Projection display

#This invention relates to a projection display for displaying an image to a viewer which is particularly, but not exclusively, suitable for use in a head up display, a helmet mounted display or a head mounted display.

#Traditionally head up displays, which may be used in an aircraft, as shown in FIG. 1 of the accompanying drawings, use a convention spherical lens system 1 to generate a collimated display from an image provider such as a cathode ray tube 2. The light rays emanating from the spherical lens system 1 are reflected by a conventional fold mirror 3 through a spherical exit lens system 4 and from there passed to a combiner 5 from which the image is reflected to provide a collimated display to the viewer 6 such as a pilot of an aircraft. Thus with these conventional displays the collimating optics used, that is the spherical lens system 1 and spherical exit lens system 4 are unnecessarily large and bulky which is undesirable. For example a thirty degree field of view to be displayed to the viewer 6 may require a six inch diameter exit lens system 4. This means that the physical size of the conventional head up display as shown in FIG. 1, which includes the combiner 5 for overlaying the projected display to be viewed by a viewer 6 looking through the combiner 5, may limit the use of such a head up display in a cockpit area with insufficient space to accommodate such a head up display.

#There is thus a need for a projection display which is smaller in size than conventional in order to fit into smaller spaces and thus be more suitable for restricted space environments such as an aircraft cockpit, a helmet mounted display or a head mounted display.

#The invention will now be described by way of example only, with reference to the accompanying drawings, in which:

#FIG. 1 is a schematic illustration of a prior art conventional projection display in the form of a head up display;

#FIG. 2 is a partial view to an enlarged scale taken in the direction A of a projection display according to the present invention as illustrated in FIG. 3;

#A projection display for displaying an image to a viewer 6 according to the invention as illustrated in FIGS. 2 to 6 of the accompanying drawings in general uses waveguiding techniques to generate a collimated display subtending a large exit pupil at the point of viewer 6 and a large field of view while using a small image-providing light source device. As illustrated, the projection display of the invention uses a rod-like substantially rectangular cross-section waveguide 7 made of light transmissive material such as glass or plastics and a plate-like waveguide 8 made from a light transmissive and transparent material such as glass or plastics.

#In more detail, a projection display according to one aspect the present invention as illustrated in FIGS. 2 and 3, wherein like references have been used to indicate similar integers in both FIGS. 2 and 3, additionally includes an image-providing light source device located at a first side 9 of the rod-like waveguide to inject image bearing light into the rod-like waveguide 7 through the first side 9.

#The image-providing light source device includes an image generating light source 10 preferably in the form of a micro-display to provide a display of information. Additionally the image-providing light source device includes an optical means 11 located between the image generating light source 10 and the first side 9 of the rod-like waveguide 7. The optical means 11 is operable to collimate light received from the image generating light source 10 and inject the collimated image bearing light into the rod-like waveguide 7 through the first side 9 thereof. The optical means 11 preferably is of a small size, typically less than 25 millimeters in diameter, and is used to collimate the light received from the image generating light source 10. The collimated light produced by the optical means 11 has a small exit pupil and is therefore fed into the rod-like waveguide 7 which performs the function of stretching the horizontal pupil. The output from the rod-like waveguide 7 is fed into the plate-like waveguide 8 which stretches the vertical pupil view and also acts as a combiner for the display. In this manner, the display information provided to the viewer 6 looking through the plate-like waveguide 8 subtends a large exit pupil and a large field of view whilst using a small optical means 11 and a small image generating light source 10 such as a micro display. This enables the projection display of the invention to be very compact in comparison with conventional displays.