The present invention relates to displaying virtual images by using a micro-display, imaging optics, and a diffractive beam expander.
Display modules are used in portable devices to display information in graphical form. Small size is an important aspect in portable devices. However, the small size of a portable device also sets a limitation to the size of a display module incorporated in said device. A typical drawback of a conventional small display is that an observer can examine only a small portion of a large displayed image at a glance, while preserving adequate resolution.
An approach to display a large image by using a small display module is to use a near-eye display. A near-eye display based on a diffractive beam expander is disclosed e.g. in a patent application EP0535402
The object of the present invention is to provide a display device.
According to a first aspect of the invention, there is provided a display device according to claim 1.
According to a second aspect of the invention, there is provided a method for displaying images according to claim 15.
According to a third aspect of the invention, there is provided a display means according to claim 18.
According to a fourth aspect of the invention, there is provided a connectable diffractive beam expander according to claim 20.
According to a fifth aspect of the invention, there is provided a connectable optical component according to claim 23.
According to a sixth aspect of the invention, there is provided a connectable micro display according to claim 24.
The display device may be adapted to display a virtual image through a viewing aperture and to project a real image on an external screen. Said virtual image and said real image may be displayed simultaneously or in different operating modes.
In an embodiment, said device has at least two operating modes: a first operating mode for displaying a virtual image and a second mode for projecting a real image on an external screen.
The display device comprises a micro-display, imaging optics having an output aperture to transmit a light beam, and a diffractive beam expander having a viewing aperture. An movable optical component of said device may have a first position with respect to said output aperture to set said diffractive beam expander into the path of said light beam in order to enable a first mode of operation, and a second position with respect to said output aperture to remove said diffractive beam expander from the path of said first light beam to enable a second mode of operation. The combination of said micro-display and said imaging optics is together adapted to form a virtual image which is observable through said viewing aperture of the diffractive beam expander in the first mode of operation. The combination of said micro-display and said imaging optics is together adapted to project said light beam onto an external screen in order to display a real image in the second mode of operation.
The virtual display mode allows viewing of images in privacy. On the other hand, the displayed real image may be viewed by two or more persons in e.g. meetings. Even when viewed by only one person, the real image displayed on an external screen allows ergonomic freedom of selecting a working position. The real image may be projected e.g. onto a white wall, onto the surface of a table, or onto a dedicated screen. The display device may be portable, lightweight and compact. A large detailed image may be examined at a glance in both operating modes.
Thanks to the use of the diffractive beam expander, the viewing aperture for a virtual image may be substantially enlarged without substantially increasing the weight and/or size of the display device.
In an embodiment, the display device comprises one or two diffractive beam expanders, which may be turned to the sides of the display device in order to select the operating mode. In another embodiment, the device comprises one or two diffractive beam expanders, which may slide with respect to the imaging optics in order to select the operating mode. Consequently, the display device may have a rather compact size in at least one of said operating modes.
In an embodiment, the display device is adapted to display a virtual image and to project a real image onto an external screen, at the same time.
The embodiments of the invention and their benefits will become more apparent to a person skilled in the art through the description and examples given herein below, and also through the appended claims.
In the following examples, the embodiments of the invention will be described in more detail with reference to the appended drawings, in which
a shows, in a cross-sectional top view, a display device adapted to display a virtual image to a person,
b shows a real primary image on a micro-display,
a shows, in a top view, a display device adapted to display a virtual image,
b shows, in a top view, the display device of
a shows, in a top view, a display device adapted to display a virtual image,
b shows, in a top view, the display device of
a shows, in a three dimensional view, the display device of
b shows, in a side view, a first operating mode of the device according to
c shows, in a side view, a second operating mode of the device according to
a shows, in a three dimensional view, a display device adapted to show a virtual image,
b shows, in a three dimensional view, the display device of
Referring to
The diffractive beam expander 10 comprises an input grating 12 and an output grating 16 implemented on a common substantially transparent substrate 7. The upper and lower surfaces of the substrate 7 are substantially planar and substantially parallel. The substrate is waveguiding, which means that in-coupled light may propagate within said substrate 7 and such that said propagating light may be confined to said substrate 7 by total internal reflections. Light B0 impinging on the input grating 12 may be coupled into the substrate 7 such that it propagates within said substrate substantially in the direction SY. Said light is subsequently coupled out by the output grating 16 providing a beam B1. The output beam B1 propagates substantially in the same direction as the input beam B0.
