Optical equipment

Abstract

An optical device and an eyeglass device including the optical device are disclosed. The optical device includes a diffraction grating configured to diffract incident light of a given wavelength on the optical device, the diffraction grating having a grating pitch higher than the given wavelength and configured to diffract the incident light with a diffraction order having an absolute value equal to or greater than 2, wherein the optical device includes an optical waveguide configured to guide the light diffracted with a diffraction order having an absolute value equal to or greater than 2. The diffraction grating includes a substrate of a first dielectric material having a refractive index n3 and at least one second dielectric material having a refractive index n2 deposited on the substrate, wherein n3<n2 or n3=n2.

Description

1. Technical Field

[0001] The present disclosure relates to the fields of optics and photonics, and more specifically to an optical device comprising at least one diffraction grating. It can be applied in the field of comfortable and wearable optical devices (i.e. AR / VR glasses (augmented reality / virtual reality)), as well as various other electronic consumer products including displays and / or lightweight imaging systems. 2. Background technology

[0002] This section is intended to introduce the reader to various aspects of the technology that may be related to various aspects of the present invention described and / or claimed below. It is believed that this discussion is helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present invention. Therefore, it should be understood that these statements should be read in this context and not as an admission of prior art.

[0003] AR / VR glasses are considered as the next generation human-machine interface, thereby increasing significant interest of major industrial players in the consumer electronics and mobile devices sector.

[0004] The development of AR / VR glasses (and more generally, eyewear electronics) 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.), which should be realistic enough to achieve a truly immersive user experience.

[0005] The trade-off between image quality and the physical size of optical components has driven the search for ultra-compact optical components that can be used as building blocks for more complex optical systems, such as AR / VR glasses. Such optical components should also be easy to manufacture and replicate.

[0006] In such AR / VR glasses, various types of refractive and diffractive lenses and beam forming components are used to direct light from a microdisplay or projector to the human eye, allowing the formation of a virtual image superimposed with 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 kinds of AR / VR glasses use optical waveguides, where light propagates into the optical waveguide by TIR (total internal reflection) only over a limited range of internal angles. The FoV (field of view) of the waveguide depends on the material of the waveguide.

[0008] The FoV of a waveguide is defined as the maximum span of its propagation into the waveguide via TIR Usually, if Figure 1A As shown, the maximum angular span that can be coupled into the waveguide is defined by two rays: The critical ray ( Figure 1A middle ) and with an incident angle The grazing ray ( Figure 1A In ). The critical ray is the one that is at the critical angle Light diffracted into the waveguide, critical angle Depend on Limit, where n 2 is the refractive index of the waveguide material, and λ is the wavelength of the incident light. The theoretical FoV of the waveguide presented above is for a single mode system, where a single diffraction mode is used to carry the image: either the +1 or -1 diffraction mode.

[0009] In WO2017180403, a waveguide with an extended field of view is proposed in which dual-mode image propagation is used. In this approach, the diffraction mode +1 is used to carry the right-hand image in one direction (negative angle of incidence on a non-coupler), while the -1 mode is used to propagate the normal incidence angle into the waveguide in the opposite direction. Figure 1B Such a system is shown, where the critical angle and grazing angle of the two diffraction modes are shown. In WO2017180403, due to the pupil expander and outcoupler at the exit of the waveguide, the two half images are combined so that the user sees a single image. The benefit of this system is to double the field of view, because each half image can use the entire angular bandwidth of the waveguide in each propagation direction.

[0010] However, such optical waveguides and most optical waveguides include a diffraction grating. The period d of such a diffraction grating (also called the grating pitch) depends on the wavelength λ of the incident light and the refractive index n of the waveguide material. 2 , and can be defined by the following formula

[0011] If we consider the ratio between grating pitch and wavelength: d / λ, in the case of equation 1 given above, then 3 / 2 < n 2 <2 and 2 / 3<d / λ<4 / 5, and in any case, d / λ<1 is a value that can be defined as a sub-wavelength. Equation 1 means in any case that the diffraction grating has a sub-wavelength structure.

[0012] In US20160231568, a waveguide for glasses is disclosed, wherein the grating pitch of the structure is between 250 and 500 nm. This geometric property makes the grating very difficult to manufacture. Photolithography cannot be achieved because the structure is sub-wavelength and the required precision is challenging even for electron beam lithography.

