Display arrangement and displaying method

Abstract

A display arrangement (100) is disclosed. Said display arrangement comprises an image source (101) configured to emit light (L1, L2) defining an image, and a transparent waveguide (120) comprising a coupling arrangement (121). The coupling arrangement further comprises a diffractive grating. Furthermore, the image source is positioned so as to transmit the light to the coupling arrangement to couple a first part of the light (L1) into the waveguide, to propagate therein, and then out of it towards a viewing position (101). Likewise, the image source is positioned so as to transmit the light in a direction enabling specular propagation of a second part of the light (L2) towards the viewing position (101). The image is formed at the viewing position by the first and the second parts of the light.

Description

[0001] DISPLAY ARRANGEMENT AND DISPLAYING METHOD

[0002] BACKGROUND

[0003] Transparent displays may be implemented by means of an image source and a waveguide with a coupl ing arrangement , wherein light emitted by the image source is coupled by the coupling arrangement into the waveguide to propagate therein, and then again out of the waveguide towards the viewer of the display . Such display devices may be implemented, for example , as augmented or extended reality glasses or head-up displays HUDs .

[0004] The feasibility of such displays may be affected by the overall efficiency of transferring the image from the image source to the user, the intensity uniformity of the image region, or the white uniformity of the image seen by the user . There is sti ll need in the art for solutions providing improvements in one or more of those aspects .

[0005] SUMMARY

[0006] 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 subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter .

[0007] According to a first aspect , a display arrangement is disclosed, which comprises an image source configured to emit light def ining an image or a part thereof , and a transparent waveguide comprising a coupling arrangement . The image source is positioned so as to transmit the light to the coupling arrangement to couple a first part of the light into the waveguide to propagate therein and then out of it towards a viewing pos ition . The image source is positioned so as to transmit the light in a direction enabling specular propagation of a second part of the light towards the viewing position to form the image or the part thereof at the viewing position by the first and the second parts of the light .

[0008] The light emitted may be transmitted into a light cone .

[0009] The image source may be positioned to transmit the light emitted into a light cone so as to fall on the transparent waveguide in an area of incidence for the coupling of the first part of the light into the waveguide taking place within, and the specular propagation of the second part of the light running via , the area of incidence .

[0010] In an embodiment , the specular propagation comprises specular reflection from the waveguide .

[0011] In an embodiment , the specular propagation comprises specular transmission through the waveguide .

[0012] In an embodiment which may be in accordance with any of the previous embodiments , the coupling arrangement comprises a diffractive grating . In an embodiment which may be in accordance with any of the previous embodiments , the diffractive grating is configured to serve for both coupling the first part of light incident on the coupling arrangement into the waveguide and then coupling it out of the waveguide .

[0013] In an embodiment which may be in accordance with any of the previous embodiments , the diffractive grating is a two-dimensional grating .

[0014] In an embodiment which may be in accordance with any of the previous embodiments , the diffractive grating has a variable fill factor configured to vary in-coupling and / or out-coupling efficiency thereof .

[0015] In an embodiment which may be in accordance with any of the previous embodiments , the image or the part thereof has an image region such as an image area divided into image elements such as pixels , and the display arrangement comprises a display control unit configured to adj ust an intensity of the light emitted by the image source , for example , so as to set the brightnes ses of the pixels or other types of image elements at the viewing position below a predetermined maximum brightness and / or above a predetermined minimum brightness .

[0016] In an embodiment in accordance with the previous embodiment , comprises an input arrangement configured to receive an eye-tracking signal indicative of the point of gaze of a user of the display arrangement , the display control unit being configured to adj ust , for example , by limiting or enhancing, the brightnesses of the pixels or other types of image elements at the viewing position in accordance with the point of gaze .

[0017] In an embodiment , which may be in accordance with any of the previous embodiments , the image source comprises a laser beam scanning (LBS ) proj ector . Other types of optical engines may also be used .

[0018] An embodiment , which may be in accordance with any of the previous embodiments , comprises a plurality of the image sources .

[0019] In an embodiment in accordance with the previous embodiment , each of the plurality of the image sources is configured to emit light to form a partial image region of the image , the partial image region differing from the partial image regions of the other image sources of the plurality of the image sources . In thi s embodiment , one image source is thus configured to emit light defining a part the image .

[0020] In an embodiment , which may be in accordance with any of the two previous embodiments , at least one of the plurality of image sources is positioned such that the specular propagation comprises specular reflection from the waveguide , and at least one of the plurality of image sources is positioned such that the specular propagation comprises specular transmission through the waveguide . According to a second aspect , a display device is disclosed, comprising a display arrangement as defined in any of the previous embodiments , implemented as an augmented reality display or a virtual reality display, such as a near eye display NED, a head-up display HUD, such as a car HUD or an airplane HUD .

