Abstract
An optical system for transmitting a source image includes a light guide, which defines a light transmission channel, an optical coupling arrangement and an optical decoupling arrangement, the coupling arrangement being designed to couple light emerging from the source image into the light guide arrangement in such a way that the light can propagate in the light guide arrangement by total reflection, and the decoupling arrangement being designed to decouple light that has propagated in the light guide arrangement from the light guide arrangement. The light guide arrangement comprises an optical deflection device, which, as viewed in the direction of propagation of the light in the light guide arrangement, is arranged between the coupling arrangement and the decoupling arrangement and is designed to deflect light ray bundles, emerging from the coupling arrangement at different beam angles and impinging divergently on the deflection device, in bundled manner towards the decoupling arrangement.
Claims
1. An optical system for transmitting a source image, comprising a light guide that defines a light transmission channel, the light guide comprising: an optical input coupling, and an optical output coupling, wherein the input coupling is configured to couple light emanating from the source image into the light guide such that the light can propagate in the light guide by way of total-internal reflection, and wherein the output coupling is configure to couple the light that has propagated in the light guide out of said light guide, an optical deflector comprising a plurality of mirrors, which as seen in a direction of propagation of the light in the light guide, disposed between the input coupling and the output coupling, the optical deflector configured to deflect light beams that emanate from the input coupling different beam angles, which are incident on the optical deflector in a divergent fashion, to the output coupling in focused fashion, wherein the mirrors are angled mirrors that are disposed along a circular line segment.
2. The optical system of claim 1, wherein the optical deflector is configured to deflect the light beams, which are incident thereon, such that an angle between the incident and deflected light beam is the same for all light beams.
3. The optical system of claim 1, wherein the optical deflector is a pupil relay optical unit, which images a source image-side entry pupil onto an eye-side exit pupil.
4. The optical system of claim 1, wherein the optical deflector is embedded in the light guide.
5. The optical system of claim 1, wherein the optical deflector is disposed adjacent to an edge of the light guide.
6. The optical system of claim 5, wherein the optical deflector is disposed at any one or more of an upper, a lower, a nasal and a temporal edge of the light guide when the optical system is worn on a user's head.
7. The optical system of claim 1, wherein the mirrors are angled mirrors, and wherein apex sections of the angled mirrors are cut off or that unused regions of the angled mirrors are non-reflective, or both cut off and non-reflective.
8. The optical system of claim 1, wherein the mirrors are angled mirrors that include a coating that is angle-selective in respect of reflection by the mirrors.
9. The optical system of claim 1, wherein the mirrors are angled mirrors that have a minimum width of 0.5 mm on an open side thereof.
10. The optical system of claim 1, wherein the mirrors are angled mirrors that have different orientations from one another, said different orientations being adapted to beam angles of the incident light beams.
11. The optical system of claim 1, wherein the angled mirrors are disposed or oriented such that points of intersection of light rays incident on the angled mirrors and reflected by the angled mirrors are located on a circular line segment.
12. The optical system of claim 1, wherein the light transmission channel is a first light transmission channel for transmitting a first partial field of the source image and the light guide comprises a second light transmission channel that transmits a second partial field of the source image, wherein the optical deflector comprises a first deflection part assigned to the first light transmission channel and a second deflection part assigned to the second light transmission channel.
13. The optical system of claim 1, wherein the input coupling includes at least one mirror or diffractive structure.
14. The optical system of claim 1, further comprising a display, which provides the source image, and a collimator that directs the light emanating from the source image onto the input coupling.
15. A pair of smartglasses, video glasses or a head-up display comprising the optical system of claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Exemplary embodiments of the invention are illustrated in the drawing and described in more detail below with reference thereto. In the figures:
(2) FIGS. 1A and 1B schematically show an optical system for transmitting a source image, FIG. 1A showing a view of the optical system from above and FIG. 1B showing a view as seen from the viewer when the optical system is worn on the head of the viewer;
(3) FIG. 2 shows an angled mirror for elucidating the beam deflection of a light ray on such an angled mirror;
(4) FIG. 3 shows three partial images for explaining the inscribed angle theorem;
(5) FIG. 4 shows a light beam path with a deflection at a deflection device having a plurality of angled mirrors disposed along a circular line segment;
(6) FIG. 5 shows a perspective illustration of an optical system for transmitting a source image having a deflection device as in FIG. 4;
(7) FIGS. 6A and 6B show two diagrams which elucidate, in exemplary fashion, the coupling of light into a light guide arrangement by means of an oblique mirror as an input coupling arrangement (FIG. 6A) and by means of a linear grating (FIG. 6B) in direction cosine space;
(8) FIGS. 7A and 7B show two diagrams which show the beam deflection within the light guide arrangement by a grating twisted about a normal of the light guide arrangement as a deflection device (FIG. 7A) and by a mirror or angled mirror at an edge of the light guide arrangement (FIG. 7B) as a deflection device;
(9) FIGS. 8A and 8B show a first exemplary embodiment of an optical system for transmitting a source image, FIG. 8A showing the geometric arrangement of parts of the system and FIG. 8B showing the associated diagram of the source image transmission in direction cosine space;
(10) FIGS. 9A and 9B show a further exemplary embodiment of an optical system for transmitting a source image, FIG. 9A showing the geometric arrangement of parts of the system and FIG. 9B showing the associated diagram of the source image transmission in direction cosine space;
(11) FIG. 10A to 10C show a further exemplary embodiment of an optical system for transmitting a source image, FIG. 10A showing the geometric arrangement of parts of the system, FIG. 10B showing the diagram of transmission of a first partial field of the source image, and FIG. 10C showing the diagram of the transmission of a second partial field of the source image in direction cosine space;
(12) FIGS. 11A and 11B show two diagrams in direction cosine space for the transmission of the two partial fields in a development of the exemplary embodiment in FIG. 10A to 10C;
(13) FIGS. 12A and 12B show a further exemplary embodiment of an optical system for transmitting a source image with a deflection device based on retroreflection, FIG. 12A showing the system in a view from a viewer and FIG. 12B showing the system in a view from above when the optical system is worn on the head of the viewer; and
(14) FIG. 13 shows a further exemplary embodiment of an optical system for transmitting a source image, in a development of the exemplary embodiment of FIG. 10A.
