Non-polarized light grating in-coupler

Abstract

In an example embodiment, a diffractive element is provided. The diffractive element can include a substrate. A plurality of grating elements are provided on the substrate. Each grating element includes a first ridge region including a first ridge body region and a first core layer element; a second ridge region including a second ridge body region and a second core layer element; and a saddle region extending between the first ridge region and the second ridge region. In some embodiments, the first ridge body, the second ridge body, and the saddle region have a first refractive index (n2), and the first core layer element and the second core layer element have a second refractive index (n4) that is greater than the first refractive index.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to European Patent Application No. 20315043.8 entitled “Unpolarized Light Grating In-Coupler”, filed on March 23, 2020, the entire contents of which are hereby incorporated by reference. Background Technology

[0003] This disclosure relates to the fields of optics and photonics, and more specifically to planar optical devices. More specifically, but not exclusively, this disclosure relates to diffraction gratings widely used in a variety of devices, such as, among other examples, displays including eyeglass electronics for AR (Augmented Reality) and VR (Virtual Reality) glasses and waveguides for head-mounted displays for light input and output coupling, such as head-up displays (HUDs) in the automotive industry, optical sensors for photographic / video / light field cameras, biological / chemical sensors including on-chip laboratory sensors, microscopes, spectroscopic and metrological systems, and solar panels.

[0004] This section is intended to introduce the reader to various aspects of the art that may relate to the various aspects of this disclosure described below and / or claimed. This discussion is intended to help provide the reader with background information to facilitate a better understanding of the various aspects of the invention. Therefore, it should be understood that these statements should be interpreted in this context, rather than as an admission of prior art.

[0005] AR / VR glasses are considered the next generation of human-computer interfaces. The development of AR / VR glasses (and more generally, protective electronic devices for glasses) is associated with many challenges, including reducing the size and weight of such devices and improving image quality (in terms of contrast, field of view, color depth, etc.) to achieve a truly immersive user experience.

[0006] The trade-off between image quality and physical size in optics has driven research into ultracompact optical components that can serve as building blocks for more complex optical systems, such as AR / VR glasses. Such optical components are expected to be easy to manufacture and replicate. In these AR / VR glasses, various types of refractive and diffractive lenses and beamforming components are used to guide light from a microdisplay or projector to the human eye, allowing the formation of a virtual image that is superimposed on the image of the physical world seen with the naked eye (in the case of AR glasses) or captured by a camera (in the case of VR glasses).

[0007] Some types of AR / VR glasses utilize optical waveguides, where light propagates into the optical waveguide only within a limited internal angle range by TIR (total internal reflection). The FoV (field of view) of the waveguide depends on the material of the waveguide, etc.

[0008] In WO2017180403, a waveguide with an extended field of view is proposed, where dual-mode image propagation is used. In this method, the diffractive mode +1 is used to carry the right-hand side image in one direction (negative incident angle on the in-coupler), and the -1 mode is used to propagate the positive incident angle in the opposite direction into the waveguide. Through the pupil expander and out-coupler at the waveguide exit, the two half-images are combined so that the user sees one image. The aim of this system is to double the field of view because each half-image can use the full angular bandwidth of the waveguide in each propagation direction.

[0009] Some optical waveguides include one or more diffraction gratings. The period d of the diffraction structure (also called the grating pitch) can be selected according to the wavelength λ of the incident light and the refractive index n3 of the waveguide material. For example, it may be necessary to select the grating pitch d to be twice the light wavelength in the waveguide medium, as shown below:

[0010]

[0011] If the ratio between the grating pitch and the wavelength is considered: d / λ, in the case of Equation 1 above, 3 / 2 < n2 < 2 and 2 / 3 < d / λ < 4 / 5 can be achieved, and in any case, d / λ < 1 is a value that can be defined as sub-wavelength. Equation 1 shows that the diffraction grating has a sub-wavelength structure in any case.

[0012] In US20160231568, a waveguide for a wearable display is disclosed, where the grating pitch of the structure is between 250 nm and 500 nm.

[0013] Grating with a very small pitch may be difficult to fabricate. When the structure is sub-wavelength, gratings with a small enough pitch are unattainable by lithography techniques, and the required precision even challenges electron beam lithography techniques.

[0014] An overview of existing optical waveguide design concepts shows that there is a lack of a reliable solution that can provide a strong response for both polarizations (transverse electric wave TE and transverse magnetic wave TM). Therefore, it is desirable to provide diffraction gratings for optical waveguides or other optical components. It is further desirable that such diffraction gratings can operate with a microdisplay or other illumination sources using unpolarized light and / or incoherent light, such as digital light processors, DLP, organic light-emitting diode-based displays, OLED, or displays using unpolarized laser beams. Summary of the Invention

[0015] The terms "an embodiment," "implementation," or "exemplary embodiment" used in the specification describe embodiments that may include specific features, structures, or characteristics; however, not every embodiment necessarily includes such features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment. Additionally, when a specific feature, structure, or characteristic is described in connection with an embodiment, such feature, structure, or characteristic may be used in conjunction with other embodiments, whether or not it is explicitly described.

[0016] According to some embodiments, the diffraction element includes a substrate and a plurality of grating elements located on the substrate. Each grating element includes: a first ridge region; a second ridge region; and a saddle-shaped region extending between the first ridge region and the second ridge region, the saddle-shaped region having a first height (H1) lower than a second height (H3) of the first ridge region and the second ridge region.

[0017] In some embodiments, the first ridge region includes a first ridge body region having a first refractive index (n2) and a first core element located within the first ridge body region, the first core element having a second refractive index (n4) greater than the first refractive index, and the second ridge region includes a second ridge body region having a first refractive index (n2) and a second core element located within the second ridge body region, the second core element having a second refractive index (n4).

[0018] In some implementations, the first core element and the second core element are in contact with the substrate.

[0019] In some implementations, the substrate has a third refractive index (n3) that is less than the first refractive index (n2).

[0020] In some implementations, grating elements are periodically arranged on the substrate at grating spacing.

[0021] In some implementations, the saddle-shaped region has a first width (W4), the ridge-shaped regions each have a second width (W3), and the sum of twice the second width (W3) and the first width (W4) is less than the grating spacing.

[0022] In some implementations, the first ridge region, the second ridge region, and the saddle region contain titanium dioxide (TiO2).

[0023] In some implementations, the substrate is in contact with the substrate medium between the continuous grating elements in the diffraction element.

[0024] In some implementations, the substrate is the waveguide of the waveguide display.

[0025] A method according to some embodiments includes directing light having a first wavelength (λ) onto a diffraction element. The diffraction element includes a substrate and a plurality of grating elements located on the substrate. Each grating element includes: a first ridge region; a second ridge region; and a saddle-shaped region extending between the first ridge region and the second ridge region, the saddle-shaped region having a first height (H1) lower than a second height (H3) of the first ridge region and the second ridge region.

