A mid-step grating waveguide and AR display device

Abstract

This invention relates to the field of AR displays and discloses a mid-echelon grating waveguide and an AR display device. The waveguide structure includes a waveguide, a coupling grating, a relay grating, and an output grating. The coupling grating, relay grating, and output grating are all mid-echelon gratings and are respectively disposed on the surface of the waveguide. The coupling grating is used to select red, green, and blue light with high diffraction order m, and to ensure that the red, green, and blue light diffract at the same diffraction angle θ. d The light enters the waveguide and is then transmitted to the relay grating; the relay grating is used to deflect and expand the pupil of red, green, and blue light, and to make the red, green, and blue light diffract at the same angle θ. d The light is transmitted to the output grating; the output grating is used to couple red, green, and blue light out of the waveguide. This solution addresses the high production cost of surface-embossed grating waveguides and the problem of multi-layer waveguide stacking, achieving easy processing, single-layer color, and thinness.

Description

Technical Field

[0001] This invention relates to the field of AR display, and more specifically, to an echelle grating waveguide and an AR display device. Background Technology

[0002] Augmented reality (AR) devices project a virtual image of a distant object onto the viewer's eye using pixels on a display and a series of optical imaging elements. AR devices require perspective; they need to see both the real external world and the virtual information, so their imaging system cannot obstruct the viewer's line of sight. Therefore, AR devices use optical combiners to integrate virtual information and the real scene in a "layered" manner, allowing them to complement and enhance each other. Currently, waveguide solutions are widely used in the optical combiners of AR devices. Specifically, after the display completes the imaging process, the waveguide couples light into its own glass lens, transmitting the light to the front of the eye and releasing it through total internal reflection. Based on the difference in the coupling structure of light entering and exiting the waveguide, waveguide solutions are divided into two main categories: geometric waveguides and diffractive waveguides.

[0003] Among these, diffractive waveguides are currently the mainstream development direction due to their simpler fabrication process. Most AR R&D companies in the industry, such as HoloLens, Vuzix Blade, and Magic Leap One, are dedicated to the development of surface relief grating waveguides (SRGs). Thanks to the flexibility of the SRG structure, they outperform holographic gratings in terms of optical efficiency, field of view, and sharpness; however, this superior performance requires a more complex structure to achieve. The fabrication of SRGs begins with creating an imprint template through electron beam lithography or ion beam etching, followed by replicating countless identical gratings using nanoimprint technology. Because the nanoscale template fabrication and the equipment used for grating replication are both expensive, there are not many manufacturers, and mass production has not yet been achieved. Companies that use volume grating waveguides (VHGs) include Diglens and Sony. The performance of VHGs is limited by the materials available for the holographic grating structure, and the refractive index difference that can be achieved is limited. Therefore, its performance is inferior to that of surface relief grating waveguides (SRGs), but it has lower manufacturing costs and is easier to process.

[0004] For surface-relief grating waveguides (SRGs), monochrome displays can be easily achieved, with coupling efficiencies reaching 0.7 and diagonal field of view exceeding 70°. However, due to the strict wavelength selectivity of diffraction elements, color displays primarily rely on stacking three or two waveguides, with each grating layer acting only for specific wavelengths. Stacking three or two waveguides results in a larger overall thickness and volume compared to a single-layer waveguide, increasing the burden on the bridge of the nose and hindering a comfortable wearing experience. Furthermore, increasing the number of waveguide layers significantly reduces ambient light transmittance, increases light energy loss from the light source, and raises internal losses, often leading to coupling efficiencies of less than 1%. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of at least one of the above-mentioned prior art and provide a mid-step grating waveguide and AR display device to solve the problems of high production cost of surface relief grating waveguide and multi-layer waveguide stacking, so as to achieve the effects of easy processing, single-layer color and thinness.

[0006] The technical solution adopted in this invention is a mid-chisele grating waveguide, comprising a waveguide, a coupling grating, a relay grating, and an output grating. RGB three-color light, namely red, green, and blue light, enters the waveguide through the coupling grating and propagates within it. It is then deflected and expanded by the relay grating, and finally exits the waveguide through the output grating. The coupling grating, relay grating, and output grating are all mid-chisele gratings and are respectively disposed on the surface of the waveguide. The coupling grating is used to select red, green, and blue light with high diffraction order m, and to ensure that the red, green, and blue light diffract at the same diffraction angle θ. d The light enters the waveguide and is then transmitted to the relay grating; the relay grating is used to deflect and expand the pupil of red, green, and blue light, and to make the red, green, and blue light diffract at the same angle θ. d Transmission to the output grating; the output grating is used to couple red, green and blue light out of the waveguide.