(15) While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular example embodiments described. On the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION
(16) In the following descriptions, the present invention will be explained with reference to various exemplary embodiments. Nevertheless, these embodiments are not intended to limit the present invention to any specific example, environment, application, or particular implementation described herein. Therefore, descriptions of these example embodiments are only provided for purpose of illustration rather than to limit the present invention.
(17) FIGS. 1A and 1B schematically show views of an optical system, provided with the general reference sign 10, for transmitting a source image. In particular, the optical system 10 can be embodied as smartglasses or video glasses, as a head-mounted display (HMD) or else as a head-up display (HUD). Here, the source image is provided by a display 12, for example a micro-display. The source image can be a live image or video sequence of a camera, or an image from another data source.
(18) The optical system 10 has a light guide arrangement 14. The light guide arrangement 14 has a single optical waveguide. The light guide arrangement 14 is transmissive to light in the visible spectrum and has a material that has a higher refractive index than air. The light guide arrangement 14 defines a light transmission channel 15 for transmitting the light emanating from the source image (display 12).
(19) The light emanating from the imaging display 12 is directed to the input coupling arrangement 18 via an optical unit 19, in particular a collimation optical unit. Should the optical unit 19 be a collimation optical unit, the light emanating from the source image is incident on the light guide arrangement 14 as a parallel light beam.
(20) To simplify the description of the directions in space, a coordinate system 16 is respectively plotted in FIGS. 1A and 1B. To simplify the understanding, the x-axis denotes the horizontal direction perpendicular to the viewing direction of the viewer in the following description and the y-axis denotes the vertical direction when the optical system 10 is worn on the head of the viewer. Here, the z-axis denotes the normal of the light guide arrangement pointing away from the viewer.
(21) The optical system 10 has an optical input coupling arrangement 18, by means of which light 20 emanating from the source image is coupled into the light guide arrangement 14 such that the light can propagate in the light guide arrangement 14 byway of total-internal reflection. The input coupling arrangement 18 can have a diffractive optical arrangement, which should also be understood to mean an arrangement with volume holograms, or a reflective optical arrangement or a structure which deflects the light beams incident thereon in such a way that said light beams are able to propagate in the light guide arrangement by way of total-internal reflection. Consequently, input coupling should be understood to mean such a deflection. The input coupling arrangement 18 defines an input coupling region 17. Light 20 emanating from the source image (display 12) has a field angle spectrum in the xy-plane, which is caused by the geometry and dimensions of the source image. By way of example, the light emanating from the source image can have a rectangular field angle spectrum, for example with a 49° vertical field (y-axis) and 27° horizontal field (x-axis).
(22) Then, the light 20 coupled into the light guide arrangement 14 via the input coupling arrangement 18 in the input coupling region 17 propagates in the light guide arrangement 14 from the input coupling arrangement 18 by way of total-internal reflection at the interfaces 22 and 24 of the light guide arrangement 14. The propagation of the light 20 in the light guide arrangement 14 by total-internal reflection requires only light beams of the light 20, which are incident on the interfaces 22, 24 at an angle of incidence that is greater than the critical angle of total-internal reflection but less than 90°. On account of tolerances from manufacturing and adjustment, a distance of approximately 5° should be maintained from the boundaries.
(23) Furthermore, the optical system 10 has an optical output coupling arrangement 26 that defines an output coupling region, by means of which the light that has propagated in the light guide arrangement 14 is coupled out of the light guide arrangement 14 to an eye 28 such that the transmitted source image can be perceived by a viewer.
