Patent Application
20250035930
This disclosure concerns display devices. In particular, this disclosure concerns waveguide-based display structures, display devices comprising such display structures, and vehicles comprising such display devices.
Generally, a small form factor is essential for various portable displays and for vehicular displays. Displays with reduced form factors may be realized by utilization of waveguide-based structures for guiding light from the optical engines of such displays towards the users' eye (s).
Since the images produced by typical optical engines are relatively small, exit-pupil-expansion methods based on pupil replication are commonly used to increase the sizes of output images in conventional waveguide-based displays. In conventional exit-pupil-expansion methods, a light beam is coupled into a waveguide such that it propagates towards a first direction through an exit pupil expansion structure, e.g., a diffraction grating or a succession of beam splitters, and the exit pupil expansion structure forms a plurality of light beams propagating towards a second direction perpendicular to the first direction. Light from such plurality of light beams is then coupled out of the waveguide to form an output image.
Although such conventional methods have been successfully utilized for generation of various portable and vehicular displays, the optical losses caused by typical exit pupil expansion structures may be excessively high. Such losses may to some extent be reduced by increasing the efficiency at which an exit pupil expansion structure reflects or diffracts in-coupled light. However, simply increasing the efficiency of an exit pupil expansion structure may result in brightness non-uniformities in an output image.
In light of this, it may be desirable to develop new solutions related to display devices.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
According to a first aspect, a display structure is provided. The display structure comprises a waveguide; an in-coupling structure configured to couple a set of input beams into the waveguide as a set of in-coupled beams associated with a set of in-coupled k-vectors defining a first domain in k-space in an annular guided propagation domain associated with the waveguide; and a diffractive exit pupil expansion structure configured to receive the set of in-coupled beams and to diffract the set of in-coupled beams to form a first set of guided beams and a second set of guided beams associated with a first set of k-vectors and a second set of k-vectors, respectively, lying in the first domain and in a second domain disjoint with the first domain, respectively. The display structure further comprises a diffractive out-coupling structure configured to receive from the exit pupil expansion structure a first diffracted set of beams and a second diffracted set of beams associated with a first diffracted set of k-vectors and a second diffracted set of k-vectors, respectively, lying in the first domain and the second domain, respectively, and the out-coupling structure is configured to couple light from the first diffracted set of beams and light from the second diffracted set of beams out of the waveguide.
According to a second aspect, a display device comprising a display structure in accordance with the first aspect is provided.
According to a third aspect, a vehicle comprising a vehicular display device in accordance with the second aspect is provided.
The present disclosure will be better understood from the following detailed description read in light of the accompanying drawings, wherein:
Unless specifically stated to the contrary, any drawing of the aforementioned drawings may be not drawn to scale such that any element in said drawing may be drawn with inaccurate proportions with respect to other elements in said drawing in order to emphasize certain structural aspects of the embodiment of said drawing.
Moreover, corresponding elements in the embodiments of any two drawings of the aforementioned drawings may be disproportionate to each other in said two drawings in order to emphasize certain structural aspects of the embodiments of said two drawings.
Concerning display structures and display devices discussed in this detailed description, the following shall be noted.
In this specification, a “display device” may refer to an operable output device, e.g., electronic device, for visual presentation of images and/or data. A display device may generally comprise any part(s) or element(s) necessary or beneficial for visual presentation of images and/or data, for example, a power unit; an optical engine; a combiner optics unit, such as a waveguide-based combiner optics unit; an eye tracking unit; a head tracking unit; a gesture sensing unit; and/or a depth mapping unit. A display device may or may not be implemented as a see-through display device and/or as a portable display device and/or a vehicular display device.
Herein, a “see-through display device” or “transparent display device” may refer to a display device allowing its user to see the images and/or data shown on the display device as well as to see through the display device.
Herein, a “portable display device” may refer to a display device configured to be easily transportable and/or configured to be carried and/or worn.
