Slab waveguide layers for improved near-eye display surface relief grating lightguides.

Abstract

FIELD OF THE DISCLOSURE Embodiments of the present disclosure generally relate to an augmented reality waveguide combiner. The waveguides have a substrate refractive index (RI) (n sub ) and a slab waveguide layer disposed on the waveguide substrate, the slab RI(n swg ) and the slab depth (d swg ), at least one grating defined by a plurality of grating structures disposed in, on, or on the slab waveguide layer, and a superstrate between and above the grating structures, the superstrate RI(n superstrate ), and a superstrate having an interface with the slab waveguide layer. swg ) is the substrate RI(n sub ) and super straight RI (n superstrate ) exceeds.

Description

[Background technology]

[0001] Technical Field TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to augmented reality waveguide combiners.

[0002] 2. Description of Related Art

[0002] Virtual reality is generally considered to be a computer-generated simulated environment in which a user feels as if they are a physical presence. Virtual reality experiences may be generated in 3D and may be viewed using a head-mounted display (HMD), such as glasses or other wearable display devices, with near-eye display panels as lenses for displaying the virtual reality environment in place of the real environment.

[0003]

[0003] Augmented reality, however, enables an experience in which a user can view their surrounding environment through the display lenses of glasses or other HMD devices, while also seeing images of virtual objects that are generated to appear and appear as part of that environment. Augmented reality can include any type of input (such as audio and tactile input), as well as virtual images, graphics, and video that enhance or augment the environment the user is experiencing. As an emerging technology, a number of challenges and design constraints exist.

[0004] One such challenge is displaying a virtual image to overlay on the surrounding environment. To assist in the image overlay, a waveguide combiner is used. Generated light is incoupled into the waveguide combiner, propagates through an extended waveguide combiner, and outcoupled from the extended waveguide combiner to be overlaid on the surrounding environment. A surface relief grating is used to incouple and outcouple the light from the extended waveguide combiner. Therefore, what is needed in the art is a waveguide combiner. Summary of the Invention

[0005] In one embodiment, a waveguide is provided, the waveguide having a substrate refractive index (RI) (n sub ) and a slab waveguide layer disposed on the waveguide substrate, the slab RI(n swg ) and the slab depth (d swg ), at least one grating defined by a plurality of grating structures disposed in, on, or on the slab waveguide layer, and a superstrate between and above the grating structures, the superstrate RI(n superstrate ), and a superstrate having an interface with the slab waveguide layer. swg ) is the substrate RI(n sub ) and super straight RI (n superstrate ) exceeds.

[0006] In one embodiment, a waveguide is provided, the waveguide having a substrate refractive index (RI) (n sub ) and a slab waveguide layer disposed on the waveguide substrate, the slab RI(n swg ) and the slab depth (d swg ), at least one grating defined by a plurality of grating structures disposed in, on, or on the slab waveguide layer, and a superstrate between and above the grating structures, the superstrate RI(n superstrate ), and a superstrate having an interface with the slab waveguide layer. swg ) is the substrate RI(n sub ) and super straight RI (n superstrate ) and the slab depth (d swg ) is the slab RI at 620 nm (n swg ) is 2.1, and the slab RI (n swg) is 2.2, and the slab RI (n swg ) is 2.3, and the slab RI (n swg ) is 2.4, and the slab RI (n swg ) is 2.5, and the slab RI (n swg ) is 2.6, it is 15nm to 50nm.

[0007] In one embodiment, a waveguide is provided, the waveguide having a substrate refractive index (RI) (n sub ) and a slab RI(n swg ) and slab depth (d swg ), a fold grating defined by a grating structure disposed within the slab waveguide layer, and a superstrate between and above the grating structure, the superstrate RI(n superstrate ), and a superstrate having an interface with the slab waveguide layer, and swg ) is the distance from the bottom to the top of the slab waveguide layer between the grating structures, and the slab RI(n swg ) is the substrate RI(n sub ) and super straight RI (n superstrate ) exceeds.

