Method and optical system for coupling light into a waveguide

• US 20050002611A1
• Filed: 05/11/2004
• Published: 01/06/2005
• Est. Priority Date: 05/13/2003
• Status: Active Grant

• Current Assignee: Magic Leap, Inc.
• Original Assignee: Nokia Corporation
• Inventors: Levola, Tapani
• Granted Patent: US 7,181,108 B2
• Time in Patent Office: Days
• US Class Current: 385/37
• CPC Class Codes: G02B 2006/12107 Grating
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 6/105 having optical polarisation effects
• CPC Class Codes: G02B 6/126 using polarisation effects G02B6/1226 takes precedence
• CPC Class Codes: G02B 6/29328 Diffractive elements operating in reflection
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence

Abstract

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 (D1) with the in-coupling grating element/elements (IG) and before a second interaction (D2) 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.

Claims

1. A method for coupling light from an incoming light wave into a light-transmittive, preferably planar waveguiding substrate, said method comprising the step of

arranging the incoming light wave to interact with a diffractive in-coupling grating element or elements arranged on or embedded within said substrate and arranged to couple the energy from said incoming light wave into a waveguided light wave propagating within said substrate wherein the method comprises further at least the step of

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 optical system for coupling light from an incoming light wave into a light-transmittive, preferably planar waveguiding substrate, said system comprising

a diffractive in-coupling grating element or elements arranged on or embedded within said substrate and arranged to interact with said incoming light wave in order to couple the energy from said incoming light wave into a waveguided light wave propagating within said substrate wherein the optical system comprises further at least

polarization conversion means 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 conversion means are 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 conversion means comprise 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 conversion means are arranged within the substrate.

8. An optical system according to the claim 3, wherein the polarization conversion means are 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.