[0007] In this scheme, on the one hand, the coupling grating, relay grating, and coupling output grating of the surface-embossed grating waveguide adopt echelle gratings with superwavelength periodicity. The grating period of the echelle grating is on the order of micrometers, significantly reducing the processing precision and eliminating the need for extremely expensive nanoscale processing and inspection equipment. Furthermore, echelle gratings are already widely used in the field of dispersive spectrometers, and their manufacturing process is mature, offering significant advantages in mass production and improved yield, enabling their widespread adoption and industrialization, thereby solving the problem of high production costs for surface-embossed grating waveguides. On the other hand, the coupling grating selects diffracted light of different high diffraction orders m for red, green, and blue light, ensuring that red, green, and blue light maintain the same diffraction angle θ. dThis method achieves low-dispersion transmission of a single-layer colored beam by propagating within the waveguide and finally coupling it out of the waveguide via an output grating, thus solving the problem of multi-layer waveguide stacking. This scheme uses echelle gratings with ultra-wavelength periodic scales as the input grating, relay grating, and output grating, respectively. It utilizes the overlapping diffraction angles of the diffracted beams of different high diffraction orders of RGB light to achieve beam combining and propagation of the three beams in the waveguide. This solves the problems of high production cost of surface-embossed grating waveguides and multi-layer waveguide stacking, achieving easy processing, single-layer color, and thinness.

[0008] Preferably, when the RGB three-color light is input, the angle between it and the normal of the coupled grating is the incident angle θ. in When the RGB three-color light is output, the angle between it and the normal of the coupled grating is the emission angle θ. out ; Angle of incidence θ in With the exit angle θ out It equals 0°.

[0009] Preferably, the product of the diffraction order m of the red, green, and blue light selected by the coupling grating and its respective wavelength λ is equal to the least common multiple of the wavelengths λ of the red, green, and blue light.

[0010] Furthermore, the coupled grating is a right-angled triangular reflective blazed grating with a grating period d. in Its blaze angle α is 2 to 5 times the wavelength λ of red, green, and blue light. in The diffraction angle θ d 1 / 2 of its grating groove depth h = d in *tanα in .

[0011] Preferably, the input grating and the output grating are arranged collinearly, and the relay grating is located on one side of the input and output gratings, forming an isosceles triangle structure. The angle between the grating vector k1 of the input grating and the grating vector k2 of the relay grating is angle β1, and the angle between the grating vector k3 of the output grating and the grating vector k2 of the relay grating is angle β2. The sum of angles β1 and β2 is 180°.

[0012] Preferably, the relay grating includes a first relay grating and a second relay grating; the first relay grating is used to deflect a portion of the red, green and blue light beams to the coupling grating, and extend another portion of the light beams to the second relay grating; the second relay grating is used to deflect all the red, green and blue light to the coupling grating.

[0013] Furthermore, the relay grating is a rectangular reflective grating with a grating period d. relay From the formula The calculation yielded the result.

[0014] Preferably, the coupling grating is a tilted triangular transmission grating with a grating period d. out The grating period d is equal to that of the coupled grating. in .

[0015] Preferably, the coupling grating, the relay grating, and the output grating are configured in a dual-channel configuration, with the gratings in both channels arranged symmetrically along the centerline. When the refractive indices of the grating waveguides are the same, the dual-channel configuration can improve the field of view (FOV).

[0016] This solution also provides an AR display device, including a microdisplay, a collimating lens, and an optical combiner. The optical combiner uses the aforementioned echelle grating waveguide; the RGB three-color light emitted by the microdisplay is collimated by the collimating lens, then incident perpendicularly onto the coupling grating and transmitted within the waveguide, deflected and expanded by the relay grating, and finally exits perpendicularly into the human eye through the output grating waveguide.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This solution uses echelle gratings with ultra-wavelength periodic scales as the input grating, relay grating, and output grating, respectively. By utilizing the overlapping diffraction angles of diffracted beams with different high diffraction orders of RGB three colors, the combined propagation of the three beams in the waveguide is achieved. This solves the problems of high production cost of surface relief grating waveguides and multi-layer waveguide stacking, achieving easy processing, single-layer color, and thinness. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the AR display device of the present invention.