[0008]

[0008] So that the above-mentioned features of the present disclosure may be understood in detail, a more particular description of the present disclosure briefly summarized above will be obtained by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only exemplary embodiments and therefore should not be considered as limiting the scope of the present disclosure, which may also admit of other equally effective embodiments. [Brief explanation of the drawings]

[0009] [Figure 1A] 1 is a cross-sectional view of a waveguide according to an embodiment. [Figure 1B] 1 is a wavenumber space (k-space) diagram of a waveguide according to an embodiment. [Figure 2] 1 is a cross-sectional view of a waveguide according to an embodiment. [Figure 3] 10 is a graph of simulated diffraction efficiencies of three waveguides. [Figure 4A] 1 is a cross-sectional view of a waveguide according to one configuration. [Figure 4B] FIG. 10 is a cross-sectional view of a waveguide according to another configuration. [Figure 4C] FIG. 10 is a cross-sectional view of a waveguide with yet another configuration. [Figure 5A] 1 is a cross-sectional view of a grating according to an embodiment. [Figure 5B] 1 is a cross-sectional view of a grating according to an embodiment. [Figure 5C] 1 is a cross-sectional view of a grating according to an embodiment. [Figure 5D] 1 is a cross-sectional view of a grating according to an embodiment. [Figure 5E] 1 is a cross-sectional view of a grating according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0015] For ease of understanding, where possible, the same reference numerals have been used to designate identical elements that are common to multiple figures. It is envisioned that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0011]

[0016] FIELD Embodiments of the present disclosure generally relate to an augmented reality waveguide combiner.

[0012]

[0017] 1A is a cross-sectional view of a waveguide 100. The waveguide 100 includes a waveguide substrate 101. An in-coupler 102, a first grating (e.g., a folded grating) 104, and a second (e.g., an out-coupler) grating 106 are disposed on the waveguide substrate 101. The in-coupler 102, the first grating 104, and the second grating 106 comprise a grating structure 108. The grating structure 108 includes a device material 103 disposed on the waveguide substrate 101.

[0013]

[0018] FIG. 1B is a wavenumber space diagram of the waveguide 100. In operation, white light is incoupled by the incoupler 102 and passes through the waveguide 100, undergoing total internal reflection (TIR), to the folded grating. Blue channel light (wavelength 380 nm to approximately 495 nm), green channel light (wavelength approximately 495 nm to approximately 590 nm), and red channel light (wavelength approximately 590 nm to approximately 750 nm) propagate with different attenuation rates under TIR. The optical channel beams (blue, green, and red channel light) undergo TIR within the folded grating until they are coupled into the outcoupler 106. The beams outcoupled from the waveguide 100 by the outcoupler 106 create a virtual image field of view that is projected into the user's eye. This field of view includes a blue field of view (FOV), a green FOV, and a red FOV.

[0014]

[0019] Dispersion of the propagation diffraction angles within the waveguide 100 causes longer wavelengths (red channel light) to interact less densely with the grating surface than shorter wavelengths (blue channel light). The angular dispersion due to diffraction is described by the diffraction equation: TIFF2026501437000002.tif11170 formula, TIFF2026501437000003.tif5170 is the output diffraction angle, TIFF2026501437000004.tif5170 is the input angle, TIFF2026501437000005.tif5170 is the free space wavelength, TIFF2026501437000006.tif4170 is the grating period, TIFF2026501437000007.tif4170 is the output medium refractive index, TIFF2026501437000008.tif4170 is the input medium refractive index, and TIFF2026501437000009.tif3170 is the diffraction order (..., -2, -1, 0, +1, +2, ...). As the wavelength increases, the diffraction angle increases.

[0015]

[0020] As shown in FIG. 1B , in the first TIR state 107 and the second TIR state 109, the dispersion of propagation angles in TIR between the blue, green, and red channel light results in blue FOV 111, green FOV 113, and red FOV 115 that are offset from one another. At the corners of the display field of view closest to the projector 105, the blue channel light is strongly outcoupled and decays more rapidly as it propagates toward the outcoupler 106, which is farthest from the projector. The red channel light dominates the image in the portion of the field of view farthest from the projector 105 due to its slower decay as it propagates. While it is desirable to minimize the number of substrates required in a near-eye display, if multiple display channels (blue, green, and red channels) are intended to propagate through the waveguide substrate 101, the diffraction efficiency of such multiple display channels must be improved.

