Patent Application
20080048936
Scanned beam displays generally operate by modulated a scanned beam of light in a pattern corresponding to an image to be displayed, such as a video image. According to various embodiments, the modulated beam of light may be scanned onto a display screen for viewing from the front or from the back, and/or may be scanned onto a viewer's retina.
According to some scanned beam display embodiments, an image plane or intermediate image plane (which may actually be a curved “plane”) may be formed coincident with a surface. One familiar display image plane is a display screen that may be directly viewed. Alternatively, an intermediate image plane may be formed, and the intermediate image projected onto a viewable screen via relay optics. In a retinal display, the intermediate image may be projected onto the viewer's retina.
An exit pupil expander located at an image plane or intermediate image plane in a scanned beam display may expand the exit pupil of the system. An expanded exit pupil may, according to embodiments, provide for some amount of misalignment and/or movement between the viewer's pupil and the display. In such an embodiment, which may be characteristic of a head-mounted display (HMD), a heads-up display (HUD), or other single-viewer display, it may be desirable to form an exit pupil expander at an intermediate image plane to expand the exit pupil a relatively small amount in order to maintain relatively high gain, i.e., to spread the display energy over a relatively small angle to maximize display brightness and/or minimize power consumption, size, and/or cost, etc. The image from the exit pupil expander may then be projected to the viewers' pupil(s) via refractive, reflective, and/or diffractive optics.
According to some embodiments, a display image may be simultaneously viewable by more than one viewer. According to other embodiments, a single viewer system may be configured to operate similarly to multi-viewer systems. While such embodiments may make use of an exit pupil expander at an intermediate image plane with subsequent relay optics configured to relay the expanded exit pupil to the eyes of the viewers, a more conventional approach may be to place a viewing screen at an image plane with the viewing screen being configured for direct viewing by the viewers. The viewing screen may be configured to provide gain to maximize brightness along and around a preferred axis. When configured for direct viewing, the apparent distance from the viewer to the image may be the actual physical distance from the viewer to the screen.
The image may be monochrome or multi-color. A multi-color image may be formed by modulating each of several component narrow-wavelength beams, for example. A monochrome image may be formed by modulating one or more relatively narrow (wavelength) band beams.
According to some embodiments, a monochrome or multi-color image may be formed using wavelength conversion. Wavelength conversion may, for example, make use of photoluminescent materials coated onto a screen. When a scanned beam of light at a first wavelength is projected onto a photoluminescent coating, the photoluminescent materials in the coating may absorb the light at the first wavelength and responsively emit light at a second wavelength. Typically, mechanisms for such emission are referred to broadly as photoluminescence, and may include fluorescence, phosphorescence, down-conversion (shifting wavelength from a shorter to a longer wavelength), and up-conversion (shifting wavelength from a longer to a shorter wavelength such as via a two-photon process). The first wavelength may be invisible (such as ultraviolet or infrared) or visible. Typically, the second wavelength is in the visible spectrum.
Relay optics may be considered a part of a scanned beam display and may be used in conjunction with a wide range of form factors including HMDs, HUDs, and multi-viewer systems.
According to an embodiment, a display screen may be formed to include one or more photoluminescent materials. The term display screen as used herein may include a directly viewable screen that may be positioned at an image plane and/or a screen at an intermediate image plane of a display system. The display screen may be configured to provide gain and/or preferred optical coupling along one or more preferred output axes. The display screen may be configured to act as an exit pupil expander. The image formed at the display screen may be directly viewable and/or relayed to the viewer or viewers via relay or projection optics.
According to an embodiment, a photoluminescent display screen may include an array, including a two-dimensional array, of cuplets configured to contain one or more photoluminescent materials. The term cuplet as used herein refers to a small container or cup having a border or walls that at least partially enclose a three-dimensional volume. The array of cuplets may be formed, for example, by indenting a thermoplastic sheet of material, by casting a sheet of material to include indentations, by coating a sheet with microspheres (the spheres themselves forming the cuplets), etc. The photoluminescent display screen may receive light at a first wavelength λ1 and convert the received light to light at a second wavelength λ2. All or portions of the walls of the cuplets may be configured to have reflective properties operative to preferentially direct the second wavelength light along a preferred output axis or axes. All or portions of the walls of the cuplets may additionally or alternatively be configured to reflect or absorb the first wavelength to prevent leakage of the first wavelength into the viewing space.