[0020] Figure 2 This is a side view of the AR display device of the present invention.

[0021] Figure 3 This is a front view of the echelle grating waveguide of the present invention.

[0022] Figure 4 This is a schematic diagram of the diffraction light distribution of each diffraction order m after the RGB three-color light of the present invention is diffracted by the coupled grating.

[0023] Where: θ d α is the diffraction angle, w is the width of the grating groove, h is the depth of the grating groove, and α is the grating groove depth. in For the shining corner.

[0024] Figure 5 The diffraction efficiency distribution curves of the light beam in the visible light wavelength range of the present invention at diffraction orders m=-3, m=-4, and m=-5 are shown.

[0025] Figure 6This is a schematic diagram showing the diffraction distribution of each diffraction order m of the RGB three-color light emitted from the coupled grating and arriving at the relay grating. Wherein, θ i Let θ be the angle of incidence. d The diffraction angle, θ is the azimuth angle, w is the width of the grating groove, and h is the depth of the grating groove.

[0026] Figure 7 This is a schematic diagram of the grating vector of the right channel stepped grating waveguide of the present invention.

[0027] Figure 8 This describes the diffraction distribution of the RGB three-color light of the present invention at each diffraction order m when it arrives at the coupling grating after being emitted from the relay grating. Wherein, θ i Let α be the incident angle, w be the width of the grating groove, h be the depth of the grating groove, and α be the angle of incidence. out For the shining corner.

[0028] Reference numerals: waveguide 11, coupling grating 12, relay grating 13, first relay grating 131, second relay grating 132, coupling grating 14, microdisplay 20, collimating lens 30, receiver 40. Detailed Implementation

[0029] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0030] Example 1

[0031] like Figure 1 , Figure 2 , Figure 3 As shown, this embodiment is a mid-chisele grating waveguide, including a waveguide, a coupling grating, a relay grating, and a coupling grating. RGB three-color light, namely red, green, and blue light, enters the waveguide through the coupling grating and propagates within it. It is then deflected and expanded by the relay grating, and finally exits the waveguide through the coupling grating. The coupling grating, relay grating, and coupling grating are all mid-chisele gratings and are respectively disposed on the surface of the waveguide. The coupling grating is used to select red, green, and blue light with high diffraction order m, and to ensure that the red, green, and blue light diffract at the same diffraction angle θ. d The light enters the waveguide and is then transmitted to the relay grating; the relay grating is used to deflect and expand the pupil of red, green, and blue light, and to make the red, green, and blue light diffract at the same angle θ. d Transmission to the output grating; the output grating is used to couple red, green and blue light out of the waveguide.

[0032] In this embodiment, the coupling grating consists of two symmetrical gratings, left and right. After diffraction by the coupling grating, the incident light will deviate from the X-axis by 30°. The propagation angle of the RGB three-color light in the waveguide is designed to be greater than the total internal reflection angle corresponding to the glass substrate material. In this way, the light beam can be effectively confined in the waveguide and will not leak out. Since the image projected by the microdisplay often needs to be expanded for better human observation, four relay gratings are designed for this purpose. Two relay gratings with different structures are seamlessly connected to form a large relay area, with one large relay area on each side containing a symmetrical structure. When the light beam reaches the first relay grating, the grating deflects part of the light towards the coupling grating by 120°, while the remaining light beam maintains its original path and continues to propagate forward until it reaches the second relay grating. The second relay grating deflects the entire light beam 120° towards the output grating, thus expanding the light twice. Similarly, the output grating also consists of two symmetrically arranged gratings, which perpendicularly couple the light from the relay grating out of the waveguide and stitch them together to form a complete image ultimately received by the human eye. This scheme, through one-dimensional expansion, doubles the exit pupil size. To conform to ergonomics, the incident and outgoing rays are located on opposite sides of the waveguide. Furthermore, the optical waveguide used in the head-mounted AR display device must be as small and lightweight as ordinary glasses; therefore, the waveguide thickness is set to 2.5mm.