Further, a “vehicular display device” may refer to a display device configured for use in a vehicle, for example, while operating said vehicle. Additionally or alternatively, a vehicular display device may refer to a display device configured to present images and/or data associated with a vehicle and/or operation thereof. Generally, a vehicular display device may or may not be implemented as a vehicle-mounted display device fixed to a vehicle.
Throughout this disclosure, a “display structure” may refer to at least part of an operable display device. Additionally of alternatively, a display structure may refer to a structure suitable for use in a display device.
Throughout this specification, a “k-vector”, or “wave vector” may refer to a vector in k-space. Additionally or alternatively, a k-vector may represent an optical beam, i.e., a ray of light, with a specific propagation direction. Generally, a k-vector associated with an optical beam propagating in a medium may have a magnitude defined by an (angular) wavenumber defined as k=nλo/2π, wherein n is the refractive index of the medium and λ0 is the wavelength of the optical beam in vacuum. As is evident based on the equation above, optical beams with shorter wavelengths have k-vectors with higher magnitudes. Additionally, a k-vector may point in the propagation direction of the optical beam that it represents. In light of the above, a k-vector (k) may be defined as k=k{circumflex over (v)}, wherein k is the wavenumber of the optical beam and {circumflex over (v)} is a unit vector pointing in the propagation direction of the optical beam.
Herein, “k-space”, or “angular space”, may refer to a framework, wherein spatial frequency space analysis is used to relate k-vectors to geometrical points. Additionally or alternatively, k-space may refer to a two-dimensional projected space associated with a waveguide. In k-space, any diffraction event occurring while light propagates in a waveguide can be represented as a translation. Using the k-space formalism, the operation of a display structure may be described by the manner in which said display structure causes a set of input k-vectors to move in k-space.
Generally, in an unbounded homogeneous medium, all propagation directions are permitted, and the magnitudes of all k-vectors of a given wavelength are the same. As such, permitted k-vectors of a given wavelength in an unbounded homogeneous medium define a hollow sphere in k-space with a radius defined by the common wavenumber of the k-vectors. Since the common wavenumber of the k-vectors is proportional to the refractive index of the medium, the radius of the hollow sphere is also proportional to the refractive index of the medium.
However, in a homogeneous waveguide extending along a plane, permitted k-vectors of a given wavelength are commonly represented by a solid disk with a radius defined by the common wavenumber of the k-vectors. Such representation may be viewed as a projection of the previously described hollow sphere onto a plane in k-space corresponding to the plane along which the waveguide extends. Every point within the boundary of the solid disk corresponds to two permitted k-vectors having components perpendicular to the plane opposite to one another. For example, in case of a homogeneous waveguide extending along the x-y plane, the out-of-plane component of kz of a k-vector with a wavenumber k is given by
wherein kx and ky are the magnitudes of the x- and y-components of the k-vector, respectively. Similarly to the case in unbounded homogeneous medium, the radius of the solid disk is proportional to the refractive index of the waveguide.
Typically, not all k-vectors permitted in a waveguide are guided in the waveguide. A waveguide is commonly surrounded by a medium having a refractive index less than that of the waveguide. Generally, a separate solid disk may be defined to represent permitted k-vectors in such medium. Since the refractive index of the surrounding medium is less than that of the waveguide, the solid disk associated with the surrounding medium has a radius less than that of the solid disk associated with the waveguide.
In general, an annular domain in k-space defined by the relative complement of such smaller solid disk in such larger solid disk, i.e., the difference of the larger solid disk and the smaller solid disk, may be referred to as a “guided propagation domain” associated with a waveguide. All k-vectors with in-plane components lying within such guided propagation domain of a waveguide may propagate in said waveguide in guided manner.
As stated above, the smaller solid disk represents permitted k-vectors in a medium surrounding a waveguide. Since light to be coupled into or out of a waveguide must be able to propagate in such surrounding medium, only k-vectors with in-plane components lying within such smaller solid disk may be coupled into or out of a waveguide. Consequently, the smaller solid disk representing permitted k-vectors in a medium surrounding a waveguide may be referred to as a “coupling domain” associated with said waveguide.
