WO2013156756A1 - Improvements in or relating to display apparatus - Google Patents

Improvements in or relating to display apparatus Download PDF

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Publication number
WO2013156756A1
WO2013156756A1 PCT/GB2013/050918 GB2013050918W WO2013156756A1 WO 2013156756 A1 WO2013156756 A1 WO 2013156756A1 GB 2013050918 W GB2013050918 W GB 2013050918W WO 2013156756 A1 WO2013156756 A1 WO 2013156756A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical element
image bearing
bearing light
display apparatus
optical
Prior art date
Application number
PCT/GB2013/050918
Other languages
French (fr)
Inventor
Michael David Simmonds
Jonathan Paul Freeman
Original Assignee
Bae Systems Plc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bae Systems Plc filed Critical Bae Systems Plc
Publication of WO2013156756A1 publication Critical patent/WO2013156756A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/017—Head mounted
    • G02B27/0172—Head mounted characterised by optical features
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/0149—Head-up displays characterised by mechanical features
    • G02B2027/0154—Head-up displays characterised by mechanical features with movable elements
    • G02B2027/0156—Head-up displays characterised by mechanical features with movable elements with optionally usable elements

Definitions

  • the present invention relates to a display apparatus, in particularly, but not exclusively, a display apparatus arranged to convey an image to an observer overlaid on a real world scene.
  • a display apparatus may be a helmet mounted display or head mounted display for use by a pilot of an aircraft.
  • a typical helmet mounted display has either one or two small image sources with a lens arrangement embedded within the structure of a helmet, eye-glasses or visor to be donned by a user, for example a pilot of an aircraft.
  • the image sources are miniaturized and may include one or more Cathode Ray Tubes (CRT), Liquid Crystal Displays (LCD) or other types of planar display.
  • CTR Cathode Ray Tubes
  • LCD Liquid Crystal Displays
  • An image source is arranged to generate images of various symbols for the representation of information under the control of a processor. From the image source, image bearing light will travel through an optical system onto a combiner mounted to the helmet such that the combiner is located in the field of view of a user.
  • the combiner is arranged to allow the transmission of real world images therethrough and to reflect image bearing light back to into the eyes of the user.
  • the combiner is part of the visor for the helmet or head mounted display.
  • Flight information from the cockpit instruments will typically include many discrete items of data that require diligent monitoring, for example, altitude, heading, attitude etc.
  • a pilot cannot afford to divert his attention to in-cockpit instrument so as to stay focussed on potential obstacles or threats to the aircraft.
  • a helmet or head mounted display can be arranged to provide head- directed sensor imagery or fire control symbology onto the eye of a user, the imagery or symbology being conformal with a real world scene observed through a semi-transparent combiner.
  • helmet or head mounted displays offer the potential for enhanced situation awareness and pilot effectiveness.
  • a display apparatus for displaying an image to an observer overlaid on a real world scene includes a first optical element having at least one associated reflective region arranged to reflect incident light, a second optical element having at least one associated reflective region arranged to reflect incident light, a display source arranged to generate image bearing light, wherein the first and second optical elements are arranged opposed to one another and arranged to transmit image bearing light from the display source to a position where the image bearing light is viewable by an observer overlaid on a real world scene observed through at least a portion of the second optical element wherein the first and second optical elements are arranged such that the angle of incidence of image bearing light reduces with each successive reflection from the optical element.
  • image bearing light will be internally reflected between the first and second optical elements until it is positioned to exit the display apparatus coincident with a line of sight of an observer using the display apparatus and the image carried by the image bearing light will appear to overlay a real world scene also seen by the observer.
  • the physical space occupied by the display apparatus can be arranged such that an image intensifier unit can be positioned for use with the display apparatus.
  • the first and second optical elements may be air spaced.
  • a relay optical arrangement may be arranged to receive image bearing light from the display source and to output image bearing light such that the angle of incidence of the image bearing light with the surface of the second optical element is such that the image bearing light reflects towards the first optical element.
  • the first and second optical elements may be arranged on surfaces of or within a solid optical piece.
  • the solid optical element may be arranged to receive image bearing light, for example the solid optical piece may include an input face for image bearing light which may be curved.
  • the relay optical arrangement may be arranged to receive image bearing light from the display source and to output image bearing light such that the angle of incidence of the image bearing light with the surface of the second optical element is such that the image bearing light reflects towards the first optical element.
  • the second optical element may include n reflective regions arranged to reflect image bearing light and the first optical element may include n-1 reflective regions arranged to reflect image bearing light towards the second optical element.
  • the second optical element may include a reflective region arranged to reflect image bearing light back through a portion of the first optical element such that the image bearing light is viewable by an observer overlaid on a real world scene observed through at least a portion of the first and second optical elements.
  • the first optical element and second optical element may be arranged such that image bearing light is first reflected from a first reflective region of the second element towards a first reflective region of the first optical element, the first reflective region of the first optical element may be arranged to reflect image bearing light towards a second reflective region of the second optical element, the second reflective region of the second optical element may be arranged to reflect image bearing light towards a second reflective region of the first optical element, the second reflective region of the first optical element may be arranged to reflect image bearing light towards a third reflective region of the second optical element, the third reflective region of the second optical element may be arranged to reflect image bearing light towards the eye of the observer to be viewed overlaid on a real world scene observed through at least a portion of the second optical element.
  • the angle of incidence of image bearing light with respect to the second optical element may decrease with each reflection from the second optical element.