According to another embodiment, the photoluminescent display screen may be configured to operate as an exit pupil expander (EPE). For example, the structure of the photoluminescent display screen may be configured to refract of diffract light received at wavelengths other than the first wavelength while photoluminescently emitting light at the second wavelength responsive to receiving light at the first wavelength.
According to another embodiment, a scanned beam display may include a photoluminescent display screen including a two-dimensional array of cuplets containing a photoluminescent material. At least one light source may be modulated to output light at a first wavelength according to received image information. A beam output from the at least one light source is periodically scanned across a field of view that includes the photoluminescent display screen having cuplets. The scanned beam sequentially excites photoluminescent material positioned corresponding to the cuplets, and light is responsively output by the photoluminescent material in a pattern corresponding to the received image information. The cuplets may be configured to direct the light output along a preferred direction, such as to provide gain in a preferred viewing direction.
According to another embodiment, a scanned beam display includes at plurality of light sources operable to produce respective modulated beams of light at a corresponding plurality of wavelengths. The respective beams are scanned across a screen by a beam director. The screen may be configured to operate as a photoluminescent wavelength converter for received light at one or more wavelengths and as an exit pupil expander (EPE) for light received at other wavelengths. A plural wavelength image may be formed for viewing from the screen. The plural wavelength image may include at least a first wavelength produced by a light source and propagated by the screen. The plural wavelength image may include at least a second wavelength photoluminescently emitted by a photoluminescent material responsive to a received scanned beam at a third wavelength, the third wavelength beam being produced by another of the light sources. One or more arrays of optical surfaces may be formed in the screen. An array of optical surfaces may act as a microlens array (MLA) to the first wavelength to expand the exit pupil of the received and propagated beam. An array of optical surfaces may act as cuplets to direct photoluminescently-produced light along a preferred output direction. The arrays acting as an MLA and as cuplets may be the same array or different arrays. The optical surfaces may be shaped to provide substantially overlapping viewing regions for the propagated and the photoluminescently-produced wavelengths.
According to an embodiment, a screen may include an array of cuplets including an incident surface that reflects light at a second wavelength λ2 and transmits light at a first wavelength λ1. This cuplet surface directs generated light of wavelength λ2 toward an output direction, enhancing the intensity of light of wavelength λ2 in the output direction.
According to another embodiment, cuplets within the display screen may be broadband reflecting on portions of their surfaces. The cuplet reflective coating may be patterned with a pinhole aperture entrance. Photoluminescent material may receive light of a first wavelength λ1, through the pinhole aperture entrance of the cuplets and responsively emit light of a second wavelength λ2. The broadband reflecting cuplet surfaces may direct the generated light of wavelength λ2 toward an output direction.
According to another embodiment, an exit pupil expander includes a microlens array (MLA) wherein the MLA contains photoluminescent material within the microlenses. Upon receiving light having first wavelength λ1, the photoluminescent material may generate light having second wavelength λ2. If the incident beam includes other wavelengths, the MLA may also expand the other wavelengths as transmitted beamlets of the other wavelengths. Light emitted by the photoluminescent material may then be output substantially superimposed with beamlets of transmitted light to form an image having a plurality of wavelengths for viewing by a viewer.
According to another embodiment, the rear surface of the MLA may be operative to transmit light at the first wavelength, reflect light at the second wavelength, and refract light at the other wavelengths. According to other embodiments, the rear surface of the MLA may be broadband reflective in a pattern that allows the entrance of the first wavelength and other wavelengths through a portion thereof, while reflecting forward light at the second wavelength that is emitted in undesirable directions.
According to another embodiment, the screen may be formed as a dual microlens array (DMLA) separated by a distance substantially equal to the focal lengths of the individual microlens arrays. According to some embodiments, the first or second (output side) of the DLMA arrays may include a photoluminescent material operative to receive light at a first wavelength and to emit light at a second wavelength.