[0013] Therefore, there is a need for an improved optical waveguide including a diffraction grating. 3. Summary of the invention

[0014] An optical device comprises a diffraction grating configured to diffract incident light, the diffraction grating having a grating pitch higher than the wavelength of the incident light and configured to diffract the incident light with a diffraction order having an absolute value equal to or greater than 2, wherein the optical device comprises an optical waveguide configured to guide the incident light diffracted with the diffraction order having an absolute value equal to or greater than 2.

[0015] Thus, according to the present disclosure, a diffraction grating is dedicated to a wavelength or a group of wavelengths. The diffraction grating is configured so that a major portion of the incident light is diffracted in diffraction orders having an absolute value equal to or greater than 2. Using higher diffraction orders than in prior art systems, meaning |M|>1, where M is the diffraction order, has the effect of multiplying the wavelength by the order, which is used in the diffraction equation. Since the grating spacing is a function of the product Mλ, this means that the grating spacing is multiplied by M and the structure for the inner coupler is much larger. This opens up new possibilities in manufacturing technology because nanoimprinting can be used. We also get fewer lines per mm for grating density and since the structure will no longer be sub-wavelength but super-wavelength, the manufacturing process can be optimized.

[0016] According to this disclosure, Where d is the grating pitch and λ is the wavelength, the diffraction grating thus has a super-wavelength structure which imposes fewer constraints on fabrication than a sub-wavelength structure.

[0017] According to an embodiment of the present disclosure, the diffraction grating includes a 3 A first dielectric material substrate and a dielectric material having a refractive index n deposited on the substrate 2 at least one second dielectric material, wherein n 3 <n 2 or 3 =n 2 .

[0018] According to an embodiment of the present disclosure, the diffraction grating includes a base pattern, the base pattern includes the second dielectric material, and the base pattern is configured to form a nanojet beam associated with an edge of the base pattern from the incident light on the diffraction grating. According to this embodiment, the base pattern of the diffraction grating includes an edge forming a step, so that when light is incident on the optical device, a nanojet beam associated with the edge of the base pattern is formed.

[0019] Advantageously, according to this embodiment of the present disclosure, the nanojet formation phenomenon is utilized to convert energy from a major portion of incident light into a secondary diffracted beam. Using a base pattern configured to form a nanojet beam from the edge of the base pattern allows providing high diffraction efficiency and high diffraction uniformity.

[0020] Prior art systems cannot operate at higher orders of diffraction because the configuration of prior art systems provides a diffraction efficiency close to 0. Using a basis pattern configured to form a nanojet beam allows high diffraction efficiency to be achieved while the diffraction uniformity is on average and at least equal to that produced by prior art systems at lower diffraction orders.

[0021] According to another embodiment of the present disclosure, the basis pattern is configured according to any one of the following arrangements:

[0022] The base pattern includes a refractive index n on top of the substrate 3 A block of a first dielectric material having a refractive index n 3 The first block of the same dielectric material is inserted into a 2 a block of the second dielectric material, or

[0023] The base pattern includes a refractive index n on top of the substrate 3 The first block of dielectric material has a refractive index of n 3 The block of the first dielectric material is placed with a refractive index n 2 Between the two blocks of the second dielectric material, the refractive index is n 3 The bulk and refractive index of the first dielectric material is n 2 The two blocks of the second dielectric material have the same height, or

[0024] The base pattern includes a refractive index n having the same width and height on top of the substrate. 2 two blocks of the second dielectric material, the two blocks being separated by a distance, or

[0025] The basic pattern includes a refractive index n on top of the substrate 2 A block of the second dielectric material, the block having a U-shape.

[0026] According to another embodiment of the present disclosure, when the base pattern includes a plurality of refractive index n having the same width and height on top of the substrate, 2 When two blocks of the second dielectric material are separated by a distance W 1 Separately, the two blocks have a height H 2 ,in Head Where W 2 is the width of each of the two blocks, and θ′ B1 and θ″ B1is the corresponding angle of nanojet beam radiation associated with an edge of the basis pattern from said light incident on said at least one diffraction grating, wherein where θ i is the angle of the incident light relative to the normal to the top surface of the diffraction grating and n 1 is the refractive index of the host dielectric in which the diffraction grating is placed.

[0027] According to another embodiment of the present disclosure, when the base pattern includes a 2 The second dielectric material has a U-shaped block, wherein the U-shaped block includes a 1 The height of the center block separation is H 2 and width W 2 Two blocks, where H 1 Lower than H 2 ,and in where θ i is the angle of the incident light relative to the normal to the top surface of the diffraction grating, and n 1 is the refractive index of the host dielectric in which the diffraction grating is placed.