(24) In FIG. 1A, the input coupling arrangement 18 and the output coupling arrangement 16 are shown as structures that are embedded in the light guide arrangement 14; however, they could also be located at one or both of the interfaces 22 and 24. The input coupling arrangement 18 can have a transmissive or reflective diffraction grating. As an alternative or in addition thereto, the input coupling arrangement 18 can have one or more volume holograms or one or more Fresnel mirrors. In further variants, a prism placed on the light guide arrangement 14 or a specifically designed edge region of the interface 22 or 24 is conceivable, for example with free-form prisms with a collimating effect. In general, such specifically designed edge regions can be characterized in that the interface 22 or 24 has a different orientation/surface normal in the input coupling region than the remaining region of the light guide arrangement 14. The input coupling arrangement 18 can be embedded in the light guide arrangement (transmissive or reflective input coupling arrangement) or on the light entry surface 24 (transmissive input coupling arrangement) or on the surface 22 located opposite the light entry surface (reflective input coupling arrangement). In the case of the design of the input coupling arrangement 18 with a mirror, which may optionally be segmented like a Fresnel mirror, for example, said mirror is suitably tilted with respect to the surface normal of the light guide arrangement and/or rotated about the normal. The input coupling arrangement 18 has the function of deflecting the light beams, which emanate from the source image, upon entry or immediately after entry into the light guide arrangement 14 in such a way that the light beams are then able to propagate in the light guide arrangement 14 by way of total-internal reflection at the interfaces 22, 24 of the light guide arrangement 14 (for example, air/glass or air/plastic transition). Likewise, the output coupling arrangement 26 can have a reflective or transmissive embodiment and have a diffraction grating or one or more mirrors which, in particular, act as a beam splitter such that the viewer can perceive through the output coupling region 27 not only the source image but also the real surroundings with a superposed source image through the light guide arrangement 14 (referred to as augmented reality).
(25) FIG. 1A shows only a single representative light ray emanating from the source image in order to simplify the representation. However, it is understood that the light emanating from the source image (display 12) is a two-dimensional field of light beams.
(26) Furthermore, the light guide arrangement 14 has an optical deflection device 30 which, as seen in the direction of propagation of the light 20 in the light guide arrangement 14, is disposed between the input coupling arrangement 18 and the output coupling arrangement 26. The deflection device 30 is embodied to deflect light beams, which emanate from the input coupling arrangement 18 with different beam or field angles and which are incident on the deflection device 30 in divergent fashion, to the output coupling arrangement 26 in focused fashion. FIG. 1B shows two marginal rays 32 and 34, which represent the envelope of the light beams (also referred to as light pipe) in the xy-plane. The light pipe has its greatest spread or width at the deflection device 30. From the deflection device 30, the spread or width of the light pipe (marginal rays 32, 34) reduces toward the output coupling arrangement 26. Consequently, the effect of the deflection device 30 is that the geometric extent of the input coupling arrangement 18 can be kept small, even in the case of a large field of view of the transmitted source image.
(27) In particular, the deflection device 30 can be embodied in such a way that the light beams incident thereon are always deflected by the same angle φ, independently of the field angle thereof.
(28) Moreover, the deflection device can be embodied as a pupil relay optical unit, in particular, which images a source image-side entry pupil, for example the entry pupil of the optical unit 19, onto a viewer-side exit pupil, for example the pupil of the eye of the viewer, as will still be described below.
(29) The deflection device 30 can have a reflective or diffractive optical structure or a combination of a reflective and diffractive structure. The term “diffractive structure” comprises not only diffraction gratings but also holographic-optical elements, in particular holographic mirrors, in particular volume holograms.
(30) The deflection device 30 can have surface gratings, mirrors or volume holograms, but could also have combinations of such structures or elements.
(31) A design of the deflection device 30 with a reflective optical structure is described below. An optical structure that is well-suited to the deflection device 30 is a structure made of a plurality of angled mirrors. FIG. 2 shows a single angled mirror 38. The angled mirror 38 has two plane mirrors 40 and 42, which are inclined to one another in roof-shaped fashion at an angle β. Independently of the angle β, the angled mirror 38 has, with respect to the beam deflection, an invariance in respect of a rotation about an axis perpendicular to the principal section, i.e., about an axis perpendicular to the plane of the drawing in FIG. 2. FIG. 2 shows an incident light ray 44, which is incident on the plane mirror 40, reflected thereby toward the plane mirror 42 and reflected by the latter to form a deflected beam 46. A deflection angle φ between the incident light beam 44 and the reflected light beam 46 is always the same size, independently of the relative rotational position of the angled mirror 38 about an axis perpendicular to the plane of the drawing, and equals φ=180°−2β.
(32) Moreover, when designing the deflection device 30, use can be made of the inscribed angle theorem, which is elucidated in FIG. 3. According to the inscribed angle theorem, for static points A and B and a movable point M all situated on a circle K, the internal angle α at the point M of the triangle ABM is constant independently of the position of the point M, as shown for three positions of the point M in FIG. 3.