The viewing aperture 15 is defined by the visible perimeter of the output grating 16. The input grating 12 has an input aperture 11, which is defined by the perimeter of the input grating 12. The width of the input aperture 11 is W1, and the width of the viewing aperture is W2.
The width of the output beam B1 is defined by the width W2 of the viewing aperture 15. The width of the output grating may be selected to be greater than the width W0 of the beam B0 provided by the optical engine 20. Consequently, the upper limit of the beam B1 is not limited to the width W0 of the exit pupil of the optical engine 20 and the diffractive beam expander 10 may expand at least one dimension of a light beam.
The width of the input grating may be selected to be greater than or equal to the width W0 of the beam of the optical engine 20, in order to maximize the brightness of the displayed virtual image.
The direction SX is perpendicular to the direction SY. The direction SZ is perpendicular to the directions SX and SY.
The apertures 11, 15 are defined by the perimeter of the gratings 12, 16. The apertures 11, 15 may also be smaller than the gratings 12, 16 if a mask is superposed on said gratings, e.g. in order to modify the visual appearance of the display module 40.
The gratings 12, 16 are diffractive elements, which may have a grating period d which is e.g. in the range of λ/2 to λ where λ is a visible wavelength of light. The visible range of wavelengths is generally considered to be 400 to 760 nm, and the grating period d may be e.g. in the range of 200 to 1520 nm, respectively. The gratings 12, 16 may be e.g. surface relief gratings implemented by molding or embossing. The gratings 12, 16 may also be holographic volume gratings. One or more gratings 12, 16 may also be embedded in the substrate 7. The display module 40 may also comprise more than two diffractive elements 12, 16.
Referring to
Referring to
The at least one beam B0 transmitted from the output aperture 21 of the optical engine 20 impinges on the input grating 12 of the diffractive beam expander 10. The beam B0 is at least partially intercepted by the input grating 12, and at least a part of the light of the beam B0 is coupled into the waveguide 7 by the input grating 12. The output grating 16 diffracts an expanded beam B1 towards the eye E1 of an observer.
The viewing aperture 15 of the grating 16 substantially defines the maximum height H2 and width W2 of the expanded light beam B1.
The diffractive beam expander 10 may be mono-ocular, i.e. it may have only one output grating 16. The expander 100 may comprise a slanted input grating 10 to increase the efficiency of coupling light towards the output grating, when compared with e.g. a binary grating having a straight rectangular profile. The input grating 12 may be adapted to diffract e.g. more than 50% of the power of the in-coupled light towards the output grating 16. The input grating 12 may be e.g. a slanted surface relief grating.
Also the output grating 16 may be slanted in order to enhance coupling of light out of the substrate of the diffractive beam expander 10, when compared with e.g. a binary grating having a straight rectangular profile.
The diffractive beam expander 10 may comprise an optical absorber 17 to absorb in-coupled light, which propagates in the wrong direction, i.e. in the direction opposite to SY. Transmission or reflection of said light at the end of the expander 10 may create adverse stray light effects, in particular when the expander is in contact with other optical components. The absorber may be e.g. a piece of absorbing glass or plastic. The absorber may be a black coating. The edge of the substrate 7 may also be chamfered to direct light into a harmless direction.
b shows a real primary image 605 formed on the micro-display 22. The primary image 605 may consist of a plurality of light-transmitting points P1 or pixels.
Referring to
Referring to
Referring to
The display module 40 may comprise one or more optical absorbers 17a, 17b to minimize stray light effects, in particular to minimize stray light effects caused by light escaping from one beam expander 10a to another 10b.