According to another embodiment, a scanned beam display system including an EPE containing photoluminescent material may contain modulation electronics that modulates one or more wavelengths of light, e.g., modulation electronics may modulate a plurality of wavelengths λ1, λ3, λ4, according to pixel values received from a video source. Light of first wavelength λ1 may be modulated according to an image pixel color and intensity, and then may be input to the exit pupil expander, which may output light of another wavelength λ2 having a modulated pattern corresponding to modulated wavelength λ1. The scanned beam display system may output an image having an expanded exit pupil including modulated wavelengths λ2, λ3, and λ4.
Aspects and advantages according to embodiments will become more readily appreciated by reference to the following non-limiting detailed description, when taken in conjunction with the accompanying drawings.
The following discussion is presented to enable a person skilled in the art to make and use the invention. The general principles described herein may be applied to embodiments and applications other than those detailed below without departing from the spirit and scope.
One example of a scanning mirror 108 is a mechanically resonant scanner, such as that described U.S. Pat. No. 5,557,444 to Melville et al., entitled MINIATURE OPTICAL SCANNER FOR A TWO-AXIS SCANNING SYSTEM, incorporated herein by reference.
According to some applications, the emitted beam may be non-visible, such as ultraviolet or infrared, and the viewable light may be at a visible wavelength. For example, the light source 102 may be an infrared laser diode operable to emit a first wavelength in the infrared, such as 1024 nanometers (nm), for example; and the screen 112 may be configured to generate a second harmonic output at a visible green wavelength 512 nm half that of the impinging scanned beam 110. According to another example, the light source 102 may be a violet laser diode operable to emit a first wavelength at about 405 to 415 nm and the screen may be configured to photoluminescently emit light at a second, longer wavelength, such as about 512 nm for example.
While the display screen 112 is illustrated as being directly viewed, the output from the display screen may alternatively be received and projected by relay or projection optics. For example, the image formed at the plane of the display screen 112 may be rear- or front-projected onto a final viewing screen. Alternatively, an ocular assembly may project the image onto the viewer's retina, optionally while changing the wavefront curvature, and hence the apparent distance from the screen 112 to the eye 116.
Optionally, a cover 208 may be placed over the array of cuplets. The cover 208 may include a filter configured to reflect first wavelength light and transmit the second wavelength light.
According to some embodiments, the surfaces 204 defining the edges of the cuplets may be optical surfaces such as spherical surface, paraboloid surfaces, hyperboloid surfaces, or other aspherical surfaces selected to provide a desired intensity pattern of emitted viewable light 114. As will be explained below, the surfaces 204 may further include an optical shape selected to refract, diffract, or reflect light having wavelengths other than the first or second wavelengths.
A wavelength-converting material is formed within or beyond the cuplet that is operative to receive the incident first wavelength of light and convert it to a second wavelength of light. As illustrated, a portion of the incident beam 110 at a first wavelength is received at a wavelength converting entity 506 and converted to a second wavelength of light. Three potential output paths are illustrated. In the output path 114a, light is emitted forward toward a viewing area. In second and third output paths 114b and 114c, light is emitted generally back toward the scanner and generally sideways along the array of cuplets respectively. The emitted light is reflected by the selective reflector 504 and directed forward toward a viewing area. Thus, the reflectance and shape of the optical surface 204 defining the cuplet can determine the range of angles over which light at the second wavelength is directed toward the viewing area. Shallower cuplets may direct the second wavelength light forward at a relatively wider range of angles such as to, for example, allow a shorter path length to a subsequent optional optical element, allow a larger subsequent optical element, or allow viewing across a wider range of angles such as nearly a half plane or an optical half angle of 0-30 degrees or less. Deeper cuplets may direct the second wavelength light forward at a relatively narrower range of angles such as to, for example, allow a longer path length to an optional subsequent optical element, allow a smaller optional subsequent optical element, or allow viewing across a narrower range of angles such as, for example 0-15 degrees optical half angle or less. A narrower viewing angle may concentrate output light across the viewable area and make the display appear relatively brighter.
