Layered optical composite having a reduced content of highly refractive layers and its application in augmented reality

1. A layered optical composite comprising:

a. a substrate having a front face and a back face; and

b. a coating comprising:

i. a type T layer, and

ii. a type C region comprising one or more type C layers;

wherein the substrate has:

i. a thickness t G in the range from 0.2 to 1.2 mm,

ii. a refractive index n G at a wavelength λ in the range from 1.6 to 2.4, and

iii. an optical absorption coefficient K G at the wavelength λ of less than 10 cm −1 ;

wherein the type C layers individually and independently have:

i. a thickness t C in the range from 9 to 250 nm,

ii. a refractive index n C at the wavelength λ in the range from 1.35 to 2.43, and

iii. an optical absorption coefficient K C at the wavelength λ of less than 10 6 cm −1 ;

wherein at least one type C layer has:

i. an optical absorption coefficient at the wavelength λ of at least 100 cm −1 ;

wherein the type T layer has:

i. a thickness t T in the range from 50 to 300 nm,

ii. a refractive index n T at the wavelength λ in the range from 1.35 to 1.96, and

iii. an optical absorption coefficient K T of less than 80 cm −1 ;

wherein the type C region and the type T layer are each superimposed over one face of the substrate with the type C region further than the type T layer from the substrate;

wherein λ is in the range from 430 to 670 nm.

2. The layered optical composite according to claim 1 , wherein the thickness of the type T layer t T layer satisfies one or both of the following criteria:

a.

t

T

≥

0

.

3

⁢

5

⁢

λ

n

T

;

and

b.

t

T

≤

0.65

·

λ

n

T

.

3. The layered optical composite according to claim 1 , wherein the refractive index of the type T layer n T is less than the refractive of the substrate n G .

4. The layered optical composite according to claim 1 , wherein the C-type region has two or more type C layers.

5. The layered optical composite according to claim 4 , wherein one or both of the following criteria are satisfied:

a. n t ≥(n G −0.03)/1.4; and

b. n t ≤(n G +0.39)/1.4.

6. The layered optical composite according to claim 4 , wherein the layered optical composite has an optical transmissivity at the wavelength λ of at least 90% for light incident normal to its front face.

7. The layered optical composite according to claim 1 , wherein the coating has a single type C layer.

8. The layered optical composite according to claim 7 , wherein the type C layer has a refractive index n C and one or more of the following criteria are satisfied:

a. n C <n T ;

b. n T ≥n G −0.11; and

c. n T ≤n G −0.03.

9. The layered optical composite according to claim 7 , wherein one or both of the following criteria are satisfied:

a. |√{square root over (n T n E )}−n C |≤0.11; and

b.



λ

4

⁢

n

C

-

t

C



≤

λ

5

⁢

0

.

10. The layered optical composite according to claim 1 , wherein one or more of the following is satisfied:

i.) A radius of curvature of the substrate is greater than 600 mm;

ii.) An in-plane optical loss of the substrate measured perpendicular to the front face is at most 20%;

iii.) A surface roughness of the substrate is less than 5 nm;

iv.) A surface roughness of the coating is less than 5 nm;

v.) A total thickness variation of the substrate is less than 5 μm;

vi.) A min-max local thickness variation over 75% of the front face is less than 5 μm;

vii.) A warp of the optical layered composite is less than 350 μm;

viii.) A bow of the optical layered composite is less than 300 μm.

11. The layered optical composite according to claim 1 , wherein the substrate is selected from glass, polymer, optoceramics, and crystals.

12. The layered optical composite according to claim 1 , further comprising a coupler for coupling light into or decoupling light out of the layered optical composite.

13. The layered optical composite according to claim 1 , wherein the layered optical composite is a wafer.

14. The layered optical composite according to claim 13 , wherein one or more, or all, of the following criteria is satisfied:

i.) The front face has a surface area in the range from 1 to 400 cm 2 ;

ii.) The thickness of the substrate t G is in the range from 50 to 1500 μm;

iii.) A radius of curvature of the substrate is greater than 600 mm;

iv.) An in-plane optical loss measured perpendicular to the front face is at most 20%;

v.) A surface roughness of the substrate is less than 5 nm;

vi.) A surface roughness of the coating is less than 5 nm;

vii.) A total thickness variation of the substrate is less than 5 μm;

viii.) A maximum local thickness variation over 75% of the front face is less than 5 μm;

ix.) A warp of the optical layered composite is less than 350 μm;

x.) A bow of the optical layered composite is less than 300 μm;

xi.) The composite has a circular or square shape.

15. The optical layered composite according to claim 1 , wherein one or more of the following is satisfied:

a. The thickness of the optical layered composite is in the range in the range from 250 to 700 μm;

b. The thickness t T of the T-type layer exceeds 60% of the total thickness t C of the grouping of C-type layers;

c. The thickness t C of the coating is less than 0.6% of the thickness t G of substrate;

d. The radius of curvature of the substrate is greater than 1100 mm;

the radius of curvature of the layered composite is greater than 800 mm;

e. The maximum local thickness variation of the substrate over 75% of the front face of less than 2 μm; and

the warp of the optical layered composite is less than 250 μm; and

the bow of the optical layered composite is less than 300 μm;

f. The surface roughness of the substrate is less than 3 nm; and

the surface roughness of the type-C-coating is less than 2 nm; and

the surface roughness of the type-T-coating is less than 4 nm;

g. The transmittance measured perpendicular to the front face is at least 85%.

16. A device comprising one or more layered optical composites according to claim 1 .

17. A process for making an augmented reality device comprising the following steps:

i.) Providing a wafer according to claim 13 ;

ii.) Reducing the surface area of the front face to obtain a portion;

iii.) Providing the portion as a viewing window in the augmented reality device.

18. An augmented reality device or virtual reality device comprising the layered optical composite according to claim 1 .