Referring to
The device 500 may comprise a hinge mechanism 485 to allow change of the operating mode from a virtual display mode to a projecting mode.
Referring to
There may be a non-zero angle γ between the planes of the output gratings 16a, 16b in order to allow room for the nose N1 of the person PR1. The angle γ may be e.g. in the range of 3 to 20 degrees. The perimeter 15 of the output gratings 16a, 16b may allow a wider angular field of view when the gratings 16a, 16b are closer to the eyes E1, E2 of the person PR1. The beam expanders 10a, 10b may block ambient light more efficiently. Also the weight of the display device 500 may be distributed more conveniently on the nose N1 and on the ears ER1, ER2.
The device 500 may also be attached to a headgear, e.g. to a helmet.
Referring to
W1 denotes the width of the input grating 10 and D1 denotes the distance between the input grating 10 and the opposite surface of the planar waveguide 5. D1 may be substantially equal to the thickness of the substrate 7. W1 may be greater than or equal to the width of the beam B0 in order to maximize coupling efficiency.
The ratio of the width W1 to the distance D1 may be selected to be smaller than or equal to a predetermined limit in order to minimize light out-coupling by the input grating 12. If the ratio of the width W1 to the distance D1 is greater than said predetermined limit, then a fraction of in-coupled light may be coupled again out of the substrate 7 by the input grating 10, as shown by the beam B9. This may lead to a reduction in the efficiency of coupling light into the substrate 7. Said predetermined limit may be calculated by using the wavelength of the beam B0, the grating constant of the input grating 12, and the refractive index of the substrate 7.
The substrate 7 may also comprise a polarization rotating film in order to increase coupling efficiency, in particular when the ratio W1/D1 is greater than said predetermined limit. The use of a polarization rotating film for said purpose has been described in the patent application US 2005/0002611.
Referring to
The width of an ineffective portion 18 between the input gratings 12a, 12b may be minimized when maximizing the coupling efficiency of the beam B0 into the beam expanders 10a, 10b.
Referring to
The display device 500 may comprise e.g. separate optical engines 20a, 20b having separately controlled micro-displays 22, and separate diffractive beam expanders 10a, 10b in order to display stereoscopic virtual images to a viewer.
The diffractive beam expanders 10, 10a, 10b may also be at least partially transparent, allowing the user to see his environment through the diffractive beam expanders 10a, 10b while also viewing a displayed virtual image 710.
Stereoscopic virtual images may be displayed by using two partially transparent diffractive beam expanders. This arrangement may be applied especially in augmented reality systems.
Referring to
In a first mode of operation, i.e. in a virtual display mode, the input gratings 10a, 10b are positioned to intercept the beam B0 transmitted from the aperture 21 of the optical engine 20. The expanders 10a, 10b provide expanded beams B1, B2, which in turn provide the impression of a virtual image to the eyes E1, E2 of a viewer.
The display device may be used e.g. such that the distance L1 between the output gratings 16a, 16b and the eyes E1, E2 may be e.g. in the range of 2 mm to 100 mm. The display device 500 may also be positioned farther away from the eyes E1, E2, e.g. at a distance in the range of 0.1 to 1 meters, but in that case the perimeter of the output gratings 16a, 16 may limit the field of view.
b shows a second mode of operation of the display device 500 according to
In the virtual display mode, the optical engine 20 is adapted to provide a substantially collimated beam B0 for each illuminated pixel of the micro-display 22. The output beam B0 may be focused in order to provide a sharp real image in the projecting mode. The focusing may be accomplished by e.g. by adjusting the distance L3 between the micro-display 22 and imaging optics 24 (
An additional optical element, e.g. a further lens may be positioned to or removed from the optical path in order to affect the focusing of the beam B0. Such an additional lens may be attached or integrated to the input grating 12a, 12b of the diffractive beam expander 10a, 10b. Electrically deformable lenses may be used.