[0016]

[0021] FIG. 2 is a cross-sectional view of a waveguide 200. The waveguide 200 of FIG. 2 has a first configuration 401. The waveguide 200 includes a waveguide substrate 201. The waveguide substrate 201 has a substrate refractive index (RI) (n sub )

[0017]

[0022] The waveguide 200 includes at least one grating defined by a plurality of grating structures 208. The waveguide 200 includes an in-coupler 202, a first grating (e.g., a folded grating) 204, and a second grating (e.g., an out-coupler) 206. The in-coupler 202, the first grating 204, and the second grating 206 include grating structures 208. A slab waveguide layer 210 is disposed on a waveguide substrate 201. In some embodiments, the slab waveguide layer 210 is disposed on a first surface 203 (i.e., top surface) of the waveguide substrate 201 or on a second surface 205 (i.e., bottom surface) opposite the first surface 203.

[0018]

[0023] In the embodiment shown in the first configuration 401, the grating structure 208 is disposed within the slab waveguide layer 210. In the embodiments shown in the third configuration 403 and the fourth configuration 404, the grating structure 208 is disposed on the slab waveguide layer 210, and in some embodiments on the surface of the slab waveguide layer 210. The grating structure 208 has a grating RI(n grat ) The lattice material of the lattice structure 208 has a lattice RI(n grat In an embodiment of the second configuration 402, the grating structure 208 of the in-coupler 202 is disposed within the slab waveguide layer 210, and the grating structures 208 of the first grating 204 and the second grating 206 are disposed on top of the slab waveguide layer 210.

[0019]

[0024] The slab waveguide layer 210 has at least one slab depth (d swg The first grid 204 includes a first slab depth (d swg1 The second grating 206 has a second slab depth (d swg2 ) Slab depth d swg is the first slab depth (d swg1 ) or second slab depth (d swg2 ) corresponds to the slab depth (d swg ) is from the bottom surface 209 to the top surface 211 of the slab waveguide layer 210. The first slab depth (d swg1) is from the lower surface 209 to the upper surface 211 of the slab waveguide layer 210 between the grating structures 208 of the first grating 204. The second slab depth (d swg2 ) is from the bottom surface 209 to the top surface 211 of the slab waveguide layer 210 between the grating structures 208 of the second grating 206. In other embodiments, the first slab depth (d swg1 ) is the thickness of the slab waveguide layer 210 below the first grating 204 (i.e., the distance from the bottom surface 209 to the top surface 211). The second slab depth (d swg2 ) is the thickness of the slab waveguide layer 210 below the second grating 206. The slab waveguide layer 210 has a slab refractive index (RI) (n swg ) The superstrate 214 corresponds to the area between and above the grating structures 208. In some embodiments, the superstrate 214 is air (refractive index 1.0). In other embodiments, as shown in FIG. 5C, the superstrate 214 is a coating 504. The superstrate 214 has a superstrate RI (n superstrate ) 。 The waveguide 200 has n superstrate and n sub Exceeds n swg It has.

[0020]

[0025] The waveguide substrate 201 may be formed from any suitable material so long as it is capable of adequately transmitting light of a selected wavelength or range of wavelengths and serving as a suitable support for the waveguide 100 described herein. Substrate options may include substrates of any suitable material, including, but not limited to, amorphous dielectrics, non-amorphous dielectrics, crystalline dielectrics, silicon oxides, polymers, and combinations thereof. In some embodiments, which may be combined with other embodiments described herein, the waveguide substrate 201 comprises glass, silicon (Si), silicon dioxide (SiO), germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), fused silica, quartz, sapphire (AlO), silicon carbide (SiC), lithium niobate (LiNbO), indium tin oxide (ITO), or combinations thereof. In some embodiments, which may be combined with other embodiments described herein, the waveguide substrate 201 comprises a high refractive index glass that contains greater than 2% by weight of lanthanide (Ln), titanium (Ti), tantalum (Ta), or a combination thereof.

[0021]

[0026] The slab waveguide layer 210 may include one or more of the following materials: silicon oxycarbide (SiOC), titanium dioxide (TiO), silicon dioxide (SiO), vanadium(IV) oxide (VO), aluminum oxide (AlO), aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), tin dioxide (SnO), zinc oxide (ZnO), tantalum pentoxide (TaO), silicon nitride (SiN), zirconium dioxide (ZrO), niobium oxide (NbO), cadmium stannate (CdSnO), titanium silicon oxide (TiSiO), or silicon carbonitride (SiCN). The grating material 212 may include one or more of the following materials: SiOC, TiO2, SiO2, VOx, Al2O3, AZO, ITO, SnO2, ZnO, Ta2O5, Si3N4, ZrO2, Nb2O5, Cd2SnO4, TiSiOx, or SiCN. In some embodiments, the slab waveguide material of the slab waveguide layer 210 and the grating material 212 are the same, such that n grat and n swg becomes the same as 。 In other embodiments, the slab waveguide material of the slab waveguide layer 210 is different from the grating material 212, so that n grat and n swg is different from.

