Optical light guide system

Abstract

The present disclosure relates to an optical system comprising: a light guide (110) having opposing first (112) and second (114) non-parallel optical surfaces, wherein at least one of the first or second optical surfaces is curved; an in-coupling diffractive optical element (120) arranged to receive reflected light from an object and to couple the reflected light into the light guide at a first location, wherein the reflected light propagates along the light guide and exits the light guide at a second location; and a light detector (140) arranged proximate the second location to receive the reflected light from the light guide. A head-mounted eye-tracking system or a world-facing camera system can comprise the optical system.

Description

Technical Field

[0001] This disclosure relates to an optical system for eye tracking or a world-facing camera system. This optical system may also be part of an augmented reality (AR), virtual reality (VR), or mixed reality (MR) system. Background Technology

[0002] Eye tracking has numerous applications in user interface research or optimization, health, and psychology, and can be used to understand user behavioral responses to stimuli such as advertisements. In the AR and VR fields, eye tracking systems can enable user interface control and / or help provide users with high-quality images.

[0003] Optical eye-tracking systems for AR and VR applications can be part of a head-mounted display, typically using invisible light sources (such as infrared light-emitting diodes (LEDs)) and infrared cameras (such as charge-coupled devices (CCDs)) to capture images of the eyes. Typically, both the LEDs and CCDs are mounted on the frame of the AR or VR device close to the user's eyes. Machine vision algorithms can then determine the eye's position based on the corneal reflection from the light source to the camera (also known as a glint or Purkinje image) and the position of the pupil. The vector between the pupil center and the glint determines the eye's rotation, thus determining the gaze direction.

[0004] Typically, eye-tracking systems utilize multiple light sources and cameras around the user's eyes within the limited space of a head-mounted device. Furthermore, for AR eye-tracking systems, machine vision requires significant computational power even at low frame rates or refresh rates (typically 30-200Hz with 4-33ms latency). The asymmetric bias in the user's eye image caused by the camera's off-axis perspective further complicates the machine vision computation.

[0005] Several known examples of eye-tracking systems involve invisible light sources, cameras (such as CCDs), and light guides to capture images of a user's eyes. One example utilizes a transparent light guide in the form of a planar structure, guiding infrared light along the guide and coupling outcouples of the infrared light onto the user's eyes. The outcoupled infrared light is then coupled back into the light guide and coupled into an infrared photodetector.

[0006] It is known to embed planar light guides of the type described above into eyeglass lenses used in AR applications. However, there are limitations to embedding such light guides into lenses. Typically, the lenses used in eyeglasses are curved, especially when the lenses are prescription lenses, while the light guides are flat. Therefore, a disadvantage of embedding the light guide in a curved lens is that the lens must be thicker and thus heavier to accommodate the planar light guide. Furthermore, none of the known solutions address the related issues of achieving the required refractive index change within the eyeglass lens to ensure that light can be guided along the light guide via total internal reflection.

[0007] Furthermore, optical systems such as head-mounted, world-facing camera systems, one commercially available example being Ray-Ban® Stories®, place a forward-facing camera next to each lens of a pair of glasses. However, due to the camera's offset relative to the user's eyes, a parallax error exists between the scene the user sees and the scene captured. While this may be imperceptible at long distances (where the scene is essentially at infinity, more than 1 meter from the user), it becomes significant at close distances (less than 1 meter from the user). This can be particularly problematic for virtual reality, augmented reality, or mixed reality systems, as users interact with both real and virtual objects viewed up close through the camera system. Summary of the Invention

[0008] An optical system is provided, comprising: a light guide having opposing first and second non-parallel optical surfaces, wherein at least one of the first or second optical surfaces is curved; an ingress-coupled diffractive optical element arranged to receive reflected light from an object and couple the reflected light into the light guide at a first position, wherein the reflected light propagates around the light guide and exits the light guide at a second position; and a photodetector arranged near the second position to receive reflected light from the light guide.

[0009] The optical system may include an ingress-coupled diffractive optics element, which may comprise a linear diffraction grating with a constant period. The center thickness of the light guide may be chosen such that light rays propagating through the light guide do not overlap. The width of the ingress-coupled diffractive optics element may be less than four times the center thickness of the light guide. The ingress-coupled diffractive optics element may include a lens function with negative power (or focal length).

