographic grating. For example, a typical thickness of a volume holographic grating can be at least 3 microns and up to 6 microns. The thickness of the volume holographic grating can be chosen depending on the desired diffraction efficiency (DE) and FOV. Increasing the thickness therein will provide a higher DE, but will reduce the FOV. This can provide a typical spectral bandwidth of about 20 nm full width half maximum (FWHM) and an angular bandwidth of about 6 degrees FWHM in air.

[0065] The outcoupler grating can be chosen to place the digital image at any distance from the viewer by adding more focusing in two planes. In the vertical plane, light incoupled to the waveguide is collimated, but light output from the outcoupler grating does not need to be collimated. To allow for multi-pupil extraction, only part of the light can be extracted at the first part of the outcoupler grating 134. To balance the uniformity of the light extracted over the outcoupler grating 134, the far end (with reference to the incoupler grating 132) of the outcoupler grating 134 has a higher efficiency than the near (receiving) end. The diffraction efficiency (DE) of the output grating is advantageously chosen low enough to allow for sufficient pupil replication at the receiving end of the output grating 134 (e.g. 5-25%), but high enough at the far end for satisfactory brightness (e.g. 10-100%).

[0066] Reference Figure 6depicts a schematic top view of the cylindrical waveguide 106 and a simplification of the outcoupling optics, including the outcoupler 134, which can be a diffractive grating. As in Figure 4 the page plane (and any parallel plane) in this figure is considered horizontal, and the vertical plane (and any parallel plane) out of the page is considered vertical. Thus, the cylindrical waveguide 106 can be visualized, for example, like a cylindrical shaped pair of goggles on a flat surface. Also shown in this simplification is a cylindrical negative lens 155, as will be discussed further below. Light rays 151 out of the outcoupling diffractive grating 134 are collimated in the vertical plane and focused in the horizontal plane, as indicated by line 152. Light rays 156 out of the cylindrical negative lens 155 are collimated in both the x horizontal plane and the y vertical plane and have an infinite focus. This is a simplification, as the cylindrical negative lens 155 is actually optically integrated within the outcoupling diffractive grating 134. Thus, power is included within the outcoupling diffractive grating to compensate and achieve collimation in both planes at the output. Thus, the outcoupling diffractive grating 134 acts as a cylindrical lens to compensate for the cylindrical curvature introduced by the in-coupling optics and in this way essentially collimates the image at infinity, as explained below.

[0067] Due to the asymmetric collimation at the in-coupling optics, the out-coupling optics compensates for the different focal positions of the horizontal (near) and vertical (far or infinite) output image planes to provide an image focused at infinity in both planes, thus providing a high quality image for the viewer. The compensation is achieved by encoding the optical power into the output grating. As Figure 6 shown, this is equivalent to placing a diverging cylindrical lens 155 (flat concave cylindrical lens; if the waveguide has a curvature radius of 200 mm, the lens will have a focal length of 200 mm) with a negative optical power equal to the waveguide curvature radius between the planar output grating and the user. The lens 155 is oriented perpendicular to the input collimating lens 135. If the collimating lens 135 is focused (or has power) in the vertical plane, the output compensating lens / grating will be focused (or have power) in the horizontal plane to produce a spherical collimated output. As mentioned above, the center of the out-coupling grating 134 has the same surface pitch (also referred to as lateral or in-plane pitch) as the input grating to allow for chromatic compensation.

[0068] The image seen by the user is at infinity. This is often the desired use case, as it means that when the user focuses on a distant object in the real world, the virtual image will be on focus, as is typical for example when fighter pilots or motorcyclists use goggles. Consumer devices using planar waveguides with pupil expansion also have images at infinity. Alternatively, instead of setting the image at infinity as discussed, the virtual image can be set closer to the user by adding negative optical power in the out-coupler. For example, a negative optical power of 1 diopter in a holographic out-coupler sets the image at 1 meter instead of infinity, which can be useful if the user wishes the virtual image to be layered on the same focal plane, for example at arm’s length.