In light of the above, k-vectors permitted in a waveguide can be depicted in k-space using a two-dimensional k-vector diagram. Herein, a “k-vector diagram” may refer to a depiction of k-space, wherein guided propagation angles for optical beams propagating in a waveguide are represented by an annular guided propagation domain associated with said waveguide. Additionally or alternatively, a k-vector diagram may refer to a depiction of k-space, wherein non-guided propagation angles of optical beams propagating in a waveguide are represented by a coupling domain associated with said waveguide.
Generally, the outer radius of a guided propagation domain may be inversely proportional to wavelength of light such that light of lower wavelength may be associated with a wider guided propagation domain. Although the width of a guided propagation domain may influence the range of k-vectors that may be guided in a waveguide, a non-dispersive waveguide may still not be generally able to support a wider field of view with lower wavelengths. This may be due to the angular extent of a field of view being inversely proportional to wavelength. In light of this, k-vector diagrams are typically normalized such that a solid disk associated with propagation in vacuum is depicted with unity radius, i.e., the plots are normalized by dividing each k-vector by its wavenumber in vacuum (ko), i.e., by k0=λo/2n.
In the embodiment of
In this disclosure, a “waveguide” may refer to an optical waveguide. Additionally or alternatively, a waveguide may refer to a two-dimensional waveguide, wherein light may be confined along a thickness direction of said waveguide. Additionally or alternatively, a waveguide may refer to a two-dimensional waveguide, wherein light may be confined between opposite faces of said waveguide by total internal reflection.
In the embodiment of
Throughout this disclosure, an “in-coupling structure” may refer to a structure configured to couple a set of input beams into a waveguide for guided propagation therein. Generally, an in-coupling structure may comprise, for example, one or more diffractive optical elements, such as diffraction gratings; and/or one or more reflective optical elements, such as mirrors; and/or one or more refractive optical elements, such as prisms.
In the embodiment of
The waveguide 1100 may be surrounded by air with a refractive index of approximately 1 throughout the visible spectrum. Consequently, light may be guided within the waveguide 1100 between opposite air-glass interfaces. In other embodiments, light may be guided within a waveguide between any suitable interfaces, for example, air-glass interfaces.
As schematically depicted in
Herein, a “set of input beams” may refer to a set of optical beams directed to an in-coupling structure and corresponding to an input image. Additionally or alternatively, a set of input beams may refer to a set of optical beams propagating towards an in-coupling structure of a display structure from a solid angle defining a field of view of said display structure. Additionally of alternatively, a set of input beams may refer to a set of optical beams associated with a set of input k-vectors lying in a coupling domain associated with a waveguide.
Further, a “set of in-coupled beams” may refer to a set of optical beams coupled into a waveguide by an in-coupling structure. Additionally or alternatively, a set of in-coupled beams may refer to a set of optical beams corresponding to an image and propagating in guided manner within a waveguide. Additionally of alternatively, a set of in-coupled beams may refer to a set of optical beams associated with a set of in-coupled k-vectors lying in a guided propagation domain associated with a waveguide.
Additionally of alternatively, a set of in-coupled beams and/or a set of input beams may correspond to a field of view of an image. The image may comprise, for example, an image to be displayed to a user.
The set of input beams 1020 and the set of in-coupled beams 1021 of the embodiment of
In the plurality of k-vector diagrams 3000 of
As is evident based on
In the embodiment of
Herein, a “first domain” may refer to a domain in k-space situated within a guided propagation domain associated with a waveguide. Additionally or alternatively, a first domain may refer to a domain in k-space defined by a set of in-coupled k-vectors coupled into a waveguide by an in-coupling structure. Herein, “a domain in k-space defined by a set of in-coupled k-vectors” may refer to a smallest non-empty connected open set within a guided propagation domain associated with a waveguide comprising each of the points representing said set of in-coupled k-vectors.
