Diffraction gratings formed by metasurfaces having differently oriented nanobeams

Patent metadata

Field	Value
Publication number	US-2018231702-A1
Application number	US-201815880404-A
Country	US
Kind code	A1
Filing date	Jan 25, 2018
Priority date	Jan 27, 2017
Publication date	Aug 16, 2018
Grant date	—

Abstract

Metasurfaces provide compact optical elements in head-mounted display systems to, e.g., incouple light into or outcouple light out of a waveguide. The metasurfaces may be formed by a plurality of repeating unit cells, each unit cell comprising two sets or more of nanobeams elongated in crossing directions: one or more first nanobeams elongated in a first direction and a plurality of second nanobeams elongated in a second direction. As seen in a top-down view, the first direction may be along a y-axis, and the second direction may be along an x-axis. The unit cells may have a periodicity in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. Advantageously, the metasurfaces provide diffraction of light with high diffraction angles and high diffraction efficiencies over a broad range of incident angles and for incident light with circular polarization.

First claim

What is claimed is:

1 . An optical system comprising:
a metasurface configured to diffract visible light having a wavelength, the metasurface comprising:
a plurality of repeating unit cells, each unit cell consisting of two to four sets of nanobeams, wherein:
a first set of nanobeams are formed by one or more first nanobeams; and
a second set of nanobeams are formed by a plurality of second nanobeams disposed adjacent to the one or more first nanobeams and separated from each other by a sub-wavelength spacing,
wherein the one or more first nanobeams and the plurality of second nanobeams are elongated in different orientation directions, and
wherein the unit cells repeat at a period less than or equal to about 10 nm to 1 μm.

2 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams are oriented at an angle relative to each other to cause a phase difference between the visible light diffracted by the one or more first nanobeams and the visible light diffracted by the second nanobeams.

3 . The optical system of claim 1 , wherein the phase difference is twice the angle.

4 . The optical system of claim 1 , wherein the wavelength in the visible spectrum corresponds to a blue light, a green light or a red light.

5 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams are oriented in orientation directions that are rotated by about 90 degrees relative to each other.

6 . The optical system of claim 1 , wherein each of the first nanobeams have a same width.

7 . The optical system of claim 1 , wherein each of the second nanobeams has a same width.

8 . The optical system of claim 1 , wherein each of the first nanobeams in each of the second nanobeams have a same spacing between individual ones of the first and second nanobeams.

9 . The optical system of claim 1 , wherein the unit cells repeat at a period less than or equal to the wavelength, wherein the wavelength is within the visible spectrum.

10 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams have a height smaller than the wavelength.

11 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams are formed of a material whose bulk refractive index is higher than 2.0 at the wavelength.

12 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams are formed of a semiconductor material or an insulating material.

13 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams are formed of a material having silicon.

14 . The optical system of claim 13 , wherein the one or more first nanobeams and the second nanobeams are formed of a material selected from the group consisting of polycrystalline silicon, amorphous silicon, silicon carbide and silicon nitride.

15 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams are configured to diffract the visible light at a diffraction efficiency greater than 10% at a diffraction angle greater than 50 degrees relative to a surface normal plane.

16 . The optical system of claim 15 , wherein the one or more first nanobeams and the second nanobeams are configured to diffract light at the diffraction efficiency for the incident light having a range of angle of incidence which exceeds 40 degrees.

17 . The optical system of claim 16 , wherein the surface normal plane extends in the first orientation direction.

18 . The optical system of claim 17 , wherein the one or more first nanobeams and the second nanobeams are configured to diffract light in a transmission mode, wherein the intensity of diffracted light on an opposite side of the one or more first nanobeams and the second nanobeams as a light-incident side is greater compared to the intensity of diffracted light on a same side of the one or more first nanobeams and the second nanobeams as the light-incident side.

19 . The optical system of claim 17 , wherein the wherein the one or more first nanobeams and the second nanobeams are configured to diffract light in a reflection mode, wherein the intensity of diffracted light on a same side of the one or more first nanobeams and the second nanobeams as a light-incident side is greater compared to the intensity of diffracted light on an opposite side of the one or more first nanobeams and the second nanobeams as the light-incident side.

20 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams are formed on a substrate and formed of a material whose bulk refractive index is greater than a refractive index of the substrate by at least 0.5.

21 . The optical system of claim 20 , wherein the substrate has a refractive index greater than 1.5.

22 . The optical system of claim 20 , wherein the substrate is configured such that light diffracted by the one or more first nanobeams and the second nanobeams propagate in the second direction under total internal reflection.

23 . The optical system of claim 1 , wherein the one or more first nanobeams and the second nanobeams have a substantially rectangular cross-sectional shape.

24 . The optical system of claim 1 , wherein the one or more first nanobeams comprise a pair of first nanobeams.

25 . The optical system of claim 24 , wherein the one or more first nanobeams are immediately adjacent to the pair of nanobeams such that the second nanobeams are directly interposed between adjacent pairs of first nanobeams.

26 . The optical system of claim 1 , wherein the one or more first nanobeams consists of one first nanobeam.

27 . The optical system of claim 1 , further comprising a third set of nanobeams formed by a plurality of third nanobeams elongated in a different orientation relative to the first one or more first nanobeams and the plurality of second nanobeams, the third nanobeams interposed between the one or more first nanobeams and the second nanobeams.

28 . The optical system of claim 26 , wherein the third nanobeams have the same length such that the third nanobeams coterminate.

29 . The optical system of claim 27 , wherein adjacent ones of the third nanobeams are separated by a constant space in the first orientation direction.

30 . The optical system of claim 27 , wherein the one or more first nanobeams span a distance in the first orientation direction corresponding to a plurality of third nanobeams.

31 . The optical system of claim 27 , wherein each of the third nanobeams has the same width and wherein a spacing between individual ones of the third nanobeams has a same width.

32 . The optical system of claim 27 , wherein the third nanobeams extend in a third orientation direction that is rotated in a counterclockwise direction relative to the one or more first nanobeams by an angle smaller than the smallest angle of rotation in the counterclockwise direction of the second nanobeams relative to the one or more first nanobeams when viewed a direction of propagation of an incident light.

33 . The optical system of claim 27 , further comprising a fourth set of nanobeams formed by a plurality of fourth nanobeams elongated in a different orientat

Assignees

• Magic Leap Inc

Inventors

• Lin Dianmin
• Klug Michael Anthony
• St Hilaire Pierre
• Melli Mauro
• Peroz Christophe
• Poliakov Evgeni

Classifications

• G02B6/0011

  the light guides being planar or of plate-like form · CPC title

• G02B6/00

  Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings · CPC title

• G02B2207/101

  Nanooptics · CPC title

• G02B5/1871 Primary

  Transmissive phase gratings · CPC title

• G02B5/1842

  Gratings for image generation (G02B5/1847 takes precedence) · CPC title