[0026] In some embodiments, the substrate has a third refractive index (n5), and the method further includes diffracting light to a diffraction order M2, wherein the grating element is in a position between... and The spacing between them is arranged basically periodically. In some such implementations, M2 = 2.

[0027] In some embodiments, the first ridge region includes a first ridge body region having a first refractive index (n2) and a first core element located within the first ridge body region, the first core element having a second refractive index (n4) greater than the first refractive index, and the second ridge region includes a second ridge body region having a first refractive index (n2) and a second core element located within the second ridge body region, the second core element having a second refractive index (n4).

[0028] In some implementations, the saddle-shaped region has a first width (W4), the ridge-shaped regions each have a second width (W3), and the sum of twice the second width (W3) and the first width (W4) is less than the grating spacing.

[0029] In some implementations, the first ridge region, the second ridge region, and the saddle region contain titanium dioxide (TiO2). Attached Figure Description

[0030] Figure 1A This is a schematic diagram of the cross-section of a waveguide display.

[0031] Figure 1B This is a schematic diagram of a binocular waveguide display with a first layout featuring diffractive optical components.

[0032] Figure 1C This is a schematic diagram of a binocular waveguide display with a second layout featuring diffractive optical components.

[0033] Figure 1D This is a schematic exploded view of a dual-waveguide display based on some implementation schemes.

[0034] Figure 1E This is a cross-sectional schematic diagram of a dual-waveguide display according to some implementation schemes.

[0035] Figure 1FThis is a schematic cross-sectional view of a dual-waveguide optical device showing the incident light angle and the incident coupled light angle.

[0036] Figure 2A This is a cross-sectional view illustrating an exemplary unit geometry of a U-shaped diffraction grating with an insert, according to some embodiments.

[0037] Figure 2B It is a schematic perspective partial cross-sectional view of multiple U-shaped diffraction grating elements with inserts arranged in a diffraction grating structure.

[0038] Figure 2C This is a cross-sectional view of a single-material U-shaped diffraction grating element.

[0039] Figure 2D It is a schematic perspective partial cross-sectional view of multiple single-material U-shaped elements arranged in a diffraction grating structure.

[0040] Figure 3A The diffraction properties of a first grating in an exemplary dual-waveguide system are shown. The first grating is configured to operate for blue and with blue transverse electric (TE) polarized light.

[0041] Figure 3B The diffraction properties of a first grating in an exemplary dual-waveguide system are shown, which operates with blue transverse magnetic wave (TM) polarized light.

[0042] Figure 4A The diffraction properties of a second grating in an exemplary dual-waveguide system are shown, which operates with blue TE-polarized light.

[0043] Figure 4B The diffraction performance of a second grating in an exemplary dual-waveguide system is shown, which operates with blue TM-polarized light.

[0044] Figure 5A The diffraction properties of a first grating in an exemplary dual-waveguide system are shown. The first grating is configured to operate for blue and green TE-polarized light.

[0045] Figure 5B The diffraction properties of a first grating in an exemplary dual-waveguide system are shown. The first grating is configured to operate for blue and green TM-polarized light.

[0046] Figure 6 This is a graph showing the refractive index of TiO2 over a range of wavelengths.

[0047] Figure 7A The diffraction performance of a first diffraction grating of an exemplary three-waveguide system according to some embodiments is shown. The first diffraction grating is configured to work for blue and with blue TE-polarized light.

[0048] Figure 7B The diffraction performance of a first diffraction grating in an exemplary three-waveguide system according to some embodiments is shown. The first diffraction grating operates with blue TM polarized light.

[0049] Figure 8A The diffraction performance of a first diffraction grating in an exemplary three-waveguide system is shown, which operates with green TE-polarized light.

[0050] Figure 8B The diffraction performance of a first diffraction grating in an exemplary three-waveguide system is shown, which operates with green TM polarized light.

[0051] Figure 9A The diffraction performance of a first diffraction grating in an exemplary three-waveguide system is shown, which operates with red TE-polarized light.

[0052] Figure 9B The diffraction performance of a first diffraction grating in an exemplary three-waveguide system is shown, which operates with red TM-polarized light.

[0053] Figure 10A The diffraction performance of a second diffraction grating in an exemplary three-waveguide system according to some embodiments is shown. The second diffraction grating is configured for green and operates with green TE-polarized light.

[0054] Figure 10B The diffraction performance of a second diffraction grating in an exemplary three-waveguide system according to some embodiments is shown, the second diffraction grating operating with green TM polarized light.

[0055] Figure 11A The diffraction performance of a second diffraction grating in an exemplary three-waveguide system is shown, which operates with red TE-polarized light.

[0056] Figure 11B The diffraction performance of a second diffraction grating in an exemplary three-waveguide system is shown, which operates with red TM-polarized light.

[0057] Figure 12A The diffraction performance of a third diffraction grating in an exemplary three-waveguide system according to some embodiments is shown. The third diffraction grating is configured to operate for red and with red TE-polarized light.

[0058] Figure 12B The diffraction performance of a third diffraction grating in an exemplary three-waveguide system is shown, which operates with red TM-polarized light. Detailed Implementation

[0059] This disclosure relates to the fields of optics and photonics, and more specifically to optical devices comprising at least one diffraction grating. Diffraction gratings as described herein can be used in the fields of conformal and wearable optics, such as AR / VR glasses, and in a variety of other consumer electronics including displays and / or lightweight imaging systems. Exemplary devices for applications may include head-mounted displays (HMDs) and light field trapping devices. Such diffraction gratings for modulating unpolarized light can be applied in solar cells.

[0060] An exemplary optical device is described, comprising a waveguide including an ultrawavelength diffraction grating that can be used to couple light into and / or out of the optical device. Such an optical device can be used as a waveguide, for example, in AR / VR glasses.

[0061] In exemplary embodiments, ultrawavelength incident coupling gratings can be used to simultaneously generate dense high diffraction orders for different polarizations (TE and TM). Compared to some single-material systems that may provide a strong response to only one polarization (TE or TM, depending on the element size), embodiments with two or more materials, including some embodiments using high-refractive-index materials, as described herein, may provide a strong response to both polarizations.

[0062] Some implementations are designed to provide high performance in terms of brightness for optical devices that couple light into them.

[0063] Figure 1A An exemplary waveguide display device that can employ a diffraction grating structure as described herein is shown. Figure 1A This is a schematic cross-sectional side view of the waveguide display device in operation. The image is projected by image generator 102. Image generator 102 can project the image using one or more of a variety of technologies. For example, image generator 102 can be a laser beam scanning (LBS) projector, a liquid crystal display (LCD), a light-emitting diode (LED) display (including organic LED (OLED) or micro LED (μLED) displays), a digital light processor (DLP), a liquid crystal on silicon (LCoS) display, or other types of image generators or light engines.