[0069] The output grating 134 can have varying diffraction grating efficiency or relatively low output efficiency (e.g., 10%). This can be achieved during recording of the holographic out-coupler. While it is desirable for the input grating 132 to have maximum diffraction efficiency (meaning that most of the light incident upon it is in-coupled into the waveguide), the output grating 134 can have low or variable efficiency, allowing for pupil expansion. A small portion of light is out-coupled upon the first interaction with the output grating 134, while most of the light continues to reflect along the waveguide, and a portion of that light is output upon the second interaction, and so on. This allows for expansion of the eyebox in the horizontal plane.

[0070] Holographic waveguide gratings (linear out-couplers or power out-couplers) can be fabricated by exposing a holographic material to two coherent beams of light, where the waveguide beam is coupled into the material via a prism, as is known in the art. Lasers of three different wavelengths (e.g., red, green, and blue, RGB) can be used to multiplex three gratings into a single holographic layer, to allow a viewer to see substantially white images from an RGB microdisplay. Alternatively, three separate layers can be stacked, one for each color.

[0071] By multiplexing multiple gratings into a single holographic layer, the FOV provided to the user can be increased, on which a uniformly bright, uniformly colored image can be seen. This can be achieved by varying the recording angle. Alternatively, multiple angle multiplexed layers can be stacked.

[0072] The input grating and the output grating can be reflective holograms, transmissive holograms, or any combination thereof. This will be understood from the theory above, as the desired effect is based only on the transverse component of the grating pitch. The transverse (cross-sectional) pitch or period can be conveniently chosen to accommodate the geometry of a reflective grating or a transmissive grating. It will also be understood that the linear grating described above means linear in the transverse direction, but can have variable transverse characteristics.

[0073] The collimation properties of the output light mean that a large eye relief (i.e. the distance that the eye can be located behind the output surface and see the image in an optimal manner) can be achieved. This is generally desirable, especially for applications with head-mounted visors rather than eyeglasses. The larger the eye relief, generally the smaller the FOV.

[0074] The curvature of the waveguide does not substantially alter the view of the real world. Normal radii of curvature for eyeglasses are 250 mm, and for visors are 150-200 mm. A user would not notice any curvature greater than 100 mm (as is the case here) as distorting the view of the real world. There would only be a very small astigmatism effect unless compensated for by additional layers of lenses (or multiple lenses).

[0075] Returning to the general sense of the present disclosure, the outcoupling optic can be considered to include an outcoupling diffractive grating. In particular, the outcoupling diffractive grating can be configured to function as a cylindrical lens (e.g. focusing in only one dimension). Additionally or alternatively, the outcoupling linear diffractive grating can have a curved grating. In preferred embodiments, the outcoupling linear diffractive grating can have internal grating angles arranged to collimate light received in a plane, or to focus light received in tangential and sagittal planes with no more than 25% (optionally 20%, 15%, or 10%) output or diffraction efficiency at a predetermined distance and / or at an end of the outcoupling diffractive grating nearest light received from the input optic.

[0076] The outcoupling optic can include an output wavefront shaping device configured to collimate light received in a single plane orthogonal to a single plane of the input wavefront shaping device. Additionally or alternatively, the outcoupling optic can include a cylindrical negative lens. Preferably, such aspects are integrated in the outcoupling diffractive grating.

[0077] The outcoupling linear diffractive grating can have the same surface pitch as the incoupling linear diffractive grating. In some embodiments, the outcoupling linear diffractive can have internal grating angles that are oppositely oriented compared to the internal grating angles of the incoupling linear diffractive grating. This is used in particular where light from the image source and light reaching the viewer (or incoupling and outcoupling optics) are on the same side of each other. This can be referred to as a “U” grating. Alternatively, the angles of the incoupling and outcoupling gratings are not oppositely oriented, and at least some light will be outcoupled on the opposite side to the incoupling light (in other words, the viewer will be on the other side compared to the incoupling light). This can be referred to as a “Z” grating.

[0078] From an alternative perspective, the methods according to the present disclosure can also be explained in terms of symmetry. These methods use a cylindrical waveguide and a cylindrical symmetric wavefront, both rotationally symmetric around their common axis.

[0079] Consider a pixel on a display or other image generating device. The wavefront from this pixel can be shaped as a cylinder. A linear diffraction grating recorded on a flat substrate and laminated onto the cylindrical waveguide has a constant period along the surface. Then, each light ray is deflected by the same angle, resulting in a light field that is symmetric around the axis of rotation. As mentioned above, light rays emitted between the cylindrical surfaces will maintain the two incidence angles on both surfaces at any number of reflections. This means that, after every two reflections, the wave will be perfectly coincident with itself. No complex images are created from this. Such a light field can propagate any distance without any light ray becoming different from the others.