In the embodiment of
In this specification, a structure being “diffractive” may refer to said structure comprising a diffractive optical element. Herein, a “diffractive optical element”, may refer to an optical element the operation of which is based on diffraction of light. Generally, a diffractive optical element may comprise structural features with at least one dimension of the order of the wavelengths of visible light, for example, at least one dimension less than one micrometer. Typical examples of diffractive optical elements include diffraction gratings, e.g., one- and two-dimensional diffraction gratings, which may be implemented as single-region diffraction gratings or as multi-region diffraction gratings. Diffraction gratings may generally be implemented, at least, as surface relief diffraction gratings or volume holographic diffraction gratings, and they may be configured to function as transmission- and/or reflection-type diffraction gratings.
Further, “exit pupil expansion”, or “EPE, may refer to a process of distributing light within a waveguide in a controlled manner so as to expand the portion of said waveguide wherefrom out-coupling of light occurs. Generally, exit pupil expansion may be accomplished in waveguide-based display structure using so-called “pupil replication” schemes, wherein a plurality of exit sub-pupils are formed in an imaging system. Consequently, an “exit pupil expansion structure” may refer to a structure suitable or configured for exit pupil expansion, for example, by pupil replication.
As schematically depicted in
When the set of in-coupled beams and/or the set of input beams correspond to a field of view of an image, the first set of guided beams 1031 and the second set of guided beams 1032 may also correspond to the field of view of the image. Thus, the exit pupil expansion structure 1300 can produce copies of the whole field of view of the image. Thus, the first set of guided beams 1031 and the second set of guided beams 1032 may comprise a copy of the whole field of view of the image.
In the embodiment of
The first domain 2310 and the second domain 2320 of the embodiment of
The display structure 1000 of the embodiment of
In this disclosure, an “out-coupling structure” may refer to a structure configured to couple light out of a waveguide.
As schematically depicted in
Throughout this specification, a “first diffracted set of beams” and a “second diffracted set of beams” may refer to sets of beams to be received by an out-coupling structure from an exit pupil expansion structure, wherein said first diffracted set of beams and said second diffracted set of beams may be associated with a first diffracted set of k-vectors lying in a first domain in k-space and second set of k-vectors lying in a second domain disjoint with said first domain, respectively. Additionally, or alternatively, a first diffracted set of beams” may refer to a set of beams comprising light from a set of in-coupled beams and/or light from a secondary set of in-coupled beams coupled into a waveguide by an in-coupling structure.
The first diffracted set of beams 1041 and a second diffracted set of beams 1042 are associated with a first diffracted set of k-vectors 3041 and a second diffracted set of k-vectors 3042, respectively. In the plurality of k-vector diagrams 3000 of
In the embodiment of
In the plurality of k-vector diagrams 3000 of
In the embodiment of
In the normalized k-vector diagram 2000 of
Herein, a “grating k-vector” may refer to a vector in k-space representing the effect of a diffractive optical element on the propagation direction of an optical beam represented by a k-vector. Additionally or alternatively, a grating k-vector associated with a diffractive optical element may refer to a vector in k-space that may be added to an in-plane component of a k-vector associated with an optical beam in order to represent the effect of said diffractive optical element on the propagation of said optical beam.
Generally, diffractive optical elements may be utilized for coupling optical beams into and/or out of a waveguide and/or for altering the propagation direction of said optical beams within said waveguide. The magnitudes and directions of a grating k-vector representing the effect of a diffractive optical element are determined by the properties of said diffractive optical element. In particular, a fundamental grating vector may be associated with each periodicity direction of a diffractive optical element, the direction and magnitude of each fundamental grating vector being determined by the direction and pitch of said diffractive optical element in its associated periodicity direction. Higher order grating vectors of a diffractive optical element may then be expressed as integer linear combinations of the fundamental grating vectors of a diffractive optical element. For example, assuming that a diffractive optical element has a first periodicity in a first direction and a second periodicity in a second direction, a first fundamental grating vector G1 and a second fundamental grating vector G2 may be associated with the first direction and the second direction, and higher order grating vectors, such as G1+G2, G1−G2, −2G1, and 3G2, may be defined based on the fundamental grating vectors.