(33) FIG. 4 now shows a design of the deflection device 30, in which the deflection device 30 has a plurality of angled mirrors 38, which may have a miniaturized embodiment, the angled mirrors 38 being disposed along a circular line K. Thus, all light beams emanating from a region A are deflected into a region B. If the pupil of the optical unit 19 in FIG. 1A is placed in the region A while the pupil of the eye 28 is located in the region B and if the region B is moved into the clear space outside of the light guide arrangement 14 by way of the input coupling arrangement 18 and if the region A is moved into the clear space outside of the light guide arrangement 14 by way of the output coupling arrangement 26, it is possible to create a pupil relay optical unit which images the pupil of the optical unit 19 in FIG. 1A onto the pupil of the eye 28. This is illustrated in FIG. 5, which shows the optical system 10 with the light guide arrangement 14, the input coupling region 17 of the light guide arrangement 14, the output coupling region 27 of the light guide arrangement 14 and the deflection device 30 of the light guide arrangement 14, the deflection device 30 having a plurality of angled mirrors 38 which, as shown in FIG. 4, are disposed on a circular line. This renders it possible to image the pupil of the optical unit 19 onto the pupil 28P of the eye 28.
(34) Independently of whether the deflection device 30 is constructed from angled mirrors, plane mirrors, prisms or other suitable optical elements, it can be embedded in the light guide arrangement 14. Here, the light deflection device 30 can preferably be disposed near an edge of the light guide arrangement 14, as shown in FIGS. 1B and 5. FIG. 5 shows an arrangement of the deflection device 30 on the upper edge of the light guide arrangement 14 when the optical system 10 is worn on the head of the viewer. However, as will be described in further exemplary embodiments below, the deflection device 30 could also be disposed on the nasal edge 46, the temporal edge 48 (on the side of the temple) or on the lower edge 50. When designing the deflection device 30 with angled mirrors 38 as shown in FIG. 5, the deflection device 30 operates in optimal fashion as a pupil relay optical unit if point of intersection 52 (see FIG. 2) of light beams 44, 46 (see FIG. 2), which are incident on the angled mirrors 38 and reflected by the respective same angled mirror 38, are located on the circular line segment K. However, a slight offset is acceptable and leads to the light beams belonging to the different field angles of the field angle spectrum not intersecting precisely at the pupil 28P of the eye.
(35) Depending on the angle of incidence of the light beam of the light 20 on the angled mirror 38, there could be only one reflection or more than two reflections on the respective angled mirror 38, possibly leading to stray light. This bothersome effect can at least partly be reduced by virtue of the rotation of the angled mirrors 38 being adapted in targeted fashion to the direction of the incident light beams. Preferably, the angles of rotation of the angled mirrors 38 have different angles of rotation from one another, as is evident from FIG. 5.
(36) Returning to FIG. 2, it is evident that the tip or the apex region 54 of the angled mirror 38 is not required for the beam deflection. Therefore, this region of the angled mirrors 38 can be cut off or removed, as indicated by a line 56 in FIG. 2. This is advantageous in that the entire deflection device 30 in the edge region of the light guide arrangement 14 can have a relatively flat embodiment.
(37) It is understood that the angled mirrors 38 can be varied in terms of their size, twisted or displaced in terms of their relative position on an individual basis.
(38) In order to avoid stray light as a result of the wrong number of reflections on the angled mirrors, angle-selective coatings could be provided on the angled mirrors where necessary. Optionally, the unused regions of the angled mirrors 38 and also the possibly present cut surfaces, at which the tips were cut off, can be blackened.
(39) The size of the angled mirrors, i.e., the width of the angled mirrors 38 at their open side, should not be too small so as to avoid diffraction effects due to the angled mirrors 38, which could lead to a loss of resolution of the source image transmission into the eye of the viewer. Therefore, it is advantageous if the angled mirrors 38 have a minimum width of 0.5 mm on their open side.
(40) As already mentioned, the deflection device 30 could also have other optical structures or elements in place of angled mirrors 38. For example, the deflection device 30 could also be realized by plane mirrors, with the pupil relay function of the deflection device 30 possibly not being able to be achieved in that case. On the other hand, this could avoid the above-described effects on account of an incoherent superposition of partial beams of light.
(41) The deflection device 30 could also have a combination of plane mirrors and angled mirrors.
(42) What field of view can be generated by an optical system with a deflection device is described below with reference to the further FIGS. 6A, 6B, 7A, 7B, while retaining the reference signs from FIGS. 1A and 1B. Representations in the direction cosine space (or else in k-space) are suitable to this end. A direction cosine diagram illustrates the light ray directions by representing the components of its direction vector. The direction cosine vector has a length of one. Consequently, the sum of all possible light ray directions is symbolized by a sphere (also called an Ewald sphere). If the component dircos.sub.x and dircos.sub.y of the direction cosine vector are known, the third component dircos.sub.z can be calculated by way of dircos.sub.z=(dircos.sub.x.sup.2+dircos.sub.y.sup.2).sup.1/2. Consequently, a two-dimensional representation in the dircos.sub.x−dircos.sub.y plane suffices for considering the propagation of the light in the light guide arrangement.