[0080] Furthermore, pupil replication at the output grating is also achieved. The partial outcoupling of light occurs at the initial interaction with the outcoupling optics, thereby leaving the remaining light to propagate and couple out at the next interaction. In this case, the different interactions can be perfectly matched without causing ghost images. When all the light rays reach the outcoupling grating, the grating can diffract them out of the waveguide, no matter the position of the grating or the position of any one light ray, as they will all arrive in a similar fashion.

[0081] A linear outcoupling grating with the same period as the incoupling grating is used to diffract the light rays again into a new cylindrical wavefront. It is well known that diffractive optical elements can combine multiple functions in an additive way. The outcoupling grating also has a focusing power in one dimension, similar to the focusing power of a cylindrical lens. This converts the diffracted light into collimated light. A viewer receiving this light will perceive a star-like point at infinity.

[0082] The above explanation can be repeated for other pixels. As mentioned above, the wavefront from these other pixels does not need to be an exact cylinder. This happens because the light rays from the non-central pixels are incident on the coupling optics at a slightly different angle than the "perfect" normal (vertical) angle. However, by hitting the incouplers at substantially the same angle relative to the surface normal at their respective points of intersection, the resulting light rays will form a field of light rays that is rotationally symmetric around the cylindrical axis and propagate in an indistinguishable manner. Using modern optical design, it is possible to design a projector that forms this light field with small errors, ideally 1 arcminute (human acuity).

[0083] If the eye-facing surface of the second lens portion 104 is concave and there is an air gap or transparent adhesive between the waveguide 106 and the second lens portion 106, the second lens portion will add converging power to the light coming out of the out-coupler, so further negative (diverging) optical power needs to be added to compensate for this. That is, the out-coupler needs to have more negative optical power (as mentioned above, it can already have some negative optical power). If an amount of negative optical power equal to the radius of curvature of the inner surface is added, the virtual image will remain at infinity. For the second lens portion 104, the world-facing surface can be cylindrical. Similarly, if the eye-facing surface of the second lens portion 104 is spherical, a spherical negative optical power can be added to the out-coupling grating and the cylindrical optical power. It should be noted that the in-couplers can be transmissive geometry or reflective geometry, although the reflective type is typically used for practical reasons. While in the figures, the in-couplers appear to function as transmissive holograms, in practice they are reflective holograms, as the light passes through the hologram and reflects off the outer hologram surface, then diffracted in the reflective geometry (for the out-coupler).

[0084] The orientation of the cylindrical waveguide can be varied. The above-described embodiments relate to a cylindrical waveguide that is oriented vertically (and so the cylindrical axis of the cylindrical waveguide extends in the horizontal direction), as this is the normal way of aligning a visor. Other orientations can be considered. Additionally or alternatively, light can enter and exit the cylindrical waveguide through different surfaces (e.g. on different sides of the waveguide). The in-coupling grating and the out-coupling grating can be positioned accordingly to achieve this. In some embodiments, more than one in-coupling grating and / or out-coupling grating can be provided.

[0085] Both the in-coupling grating and the out-coupling grating can be reflective gratings or transmissive gratings, and can be placed on an inner surface or an outer surface of the waveguide (or another surface of the waveguide). The skilled person will appreciate such variations of the embodiments shown herein.

[0086] Furthermore, it is well known that the human eye seems to prefer to watch a horizontal aspect ratio (e.g. televisions are optimised for this, and so are most spectacle lenses), and so the out-coupler has an aspect ratio that matches that of the lens. Furthermore, the fact that the IPD varies more in the horizontal direction than in the vertical direction, it is advantageous for the user to have a greater horizontal eye movement range than a vertical eye movement range.

[0087] The input pupil is twice the width of a single reflection, so the edge rays do not stack with the grating layers inside the coupler. The optimal pupil width is set by the waveguide thickness and guide angle, and is about twice the waveguide thickness. So a very thin waveguide means a very small pupil (0.5mm thick = 1mm pupil), so you need to stack many pupils at the outcoupler grating to get a large eyebox.

