DIFFRACTIVE BEAM EXPANDER AND A VIRTUAL DISPLAY BASED ON A DIFFRACTIVE BEAM EXPANDER

• US 20100214659A1
• Filed: 06/04/2007
• Published: 08/26/2010
• Est. Priority Date: 06/04/2007
• Status: Active Grant

• Current Assignee: Magic Leap, Inc.
• Original Assignee: Nokia Corporation
• Inventors: Levola, Tapani
• Granted Patent: US 8,320,032 B2
• Time in Patent Office: Days
• US Class Current: 359/566
• CPC Class Codes: G02B 2027/0125 Field-of-view increase by wavefront division
• CPC Class Codes: G02B 2027/0178 Eyeglass type eyeglass details G02C
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 27/4272 having plural diffractive elements positioned sequentially along the optical path
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 6/0016 Grooves, prisms, gratings, scattering particles or rough surfaces
• CPC Class Codes: G02B 6/0018 Redirecting means on the surface of the light guide
• CPC Class Codes: G02B 6/0035 provided on the surface of the light guide or in the bulk of it

Abstract

A diffractive beam expander (50) comprises a substantially planar waveguiding substrate, an input grating (10) to provide an in-coupled beam (B1) propagating within said substrate, and an output grating (30) to provide an out-coupled beam. The expander (50) comprises also four or more further grating portions to expand the height of the in-coupled beam (B1). A part of the in-coupled light is diffracted by a first deflecting grating portion (21 a) to provide a first deflected beam. A part of the in-coupled light is diffracted by a second deflecting grating portion (22a) to provide a second deflected beam. The first deflected beam propagates downwards and the second deflected beam propagates upwards with respect to the in-coupled beam (B1). The first deflected beam impinges on a first direction-restoring grating portion (21 b) and the second deflected beam impinges on a second direction-restoring grating portion (22b). The first restoring grating portion (21 b) provides a first restored beam (V1) and the second restoring grating portion (22b) provides a second restored beam (V2), which both have the same direction as the in-coupled beam (B1). Out-coupling provides an output beam which is parallel to the input beam, and has a greater vertical dimension than said input beam.

Claims

1. A device comprising:

a substantially planar waveguiding substrate;

an input grating to provide an in-coupled beam propagating within said substrate by diffracting light of an input beam into said substrate;

a first deflecting grating portion to provide a first deflected beam by diffracting a part of said in-coupled beam such that the difference between the azimuth angle of said first deflected beam and the azimuth angle of said in-coupled beam is negative, said first deflecting grating portion comprising substantially linear diffractive features;

a second deflecting grating portion to provide a second deflected beam by diffracting a part of said in-coupled beam such that the difference between the azimuth angle of said second deflected beam and the azimuth angle of said in-coupled beam is positive, said second deflecting grating portion comprising substantially linear diffractive features, the diffractive features of said second deflecting grating portion having a different orientation than the diffractive features of said first deflecting grating portion;

a first restoring grating portion to provide a first restored beam by diffracting light of said first deflected beam;

a second restoring grating portion to provide a second restored beam, said second restored beam being substantially parallel to said first restored beam; and

an output grating to provide an out-coupled beam by diffracting light of said first restored beam and said second restored beam out of said substrate, said output beam being substantially parallel to said input beam.

2. The device of claim 1 wherein said first deflecting grating portion and said second restoring grating portion are on a first side of a reference plane, and said second deflecting grating portion and said first restoring grating portion are on a second side of said reference plane, said reference plane being substantially perpendicular to the plane of said input grating.

3. The device of claim 2 comprising a third deflecting grating portion to provide a third deflected beam by diffracting a part of said in-coupled beam such that the azimuth angle of said third deflected beam is smaller than the azimuth angle of said in-coupled beam, said third deflected beam being adapted to impinge on a restoring grating portion to provide a third restored beam having the same direction as said first restored beam, said third deflecting grating portion being on the second side of said reference plane.

4. The device of claim 3 wherein said first restoring portion and said third deflecting grating portion form together a first intermediate grating having a substantially continuous grating structure.

5. The device according to claim 1, wherein said in-coupled beam is adapted to shift with respect to said deflecting portions according to the direction of said in-coupled beam.

6. The device according to claim 1 wherein said first restored beam and said second restored beam are substantially parallel to the direction of said in-coupled beam, and the output grating is further adapted to diffract a part of said in-coupled beam out of said substrate.

7. The device according to claim 1 wherein an angle between the direction of the diffractive features of said first deflecting grating portion and the direction of the diffractive features of said input grating is in the range of 55 to 65 degrees.

