WO2001081978A1

WO2001081978A1 - Improvements in or relating to display illuminators

Info

Publication number: WO2001081978A1
Application number: PCT/GB2001/001565
Authority: WO
Inventors: Michael David Simmonds
Original assignee: Bae Systems Electronics Limited
Priority date: 2000-04-20
Filing date: 2001-04-05
Publication date: 2001-11-01
Also published as: GB0009781D0; GB2361573A; AU2001244408A1

Abstract

An illuminator (30) for a primary display (31) has a light source (32) that provides light (33) which traverses an optical pathway (34a to 34c). The illuminator (30) also comprises, along the pathway (34a to 34c), a polariser (35), a field lens (37), a reflective flat panel display (38) and a second polariser (39). Light (33) is linearly polarised by the first polariser (35) to produce polarised light (36) that passes through the lens (37) which focusses the light (36) onto a surface (40) of the display (38). The first polariser (35) is arranged to polarise the light (33) such that it will pass through the second polariser (39) when reflected from the flat panel display (38). The surface (40) comprises a plurality of pixels, each of which are capable of rotating the polarisation of any light (36) falling on the pixel. When an activated pixel rotates the polarisation of light (36) to a given orientation it will not be capable of passing through the second polariser (39) upon reflection from the surface (31). Light passing through the second polariser (39) passes to the screen (44) of display (31).

Description

IMPROVEMENTS IN OR RELATING TO DISPLAY ILLUMINATORS

The present invention relates to an illuminator for a screen of a display.

The primary function of an aircrew helmet is to protect the user. Helmet mounted displays are now an important element of the cockpit display system providing

information such as aircraft attitude and status to a user, typically a pilot, of the aircraft.

However, the advent of helmet mounted displays places additional constraints on the

helmet. Development of a helmet mounted display is a demanding task if operational

benefits are to be realised without affecting user safety.

Typically a helmet mounted display comprises one or more cathode ray tubes, each

having an associated high voltage power supply, arranged to generate an image which is

conveyed to one or both eyes of the user via an associated optical relay system. The

helmet is usually adapted to allow each cathode ray tube and its optical relay system to

be fitted to the helmet. It will be appreciated that the mass of each helmet mounted

cathode ray tube and its associated power supply will generate a given moment on the

head and a neck pivot position of a user that wears the helmet.

The mass of the helmet is a particular concern when using such helmet mounted displays in an aircraft capable of performing high gravitational force manoeuvres. In general, most

current in service helmets were not initially designed for such applications and they have

been adapted by altering the external shape of the helmet to facilitate the fitting of the

helmet mounted display. It has been found that the mass and the poor centre of gravity of the mass of the helmet mounted display induces user fatigue as a result of the user

having to support the mass about a neck pivot position. That is any unbalanced mass will

result in fatigue being induced on the user. Furthermore, any unbalanced mass, even of

small magnitude, could be a danger to the user under high gravitational force manoeuvres. A further point to be considered is that the safety of the user can also be

compromised during ejection from the aircraft at high speed, as the mass of the helmet

and helmet mounted display may cause damage to a user and the external shape of the

helmet may cause excessive wind drag.

It is an object of the present invention to obviate or mitigate the disadvantages associated

with the prior art.

According to the present invention an illuminator for a screen of a primary display

comprises a light source, a flat panel display having a surface arranged to rotate the

polarisation of incident light at, and reflect light from, at least one active position, along

a first optical path to the screen of the primary display, a first polariser arranged to

polarise light from the light source and a second polariser arranged to polarise light

reflected from the surface of the flat panel display, wherein the light from the light source

is arranged to propagate along a second optical path to the surface of the flat panel display, the second optical path being inclined to the first optical path.

It should be noted that polarised light is conveyed to the surface of the flat panel display

along a secondary optical axis, that is polarised light is provided off-axis. In this manner,

the primary display is rendered smaller and lighter with respect to a conventional cathode ray tube display which incorporates an associated high voltage power supply.

Furthermore, by the activation of one or more active positions of the flat panel display, a desired image can be conveyed to the screen of the primary display. The activation of

the desired positions can be controlled by a suitable processor.