[0028] According to another embodiment of the present disclosure, W 1 is the distance separating two blocks or the width of the center block of a U-shaped block, W 2 is the width of each of the two blocks or the width of each of the two lobes, W 1 and W 2 depends on the grating spacing d of the diffraction grating, where and

[0029] According to another embodiment of the present disclosure, the basic pattern has a symmetrical geometric structure.

[0030] According to this embodiment, the optical device can be used in a dual mode. For example, it can be implemented in a waveguide that separates the right-hand side and the left-hand side of the input image to double the field of view of the waveguide.

[0031] According to another embodiment of the present disclosure, the basic pattern has an asymmetric geometric structure.

[0032] According to this embodiment, the optical device is designed for single mode

[0033] Diffraction, such as an inner coupler used to shift the image to a single side of the waveguide. This embodiment allows to have even larger grating pitches.

[0034] According to another embodiment of the present disclosure, the diffraction grating is configured to diffract light of a group of wavelengths including more than one wavelength, and the grating pitch is greater than a highest wavelength of the group of wavelengths.

[0035] According to another embodiment of the invention, the optical device according to any one of the embodiments disclosed above comprises one diffraction grating per red, green and blue color.

[0036] According to another embodiment of the present invention, the optical device is an optical waveguide. The optical device can be advantageously used as a waveguide, such as a waveguide for AR / VR glasses.

[0037] According to another embodiment of the present disclosure, the diffraction grating is configured for in-coupling light into the optical waveguide or for extracting light from the optical waveguide.

[0038] According to another embodiment of the present disclosure, the diffraction grating is configured to in-couple light entering the optical waveguide, and the optical waveguide includes another diffraction grating configured to extract light from the optical waveguide, the other diffraction grating having a grating pitch greater than a wavelength of the extracted light, and the other diffraction grating is configured to diffract the extracted light with a diffraction order having an absolute value equal to or greater than 2.

[0039] According to another aspect of the present disclosure, a pair of glasses is disclosed, which includes at least one optical device according to any one of the above embodiments.

[0040] According to an embodiment of the present invention, the eyeglass device comprises:

[0041] - a light display engine configured to emit an image to be displayed,

[0042] - an optical device group configured to couple incident light from the light display engine to the optical waveguide,

[0043] - the optical waveguide is configured for directing the incident light towards an eye of a user so that the image is visible to the user. 4. Description of the drawings

[0044] The present disclosure may be better understood with reference to the following description and accompanying drawings, which are given by way of example and not limiting the scope of protection, and in which:

[0045] - Figure 1A The definition of theoretical critical rays and grazing rays in a single mode is shown,

[0046] - Figure 1B The definition of theoretical critical rays and grazing rays in dual mode is shown.

[0047] - Figure 2 shows the diffraction pattern of an incident plane wave,

[0048] - Figure 3 shows the definition of important rays in negative angle input space,

[0049] - Figure 4A and 4B An exemplary 60° field of view light engine 60 is shown.

[0050] - Figure 5 Shows Figure 4A and 4B Schematic diagram of an optical engine in which a waveguide is provided with an internally coupled grating.

[0051] - Figure 6 Exemplary geometries and pitch dimensions of the basis pattern of a diffraction grating are shown.

[0052] - Figure 7 Shows Figure 6 Diffraction performance of the grating structure shown.

[0053] - Figure 8 Shows Figure 6 Diffraction performance of a grating structure without high refractive index material is shown.

[0054] - Fig. 9 It shows that (a) has Figure 6 (a) a cross-sectional view of a bi-material metaelement of the insert shown; (b) power density distribution in the xy plane of the metaelement with the following parameters: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =100nm, H =700nm, H 2 =300nm,λ=625nm,θ i =0°.

[0055] - Fig.10 It shows that (a) has Figure 6 (a) A cross-sectional view of a bi-material metaelement of the insert shown; (b) Power density distribution in the xy plane of a metaelement with the following parameters: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =100nm, H =700nm, H 2 =300nm,λ=625nm,θ i =30°.

[0056] - Fig.11Shows Figure 6 (a) Hy component distribution and (b) power density distribution of the superelement in the xy plane, where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =100nm, H =700nm, H 2 =300nm, λ=625nm.

[0057] - Fig.12 Exemplary geometries and pitch dimensions for alternative embodiments of the basis pattern of the diffraction grating are shown.

[0058] - Fig.13 Shown based on Fig.12 Performance of gratings for the shown geometries.

[0059] - Fig.14A A cross-sectional view of a bi-material metaelement with equal height inserts (left) and the power density distribution of the metaelement in the xy plane (right) are shown, where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H =305nm, H 2 =300nm, λ=625nm and θ i =0°.