[0088] The linear input grating can have an angle of any orientation. The light does not need to be redirected in the cylindrical circumferential direction (perpendicular to the cylindrical axis, which in the above embodiments is horizontal). The light can be directed along the cylindrical axis (vertical). Alternatively, the light can be directed at 45 degrees or in any other diagonal direction. This allows design freedom, for example to conveniently position the projection module at the temple of a glass, eyeglass. This also has important implications for the intermediate grating that implements the 2D pupil expansion. The intermediate linear grating can redirect and / or split the light while keeping the respective angle of each redirected light ray the same for light rays from the same pixel.

[0089] The system allows the use of laser light rays or LED light rays, which has flexibility. Typically, LED light rays are used (e.g. LCOS (Liquid Crystal on Silicon) plus LED or micro-LED microdisplay), but laser light rays can also be used if high efficiency and thus high brightness is required. Laser beam mirror scanning systems (MEMS) and micro-opto-electro-mechanical systems can also be used. Laser light rays have some drawbacks in terms of cost, speckle (loss of resolution) and eye safety issues.

[0090] If a refractive element (e.g. a prism) is used together with a diffractive in-coupler or diffractive out-coupler as in-coupler or out-coupler, the uncompensated chromatic dispersion can make it possible to use only narrow-band sources (e.g. lasers). Additionally, refractive couplers tend to be bulky and expensive.

[0091] By adding a spherical light power to the waveguide output, it is possible to set the virtual image at different focal distances. It is also possible to set the focal distance closer by using an additional pair of lenses before and after the waveguide (the second lens to compensate for the effect of the first pair of lenses on the real world). An additional possibility is to add electrically addressable switchable (liquid crystal based) holographic output gratings that can be turned on or off to provide different focal planes for the image. Additionally or alternatively, the input grating can be switched in the same way to provide a larger FOV as can be achieved with angularly multiplexed gratings. The switching can be synchronized with a time-multiplexed microdisplay.

[0092] Optionally, multiple focal planes can be achieved by using multiple (stacked) cylindrical waveguides. Light will propagate as described above, but exit with different focal points created by the gratings. Adding an axisymmetric optical power (as the optical power of a normal spherical lens) to the output of the cylindrical waveguide will result in the perception of this point at a finite distance (say 1 m).

[0093] The cylindrical waveguide can form part of a larger (overall) waveguide structure, only part of which can be cylindrical. Embodiments can be considered in which no in-coupling optics are required. For example, light can enter the waveguide at a non-cylindrical portion of the waveguide (e.g. due to an embedded image source) or originate from the waveguide at a non-cylindrical portion of the waveguide, and wavefront shaping can be performed in this portion. Thus, this portion of the waveguide can form part of the input optics.

[0094] The vertical eyebox can also be extended by multiple input projectors vertically displaced. The typical approach used to extend the vertical eyebox in a planar waveguide is to use “rotating” gratings that propagate the pupil vertically to give a 2D exit pupil expansion. There are multiple approaches to vertically expanding the eyebox, including input gratings, rotating gratings and output gratings, such as those implemented in products by Vuzix Corporation or DigiLens Inc. An alternative approach is to use “butterfly” rotating gratings that expand the eyebox and also expand the FOV by splitting the FOV into two parts at the input and recombining at the output (as used by the HoloLens (RTM) sold by Microsoft Corporation). A further option is to use mutually multiplexing gratings that waveguide part of the light and out-couple part of the light over an expanded eyebox (as used in products by WaveOptics, Ltd).

[0095] All of these prior art approaches benefit from the use of collimated light routed by linear gratings and planar waveguides. With the present disclosure using cylindrical waveguides, these techniques of splitting light and replicating pupils by intermediate linear gratings can be implemented after in-coupling into the cylindrical waveguide. The light can then finally be out-coupled with the grating having a negative cylindrical focusing function.

[0096] The rotationally symmetric structure of embodiments according to the present disclosure allows the input and output gratings to be placed at any location on the concentric cylindrical waveguide. For example, in addition to the typical planar horizontal configuration discussed above, the orientation can be vertical or at an angle to the waveguide (e.g. in eyewear implementations). This allows flexibility in placing the projectors and eyebox locations in the final design. It also allows the pupil replication and vertical eyebox expansion methods discussed in the preceding paragraphs.