Preferably, the polarisation of the first and second polarisers may be mutually orthogonal.

The flat panel display may be a reflective liquid crystal display.

The light source may be arranged to provide light comprising at least two colours of the

visual light spectrum. In this manner, an image comprising more than one colour may

be conveyed to the screen of the primary display. Preferably, the light source may be

arranged to generate three colours such that a full coloured image may be conveyed to the

screen of the primary display. This is advantageous over the prior art as such helmet

mounted displays can normally only provide a single colour display so as to minimise the

mass of cathode ray tube and associated high voltage power supply.

Preferably, in one embodiment a reflective surface may be arranged to reflect polarised light from the first polariser onto the surface of the flat panel display. The reflective

surface may be a fold mirror.

A first field lens may be arranged to collimate polarised light from the first polariser

before it illuminates the surface of the flat panel display and to focus light reflected from

the surface of the flat panel display along the first optical path. A relay lens arrangement may be arranged to convey light reflected from the surface of the flat panel display to the

screen of the primary display. The relay lens arrangement may be colour corrected. A

second field lens may be arranged in the first optical path to provide a normal illumination of the screen of the primary display. Alternatively, a second field lens may

be arranged in the first optical path to couple the numerical aperture of the illuminator to an existing optical system. A surface relief diffuser may be arranged in the first optical

path to couple the numerical aperture of the existing optical system to the relay lens

arrangement.

Preferably, the illuminator may be adapted to be mounted to a helmet. In this manner,

the lower mass of the illuminator, and hence the lower mass of the primary display, can

be arranged to have a better centre of gravity when mounted to the helmet, thereby

reducing the mass of the helmet and the moment about a neck pivot position of a user wearing the helmet. The smaller illuminator, and hence the smaller display, may be

incorporated within the helmet with less or no modification to its external shape, thereby

reducing wind drag on the helmet if the user were to eject from the aircraft at high speed.

Alternatively, the illuminator may be used within a head up display. As a further alternative, the illuminator may be used within a head down display.

According to another embodiment a helmet comprises an illuminator as described above. In this case, the illuminator may be arranged to be mounted between the helmet and a

visor associated with the helmet. According to a further embodiment a head up display

comprises an illuminator as described above. According to another embodiment a head down display comprises an illuminator as described above.

The invention will now be described, by way of example only, with reference to the

accompanying drawings, in which:

Figure 1 illustrates a ray trace diagram of an off-axis optical system according to one

embodiment of the invention;

Figure 2 illustrates a ray trace diagram of an alternative off-axis optical system to that

shown in Figure 2;

Figure 3 illustrates a helmet mounted display according to the invention;

Figure 4 illustrates a head up display according to the invention, and

Figure 5 illustrates a head down display according to the invention.

Referring to Figure 1, an illuminator 30 for a primary display 31 comprises a light source

32 arranged to provide light 33, in this instance all three colours of the visual spectrum,

and the light 33 is arranged to traverse an optical pathway 34a to 34c, indicated by a

plurality of ray traces. The illuminator 30 also comprises, along the pathway 34a to 34c, a polariser 35 arranged to polarise the light 33 so as to generate polarised light 36, a first

field lens 37, a reflective flat panel display 38 and a second polariser 39.

In operation, the light source 32 generates light 33 which is linearly polarised by the first polariser 35 to produce polarised light 36. The polarised light 36 then passes through

the first field lens 37 that is arranged to focus the polarised light 36 onto a surface 40 of

the reflective flat panel display 38.

The first polariser 35 is arranged to linearly polarise the light 33 such that the polarised

light 36 can pass through the second polariser 39 when reflected from the flat panel

display 38. The surface 40 comprises a plurality of pixels, each of which are capable of

rotating the polarisation of any polarised light 36 falling on the pixel. In one embodiment, it will be understood that if an activated pixel rotates the polarisation of the

polarised light 36 to a given orientation that it will not be capable of passing through the

second polariser 39 upon reflection from a reflective surface 41 of the reflective flat panel

display 38. Alternatively, in another embodiment, if an activated pixel rotates the polarisation of the polarised light 36 to a given orientation the second polariser 39 can

be arranged to allow that polarised light 36 to pass through upon reflection from the

reflective surface 41 of the reflective flat panel display 38. Accordingly, by addressing

desired pixels on the surface 40 using a processor 42, it is possible to determine which

pixels of the surface 40 allow reflection of the polarised light 36 through the second polariser 39. In this manner, an image can be conveyed to the primary display 31.