[0060] - Fig. 14B A cross-sectional view of a bi-material metaelement with equal height inserts (left) and the power density distribution of the metaelement in the xy plane (right) are shown, where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H =305nm, H 2 =300nm, λ=625nm and θ i =30°.

[0061] - Fig.15 Shows Fig.12 (a) Hy component distribution and (b) power density distribution of the superelement in the xy plane, where the parameters are: n 1 =1.0,n 2 =2.105,n 3=1.52,W 1 =260nm, W 2 =130nm, H =305nm, H 2 =300nm, λ=625nm.

[0062] - Fig.16 Another exemplary geometry of a basis pattern of a diffraction grating according to an embodiment of the present disclosure is shown.

[0063] - Fig.17 Shows Fig.16 Performance of the structure shown.

[0064] - Fig.18 An exemplary regular structure of a diffraction grating according to is shown.

[0065] - Fig.19 Shows Fig.18 Diffraction efficiency of the shown structure.

[0066] - Fig. 20 Shows Fig.16 (left) and Fig.18 (right) shows a cross-sectional view of a single-material metaelement with the following parameters: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =130nm, H = 200nm, θ i =0°.

[0067] - Fig.21 Shows Fig.16 (left) and Fig.18 (right) shows a cross-sectional view of a single-material metaelement with the following parameters: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =130nm, H = 200nm, θ i =30°.

[0068] - Fig.22A Shown for Fig.18 (a) Hy component distribution and (b) power density distribution in the xy plane of a single NJ element shown in FIG. 1 , where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H 2 =200nm,λ=625nm.

[0069] - Fig. 22B Shows Fig.16 (c) Hy component distribution and (d) power density distribution of the twin structure superelement in the xy plane, where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H 2 =200nm,λ=625nm.

[0070] - Fig.23 Shows Fig.16 The power density distribution of the twin structure superelement in the xy plane is shown, and the parameters are: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =130nm, H 2 =200nm,λ=625nm;n 3 (in the left column) = 2.105, n 3 (in the right column) = 1.52.

[0071] - Fig.24 Another exemplary geometry of a basis pattern of a diffraction grating according to an embodiment of the present disclosure is shown.

[0072] - Fig.25 Shows Fig.24 Performance of the U-shaped structure shown.

[0073] - Fig.26 Shows Fig.24 (a) Hy component distribution and (b) power density distribution of the U-shaped superelement in the xy plane, where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H 2 =200nm, H 1 =50nm,λ=625nm.

[0074] - Fig. 27 Shown for Fig.24 The U-shaped structure shown has performance for different pitch sizes of d = 823 ± 5 nm: the top shows the performance for d = 818 nm, and the bottom shows the performance for d = 832 nm.

[0075] - Fig.28 An exemplary geometry and pitch dimensions of another embodiment of a base pattern of a diffraction grating are shown.

[0076] - Fig.29 Shows Fig.28 The performance of the geometry shown, showing the +2 diffraction order efficiency as a function of the angle of incidence.

[0077] - Fig.30 A schematic perspective view showing an eyeglass device according to an embodiment of the present disclosure is shown,

[0078] - Fig.31 Shows Fig.30 A schematic front view of the goggle device shown,

[0079] - Fig.32 shows an exemplary diffraction grating according to an embodiment of the present disclosure,

[0080] - Fig.33 A single-material meta-element with non-vertical edges (n 2 =n 3 ) of a cross-sectional view ( Fig.33 a, Fig.33 b) and a single-material metaelement with a top surface that is not parallel to the xz plane (n 2 =n 3 ) of a cross-sectional view ( Fig.33 c),

[0081] - Fig.34 (a) shows a cross-sectional view of a diffraction grating unit cell; Fig.34 (b) shows Fig.34 (a) Diffraction performance of the grating shown. 5. Specific implementation methods

[0082] According to the present principles, an optical device including at least one diffraction grating will be described. According to an embodiment of the present disclosure, such an optical device can be used as a waveguide for AR / VR glasses, for example.

[0083] According to the present disclosure, an optical device exhibits a specific diffraction grating, which can be used to incouple light into the optical device and / or outcouple light from the optical device.

[0084] According to the present principles, the diffraction grating is configured to diffract incident light with diffraction orders having an absolute value equal to or greater than 2.