  • the angle of incidence of image bearing light with respect to the first optical element may decrease with each reflection from the first optical element.
  • the shape of first optical element may be flat, curved toric, spherical or freeform aspheric and the shape of the second optical element may be curved toric, spherical or freeform aspheric.
  • the first optical element may be arranged to allow incident image bearing light substantially normal to the face of the first optical element to pass therethrough and to reflect incident image bearing light off-axis to the normal of the first optical element.
  • the second optical element may be a portion of a visor.
  • At least a portion of the second optical element may include a layer arranged to reflect image bearing light towards the eye of the observer and to allow the observer to view a real world scene through the portion of the second optical element.
  • the display apparatus may be arranged to be used within an image intensifier unit wherein the image intensifier unit may be arranged to intersect a line of sight of an observer, between the real world scene and the second optical element.
  • the first and second optical elements and display source may be mounted on a helmet.
  • the image intensifier may be mounted on to the helmet.
  • Figure 1 shows in side elevation a ray trace diagram of a display apparatus according to the present invention
  • Figure 2 shows in side elevation a single ray trace diagram of the display apparatus of Figure 1 ;
  • Figures 3a to 3c are schematic diagrams of a display apparatus according to the present invention mounted on a helmet;
  • Figures 4a to 4c are schematic diagrams of a display apparatus according to the present invention mounted on helmet with a set of night vision goggles;
  • Figure 5 shows in side elevation a ray trace diagram of an alternative apparatus according to the present invention.
  • a display apparatus 10 includes a first optical element 12 and a second optical element 14 arranged to oppose the first optical element 12 such the first and second optical elements 12, 14 are air spaced.
  • the first optical element 12 is formed from a high-index optical glass, for example N_BK7 or polycarbonate and defines a substantially flat area.
  • the first optical element 12 may define a spherical, aspherical, cylindrical or freeform area.
  • the second optical element 14 is formed from a high-index optical glass, for example N-BK7 or polycarbonate and defines a substantially spherical shaped area.
  • the second optical element 14 may define an aspherical or freeform area.
  • the second optical element 14 can be formed by a portion of a visor of a helmet or head mounted display system, not illustrated.
  • the first and second optical elements 12, 14 are arranged to be carried and retained in the correct position in relation to one or both eyes 16 of an observer that dons the helmet.
  • a display source 18 under the control of a suitable processor is arranged to generate image bearing light 20 that is to convey symbology or image information to the observer.
  • the image bearing light 20 is manipulated by a relay optical arrangement 22, which incorporates suitable lens, such that the relay optical arrangement 22 will inject image bearing light 20 between the first and second optical elements 12, 14.
  • the first and second optical elements 12, 14 are arranged opposed to one another such that injected image bearing light 20 is internally reflected between the first and second optical elements 12, 14 to transmit the image bearing light 20 to a position that is viewable by the eye 16 of the observer to present a substantially collimated image to the observer. It will be understood, that the observer will view a real world scene 24 along a line of sight 26 and that the image bearing light 20, being focussed at or near infinity, will appear to the observer to be overlaid upon the real world scene 24. ln this embodiment of the invention, it will be understood that the first and second optical elements 12, 14 are air spaced having a suitable optical coating thereon to reflect the image bearing light 20 to the eye 16.
  • the optical coatings applied to the first and second optical elements 12, 14 are arranged to allow internal reflection between the first and second optical elements 12, 14 and that in the region of the eye 16, along the line of sight 26, that the observer will be able to see through the first and second optical elements 12, 14 and any optical coating carried thereon so as to be able to also view the real world scene 24.
  • the optical coating can be suitable a metallic or dielectric coating, for example aluminium, titanium dioxide or magnesium fluoride. It will be understood that a combination of coatings can be utilised in different regions of the coatings on the first or second optical elements 12, 14 to provide appropriate properties for that region.
  • the display source 18 and relay optical arrangement 22 can be carried on or incorporated within a lower section 28 of the second optical element 14. It will be understood that the first and second optical elements 12, 14 can be mounted to a helmet, not illustrated via lower section 28 of the second optical element 14 and that the mounting to the helmet can be via housing 30 for the display source 18 and relay optical arrangement 22. Referring to Figure 2, wherein like references have been used to indicate similar integers to those described with reference to Figure 1 , in operation the display apparatus 10 directs image bearing light 20, in this case indicated for a single ray, from the display source 18 via the relay optical arrangement 22 to be incident on the second optical element 14 at a given angle A measured from a normal to the second optical element 14 where the light is incident.
  • the angle of incidence A is determined by the positioning of the relay optical arrangement 22 and display source 18 and will be greater than 0° and less than 90°, such that the image bearing light 20 is internally reflected between the first and second optical elements 12, 14 to a position in front of the eye 16.
  • the optical coating applied to the second optical element 14, in the region that light is first incident thereon is arranged to reflect the wavelengths of the image bearing light 20 back to the first optical element 12 to be incident on the first optical element 12 at a given angle D measured from a normal to the first optical element 12 where the light is incident.
  • the optical coating applied to the first optical element 12, in the region that light is first incident thereon, is arranged to reflect the image bearing light 20 back to the second optical element 14 to be incident on the second optical element 14 at a given angle B measured from the normal to the second optical element 14 where the light is incident.
  • the optical coating applied to the second optical element 14, in the region that light is second incident thereon is arranged to reflect the image bearing light 20 back to the first optical element 12 to be incident on the first optical element 12 at a given angle E measured from a normal to the first optical element 12 where the light is incident.
  • the optical coating applied to the first optical element 12, in the region that light is second incident thereon is arranged to reflect the image bearing light 20 back to the second optical element 14 to be incident on the second optical element 14 at a given angle C measured from the normal to the second optical element 14 where the light is incident.