[0022]

[0027] The blue, green, and red channel light propagating through both the waveguide substrate 201 and the slab waveguide layer 210 will be subject to a resonance condition because the light can be reflected at the interface between the superstrate and the substrate. superstrate ), Slab RI(n swg ), and the first slab depth (d swg1 ) and the second slab depth (d swg2 slab depth (d swg ) should be selected to reduce the diffraction efficiency ratio of blue channel light to red channel light.

[0023]

[0028] The resonance conditions for the substrate modes in the waveguide 200 occur when the following conditions are met: TIFF2026501437000010.tif6170, TIFF2026501437000011.tif5170 is Slab RI (n swg ) and TIFF2026501437000012.tif5170 is the wave number of light ( TIFF2026501437000013.tif5170), and d is the slab depth (d swg ) and TIFF2026501437000014.tif4170 is the propagation angle of light in the slab waveguide layer, TIFF2026501437000015.tif5170 is the phase accumulated during reflection at the interface between the slab waveguide and the substrate, TIFF2026501437000016.tif6170 is the phase accumulated upon reflection at the interface 213 between the slab waveguide and the superstrate. TIFF2026501437000017.tif5170 and TIFF2026501437000018.tif6170 can be calculated using the Fresnel equations.

[0024]

[0029] The slab depth between the resonance peaks (d swg The change Δd in TIFF2026501437000019.tif12170TIFF2026501437000020.tif4170 is the wavelength ( TIFF2026501437000021.tif5170) and propagation angle ( TIFF2026501437000022.tif4170). TIFF2026501437000023.tif5170 corresponds to the wavelengths of blue channel light (wavelength 380 nm to approximately 495 nm), green channel light (wavelength approximately 495 nm to approximately 590 nm), and red channel light (wavelength approximately 590 nm to approximately 750 nm).

[0025]

[0030] The diffraction efficiency of the waveguide 200 is modeled through optical simulations, including rigorous coupled-wave analysis (RCWA), finite-difference time-domain (FDTD) method, finite-element method (FEM), other simulation methods, and combinations thereof. The modeling allows for the optimal slab RI (n swg ) and slab depth (d swg ) is selected.

[0026]

[0031] 3 is a graph of simulated diffraction efficiencies for three waveguides. The simulated waveguide 100 does not include the slab waveguide layer 210. The diffraction efficiency ratio is the ratio of the minimum diffraction efficiency for blue channel light to the maximum diffraction efficiency for red channel light. The modeled waveguide 100 described herein has a diffraction efficiency DE1 of 4.5:1.0 (minimum diffraction efficiency of 18% for blue channel light vs. maximum diffraction efficiency of 4% for red channel light). Waveform 301A shows the diffraction efficiency DE1 for a wavelength of 450 nanometers (nm) for the first model of waveguide 200. Waveform 301B is the diffraction efficiency of blue channel light at a wavelength of 520 nm for the first model of waveguide 200. Waveform 301C is the diffraction efficiency of the green channel light at a wavelength of 620 nm for the first model of waveguide 200. Diffraction efficiency of red channel light in TIFF2026501437000026.tif5170. The first model of the waveguide 200 is sub A waveguide substrate 201 having a refractive index of 2.0 and a swg The waveguide 200 has a slab waveguide layer 210 of amorphous TiOx with diffraction efficiency DE2 of 2.45 at 450 nm, 2.37 at 520 nm, and 2.31 at 620 nm. A first model of the waveguide 200 has a diffraction efficiency DE2 of 1.8:1.0 at 50 nm. To improve the diffraction efficiency ratio, the waveguide 200 is modeled a second time.

[0027]

[0032] Waveform 302A is a second model of waveguide 200 with a wavelength of 450 nm. Waveform 302B is the diffraction efficiency of blue channel light at a wavelength of 520 nm for the first model of waveguide 200. Waveform 302C is the diffraction efficiency of the green channel light at a wavelength of 620 nm for the third model of waveguide 200. Diffraction efficiency of red channel light in TIFF2026501437000029.tif5170. The second model of the waveguide 200 is sub A waveguide substrate 201 having a refractive index of 2.0 and a swg The slab waveguide layer 210 is made of crystalline TiOx, with average n swg is 2.62. The second model of waveguide 200 has a diffraction efficiency DE3 of 1.1:1.0 at 35 nm. Therefore, the second model of waveguide 200 has an n of 2.0. sub , mean n of 2.62 swg , slab depth (d swg ) is included.