[0085] 5.1 Diffraction Pattern

[0086] Figure 2 schematically shows what happens to a plane wave (PW) incident on a linear grating (DG). The plane wave is split into diffraction modes (-2, -1, 0, +1, +2), which are angularly spaced beams of local maximum intensity. Although only diffraction mode numbers -2, -1, 0, 1, and 2 are shown, higher orders exist. The zeroth order usually has greater power and is the natural mode where normal refraction or reflection will occur. Reflected diffraction modes may also exist.

[0087] Typically, a grating produces many diffraction orders. In many applications, it is desirable to use only the first order and avoid all other modes. An example of such a grating is a thick hologram made by the interference of two plane waves.

[0088] The purpose of the structure of the diffraction grating is then to give priority to the first diffraction order and to suppress the remaining diffraction orders as much as possible.

[0089] All diffraction orders are linked to the incident beam by the following mathematical formula: 2 (λ)sinθ 2 -n 1 (λ)sinθ 1 =MλT,

[0090] Among them, n 1 (λ) and n 2 (λ) is the refractive index of the dielectric into which the light propagates, respectively, where, in most cases, n 1 (λ)=1,θ 1 is the angle of incidence, θ 2 is the diffraction angle, M is the diffraction order, λ is the wavelength, and T is the grating frequency. If the wavelength is also expressed in μM, the grating frequency is expressed in the number of lines per μM.

[0091] For diffraction order M = 0, this formula simplifies to the well-known Snell-Descartes law of refraction. However, this equation does not take into account different phenomena. Depending on the polarization of the input beam, the geometry of the basic structure used to build the array, and the materials used, there may be missing modes. Furthermore, this equation does not take into account the energy redistribution of the basic structure.

[0092] 5.2 Specifying wavelength

[0093] Typically, a light engine includes a light source and a display. The light source is a power LED that is driven sequentially in time. The design of the planar optics should be adapted to the wavelength of the LED. Examples of common LEDs for near-eye projection are: 459nm blue, 530nm true green, 625nm red. The diffraction process is very dispersed. The diffraction angle is different for different wavelengths because it varies linearly with wavelength (MλT), which is a considerable variation. Therefore, it is necessary to find a way to minimize chromatic aberration. One way to deal with this is to have one waveguide per color band, because for each color band (e.g., red, green, blue), the diffraction grating of each waveguide is configured differently depending on the color band. Therefore, if RGB true color images are considered, three waveguides are required, which may complicate their design.

[0094] 5.3 Ultra-wavelength internal coupling grating design

[0095] Figure 3 The definitions of some important rays used to characterize waveguides are shown. and denote the grazing ray and the critical ray, respectively. If the subscript is 1, the ray is outside the waveguide, and if the subscript is 2, the ray is inside the waveguide. In principle, the maximum input angular bandwidth of the grating according to the figure is and the maximum waveguide angular bandwidth is That is, the rays is not a desirable choice, since it is not possible to extract this ray. Therefore, in practice, the angular bandwidth inside the waveguide will be limited to ( Figure 3 The angle sector indicated by ABDW on the upper left is the angle sector of the input

[0096] Regarding the angle sign convention, positive angle measures are oriented in the trigonometric direction, which means that on the diagram And all other Another convention: the diffracted rays in the figure are all positive, the diffraction pattern is positive, M>0, and if we apply the diffraction equation to this set of rays, we get the following 4:

[0097]

[0098]

[0099]

[0100]

[0101] In order to select a beam that can diffract Figure 3The grating period d of the rays shown may require some selection, especially with respect to the rays inside the waveguide. The selection can be based on the distance the image must travel in the waveguide before being extracted, the number of TIR bounces, and the thickness of the waveguide.

[0102] For example, if one needs to extract an image about 4 cm from an injection in a waveguide, which is the distance between the exit pupil of the light engine in the eye branch and the eye. Then, when assuming that the light engine and the eye are in the same half-space relative to the waveguide, this means that the extraction ports are even. i C，G represents the distance between the point inside the waveguide where the critical or grazing ray enters and the point on the face of the waveguide where the ray bounces for the i-th time. The index i represents the number of times the ray inside the waveguide bounces before being extracted, i may also be referred to as the extraction port. If i is even, the extraction port is on the same side of the waveguide as the light engine, and if i is odd, the extraction port is on the opposite side of the waveguide relative to the light engine. The way this definition of the extraction port is actually used is to define the extraction port at the point [X 2 C , X 2 G ], the result will be an image of the output of the waveguide collected by the diffraction between these two points. In other words, the image is collected at the second extraction point, i.e., the image is considered to be extracted at port number 2.