[0097] In embodiments, the wavefront shaping device can comprise a concave (cylindrical) mirror. Optionally, the image source and / or the image source mount can be positioned closer to an outer surface of the cylindrical waveguide than to an inner surface of the cylindrical waveguide. The mirror, which is preferably the wavefront shaping device, can then be arranged to receive light from the image source and reflect the received light towards the cylindrical waveguide. In some embodiments, the mirror and the image source and / or the image source mount are configured such that light from the image source passes through the cylindrical waveguide before reaching the mirror. In certain embodiments, respective portions of the input optics proximate to the cylindrical waveguide (e.g., in-coupling gratings) and the out-coupling optics proximate to the cylindrical waveguide (e.g., out-coupling gratings) are located on opposite sides of the cylindrical waveguide.

[0098] In certain embodiments, the input optics further comprise one or more spherical lenses. Additionally or alternatively, the out-coupling optics further comprise one or more spherical lenses. The spherical lenses can be used to change the optical path length of the light and / or to change the focus of the light.

[0099] In embodiments, the input optics can further comprise a waveguide portion integrated with the cylindrical waveguide. Advantageously, the waveguide portion forming at least a portion of the input optics is non-cylindrical and / or does not have concentric surfaces. In some embodiments, only a portion of the waveguide shape can be cylindrical.

[0100] In some embodiments, one or more intermediate optical gratings can be provided in the cylindrical waveguide. One, some or all of the one or more intermediate optical gratings can be linear. The one or more intermediate optical gratings can be arranged to re-direct, diffract and / or split light before the out-coupling optics. However, the relative angles of the light rays from the same pixel advantageously remain the same. The intermediate linear optical gratings advantageously preserve the angular properties of the propagating light (TIR condition, and for the cylindrical axis, all light rays from the same pixel are incident on the cylindrical waveguide surface at the same angle with respect to the surface normal and at the same angle with respect to the plane normal), allowing for aberration-free two-dimensional pupil expansion.

[0101] The out-coupling optics can comprise an out-coupling diffractive grating having one or more of the following: an internal grating angle arranged to refract the received light; a variable diffraction efficiency along the length of the out-coupling diffractive grating; and a switchable diffractive grating configuration (e.g., allowing for modulation of the output light). Optionally, the in-coupling diffractive grating can have a switchable diffractive grating configuration.

[0102] Figures 7a to 7cAn alternative arrangement of the eyeglass lens described above is shown, differing in that the waveguide 106 extends beyond the area of the first and second lens portions 102, 104 as an in-coupling tab 161. The in-coupler 132 can be formed on or affixed to the in-coupling tab 161, and typically the in-coupling tab will be formed on the side of the AR eyeglass frame that includes the input light source. Additionally, in-coupling optics such as collimating lens 135 can be arranged on the in-coupling tab 161.

[0103] A plurality of cylindrical waveguides can be provided. For example, a second cylindrical waveguide having concentric inner and outer surfaces can be provided. The first and second (or more) cylindrical waveguides can be stacked. Some or all of the plurality of cylindrical waveguides can have a common cylindrical axis. In all such cases, the input optics can be arranged to cause some of the received light to enter each of the plurality of cylindrical waveguides, such that for each cylindrical waveguide, at each point of incidence, all light rays originating from the same pixel of the image source impinge on the surface of the respective cylindrical waveguide at the same angle with respect to the surface normal and at the same angle with respect to the plane normal, thus preserving their directional angles as the in-coupled light propagates along the respective cylindrical waveguide. Advantageously, the out-coupling optics can be arranged to focus the light propagating along each cylindrical waveguide at different focal points. For example, the out-coupling optics can be arranged to focus light propagating along a first cylindrical waveguide at a first focal point, and to focus light propagating along a second cylindrical waveguide at a second, different focal point. Embodiments with a plurality of image sources, advantageously vertically displaced from one another, can be considered.