[0021] According to a third aspect , a displaying method is disclosed . The displaying method comprises the operations of emitting light defining an image or a part thereof ; coupling a first part of the light into a waveguide to propagate therein and then out of it towards a viewing position ; and guiding a second part of the light by specular propagation towards the viewing position ; thereby forming the image or the part thereof at the viewing position by the first and the second parts of light .

[0022] The light emitted may be transmitted into a light cone .

[0023] The light emitted may be transmitted so as to fall on the transparent waveguide in an area of incidence , the first part of the light being coupled into the waveguide within, and the second part of the light being guided via, the area of incidence .

[0024] In an embodiment , the second part of light is guided by specular reflection .

[0025] In an embodiment , the second part of light is guided by specular transmission through the waveguide . In an embodiment , which may be in accordance with any of the previous embodiments , the first part of light is coupled into and out of the waveguide by a di ffractive grating .

[0026] In an embodiment , the image or the part thereof has an image region such as an image area divided into pixels or other types of image elements , and the emitting the light comprises adj usting an intensity of the light , for example , so as to limit the brightness of the image elements at the viewing position below a predetermined maximum brightness and / or above a predetermined minimum brightness .

[0027] An embodiment , which may be in accordance with the previous embodiment, involves receiving an eye-tracking signal indicative of the point of gaze of a user of the display arrangement , wherein the brightnesses of the image elements are adj usted, for example , by limiting or enhancing, in accordance with the point of gaze .

[0028] In an embodiment , which may be in accordance with any of the previous embodiments , the operation of emitting light comprises emitting a plurality of light beams , light fields , or light cones .

[0029] In an embodiment , which may be in accordance with any of the previous embodiments , each of the light beams , light field, or light cones comprises light to form a partial image region of the image , the partial image region di ffering from the partial image regions of the other l ight beams , light fields , or l ight cones of the plurality of the light beams , light fields , or light cones .

[0030] In an embodiment which may be in accordance with any of the two precedent embodiments , at least for one light beam, light field, or light cone , the operation of guiding a second part of the light by specular propagation towards the viewing position comprises guiding the light by specular reflection, and at least for one light beam, light field, or light cone , the operation of guiding a second part of the light by specular propagation towards the viewing position comprises guiding the light by specular transmission through the waveguide .

[0031] Further embodiments of the above aspects may be implemented within the scope of the claims .

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present disclosure will be better understood from the following detailed description read in view of the accompanying drawings , wherein :

[0034] FIG . 1 shows a display arrangement where part of the light is specularly reflected towards the user .

[0035] FIG . 2 shows a display arrangement where part of the light is specularly transmitted towards the user .

[0036] FIG . 3 shows a display arrangement of a head-up display (HUD) where part of the light is specularly reflected towards the user . FIG . 4 shows a display arrangement with a plural ity of light sources .

[0037] FIG . 5 shows a near-eye display (NED) where an image source and a waveguide are configured to specularly reflect part of the light towards the user .

[0038] FIG . 6 shows a car with a head-up display (HUD) where an image source and a waveguide are configured to specularly reflect part of the light towards the user .

[0039] FIG . 7 shows a flow chart of a displaying method .

[0040] Unless specif ical ly stated to the contrary, any of the aforementioned drawings may be schematic and drawn not 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 emphasi ze certain structural aspects of the embodiment of said drawing .

[0041] Moreover, corresponding elements in the embodiments of any two drawings of the aforementioned drawings may be di sproportionate to each other in said two drawings in order to emphasi ze certain structural aspects of the embodiments of said two drawings .

[0042] DETAILED DESCRIPTION

[0043] It is apparent 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 or hereinafter, instead they may vary within the scope of the claims . The display arrangement 100 in Fig. 1 comprises an image source 110.

[0044] Any of the display arrangements of FIGs. 1 to 4 may form or serve as a part of a display device.

[0045] A display arrangement refers to an arrangement suitable for displaying, by means of light, visual content as an image. An image may contain any graphics, figures, text, and other visually observable content. An image may have an image region which may comprise or be divided into a plurality of image elements, each defining a part of the image. An image may refer to a two-dimensional visual representation. An image may also refer to a three- dimensional visual representation. An image region may therefore refer to an image area extending along a (fictitious) surface or an image volume. Accordingly, an image element may be, for example, a two-dimensional pixel or a three-dimensional voxel. In the example of FIG. 1, the two-dimensional image 102 comprises a picture of a flower, the image area being divided into a two-dimensional array of pixels 103.

[0046] A display arrangement refers to an entity which may form, or serve as, a part of an operable display device. It thus may form, or serve as, a building block for such display device. Then, the complete operable display device may comprise any appropriate further parts, elements, or members. In some embodiments, a display device may substantially entirely be formed of a display arrangement .