(43) If the light emanating from the source image, i.e., from the imaging display 12, is incident on the light guide arrangement 14, there initially is a refraction of the light at the interface 24 (see FIG. 1A) (unless input coupling arrangement 18 is located exactly on the light entry surface 24 such that the beam deflection at the input coupling arrangement 18 is the dominant effect). As a result of the higher refractive index of the light guide arrangement 14, the light rays are refracted toward the surface normal of the interface 24 and the angle range used by the light rays is reduced accordingly. Then, the light rays are deflected further at the input coupling arrangement 18.
(44) FIGS. 6A and 6B show direction cosine diagrams which the entry of the light into the light guide arrangement 14 and the deflection of the light rays at the input coupling arrangement 18 for two different designs of input coupling arrangements, specifically an input coupling arrangement formed by an oblique mirror (not illustrated) (FIG. 6A) and an input coupling arrangement having a linear diffraction grating at the interface 22 of the light guide arrangement 14.
(45) In the diagrams as per FIGS. 6A and 6B, dircos.sub.y denotes the direction cosine of the light beams with the y-axis and dircos.sub.x denotes the direction cosine of the light beams with the x-axis.
(46) In FIGS. 6A and 6B, an inner circle 60 in direction cosine space describes the critical angle of total-internal reflection and an outer circle 62 describes the angle of grazing incidence (90° with respect to the surface normal) on the interfaces 22 and 24 of the light guide arrangement 14. Only light rays with a beam or field angle located between the circles 60 and 62 can propagate in the light guide arrangement 14.
(47) Furthermore, by way of a large rectangle 64, FIGS. 6A and 6B show a rectangular beam or field angle distribution (field angle spectrum) of the light 20 emanating from the source image prior to the incidence thereof in the light guide arrangement 14. A small rectangle 66 in FIGS. 6A and 6B shows, in direction cosine space, the beam or field angle distribution of the light following refraction at the entry interface (interface 24 in FIG. 1A) in the light guide arrangement 14. In exemplary fashion, this shows a source image with a field of 25° in the horizontal (x-direction) and 50° in the vertical (y-direction). As already mentioned above, the field angle spectrum reduces on account of the refraction upon entry into the light guide arrangement 14, as yielded by a comparison of the rectangles 64 and 66.
(48) The input coupling arrangement 18 brings about a coupling of the light into the light guide arrangement 14, tantamount to a conversion of the field angle distribution, with which the light has entered into the light guide arrangement 14 (rectangle 66), between the circles 60 and 62, as shown in FIG. 6A by a frame 68 and in FIG. 6B by a frame 70. FIG. 6A describes the case where the input coupling arrangement is a mirror, which is tilted through 25° with respect to the normal of the light guide arrangement and not twisted about the normal of the light guide arrangement 14. FIG. 6B describes the case where the input coupling arrangement 18 has a linear grating, with a grating period of 1.8 lines per μm and without a rotation of the grating about the normal of the light guide arrangement 14.
(49) So that all of the image information of the source image can be guided to the eye 28 of the viewer through the light guide arrangement 14 by way of total-internal reflection, the field angle distributions (frames 68 and 70) of the light beams in the light guide arrangement 14 must fit, in the entirety thereof, between the circles 60 and 62 for total-internal reflection and grazing incidence. The two limits should not be fully exploited on account of manufacturing-related tolerances and adjustment tolerances.
(50) As a result of the deflection device 30, which may have further gratings or mirrors within the beam path of the light 20 in the light guide arrangement 14, for example the angled mirrors 38 as shown in FIG. 5, the field angle distribution of the light beam in the light guide arrangement 14 can be effectively deflected. The effect of such deflecting elements is elucidated in FIGS. 7A and 7B. FIG. 7A shows the case where the deflection device 30 has a grating which is twisted about the normal of the light guide arrangement 14. Such a grating leads to a displacement in the field angle distribution (frame 70) in the direction cosine space, as elucidated by a frame 70′ in FIG. 7A.
(51) FIG. 7B shows the case of the deflection device 30 having one or more mirrors, the normal vectors of which lie in the xy-plane, i.e., parallel to the interfaces 22 and 24. In the case of such a configuration of the deflection device 30, the field angle distribution (frame 70) coupled into the light guide arrangement 14 is twisted about the origin of the direction cosine space, as elucidated by a frame 70″ in FIG. 7B.
(52) Moreover, FIG. 7A elucidates that the field angle spectrum of the light beams within the light guide arrangement 14 can be cropped by a disadvantageous deflection by the deflection device 30 since parts of the field are coupled out of the light guide arrangement 14 at the wrong location due to the critical angle of the total-internal reflection being undershot or since parts of the field propagate with grazing incidence in the light guide arrangement. Thus, overall, this means that some of the light carrying the image information is coupled out of the light guide arrangement at a wrong location and consequently does not reach the eye of the viewer, as a result of which image information is lost.
(53) The problem of cropping the field angle distribution can be rectified by virtue of the source image being transmitted in segmented fashion, as will still be described below.
(54) Exemplary embodiments for the optical system 10 are described below, with the spectral distribution of the light also being considered at least in part, specifically for two wavelengths. Below, two wavelengths of the light are considered in each case, said wavelengths being shifted by 30 nm from one another. Here, a wavelength at 500 nm in the blue spectral range and a wavelength of 530 nm in the green spectral range are taken into account.