The beam B0 is substantially collimated in the virtual display mode. The beam B0 may remain to be substantially collimated also in the projecting mode, but in that case the resolution of the displayed real image is limited to the width W0 of the beam B0. However, this may be adequate in some applications, especially when the width of the beam B0 is small when compared with the width W4 of the displayed real image (
Thanks to the slide mechanism 320, the distance between the beam expanders 10a, 10b may be slightly adjusted, in order to correspond to different interpupillary distance of different users, i.e. to different distance between the pupils of the eyes E1, E2 of a user.
Referring to
b shows the device of
The display device 500 may further comprise one or more position sensors 310 to sense the position of at least one diffractive beam expander 10a, 10b with respect to the output aperture 21 of the optical engine 200. The position sensors 310 may be used e.g. in the adjustment of the optical power of the beam B0 such that a high operating power of the projecting mode is enabled only if the sensors 310 sense that both expanders 10a, 10b are fully removed from the path of the beam B0. Thus, the sensors 310 may be used to implement a safety feature. The sensors 310 may be e.g. optical or electromechanical switches. The switches may e.g. provide a signal to a control unit 200 (
Referring to
Consequently, the diffractive beam expanders 10a, 10b could be delivered as separate accessories and attached to the optical engine 20 by an end user.
a shows the display device 500 of
The display device 500 may comprise a hinge 350 to move the optical engine 20 with respect to the beam expanders 10a, 10b. The hinge 350 may also be used to manually adjust the desired vertical position of the displayed image 610, provided that said hinge 350 has adequate friction to enable the selection of intermediate mechanical positions.
The earpieces 360 may be adapted to act as a base or stand for the display device 500. The horizontal position of the displayed image 610 may be selected by horizontally turning the whole display device 500.
b shows the display device 500 of
c shows the display device 500 of
Referring to
The display device 500 may have a body 510 and cover 520, which cover 520 is adapted to be movable with respect to the body 510 by a slide mechanism. The slide mechanism may comprise e.g. grooves and ridges. The optical engine 20 may be attached to the body 510 and the beam expander 10 may be attached to the cover 520.
The display device 500 may further comprise a key set 230.
b shows the display device 500 of
If desired, the display device 500 may be positioned e.g. upside down on a supporting surface, e.g. on a table. The orientation of the displayed image may be automatically or manually selectable, respectively.
An optical fiber 850, or a power cable may be attached to the display device 500 in order to supply extra power, which may be needed in the projecting mode. The beam B0 may be refocused in order to attain a sharp image.
The display device 500 may also have a third operating mode, a private virtual display mode, in contrast to the more public virtual display mode of
Referring to
The condenser 26 concentrates light emitted by the light source 25 towards the micro-display 22. The light source may be e.g. a laser, light emitting diode, a gas discharge lamp, incandescent lamp, or a halogen lamp. The condenser may comprise one or more lenses, mirrors, prisms or diffractive elements. The micro-display 22 may be e.g. a liquid crystal display or an array of micromechanically movable mirrors. Also a reflective arrangement may be used instead of the transmissive shown in
The imaging optics 24 collimates or focuses light sent by the pixels of the micro-display 22, thereby forming the beam B0 provided by the optical engine 20.
The control unit 200 may control the power and the operation of the light source 25 by controlling the light source driver 250. If additional electrical power is needed in the projecting mode, it may be supplied via the power connector 255. The control unit 200 may control the displayed image via the display driver 220. The control unit 200 may adjust the focusing or collimation via the focusing actuator 240. The focusing actuator 240 may move the imaging optics 24, and/or the micro-display. The focusing actuator 240 may also insert or remove a further optical element into/from the optical path between the micro-display 22 and the imaging optics, or into/from between the imaging optics 24 and a beam expander 10. The actuator 240 may be e.g. a piezoelectric actuator. Said further optical element may be e.g. a convex lens, concave lens or a planar plate of transmissive material.
The control unit 200 may be in connection with the data communications unit 270, the memory unit 275, the position sensor 310, and the key set 230.