[0047] An image source refers to an element or device capable of emitting light which defines an image. Defining an image may refer to defining the entire image area of the image in question, or a part thereof. Thus, the light emitted by one image source may refer to light which defines entirely or partially the image area of the image to be displayed, i.e. an image or at least a part thereof. In the latter case, a display arrangement may comprise image sources each emitting light to form or define a partial image region of the image to be displayed. Examples of this kind of approach are discussed below with reference to FIG. 4.

[0048] Light defining an image may also be referred to as, for example, image-bearing light rays / beams, or imagecarrying light rays / beams. The image source may be or comprise a projector, for example a Laser-Beam Scanning (LBS) projector. An LBS projector may allow for individual pixel or image element brightness adjustments by its inherent capability of modulating the pixels or image elements. Said adjustment may be implemented by adjusting the intensity distribution of the emitted light .

[0049] The display arrangement in Fig. 1 further comprises a transparent waveguide 120. A waveguide, also referred to as a light guide, refers to a structure which may be in the form of a plate, a film or a sheet, in which structure light can propagate by total internal reflections at opposite surfaces of the waveguide structure .

[0050] The light guide comprises a coupling arrangement 121. In the example of FIG. 1, the coupling arrangement lies on a surface of the waveguide at the side of the image source . In other embodiments , a coupling arrangement may lie on a surface at the side oppos ite to an image source . In some embodiments , there may be coupling arrangements on two opposite surfaces of a waveguide . In other embodiments , the coupling arrangement may lie on a surface of a plurality of waveguides arranged as a stack .

[0051] A coupling arrangement refers to an arrangement capable of coupling light between the waveguide and the ambient . The coupling arrangement , illustrated schematically and simplistically in FIG . 1 , comprises a diffractive grating 122 capable of serving for this coupl ing purpose .

[0052] The waveguide and the diffractive grating may be designed for operation at one or more design wavelengths . The design wavelength ( s ) may be selected to lie in the range of visible wavelengths . For example , one or more design wavelengths may l ie in the range of about 350 to 800 nm, for example , in the range of about 380 to 780 nm .

[0053] In some embodiments , a waveguide may form or serve as at least a part of , or be attached to , any appropriate transparent support element , such as a window, a windscreen of a vehicle or an aircraft , a visor of a helmet incorporating a HUD, or a lens of smart glasses . In other embodiments , a waveguide may be embedded between any appropriate transparent support elements . Thereby, display devices may be implemented, for example , as an augmented reality display or a virtual reality display, such as a near eye display NED, a head- up display HUD, such as a car HUD, or an aircraft HUD .

[0054] "Transparent" refers to the waveguide 120 being at least partially transparent for the design wavelength ( s ) in a direction perpendicular to the waveguide base plane . For example , in the case of the design wavelength ( s ) lying in the visible spectrum range, for example , the transparency may enable the waveguide to form a part of a transparent display assembly through which the viewer of the display assembly can see .

[0055] The coupling arrangement lying "on" a surface refers the coupling arrangement lying at or close to that surface . For example , the diffractive grating of the coupling arrangement may be formed as a surface relief structure at a surface of the waveguide . There may be some additional layer ( s ) on such grating, for example , for protective purposes . In some embodiments , a coupling arrangement may be implemented as a buried an embedded structure or arrangement lying within a layer of a material . Then, the coupling arrangement may lie , in the thickness direction of the waveguide , at a distance from an outer surface of the waveguide .

[0056] The purpose of the coupling arrangement is to couple a first part Lx of the light L emitted by the image source 110 into the waveguide 120 , and couple at least a portion of the first part of the light propagated within the waveguide then again out of it towards a viewing position 101 . In the drawing of FIG . 1 , opposite edges Lla, Llbof the first part Lx of the emitted light L are illustrated as propagating in different directions in the waveguide .

[0057] A viewing position refers to an expected or predefined location where a viewer or a user of the display may look at the display to see the displayed content . A viewing position may also be called a viewing point .

[0058] To enable the in-coupling, the image source 110 is positioned such that the light L it emits is transmitted in a direction where the light L can hit the diffractive grating of the coupling arrangement .

[0059] The diffractive grating 122 may serve for both the incoupling and out-coupling purposes . Thus , the coupling arrangement may comprise one single diffractive grating instead of separate in-coupling and out-coupling gratings . In other embodiments , there may be different in-coupling and out-coupling gratings .

[0060] A "single" grating may refer to a grating with a continuous grating area having the same grating vectors throughout the whole area .