Claims

1. An eyeglass lens for augmented reality display, the eyeglass lens comprising: a first lens portion and a second lens portion with a cylindrical waveguide between the first lens portion and the second lens portion; the cylindrical waveguide with cylindrical concentric opposing surfaces to propagate light along a waveguide with rotational symmetry, the cylindrical concentric opposing surfaces defining a first cylindrical interface with the first lens portion and a second cylindrical interface with the second lens portion, and wherein the cylindrical waveguide is transparent and comprises a central waveguide core with a transparent medium at the first cylindrical interface and the second cylindrical interface, wherein the central core has a higher refractive index than the transparent medium, and the transparent medium is an adhesive material, and an input optic to couple light into the cylindrical waveguide and configured to receive light from a light source, the input optic comprising a wavefront shaping device configured to quasi-directly receive the light in a single plane only, wherein the wavefront shaping device is configured such that the single plane passes through a cylindrical axis of the cylindrical waveguide, and light rays from a same pixel of the light source are incident on the waveguide at a same angle, and wherein a center of the light source is arranged at the cylindrical axis.

2. The eyeglass lens of claim 1, wherein the first lens portion, the second lens portion, the cylindrical waveguide, and the transparent medium are arranged in an optical stack.

3. The eyeglass lens of claim 1, wherein the eyeglass lens has a primary axis and a secondary axis, the first cylindrically shaped interface and the second cylindrically shaped interface have a curved profile along the primary axis.

4. The eyeglass lens of claim 3, wherein the first cylindrically shaped interface and the second cylindrically shaped interface have a linear profile along the secondary axis.

5. The eyeglass lens of claim 2, wherein the first lens portion and the second lens portion have a spherical outer profile.

6. The eyeglass lens of claim 1, wherein the input optic comprises an in-coupling linear diffraction grating with a constant period applied to a surface of the waveguide.

7. The eyeglass lens of claim 6, wherein the in-coupling linear diffraction grating is attached to the waveguide at the first cylindrical interface or the second cylindrical interface.

8. The eyeglass lens of claim 7, wherein the in-coupling linear diffraction grating is switchable.

9. The eyeglass lens of claim 8, wherein the in-coupling linear diffraction grating is formed from a holographic material.

10. The eyeglass lens of any of claims 1 to 9, wherein the input optics are configured and arranged to receive light rays from an image source and to cause the light rays to enter the cylindrical waveguide such that at each point of incidence, for a common cylindrical axis, all light rays originating from a same pixel of the image source are incident on the surface of the cylindrical waveguide at a same angle with respect to a surface normal and at a same angle with respect to a plane normal, so that the in-coupled light maintains its directional angles as it propagates along the cylindrical waveguide.

11. The eyeglass lens of any of claims 1 to 9, further comprising output optics configured and arranged to receive propagating light from the cylindrical waveguide and to present the light as an image to a user’s eye.

12. The eyeglass lens of claim 11, wherein the output optics comprise an out-coupling linear diffraction grating of constant period applied to a surface of the waveguide.

13. The eyeglass lens of claim 12, wherein the out-coupling linear diffraction grating is attached to the waveguide at the first cylindrical interface or the second cylindrical interface.

14. The eyeglass lens of claim 13, wherein the out-coupling linear diffraction grating is switchable.

15. The eyeglass lens of any of claims 12 to 14, wherein the out-coupling linear diffraction grating is formed from a holographic material.

16. A method of manufacturing an eyeglass lens for augmented reality display, the method comprising: forming a first lens portion and a second lens portion and inserting a cylindrical waveguide between the first lens portion and the second lens portion; forming the cylindrical waveguide having cylindrical concentric opposing surfaces to propagate light along a waveguide having rotational symmetry, the cylindrical waveguide defining a first cylindrical interface having the first lens portion and a second cylindrical interface having the second lens portion, and wherein the cylindrical waveguide is transparent and comprises a central waveguide core having a transparent medium at the first cylindrical interface and the second cylindrical interface, wherein the central core has a higher refractive index than the transparent medium and the transparent medium is an adhesive material, and forming input optics for coupling light into the cylindrical waveguide and configured to receive light from a light source, the input optics comprising a wavefront shaping device configured to quasi-directly receive light in a single plane, the wavefront shaping device configured such that the single plane passes through a cylindrical axis of the cylindrical waveguide, and light rays from a same pixel of the light source are incident on the waveguide at a same angle, and wherein a center of the light source is arranged at the cylindrical axis.

17. The method of claim 16, wherein the first lens portion, the second lens portion, the cylindrical waveguide, and the transparent medium are arranged in an optical stack.

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