Polarised light 36 which is reflected from the reflective surface 41 of the flat panel

display 38 is focussed by the first field lens 37 through a relay lens arrangement 43 which is arranged to project the polarised light 36 through the second polariser 39 and onto a screen 44 of the display 31. A second field lens 45 can be arranged either to provide a normal illumination of the

screen 44 or to efficiently couple the numerical aperture of the illuminator 30 to an existing optical system, not illustrated. Furthermore, in the latter case, a surface relief diffuser 46 can also be arranged to efficiently couple the numerical aperture of an existing

optical system to the numerical aperture of the relay lens arrangement 43.

It should be noted, that light 33 is generated off-axis to a first optical path 47 through the

illuminator 30. That is the light 33 is generated and polarised by first polariser 35 to form

polarised light 36 which propagates along a second optical path 48 which is inclined with

respect to the first optics path 47. Light 33 can be injected into the illuminator 30 using

a fibre optical lead, not illustrated, connected at one end to one or more coloured lasers,

e.g. red, green and/or blue, within the visual spectrum and at the other end to the light

source 32. Alternatively, the coloured lasers can be replaced with light emitting diodes

or the light source 32 can comprise one or more light emitting diodes arranged to

generate the light 33.

Referring to Figure 2, an illuminator 50 for a primary display 51 comprises a light source

52 arranged to provide light 53, in this instance all three colours of the visual spectrum,

and the light 53 is arranged to traverse an optical pathway 54a to 54c, indicated by a

plurality of ray traces. The illuminator 50 also comprises, along the pathway 54a to 54c,

a polariser 55 arranged to polarise the light 53 to generate polarised light 56, a reflective surface 57, a first field lens 58, a reflective flat panel display 59 and a second polariser 60. In operation, the light source 52 generates light 53 which is linearly polarised by the first

polariser 55 to produce polarised light 56. The polarised light 56 is then reflected by the reflective surface 57 through the first field lens 58 that is arranged to focus the polarised

light 53 onto a surface 61 of the reflective flat panel display 59.

The first polariser 55 is arranged to linearly polarise the light 53 such that the polarised

light 56 can pass through the second polariser 60 when reflected from the flat panel

display 59. The surface 61 comprises a plurality of pixels, each of which are capable of

rotating the polarisation of any polarised light 56 falling on the pixel. In one embodiment,

it will be understood that if an activated pixel rotates the polarisation of the polarised

light 56 to a given orientation that it will not be capable of passing through the second

polariser 60 upon reflection from a reflective surface 62 of the reflective flat panel display 59. Alternatively, in another embodiment, if an activated pixel rotates the

polarisation of the polarised light 56 to a given orientation the second polariser 60 can

be arranged to allow that polarised light 56 to pass through upon reflection from the

reflective surface 62 of the reflective flat panel display 59. Accordingly, by addressing

desired pixels on the surface 61 using a processor 63, it is possible to determine which

pixels of the surface 61 allow reflection of the polarised light 56 through the second polariser 60. In this manner, an image can be conveyed to the primary display 51.

Polarised light 56 which is reflected from the reflective surface 62 of the flat panel

display 59 is focussed by the first field lens 58 via reflection from the reflective surface 57 through a relay lens arrangement 64 which is arranged to project the polarised light

56 through the second polariser 60 and onto a screen 65 of the display 51. A second field lens 66 can be arranged either to provide a normal illumination of the

screen 65 or to efficiently couple the numerical aperture of the illuminator 50 to an existing optical system, not illustrated. Furthermore, in the latter case, a surface relief

diffuser 67 can also be arranged to efficiently couple the numerical aperture of an existing

optical system to the numerical aperture of the relay lens arrangement 64.