[0103] Taking the example of a 24 degree field of view required for a glass substrate with a refractive index of 1.5, some values ​​useful for the design of a system can be defined in Table 1. The values ​​in the "Input" column are appropriate values ​​that have been selected for designing the system, while the values ​​in the "Calculated" column are the parameters of the system obtained by using the "Input" values.

[0104]

[0105] Table 1: Parameters of grating design

[0106] In this exemplary typical system, reasonable values ​​for the grazing angle in the waveguide can be chosen to be between 60° and 90°, for example the grating angle is chosen to be approximately This value of the grazing angle makes it easier to extract from the waveguide, however, The value of can also be chosen, for example In practice, it is desirable to design a diffraction grating that diffracts all θ1 angles of a particular sign into one direction, and diffracts angles of the opposite sign into the opposite direction.

[0107] In this way, the waveguide will operate in a dual mode, according to which the field of view is split in half, with half of the field of view (i.e. half of the image) being directed in one direction and the other half being directed in the other direction, with the positive result of doubling the field of view. This means Need to be selected with Same angle sign and near the normal.

[0108] Another condition is that there should be no crosstalk between the positive and negative poles, meaning that for a given orientation striking the inner coupler, there should always be one and only one diffraction direction, with no energy going into other directions. Figure 3 In this condition, Satisfy, and in order not to reduce the input field of view, preferably, From Equation 2 discussed above, the grating spacing can be obtained as:

[0109] By using Equation 3 discussed above, According to the following formula:

[0110] The maximum angular span of a negative angle input beam is It is coupled into the waveguide to span the angular bandwidth

[0111] For n 2 ∈[3 / 2, 2], and considering the second diffraction order, |M|=2, in any case the relationship between the pitch size and the wavelength is d / λ≥1, which means that the structure of the grating will be super-wavelength.

[0112] If, instead of coupling the first diffraction order into the waveguide, the pitch of the grating is chosen in such a way that higher orders are coupled, the pitch of the grating can be larger and the limits of the microfabrication process are avoided.

[0113] Table 2 shows the difference between a grating designed to couple the second order and the one used for the first order. The difference in pitch size is almost double. For the second diffraction order, we obtain the following values ​​of pitch for the RGB intercoupler: d 625 =822.4nm,d 530 =697.4nm,d 460 = 605.3 nm instead of the very small spacing size obtained for the first diffraction order: d 625 =411.2nm,d 530 =348.7nm, d 46 0=302.7nm.

[0114] Gratings using the second diffraction order are called superwavelength gratings because their pitch is always larger than the wavelength of the color band they are designed for. Gratings using the first diffraction order are called subwavelength gratings because their pitch is smaller than the wavelength of the color band they are designed for.

[0115] The field of view FoV in Table 2 is given for a system using two ±2 diffraction orders. It is twice the field of view of previous systems operating in only one direction into the waveguide.

[0116] The advantage of using ±1 orders is that for very low diffraction orders, a symmetrical response curve is provided in both directions, while emphasizing the +1st or -1st order with very high diffraction efficiency and high diffraction uniformity.

[0117] As described below, the nanojet-based diffraction gratings disclosed herein allow for a symmetric response of ±2 diffraction orders with very high diffraction uniformity, which is advantageous.

[0118]

[0119] Table 2: Grating pitch and angular bandwidth

[0120] Figure 4A and 4B An exemplary schematic light engine providing a 60° field of view is shown.

[0121] The light engine includes a display that emits incident light toward a set of optics that couples the incident light to an exit pupil disposed at a final surface after a final lens of the set of optics, where light rays intersect into a minimum circular cross-section.

[0122] like Figure 5 As shown, the diffraction grating will be placed at the exit pupil. Figure 4A In the case of the display, only rays with negative angles of incidence enter the incoupling grating (exit pupil). These rays come from the upper part of the display. Figure 4B In the example above, only light with a normal incidence angle enters the in-coupling grating (exit pupil). These rays come from the bottom of the display.

[0123] Figure 5 Shown from Figure 4A and 4B Figure 1. A light engine with a waveguide (WG) provided with an in-coupling grating. Order M=2 on the left hand side and order M=-2 on the right hand side. If the display is switched on, both ray paths exist simultaneously. Along the central horizontal part of the display there is an angle range of ±2.97° from which light is not coupled into the waveguide. This part of the display will always be black.

[0124] Figure 5is a schematic diagram of the light engine obtained from simulation. Only the incoupling of the incident light into the waveguide is shown. On the simulation view, no extraction port is used at the output to extract the light.