Throughout this specification, “Nth-order diffraction”, e.g., first-order diffraction or second-order diffraction, may refer to positive Nth-order diffraction and/or negative Nth-order diffraction. Additionally or alternatively, a structure being configured to “diffract a set of beams by Nth-order diffraction” may refer to said structure being configured to diffract said set of beams in a manner representable by a grating k-vector ±NGf, wherein Gf is a fundamental grating k-vector of a diffractive optical element of said structure.
In other embodiments, an exit pupil expansion structure may or may not be configured to diffract a set of in-coupled beams by zeroth-order and first-order diffractions to form a first set of guided beams and a second set of guided beams. For example, in some embodiments, an exit pupil expansion structure may be configured to diffract a set of in-coupled beams by zeroth-order diffraction to form a first set of guided beams and by second-order diffraction to form a second set of guided beams. In such embodiments, said exit pupil expansion structure may be configured to diffract said set of in-coupled beams by first-order diffraction to form a third set of guided beams associated with a third set of k-vectors lying in a third domain disjoint with each of a first domain and a second domain. In some such embodiments, an out-coupling structure may be configured to receive from said exit pupil expansion structure a third diffracted set of beams associated with a third diffracted set of k-vectors lying in said third domain and to couple light from light from said third diffracted set of beams out of a waveguide.
As schematically depicted in
In the embodiment of
In other embodiments, an exit pupil expansion structure may or may not comprise a one-dimensional exit pupil expansion grating. For example, in some embodiments, an exit pupil expansion structure may comprise a two-dimensional diffractive exit pupil expansion element. In some such embodiments, said exit pupil expansion element may have a primary periodicity along a primary direction for diffracting a set of in-coupled beams to form a first set of guided beams and a second set of guided beams and a secondary periodicity along a secondary direction different to the primary direction. In some such embodiments, said secondary periodicity may be defined by a pitch preventing diffraction of light received by said exit pupil expansion structure along said secondary direction.
In the embodiment of
Herein, a domain in k-space situated within a guided propagation domain associated with a waveguide “defining a light guiding direction” may refer to said waveguide extending laterally along a plane and said domain comprising a characteristic point, e.g., centroid of said domain, defining said light guiding direction along said plane.
As schematically depicted in
The first additional set of beams 1043 and a second additional set of beams 1044 are associated with a first additional set of k-vectors 3043 and a second additional set of k-vectors 3044, respectively. In the plurality of k-vector diagrams 3000 of
Generally, an out-coupling structure being configured to diffract a first diffracted set of beams and/or a second diffracted set of beams to form a first additional set of beams and/or a second additional set of beams, respectively, associated with a first additional set of k-vectors and/or a second additional set of k-vectors, respectively, lying in a second domain and/or a first domain, respectively, may facilitate reducing spatial image brightness variations throughout an out-coupling structure. In other embodiments, an out-coupling structure may or may not be configured in such manner.
In the embodiment of
Generally, out-coupling structure comprising a two-dimensional out-coupling grating having a first periodicity for coupling light from a first diffracted set of beams out of a waveguide, a second periodicity for coupling light from a second diffracted set of beams out of said waveguide, and a third periodicity for forming a first additional set of beams and/or a second additional set of beams may enable forming an out-coupling structure with single-sided fabrication methods.
In other embodiments, an out-coupling structure may or may not comprise such a two-dimensional out-coupling grating. For example, in some embodiments, wherein an out-coupling structure is configured to diffract a first diffracted set of beams and/or a second diffracted set of beams to form a first additional set of beams and/or a second additional set of beams, respectively, said out-coupling structure may comprise at least two mutually at least partly laterally overlapping diffractive optical elements for coupling light from both a first diffracted set of beams and from a second diffracted set of beams out of a waveguide and for forming a first additional set of beams and/or a second additional set of beams.