[0033] Table 5: Parameters of the input grating, relay grating, and output grating, and their diffraction efficiency for RGB light and the coupling efficiency of the entire waveguide for RGB light. The output pupil region closer to the input grating is designated as pupil region 1, and the output pupil region farther from the input grating is designated as pupil region 2.

[0034]

[0035] As shown in Table 5, the overall coupling efficiency of the echelle grating waveguide in this embodiment is between 0.056 and 0.08. In previous studies of diffractive waveguides, the coupling efficiency of the waveguide after pupil expansion was typically less than 0.03. This embodiment can improve it by 2 times or even more, which can improve the light energy utilization of the light source and reduce electrical losses. In addition, the difference in the overall coupling efficiency of each color light does not exceed 0.024, which can ensure that the input image will not produce obvious color difference after waveguide expansion. Of course, color balance can also be further achieved by adjusting the output power of each monochromatic light source.

[0036] This embodiment proposes a single-layer color dual-channel waveguide structure with an echelle grating for an AR display device, using three types of echelle gratings with ultra-wavelength periodic scales as optical input, deflection, and output elements. The -3rd, -4th, and -5th order high diffraction orders generated by echelle gratings with periods of 2.09 μm and 1.2 μm under normal incident RGB three-color light at 740 nm, 555 nm, and 444 nm are used to achieve beam splitting at the input end, deflection and pupil expansion at the relay end, and beam combining at the output end of the waveguide. The secondary diffraction of the relay grating achieves beam pupil expansion, and the conical diffraction generated by its tilted grating deflects the beam to the output grating below. The output grating with tilted gratings ensures that the conical diffracted beam exits perpendicularly to the waveguide.

[0037] This embodiment, based on vector diffraction theory, calculates the blaze angle, aspect ratio, and groove depth of three types of echelle gratings—small blaze angle triangular groove, rectangular groove, and large blaze angle triangular groove—and their corresponding diffraction efficiencies. Optimization yields the grating structure parameters and tolerance ranges corresponding to high diffraction efficiency, achieving average diffraction efficiencies of over 74%, 24%, and 35% for the three primary colors of the reflection-coupled, reflection-relay, and transmission-coupled-out gratings, respectively, resulting in dual-channel one-dimensional pupil expansion of the original image pair. Calculation results demonstrate that using high-diffraction-order, cone-shaped diffraction-utilizing, and high-diffraction-efficiency echelle gratings constitutes a solution for a single-layer color waveguide display device.

[0038] Example 2

[0039] like Figure 1 , Figure 2 As shown, this embodiment is an AR display device, including a microdisplay, a collimating lens, and an optical combiner. The optical combiner is the echelle grating waveguide of Embodiment 1; the RGB three-color light emitted by the microdisplay is collimated by the collimating lens, then incident perpendicularly onto the coupling grating and transmitted within the waveguide, deflected and expanded by the relay grating, and finally exits perpendicularly into the human eye through the output waveguide of the coupling grating.

[0040] In this embodiment, the color image source emitted by the microdisplay is collimated by a collimating lens and incident perpendicularly onto the coupling grating. After the first diffraction and total internal reflection in the waveguide, the light enters the relay gratings distributed diagonally downwards on the left and right sides. The RGB three-color light undergoes a second diffraction and total internal reflection before entering the coupling grating. After completing a third diffraction, it leaves the waveguide and enters the human eye. This scheme utilizes the high diffraction orders of three types of echelle gratings and achieves the beam-combining diffraction and transmission of RGB three-color light by overlapping the diffraction angles corresponding to the orders.

[0041] Example 3

[0042] like Figure 3 , Figure 4As shown, this embodiment is a coupling grating used in Embodiment 1.

[0043] In this embodiment, since the coupling grating is structurally symmetrical, only the grating structure of the right channel is designed, optimized, and described. The grating structure of the left channel is composed of... Figure 3 The Y-axis symmetry in the model is sufficient to obtain the result, and will not be elaborated further. The coupling grating is the most crucial component of the entire system. Before designing the specific structure of the grating, it is necessary to determine some basic parameters of the grating.