[0010] In the optical system according to the embodiment, light rays exiting the light guide may converge onto the entrance pupil of the photodetector. The center thickness of the light guide is in the range of 1 mm to 10 mm, preferably 3 mm. The detector may be tilted relative to the angle at which the light rays exit the light guide.

[0011] In the optical system according to the embodiment, the second position is the output end, and an output coupler is arranged at the output end. The output coupler can change the angle of light rays leaving the light guide. The output coupler is a diffractive output coupler, a reflective output coupler, or a refractive output coupler.

[0012] The photodetector can be a charge-coupled device (CCD). A focusing lens may be arranged to focus light from the light guide onto the photodetector. The focusing lens can be a combination of cylindrical and spherical lenses.

[0013] According to the embodiments, the light guide may be a transparent ophthalmic lens, and the first and second optical surfaces are optical surfaces of the ophthalmic lens.

[0014] The light source may be arranged to illuminate the user's eyes or the scene being viewed, and the light source is arranged to emit invisible light. The light source can be a narrowband infrared light-emitting diode or a laser diode.

[0015] It also offers head-mounted eye-tracking systems or world-oriented camera systems, including the optical system.

[0016] Therefore, the purpose of the embodiments disclosed herein is to avoid or mitigate one or more of the above-mentioned disadvantages.

[0017] In this context, the claims provide an optical system for eye-tracking or world-oriented camera systems. Other preferred and optional features are defined in the other claims and discussed in this disclosure. Attached Figure Description

[0018] To provide a detailed understanding of the features of this disclosure, reference is made to embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings illustrate only typical embodiments and should not be construed as limiting the scope of the disclosure. The drawings are for illustrative purposes and are not necessarily drawn to scale. It should be noted that features shown in the drawings have been enlarged for illustrative purposes and no dimensions should be inferred (unless otherwise stated in the text or drawings). Those skilled in the art will appreciate the advantages of the embodiments upon reading this specification in conjunction with the accompanying drawings, wherein the same reference numerals are used to designate the same elements, and wherein: Figure 1 An eye-tracking optical system utilizing spectacle lenses as light guides according to one embodiment is shown; Figure 2 A world-facing camera using eyeglass lenses as light guides according to another embodiment is shown; Figure 3a An optical system without an output coupler according to an embodiment is shown; Figure 3b The propagation of light through a light guide according to an embodiment is shown; and Figure 4 A head-mounted device including an optical system is shown according to an embodiment. Detailed Implementation

[0019] Figure 1 An optical system 100 according to an embodiment is schematically illustrated. The optical system 100 includes a light guide (or waveguide) 110 having non-parallel opposing first and second main surfaces 112, 114. An optical incoupler 120 and an optional optical outcoupler 130 are arranged on the first main surface 112 to couple light into and out of the light guide 110, respectively. Although Figure 1 The optical inlet coupler 120 and optical outlet coupler 120 are shown on the same side of the light guide 110, in this case, the first main surface 112. However, the optical inlet coupler 120 and optical outlet coupler 120 may be on opposite sides of the light guide 110, i.e., one on the first main surface 112 and the other on the second main surface 114. Furthermore, one or both of the optical inlet coupler 120 or optical outlet coupler 130 may be embedded within the body of the light guide 110.

[0020] Optical inlet coupler 120 is arranged to collect light reflected from an object or scene (e.g., a user's eye 150) when the optical system 100 is in use. Optical outlet coupler 130 is arranged to guide light from light guide 110 to photodetector 140.

[0021] In use, the optical inlet coupler 120 is arranged to collect light reflected from an object or scene (such as the user's eye 150). The reflected light is coupled into the light guide 110, allowing the light to propagate along the light guide 110 via total internal reflection. The optical inlet coupler 120 is arranged as a diffractive optical element (DOE) with a diverging (or concave) lens function. In other words, the optical inlet coupler includes negative optical power to image the entire surface object and couple the image object into the light guide. Typically, for an optical eye-tracking system to function properly, it is preferable to image at least the white part of the eye (sclera), the iris, and the pupil so that the relevant software can determine the rotation of the eye and thus its position. In this respect, there is a trade-off between the thickness of the light guide 110 and the imageable area. A thinner light guide is preferred to keep the overall weight of the eye-tracking system as low as possible, which is required for head-mounted optical systems. However, the thinner the light guide, the smaller the imageable area of ​​the eye. In other words, the field of view (FOV) is limited by the thickness of the light guide. The FOV is linearly proportional to the thickness of the light guide. Typically, the FOV is approximately equal to the thickness of the light guide. By utilizing an optical input coupler that includes negative optical power, the field of view (FOV) can be increased without increasing the thickness of the light guide 110 to image the sclera, iris, and pupil, so that the relevant software can determine the rotation and position of the eye. In other words, light from the entire range of the user's eye can be coupled into and propagated through the light guide, converging on the detector or the detector's entrance pupil after leaving the light guide.