[0061] In addition to a diffractive grating, a coupl ing arrangement may comprise any other appropriate elements ( s ) , layer ( s ) , or structure ( s ) contributing to the designed coupling function ( s ) . For example , there may be an anti-reflection coating or film . On the other hand, also refractive and / or reflective interfaces may be used . Advantageously, the image source 110 is secondly positioned such that the light L it emits is transmitted in a direction where a second part L2 thereof may be specularly reflected from the waveguide towards the viewing position .

[0062] Thereby, a first part Lx of the light emitted by the image source 110 is coupled by the coupling arrangement into the waveguide 120 to propagate therein by total internal reflections , and at least part of it is then coupled out of the waveguide towards the viewing position 101 . A second part L2 of the light is specularly reflected from the waveguide 120 towards the viewing position 101 . It is to be noted that although only the opposite edges Lla, Llbof the first part Lx of the emitted light L are illustrated in FIG . 1 , coupling of the first part Lx of the emitted light L into the waveguide may take place at any point of the coupl ing arrangement 121 . Thus , in-coupling may take place , for example , at the location of the specular reflection of the second part L2 of the light .

[0063] Thereby, the first and second parts Lx , L2 of the initially emitted light L do not need to be spatially separated or otherwise predetermined . They may be formed by specific portions or percentages of light emitted into a given direction . Then, for example , at a location where specular reflection, or specular transmission in another embodiment , takes place , part of the light intensity or energy may be coupled into the waveguide whereas another part thereof is specularly reflected from or transmitted through the waveguide . Such overlap or superposition of the first and second parts Ll zL2 of the initially emitted and transmitted light L is illustrated in FIG . 1 in that the image source 110 transmits the l ight L compri sing the first and the second parts Lx , L2 of it into a single light cone 111 .

[0064] A light cone refers to the volume into which the l ight L is transmitted . As illustrated in the example of FIG . 1 , the light cone may be conical , thus having an expanding cross-sectional area . The light field within a cross-section of a light cone may be continuous . On the other hand, in the case of a light source comprising an LBS proj ector, the light field within a cross-section of a light cone may be formed by one or more laser beams scanning through the image area .

[0065] The image source 110 is pos itioned such that the light L transmitted so as to fall on the waveguide 120 within an area of incidence A . In the example of FIG . 1 , the area of incidence A coincides with the proj ection of the light cone 111 on the waveguide 120 .

[0066] Both the in-coupling of the first part Lx of the light and the specular reflection of the second part L2 of the light L takes within the area of incidence A . In embodiments of the specular propagation comprising specular transmission through the waveguide , the specular propagation of the second part of the light may run via the area of incidence .

[0067] The user or viewer looking at the display arrangement from or at the viewing position 101 then sees an image formed by the out-coupled portion of the first part Lx , and the specularly reflected second part L2 , of the light L emitted by the image source . The user or viewer seeing an image may be considered referring to the image being formed on the retina of the user or viewer at the image position .

[0068] The image being formed by the first ad the second parts of the same initially emitted and transmitted light may provide certain advantages . First , the overall efficiency may be improved as a result of a decrease of the coupling losses and propagation losses in the waveguide . Said propagation losses may be caused by, for example , absorption of light into the waveguide material , undesirable diffraction while light propagates within the waveguide , and / or weak desirable diffraction . On the other hand, also the white uniformity may be improved when only a part of the light forming the image seen by the viewer or user of the device has been coupled by a diffractive grating possibly having a non-uniform wavelength response . The efficiency and white uniformity improvement may apply to both the second part of light L2 and the light rays of the first part of light Lx which travel in the vicinity of the path defined by the second part of light L2.

[0069] Additional advantages may include a proj ector si ze reduction compared to systems with only reflection . A smaller si ze may imply lower energy consumption . Travel distance of light inside the waveguide may also be advantageously reduced . That may lead to a higher efficiency and less interference effects , as well as less colour separation . The use of waveguides may be cheaper to manufacture . A smal ler proj ector si ze may also facilitate the implementation of the display arrangement in various applications .

[0070] Besides those advantageous effects , the performance of the display arrangement may be further improved, for example, by controlling the brightness of the pixels of the image area at the viewing position . For example , the specularly propagated second part L2 of the light emitted by the image source may result in a specular highlight , i . e . a locally increased brightness , in the image area . On the other hand, the out-coupled intensity of light may vary along the image area such that , for example , the out-coupled intensity decreases as the distance the light propagates within the waveguide increases . It may therefore be useful , for example , to adj ust the brightnesses of the pixels to limit the brightnesses at the viewing position below a predetermined maximum brightness and / or above a predetermined minimum brightness . Such limiting may be carried out by adj usting the intensity distribution of the light emitted by the image source . Limiting the brightness of pixels as an example of image elements is one example of adj usting the brightnesses . In other embodiments or applications , adj usting the brightnesses of pixels or other types if image elements such as 3D pixels or voxels may comprise enhancing the brightness thereof . In some applications or embodiments , adj usting the brightness of the image elements may comprise adj usting the brightnesses so as to lie between a maximum and a minimum brightness .