8. A method for expanding a light beam comprising:

diffracting light of an input beam into a substantially planar waveguiding substrate in order to provide an in-coupled beam propagating within said substrate;

providing a first deflected beam by diffracting a part of said in-coupled beam by using a first deflecting grating portion such that the difference between the azimuth angle of said first deflected beam and the azimuth angle of said in-coupled beam is negative;

providing a second deflected beam by diffracting a part of said in-coupled beam by using a second deflecting grating portion such that the difference between the azimuth angle of said second deflected beam and the azimuth angle of said in-coupled beam is positive;

providing a first restored beam by diffracting a part of said first deflected beam by using a first restoring grating portion;

providing a second restored beam by diffracting a part of said second deflected beam by using a second restoring grating portion, said second restored beam being substantially parallel to said first restored beam; and

coupling light of said first restored beam and said second restored beam out of said substrate to provide an output beam, said output beam being substantially parallel to said input beam;

wherein said first deflecting grating portion comprises substantially linear diffractive features, and said second deflecting grating portion comprising substantially linear diffractive features, the diffractive features of said second deflecting grating portion having a different orientation than the diffractive features of said first deflecting grating portion.

9. The method according to claim 8, wherein said first deflecting grating portion and said second restoring grating portion are on a first side of a reference plane, and said second deflecting grating portion and said first restoring grating portion are on a second side of reference plane, said reference plane being substantially perpendicular to the plane of said input grating.

10. A device comprising an optical engine to provide at least one light beam, and a diffractive beam expander to expand said at least one light beam such that a virtual image is observable through a viewing aperture of said diffractive beam expander, said diffractive beam expander in turn comprising:

a substantially planar waveguiding substrate,

an input grating to provide an in-coupled beam propagating within said substrate by diffracting light of an input beam into said substrate;

a first deflecting grating portion to provide a first deflected beam by diffracting a part of said in-coupled beam such that the difference between the azimuth angle of said first deflected beam and the azimuth angle of said in-coupled beam is negative, said first deflecting grating portion comprising substantially linear diffractive features;

a second deflecting grating portion to provide a second deflected beam by diffracting a part of said in-coupled beam such that the difference between the azimuth angle of said second deflected beam and the azimuth angle of said in-coupled beam is positive, said second deflecting grating portion comprising substantially linear diffractive features, the diffractive features of said second deflecting grating portion having a different orientation than the diffractive features of said first deflecting grating portion;

a first restoring grating portion to provide a first restored beam by diffracting light of said first deflected beam;

a second restoring grating portion to provide a second restored beam, said second restored beam being substantially parallel to said first restored beam; and

an output grating to provide an out-coupled beam by diffracting light of said first restored beam and said second restored beam out of said substrate, said output beam being substantially parallel to said input beam.

11. The device of claim 10 wherein said optical engine comprises a micro-display to display a real image.

12. A method comprising providing at least one input beam and expanding said at least one input beam such that a virtual image is observable through a viewing aperture, said expanding comprising:

diffracting light of said input beam into a substantially planar waveguiding substrate in order to provide an in-coupled beam propagating within said substrate;

providing a first deflected beam by diffracting a part of said in-coupled beam by using a first deflecting grating portion such that the difference between the azimuth angle of said first deflected beam and the azimuth angle of said in-coupled beam is negative;

providing a second deflected beam by diffracting a part of said in-coupled beam by using a second deflecting grating portion such that the difference between the azimuth angle of said second deflected beam and the azimuth angle of said in-coupled beam is positive;

providing a first restored beam by diffracting a part of said first deflected beam by using a first restoring grating portion;

providing a second restored beam by diffracting a part of said second deflected beam by using a second restoring grating portion, said second restored beam being substantially parallel to said first restored beam; and

coupling light of said first restored beam and said second restored beam out of said substrate to provide an output beam such that said output beam is substantially parallel to said input beam;

wherein said first deflecting grating portion comprises substantially linear diffractive features, and said second deflecting grating portion comprises substantially linear diffractive features, the diffractive features of said second deflecting grating portion having a different orientation than the diffractive features of said first deflecting grating portion.

13. The method of claim 12 wherein said first deflecting grating portion and said second restoring grating portion are on a first side of a reference plane, and said second deflecting grating portion and said first restoring grating portion are on a second side of said reference plane said reference plane being substantially perpendicular to the plane of said input grating.

14. A device comprising:

a waveguiding means;

a diffractive input means to provide an in-coupled beam propagating within said substrate by diffracting light of an input beam into said waveguiding means;

a first deflecting means to provide a first deflected beam by diffracting a part of said in-coupled beam such that the difference between the azimuth angle of said first deflected beam and the azimuth angle of said in-coupled beam is negative, said first deflecting means comprising substantially linear diffractive features;

a second deflecting means to provide a second deflected beam by diffracting a part of said in-coupled beam such that the difference between the azimuth angle of said second deflected beam and the azimuth angle of said in-coupled beam is positive, said second deflecting means comprising substantially linear diffractive features, the diffractive features of said second deflecting grating portion having a different orientation than the diffractive features of said first deflecting means;

a first restoring means to provide a first restored beam by diffracting light of said first deflected beam;

a second restoring means to provide a second restored beam, said second restored beam being substantially parallel to said first restored beam; and

an output means to provide an out-coupled beam by diffracting light of said first restored beam and said second restored beam out of said substrate, said output beam being substantially parallel to said input beam.

15. The device of claim 14 wherein said first deflecting means and said second restoring means are on a first side of a plane, and said second deflecting means and said first restoring means are on a second side of said plane, said reference plane being substantially perpendicular to the plane of said diffractive input means.