[0125] 5.4 Nanojet-based geometric elements for dual-mode and 2-order diffraction gratings

[0126] In all of the following subsections, different exemplary geometries will be presented that achieve high performance for the new principles presented in this disclosure.

[0127] In addition, a set of equations are provided to demonstrate the contribution of the edge diffraction phenomenon disclosed in "Near field focusing by edge diffraction, A. Boriskin, V. Drazic, R. Keating, M. Damghanian, O. Shramkova, L. Blondé, Optics Express, Vol. 43, No. 16, pp. 4053-4056 (2018)" in the case of a single element entering the total response of the diffraction grating.

[0128] The presented data were obtained using COMSOL multiphysics software. The presented analysis of the field and power distribution within the so-called super-element of the grating helps to explain the physics of the edge diffraction phenomenon and to derive the optimal topology. The system is assumed to be illuminated by a linearly polarized plane wave E = {0, 0, 1} (TE). The effect of the parameters of the individual super-elements on the system functionality is considered. As demonstrated in the literature cited above, the nanojet (NJ) beamforming phenomenon is associated only with the edges of the system. Based on the analysis of the wedge diffraction phenomenon disclosed in “Near field focusing by edge diffraction, A. Boriskin, V. Drazic, R. Keating, M. Damghanian, O. Shramkova, L. Blondé, Optics Express, Vol. 43, No. 16, pp. 4053-4056 (2018)”, the deflection angle of the nanojet (NJ) beam in a denser dielectric can be obtained under the condition of normal incidence of the electromagnetic wave (θi=90°).

[0129]

[0130] According to the embodiments of the present disclosure, n L is the refractive index of the bulk dielectric, n H is the refractive index of the higher refractive index material.

[0131] In the case of a single wedge of a single material element, the constructive interference phenomenon between the jet waves generated by the wedge and the plane waves refracted by the edge of the wedge results in the generation of an NJ beam.

[0132] It should also be noted that, in the following text, unless otherwise stated, n 1 is the refractive index of the bulk dielectric, n 2 represents the refractive index of the high refractive index material, and n 3 Represents a lower refractive index, such as that of a glass substrate.

[0133] 5.2.1 Dual-material solution with insert

[0134] Figure 6 An exemplary geometry of a basis pattern of a diffraction grating configured to diffract light having a diffraction order having an absolute value equal to or greater than 2 is disclosed in .

[0135] exist Figure 6 The base pattern consists of two dielectric materials: 2 A block of dielectric material ME2, which is placed on a refractive index n 3 Layer ME3 presents a block B3 of the same dielectric material, which is inserted in block ME2.

[0136] Figure 6 The structure of has been optimized to provide the best performance for the red wavelength of λ=625nm. Other slightly varying parameters can be used for variable aspects of the diffraction curve. This structure is symmetrical in that it requires the positive and negative diffraction orders to be fed in a symmetrical manner.

[0137] To make this structure, glass etching is first required to create the first structure (layer ME3) in the base material of the waveguide. Then an electron beam lithography resist is spin coated on top of this structure and exposed and etched again to add the second component (ME2 block).

[0138] Both ME2 and ME3 components are dielectric transparent materials. Figure 6 The dimensions shown show that the structure has a much larger pitch than the prior art: 822.4 nm instead of 496 nm. The aspect ratio is 700 / 460≈1.5, which is a low aspect ratio, and the depth is not much larger than the width.

[0139] Figure 7 Shows Figure 6 The diffraction performance of the grating shown, which shows that for a field of view of 2×(30°-3°)=54°, η max ≈65%, Each design has absolutely no crosstalk between the +2nd and -2nd orders. Some angles that have diffraction as +2nd and -2nd orders should be avoided at this design stage. The 0th, +1st and -1st orders are not coupled into the waveguide. They are transmitted through it and therefore do not reduce the contrast of the virtual image projected by the light engine display.

[0140] exist Figure 7 In , when using second-order diffraction instead of first-order diffraction, the diffraction uniformity is of the same order of magnitude as in prior art systems. Very high diffraction efficiencies are obtained, such as Figure 8 As highlighted in , represents the diffraction efficiency of the same system without nanojet enhancement (i.e., removing the high refractive index material ME2 to retain only the etched waveguide). Figure 8 As shown, in this case the diffraction efficiencies of the +2 and -2 orders are unimportant.

[0141] Fig. 9 It shows (a) that there are, for example, Figure 6 A cross-sectional view of a bi-material metaelement of the insert shown, and (b) the power density distribution in the xy plane of such a metaelement with the following parameters: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =100nm, H =700nm, H 2 =300nm. λ=625nm, θi=0°.