(55) FIG. 8A shows an exemplary embodiment of an optical system 10 which corresponds to the optical system 10 in FIG. 5; the light guide arrangement is not illustrated in FIG. 8A, but the input coupling region 17 and output coupling region 27 thereof are shown. The deflection device 30 has angled mirrors 38, which are disposed along the circular line segment as described with reference to FIGS. 4 and 5.
(56) It is assumed that the light guide arrangement has an optical waveguide made of polycarbonate with a refractive index n.sub.1=1.5922 at a wavelength of λ.sub.1=530 nm and a refractive index n.sub.2=1.5969 at a wavelength of λ.sub.2=500 nm. Furthermore, the assumption is made that the source image in air has a rectangular field angle spectrum with 48° vertical field (y-direction) and 27° horizontal field (x-direction).
(57) FIG. 8B shows the associated direction cosine diagram of the source field transmission for the optical system 10 in FIG. 8A.
(58) In FIG. 8B, A shows, in the direction cosine space, the rectangular field angle spectrum of the source image, as emanates from the display 12, in air. The input coupling arrangement has a diffraction grating at 45° with respect to the surface normal of the light guide arrangement. Coupling in the light displaces the field angle spectrum into the right upper corner of the direction cosine space as per an arrow 1, with the displaced field angle spectrum being denoted by B. On account of the wavelength-dependence of the diffraction at the diffractive input coupling arrangement, two field angle distributions B.sub.1 and B.sub.2, which are slightly offset from one another, arise for the wavelengths displaced by 30 nm considered here. FIG. 8B shows two inner circles 60.sub.1 and 60.sub.2, the circle 60.sub.1 indicating the critical angle of the total-internal reflection and the circle 60.sub.2 indicating the critical angle of the total-internal reflection minus a tolerance of approximately 5°.
(59) An arrow 2 in FIG. 8B describes the effect of the deflection device 30 with the angled mirrors 38, which brings about a rotation of the field angle spectrum through 90° from state B into state C by virtue of the light beams incident on the deflection device 30 being deflected through 90°. The rotation of the field angle spectrum now yields a horizontal field of 48° and a vertical field of 27° (viewed in air). At the same time, the field angle spectrum is displaced from the right upper corner of the direction cosine space into the left upper corner of the direction cosine space.
(60) In the exemplary embodiment in FIG. 8A, the output coupling arrangement has a diffraction grating that is twisted through 90° with respect to the diffraction grating of the input coupling arrangement. As per an arrow 3, this brings about an output coupling of the light that has propagated in the light guide arrangement and transfers the field angle spectrum from the state C into the center of the direction cosine space, as denoted by D. Since the field angle spectrum in state D is no longer located in the region of total-internal reflection of the light guide arrangement, it is coupled out of the light guide arrangement into the air to the eye of the viewer. The output coupled light has a field angle spectrum with a 27° vertical field and a 48° horizontal field.
(61) As emerges from FIG. 8B, the field angle spectrum originally coupled into the light guide arrangement is only transmitted in part since parts of the field angle spectrum are located outside of the region between the circles 60.sub.1 and 62 in both states D and C. Field angle regions located within the circle 60.sub.1 are output coupled at the wrong position of the light guide arrangement and field angle ranges located outside of the circle 62 are extinguished. As already mentioned above, this problem can be rectified by segmenting the source image into a plurality of partial fields and by transmitting individual partial fields in different light transmission channels of the light guide arrangement, as will still be described below.
(62) FIG. 9A shows a further exemplary embodiment of an optical system 10, the light guide arrangement not being shown but only the input coupling region 17 thereof, which has assigned an input coupling arrangement, and the output coupling region 27, which has assigned an output coupling arrangement, thereof. In this exemplary embodiment, the input coupling and output coupling regions 17, 27 are offset from one another vertically (i.e., in the y-direction) and the deflection device 30 has a tilted arrangement in relation to the deflection device 30 in FIG. 8A.
(63) The same wavelengths of the light are considered like in FIG. 8A.
(64) FIG. 9B shows the associated direction cosine diagram. The field angle spectrum of the source image, which is rectangular once again, was adjusted in relation to the exemplary embodiment in FIGS. 8A and 8B to a 37° vertical field and 21° horizontal field with a tolerance to the critical angle of the total-internal reflection. In FIG. 9B, a circular line 60.sub.2 once again denotes the tolerance to the critical angle of the total-internal reflection, which is represented by the line 60.sub.1.
(65) The field angle spectrum emanating from the source image, which is denoted by A in FIG. 9B, is coupled into the light guide arrangement by the input coupling arrangement, which has an input coupling grating with vertical grating lines (y-direction). As per an arrow 1, this leads to a displacement of the field angle spectrum in the direction cosine space to the right side between lines 60.sub.2 and 62 (state B). As emerges from FIG. 9B, field cropping does not occur in the process.