[0022] The thickness of the light guide represents a balance between weight and robustness. If it is too thin, the light guide is easily damaged. If it is too thick, the light guide 110 may be too heavy for all-day wear. Therefore, the thickness of the light guide 110 is typically between 1 and 10 mm, preferably 5 mm. In the context of this disclosure, the thickness of the light guide is the center thickness measured along the optical axis.

[0023] For a light guide thickness of 3 mm and an inlet coupler width of 12 mm (where the inlet coupler width is defined as the net direction of light propagation along the light guide), and an eye relief distance of 25 mm to image the entire range of a typical eyeball with a diameter of approximately 24 mm, the optical power of the negative lens function of the optical inlet coupler 120 should be -40 diopters (m). -1(or 1 / 0.025m). The width of the optical coupler is less than or equal to four times the center thickness of the light guide because the negative optical power of the optical coupler reduces the image. As the eye release distance increases, the optical power of the negative lens function decreases proportionally. In this context, the eye release distance is the distance from the surface of the user's eye to the optical coupler 120, and is typically between 10mm (for eyeglasses) and 50mm (for helmet visors), depending on the type of head-mounted system used by the optical system 100. The field of view (FOV) generated by the negative optical power of the coupler 120 can be approximated by the following expression: FOV ≈ arctan(in-coupler width x in-coupler power)... (1) in: In-line coupler width Defined in meters, and Optical power of the in-coupler Defined in units of diopters 。

[0024] The optical coupler may be a volume holographic material applied to the surface of the light guide 110. For example, the coupler may be formed on an optical polymer (e.g., Bayfol (RTM) or silver halide film sold by Covestro AG) and then attached to the surface of the light guide, conforming to its surface. Alternatively, the optical coupler 120 may be a surface relief grating or Fresnel lens formed on or embedded in the surface of the light guide 110. Alternatively, the coupler 120 may be formed of a holographic material selected from one of an optical polymer, silver halide, dichromate gelatin, or SHSG. When the optical coupler 120 is holographic, it can be a transmissive or reflective holographic coupler. The coupler 120 is advantageously positioned close to the optical axis of the lens.

[0025] In addition to reducing the negative optical power of the image, the optical coupler 120 also includes a linear grating term to deflect light into the light guide 110 at an angle greater than the angle at which total internal reflection occurs, allowing the coupled light to propagate around the light guide 110. The negative optical power of the optical coupler 120 results in an increased field of view compared to an optical coupler of the same size without negative optical power. The negative optical power feature is advantageous compared to increasing the coupler size because increasing the field of view without negative optical power would lead to image overlap at the photodetector. In other words, the footprints of light rays at the point of incidence on the surface of the light guide 110 are substantially non-overlapping within the light guide, thus avoiding image overlap at the photodetector 140. The overall phase function of the optical coupler can be described by the following expression: Phase = Ax + By + Cx 2 + Dy2 …. (2) in: x and y Define the coordinates on the in-coupler A and B These are the coefficients that define the amount of light deflection in the x and y directions, respectively; and C and D These are the negative optical power coefficients in their respective x and y directions. In use, an optional optical output coupler 130 is arranged to output light propagating along the light guide 110 via total internal reflection to the photodetector 140. In this way, an image of the user's eye 150 is projected onto the photodetector. The optical output coupler 130 is arranged as a diffractive optical element (DOE) having a converging (or convex) lens component. Alternatively, the optical output coupler 130 may include linear diffraction terms, and an optional convex lens element 150 may be placed between the optical output couplers 130 to project the image of the user's eye 150 onto the detector 140. Like the optical input coupler 120, the optical output coupler 130 may be a volume holographic material applied to the surface of the light guide 110. For example, the input coupler may be formed on a photopolymer (e.g., Bayfol (RTM) or silver halide film sold by Covestro AG) and then attached to the surface of the light guide 110, consistent with its main surface. Alternatively, the optical output coupler 130 may be a surface relief grating or Fresnel lens formed on or embedded in the surface of the light guide 110. The optical output coupler 130 may be a refractive or reflective element, such as an optical facet or prism formed on or embedded in the surface of the light guide 110 facing the photodetector 140, to guide light from the light guide 110 to the photodetector 140. However, according to the following... Figure 3b From the discussion, those skilled in the art will understand that a specific output coupler is not necessary. The output coupler 130 may be formed of a holographic material, wherein the holographic material is selected from one of photopolymers, silver halides, dichromate gelatin, or SHSG.