[0064] Light representing the image 112 generated by the image generator 102 is coupled into the waveguide 104 via a diffraction coupler 106. The coupler 106 diffracts the light representing the image 112 into one or more diffraction orders. For example, a ray 108 that is part of the bottom of the image is diffracted by the coupler 106, and one of the diffraction orders 110 (e.g., second order) is at an angle that allows it to propagate through the waveguide 104 via total internal reflection.

[0065] At least a portion of the light 110 coupled into waveguide 104 via diffraction-in coupler 106 is coupled out of the waveguide via diffraction-out coupler 114. At least some of the light coupled out of waveguide 104 replicates the angle of incidence of the light coupled into the waveguide. For example, in the illustration, the out-coupled rays 116a, 116b, and 116c replicate the angle of the in-coupled ray 108. Since the light leaving the out-coupler replicates the direction of the light entering the in-coupler, the waveguide essentially replicates the original image 112. The user's eye 118 can focus on the replicated image.

[0066] exist Figure 1A In the example, out-coupler 114 outcouples only a portion of the light in each reflection, allowing a single input beam (such as beam 108) to generate multiple parallel output beams (such as beams 116a, 116b, and 116c). In this way, even if the eye is not perfectly aligned with the center of the out-coupler, at least some light from each part of the image may reach the user's eye. For example, if eye 118 moves downwards, beam 116c may enter the eye even if beams 116a and 116b do not, so the user can still perceive the bottom of image 112 despite the positional shift. Therefore, out-coupler 114 partially operates as an out-pupil expander in the vertical direction. The waveguide may also include one or more additional out-pupil expanders (…). Figure 1A (not shown in the image) to expand the exit pupil in the horizontal direction.

[0067] In some embodiments, waveguide 104 is at least partially transparent to light originating from outside the waveguide display. For example, at least some light 120 from a real-world object (such as object 122) passes through the waveguide 104, allowing the user to see the real-world object while using the waveguide display. Since the light 120 from the real-world object also passes through diffraction grating 114, multiple diffraction orders will exist, and thus multiple images will exist. To minimize the visibility of multiple images, it is desirable that diffraction order zero (not deflected by 114) has high diffraction efficiency for light 120, while higher diffraction orders have lower energy. Therefore, in addition to extending and outcoupling virtual images, outcoupler 114 is preferably configured to pass through the zero order of the actual image. In such embodiments, the image displayed by the waveguide display may appear to be superimposed on the real world.

[0068] In some implementations, as described further in detail below, the waveguide display includes more than one waveguide layer. Each waveguide layer can be configured to preferentially deliver light with a specific wavelength range and / or angle of incidence from the image generator to the viewer.

[0069] like Figure 1B and Figure 1CAs shown, waveguide displays with inlet couplers, outlet couplers, and pupil expanders can have various different configurations. Figure 1B An exemplary layout of a binocular waveguide display is shown. Figure 1B In the example, the display includes waveguides 152a and 152b for the left and right eyes, respectively. The waveguides include in-line couplers 154a and 154b, pupil expanders 156a and 156b, and components 158a and 158b, which operate as out-couplers and horizontal pupil expanders. The pupil expanders 156a and 156b are arranged along an optical path between the in-line and out-couplers. An image generator (not shown) can be provided to each eye and is arranged to project light representing the image on the corresponding in-line coupler.

[0070] Figure 1C Another exemplary layout of a binocular waveguide display is shown in the image. Figure 1C In the example, the display includes waveguides 160a and 160b for the left and right eyes, respectively. The waveguides include ingress couplers 162a and 162b. Light from different parts of the image can be coupled by the ingress couplers 162a and 162b to different directions within the waveguides. Ingress-coupled light traveling to the left passes through pupil expanders 164a and 164b, while ingress-coupled light traveling to the right passes through pupil expanders 166a and 166b. Once the light has passed through the pupil expanders, components 168a and 168b are used to couple the light out of the waveguides, operating as both an outgress coupler and a vertical pupil expander to substantially replicate the image provided at the ingress couplers 162a and 162b.

[0071] In different implementations, different features of the waveguide display can be disposed on different surfaces of the waveguide. For example (e.g.) Figure 1A In some configurations, both the ingress and egress couplers can be positioned on the front surface of the waveguide (away from the user's eye). In other embodiments, the ingress and / or egress couplers can be positioned on the rear surface of the waveguide (facing the user's eye). The ingress and egress couplers can be positioned on opposite surfaces of the waveguide. In some embodiments, one or more of the ingress, egress, and pupil expanders can be present on both surfaces of the waveguide. The image generator can be positioned facing either the front or rear surface of the waveguide. The ingress coupler is not necessarily on the same side of the waveguide as the image generator. Any pupil expander in the waveguide can be positioned on the front, rear, or both surfaces of the waveguide. In displays with more than one waveguide layer, different layers can have different configurations of ingress, egress, and pupil expanders.

[0072] Figure 1D This is a schematic exploded view of a dual-waveguide display according to some embodiments, including an image generator 170, a first waveguide (WG1) 172 and a second waveguide (WG2) 174. Figure 1E This is a schematic side view of a dual-waveguide display according to some embodiments, including an image generator 176, a first waveguide (WG1) 178, and a second waveguide (WG2) 180. The first waveguide includes a first transmission diffraction-in coupler (DG1) 180 and a first diffraction-out coupler (DG6) 182. The second waveguide has a second transmission diffraction-in coupler (DG2) 184, a reflection diffraction-in coupler (DG3) 186, a second diffraction-out coupler (DG4) 188, and a third diffraction-out coupler (DG5) 190. Different embodiments may use different arrangements of optical components (such as different arrangements of pupil expanders) on the first and second waveguides.

[0073] Although Figures 1A to 1E The diagram illustrates the use of waveguides in near-eye displays, but the same principle can be applied to other display technologies, such as head-up displays for automotive or other applications.

[0074] Figure 1F This is a schematic cross-sectional view of a dual-waveguide optical device showing the incident light angle and the incident coupled light angle. The grating spacing of one or more diffraction gratings as described herein can be selected based on the desired range and relationship between the incident light and the incident coupled light.

[0075] Figure 1F The dual-waveguide device can use higher-order modes (diffraction order with an absolute value greater than 1) and ultrawavelength gratings to provide a high field of view. Figure 1F In this context, the angle in air is represented by the letter Θ. The angle in the waveguide is represented by the letter Φ, and is located in the waveguide and measures the angle of the diffracted light ray. The superscript C indicates the critical ray in air or the waveguide, and the superscript G indicates the grazing ray.