  • the optical coating applied to the second optical element 14, in the region that light is third incident thereon is arranged to reflect the image bearing light 20 back to the first optical element 12 to be incident on the first optical element 12 normal to the first optical element 12 where the light is incident.
  • the optical coatings applied to the first and second reflection regions of the first optical element 12 and the first and second reflection regions of the second optical element 14 are arranged to reflect wavelengths of light generated by the display source 18.
  • the optical coating applied to the third reflection region of the second optical element 14 is arranged to reflect wavelengths of image bearing light 20 generated by the display source 18 and shall be optimised to allow a proportion of light from the real world scene 24 to pass therethrough.
  • This coating can be a frequency selective coating arranged to (i) reflect a specific band of wavelengths generated by the display source 18, but to allow other wavelengths to pass therethrough or (ii) reflect a broader band of wavelengths than that generated by the display source 18, but at a lower efficiency to improve the transmission of light from the real world scene 24 through the second optical element 14.
  • the shape of the second optical element 14 or a combination of the shape of the first and second optical elements 12, 14 determines the angle of incidences A, B, C, D and E for any given ray of the image bearing light 20. That is the angle of the second optical element 14 relative to the first optical element 12 for a given region will determine the angle of incidence of image bearing light 20 at that region. Furthermore, it will be noted that the shape of the second optical element 14 or the first and second optical elements 12, 14 ensured that the angle of incidence with the second optical element 14 for any given ray decreases with each subsequent reflection, i.e. the angle of incidence for angle A > B > C and that the angle of incidence with the first optical element 12 for any given ray decreases with each subsequent reflection, i.e. the angle of incidence for angle D > E until image bearing light 20 is positioned in front of the eye 16. At this region the angle of incidence with the first optical element 12 is normal to the first optical element 12.
  • the first optical element 12 is arranged to allow image bearing light 20 to transmit therethrough in the region of the eye 16 if the image bearing light 20 is substantially normal to the first optical element 12. This is achieved using a suitable optical coating arrangement on the first optical element 12 or ensuring that there is no optical coating on the first optical element 12 in the region of the eye 16.
  • the first optical element 12 can be arranged to terminate such that it is not present in the region of the eye 16 thereby allowing the image bearing light reflected from the second optical element at angle C to follow a path coincident with the line of sight 26 of the eye 16 of the observer.
  • the second optical element in the region of the third reflection can be arranged to carry a semi-silvered optical coating or angularly selective and/or graded coating.
  • first and second optical elements 12, 14 in the region arranged in front of the eye 16 can be minimised to allow the observer a clearer view of the forward scene 24.
  • a make-up piece can be located at the third region of the second optical element 14, the make-up piece being arranged to null the overall prismatic powers incurred by the shape of the first or second optical elements 12, 14.
  • an observer 40 that has donned a helmet 42 will be able to view a real world scene through the first and second optical elements 12, 14 of the display apparatus 10 combined with an overlaid image generated by an image source 18.
  • the image to be conveyed to the observer is internally reflected between the first and second optical elements 12, 14 until it is in front of the eye 16 of the observer as previously described.
  • the observer 40 will be able to use the display apparatus 10 with an image intensifier unit or night vision system 44.
  • the direction of travel of the image intensifier unit 44 from stowed to deployed positions, S to T is indicated by the double headed arrow 46 in Figure 4c.
  • the image intensifier unit 44 travels from the stowed position S in the direction indicated by arrow 48 to rotate the image intensifier unit 44 and then into the final deployed position T in the direction indicated by arrow 50.
  • the image intensifier unit 44 can be locked in either a stowed or deployed position S, T. Accordingly, the dimensions of the display apparatus 10 can be arranged to allow the observer 40 to use the display apparatus 10 with a suitable image intensifier unit or night vision system 44.
  • the first and second optical elements 12, 14 can be part of a solid optical piece 60, wherein the first and second optical elements 12, 14 are formed at or near opposing sides of the optical piece 60.
  • the image bearing light 20 is arranged to enter the optical piece 60 via an input section 62 of optical piece 60 so as to be incident on the second optical element 14 at the appropriate angle to provide total internal reflection within the optical piece 60.
  • the embodiment of Figure 5 operates and is located in a similar general manner to that described with reference to Figures 1 and 2.
  • a suitable optical coating can be formed at or near the surface of the opposing sides of the optical piece 60 to generate the first and second optical elements 12, 14 to enable total internal reflection of image bearing light 20 within the optical piece 60.
  • the optical piece 60 can be carried by a visor of a helmet mounted display system, not illustrated. It will be understood, that the optical coating applied to create the first and second optical elements 12, 14 will allow internal reflection between the first and second optical elements 12, 14 and that in the region of the eye 16, along the line of sight 26, that the observer will be able to see through the optical piece 60 and any optical coating carried thereon or therein to form the first and second optical elements 12, 14
  • a solid optical piece 60 can be formed from by filling an air spaced region between first and second optical elements 12, 14 with a suitable medium or resin having a reflective index greater than one, for example N-BK7 or polycarbonate.
  • first and second optical elements 12, 14 in the region arranged in front of the eye 16 can be minimised to allow the observer a clearer view of the forward scene 24.
  • a make-up piece 64 can be located at the third region of the second optical element 14, the make-up piece 64 being arranged to null the overall prismatic powers incurred by the shape of the first or second optical elements 12, 14.
  • image bearing light 20 will be internally reflected between the first and second optical elements 12, 14 until it is positioned to exit the display apparatus 10 coincident with a line of sight 26 of an observer using the display apparatus 10 and the image carried by the image bearing light 20 will appear to overlay a real world scene 24 also seen by the observer.
  • the physical space occupied by the display apparatus 10 can be arranged such that an image intensifier unit 44 can be positioned for use with the display apparatus 10.

