Waveguide-based transmitters with adjustable lighting

1. An optical transmission device, comprising:

a waveguide comprising a transparent medium having mutually-parallel first and second surfaces arranged so that light propagates within the waveguide by internal reflection between the first and second surfaces;

at least one light source, which is configured to inject coherent light into the waveguide;

a first array of diffractive structures applied to the waveguide and configured to couple respective beams of the coherent light out through the first surface of the waveguide; and

a second array of tunable optical phase modulators, which are overlaid on respective ones of the diffractive structures in the first array and are configured to apply different respective phase shifts to the respective beams, thereby modulating a far-field light pattern formed by interference between the beams.

2. The device according to claim 1 , wherein the first and second arrays are two-dimensional arrays.

3. The device according to claim 2 , wherein the waveguide comprises a slab of the transparent medium.

4. The device according to claim 3 , wherein the at least one light source is configured to inject multiple beams of the coherent light into the slab so that the beams propagate within the slab along respective beam paths that are aligned to impinge on different respective groups of the diffractive structures in the first array.

5. The device according to claim 3 , and comprising a beam-splitting structure, which is configured to divide the coherent light injected by the at least one light source into multiple beams, which propagate within the slab along respective beam paths that are aligned to impinge on different respective groups of the diffractive structures in the first array.

6. The device according to claim 2 , wherein the waveguide comprises multiple beam-guiding channels between the first and second surfaces, and wherein the diffractive structures are applied to the beam-guiding channels.

7. The device according to claim 1 , and comprising a further diffractive structure applied to the waveguide to couple the coherent light from the at least one light source through one of the first and second surfaces into the waveguide.

8. The device according to claim 1 , wherein the diffractive structures comprise surface-relief phase structures having dimensions smaller than a wavelength of the coherent light.

9. The device according to claim 1 , wherein the tunable optical phase modulators comprise electro-optical modulators.

10. The device according to claim 9 , wherein the electro-optical modulators comprise liquid crystal cells.

11. The device according to claim 1 , wherein the second array extends over an area of the first surface of the transparent medium, and the tunable optical phase modulators cover a part of the area with a fill factor that is less than 20%.

12. The device according to claim 1 , and comprising a controller coupled to apply control signals to the optical phase modulators to tune the respective phase shifts applied by the optical phase modulators to the respective beams.

13. The device according to claim 12 , wherein the far-field light pattern comprises a third array of spots, and wherein the controller is configured to tune the respective phase shifts to shift the spots.

14. The device according to claim 12 , wherein the far-field light pattern comprises a third array of spots, and wherein the controller is configured to tune the respective phase shifts to change a number of the spots in the third array.

15. The device according to claim 12 , wherein the far-field light pattern comprises a third array of spots, and wherein the controller is configured to tune the respective phase shifts to change respective intensities of the spots.

16. A method for optical transmission, comprising:

providing a waveguide comprising a transparent medium having mutually-parallel first and second surfaces arranged so that light propagates within the waveguide by internal reflection between the first and second surfaces;

injecting coherent light into the waveguide;

applying a first array of diffractive structures to the waveguide to couple respective beams of the coherent light out through the first surface of the waveguide; and

applying, by a second array of tunable optical phase modulators, which are overlaid on respective ones of the diffractive structures in the first array, different respective phase shifts to the respective beams, thereby modulating a far-field light pattern formed by interference between the beams.

17. The method according to claim 16 , wherein injecting the coherent light comprises applying a further diffractive structure to the waveguide to couple the coherent light from a light source through one of the first and second surfaces into the waveguide.

18. The method according to claim 16 , wherein the diffractive structures comprise surface-relief phase structures having dimensions smaller than a wavelength of the coherent light.

19. The method according to claim 16 , wherein the tunable optical phase modulators comprise electro-optical modulators.

20. The method according to claim 16 , wherein applying the different respective phase shifts comprises applying control signals to the optical phase modulators to tune the respective phase shifts applied by the optical phase modulators to the respective beams.