[0076] Figure 1F An optical device comprising a first optical waveguide WG1 and a second optical waveguide WG2 is shown. WG1 has a refractive index n3, and WG2 has a refractive index n5. These refractive indices may be the same, or they may be different from each other. Such an optical device is configured to guide an angular range of incident light comprising a series of wavelengths. Corresponding to in the Limited critical angle Let n3 be the incident angle of the critical ray diffracted into the first waveguide WG1 using diffraction order M1, where n3 is the refractive index of the first waveguide material. Assume n5 is the refractive index of the second waveguide material. For the material of the second waveguide, we use... like Figure 1FAs shown, the first waveguide WG1 is placed in front of the second optical waveguide WG2 according to the direction of light propagation. The incident light is first transmitted or diffracted by the first waveguide WG1, and then a portion of the incident light transmitted by the first waveguide WG1 is transmitted or diffracted by the second waveguide WG2 using diffraction order M2.

[0077] The first waveguide includes a diffraction grating with an ultra-wavelength grating spacing configured for second-order diffraction. This allows for the coupling of very high incident angles with extremely high field of view into the first waveguide WG1. Coupling very high incident angles without second-order diffraction would be very difficult, as it would require a very small grating spacing.

[0078] from Figure 1F It can be observed that the angular range and The first waveguide WG1 is diffracted into angular ranges respectively. and It can be seen that the angular range Angular range The range of symmetrical angles relative to the incident axis of light incident on the optical device.

[0079] Between The angular range between them is also called the transmitted beam T0, which is efficiently transmitted through the diffraction grating of the first waveguide WG1.

[0080] In the first waveguide WG1, the left-hand side of the image will propagate to the left into waveguide WG1, while the right-hand side of the image will propagate to the right.

[0081] The transmitted beam T0 has from Within the angular range, the grazing ray is located near the normal. The transmitted beam T0 will diffract on the second grating located on the second waveguide WG2, and the positive incident angle will propagate to the left in waveguide WG2, while the negative incident angle will propagate to the right in WG2.

[0082] The second grating can differ from the first grating by having a different spacing dimension, but the shapes of the first and second gratings can be similar. The shapes of the first and second gratings can be configured to highlight the nanojet wave. The second grating located in waveguide WG2 has an ultrawavelength grating spacing configured for second-order diffraction.

[0083] According to some implementations, the first grating and the second grating are configured with a grating spacing to diffract a specific corresponding angular range of light as specified above for a given wavelength, as shown below.

[0084] In some implementations, the following diffraction equation is used to calculate the spacing dimensions d1 and d2 of the diffraction gratings for each of the two corresponding waveguides WG1 and WG2, and by... Figure 1F The total field of view coupled by the optical device shown:

[0085]

[0086]

[0087]

[0088]

[0089] Here we assume n1 = 1, where n1 is the refractive index of the substrate material. Some values ​​are known. as well as Furthermore, some other values ​​are design parameters. According to an embodiment of this disclosure, and It was chosen to be approximately 75°.

[0090] It should be noted that other values ​​can be selected for the design parameters described in this paper. For example, these values ​​can be selected based on the distance the image must travel into the waveguide before being extracted, the number of total internal reflection bounces, and the waveguide thickness. and The value of is also noted. It should be pointed out that in the specific examples given above, the first and second waveguides have the same refractive index, i.e., n². However, in other embodiments, the first and second waveguides may have different refractive indices.

[0091] According to some of the implementation schemes described in this article For example, -3° is chosen. Other values ​​are possible depending on design conditions, such as whether it is desired to overlay the left and right images in the middle of the final image, or whether it is desired that the left and right images do not intersect. In the disclosed embodiment, the value -3° may produce a final image comprising left and right images with a black band in the middle. However, in some applications, this band is not desired, and it can be selected... Other values.

[0092] The previous set of equations can be used to solve for the spacing dimensions. According to the last equation:

[0093]

[0094] Substituting into the above equation, we can obtain the critical incident angle of the second grating:

[0095]

[0096] Subsequently, due to therefore and

[0097]

[0098] U-shaped structure with high refractive index insert

[0099] Exemplary implementations include ultrawavelength-input coupling gratings that can simultaneously generate dense, high diffraction orders for both transverse electric (TE) and transverse magnetic (TM) polarization. Compared to single-material U-shaped systems that provide a strong response to only one polarization (TE or TM, depending on element size), using a dual-material U-shaped system provides a diffraction grating with a strong response to both polarizations. In some examples, the element size within the unit cell of the diffraction grating constructed for TM polarization is larger than the element size within the unit cell of the grating constructed for TE polarization. By maintaining the external parameters of the system constructed for TM polarization, inserts with a refractive index of n4 (n4 > n2, the ratio between refractive indices n2 and n4 is expected to provide the desired nanojet beam radiation angle) can be added. In some implementations, it has been found that two additional nanojet beams are generated within each insert, combined with total internal reflection at the outer walls of the element within the unit cell, to provide additional input resulting in a high-intensity response to TE polarization.

[0100] As described below, an exemplary topology can be represented as a U-shaped structure, where a high-refractive-index insert provides a high-efficiency response for the system. In some embodiments, the sides of the U-shaped structure can be described as ridge regions, and the base of the U-shaped structure can be described as a saddle-shaped region, and the insert can be described as a core element. In the examples described herein, n1 is the refractive index of the substrate medium (e.g., ambient air), n3 is the refractive index of the substrate, and n1 <n3<n2<n4。

[0101] Figure 2A A cross-sectional view of an exemplary unit geometry of a U-shaped diffraction grating with an insert, according to some embodiments, is shown. Figure 2B A schematic perspective cross-sectional view is provided of multiple U-shaped diffraction grating elements with inserts arranged in a diffraction grating structure. Figure 2B In the grating structure, the grating elements are substantially straight and arranged substantially parallel to each other. Although Figure 2B Only three grating elements are shown, but some implementations include thousands of grating elements. Grating structures, such as Figure 2B The grating structure can be used as a diffraction in-coupler or out-coupler for waveguide displays.

[0102] Figure 2BA diffraction element 200 including a substrate 202 is shown. A plurality of grating elements 204, 206, and 208 are arranged on the substrate. Each grating element includes a first ridge region 210 having a first ridge body region 212 and a first core layer element 214. Each grating element further includes a second ridge region 220 having a second ridge body region 222 and a second core layer element 224. A saddle-shaped region 226 extends between the first and second ridge regions. In some embodiments, the first ridge body, the second ridge body, and the saddle-shaped region have a first refractive index (n2), and the first and second core layer elements have a second refractive index (n4) greater than the first refractive index.

[0103] The saddle-shaped region has a first height (H1), which is lower than the second height (H3) of the first ridge region and the second ridge region. In some embodiments, the substrate is in contact with a substrate medium between successive grating elements in the diffraction element, as shown, for example, at region 270 of substrate 202. The grating elements may be arranged in a one-dimensional grating array.