[0044] When a beam is incident perpendicularly to a grating, the diffraction of the beam satisfies the following equation:

[0045] mλ=n g dsinθ d

[0046] Where λ is the wavelength of the light beam, m is the diffraction order, and n g θ is the refractive index, d is the grating period, and θ is the grating period. d It is the diffraction angle.

[0047] When a light beam propagates through total internal reflection in a waveguide, the diffraction angle of the beam, i.e., the transmission angle, satisfies the following equation:

[0048]

[0049] D = 2 × H × tanθ d

[0050] Where, n air Let n be the refractive index of air. glass Let be the refractive index of the waveguide, D be the distance for a light ray to undergo a single total internal reflection, and H be the thickness of the waveguide.

[0051] For RGB light, namely red, green and blue light, the following set of grating equations applies:

[0052] m R λ R =n glass dsinθ d

[0053] m G λ G =n glass dsinθ d

[0054] m B λ B =n glass dsinθ d

[0055] In this embodiment, the waveguide is selected from a glass substrate with a refractive index n. glass=1.85, thickness H=2.5mm, minimum total reflection angle θ TIR =32.5°, the distance D for one total internal reflection of light is 3.5mm. The RGB three-color light used in the coupling grating has a red light wavelength λ. R =740nm, green light wavelength λ G =555nm, blue light wavelength λ B =444nm. The diffraction orders of the diffracted light selected by the coupling grating are as follows: red light m R =-3, green light m G =-4, blue light m B = -5, diffraction angle θ d = 35° (greater than the minimum total internal reflection angle θ) TIR =32.5°). The grating period d of the coupled grating in =2.09μm, which is 2 to 5 times the wavelength of RGB light. To avoid back-coupling of light, the width of the coupling grating should be less than the distance D = 3.5mm for a single total internal reflection. Therefore, the width of the coupling grating is set to 3mm.

[0056] In existing research on diffractive waveguides, the periods of the gratings are all at the nanometer level, and light transmission is mostly carried out using the ±1 order of the diffraction grating. This requires a relatively complex structure to concentrate energy on the lower diffraction orders, such as tilted gratings or blazed gratings. In terms of fabrication, grayscale lithography similar to laser or electron beam direct writing can be used, but the etching yield needs to be strictly controlled, and the processing cost and risk are also extremely high. For echelle gratings with periods at the micrometer level, there will be less difficulty in fabrication and less processing error.

[0057] Blazed gratings can concentrate light energy to higher diffraction orders, a property that will be well utilized in the design of coupling gratings. For example... Figure 4 As shown, the coupling grating in this embodiment is a reflective blazed grating with a right-angled triangular side profile, and its lower surface is coated with a 120nm thick Ag film. Its structure is designed to effectively reduce the incident angle θ. in The light energy of RGB three-color light with a 0° angle shines to m respectively R =-3,m G =-4,m B At higher diffraction orders of -5, these diffraction orders correspond to the same diffraction angle θ. d This diffraction angle will then be used for image transmission. To avoid stray light and dispersion, light from other diffraction orders not used for imaging must be suppressed. For the case of perpendicular incident light onto a reflective blazed grating, when the blaze angle α of the grating... in With diffraction angle θ d The relationship between them satisfies

[0058]

[0059] At this time, the diffracted light will be effectively concentrated at the diffraction angle θ. d Therefore, the blaze angle α of the coupled grating is... in The angle is set to 17.5°, and theoretically, it is easy to see that the reflectivity is highest and the most light energy can be effectively utilized when the duty cycle of the reflection grating is 1. Therefore, only structures with a duty cycle of 1 are considered for the coupling grating. Furthermore, the blaze angle α of the grating... in The grating groove depth h satisfies a trigonometric function relationship:

[0060] h = d in *tanα in

[0061] Therefore, the optimal grating groove depth h is calculated to be 0.66 μm.

[0062] To verify that the coupled grating structure has good performance in concentrating energy to high diffraction orders, this embodiment models the structure of the coupled grating and calculates the transmission efficiency of RGB three-color light under different structures. The blaze angle α of the coupled grating is calculated using DELT software. in Within a range of 15° to 20°, the grating groove depth h was scanned from 0.5 μm to 1 μm, and the diffraction orders of RGB light under different structures were calculated: m R =-3,m G =-4,m B The diffraction efficiency at α = -5. Simulation results show that the blaze angle α in The optimal diffraction efficiency is obtained when the angle is 17.5° and the grating groove depth is h = 660 nm, respectively: η R =0.80, η G =0.76, η B =0.74.

