Image projector using a phase image generator
An image projector with a high optical efficiency projects an image at an arbitrary distance from an observer. The image projector includes an illumination module having at least one spatially coherent light source; a phase image generator with an array of optical phase shifting elements; an electronic image controller connected electrically to the phase image generator; and a waveguide which includes at least one embedded partial reflector. The waveguide may be positioned either between the illumination module and the waveguide, or between the waveguide and the observer. The phase image generator may include phase shifts for canceling speckle, correcting optical aberrations, and/or compensating interference caused by light rays having different optical path lengths.
1. An image projector comprising:
an illumination module comprising at least one spatially coherent light source;
a phase image generator comprising an array of optical phase shifting elements;
an electronic image controller in electrical communication with the phase image generator; and
a waveguide interposed between the illumination module and an observer and comprising at least two embedded partial reflectors;
wherein the phase image generator is interposed between the illumination module and the waveguide, or between the waveguide and the observer, and the phase image generator includes phase shifts for correcting optical aberrations.
2. The image projector of claim 1 wherein the phase image generator is positioned at an entrance pupil of the waveguide or at an image of the entrance pupil.
3. The image projector of claim 1 wherein the phase image generator generates at least two non-zero diffraction orders which are coupled into the waveguide.
4. The image projector of claim 1 wherein the phase image generator is reflective and a positive lens is interposed between the waveguide and the phase image generator or between the phase image generator and the observer.
5. The image projector of claim 1 wherein the phase image generator comprises a component selected from a group consisting of a liquid crystal display, a liquid crystal on silicon device, a holographic optical element, and a spatial light modulator.
6. The image projector of claim 1 wherein the phase image generator includes time-varying phase shifts for canceling speckle.
7. The image projector of claim 1 wherein the phase image generator includes phase shifts for compensating interference caused by light rays having different optical path lengths.
8. The image projector of claim 1 wherein the at least one spatially coherent light source has an intensity which is modulated in time.
9. The image projector of claim 1 wherein the at least one spatially coherent light source comprises a component selected from a group consisting of a laser diode, a diode pumped solid-state laser, and a super-luminescent light emitting diode (SLED).
10. The image projector of claim 1 wherein the illumination module comprises at least two light sources having different wavelengths.
11. The image projector of claim 1 wherein the illumination module further comprises a focusing optical element which comprises a lens, a mirror, or a biconic optical component.
12. The image projector of claim 1 wherein the at least one embedded partial reflector comprises a component selected from a group consisting of a diffraction grating, a diffractive optical element, and a partially reflecting surface.
13. The image projector of claim 1 further comprising an image amplitude modulator.
14. The image projector of claim 1 further comprising an optical beam splitter which comprises a polarizing beam splitter.
15. The image projector of claim 1 further comprising a microlens array and/or a diffuser which is an etendue expander.
16. The image projector of claim 1 further comprising one or more scanning mirrors.