[0026] The light guide 110 is formed of a transparent material with a refractive index higher than that of the surrounding environment, such as air. Therefore, the light guide 110 guides light from the optical input coupler 120 to the optical output coupler 130 via total internal reflection. The light guide 110 is also transparent to ambient light, allowing the user to view the outside world through it. In this way, the light guide 110 acts as an ophthalmic lens, and in this respect, those skilled in the art will understand that the light guide 110 is a curved light guide 110. That is, the first and / or second main interfaces 112, 114 will be appropriately curved according to the ophthalmic properties of the light guide discussed below. Those skilled in the art will also understand that one of the main surfaces may be planar, and the first and second main surfaces are not parallel.

[0027] The first main interface 112 can be considered as the surface facing the eye, and the second main interface 114 can be considered as the surface facing the world. One or both of the first and second main interfaces 112, 114 of the light guide 110 may be curved in the same manner as the respective curved surfaces that an ophthalmic lens may have. In this respect, the light guide 110 may be a corrective (i.e., having optical power) ophthalmic lens or a zero-prescription (i.e., no optical power) lens. For example, the first main interface 112 may have a radius of curvature of 240 mm, and the second main interface 114 may have a second radius of curvature of 120 mm, such that the optical power of the light guide 110 is 2 diopters (m). -1 This would make the lens a positive lens. Similarly, the radii of curvature of the first and second main interfaces 112, 114 may be equal, resulting in a zero-power lens. Furthermore, the radii of curvature of the first and second main interfaces 112, 114 may result in a negative power of the light guide 110. The light guide may also incorporate bifocal or progressive multifocal lens functionality. Those skilled in the art will understand that the curvature of the light guide 110 and the negative power of the ingress coupler 120 will cause image distortion, i.e., deviation from linear projection, and that the distortion will be constant for a given geometric configuration of the light guide 110. While beyond the scope of this disclosure, appropriate image processing algorithms may be used to correct any distortion. Such algorithms may advantageously perform image remapping, one example being a warping technique. Remapping can be fixed, for example, by applying a constant lookup table to the distorted image.

[0028] The thickness of the light guide 110 is greater than one-quarter of the width w of the optical ingress coupler 120, where the width of the ingress coupler is in the lateral direction along the surface of the light guide. In this way, light rays from a specific point in the human eye will propagate through the light guide 110 without overlapping, and the image from the user's eye will be relayed to the output of the light guide 110. In this way, light rays will propagate through and exit the light guide 110, causing them to converge at the entrance pupil of the photodetector 140.

[0029] The photodetector 140 can be any suitable photodetector, such as a CCD, for detecting light reflected from the eye 150 and coupled out of the light guide 110. The photodetector 140 will be selected to operate at an appropriate wavelength to detect the wavelength of light reflected from the eye, such as infrared light, but any invisible wavelength is suitable. Typically, eye-tracking systems use infrared light. The photodetector generates data corresponding to the light reflected from the user's eye 150. This data is used by a computing system (not shown) to determine the position of the user's eye 150. The photodetector 140 will be positioned relative to the light guide 110 at the appropriate point where the light exits the light guide 110.

[0030] A focusing lens 160 may be placed between the output coupler 130 and the photodetector 140 to image the output of the light guide 110 onto the photodetector. In other words, the image from the user's eye, propagated along the optical path from the optical input coupler 120 to the optical output coupler 130 via total internal reflection, is imaged onto the photodetector by the focusing lens 160. The focusing lens 160 may be formed on the surface of the light guide. Alternatively, it may be integrally formed with the photodetector 140. Astigmatism at the photodetector 140 may be corrected by using a combination of spherical and cylindrical lenses as the focusing lens 160. Similarly, the detector may be tilted relative to its optical axis. Or, in other words, at an angle relative to the normal to the center ray of the detector. Astigmatism correction and detector tilt improve image focusing across the entire field of view.