[0063] Furthermore, the simulation results also show that at the blaze angle α in Within a structural region with an angle of 17° to 18° and a grating groove depth h of 0.65 μm to 1 μm, RGB light exhibits a diffraction efficiency greater than 0.6, demonstrating a wide tolerance range. Blazed grating fabrication primarily involves four methods: mechanical scribing, wet etching, electron beam lithography, and holographic ion beam etching. Mechanical scribing is the main method for producing blazed gratings. Echo gratings with triangular grooves are suitable for fabrication using mechanical scribing; however, due to limitations in the mechanical scribing process, the metal film springs back after being compressed during scribing, often causing the groove shape and angle to deviate from the design values. The coupled grating structure in this embodiment maintains high diffraction efficiency within a wide tolerance range.

[0064] To better reflect the blaze capability of the coupled grating, Table 1 records the diffraction efficiency of RGB three-color light at some lower diffraction orders such as m=0, m=-1, and m=-2, and uses the diffraction angle θ as a metric. d and azimuth To indicate the direction of the diffracted rays. For example... Figure 4 As shown, θ d The angle between the diffracted ray and the grating normal is... Let θ be the angle between the projection of the diffracted ray onto the x'oy' plane and the positive x' axis.

[0065] Table 1 shows the spatial distribution and diffraction efficiency of the diffracted light at each diffraction order after the RGB three-color light passes through the coupling grating.

[0066]

[0067]

[0068] Furthermore, the bandwidth that the coupled grating can respond to is also a key concern in order to adapt to or match different light sources, such as... Figure 5 As shown, this embodiment analyzes the diffraction efficiency of the coupling grating for all visible light wavelengths at diffraction orders m = -3, m = -4, and m = -5. At the m = -3 diffraction order, red light has a bandwidth of 130 nm and a diffraction efficiency greater than 0.6, while green and blue light are effectively suppressed at this order. Similarly, at the m = -4 diffraction order, green light has a bandwidth of 77 nm and a diffraction efficiency greater than 0.6, while red and blue light are effectively suppressed at this order. At the m = -5 diffraction order, blue light has a bandwidth of 44 nm and a diffraction efficiency exceeding 0.6, while the diffraction efficiency of red and green light at this order is close to zero. The coupling grating of this embodiment not only provides high diffraction efficiency for all three colors of light (RGB) but also has a wide blaze bandwidth.

[0069] Example 4

[0070] like Figure 6 As shown, this embodiment is a relay grating used in Embodiment 1. Similar to the coupling grating, this example only designs, optimizes, and explains the relay grating structure of the right channel.

[0071] Since the entrance pupil needs to be doubled, two relay gratings are required. In this embodiment, the two relay gratings are rectangular reflection gratings. The diffraction requirements of the first relay grating are mainly focused on the diffraction orders of the spreading ray and the deflecting ray. The diffraction order of the spreading ray of the RGB three-color light is m=0, and the diffraction orders of the deflecting rays are m and m respectively. R =3,m G =4,m B=5. The diffracted light from the second relay grating is primarily focused on the diffraction orders corresponding to the deflected rays; extended orders are not required. When the light from the coupled grating is at an incident angle θ... i =35°, azimuth angle After incident on the relay grating, the angle between the projections of the deflected ray and the extended ray onto the grating plane x'oy' is 120°, meaning the relay grating can deflect the original ray by 120°. To meet this requirement, the grating vectors k of the input grating, relay grating, and output grating need to satisfy certain physical relationships.

[0072] like Figure 7 As shown, the grating vector represents the orientation of the grating. k1, k2, and k3 represent the grating vectors of the coupled grating, the relay grating, and the coupled-out grating in the right channel, respectively. The angle β1 between k1 and k2 is 30°, and the angle β2 between k3 and k2 is 150°. Furthermore, the grating period d of the relay grating... relay The grating period d of the coupled grating in The angle β1 between k1 and k2 determines the following:

[0073]

[0074] Therefore, the grating period d of the relay grating relay =1.2μm.