[0071] In the example of FIG . 1 , the second part L2 of the light emitted by the image source 110 is reflected specularly by the waveguide . In other embodiments , examples of which are illustrated in FIGs . 2 , 3 and 4 , a second part of the light emitted by an image source and not coupled into a waveguide may be transmitted specularly through the waveguide towards a viewing position . In general , a second part of the light emitted by an image source and not coupled into a waveguide may thus be specularly propagated towards a viewing position .

[0072] Specular propagation may refer to propagation of light occurring substantially without a plurality of successive total internal reflections ( TIR) , absorption, diffusion, scattering, or diffraction . Specular propagation may comprise reflection, transmission, and / or refraction .

[0073] "Towards" a viewing position refers to the out-coupled and / or specularly propagated part of the light emitted by the image source being coupled and / or propagated, respectively, into an optical path leading to the viewing position . The optical path may be a straight path . Alternatively, the optical path may comprise , for example, point ( s ) of reflection and / or refraction where the direction of the propagation of the l ight changes , such that the optical path finally reaches the viewing position .

[0074] The diffractive grating 122 may be a two-dimensional grating . A two-dimensional grating generally refers to a grating structure having periodicity in at least two non-parallel directions . A two-dimensional grating thus has periodically repeating grating features in each of the at least two directions . In a simple case , a two- dimensional grating may comprise two one-dimensionally periodic grating structures overlayed non-parallel to each other . Such construction may also be considered as two separate , although spatially overlapping, grating areas with different grating vectors . In other embodiments , more complex grating structures providing periodicities in at least two non-parallel directions may be used . For example , a two-dimensional grating may comprise repeating unit cells , each unit cell itself comprising a two-dimensional arrangement of a plurality of grating features .

[0075] On the other hand, two-dimensional and one-dimensional gratings can be considered being related to each other in that bas ically, a one-dimensional grating is a two- dimensional grating with some diffraction orders having zero diffraction efficiency . A two-dimensional grating may provide , for example , expansion of the image si ze by spreading the light coupled into the waveguide . Thereby, a two-dimensional grating may serve for exit pupil expansion, i . e . serve as a part of an exit pupil expander .

[0076] In other embodiments , a one-dimensional diffractive grating may be used .

[0077] The display arrangement 100 of FIG . 1 comprises a display control unit 130 for controlling the image source 110 . The di splay control unit may be a separate control unit specifically configured to control the image source . In other embodiments , a display control unit may be a part of a larger control arrangement or system for carrying out also other functions or operations . For example , in a display arrangement forming a part of or serving as a car Head Up Display HUD, a display control unit may be incorporated in or forming a part of a general control unit of the car user interface of vehicle intelligence system .

[0078] A display control unit may comprise , for example , one or more processors connected to a memory containing or including program code instructions or a program code configured to , with the at least one processor, cause the display control unit at least to carry out one or more display control operations or functions . On the other hand, a display control unit may comprise at least one processor and at least one memory storing instructions that , when executed by the at least one processor, cause the display control unit apparatus at least to carry out one or more display control operations or functions .

[0079] Such display control operations or functions may comprise , for example , adj usting an intensity of the light L emitted by the image source 110 to adj ust or limit the brightness of the pixels of the image area of the image ( s ) defined by the light received at the viewing position . Such adj ustment may be carried out, for example , as described above , so as to set the brightnesses of the pixels below a predetermined maximum brightness and / or above a predetermined minimum brightness .

[0080] Alternatively, the image sent to the light source may be recreated to counter the display effect ( s ) . Such recreation may be carried out, for example , by manipulating the image sent to the l ight source from a processor memory .

[0081] In some applications , the image element or image region brightness may be useful to be adj usted or limited in accordance with the direction of the gaze of the user or viewer of the display arrangement or display device . Thereby, it may be ensured, for example , that the brightness of the image elements at the point of gaze , thus at the point on the image region the viewer or user of the display arrangement looks at , does not exceed a predetermined value . The display control unit may thus be configured to adj ust the brightnesses of the image elements in accordance with the point of gaze .

[0082] For the purpose of controlling the brightness on the basis of the point of gaze , the display arrangement of FIG . 1 comprises an input interface 131 for receiving an eye-tracking signal 132 indicative of the point of gaze of a user of the display arrangement . The eyetracking signal may be transmitted to and received by the input interface via a wired or a wireless data or signal transfer path (not illustrated) . The input interface forms at least part of an input arrangement .