While emitted light projected in a rightward direction in
Although the wavelength converting material is shown substantially filling the cuplets, the material may be distributed non-uniformly within the cuplets. For example, a transparent layer may be formed around the edges of the cuplets and the wavelength converting material may be concentrated near a focus or foci. Alternatively, the wavelength converting material may be disposed within an overlying plane of material 208 (not shown).
As indicated above, a number of wavelength converting materials may be appropriate to provide various types of wavelength conversion. For example, a slab, a piece, or a plurality of pieces of periodically-polled lithium niobate may act as a second harmonic generator and result in a second wavelength half that of the first wavelength. Alternatively, down-converting or up-converting photoluminescent materials may be used to shift wavelengths by differing amounts.
Examples of materials suitable for the wavelength converting material 502 include, but are not limited to, green emitting phosphors such as zinc sulfide doped with copper and aluminum (ZnS:Cu,Al), blue emitting phosphors such as (SrCaBa)5Cl(PO4)3:Eu, and red emitting phosphors such as Mg4F1GeO6:Mn. Fluorescent dyes such as coumarin, fluorescein, and rhodamine; nanoparticles (e.g., quantum dots) supported by or dispersed in liquids or solids; doped crystal solids such as neodymium doped yttrium aluminum garnet (Nd:YAG)(Y3Al5O12:Nd); and doped glasses are other materials that may be suitable for the photoluminescent material 502. The photoluminescent material 502 may be of a type described in, for example; Shigeo Shionoya and William M. Yen, eds, PHOSPHOR HANDBOOK, CRC Press (1999); Wise, Donald L. et al., eds, PHOTONIC POLYMER SYSTEMS, Marcel Dekker (1998); and/or Berlman, Isadore B., HANDBOOK OF FLUORESCENCE SPECTRA OF AROMATIC MOLECULES, Academic Press (1965); all hereby incorporated by reference. The photoluminescent material 502 may alternatively exhibit fluorescent or phosphorescent characteristics, consistent with the decay requirements necessitated by frame duration.
A second array of optical surfaces 302 may be defined on the opposite surface of the substrate 202 as shown. According to some embodiments, each first surface 204 is formed opposite a corresponding second surface 302. The second array of optical surfaces reflects, refracts, or diffracts the input beam 110 toward the corresponding elements of the first array of surfaces. The second array of surfaces 302 may act as diffracting, reflecting, or reflecting optical elements to at least some wavelengths of light.
An exemplary incident light beam 110 at a first wavelength 110 is illustrated refracted by a second optical surface 302, penetrating the substrate 202, and passing through an aperture 602 in the mirror 504 into a cuplet 206. As described above, a wavelength-converting material is formed within or beyond the cuplet that is operative to receive the incident first wavelength of light and convert it to a second wavelength of light. As illustrated, at least a portion of the incident beam 110 at a first wavelength is received at a wavelength converting entity 506 and converted to a second wavelength of light. One potential output path 114 is illustrated. The reflectance and shape of the optical surface 204 defining the cuplet and the size of the aperture 602 can determine the range of angles over which light at the second wavelength is directed toward the viewing area. Considerations may be similar to those described above. As one alternative to refracting input light 110, the second array of optical surfaces may form light gathering reflective surfaces configured to direct received light toward an aperture formed in the rightmost tip thereof. In some embodiments, the reflective surfaces may be hyperboloid in shape.
Referring back to
As an alternative to refracting surfaces 302, the walls 302 of the shapes on the input side of the display screen 112 may be formed as reflecting surfaces. According to an embodiment, the shape of the input surfaces may be formed as hyperboloid, paraboloid, etc. configured to reflect incident light energy toward a focus substantially corresponding to the input aperture 602 of the cuplets 206.
