Method and optical system for coupling light into a waveguide
View Patent ↗A method and optical system for coupling light from an incoming light wave (WI) into a waveguiding substrate (S) arranges the light wave (WI) to interact with a diffractive in-coupling grating element or elements (IG) arranged on or embedded within the substrate (S) and arranged to couple the energy from the light wave (WI) into a waveguided light wave (WG). The polarization state of the light wave (WI) is converted after its first interaction (D 1 ) with the in-coupling grating element/elements (IG) and before a second interaction (D 2 ) with the grating element/elements (IG) takes place. The method minimizes any “reverse” diffractions, which would direct light back towards the front-end optics and therefore to increase the width W of the in-coupling grating/gratings (IG). Preferred embodiments include diffractive beam expanders for virtual displays.
1. A method comprising:
arranging an incoming light wave to interact with a diffractive in-coupling grating element or elements arranged on or embedded within a planar waveguiding substrate and arranged to couple energy from said incoming light wave into a waveguided light wave propagating within said substrate, and
converting the polarization state of the light wave after its first interaction with said in-coupling grating element or elements and before a second interaction with said in-coupling grating element or elements takes place.
2. A method according to the claim 1 , wherein the polarization state of the light wave is converted from TE polarization to TM polarization.
3. An apparatus comprising:
a diffractive in-coupling grating element or elements arranged on or embedded within a planar waveguiding substrate and arranged to interact with said incoming light wave in order to couple energy from said incoming light wave into a waveguided light wave propagating within said substrate, and
a polarization converter to convert the polarization state of the light wave after its first interaction with said in-coupling grating element or elements and before a second interaction with said in-coupling grating element or elements takes place.
4. An optical system according to the claim 3 , wherein the polarization converter is arranged to change the polarization state of the light wave from TE polarization to TM polarization.
5. An optical system according to the claim 3 , wherein the polarization converter comprises at least one polarization retarding layer arranged on at least one interface of the waveguiding substrate.
6. An optical system according to the claim 5 , wherein the polarization retarding layer/layers is/are arranged to give rise to the total internal reflections required for waveguiding the light wave within the substrate.
7. An optical system according to the claim 3 , wherein the polarization converter is arranged within the substrate.
8. An optical system according to the claim 3 , wherein the polarization converter is arranged to comprise the in-coupling grating element or elements in a combined structure.
9. An optical system according to the claim 3 , wherein the period of the in-coupling grating/gratings is in the order of the wavelength of the incoming light wave to substantially allow only first diffraction orders in the first interaction with said grating/gratings.
10. An optical system according to the claim 3 , wherein the in-coupling grating/gratings have substantially binary grating profile/profiles.
11. An optical system according to the claim 3 , wherein the in-coupling grating/gratings have a aspect ratio value less than 50%.
12. An optical system according to the claim 3 , wherein the in-coupling grating/gratings operate in reflective mode.
13. An optical system according to the claim 12 , wherein the in-coupling grating/gratings comprise a reflection coating/coatings.
14. An optical system according to the claim 3 , wherein the in-coupling grating/gratings operate in transmissive mode.
15. An optical system according to the claim 3 , wherein the substrate material is a high refractive index plastic.
16. An optical system according to the claim 3 , wherein said optical system comprises further a diffractive out-coupling grating element or elements to couple energy from the waveguided light wave out from the substrate and arranged to function as a diffractive beam expander.
17. An optical system according to the claim 16 , wherein said diffractive beam expander is used in a virtual display device.
18. An apparatus comprising:
means embedded within a planar waveguiding substrate and arranged for interacting with an incoming light wave in order to couple energy from said incoming light wave into a waveguided light wave propagating within said substrate, and
means for converting the polarization state of the light wave after its first interaction with said means for interacting and before a second interaction with said means for interacting takes place.
19. An apparatus according to claim 18 , wherein the means for converting are arranged to change the polarization state of the light wave from TE polarization to TM polarization.