[0104] Figure 2B The diffraction element 200 may alternatively be described as comprising a substrate 202 and a plurality of grating core elements 214, 224, 234, 244, 254, 264 arranged substantially parallel to each other on the substrate, wherein the grating core elements have a second refractive index (n4). A plurality of cover elements 215, 235, 255 are arranged substantially periodically, each cover element successively covering two adjacent grating core elements. The cover elements have a first refractive index (n2) lower than the second refractive index (n4).

[0105] In an exemplary embodiment, a diffraction grating is provided, wherein the diffraction grating has a U-shaped unit cell including an insert region. In some embodiments, one or more such diffraction gratings are provided for one or more waveguides in a waveguide display with a wide field of view. In one embodiment, in a monochromatic system with λ = 460 nm, a combination of two waveguides is provided.

[0106] In some implementations, the spacing size can be selected for the blue color and the substrate with a refractive index of n3 = n5 = 1.52. The elements of the U-shaped diffraction grating with inserts combine components with refractive indices of n2 = 2.5 and n4 = 3.4. The first grating has a spacing size d1 = 467.1 nm, and the U-shaped structure will have W1 = 140 nm; H1 = 20 nm; W2 = 100 nm; H2 = 220 nm; W3 = 140 nm; H3 = 240 nm; W4 = 100 nm. For the second exemplary waveguide, the diffraction grating has a spacing size equal to d2 = 605.5 nm and parameters W1 = 220 nm; H1 = 10 nm; W2 = 60 nm; H2 = 160 nm; W3 = 115 nm; H3 = 200 nm; W4 = 190 nm.

[0107] Figure 3A The performance of a first diffraction grating in an exemplary dual-waveguide system is shown. The first diffraction grating is configured for blue (λ = 460 nm) and operates with TE polarization. Figure 3B The performance of a first grating in an exemplary dual-waveguide system is shown, which operates with blue TM-polarized light. Figure 4A and Figure 4B The performance of the second diffraction grating in an exemplary dual-waveguide system is shown.

[0108] Figure 3A and Figure 3B The diffraction performance of the first grating is shown. The ±2 diffraction order exhibits high efficiency and high uniformity over an angular range of 30° to 72° (-30° to -72°), and it also demonstrates very high transmission efficiency for a field of view of ±30°. Figures 3A to 3B It can be observed that in the first waveguide (WG1), high diffraction efficiency of ±2 diffraction orders (up to 80% for both polarizations) and high transmittance of order 0 in the angular range of 30° to 72° (-30° to -72°) are obtained.

[0109] Figures 4A to 4B The second grating used for the second waveguide (WG2) is shown to provide high diffraction efficiency. For example, Figure 4A The results show approximately 50% diffraction efficiency for TE polarization with ±2 diffraction orders within the angular range of -30° to 30°. Figure 4B The diffraction efficiency of approximately 80% for ±2 diffraction orders of TM polarization is shown within the angular range of -30° to 30°. Figure 4A and Figure 4B It is shown that for a transmission field of ±30° through the first grating, very high diffraction efficiency and uniformity are again obtained within this angular range.

[0110] Waveguide Combination

[0111] Some implementations combine waveguides for use in full RGB systems. As mentioned earlier, by analyzing the diffraction performance of diffraction gratings constructed for the three wavelengths corresponding to red (625nm), green (530nm), and blue (460nm), it can be deduced that in some implementations, a full RGB display system requires only four waveguides instead of six.

[0112] If the two waveguides previously shown and configured for blue are used in a full RBG system, the transmittance at 0 diffraction order is of interest to the waves corresponding to green and red. For example, at λ = 530 nm, in an angular range of 30° to 20° (-30° to -20°), the system shown has a very low transmittance at 0 diffraction order, such as... Figure 5A and Figure 5B As shown.

[0113] Figure 5A and Figure 5B The diffraction properties of the first grating at λ = 530 nm (green) are shown. Figure 5A The reflection and transmission of TE waves are shown, and Figure 5B The reflection and transmission of TM waves are shown.

[0114] It should be noted that the simulation did not account for the dispersion of the insert material at visible wavelengths. This fact can be modified, and in some cases, can even improve the system's performance.

[0115] U-shaped structure of high refractive index material

[0116] Some implementations include ultrawavelength ingress coupling gratings with a high-refractive-index monomaterial U-shaped element that does not have an insert, which can simultaneously produce dense ±2 diffraction steps for two polarizations (TE and TM). Figure 2C The image shows a cross-sectional view of a single-material U-shaped element. Figure 2D A schematic perspective partial cross-sectional view of multiple single-material U-shaped elements arranged in a diffraction grating structure is provided. Figure 2D In a grating structure, the grating elements are substantially straight and arranged substantially parallel to each other. In alternative diffraction structures, such as those used to focus incident light, the grating elements can be curved (e.g., different grating elements can be concentric with each other). Although Figure 2D Only three grating elements are shown, but some implementations include thousands of grating elements. Grating structures, such as Figure 2D The grating structure can be used as a diffraction in-coupler or out-coupler for waveguide displays.

[0117] Figure 2DA diffractive optical element 300 including a substrate 302 is shown. A plurality of grating elements 304, 306, and 308 are arranged on the substrate. Each grating element includes a first ridge region 310, a second ridge region 312, and a saddle-shaped region 314 extending between the first and second ridge regions. The saddle-shaped region has a first height (H1) lower than a second height (H3) of the first and second ridge regions. The saddle-shaped region may be adjacent to the ridge regions.

[0118] Compared to previous diffraction grating systems that primarily provided a strong response to a single polarization (TE or TM, depending on the element size), it has been demonstrated that increasing the refractive index of the element can produce a diffraction grating that is essentially independent of polarization. The data shown were obtained using COMSOL Multiphysics software. The system was constructed by using TiO2 as the material for the U-shaped elements and a glass with a refractive index n3 = 1.7 as the substrate material for all three waveguides. The numerical simulations shown account for the dispersion of TiO2, as described in JRDevore's "Refractive indices of rutile and sphalerite," Journal of the Optical Society of America (J. Opt. Soc. Am.) 41, 416-419 (1951). Figure 6 This is a graph showing the refractive index values ​​of TiO2 over a range of wavelengths.

[0119] According to such Figure 6 The ordinary spectral measurement results shown yielded the following refractive index values ​​for three different colors: n² = 2.7878 for blue (λ = 460 nm); n² = 2.6702 for green (λ = 530 nm); and n² = 2.5884 for red (λ = 625 nm).