In the normalized k-vector diagram 2000 of
Further, in the normalized k-vector diagram 2000 of
As indicated schematically in
In other embodiments, an in-coupling structure may or may not be configured to couple a set of input beams into a waveguide such that light from a set of in-coupled beams is guided to an out-coupling structure without being subjected to non-zeroth-order diffractions. For example, in some embodiments, an in-coupling structure may be configured to couple a set of input beams into a waveguide such that light from a set of in-coupled beams, which is guided solely by non-zeroth-order diffractions, is guided past an exit pupil expansion structure. Such arrangement may generally facilitate reducing spatial image brightness variations throughout an out-coupling structure.
As indicated in
The secondary set of in-coupled beams 1022 of the embodiment of
In other embodiments, an in-coupling structure may or may not be configured to couple a set of input beams into a waveguide as a secondary set of in-coupled beams associated with a secondary set of in-coupled k-vectors lying in a second domain.
Generally, a display structure and/or any part(s) thereof may or may not be configured to control propagation of light from a secondary set of in-coupled beams in manners corresponding with manners in which propagation of light from a set of in-coupled beams is controlled.
For example, as shown schematically in
The first secondary set of guided beams 1033 and the second secondary set of guided beams 1034 may be associated with a first secondary set of k-vectors 3033 and a second secondary set of k-vectors 3034, respectively. In the plurality of k-vector diagrams 3000 of
Generally, a diffractive exit pupil expansion structure being configured to receive a secondary set of in-coupled beams from an in-coupling structure and to diffract said secondary set of in-coupled beams to form a first secondary set of guided beams and a second secondary set of guided beams associated with a first secondary set of k-vectors and a second secondary set of k-vectors, respectively, lying in a first domain and a second domain, respectively, may facilitate reducing spatial image brightness variations throughout an out-coupling structure.
In other embodiments, wherein an in-coupling structure is configured to couple a set of input beams into a waveguide as a secondary set of in-coupled beams associated with a secondary set of in-coupled k-vectors lying in a second domain, an exit pupil expansion structure may or may not be configured to receive said secondary set of in-coupled beams and to diffract said secondary set of in-coupled beams to form a first secondary set of guided beams and a second secondary set of guided beams associated with a first secondary set of k-vectors and a second secondary set of k-vectors, respectively, lying in a first domain and a second domain, respectively.
In the normalized k-vector diagram 2000 of
In the embodiment of
The in-coupling grating 1210 of the embodiment of
In the normalized k-vector diagram 2000 of
In the embodiment of
Any diffractive optical element(s) in the display structure 1000, including the in-coupling grating 1210, the exit pupil expansion grating 1310, and the out-coupling grating 1410, may be formed at least partly using nanoimprint lithography. In other embodiments, any suitable fabrication method(s), for example, nanoimprint lithography and/or electron-beam lithography, may be used.
It is to be understood that the embodiments of the first aspect described above may be used in combination with each other. Several of the embodiments may be combined together to form a further embodiment.
Above, mainly features related to display structures are discussed. In the following, more emphasis will lie on aspects related to display devices. What is said above about the ways of implementation, definitions, details, and advantages applies, mutatis mutandis, to the display devices discussed below. The same applies vice versa.
In the embodiment of
Herein, a “head-mounted display device” may refer to a portable display device configured to be worn on the head, as part of a piece of headgear, and/or on or over the eyes. Generally, a head-mounted display device may or may not be implemented as a see-through display device and/or as a vehicular display device.
In the embodiment of
As shown in
In the embodiment of
The vehicular display device 5100 of the embodiment of
The vehicular display device 5100 of the embodiment of
Herein, a “head-up display device” may refer to a see-through vehicular display device configured to present images and/or data to a steerer, e.g., a driver or a pilot, of a vehicle without requiring said steerer to look away from usual viewpoints thereof. Generally, a head-up display device may or may not be implemented as a vehicle-mounted display device.
In the embodiment of
It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above, instead they may vary within the scope of the claims.
It will be understood that any benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages.
The term “comprising” is used in this specification to mean including the feature(s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts. It will further be understood that reference to ‘an’ item refers to one or more of those items.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20216248 | Dec 2021 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2022/050773 | 11/21/2022 | WO |