[0083] In other embodiments , an input arrangement may comprise any appropriate means , elements , and components enabling an eye-tracking signal to be received via a wired or a wireless data or signal transfer path .

[0084] In some embodiments , an eye-tracking system configured to produce an eye-tracking signal may belong to, be incorporated in, or form a part of , a larger control arrangement or system. For example , such larger control arrangement or system may serve for various control operations or functions of a vehicle such as a car or an aircraft . Such larger control arrangement or system may comprise the display control unit as a part thereof .

[0085] The display arrangement 200 of FIG . 2 distinguishes from that of FIG . 1 in that the image source 210 lies , relative to the viewing position 201 , at the opposite side of the waveguide 220 . A first part of the light emitted by the image is coupled by the coupling arrangement first into the waveguide and thereafter out of it towards the viewing position 201 . The image source is positioned and directed such that a second part L2 of the light emitted by the image source is transmitted specularly through the waveguide and the coupling arrangement thereof towards the viewing position . In the case of the coupling arrangement comprising a diffractive grating, the specularly transmitted second part of the light may correspond to or be formed by the light actually coupled to the zeroth diffraction order .

[0086] The display arrangement 300 of FIG . 3 forms or serves as a part of a display device 30 which may be implemented, for example , as a car HUD . The display arrangement 300 is similar to that of FIG . 2 in that the waveguide 320 is positioned between the image source 310 and the display position 301 , and the second part of light L2 emitted by the image source and not coupled into the waveguide is specularly transmitted through the waveguide 320 . The display arrangement however distinguishes from that of FIG . 2 in that both the out- coupled light and the specularly transmitted first part Lx of the emitted light L propagates first towards a transparent object capable of reflecting the image, for example, a windshield 330, and is reflected therefrom towards the viewing position 301.

[0087] In the examples of FIGs. 1 to 3, the display arrangements 100, 200, 300 are illustrated as having one single image source 110, 210, 310. In other embodiments, a display arrangement may comprise a plurality of image sources. This may advantageously provide multiple specular propagation events, which may multiply the benefits already mentioned for a single specular highlight. One example is illustrated in FIG. 4.

[0088] The display arrangement 400 of FIG. 4 shares aspects with each of the display arrangements of FIGs. 1 to 3. It distinguishes from the display arrangements of FIGs. 1 to 3 in that it comprises a plurality of image sources 410i, 4102, 4103, 4104, 410S.

[0089] Four image sources 410i, 4102, 4103, 4104, lie on the same side of the waveguide 420 as the viewing position 401, thus similarly to the image sources of FIGs. 1 and 2. Each of those image sources is positioned and directed so as to enable a second part L2of the light emitted thereby to be specularly reflected by the waveguide towards the viewing position 401. A first part of light emitted (not illustrated) by each or some of those image sources is coupled into the waveguide 420 to propagate therein, and is then coupled out of the waveguide towards the viewing position 401.

[0090] One image source 4103lies, similarly to the image source of FIG. 3, at the opposite side of the waveguide 420. The light emitted thereby is propagated, except of the reflection from the windshield, similarly to the light emitted by the image source of FIG . 2 . Thus , a second part L2 of the light is transmitted through the waveguide 420 towards the viewing position 401 , whereas a first part of light emitted (not illustrated) by that image source i s coupled by the coupling arrangement 421 into the waveguide 420 to propagate therein . At least a portion of it is then coupled out of the waveguide towards the viewing position 401 .

[0091] A plurality of image sources , each or at least some emitting light to the viewing position both by specular propagation and by in-coupling into and out-coupling out of the waveguide may enable improving even further the efficiency and white uniformity of transferring the image from the image source to the user .

[0092] Each of a plurality of image sources in a display arrangement may be configured to , or controlled to , emit light to define the entire image region of the image to be displayed . Alternatively, different image sources may be configured to or controlled to emit light to def ine a part of the image region of the image to be displayed . Then, the image displayed to the user or viewer of the display arrangement may be composed of partial image regions , each defined by light emitted by one or more of the plurality of image sources . In one embodiment , each of the plurality of the image sources is configured to emit light to form a partial image region of the image , the partial image region differing from the partial image regions of the other image sources of the plurality of the image sources . In the example of FIG . 4 , the plurality of image sources comprises four image sources being located such that the specular propagation comprises specular reflection from the waveguide . For the fifth image source , the specular propagation comprises specular transmission through the waveguide .

[0093] In other embodiments , a plurality of image sources may be distributed with any appropriate numbers of image sources positioned to provide specular reflection and transmission . In some embodiments , all image sources of a plurality of image sources may be positioned at the same side of a waveguide to enable specular propagation comprising specular reflection or specular transmission .