It should be noted, that light 53 is generated off-axis to a first optical path 68 through the

illuminator 50. That is the light 53 is generated and polarised by first polariser 55 to form

polarised light 56 which propagates along a second optical path 69 which is inclined with respect to the first optics path 68. Light 53 can be injected into the illuminator 50 using

source 52. Alternatively, the coloured lasers can be replaced with light emitting diodes

or the light source 52 can comprise one or more light emitting diodes to generate the light

53.

In Figure 3, a helmet 60 having a visor 61 is adapted to fit a user 62. The helmet 60 has

an illuminator 63, as described with reference to Figures 1 or 2, positioned such that light

64 provided by a primary display of the illuminator 63 is reflected from an internal surface of the visor 61 to an eye 65 of the user 62. In this manner, the user 62 can view

a scene through the visor 61, along a line of sight 66, and the light 64 forming an image will appear to be superimposed on the scene.

In Figure 4, a combiner element 70 is adapted to reflect light 71 from a primary display of an illuminator 72, as described with reference to Figures 1 or 2, to a eye 73 of a user

74 so that the user can view light 71 in the form of an image from the primary display, along a line of sight 75, superimposed with a scene through the combiner element 70.

In Figure 5, an illuminator 80, as described with reference to Figures 1 and 2, is provided

off a primary line of sight 81 of an eye 82 of a user 83 such that the user 83 is required

to look away from the primary line of sight 81, in this case downwardly, to view light 84

from a primary display of the illuminator 80.

Claims

1. An illuminator for a screen of a primary display, comprising

a light, a flat panel display having a surface arranged to rotate the polarisation of incident

light at, and reflect light from, at least one active position along a first optical

path to the screen of the primary display, a first polariser arranged to polarise light from the light source, and

a second polariser arranged to polarise light reflected from the surface of the flat

panel display, wherein the light from the light source is arranged to propagate along a second

optical path to the surface of the flat panel display, the second optical path being

inclined to the first optical path.

2. An illuminator, as in Claim 1, wherein the polarisation of the first and second

polarisers are mutually orthogonal.

3. An illuminator, as in Claims 1 or 2, wherein the flat panel display is a reflective liquid crystal display.

4. An illuminator, as in any preceding claim, wherein the light source is arranged to

provide light comprising at least two colours of the visual light spectrum.

5. An illuminator, as in any preceding claim, wherein a reflective surface is arranged to reflect polarised light from the first polariser onto the surface of the flat panel

display.

6. An illuminator, as Claim 5, wherein the reflective surface is a fold mirror.

7. An illuminator, as in any preceding claim, wherein a first field lens is arranged

to collimate polarised light from the first polariser before it illuminates the

surface of the flat panel display and to focus light reflected from the surface of the

flat panel display along the first optical path.

8. An illuminator, as in any preceding claim, wherein a relay lens arrangement is

arranged to convey light reflected from the surface of the flat panel display to the

screen of the primary display.

9. An illuminator, as in Claim 8, wherein the relay lens arrangement is colour

corrected.

10. An illuminator, as in any preceding claim, wherein a second field lens is arranged

in the first optical path to provide a normal illumination of the screen of the

primary display.

11. An illuminator, as in any one of Claims 1 to 9, wherein a second field lens is

arranged in the first optical path to couple the numerical aperture of the

illuminator to an existing optical system.

12. An illuminator, as in Claims 9 to 11, wherein a surface relief diffuser is arranged

in the first optical path to couple the numerical aperture of the existing optical

system to the relay lens arrangement.

13. An illuminator, as in any preceding claim, adapted to be mounted to a helmet.

14. An illuminator, as in Claims 1 to 12, used within a head up display.

15. An illuminator, as in Claims 1 to 12, used within a head down display.

16. An illuminator substantially as illustrated in and/or described with reference to the accompanying drawings.

17. A helmet comprising an illuminator as in Claims 1 to 13.

18. A helmet, as in Claim 17, wherein the illuminator is arranged to be mounted

between the helmet and a visor associated with the helmet.

19. A head up display comprising an illuminator as in Claims 1 to 12.

20. A head down display comprising an illuminator as in Claims 1 to 12.