Abstract

IMPROVEMENTS IN OR RELATING TO A DISPLAY A display apparatus 10 for displaying an image to an observer overlaid on a real world scene24includes a first optical element 12 having at least one associated reflective region arranged to reflect incident light, a second optical element 14 having at least one associated reflective region arranged to reflect incident light, a display source18arranged to generate image bearing light20 wherein the first and second optical elements12, 14are arranged opposed to one another and arranged to transmit image bearing light20from the display source18to a position where the image bearing light20is viewable by an observer overlaid on a real world scene24observed through at least a portion of the second optical element14. Figure 2

Description

IMPROVEMENTS IN OR RELATING TO DISPLAY APPARATUS
The present invention relates to a display apparatus, in particularly, but not exclusively, a display apparatus arranged to convey an image to an observer overlaid on a real world scene. Such a display apparatus may be a helmet mounted display or head mounted display for use by a pilot of an aircraft.
A typical helmet mounted display has either one or two small image sources with a lens arrangement embedded within the structure of a helmet, eye-glasses or visor to be donned by a user, for example a pilot of an aircraft. The image sources are miniaturized and may include one or more Cathode Ray Tubes (CRT), Liquid Crystal Displays (LCD) or other types of planar display.
An image source is arranged to generate images of various symbols for the representation of information under the control of a processor. From the image source, image bearing light will travel through an optical system onto a combiner mounted to the helmet such that the combiner is located in the field of view of a user. The combiner is arranged to allow the transmission of real world images therethrough and to reflect image bearing light back to into the eyes of the user. Typically, the combiner is part of the visor for the helmet or head mounted display.
Due to the increasing complexity of aircraft instrumentation, pilots are burdened with numerous monitoring activities, even during normal operations. Flight information from the cockpit instruments will typically include many discrete items of data that require diligent monitoring, for example, altitude, heading, attitude etc. However, when flying in an operational mode, a pilot cannot afford to divert his attention to in-cockpit instrument so as to stay focussed on potential obstacles or threats to the aircraft.
A helmet or head mounted display can be arranged to provide head- directed sensor imagery or fire control symbology onto the eye of a user, the imagery or symbology being conformal with a real world scene observed through a semi-transparent combiner. As such, helmet or head mounted displays offer the potential for enhanced situation awareness and pilot effectiveness.
According to an aspect of the invention, a display apparatus for displaying an image to an observer overlaid on a real world scene includes a first optical element having at least one associated reflective region arranged to reflect incident light, a second optical element having at least one associated reflective region arranged to reflect incident light, a display source arranged to generate image bearing light, wherein the first and second optical elements are arranged opposed to one another and arranged to transmit image bearing light from the display source to a position where the image bearing light is viewable by an observer overlaid on a real world scene observed through at least a portion of the second optical element wherein the first and second optical elements are arranged such that the angle of incidence of image bearing light reduces with each successive reflection from the optical element. In this manner, image bearing light will be internally reflected between the first and second optical elements until it is positioned to exit the display apparatus coincident with a line of sight of an observer using the display apparatus and the image carried by the image bearing light will appear to overlay a real world scene also seen by the observer. Furthermore, the physical space occupied by the display apparatus can be arranged such that an image intensifier unit can be positioned for use with the display apparatus.
The first and second optical elements may be air spaced. A relay optical arrangement may be arranged to receive image bearing light from the display source and to output image bearing light such that the angle of incidence of the image bearing light with the surface of the second optical element is such that the image bearing light reflects towards the first optical element.
Alternatively, the first and second optical elements may be arranged on surfaces of or within a solid optical piece. The solid optical element may be arranged to receive image bearing light, for example the solid optical piece may include an input face for image bearing light which may be curved. Again, the relay optical arrangement may be arranged to receive image bearing light from the display source and to output image bearing light such that the angle of incidence of the image bearing light with the surface of the second optical element is such that the image bearing light reflects towards the first optical element. The second optical element may include n reflective regions arranged to reflect image bearing light and the first optical element may include n-1 reflective regions arranged to reflect image bearing light towards the second optical element.
The second optical element may include a reflective region arranged to reflect image bearing light back through a portion of the first optical element such that the image bearing light is viewable by an observer overlaid on a real world scene observed through at least a portion of the first and second optical elements.