Third and fourth wavelength components 802 of the incident beam 718 are refracted by the optional second array of optical surfaces 302 and directed toward the corresponding first array of surfaces 204. The selectively reflective surface 504 of the first array of surfaces is configured to pass the third and fourth wavelengths. A contrasting index of refraction between the substrate 202 and the opposite side of the first optical surfaces (I.e., the interior of the cuplets) causes refraction to occur at the first optical surfaces. Accordingly, the transmitted third and fourth wavelength components of the viewable light 720 are propagated to form beamlets in the far field having and expanded exit pupil formed by the DMLA of the screen 112. According to some embodiments, the divergence angle of the second wavelength light 114 may be matched to the range of beamlet angles of the third and fourth wavelength light 804 to form a plural color image that is viewable over an expanded exit pupil.
According to some embodiments, the first light source 102 is a violet laser diode operable to emit a first wavelength in the violet range of the spectrum such as around 408 nm, the second light source 702 is a blue laser diode operable to emit a third wavelength in the blue range of the spectrum such as around 420 nm, and the third light source 708 is a red laser diode operable to emit a fourth wavelength in the red range of the spectrum such as around 625 nm. The selectively reflective coating 504 may include a green-reflecting notch reflector that is operable to transmit violet, blue, and red light but reflect green light. Other combinations of wavelengths may similarly be used.
A monolayer of microspheres 902 containing wavelength converting material are disposed upon a first surface of a substrate 202. The microspheres 902 form cuplets 206. The microspheres 902 may be adhered to the substrate with a substantially transparent optical adhesive 904. Alternatively, the optical adhesive 904 may be selected or formulated to reflect received light 110 at a first wavelength and to transmit photoluminescently emitted light at a second wavelength. According to one embodiment, a contrasting refractive index between the top surface of the microspheres 902 and an overlying material 906 may provide at least partial preferential reflection of photoluminescently emitted light energy in the downward direction. According to an embodiment, the overlying material 906 may consist substantially of air, dry air, carbon dioxide, argon, or other gas. According to another embodiment, the overlying material 902 may comprise a fluid. According to another embodiment, the overlying material 906 may comprise a cured polymer selected or configured to transmit received light 110 at a first wavelength and reflect photoluminescently emitted light at a second wavelength. Optionally, a filter 208 may be disposed one or both surfaces of the substrate 202. According to an embodiment, the filter 208 may be configured to reflect or absorb incident light 110 at the first wavelength and transmit photoluminescent light at the second wavelength.
Alternatively, the display screen configuration describe above may be altered somewhat. For example, the incident light 110 may be violet and may impinge upon the display screen 112 from the bottom. The filter layer 208 may be omitted. The optical adhesive 904 may be configured or selected to transmit violet light and reflect visible light such as green light (VTGR). The overlying layer 906 may substantially comprise viewing room air, may comprise a dry gas or a fluid, or may comprise a green transmitting, violet reflecting (GTVR) material such as a polymer, suspension, vacuum/plasma deposited layer or other material construction.
A monolayer of microspheres of wavelength converting material 902 may be disposed on a substrate 202 to form cuplets 206. According to an embodiment, the microspheres 902 may be joined to the substrate with an optical adhesive 904. The microspheres may be provided a coating 504 of VTGR material. Additionally or alternatively the optical adhesive 904 may be configured as a VTGR material. After curing the monolayer thus deposited on the substrate 202, the output face 1002 may be ground to substantial flatness, surface peened, abrasive jet treated, or otherwise treated to expose the inner portion of the cuplets 206 substantially without an overlying VTGR layer. The output face 1002 may then be polished, coated, and/or may be otherwise treated to best provide desired mechanical, optical, visual, electrical, or other requirements.
Of course, the embodiment shown in
While the microsphere layers shown in
While the term photoluminescence and its derivatives have been used extensively throughout, the light emitted at the second wavelength 2 need not, strictly speaking, be the result of a purely photoluminescent process. As used herein, the term may extend to other processes such as second harmonic generation, surface plasmon resonance, etc.
From the foregoing discussion, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention, which will be limited only by the claims.
This application claims priority from and incorporates by reference U.S. Provisional Patent Application Ser. No. 60/837,160; filed Aug. 10, 2006; entitled DISPLAY AND DISPLAY SCREEN HAVING WAVELENGTH CONVERSION.
| Number | Date | Country | |
|---|---|---|---|
| 60837160 | Aug 2006 | US |