[0094] In the example of FIG . 4 , light from each light source is divided to a first part coupled into the waveguide and a second part propagating specularly . In other embodiments , a display arrangement may comprise at least one light source positioned and directed such that no specular propagation of a second part of the light emitted by that light source towards the viewing position takes place . For such source , there is thus only the first part of the emitted light , i . e . the part coupled into the waveguide for propagating therein by total internal reflections .

[0095] The NED display device 50 of FIG . 5 is implemented as smart glasses . The NED display device comprises an image source 510 which emits light L towards a waveguide 520 in the form of a lens . The waveguide comprises a coupling arrangement 521 which may comprise a diffraction grating 522 . A second part of the light may be specularly reflected from the lens towards a viewing position behind the glasses . A first part of the light is incoupled into the waveguide and thereafter out-coupled from the waveguide towards the viewing position .

[0096] The display device 60 of FIG . 6 is implemented as a car HUD . The HUD display device comprises an image source 510 which emits light L towards a waveguide 620 . The waveguide comprises a coupling arrangement 621 which may comprise a diffraction grating 622 . A second part of the light may be specularly reflected towards a viewing position where a driver of the car may see an image formed by the light emitted by the image source 610 . A first part of the light may be in-coupled into the waveguide and thereafter out-coupled from the waveguide towards the viewing position .

[0097] In the above , aspects of display arrangements and devices are discussed . Below, the focus lies on a method aspect . What is said above concerning the principles , detai ls , and ways of operation of the arrangements and devices apply, mutate mutandis , to the method aspect discussed below . The same applies vice versa . The display arrangements and devices discussed above may operate to carry out methods in accordance with those discussed below . Vice versa, methods discussed below may be carried out by display arrangements and devices in accordance with those discussed above . The displaying method 700 of FIG . 7 may be used for displaying an image for being visible for a user or a viewer . The method 700 compri ses , in an emitting operation 720 , emitting light defining an image to be di splayed . The l ight may be emitted, for example , by a proj ector, such as an LBS proj ector .

[0098] The emitted light is transmitted, in a transmitting operation 730 , towards a viewing position where a user or a viewer may see the image formed by the light . In a coupling sub-operation 731 , a first part of the emitted light is coupled into a waveguide to propagate therein by total internal reflections . Then, after propagation in the waveguide , at least a part of the l ight coupled into the waveguide is again coupled out of it towards a viewing position in sub-operation 732 . In a specular guiding sub-operation 733 , a second part of the emitted light is guided by specular propagation towards the viewing position . Specular propagation may comprise specular reflection or specular transmission .

[0099] All the light emitted may be transmitted into a one single light cone .

[0100] The light emitted comprising the first and the second parts thereof may be transmitted so as to fall on the transparent waveguide in an area of incidence , whereby the first part of the light may be coupled into the waveguide within, and the specularly propagating second part of the light may be guided via, that area of incidence . Guiding the second part of light by specular reflection may comprise , for example , directing the emitted light such that a part of it can be specularly reflected from a surface of the waveguide towards the viewing position .

[0101] The image is formed at the viewing position by at least portions of the first and the second parts of the light initially emitted . Brightness of a point or a sub-region of the image region then depends on the total intensity of light , received at the viewing position, forming that part of the image . The image region such as a two- dimensional image area may be divided into a plural ity of image elements such as pixels such that the intensity of the emitted light for an image element or a group of image elements is adj ustable . Then, the emitting operation 720 may comprise adj usting, in an adj ustment sub-operation 721 , the intensity of the emitted light such that the brightnesses of the image elements of the image region at the viewing position is adj usted, to limit the brightnesses below a predetermined maximum brightness and / or above a predetermined minimum brightness . Thereby, too high and / or too low brightnesses in the image region may be avoided . On the other hand, possible brightness differences between different points or sub-regions of the image regions may be decreased . Additionally, image elements adj usted in accordance a minimum and / or a maximum brightness can be further adj usted to match the original full image , or based on some other algorithm . Such adjustment may thus comprise emitting light to form different parts, sub-regions, or image elements of the image region with different intensities. The displaying method 700 may comprise an eye-tracking operation 710 for receiving an eye-tracking signal indicative of the point of gaze of a user or viewer viewing the image of the display arrangement. Then, possible adjustment sub-operation 721 may comprise a further adjustment controlling sub-operation 722 wherein the intensity of the emitted light and thus the brightnesses of the image elements are adjusted in accordance with the point of gaze. Adjusting the brightness "in accordance" with the point of gaze refers, first, to the adjustment being carried out such that the point of gaze affects the adjustment. In practice, said affecting may comprise, for example, adjusting the emitted intensity such that at the point of gaze, the brightness of the image exceeds a predetermined minimum brightness or remains below a predetermined maximum brightness.

[0102] 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.

[0103] 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.