The first optical element and second optical element may be arranged such that image bearing light is first reflected from a first reflective region of the second element towards a first reflective region of the first optical element, the first reflective region of the first optical element may be arranged to reflect image bearing light towards a second reflective region of the second optical element, the second reflective region of the second optical element may be arranged to reflect image bearing light towards a second reflective region of the first optical element, the second reflective region of the first optical element may be arranged to reflect image bearing light towards a third reflective region of the second optical element, the third reflective region of the second optical element may be arranged to reflect image bearing light towards the eye of the observer to be viewed overlaid on a real world scene observed through at least a portion of the second optical element.
The angle of incidence of image bearing light with respect to the second optical element may decrease with each reflection from the second optical element. The angle of incidence of image bearing light with respect to the first optical element may decrease with each reflection from the first optical element. The shape of first optical element may be flat, curved toric, spherical or freeform aspheric and the shape of the second optical element may be curved toric, spherical or freeform aspheric.
The first optical element may be arranged to allow incident image bearing light substantially normal to the face of the first optical element to pass therethrough and to reflect incident image bearing light off-axis to the normal of the first optical element.
The second optical element may be a portion of a visor.
At least a portion of the second optical element may include a layer arranged to reflect image bearing light towards the eye of the observer and to allow the observer to view a real world scene through the portion of the second optical element.
The display apparatus may be arranged to be used within an image intensifier unit wherein the image intensifier unit may be arranged to intersect a line of sight of an observer, between the real world scene and the second optical element.
The first and second optical elements and display source may be mounted on a helmet. The image intensifier may be mounted on to the helmet.
The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 shows in side elevation a ray trace diagram of a display apparatus according to the present invention;
Figure 2 shows in side elevation a single ray trace diagram of the display apparatus of Figure 1 ; Figures 3a to 3c are schematic diagrams of a display apparatus according to the present invention mounted on a helmet;
Figures 4a to 4c are schematic diagrams of a display apparatus according to the present invention mounted on helmet with a set of night vision goggles; Figure 5 shows in side elevation a ray trace diagram of an alternative apparatus according to the present invention.
With reference to Figure 1 , a display apparatus 10, includes a first optical element 12 and a second optical element 14 arranged to oppose the first optical element 12 such the first and second optical elements 12, 14 are air spaced. The first optical element 12 is formed from a high-index optical glass, for example N_BK7 or polycarbonate and defines a substantially flat area. Alternatively, the first optical element 12 may define a spherical, aspherical, cylindrical or freeform area. The second optical element 14 is formed from a high-index optical glass, for example N-BK7 or polycarbonate and defines a substantially spherical shaped area. Alternatively, the second optical element 14 may define an aspherical or freeform area. The second optical element 14 can be formed by a portion of a visor of a helmet or head mounted display system, not illustrated. The first and second optical elements 12, 14 are arranged to be carried and retained in the correct position in relation to one or both eyes 16 of an observer that dons the helmet.
A display source 18 under the control of a suitable processor is arranged to generate image bearing light 20 that is to convey symbology or image information to the observer. The image bearing light 20 is manipulated by a relay optical arrangement 22, which incorporates suitable lens, such that the relay optical arrangement 22 will inject image bearing light 20 between the first and second optical elements 12, 14.
The first and second optical elements 12, 14 are arranged opposed to one another such that injected image bearing light 20 is internally reflected between the first and second optical elements 12, 14 to transmit the image bearing light 20 to a position that is viewable by the eye 16 of the observer to present a substantially collimated image to the observer. It will be understood, that the observer will view a real world scene 24 along a line of sight 26 and that the image bearing light 20, being focussed at or near infinity, will appear to the observer to be overlaid upon the real world scene 24. ln this embodiment of the invention, it will be understood that the first and second optical elements 12, 14 are air spaced having a suitable optical coating thereon to reflect the image bearing light 20 to the eye 16. The optical coatings applied to the first and second optical elements 12, 14 are arranged to allow internal reflection between the first and second optical elements 12, 14 and that in the region of the eye 16, along the line of sight 26, that the observer will be able to see through the first and second optical elements 12, 14 and any optical coating carried thereon so as to be able to also view the real world scene 24.
The optical coating can be suitable a metallic or dielectric coating, for example aluminium, titanium dioxide or magnesium fluoride. It will be understood that a combination of coatings can be utilised in different regions of the coatings on the first or second optical elements 12, 14 to provide appropriate properties for that region.