[0028]

[0033] In some embodiments, the substrate RI (n sub ) is 1.8 to 2.10. In another embodiment, the substrate RI (n sub ) is greater than 2.77. Table 1 shows the substrate RI (n sub ) and the corresponding slab RI(n swg ) based on the slab depth (d swg ) shows the optimal range. TIFF2026501437000030.tif74170

[0029]

[0034] 4A-4C are cross-sectional views of the waveguide 200 in different configurations. In a second configuration 402 (see FIG. 4A), the grating structure 208 of the in-coupler 202 is disposed within a slab waveguide layer 210, and the grating structures 208 of the first grating 204 and second grating 206 are disposed on top of the slab waveguide layer 210. The grating material 212 of the grating structure 208 on top of the slab waveguide layer 210 has a grating RI (n grat In some embodiments, the slab waveguide layer 210 and the grating material 212 are the same, so that n grat and n swg In other embodiments, the slab waveguide layer 210 and the grating material 212 are different, so that n grat and n swg The third configuration 403 (see FIG. 4B ) and the fourth configuration 404 (see FIG. 4C ) include a grating structure 208 disposed on the slab waveguide layer 210 (in some embodiments, on the surface of the slab waveguide layer 210). The fourth configuration 404 of the waveguide 200 includes a second slab waveguide layer 410. The slab waveguide layer 210 and the second slab waveguide layer 410 are disposed on opposite sides of the waveguide substrate 201. The second slab waveguide layer 410 includes at least a third grating 407 disposed on the second slab waveguide layer 410. In some embodiments, a fourth grating 409 is disposed on the second slab waveguide layer 410.

[0030]

[0035] 5A-5E are cross-sectional views of a grating 500. The grating 500 may correspond to at least one of the in-coupler 202, the first grating 204, or the second grating 206 of the waveguide 200. As shown in FIG. 5A, the grating structure 208 is a blazed grating structure. As shown in FIG. 5B, the grating structure 208 has parallel sidewalls 502 that are angled relative to the first surface 203 of the waveguide substrate 201. As shown in FIG. 5C, the grating structure 208 has parallel sidewalls 502 that are perpendicular to the first surface 203 of the waveguide substrate 201. The superstrate 214 is a coating 504. As shown in FIG. 5D, the grating structure 208 includes a first layer 506 of a first material and a second layer 508 of a second material. As shown in FIG. 5E, the grating structure 208 has two-dimensional periodicity.

[0031]

[0036] While the foregoing is directed to examples of the present disclosure, other and further examples of the disclosure may be devised without departing from the basic scope thereof, the scope of which is determined by the claims that follow.

Claims

1. A waveguide, Substrate refractive index (RI) (n sub a waveguide substrate having a slab waveguide layer disposed on the waveguide substrate, the slab RI(n swg ) and the slab depth (d swg a slab waveguide layer having at least one grating defined by a plurality of grating structures disposed in, on, or on the slab waveguide layer; a superstrate between and above the lattice structure, the superstrate RI(n superstrate ), and a superstrate having an interface with the slab waveguide layer, wherein the slab RI(n swg ) is the substrate RI(n sub ) and the superstrate RI (n superstrate ) exceeding Waveguide.

2. The waveguide of claim 1 , wherein the slab waveguide layer is disposed on the waveguide substrate.

3. The waveguide of claim 1 , wherein the grating structure comprises a grating material that is different from the slab waveguide of the slab waveguide layer.

4. 10. The waveguide of claim 1, wherein the grating is an in-coupler, a folded grating, or an out-coupler.

5. The slab depth (d swg 2. The waveguide of claim 1, wherein:

6. The waveguide substrate may be made of glass, silicon (Si), silicon dioxide (SiO 2 ), germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), fused silica, quartz, sapphire (Al 2 O 3 ), silicon carbide (SiC), lithium niobate (LiNbO 3 10. The waveguide of claim 1, comprising: a SiO 2 thin film (SiO 3 ), an Indium Tin Oxide (ITO), or a combination thereof.