Claims

CLAIMS1. A display arrangement (100) comprising an image source (110) configured to emit light (L) defining an image (102) , and a transparent waveguide (120) comprising a coupling arrangement (121) , wherein the image source is positioned so as to transmit the light to the coupling arrangement to couple a first part of the light (Lx) into the waveguide to propagate therein and then out of it towards a viewing position (101) , c h a r a c t e r i z e d b y the image source being positioned so as to transmit the light in a direction enabling specular propagation of a second part of the light (L2) towards the viewing position (101) to form the image at the viewing position by the first and the second parts of the light.

2. A display arrangement (100) as defined in claim 1, wherein the light (L) emitted is transmitted into a light cone (111) .

3. A display arrangement (100) as defined in claim 1 or 2, wherein the image source (110) is positioned to transmit the light L emitted so as to fall on the transparent waveguide (120) in an area of incidence (A) for the coupling of the first part of the light (Lx) into the waveguide taking place within, and the specular propagation of the second part of the light (Lx) running via, the area of incidence.

4. A display arrangement (100) as defined in any of claims 1 to 3, wherein the specular propagation comprises specular reflection from the waveguide (120) .

5. A display arrangement (100) as defined in any of claims 1 to 4, wherein the specular propagation comprises specular transmission through the waveguide (220) .

6. A display arrangement (100) as defined in any of claims 1 to 5, wherein the coupling arrangement (121) comprises a diffractive grating.

7. A display arrangement (100) as defined in any of claims 1 to 6, wherein the diffractive grating (122) is configured to serve for both coupling the first part of light (LlzL2) incident on the coupling arrangement (121) into the waveguide (120) and then coupling it out of the waveguide (120) .

8. A display arrangement (100) as defined in any of claims 1 to 7, wherein the diffractive grating is a two- dimensional grating.

9. A display arrangement (100) as defined in any of claims 1 to 8, wherein the image (102) has an image region such as an image area divided into image elements such as pixels (103) , and the display arrangement comprises a display control unit (130) configured to adjust an intensity of the light emitted by the image source, for example, so as to set the brightnesses of the image elements at the viewing position between a predetermined maximum brightness and / or a predetermined minimum brightness.

10. A display arrangement (100) as defined in claim 9, further comprising an input arrangement (131) configured to receive an eye-tracking signal (132) indicative of the point of gaze of a user of the display arrangement, the display control unit (130) being configured to adjust, for example, by limiting or enhancing, the brightnesses of the image elements in accordance with the point of gaze.

11. A display arrangement (100) as defined in any of claims 1 to 10, wherein the image source comprises a laser beam scanning (LBS) projector.

12. A display arrangement (400) as defined in any of claims 1 to 11, comprising a plurality of the image sources (410i - 4105) .

13. A display arrangement (400) as defined in claim 12, wherein each of the plurality of the image sources (410i - 410s) is configured to emit light to form a partial image region of the image, the partial image region differing from the partial image regions of the other image sources of the plurality of the image sources.

14. A display arrangement (400) as defined in claims 12 and 13, wherein at least one of the plurality of image sources (410i - 4IO4) is positioned such that the specular propagation comprises specular reflection from the waveguide (420) , and at least one of the plurality of image sources (410s) is positioned such that the specular propagation comprises specular transmission through the waveguide (420) .

15. A display device comprising a display arrangement as defined in any of claims 1 to 14, implemented as an augmented reality display or a virtual reality display, such as a near eye display NED (50) , a head-up display HUD, such as a car HUD (60) or an aircraft HUD.

16. A displaying method (700) , comprising the operations of : emitting light defining an image (720) ; coupling a first part of the light into a waveguide to propagate therein and then out of it towards a viewing position (731, 732) ; c h a r a c t e r i z e d by guiding a second part of the light by specular propagation towards the viewing position (733) ; thereby forming the image at the viewing position by the first and the second parts of light.

17. A method as defined in claim 16, wherein the light emitted is transmitted into a light cone.

18. A method as defined in any of claims 16 or 17, wherein the light emitted is transmitted so as to fall on the transparent waveguide in an area of incidence, the first part of the light being coupled into the waveguide within, and the second part of the light being guided via, the area of incidence.

19. A method (700) as defined in any of claims 16 to 18, wherein the image has an image region such as an image area divided into image elements such as pixels, and theemitting the light (720) comprises adjusting an intensity of the light, for example, so as to set the brightness of the image elements at the viewing position below a predetermined maximum brightness and / or above a predetermined minimum brightness (721) .

20. A method (700) as defined in claim 19, comprising receiving an eye-tracking signal indicative of the point of gaze of a user of the display arrangement (710) , wherein the brightnesses of the image elements are adjusted (721) , for example, by limiting or enhancing in accordance with the point of gaze (722) .

Images