The display source 18 and relay optical arrangement 22 can be carried on or incorporated within a lower section 28 of the second optical element 14. It will be understood that the first and second optical elements 12, 14 can be mounted to a helmet, not illustrated via lower section 28 of the second optical element 14 and that the mounting to the helmet can be via housing 30 for the display source 18 and relay optical arrangement 22. Referring to Figure 2, wherein like references have been used to indicate similar integers to those described with reference to Figure 1 , in operation the display apparatus 10 directs image bearing light 20, in this case indicated for a single ray, from the display source 18 via the relay optical arrangement 22 to be incident on the second optical element 14 at a given angle A measured from a normal to the second optical element 14 where the light is incident. The angle of incidence A is determined by the positioning of the relay optical arrangement 22 and display source 18 and will be greater than 0° and less than 90°, such that the image bearing light 20 is internally reflected between the first and second optical elements 12, 14 to a position in front of the eye 16. In detail, the optical coating applied to the second optical element 14, in the region that light is first incident thereon is arranged to reflect the wavelengths of the image bearing light 20 back to the first optical element 12 to be incident on the first optical element 12 at a given angle D measured from a normal to the first optical element 12 where the light is incident. The optical coating applied to the first optical element 12, in the region that light is first incident thereon, is arranged to reflect the image bearing light 20 back to the second optical element 14 to be incident on the second optical element 14 at a given angle B measured from the normal to the second optical element 14 where the light is incident. The optical coating applied to the second optical element 14, in the region that light is second incident thereon is arranged to reflect the image bearing light 20 back to the first optical element 12 to be incident on the first optical element 12 at a given angle E measured from a normal to the first optical element 12 where the light is incident. The optical coating applied to the first optical element 12, in the region that light is second incident thereon is arranged to reflect the image bearing light 20 back to the second optical element 14 to be incident on the second optical element 14 at a given angle C measured from the normal to the second optical element 14 where the light is incident. The optical coating applied to the second optical element 14, in the region that light is third incident thereon is arranged to reflect the image bearing light 20 back to the first optical element 12 to be incident on the first optical element 12 normal to the first optical element 12 where the light is incident.
The optical coatings applied to the first and second reflection regions of the first optical element 12 and the first and second reflection regions of the second optical element 14 are arranged to reflect wavelengths of light generated by the display source 18. The optical coating applied to the third reflection region of the second optical element 14 is arranged to reflect wavelengths of image bearing light 20 generated by the display source 18 and shall be optimised to allow a proportion of light from the real world scene 24 to pass therethrough. This coating can be a frequency selective coating arranged to (i) reflect a specific band of wavelengths generated by the display source 18, but to allow other wavelengths to pass therethrough or (ii) reflect a broader band of wavelengths than that generated by the display source 18, but at a lower efficiency to improve the transmission of light from the real world scene 24 through the second optical element 14. It could also be possible to provide a compromise solution incorporating a combination of arrangements (i) and (ii). If there is an optical coating carried by the first optical element 12 in the region in front of the eye 16, then this will be partially reflective to allow image bearing light 20 substantially normal to the first optical element 12 and light from the forward scene 24 to pass therethrough.
It will be understood that the shape of the second optical element 14 or a combination of the shape of the first and second optical elements 12, 14 determines the angle of incidences A, B, C, D and E for any given ray of the image bearing light 20. That is the angle of the second optical element 14 relative to the first optical element 12 for a given region will determine the angle of incidence of image bearing light 20 at that region. Furthermore, it will be noted that the shape of the second optical element 14 or the first and second optical elements 12, 14 ensured that the angle of incidence with the second optical element 14 for any given ray decreases with each subsequent reflection, i.e. the angle of incidence for angle A > B > C and that the angle of incidence with the first optical element 12 for any given ray decreases with each subsequent reflection, i.e. the angle of incidence for angle D > E until image bearing light 20 is positioned in front of the eye 16. At this region the angle of incidence with the first optical element 12 is normal to the first optical element 12.