[0120] The figures discussed below illustrate a set of numerical simulations of a diffraction grating with a high-refractive-index U-shaped topology constructed for two polarizations. In the simulations, n1 is the refractive index of the substrate medium, and n1 = 1. Waveguide combinations that may be used in a full RGB system are considered. As described in EP 3588150A1, a full RGB system with FoV = 88° is provided using three waveguides with diffraction gratings constructed for three wavelengths corresponding to red (625 nm), green (530 nm), and blue (460 nm) with n3 = 1.7.

[0121] Figure 7A and Figure 7BThe diffraction performance of the first waveguide (WG1) for blue (λ = 460 nm) is shown. The first grating of the first waveguide (WG1) is configured for blue to achieve high diffraction efficiency in ±2 diffraction orders over an angular range of 0° to 44° (-44° to 0°). The first grating of WG1 has a spacing dimension d1 = 542.96 nm, and the U-shaped structure has W4 = 150 nm; H1 = 10 nm; W3 = 110 nm; H3 = 180 nm. By combining the responses of the two polarizations, fairly good diffraction homogeneity can be obtained in ±2 order transmitted waves. Figure 8A and Figure 8B The diffraction performance of WG1 for green (λ = 530 nm) is shown. It is known that at the wavelength corresponding to green (530 nm), this diffraction grating will provide high diffraction efficiency of ±2 diffraction orders for both polarizations in the angular range of 14.6° to 72° (-14.6° to -72°) (up to 77% for TE polarization and up to 36% for TM polarization). For both polarizations, there is also high transmittance of the 0th order (approximately 80%) in the range of -14.6° to 14.6°. In the case of TM polarization, the relatively high intensity of the transmitted 0th order wave can be used to generate dense ±2 orders in the next waveguide at angles above 14.6° and below -14.6°. Figure 9A and Figure 9B The diffraction performance of WG1 for red (λ = 625 nm) is shown. Red light passes through a first diffraction grating, which has high transmittance of order 0 in the angular range of -37° to 37°. High diffraction efficiency of ±2 diffraction orders with TE polarization is also observed at angles of -90° to -37° and 37° to 90°. In the case of TE polarization, the corresponding input for ±2 diffraction orders will be 1 / 2 cycle (less than 15%).

[0122] Figure 10A and Figure 10B The diffraction performance of the second waveguide (WG2) for green (λ = 530 nm) is shown. The grating of WG2 is constructed for green to achieve high diffraction efficiency of ±2 diffraction orders within an angular range of 0° to 44° (-44° to 0°). The grating of WG2 has a spacing dimension d2 = 625.58 nm and such parameters W4 = 180 nm; H1 = 20 nm; W3 = 140 nm; H3 = 220 nm. The combination of the responses of the two polarizations provides high diffraction uniformity of the overall response. Figure 11A and Figure 11BThe diffraction performance of WG2 for red (λ = 625 nm) is shown. It is known that for red (625 nm), this diffraction grating will have dense ±2 diffraction orders in the angular range of 17° to 86.5° (-86.5° to -17°). As in the previous case, the 0th order transmittance in the range of -17° to 17° is good. It is fairly uniform for both polarizations and is approximately 80%. In the case of TM polarization, the fairly high transmittance of the 0th order at angles above 17° and below -17° will be input into the ±2 diffraction orders generated by the next waveguide.

[0123] Figure 12A and Figure 12B The diffraction performance of a third waveguide (WG3) diffraction grating for red (λ = 625 nm) is shown. The grating of WG3 is constructed for red at λ = 625 nm to achieve high diffraction efficiency of ±2 diffraction orders within an angular range of 0° to 44° (-44° to 0°). The grating of WG3 has a spacing dimension d3 = 737.72 nm, and the U-shaped structure has W4 = 210 nm; H1 = 40 nm; W3 = 160 nm; H3 = 300 nm.

[0124] Other implementation plans

[0125] Examples of ultra-wavelength incident coupling gratings with inserts can simultaneously produce dense high diffraction orders for both polarizations (TE and TM). In some embodiments, two waveguides with diffraction gratings constructed for a specific wavelength can be implemented in a monochrome display system with a substantially hemispherical field of view. In some embodiments, a combination of waveguides including U-shaped grating elements with inserts can be implemented in a full RGB system. To obtain a full RGB system, some embodiments use four waveguides instead of six. The system can be configured to achieve a proper balance of system performance by considering the pure response of the system at certain incident angles. To fabricate such diffraction gratings, silicon can be used as the material for the inserts.

[0126] It has been demonstrated that ultrawavelength coupling implementations using high-refractive-index dispersive material gratings can simultaneously produce dense, high-diffraction orders for two polarizations (TE and TM). Combining three waveguides with diffraction gratings configured to correspond to the three wavelengths corresponding to red, green, and blue yields a high-performance full RGB system. In some implementations, four waveguides are used instead of six to achieve a full RGB stereo system with a wide FoV. Three waveguides can also be used when the waveguide material has a high refractive index. In some implementations, additional waveguides can be used to increase the system's field of view.

[0127] While the examples above primarily involve the use of couplers configured for visible light, other embodiments are configured to use longer or shorter wavelengths, such as infrared or ultraviolet, or other portions of the electromagnetic spectrum. Such embodiments may employ materials that are transparent to their designed wavelength.

[0128] In various implementations, the diffraction grating structure described herein can be used as an input coupler, an output coupler, or both. For example, a waveguide can be provided in which a diffraction grating as described herein serves as the input coupler, and another diffraction grating as described herein serves as the output coupler. In some such implementations, the input and output couplers may have the same spacing and / or may have common other optical properties.

[0129] The implementation of using a U-shaped structure to construct gratings for higher-order diffraction allows for the use of substantially larger spacing dimensions, making it easier to manufacture what was difficult to do using previous techniques.

[0130] In some implementations, the diffractive element is used as the input coupler for the first waveguide in a dual-waveguide system, such as... Figure 1F The system shown. In such embodiments, the grating elements can be arranged substantially periodically at a spacing between the following two:

[0131]

[0132] and

[0133]

[0134] Where M1 is an integer representing the diffraction order, λ is the wavelength of the incident light, and n3 is the refractive index of the substrate of the first waveguide.

[0135] In some implementations, the diffractive element is used as the input coupler for the second waveguide in a dual-waveguide system, such as... Figure 1F The system shown. In such embodiments, the grating elements can be arranged substantially periodically at a spacing between the following two:

[0136]

[0137] and

[0138]

[0139] Where M2 is an integer representing the diffraction order, λ is the wavelength of the incident light, and n5 is the refractive index of the substrate of the second waveguide.