[0031] When using ambient light, a narrowband optical filter (not shown) may be incorporated into or mounted on the photodetector 140 to filter out any unwanted light. This improves the contrast between image light and stray light.

[0032] As an alternative to or supplement to ambient light as an eye illumination source, one or more light sources (not shown) may be placed near the user's eye 150. The light source may be an LED operable to emit invisible light, such as infrared light. The operating wavelength of the LED will be matched to the operating wavelength of the photodetector. A narrowband optical filter may be arranged at the photodetector to filter out any unwanted light wavelengths, which is particularly beneficial in cases where eye illumination is achieved through ambient light. However, those skilled in the art will understand that when eye illumination is achieved through a narrowband light source (such as a narrowband LED or laser diode) matched to the detection wavelength of the photodetector, an optical filter will not be necessary.

[0033] Regarding the above discussion, those skilled in the art will understand that... Figure 1 The described arrangement of an optical system utilizing spectacle lenses could be used in an optical eye-tracking system. Similarly, and in reference... Figure 2Those skilled in the art will understand that this optical system could be used in a world-class camera system. Figure 2 The optical system 200 is a world-oriented camera system, comprising a light guide (or waveguide) 210 having opposing first and second main interfaces 212, 114. An optical input coupler 220 and an optional optical output coupler 230 are arranged on the first main surface 212 to couple light into and out of the light guide 210, respectively. Figure 1 Similar to the arrangement, the input coupler and output coupler may be arranged on opposing surfaces or embedded in the body of the light guide. A photodetector 240 is arranged to collect light coupled from the light guide 210 by the optical output coupler 230. An optical input coupler 220 is arranged to collect light reflected from an object or multiple objects 252 (the scene being viewed) visible to the user's eye 250 at a distance when the optical system 200 is in use. Typically, the object or multiple objects will be the scene being viewed by the user. In this embodiment, the optical input coupler 220 is arranged on the first main surface 212 of the light guide 210, i.e., on the eye side of the light guide 210. Light from the object 252 is coupled into the light guide 210 through the optical input coupler 220, propagates around the light guide 210, and exits the light guide 210 at the optical output coupler 230. Light from the object 252 will also reach the user's eye 250 through the light guide so that the scene can be viewed. As described above, the light guide 210 may be in the form of an ophthalmic lens, which can correct the user's vision to allow them to view the scene. The optical coupler 230 couples light to the photodetector 240. In this way, an image of the object or scene viewed by the user can be captured without parallax error. (See below for details.) Figure 3b The specific optical output coupler 230 discussed is not necessary because light may leave the light guide 210 and enter the photodetector when the critical angle for total internal reflection within the light guide 210 is broken. For Figure 2 In a world-oriented camera system, the negative focal length of the ingress coupler 220 should be sufficiently large to capture a wide field of view. For example, a negative focal length of -12mm would give a field of view of approximately 60 degrees. The world-oriented camera system 200 may also include a light source, such as an infrared LED suitable for illuminating the world environment being viewed, and may include time-of-flight detection.

[0034] Figure 3a It shows Figure 1 An alternative arrangement for the optical system 100. With Figure 1 The optical system is similar to 100. Figure 3aThe optical system 300 includes a light guide (or waveguide 110) 310 having opposing first and second main interfaces 312, 314, and an optical input coupler 320 for coupling light into the light guide 310. A photodetector 340 is arranged to collect light coupled from the light guide by the optical output coupler 330. The optical input coupler 320 is arranged to collect light reflected from the user's eye 350 when the optical system 200 is in use. Figure 1 and Figure 2 The optical systems 100 and 200 are different. Figure 3a The optical system 100 does not include a specific optical output coupler. Figure 3a In this arrangement, the photodetector 340 is positioned at an angle relative to the light guide 310. More specifically, the photodetector 340 follows the angle of the light ray (xx) that propagates through and then exits the light guide 340. The angle of the light ray xx will depend on the refractive index n of the light guide material, but the angle θ is greater than the critical angle of the light guide 340. Specifically, the angle θ is the angle of the light ray relative to the surface normal at the point of incidence on the surface of the light guide 310. Therefore, those skilled in the art will see in this respect that a specific optical coupler is not necessary, but the light can exit the light guide 340 when the angle of the light ray is greater than the critical angle of the light guide 340.