[0075] In this embodiment, in order to optimize the structure of the relay grating, the grating period d was also calculated using DELT software. relay When the grating depth is 1.2 μm, the diffraction efficiency η1 in the light deflection direction and η2 in the light spreading direction are observed for the relay grating under different grating groove depths h: 0.5 μm to 5 μm (considering that the aspect ratio of the grating should not be too large during processing, otherwise the structure will be unstable) and grating groove widths w: 0.24 μm to 1.9 μm. To maintain the uniformity of brightness in the spread image as much as possible, the first relay grating does not need a very high diffraction efficiency in the light deflection direction; η1 around 0.2 to 0.3 is sufficient, and a larger portion of the light needs to be distributed in the light spreading direction. For the second relay grating, a higher deflection diffraction efficiency η1 is required because the total efficiency η of the deflected beam it provides is the product of the spreading diffraction efficiency η1 of the first relay grating and the deflection diffraction efficiency η2 of the second relay grating.

[0076] The structures of the first and second relay gratings that meet our requirements were selected from the simulation results, and the specific parameters are shown in Table 2. In this embodiment, the total diffraction efficiency η of the RGB three-color light of the relay grating is between 0.2 and 0.3, and the difference in diffraction efficiency does not exceed 0.07, which can provide a relatively uniform light spot for the subsequent coupling grating. In addition, the spatial distribution and diffraction efficiency of the diffracted light of each diffraction order after the RGB three-color light passes through the relay grating can also be obtained from the simulation results, and the specific parameters are shown in Table 3.

[0077] Table 2: Structural parameters of the first and second relay gratings and their different diffraction efficiencies for RGB three-color light.

[0078]

[0079]

[0080] Table 3: Spatial distribution and diffraction efficiency of diffracted light at each diffraction order after RGB three-color light passes through the relay grating

[0081]

[0082]

[0083] Example 5

[0084] like Figure 8 As shown, this embodiment is a coupling grating used in Embodiment 1. Similar to the coupling grating, this example only designs, optimizes, and explains the coupling grating structure of the right channel.

[0085] In this embodiment, the coupling grating is a transmission grating with an inclined triangular side profile. Its structure is designed to effectively couple the diffracted light from the relay grating vertically out of the waveguide, so that the final image is received by the human eye. Unlike virtual reality (VR) display devices, the coupling grating needs to maintain good transmittance to ambient light to meet the needs of AR display devices to integrate virtual information into different real-world scenarios.

[0086] When RGB three-color light is coupled into and out of the echelle grating waveguide, the following grating equations must be satisfied:

[0087] n glass d in sinθ d -n air d in sinθ in =mλ

[0088] n air d out sinθ out -n glass dout sinθ d =-mλ

[0089] Where, d in The grating period of the coupled grating is d out θ is the grating period of the coupled grating. in Let θ be the angle between the incident ray and the normal to the coupled grating. d θ is the diffraction angle of the light beam after passing through the coupling grating, which is also the propagation angle in the waveguide. out The angle between the outgoing ray and the normal of the coupling grating.

[0090] To ensure the conservation of the field of view, the echelle grating waveguide must satisfy the following:

[0091] θ in =θ out

[0092] From the above two sets of equations, we can derive that: d out =d in That is, the period of the output grating must be consistent with the period of the input grating, d out =2.09μm. For the coupling grating, further investigation was conducted on how the grating couples RGB three-color light to m under different structural parameters. R =-3,m G =-4,m B = -5 is the diffraction efficiency at higher diffraction orders, which correspond to the same exit angle θ. out =0°. The diffraction efficiency is also affected by the grating shape. Considering that a grating duty cycle of 1 best couples light out of the waveguide, since total internal reflection will continue when light enters a region without microstructures, this embodiment only considers the grating structure with a duty cycle of 1. The blaze angle α of the coupling grating. out The grating groove depth h will completely determine the shape of the grating. Therefore, the blaze angle α of the grating is coupled out again using DELT software. out The scanning calculations were performed from 56° to 66°, with the grating groove depth h ranging from 2μm to 3μm. Simulation results show that RGB light corresponds to a wide range that allows the coupling efficiency to reach above 0.3, which can be considered as the manufacturing tolerance range of the coupling grating.