[0140] In some embodiments, the grating elements of the first diffraction grating are arranged substantially periodically with a spacing between 160 nm and 390 nm, wherein n3 and n5 are between 1.5 and 2.0, M1 = 1, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0141] In some embodiments, the grating elements of the first diffraction grating are arranged substantially periodically with a spacing between 320 nm and 780 nm, wherein n3 and n5 are between 1.5 and 2.0, M1 = 2, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0142] In some embodiments, the grating elements of the second diffraction grating are arranged substantially periodically with a spacing between 170 nm and 355 nm, wherein n5 is between 1.5 and 2.0, M2 = 1, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0143] In some implementations, the grating elements of the first diffraction grating are arranged substantially periodically with a spacing between 340 nm and 710 nm, where n3 is between 1.5 and 2.0 and M2 = 2.

[0144] In some implementations, the grating elements of the diffraction grating are arranged substantially periodically with a spacing between 160 nm and 390 nm, wherein n3 and n5 are between 1.5 and 2.0, M1 = M2 = 1, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0145] In some implementations, the grating elements of the diffraction grating are arranged substantially periodically with a spacing between 320 nm and 780 nm, wherein n3 and n5 are between 1.5 and 2.0, M1 = M2 = 2, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0146] In some embodiments, the grating elements of the diffraction grating are arranged substantially periodically with a spacing between 160 nm and 780 nm, wherein n3 and n5 are between 1.5 and 2.0, M1 and M2 are 1 or 2, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0147] In some implementations, the grating elements are arranged substantially periodically with a spacing between 230 nm and 520 nm, where n3 and n5 are between 1.5 and 2.0, M = 1, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0148] In some implementations, the grating elements are arranged substantially periodically with a spacing between 460 nm and 1040 nm, where n3 is between 1.5 and 2.0, M = 2, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0149] In some implementations, the grating elements are arranged substantially periodically with a spacing between 230 nm and 1040 nm, where n3 is between 1.5 and 2.0, M is equal to 1 or 2, where M is the diffraction order of the diffraction grating, and the wavelength (λ) of the incident light is between 460 nm and 625 nm.

[0150] According to some embodiments, a diffraction element includes a substrate and a plurality of grating elements located on the substrate, each grating element including: a first ridge region including a first ridge body region and a first core element; a second ridge region including a second ridge body region and a second core element; and a saddle region extending between the first ridge region and the second ridge region; wherein the first ridge body, the second ridge body, and the saddle region have a first refractive index (n2), and the first core element and the second core element have a second refractive index (n4) greater than the first refractive index.

[0151] In some implementations, the substrate has a third refractive index (n3) that is less than the first refractive index (n2).

[0152] In some implementations, grating elements are arranged substantially periodically on the substrate.

[0153] In some implementations, the grating elements are arranged substantially periodically at a selected spacing, wherein the spacing is selected based on the wavelength, the third refractive index (n3) of the substrate, and the diffraction order.

[0154] In some implementations, the grating element is positioned between and The spacing between them is arranged periodically, where M2 is an integer representing the diffraction order (e.g., 1 or 2), λ is the wavelength of the incident light, and n5 is the refractive index of the substrate of the second waveguide.

[0155] In some implementations, the grating element is positioned between and The spacing between them is arranged basically periodically, where M1 is an integer representing the diffraction order (e.g., 1 or 2), λ is the wavelength of the incident light, and n3 is the refractive index of the substrate of the first waveguide.

[0156] In some implementations, the grating elements are arranged substantially periodically with a spacing between 400 nm and 800 nm.

[0157] In some implementations, the grating elements are arranged substantially periodically with a spacing of less than 400 nm.

[0158] In some implementations, the grating elements are arranged substantially periodically with a spacing greater than 800 nm.

[0159] In some implementations, the first ridge region and the second ridge region each have a width between 100 nm and 200 nm.

[0160] In some implementations, the first ridge region and the second ridge region each have a width of the grating element spacing between 0.1 and 0.3.

[0161] In some embodiments, the saddle-shaped regions have a first height (H1) and a first width (W4), and the ridge-shaped regions each have a second height (H3) and a second width (W3), wherein H1 is lower than H3; and in Where θ i It is the angle between the incident light and the normal to the top surface of the diffraction grating, and n1 is the refractive index of the substrate medium in which the diffraction element is placed.

[0162] In some implementations, the first width (W4) of the saddle-shaped region is less than one-third of the spacing between the diffraction elements.

[0163] In some implementations, twice the second width (W3) plus the first width (W4) is less than the spacing of the diffraction element.

[0164] In some implementations, the first core element and the second core element each have a width between 50 nm and 200 nm.

[0165] In some implementations, the first core element and the second core element each have a width between 0.4 and 0.8, which is the same as the width of the first ridge region and the second ridge region, respectively.

[0166] In some implementations, the first core element and the second core element are in contact with the substrate.

[0167] In some implementations, the substrate is in contact with the substrate medium between the continuous grating elements in the diffraction element.

[0168] In some implementations, the multiple grating elements are substantially straight and substantially parallel to each other.

[0169] In some implementations, multiple grating elements are arranged in a one-dimensional grating.

[0170] In some implementations, the diffraction element is configured as the input coupler of the waveguide.

[0171] In some implementations, the substrate is made of a material selected from the group consisting of glass, plastic and polymer materials.

[0172] In some implementations, the substrate has a third refractive index (n3) of 1.5 ± 5%.

[0173] In some implementations, the substrate has a third refractive index (n3) of no more than about 1.7.

[0174] In some implementations, the substrate has a third refractive index (n3) of no more than about 2.0.

[0175] In some implementations, the first ridge region, the second ridge region, and the saddle region are essentially composed of TiO2.

[0176] In some implementations, the first ridge region, the second ridge region, and the saddle region have a first refractive index (n2) of about 2.5.

[0177] In some implementations, the first ridge region, the second ridge region, and the saddle region have a first refractive index (n2) greater than 2.0.

[0178] In some implementations, the core refractive index (n4) is greater than 2.5.

[0179] In some implementations, the core refractive index (n4) is greater than 2.0.

[0180] In some implementations, the first and second core elements are essentially composed of silicon.

[0181] A method for manufacturing a diffraction element according to some embodiments includes: forming a plurality of grating elements on a substrate, each grating element comprising: forming a first core layer region and a second core layer region on the substrate; forming a first ridge body on the first core layer region, forming a second ridge body on the second core layer region, and forming a saddle region on the substrate between the first core layer region and the second core layer region; wherein the first ridge body, the second ridge body and the saddle region are formed of a material having a first refractive index (n2), and the first core layer and the second core layer are formed of a material having a core layer refractive index (n4) greater than the first refractive index.

[0182] According to some embodiments, the diffraction element includes: a substrate; a plurality of grating core elements arranged substantially parallel to each other on the substrate, the grating core elements having a core refractive index (n4); and a plurality of cover elements arranged substantially periodically, each cover element successively covering two adjacent grating core elements, the cover element having a first refractive index (n2) lower than the second refractive index (n4).

[0183] In some implementations, each grating core element in the grating core element is substantially covered by one of the covering elements.