The position sensor provides information on the position of the beam expander 10 with respect to the optical engine 20. This information may be used e.g. for adjusting the power of the lamp, focusing, and the orientation of the image. The user may give commands by the key set 230 to the control unit 200. The key set 230 may be e.g. a keypad or a keyboard. The data communications unit 270 may e.g. provide access to the internet or to a local area network, e.g. by radio frequency or optical communication. The memory unit 275 provides memory for storing e.g. video clips.
The optical engine 22 may comprise only the micro-display 22, imaging optics 24, and the actuator 240. One or more of the above-mentioned components and units may be attached to the optical engine 20 by an optical and/or electrical cable. This may help to save weight, especially in case of the goggle-type display devices 500 of
The maximum optical power, i.e. the maximum luminous flux of the optical engine 20 may be substantially increased in the projecting mode when compared with the luminous power of the optical engine in the virtual display mode. The maximum luminous flux of the optical engine 20 may be e.g. in the range of 0.1 to 1 lumen in the virtual display mode and in the range of 1 to 100 lumen in the projecting mode. A luminous power in the order of 100 lumens may be provided e.g. by using a white light emitting diode (LED) of 4 W electrical power as the light source 25. In order to project images to a large audience, the maximum luminous flux of the optical engine 20 may even be in the range of 100 to 10 000 lumens in the projecting mode.
Instead of adjusting the optical power of the beam B0, i.e. instead of adjusting the luminous flux of the optical engine 200, the diffractive beam expanders 10, 10a, 10b may comprise one or more light-absorbing layers, portions or components to reduce the brightness of the displayed virtual image displayed through the diffractive beam expander.
Referring to
Referring to
The display device 500 may comprise an optical element 379, e.g. a concave lens to re-collimate a focused beam B0 before it impinges on the input grating 12. The optical element 379 may be attached e.g. to a movable prism 380 or a mirror, as shown in
The diffractive beam expander 10 may comprise e.g. a concave lens to collimate the beam B0 before it impinges on the input grating 12 of the diffractive beam expander 10.
Referring to
The diffractive beam expander 10 or expanders 10a, 10b may be positioned completely into the path of the light beam B0 and/or the diffractive beam expanders 10a, 10b may also be completely removed from the path of the light beam B0.
However, referring to
It should be noticed that selecting between a virtual display mode and a projecting mode may not be necessary when the device simultaneously displays the virtual image and the projected real image.
However, the embodiment of
Referring to
The virtual display mode and the projecting mode of the device 500 may be selected by changing a state of at least one optical component. The state of an optical component comprises the position of said optical component. However, the state of an optical component may also be changed without a changing its position.
Referring to
Referring to
The prism 381 may be set to a reflecting state or to a transmitting state also without the liquid 383, by moving the position of the first prism 381 or the second prism 382 such that the gap G1 is closed or opened.
The displayed virtual image 710 may also be closer than at infinity by using a substrate 7 which has slightly cylindrical surfaces, as disclosed e.g. in a patent application PCT/IB2004/004094. Thus, the displayed virtual image 710 may be at a distance of e.g. 1 to 2 meters from the eyes E1 of the viewer
The device 500 may be, for example, selected from the following list: a display module connectable to a further device, portable device, device with wireless telecommunicating capabilities, imaging device, mobile phone, gaming device, music recording/playing device (based on e.g. MP3-format), remote control transmitter or receiver, navigation instrument, measuring instrument, target finding device, aiming device, navigation device, personal digital assistant (PDA), communicator, portable internet appliance, hand-held computer, accessory to a mobile phone.
The diffractive beam expander 10a, 10b shown
The micro-display 22, the imaging optics 24, the diffractive beam expander 10, the optical engine 20, the display module 40, and/or the optical component 10, 12, 380, 381 for changing the operating mode of the device 500 may be delivered as separate custom-made components which may be optically, mechanically and/or electrically connectable to the other components of the device 500.
For the person skilled in the art, it will be clear that modifications and variations of the devices and the method according to the present invention are perceivable. The drawings are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FI2006/050556 | 12/14/2006 | WO | 00 | 5/27/2010 |