Waveguide structure and display device using the same
A waveguide structure is provided. The waveguide structure includes waveguide combiners stacked one upon the other. Each waveguide combiner includes a waveguide plate and an input coupler disposed on the waveguide plate. The input coupler of at least one waveguide combiner includes first grating pillars, and each first grating pillar has a gradually changing refractive index.
1 . A waveguide structure, comprising:
waveguide combiners stacked one upon the other, wherein each of the waveguide combiners comprises:
a waveguide plate; and
an input coupler disposed on the waveguide plate;
wherein the input coupler of at least one of the waveguide combiners comprises first grating pillars, each of the first grating pillars has a plurality of stacked layers, a lower stacked layer of the plurality of stacked layers includes at least one upper surface exposed from an upper stacked layer of the plurality of stacked layers, and each of the first grating pillars has a gradually increasing refractive index from a topmost layer to a bottommost layer of the plurality of stacked layers.
2 . The waveguide structure as claimed in claim 1 , wherein the number of waveguide combiners is greater than or equal to two.
3 . The waveguide structure as claimed in claim 1 , wherein the number of the plurality of stacked layers is less than or equal to thirty.
4 . The waveguide structure as claimed in claim 3 , wherein thicknesses of the plurality of stacked layers are different.
5 . The waveguide structure as claimed in claim 3 , wherein a total height of the plurality of stacked layers is in a range from 40 nm to 1000 nm.
6 . The waveguide structure as claimed in claim 1 , wherein the gradually increasing refractive index has a maximum refractive index and a minimum refractive index, and the difference between the maximum refractive index and the minimum refractive index is greater than 0, and less than or equal to 2.1.
7 . The waveguide structure as claimed in claim 1 , wherein the gradually increasing refractive index is in a range from 1.4 to 3.5.
8 . The waveguide structure as claimed in claim 1 , wherein the first grating pillars are formed in a periodic arrangement, and a period of the periodic arrangement is in a range from 250 nm to 750 nm.
9 . The waveguide structure as claimed in claim 1 , wherein from a cross-sectional view of the waveguide structure, a profile of each of the first grating pillars has two parallel sides.
10 . The waveguide structure as claimed in claim 9 , wherein the profile of each of the first grating pillars is a trapezoid, the two parallel sides are an upper base and a lower base, and the lower base is closer to the waveguide plate than the upper base.
11 . The waveguide structure as claimed in claim 10 , wherein the lower base is longer than the upper base.
12 . The waveguide structure as claimed in claim 1 , wherein the waveguide plate has a constant refractive index in a range from 1.5 to 3.
13 . The waveguide structure as claimed in claim 1 , wherein each of the waveguide combiners further comprises:
an expander disposed on the waveguide plate and adjacent to the input coupler.
14 . The waveguide structure as claimed in claim 13 , wherein the expander comprises second grating pillars, and a distance between two adjacent second grating pillars is constant.
15 . The waveguide structure as claimed in claim 14 , wherein the second grating pillars have different widths.
16 . The waveguide structure as claimed in claim 14 , wherein the second grating pillars have different thicknesses.
17 . The waveguide structure as claimed in claim 13 , wherein each of the waveguide combiners further comprises:
an output coupler disposed on the waveguide plate,
wherein the expander is disposed between the input coupler and the output coupler.
18 . The waveguide structure as claimed in claim 1 , wherein the waveguide combiners are used to couple different color lights, and the different color lights have wavelengths from 380 nm to 750 nm.
19 . A display device, comprising:
an image source; and
a waveguide structure configured to couple lights from the image source, wherein the waveguide structure comprises:
waveguide combiners stacked one upon the other, wherein each of the waveguide combiners comprises:
a waveguide plate; and
an input coupler disposed on the waveguide plate;
wherein the input coupler of at least one of the waveguide combiners comprises first grating pillars, each of the first grating pillars has a plurality of stacked layers, a lower stacked layer of the plurality of stacked layers includes at least one upper surface exposed from an upper stacked layer of the plurality of stacked layers, and each of the first grating pillars has a gradually increasing refractive index from a topmost layer to a bottommost layer of the plurality of stacked layers.
20 . The display device as claimed in claim 19 , further comprising:
a collimator disposed between the image source and the waveguide structure.