Compact holographic illumination device
There is provided a color sequential illumination device comprising in series: first and second light sources; a condenser lens; and a grating device. The grating device comprises at least one Bragg grating. The condenser lens directs light from the first and second sources into the grating device at first and second incidence angles respectively. The grating device diffracts light from the first and second sources into a common direction. Desirably, the Bragg gratings are Electrically Switchable Bragg Gratings. In one embodiment of the invention the light sources are Light Emitting Diodes. Alternatively lasers may be used.
1. An illumination device comprising in series:
at least first and second light sources;
a lens;
a first grating layer;
a second grating layer;
a half wave plate;
a third grating layer; and
a fourth grating layer,
wherein said third grating layer and said first grating layer have identical optical prescriptions and said fourth grating layer and said second grating layer have identical optical prescriptions,
wherein each said grating layer is operative to diffract light from at least one source into an illumination direction,
wherein said lens collimates and directs a first polarization of light from said first source into a direction at a first angle to said illumination direction and collimates and directs a first polarization of light from said second source into a direction at second angle to said illumination direction.
2. The apparatus of claim 1 , wherein at least one of said first or second grating layer multiplexes gratings for diffracting light from at least two of said sources into an illumination direction.
3. The apparatus of claim 1 , wherein said first grating layer, said second grating layer, said half wave plate, said third grating layer and said fourth grating layer are configured as stack of layers.
4. The apparatus of claim 1 , wherein said light sources are characterized by at least two different wavelengths.
5. The apparatus of claim 1 , wherein said illumination direction is normal to planes of said grating layers.
6. The apparatus of claim 1 , wherein said grating layers include at least one pair of Bragg gratings of identical prescription.
7. The apparatus of claim 1 wherein said grating layers include at least one pair of switchable gratings of identical prescription.
8. The apparatus of claim 1 wherein said grating layers include at least one pair of Electrically Switchable Bragg Gratings of identical prescription.
9. The apparatus of claim 1 wherein each said grating layer has a high diffraction efficiency for said first polarization light and a low diffraction efficiency for light having a polarization orthogonal to said first polarization.
10. The apparatus of claim 1 wherein each said grating layer is a switchable grating, wherein at least two sources of different wavelengths are provided and wherein said source and said gratings are switched on and off synchronously to provide color sequential illumination.
11. The apparatus of claim 1 wherein said sources are Light Emitting Diodes.
12. The apparatus of claim 1 wherein said sources are lasers.
13. The apparatus of claim 1 used to illuminate a microdisplay.
14. The apparatus of claim 1 used to color-sequentially illuminate a microdisplay.
15. The apparatus of claim 1 further comprising a beam shaping optical element operative to modify at least one of the intensity profile or cross section geometry of said light.
16. The apparatus of claim 1 further comprising at least one light guiding element for controlling the direction of light from a source.
17. The apparatus of claim 1 further comprising a dichroic beamsplitter.
18. The apparatus of claim 1 wherein said first and second light sources are disposed on a curved substrate.
19. The apparatus of claim 1 further comprising a layer for controlling stray light.
20. The apparatus of claim 1 further comprising a beam folding mirror.