Method and system for beam expansion in a display device

• US 20040062502A1
• Filed: 09/30/2002
• Published: 04/01/2004
• Est. Priority Date: 09/30/2002
• Status: Active Grant

• Current Assignee: Magic Leap, Inc.
• Original Assignee: Nokia Corporation
• Inventors: Levola, Tapani
• Granted Patent: US 6,805,490 B2
• Time in Patent Office: Days
• US Class Current: 385/129
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 6/0016 Grooves, prisms, gratings, scattering particles or rough surfaces
• CPC Class Codes: G02B 6/0076 Stacked arrangements of multiple light guides of the same or different cross-sectional area
• CPC Class Codes: G02B 6/29323 Coupling to or out of the diffractive element through the lateral surface of the light guide evanescent grating couplers G02B6/29332
• CPC Class Codes: G02B 6/29329 Diffractive elements operating in transmission
• CPC Class Codes: G02B 6/29371 operating principle based on material dispersion
• CPC Class Codes: G02B 6/4215 the intermediate optical elements being wavelength selective optical elements, e.g. variable wavelength optical modules or wavelength lockers G02B6/4246 takes precedence
• CPC Class Codes: G02B 6/4298 coupling with non-coherent light sources and/or radiation detectors, e.g. lamps, incandescent bulbs, scintillation chambers

Abstract

A planar substrate having a first diffractive element for coupling light waves of different colors into the substrate and guiding the light waves by successive internal reflections. A second diffractive element, disposed on the substrate, causes the guided light waves to be partially transmitted out of the substrate where the light waves encounter the second diffractive element. Because light waves of each color are reflected at different reflection angles, the light waves with smaller reflection angles encounter the second diffractive element at more locations than those with larger reflection angles, resulting in color non-uniformity in the light transmitted out from the substrate surface. One or more interfaces are provided between the surfaces of the substrate to selectively reflect the light waves having larger reflection angles toward the second diffraction element, so that light waves of different colors encounter the second diffraction element substantially at the same number of locations.

Claims

1. An optical device (10) comprising:

a substantially planar light-guiding member (60) having a first surface (32) and an opposing second surface (52), and

a light coupling structure (H1) positioned relative to the light-guiding member for coupling light waves (70) into the light-guiding member, the light-guiding member guiding the light waves (72, 74) within the light-guiding member based substantially on successive internal reflections as the light waves travel between the first and second surfaces, the light waves comprising at least first light waves of a first color (λ

₁) and second light waves of a second different color (λ

₂), wherein the first light waves are internally reflected at a first reflection angle (θ

_m1) and the second light waves are internally reflected at a second reflection angle (θ

_m2) greater than the first reflection angle in reference to a surface normal (N) of the second surface, said optical device characterized by

at least one substantially planar interface (40) provided between the first surface and the second surface substantially parallel to the first surface to reflect the second light waves toward the second surface as the second light waves travel from the second surface toward the first surface, while allowing the first light waves to be transmitted through the planar interface.

2. The optical device of claim 1, wherein

the successive internal reflections by the first light waves at the second surface occur at a plurality of first reflection points separated by a first reflection interval (L1), and

the successive internal reflections by the second light waves at the second surface occur at a plurality of second reflection points separated by a second reflection interval (L2), said optical device further characterized in that

the planar interface is positioned between the first and second surfaces such that the first reflection interval is substantially equal to the second reflection interval.

3. The optical device of claim 1, further characterized by

a further light coupling structure (H2) positioned relative to the light-guiding member to cause the light waves encountering the second surface to be partially transmitted through the second surface and partially reflected toward the first surface.

4. The optical device of claim 1, further characterized by

a further light coupling structure (H2) positioned relative to the light-guiding member to cause the light waves encountering the second surface to be partially transmitted through the planar interface (40) and then the first surface (32), and partially reflected from the second surface toward the first surface while maintaining the reflection angles.

5. The optical device of claim 1, characterized in that the light coupling structure (H1) comprises a diffractive element.

6. The optical device of claim 3, characterized in that the further light coupling structure (H2) comprises a diffractive element.

7. The optical device of claim 4, characterized in that the further light coupling structure (H2) comprises a diffractive element.

8. The optical device of claim 3, characterized in that the light coupling structure (H1) and the further light-coupling structure (H2) are holographic diffractive elements imparted on the light-guiding member.

9. The optical device of claim 1, wherein the light waves further comprise third light waves of a third color (λ

₃) different from the first and second colors, wherein the third light waves are internally reflected at a third reflection angle (θ

_m3) smaller than the first and the second reflection angles, said optical device further characterized by

a further planar interface (42) provided between the first surface (32) and the planar interface (40) so as to reflect the first light waves toward the second surface as the first light waves travel from the second surface toward the first surface, while allowing the third light waves to be transmitted through the further planar interface.

10. The optical device of claim 1, wherein the light-guiding member is made of an optical material having a first refractive index, said optical device further characterized in that

the planar interface (40) is a layer made of an optical material having a second refractive index smaller than the first refractive index so that the reflections by the second light waves at the planar interface are total internal reflections.

11. The optical device of claim 9, wherein the light-guiding member is made of an optical material having a first refractive index, said optical device further characterized in that

the further planar interface (42) is a layer made of an optical material having a second refractive index smaller than the first refractive index so that the reflections by the first light waves at the further planar interface are total internal reflections.

12. A method of improving color uniformity in an optical device (10), the optical device comprising:

a substantially planar light-guiding member (60) having a first surface (32) and an opposing second surface (52), and

a light coupling structure (H1) positioned relative to the light-guiding member for coupling light waves (70) into the light-guiding member, the light-guiding member guiding the light waves (72, 74) within the light-guiding member based substantially on successive internal reflections as the light waves travel between the first and second surfaces, the light waves comprising at least first light waves of a first color (λ

₁) and second light waves of a second different color (λ

₂), wherein the first light waves are internally reflected at a first reflection angle (θ

_m1) and the second light waves are internally reflected at a second reflection angle (θ

_m2) greater than the first reflection angle in reference to a surface normal (N) of the second surface, said method characterized by

providing at least one substantially planar interface (40) between the first surface and the second surface substantially parallel to the first surface to reflect the second light waves toward the second surface as the second light waves travel from the second surface toward the first surface, while allowing the first light waves to be transmitted through the planar interface.

13. The method of claim 12, wherein

the successive internal reflections by the first light waves at the second surface occur at a plurality of first reflection points separated by a first reflection interval (L1), and

the successive internal reflections by the second light waves at the second surface occur at a plurality of second reflection points separated by a second reflection interval (L2), said method further characterized in that

the planar interface is provided at a position between the first and second surfaces such that the first reflection interval is substantially equal to the second reflection interval.