(66) The deflection device 30 rotates the field angle spectrum through 90° and, at the same time, displaces the latter downward in the direction cosine space as per an arrow 2 (state C). Field cropping does not occur here either.
(67) In the exemplary embodiment, the output coupling arrangement has a diffraction grating with horizontal grating lines that is twisted through 90° with respect to the diffraction grating of the input coupling arrangement. The latter displaces the horizontally located field angle spectrum (state C) into the center of the direction cosine space (state D).
(68) The field angle spectrum with 21° vertical field and 37° horizontal field now is no longer located within the total-internal reflection region and coupled out of the light guide arrangement 14.
(69) The original field angle spectrum emanating from the source image is transmitted in its entirety in this exemplary embodiment.
(70) FIG. 10A shows an exemplary embodiment of an optical system 10 for transmitting a source image, the light guide arrangement 14 of which has two transmission channels 15a and 15b, which are disposed above one another in the vertical direction (y-direction). Therefore, in the following, the light transmission channel 50a is also referred to as upper light transmission channel and the light transmission channel 50b is referred to as lower light transmission channel. In accordance with the number of light transmission channels, two input coupling regions 17a, 17b with the associated input coupling arrangements and two output coupling regions 27a, 27b with the associated output coupling arrangements are present.
(71) For the light transmission channels 15a and 15b, the light guide arrangement 14 has a deflection device 30a and 30b, respectively, in each case, which both have a plurality of angled mirrors 38a and 38. The deflection devices 30a and 30b are disposed at the upper and lower edge of the light guide arrangement. The light guide arrangement 14 can have a single optical waveguide, in which both the light transmission channels are realized.
(72) FIG. 10B shows the direction cosine diagram for the upper transmission channel 15a and FIG. 10C shows the direction cosine diagram for the lower light transmission channel 15b.
(73) The rectangular field angle spectrum emanating from the source image is divided into two partial fields, one of which is coupled into the light guide arrangement 14 via the input coupling arrangement 18a and the other partial field is input coupled via the input coupling arrangement 18b.
(74) In FIG. 10B and FIG. 10C, A denotes the respective portion of the field angle spectrum before coupling into the light guide arrangement 14. B denotes the respective rectangular field angle spectrum, i.e., the respective portion of the field angle spectrum, after refraction into the light guide arrangement 14, within the scope of which the light beams are refracted toward the surface normal and the extent of the field angle spectrum is reduced in the direction cosine space.
(75) An arrow 1 shows a transfer of the respective portion of the field angle spectrum into the state C, this transfer being implemented by input coupling of the respective portion of the field angle spectrum at the input coupling arrangements 18a and 18b. Here, the input coupling arrangements 18a and 18b each have grating lines rotated through 30° in relation to the horizontal. The input coupling arrangements 18a and 18b convert the respective field angle spectrum to the outside into the region of total-internal reflection in the light guide arrangement, with field cropping occurring in both light channels in this case. The respective deflection device 30a or 30b rotates the respective portion of the field angle spectrum through 60° and displaces the latter such that the field angle spectrum transitions to state D as per arrow 2. The output coupling arrangements 26a and 26b, which each have a diffraction grating with vertical grating lines, displace the respective portion of the field angle spectrum as per arrow 3 into the state E in the center of the direction cosine space. Consequently, one part of the entire transmitted field is respectively transmitted in the two light transmission channels 15a and 15b, with these two parts emerging without an edge to form an overall field or overall field angle spectrum after being decoupled from the light guide arrangement. This overall field is formed by the overall area of the two rectangles at E.
(76) In the exemplary embodiment as per FIGS. 10A to 10C, the assumption is made that the two partial fields of the source image are sharply adjacent to one another when they are coupled out of the light guide arrangement 14. This means that the output coupling regions of the light guide arrangement 14 as per the output coupling arrangements 18a and 18b are sharply adjacent to one another. So that the entire visual field can be perceived without loss of brightness or information even in the case of a lateral displacement of the eye 28 of the viewer for example, an overlap of the image information in the individual light transmission channels 15a and 15b is advantageous.
(77) To this end, FIGS. 11A and 11B show two direction cosine diagrams of an exemplary embodiment that has been slightly modified in relation to the exemplary embodiment of FIGS. 10A to 10C. In this exemplary embodiment, an overlap region of, e.g., 10° is realized between the transmitted portions of the field angle spectrum. This can be realized by a different grating period of the gratings (input coupling grating and/or coupling grating) for the upper light transmission channel 15a and the lower light transmission channel 15b. The overlap region of the two partial fields in the state E decoupled from the light guide arrangement 14 is denoted by E.sub.1 and E.sub.2 in FIGS. 11A and 11B, respectively.