The first optical element 12 is arranged to allow image bearing light 20 to transmit therethrough in the region of the eye 16 if the image bearing light 20 is substantially normal to the first optical element 12. This is achieved using a suitable optical coating arrangement on the first optical element 12 or ensuring that there is no optical coating on the first optical element 12 in the region of the eye 16. Alternatively, the first optical element 12 can be arranged to terminate such that it is not present in the region of the eye 16 thereby allowing the image bearing light reflected from the second optical element at angle C to follow a path coincident with the line of sight 26 of the eye 16 of the observer. Furthermore, the optical coating carried by the second optical element 14 in the region of the eye 16, i.e. along the line of sight 26 or a potential line of sight 26 is such that it reflects image bearing light 20 incident thereon, at the third reflection region of the second optical element 14 and also allows the eye of the observer to view the forward scene 24 through the second optical element 14. For example, the second optical element in the region of the third reflection can be arranged to carry a semi-silvered optical coating or angularly selective and/or graded coating.
It will be understood that the prismatic powers of first and second optical elements 12, 14 in the region arranged in front of the eye 16 can be minimised to allow the observer a clearer view of the forward scene 24. Alternatively, a make-up piece, not illustrated, can be located at the third region of the second optical element 14, the make-up piece being arranged to null the overall prismatic powers incurred by the shape of the first or second optical elements 12, 14.
Referring to Figures 3a to 3c, wherein in like references have been used to indicate similar integers to those described with reference to Figure 1 , an observer 40 that has donned a helmet 42 will be able to view a real world scene through the first and second optical elements 12, 14 of the display apparatus 10 combined with an overlaid image generated by an image source 18. The image to be conveyed to the observer is internally reflected between the first and second optical elements 12, 14 until it is in front of the eye 16 of the observer as previously described.
Referring to Figures 4a to 4c, wherein in like references have been used to indicate similar integers to those described with reference to Figures 3a to 3c, the observer 40 will be able to use the display apparatus 10 with an image intensifier unit or night vision system 44. In Figures 4a to 4c, the extremes of movement of image intensifier unit 44 from a stowed position S above the line of sight of the observer 40 so as not disposed in front of the eye 16 of the observer or to a deployed position T so as to be placed in front of the eye 16 of the observer 40. Note that the direction of travel of the image intensifier unit 44 from stowed to deployed positions, S to T, is indicated by the double headed arrow 46 in Figure 4c. As can be appreciated the image intensifier unit 44 travels from the stowed position S in the direction indicated by arrow 48 to rotate the image intensifier unit 44 and then into the final deployed position T in the direction indicated by arrow 50. The image intensifier unit 44 can be locked in either a stowed or deployed position S, T. Accordingly, the dimensions of the display apparatus 10 can be arranged to allow the observer 40 to use the display apparatus 10 with a suitable image intensifier unit or night vision system 44.
In an alternative embodiment of the invention, as shown in Figure 5, wherein like references have been used to indicate similar integers to those described with reference to Figure 1 and 2, the first and second optical elements 12, 14 can be part of a solid optical piece 60, wherein the first and second optical elements 12, 14 are formed at or near opposing sides of the optical piece 60. The image bearing light 20 is arranged to enter the optical piece 60 via an input section 62 of optical piece 60 so as to be incident on the second optical element 14 at the appropriate angle to provide total internal reflection within the optical piece 60. Otherwise, the embodiment of Figure 5 operates and is located in a similar general manner to that described with reference to Figures 1 and 2. In this case, a suitable optical coating can be formed at or near the surface of the opposing sides of the optical piece 60 to generate the first and second optical elements 12, 14 to enable total internal reflection of image bearing light 20 within the optical piece 60. The optical piece 60 can be carried by a visor of a helmet mounted display system, not illustrated. It will be understood, that the optical coating applied to create the first and second optical elements 12, 14 will allow internal reflection between the first and second optical elements 12, 14 and that in the region of the eye 16, along the line of sight 26, that the observer will be able to see through the optical piece 60 and any optical coating carried thereon or therein to form the first and second optical elements 12, 14
Furthermore, it will be understood, that a solid optical piece 60 can be formed from by filling an air spaced region between first and second optical elements 12, 14 with a suitable medium or resin having a reflective index greater than one, for example N-BK7 or polycarbonate.
It will be understood that the prismatic powers of first and second optical elements 12, 14 in the region arranged in front of the eye 16 can be minimised to allow the observer a clearer view of the forward scene 24. Furthermore, a make-up piece 64 can be located at the third region of the second optical element 14, the make-up piece 64 being arranged to null the overall prismatic powers incurred by the shape of the first or second optical elements 12, 14.
In this manner, image bearing light 20 will be internally reflected between the first and second optical elements 12, 14 until it is positioned to exit the display apparatus 10 coincident with a line of sight 26 of an observer using the display apparatus 10 and the image carried by the image bearing light 20 will appear to overlay a real world scene 24 also seen by the observer.
Furthermore, the physical space occupied by the display apparatus 10 can be arranged such that an image intensifier unit 44 can be positioned for use with the display apparatus 10.