[0035] Figure 3b This illustrates how light propagates through light guide 110 and exits at exit point 132 without requiring a specific optical coupler. For clarity, only a single ray of light propagating through and exiting light guide 110 is shown. A ray X from an object (in this case, a reflection from the user's eye) is coupled into light guide 110 at the first main interface 112 via optical coupler 120. Optical coupler 110 is coupled at a critical angle θ greater than that of light guide 120. c The in-coupling angle θ i The ray X is coupled in such a way that it is reflected from inside the second primary interface 114 at point A, and according to Snell's Law, ray X will be reflected at an angle θ1 equal to the angle of incidence of ray X from the optical coupler 120. Ray X then enters at an angle θ2 relative to the surface normal at point B on the first primary interface 112, and is thus reflected towards point C on the second primary interface 114 at an angle θ3. Ray X then enters at the exit point 132 at an angle θ4, because angle θ4 is less than the critical angle θ of the light guide 110. c The light will exit the light guide 110. Because the first and second main interfaces 112 are not parallel, the reflection angle decreases after each successive reflection until the incident angle is less than the critical angle of the light guide 110, at which point the light leaves the light guide. This allows light to couple into and then out of the light guide without requiring an output coupler.

[0036] In the above, all incident angles or reflection angles θ1, etc., are given relative to the surface normal at the incident or reflection point of the surface.

[0037] For example, when the light guide 110 material is Trivex® with a refractive index n1 = 1.53, the critical angle θ at the air interface with a refractive index n2 = 1... c The angle will be 40°. Therefore, the optical ingress coupler 120 should be arranged to couple light into the light guide 110 at an angle greater than 40°. For each successive total internal reflection from their respective main interfaces, the angle of incidence will decrease so that eventually, when the critical angle is broken, light will exit from the light guide 110. The number of reflections as light propagates through the light guide 110 will depend on the ingress angle at the optical ingress coupler 120 entering the light guide 110, the refractive index of the material, and the thickness variation of the light guide 110 from the ingress coupler to the exit point. A mirror 115 may be provided on the second main surface 114 of the light guide 110 to help reflect light to the output end of the light guide at that point.

[0038] Although Figure 3b This illustrates the propagation of light through the light guide 100 and the emission of light from the light guide 100, but it also applies to... Figure 1 , Figure 2 or Figure 3a The arrangement of the light guides 110 and 210 is also understood by those skilled in the art. For light guides 110 and 210 with uneven distances between the first and second primary surfaces, multiple images or ghosting will occur due to overlapping of light rays as they propagate around the light guides 110 and 210. For the optical systems 100 and 200 discussed herein, the negative optical power of the inlet couplers 120 and 220 overcomes this problem. Furthermore, because the negative optical power of the inlet couplers 120 and 220 increases the field of view, the width of the inlet couplers 120 and 220 can be reduced compared to inlet couplers without negative optical power.

[0039] Figure 4 A head-mounted device 400 is shown, comprising at least one optical system 100, 200 as described above. The head-mounted eye-tracking system may form part of a broader head-mounted display, such as augmented reality glasses. Like known types of glasses, the head-mounted eye-tracking system 400 includes a frame 402. The frame 402 includes temples 404 and lens mounting portions 406 connected via a bridge portion 408. One of the temples 404 includes a mounting portion 410 in which light detectors 140, 240 (as described above) are fixedly mounted to collect light exiting light guides 110, 210. The light detectors 140, 240 are positioned in this manner to place them outside the user's field of vision. The light guides 110, 210 (as described above) may be mounted in one of the lens mounting portions 406 of the frame 402.

[0040] Those skilled in the art will understand that light guides 110 and 220 will be mounted in the lens mounting portions adjacent to photodetectors 140 and 240. They will also understand that two light guides 110 and 210 (of the type described above) may be mounted in the frame 402, each in its respective lens mounting portion 306. When two light guides 110 and 210 are used, two photodetectors 140 and 240 will be suitably mounted on the temples 404 of the frame 402.

[0041] The peripheral edges of light guides 110 and 210 may include absorbing surfaces, such as a black coating, to prevent stray light from entering the light guides 110 and 210, thereby improving image contrast.

