METHODS AND APPARATUS FOR WEARABLE DISPLAY DEVICE WITH VARYING GRATING PARAMETERS

1 . A device for viewing a projected image, the device comprising:

an input coupling grating operable to receive light related to the projected image from a light source;

an expansion grating having a first grating structure characterized by a first set of grating parameters varying in one or more dimensions, wherein the expansion grating structure is operable to receive light from the input coupling grating and to multiply the light related to the projected image; and

an output coupling grating having a second grating structure characterized by a second set of grating parameters and operable to output the multiplied light in a predetermined direction.

2 . The device of claim 1 , wherein the first grating structure comprises a plurality of grating teeth interleaved with a plurality of spaces, wherein:

one of the plurality of spaces is characterized by a space width;

a first adjacent space on a first side of the one of the plurality of spaces is characterized by a narrower width than the space width; and

and a second adjacent space on a second side of the one of the plurality of spaces opposing the first side is characterized by a wider width than the space width.

3 . The device of claim 1 , wherein:

the first grating structure has a plurality of grating teeth disposed between a first side/end and a second side/end;

each grating tooth of the plurality of grating teeth is defined/bounded by a pair of spaces; and

for each pair of spaces, a first space of the pair of spaces closer to the first side of the first grating structure is narrower than a second space of the pair of spaces closer to the second side.

4 . The device of claim 1 , wherein the first set of grating parameters comprises grating pitch.

5 . The device of claim 1 , wherein the second set of grating parameters comprises grating height.

6 . The device of claim 1 , wherein the expansion grating and the output coupling grating at least partially spatially overlap in a plane normal to the predetermined direction.

7 . The device of claim 1 , wherein the first set of grating parameters define a first phase variation pattern.

8 . The device of claim 7 , wherein the first phase variation pattern is periodic.

9 . The device of claim 8 , wherein a period of the first phase variation pattern is between 100 μm and 5 cm.

10 . The device of claim 7 , wherein the expansion grating comprises a first expansion grating region and a second expansion grating region laterally offset from the first expansion grating region, and wherein the first phase variation pattern comprises a graded periodic pattern having a graded period that continuously increases in a direction extending from the first expansion grating region toward the second expansion grating region.

11 . The device of claim 1 , wherein the one or more dimensions include at least two of pitch, angle, apex angle, refractive index, height, and duty cycle.

12 . The device of claim 1 , further comprising a substrate having a first surface and a second surface, wherein:

the input coupling grating is coupled to the substrate;

the expansion grating is disposed on the first surface of the substrate; and

the output coupling grating is disposed on the second surface of the substrate.

13 . An augmented reality (AR) system comprising:

a headset including a frame;

a set of projectors coupled to the frame;

an eyepiece mechanically mounted to the frame and optically coupled to the set of projectors, wherein the eyepiece is operable to direct light from each of the set of projectors towards eyes of a user, and wherein the eyepiece comprises:

a diffractive incoupling interface operable to receive virtual content from the the set of projectors and incouple the virtual content into the eyepiece; and

a diffractive outcoupling interface operable to receive the virtual content and output a virtual image associated with the virtual content toward the eyes of the user, wherein the diffractive outcoupling interface is characterized by a first grating structure having a first set of varying grating parameters and a second grating structure having a second set of varying grating parameters.

14 . The AR system of claim 13 , wherein:

the first set of varying grating parameters define a first phase variation pattern;

the diffractive outcoupling interface comprises a first diffractive outcoupling interface region and a second diffractive outcoupling interface region laterally offset from the first diffractive outcoupling interface region; and

the first phase variation pattern comprises a graded periodic pattern having a graded period that continuously increases in a direction extending from the first diffractive outcoupling interface region toward the second diffractive outcoupling interface region.

15 . The AR system of claim 13 , wherein the first grating structure comprises a plurality of grating teeth interleaved with a plurality of spaces, wherein:

one of the plurality of spaces is characterized by a space width;

a first adjacent space on a first side of the one of the plurality of spaces is characterized by a narrower width than the space width; and

and a second adjacent space on a second side of the one of the plurality of spaces opposing the first side is characterized by a wider width than the space width.

16 . The AR system of claim 13 , wherein:

the first grating structure has a plurality of grating teeth disposed between a first side/end and a second side/end;

each grating tooth of the plurality of grating teeth is defined/bounded by a pair of spaces; and

for each pair of spaces, a first space of the pair of spaces closer to the first side of the first grating structure is narrower than a second space of the pair of spaces closer to the second side.

17 . The AR system of claim 13 , wherein the first set of varying grating parameters comprises grating pitch and the second set of varying grating parameters comprises grating height.

18 . The AR system of claim 13 , wherein the diffractive outcoupling interface comprises an expansion grating and an output coupling grating at least partially spatially overlapping in a plane normal to the eyepiece.

19 . The AR system of claim 18 , wherein the first set of varying grating parameters define a periodic phase variation pattern.

20 . The AR system of claim 19 , wherein the expansion grating comprises a first expansion grating region and a second expansion grating region laterally offset from the first expansion grating region, and wherein the periodic phase variation pattern comprises a graded periodic pattern having a graded period that continuously increases in a direction extending from the first expansion grating region toward the second expansion grating region.