[0093] From the simulation results above, an optimal coupling grating structure was selected. This structure achieves a balance between the diffraction efficiency of RGB light and the difference between their diffraction efficiencies. The final structure of the coupling grating is determined as follows: blaze angle α out =63°, grating groove depth h = 2.65μm. The diffraction efficiencies corresponding to the RGB three colors are: η R =0.36, η G=0.35, η B =0.36, exhibiting good diffraction efficiency, with differences in diffraction efficiency not exceeding 0.01. Besides diffraction efficiency, the transmittance of the coupling grating to ambient light also needs attention. Further simulation calculations show that the coupling grating has a transmittance of over 0.9 for visible light wavelengths from 400nm to 780nm, meeting the requirements for ambient light transmittance.

[0094] Table 4: Spatial distribution and diffraction efficiency of diffracted light at each diffraction order after RGB three-color light passes through the coupling grating

[0095]

[0096]

[0097] Obviously, the above embodiments of the present invention are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A mid-stepped grating waveguide, comprising a waveguide, an input grating, a relay grating, and an output grating; RGB three-color light, namely red, green, and blue light, enters the waveguide through the input grating and propagates within the waveguide, is deflected and expanded by the relay grating, and finally exits the waveguide through the output grating; characterized in that, The input grating, relay grating, and output grating are all echelle gratings and are respectively disposed on the surface of the waveguide; When the RGB three-color light is input, the angle between it and the normal of the coupled grating is the incident angle θ. in When the RGB three-color light is output, the angle between it and the normal of the coupled grating is the emission angle θ. out ; Angle of incidence θ in With the exit angle θ out Equal to 0°; The coupling grating is used to select red, green, and blue light with high diffraction order m, and to make the red, green, and blue light diffract at the same diffraction angle θ. d The light enters the waveguide and is then transmitted to the relay grating. The product of the diffraction order m of the selected red, green, and blue light and its respective wavelength λ is equal to the least common multiple of the wavelengths λ of the red, green, and blue light. The coupling grating is a right-angled triangular reflective blazed grating with a grating period d. in Its blaze angle α is 2 to 5 times the wavelength λ of red, green, and blue light. in The diffraction angle θ d 1 / 2 of its grating groove depth h = d in *tanα in ; The relay grating is used to deflect and expand the pupils of red, green, and blue light, and to make the red, green, and blue light diffract at the same angle θ. d Transmitted to the output grating; The coupling grating is used to couple red, green and blue light out of the waveguide.

2. The echelle grating waveguide according to claim 1, characterized in that, The input grating and the output grating are arranged collinearly, and the relay grating is located on one side of the input and output gratings, forming an isosceles triangle structure. The angle between the grating vector k1 of the input grating and the grating vector k2 of the relay grating is angle β1, and the angle between the grating vector k3 of the output grating and the grating vector k2 of the relay grating is angle β2. The sum of angles β1 and β2 is 180°.

3. The echelle grating waveguide according to claim 1, characterized in that, The relay grating includes a first relay grating and a second relay grating; the first relay grating is used to deflect a portion of the red, green and blue light beams to the output grating, and extend another portion of the beams to the second relay grating; the second relay grating is used to deflect all the red, green and blue light to the output grating.

4. The echelle grating waveguide according to claim 2, characterized in that, The relay grating is a rectangular reflective grating with a grating period d. relay From the formula Calculation determines.

5. The echelle grating waveguide according to claim 1, characterized in that, The coupling grating is a tilted triangular transmission grating with a grating period d. out The grating period d is equal to that of the coupled grating. in .

6. The echelle grating waveguide according to claim 1, characterized in that, The coupling grating, the relay grating, and the coupling output grating are configured in a dual-channel configuration, with the gratings of the two channels arranged symmetrically along the center line.

7. An AR display device, comprising a microdisplay, a collimating lens, and an optical combiner; characterized in that, The optical combiner employs a echelle grating waveguide as described in any one of claims 1 to 6; the RGB three-color light emitted by the microdisplay is collimated by a collimating lens, then incident vertically onto the coupling grating and transmitted within the waveguide, deflected and expanded by the relay grating, and finally exits vertically into the human eye through the output waveguide of the coupling grating.

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