(78) FIGS. 12A and 12B show a further exemplary embodiment of an optical system 10 for transmitting a source image, which is once again provided by a display 12. The light emanating from the source image is coupled into a light guide arrangement 14 by way of an optical unit 19, for example a collimation optical unit. The light guide arrangement 14 has a deflection device 30, which is embodied as a 2-dimensional retroreflector and which is located at a lateral edge 48 of the light guide arrangement 14. Here, the lateral edge 48 can be the nasal edge of the light guide arrangement 14. The deflection device 30 once again causes focusing of the light beams incident thereon in divergent fashion, here with two marginal rays 32 and 34 of the light propagating in the light guide arrangement 14 being shown, said marginal rays representing the envelope or the light pipe of the beam path in the light guide arrangement 14.
(79) In this exemplary embodiment, the input coupling is implemented in the temporal edge region of the light guide arrangement 14. The field angle spectrum emanating from the source image is input coupled in the input coupling region of the input coupling arrangement 18, which may have a diffraction grating with horizontal grating lines, in such a way that a central ray 78 of the field angle spectrum extends horizontally in the direction of the deflection device 30. The deflection device 30 casts the angle spectrum in the xy-plane back on itself, as indicated by a double-headed arrow 80. From the deflection device 30, the light 20 with the entire field angle spectrum is directed to the output coupling arrangement 26, which cancels the effect of the input coupling arrangement 18 so that light with the field angle spectrum leaves the light guide arrangement 14 in the direction of the eye of the viewer, as elucidated by arrows 82.
(80) Within the scope of input coupling, different relative pupil positions can be chosen within or outside of the light guide arrangement 14. FIG. 12A shows a variant in which the pupil of the input coupling arrangement 18 is located in the light guide arrangement 14, as elucidated here by a point of intersection 84 of the two lines of the input coupling ellipse 86. This pupil would be imaged in itself again by way of the retroreflector of the deflection device 30 at the nasal edge 48 of the light guide arrangement 14. However, the light beam returning from the retroreflector is steered out of the light guide arrangement 14 by the output coupling arrangement 26. The image of the input coupling pupil then forms the eyebox.
(81) In this exemplary embodiment, the distance between the light guide arrangement 14 and eyebox can easily be set by varying the relative lateral position (x-direction) of the input coupling arrangement 18 or by the distance between the input coupling pupil (point of intersection 84) and the output coupling arrangement 26.
(82) FIG. 13 shows a further exemplary embodiment of an optical system 10, which is a development of the exemplary embodiment shown in FIGS. 10A to 10C. The optical system 10 for transmitting a source image as per FIG. 13A likewise has two light transmission channels 15a and 15b in the light guide arrangement 14 and a respective deflection device 30a or 30b, each with angled mirrors 38a or 38b, for each light transmission channel 15a and 15b. In accordance with the number of light transmission channels, two input coupling regions 17a, 17b with the associated input coupling arrangements and two output coupling regions 27a, 27b with the associated output coupling arrangements are present.
(83) In contrast to the exemplary embodiment in FIG. 10A, the two deflection devices 30a and 30b are not disposed at the upper and lower edge of the light guide arrangement 14, but instead at the temporal edge 46 of the light guide arrangement 14.
(84) The exemplary embodiment as per FIG. 13 can also be constructed with a single light transmission channel 15 and a retroreflector as a deflection device 30, similar to the exemplary embodiment in FIGS. 12A and 12B, with the retroreflector in this case being situated at the temporal edge 46 of the light guide arrangement 14. A further embodiment variant can combine a deflection device 38a and 38b at the temporal and nasal edge of the light guide arrangement 14 in order thus to span a larger field by combining the two light paths 15a and 15b.
(85) Instead of being straight, the light guide arrangement 14 could also be curved, corresponding to a curvature as is usually present in the case of spectacle lenses.
(86) According to further exemplary embodiments, the deflection device 30 can have one or more holographic-optical elements, in particular holographic mirrors, in particular volume holograms. By way of example, a multiplexed (i.e., multiply exposed) volume hologram can be designed in such a way that it acts like a mirror for a defined angular or spectral range. It is also possible to generate holographic mirror surfaces that are perpendicular in the light guide arrangement 14, i.e., the normal of the mirror is perpendicular to the normal of the light guide arrangement 14. The holographic mirror surfaces are almost completely transparent to the angular and spectral ranges for which they are not designed. Consequently, such elements can also be positioned in the viewing region (region through which the case is directed) of the light guide arrangement 14 without being perceived by the user. Volume holograms consequently allow deflection devices for optical systems for transmitting source images to be realized in a very flexible fashion. By way of example, the distance of the deflection device from the output coupling and input coupling elements 26 and 18 (FIGS. 1A, 1B) can be flexibly varied.
(87) The above-described angled mirrors 38 could also be embodied as holographic mirrors.
(88) On account of the great angle selectivity of the volume holograms, it is also possible to avoid more than two reflections occurring in one angled mirror since the hologram for the first mirror surface of the angled mirror is almost completely transparent to light rays that have already been deflected twice.
(89) While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiments. It will be readily apparent to those of ordinary skill in the art that many modifications and equivalent arrangements can be made thereof without departing from the spirit and scope of the present disclosure, such scope to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products. Moreover, features or aspects of various example embodiments may be mixed and matched (even if such combination is not explicitly described herein) without departing from the scope of the invention.