Claims

A display apparatus for displaying an image to an observer overlaid on a real world scene, wherein the display apparatus includes: a first optical element having at least one associated reflective region arranged to reflect incident light; a second optical element having at least one associated reflective region arranged to reflect incident light; a display source arranged to generate image bearing light; wherein the first and second optical elements are arranged opposed to one another and arranged to transmit image bearing light from the display source to a position where the image bearing light is viewable by an observer overlaid on a real world scene observed through at least a portion of the second optical element and wherein the first and second optical elements are arranged such that the angle of incidence of image bearing light reduces with each successive reflection from the optical element.
A display apparatus, as claimed in Claim 1 , wherein first and second optical elements are air spaced.
A display apparatus, as claimed in Claim 1 , wherein the first and second optical elements are arranged on surfaces of or within a solid optical piece.
A display apparatus, as claimed in any preceding claim, wherein a relay optical arrangement is arranged to receive image bearing light from the display source and to output image bearing light such that the angle of incidence of the image bearing light with the surface of the second optical element is such that the image bearing light reflects towards the first optical element.
A display apparatus as claimed in any preceding claim, wherein the second optical element includes n reflective regions arranged to reflect image bearing light and the first optical element includes n-1 reflective regions arranged to reflect image bearing light towards the second optical element.
A display apparatus, as claimed in any preceding claim, wherein the second optical element include a reflective region arranged to reflect image bearing light back through a portion of the first optical element such that the image bearing light is viewable by an observer overlaid on a real world scene observed through at least a portion of the first and second optical elements.
A display apparatus, as claimed in any preceding claim, wherein the first optical element and second optical element are arranged such that image bearing light is first reflected from a first reflective region of the second element towards a first reflective region of the first optical element, the first reflective region of the first optical element is arranged to reflect image bearing light towards a second reflective region of the second optical element, the second reflective region of the second optical element is arranged to reflect image bearing light towards a second reflective region of the first optical element, the second reflective region of the first optical element is arranged to reflect image bearing light towards a third reflective region of the second optical element, the third reflective region of the second optical element is arranged to reflect image bearing light towards the eye of the observer to be viewed overlaid on a real world scene observed through at least a portion of the second optical element.
A display apparatus, as claimed in any preceding claim, wherein the angle of incidence of image bearing light with respect to the second optical element decreases with each reflection from the second optical element.
A display apparatus, as claimed in any preceding claim, wherein the angle of incidence of image bearing light with respect to the first optical element decreases with each reflection from the first optical element.
10. A display apparatus, as claimed in any preceding claim, wherein the first optical element is arranged to allow incident image bearing light substantially normal to the face of the first optical element to pass therethrough and to reflect incident image bearing light off-axis to the normal of the first optical element.
1 1 . A display apparatus, as claimed in any preceding claim, wherein the second optical element is a portion of a visor.
12. A display apparatus, as claimed in any preceding claim, wherein at least a portion of the second optical element includes a layer arranged to reflect image bearing light towards the eye of the observer and to allow the observer to view a real world scene through the portion of the second optical element.
13. A display apparatus, as claimed in any preceding claim, arranged to be used within an image intensifier unit wherein the image intensifier unit is arranged to intersect a line of sight of an observer, between the real world scene and the second optical element.
14. A display apparatus, as claimed in Claim 13, wherein the first and second optical elements and display source are mounted on a helmet.
15. A display apparatus, as claimed in either Claim 13 or Claim 14, wherein the image intensifier is mounted on to the helmet.
16. A display apparatus substantially as hereinbefore described and/or as illustrated with reference to the accompanying drawings.
PCT/GB2013/050918 2012-04-19 2013-04-10 Improvements in or relating to display apparatus WO2013156756A1 (en)

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CN107367842A (en) * 2017-08-30 2017-11-21 深圳超多维科技有限公司 A kind of head-mounted display apparatus

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US20020105737A1 (en) * 1997-05-07 2002-08-08 Junko Takahashi Prism optical element, image observation apparatus and image display apparatus

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GB9208705D0 (en) * 1992-04-22 1992-07-22 Smiths Industries Plc Head-mounted display assemblies
DE102007046505B4 (en) * 2007-09-28 2019-08-01 Carl Zeiss Ag Display device and stereo display module

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EP0790516A1 (en) * 1996-02-13 1997-08-20 Olympus Optical Co., Ltd. Image display apparatus
US20020105737A1 (en) * 1997-05-07 2002-08-08 Junko Takahashi Prism optical element, image observation apparatus and image display apparatus
US20020060851A1 (en) * 2000-09-27 2002-05-23 Shoichi Yamazaki Image display apparatus and head mounted display using it

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