7. The slab waveguide layer may be made of silicon oxycarbide (SiOC), titanium dioxide (TiO 2 ), silicon dioxide (SiO 2 ), vanadium (IV) oxide (VOx), aluminum oxide (Al 2 O 3 ), aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), tin dioxide (SnO 2 ), zinc oxide (ZnO), tantalum pentoxide (Ta 2 O 5 ) Silicon nitride (Si 3 N 4 ), zirconium dioxide (ZrO 2 ), niobium oxide (Nb 2 O 5 ), cadmium stannate (Cd 2 SnO 4 10. The waveguide of claim 1, comprising one or more of the following materials: titanium silicon oxide (TiSiOx), or silicon carbonitride (SiCN).

8. The substrate RI at 620 nm (n sub 2. The waveguide of claim 1, wherein σ is between 1.8 and 2.

10.

9. The substrate RI at 620 nm (n sub ) is greater than 2.

77.

10. The slab RI at 620 nm (n swg 2. The waveguide of claim 1, wherein σ is between 1.8 and 2.

6.

11. The slab depth (d swg )but, The slab RI at 620 nm (n swg ) is 2.1, and is 75 nm to 110 nm; The slab RI at 620 nm (n swg ) is 2.2, and is 55 nm to 100 nm; The slab RI at 620 nm (n swg ) is 2.3, and the thickness is 35 nm to 85 nm; The slab RI at 620 nm (n swg ) is 2.4, and is 30 nm to 70 nm; The slab RI at 620 nm (n swg ) is 2.5, and the thickness is 25 nm to 60 nm; The slab RI at 620 nm (n swg 2. The waveguide of claim 1, wherein the waveguide is 15 nm to 50 nm when .gtoreq..times ...

12. 10. The waveguide of claim 1, wherein the waveguide has a diffraction efficiency ratio of blue channel light to red channel light of 1.1:1.

0.

13. 10. The waveguide of claim 1, wherein the grating structure is a blazed grating structure.

14. The waveguide of claim 1 , wherein the grating structure has parallel sidewalls that are angled relative to the waveguide substrate.

15. The waveguide of claim 1 , wherein the grating structure has two-dimensional periodicity.

16. The waveguide of claim 1 , wherein the superstrate is a coating.

17. The waveguide is The resonance condition is During the ceremony, is the wave number of light ( ) and d is the slab depth (d swg ) and is the propagation angle of light in the slab waveguide layer, is the phase accumulated upon reflection at the interface, 10. The waveguide of claim 1, wherein ∑ is the phase accumulated upon reflection at the interface.

18. The slab depth between the resonance peaks (d swg The change Δd in During the ceremony, 18. The waveguide of claim 17, wherein λ corresponds to a wavelength of blue, green, or red channel light.

19. A waveguide, Substrate refractive index (RI) (n sub a waveguide substrate having a slab waveguide layer disposed on the waveguide substrate, the slab RI(n swg ) and the slab depth (d swg a slab waveguide layer having at least one grating defined by a plurality of grating structures disposed in, on, or on the slab waveguide layer; a superstrate between and above the lattice structure, the superstrate RI(n superstrate ), and a superstrate having an interface with the slab waveguide layer, wherein the slab RI(n swg ) is the substrate RI(n sub ) and the superstrate RI (n superstrate ) and the slab depth (d swg )teeth, The slab RI at 620 nm (n swg ) is 2.1, and is 75 nm to 110 nm; The slab RI at 620 nm (n swg ) is 2.2, and is 55 nm to 100 nm; The slab RI at 620 nm (n swg ) is 2.3, and the thickness is 35 nm to 85 nm; The slab RI at 620 nm (n swg ) is 2.4, and is 30 nm to 70 nm; The slab RI at 620 nm (n swg ) is 2.5, and the thickness is 25 nm to 60 nm; The slab RI at 620 nm (n swg ) is 2.6, it is 15 nm to 50 nm, Waveguide.

20. A waveguide, Substrate refractive index (RI) (n sub a waveguide substrate having A slab RI(n swg ) and slab depth (d swg a slab waveguide layer having a folded grating defined by a grating structure disposed within the slab waveguide layer; a superstrate between and above the lattice structure, the superstrate RI(n superstrate a superstrate having an interface with the slab waveguide layer; Equipped with The slab depth (d swg ) is from the bottom surface to the top surface of the slab waveguide layer between the grating structures, and the slab RI(n swg ) is the substrate RI(n sub ) and the superstrate RI (n superstrate ) exceeding Waveguide.

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