[0184] In some implementations, the core elements are arranged substantially periodically.

[0185] In some implementations, the cover elements are arranged substantially periodically at a first spacing, and the core elements are arranged substantially periodically at a second spacing, which is substantially half the first spacing.

[0186] In some implementations, the cover elements are substantially parallel to each other and parallel to the grating core elements.

[0187] A method for manufacturing a diffractive element according to some embodiments includes: forming a plurality of grating core elements on a substrate, the plurality of grating core elements being arranged substantially parallel to each other on the substrate, the grating core elements having a core refractive index (n4); and forming a plurality of cover elements, each of the plurality of cover elements continuously covering two adjacent grating core elements, the cover element having a first refractive index (n2) lower than the second refractive index (n4).

[0188] According to some embodiments, the diffraction element includes: a substrate; a plurality of grating elements located on the substrate, each grating element including: a first ridge region; a second ridge region; and a saddle region extending between the first ridge region and the second ridge region.

[0189] In some implementations, grating elements are arranged substantially periodically on the substrate.

[0190] In some implementations, the multiple grating elements are substantially straight and substantially parallel to each other.

[0191] In some implementations, the first ridge region, the second ridge region, and the saddle region have a refractive index greater than 2.0 for visible light.

[0192] In some implementations, the first ridge region, the second ridge region, and the saddle region have a refractive index greater than 2.4 for visible light.

[0193] In some implementations, the refractive index of the first ridge region, the second ridge region, and the saddle region for visible light is greater than 1.2 times the refractive index of the substrate for visible light.

[0194] In some implementations, the refractive index of the first ridge region, the second ridge region, and the saddle region for visible light is greater than 1.4 times the refractive index of the substrate for visible light.

[0195] In some implementations, the first ridge region, the second ridge region, and the saddle region comprise TiO2.

[0196] In some implementations, the first ridge region, the second ridge region, and the saddle region are essentially composed of TiO2.

[0197] In some implementations, the first ridge region, the second ridge region, and the saddle region are made of a dispersive material.

[0198] A method for manufacturing a diffractive element according to some embodiments includes forming a plurality of grating elements on a substrate, wherein forming each grating element includes forming a first ridge on the substrate, forming a second ridge on the substrate, and forming a saddle-shaped region on the substrate located between the first ridge and the second ridge.

[0199] The method according to some embodiments includes: guiding light having a first wavelength onto a diffraction element, wherein the diffraction element includes: a substrate having a third refractive index (n3); a plurality of grating elements located on the substrate, each grating element including: a first ridge region including a first ridge body region and a first core element; a second ridge region including a second ridge body region and a second core element; and a saddle region extending between the first ridge region and the second ridge region; wherein the first ridge body, the second ridge body, and the saddle region have a first refractive index (n2), and the first core element and the second core element have a second refractive index (n4) greater than the first refractive index.

[0200] In some implementations, the grating elements are arranged substantially periodically at a spacing between 1.0 and 1.2 times the first wavelength.

[0201] In some implementations, the grating elements are arranged substantially periodically with a spacing between 400 nm and 800 nm, wherein the third refractive index (n3) is 1.52, and wherein the first wavelength is between 450 nm and 700 nm.

[0202] In some embodiments, the grating elements are arranged substantially periodically with a spacing between 400 nm and 800 nm, wherein the third refractive index (n3) is 1.5 ± 5%, wherein the first wavelength is between 450 nm and 700 nm, and wherein the diffraction elements diffract at least a portion of the light to the second diffraction order.

[0203] In some implementations, the light is unpolarized.

[0204] In some implementations, the light includes TE-polarized light and TM-polarized light.

[0205] In some embodiments, the first ridge region, the second ridge region, and the saddle region have a refractive index greater than 2.0, and the substrate has a refractive index less than 2.0.

[0206] Although the features and elements have been described above in specific combinations, those skilled in the art will understand that each feature or element may be used alone or in any combination with other features and elements.

Claims

1. A diffraction element, the diffraction element comprising: Substrate; A plurality of grating elements are located on the substrate, each grating element having a U-shaped cross-section and comprising: First ridge-shaped region; The second ridge-shaped region; and A saddle-shaped region extending between the first ridge region and the second ridge region, the saddle-shaped region having a first height (H1) lower than a second height (H3) of the first ridge region and the second ridge region. The first ridge region includes a first ridge body region having a first refractive index (n2) and a first core element located inside the first ridge body region, wherein the first core element has a second refractive index (n4) greater than the first refractive index; and The second ridge region includes a second ridge body region having the first refractive index (n2) and a second core element located inside the second ridge body region, the second core element having the second refractive index (n4).

2. The diffraction element according to claim 1, wherein the first core element and the second core element are in contact with the substrate.

3. The diffraction element according to claim 1, wherein the substrate has a third refractive index (n3) that is less than the first refractive index (n2).

4. The diffraction element according to any one of the preceding claims, wherein the grating elements are periodically arranged on the substrate at a grating spacing.

5. The diffraction element according to claim 4, wherein the saddle-shaped region has a first width (W4), each of the ridge-shaped regions has a second width (W3), and the sum of twice the second width (W3) and the first width (W4) is less than the grating spacing.

6. The diffraction element according to claim 1, wherein the first core element and the second core element are composed of silicon.

7. The diffraction element according to claim 1, wherein the substrate is in contact with a substrate medium between the successive grating elements in the diffraction element.

8. The diffraction element according to claim 1, wherein the substrate is a waveguide of a waveguide display.

9. A method for a diffractive element, the method comprising: Will have the first wavelength ( The light is guided onto the diffraction element, wherein the diffraction element comprises: Substrate; A plurality of grating elements are located on the substrate, each grating element comprising: First ridge-shaped region; The second ridge-shaped region; and A saddle-shaped region extending between the first ridge region and the second ridge region, the saddle-shaped region having a first height (H1) lower than a second height (H3) of the first ridge region and the second ridge region. The first ridge region includes a first ridge body region having a first refractive index (n2) and a first core element located inside the first ridge body region, wherein the first core element has a second refractive index (n4) greater than the first refractive index; and The second ridge region includes a second ridge body region having the first refractive index (n2) and a second core element located inside the second ridge body region, the second core element having the second refractive index (n4).

10. The method of claim 9, wherein the substrate has a third refractive index (n5), wherein the method further comprises diffracting the light to a diffraction order. And wherein the grating elements are arranged substantially periodically at a spacing between the following two: and 。 11. The method of claim 10, wherein .

12. The method of claim 9, wherein the saddle-shaped region has a first width (W4), each of the ridge-shaped regions has a second width (W3), and the sum of twice the second width (W3) and the first width (W4) is less than the grating spacing.

13. The method of claim 9, wherein the first core element and the second core element are composed of silicon.

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