[0042] One or two temples 404 may also be adapted to house a battery (not shown) to power the light detectors 140, 240, the illumination source, and the processing electronics (not shown). Furthermore, one or two temples 404 may also be adapted to house the processing electronics, which calculate the movement of the user's eyes 150, 250 and execute any distortion correction algorithms.

[0043] Similarly, for Figure 2 In a world-oriented camera system, those skilled in the art will understand that the light guide 210 may be mounted in the lens mount portion, and the light detector may be placed in a suitable forward position on the frame, such as at the junction of the temple and the lens mount portion. Those skilled in the art will also understand that the light detector may be placed in each position, and the corresponding light guide according to the embodiment is mounted in the lens mount portion.

[0044] Specific and preferred aspects of this disclosure are set forth in the appended independent claims. Combinations of features from dependent and / or independent claims may be appropriately combined, and not limited to those described in the claims.

[0045] The scope of this disclosure includes any novel feature or combination of features, or any generalization thereof, explicitly or implicitly disclosed herein, whether or not it relates to the claimed disclosure or mitigates any or all the problems addressed by this disclosure. The applicant hereby declares that new claims may be formulated for such features during the examination of this application or any such further application derived therefrom. In particular, with reference to the appended claims, features from dependent claims may be combined with features from independent claims, and features from each independent claim may be combined in any suitable manner, not just the specific combinations listed in the claims.

[0046] Features described in the context of a single embodiment may also be provided in combination in a single embodiment. Conversely, various features described in the context of a single embodiment for the sake of brevity may also be provided individually or in any suitable sub-combination.

[0047] The term "comprising" does not exclude other elements or steps, and the terms "a" or "an" do not exclude multiple. Reference numerals in the claims should not be construed as limiting the scope of the claims.

Claims

1. An optical system, including: A light guide having opposing first and second non-parallel optical surfaces, wherein at least one of the first or second optical surfaces is curved; An ingress-coupled diffractive optical element is arranged to receive reflected light from an object and couple the reflected light into a light guide at a first position, wherein the reflected light propagates around the light guide and exits the light guide at a second position. as well as A photodetector is positioned near a second location to receive reflected light from a light guide.

2. The optical system of claim 1, wherein the ingress-coupled diffractive optical element comprises a linear diffraction grating having a constant period.

3. The optical system of claim 1, wherein the center thickness of the light guide is such that light rays propagating through the light guide do not overlap.

4. The optical system of claim 3, wherein the width of the ingress-coupled diffractive optical element is less than four times the center thickness of the light guide.

5. The optical system of claim 1, wherein the ingress-coupled diffractive optical element includes a lens function with negative optical power.

6. The optical system according to any one of claims 1 to 5, wherein light rays exiting the light guide converge to the entrance pupil of the photodetector.

7. The optical system according to any of the preceding claims, wherein the center thickness of the light guide is in the range of 1 mm to 10 mm, preferably 3 mm.

8. The optical system according to any of the preceding claims, wherein the detector is tilted relative to the angle at which the light leaves the light guide.

9. The optical system of claim 1, wherein the second position is an output end and an output coupler is arranged at the output end.

10. The optical system of claim 9, wherein the outgoing coupler can change the angle of light rays leaving the light guide.

11. The optical system according to claim 9 or 10, wherein the output coupler is a diffraction output coupler, a reflection output coupler, or a refraction output coupler.

12. The optical system according to any of the preceding claims, wherein the photodetector is a charge-coupled device (CCD).

13. The optical system according to any of the preceding claims further includes a focusing lens arranged to focus light from the light guide onto the photodetector.

14. The optical system of claim 13, wherein the focusing lens is a combination of a cylindrical lens and a spherical lens.

15. The optical system according to any of the preceding claims, wherein the light guide is a transparent ophthalmic lens, and the first and second optical surfaces are optical surfaces of the ophthalmic lens.

16. The optical system according to any of the preceding claims further includes a light source arranged to illuminate a user's eye or a scene being viewed, wherein the light source is arranged to emit invisible light.

17. The optical system of claim 16, wherein the light source is a narrowband infrared light-emitting diode or a laser diode.

18. A head-mounted eye-tracking system, comprising the optical system described in any of the preceding claims.

19. A world-oriented camera system, including the optical system described in any of the preceding claims.

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