[0142] The symmetric metaelement will have a refractive index n 3 , Width W 1 and height H 2 The dielectric block is combined in a dielectric block having a refractive index n 2 、Width 2W 2 +W 1 and a dielectric block with a total height H (such as Fig. 9 Assume that n 1 is the refractive index of the main dielectric, and n 1 <n 2 <n 3 As a result, in the proposed system, for θ i =O°(θ i is the angle of incidence), we will observe radiation from 4 nanojets with the following offset angles:

[0143]

[0144] For the proposed symmetric system, the two opposite edges of the block ( Fig. 9 ME2 in (a) is generated in a layer with a refractive index n 2 The propagation inside block ME2 has a radiation angle θB1 The two nanojets (NJ1, see Fig. 9 (a) starting at the top edge of block ME2), Fig. 9 The hot spot of the power distribution inside the superelement in (b) corresponds to the intersection of these two NJs. Fig. 9 In this cross-sectional view, the refraction phenomenon at the boundary between the insert B3 and the main block ME2 is not considered.

[0145] At a refractive index of n 2 The block ME2 has a radiation angle θ B2 The second pair NJ consists of a refractive index of n 3 The edge of the center block B3 is generated (NJ2, see Fig. 9 (a) starting from the top edge of block B3). Due to the total internal reflection of the waves on the vertical edge of block ME2, the propagation direction of these NJs changes. As a result, at the bottom surface of the superelement, we can observe two less dense hot spots at the intersection of NJ1 and NJ2 (intersection of the dashed lines NJ1 and NJ2 on each side of block B3, ref. CR1 and CR2).

[0146] Fig.10 (a) shows a cross-sectional view of a bi-material meta-element with an insert, such as Figure 6 and (b) the power density distribution in the xy plane of a superelement with the following parameters: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =100nm, H =700nm, H 2 =300nm. λ = 625nm, θ i =30°.

[0147] The radiation angles θ′ and θ″ of opposite edges of the system are not equal (see Fig.10 (a)). As a result, for block ME2:

[0148]

[0149] In a similar manner, the radiation angle of the nanojet of the insert (Block B3) can be determined as:

[0150]

[0151] The reflection of the generated waves leads to the creation of new NJ hotspots (crossing points) at the edges of the components of the meta-element and an asymmetric redistribution of the total power inside the meta-element, such as Fig.10 (b) as shown.

[0152] like Figure 6 As shown, blocks ME2 and B3 are placed on a 3 on the substrate ME3. Fig.11 (a) shows that Figure 6 The Hy component field distribution of the meta-element in the xy plane (i.e., the distribution corresponding to the projection of the magnetic field on the y-axis), and Fig.11 (b) shows that Figure 6 The power density distribution of the superelement in the xy plane is shown, and the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =100nm, H =700nm, H 2 =300nm. For three different incident angles θ i ,λ=625nm.

[0153] Below the meta-element, NJ is obtained inside the substrate (ME3) after a corresponding wave refraction at the substrate surface. Fig.11 The power distribution shown in (b) shows the dense lobes within the substrate generated by the wave interference. The constructive interference between the refracted waves obtained from the wedge-shaped diffraction of the periodic array of superelements leads to a power redistribution between the corresponding diffraction orders. The central insert (B3) with a lower refractive index helps to almost completely suppress the intensity of the 0th diffraction order in the case of normal incidence, while significantly reducing this intensity in the case of oblique incidence. In addition, the presented topological structure helps to change the propagation direction of the waves diffracted by the wedges of the elements of the diffraction grating and helps to increase the intensity of the ±2nd diffraction orders (see Figure 7 ).

[0154] 5.2.2 Dual-material and equal-height inserts

[0155] Figure 6 The structure of is not the only structure that can be used to achieve the correct performance, even though it may be a preferred structure for the microfabrication process. Another geometric structure of the basic pattern according to another embodiment is Fig.12 It is shown in Figure 5 that this geometry can achieve comparable performance.

[0156] exist Fig.12 In the embodiment shown in FIG. 1 , the base pattern comprises a material having the same refractive index n as the material of the substrate ME3. 3 Block B3 of the same dielectric material. Block B3 is placed on top of substrate ME3 and is located at a position with a refractive index of n 2 The two blocks ME21 and ME22 of dielectric material are arranged between them. Blocks B3, ME21 and ME22 have the same height.

[0157] Fig.12 The values ​​shown in have been optimized for a wavelength of 625 nm. However, slightly different values ​​may be used for a wavelength of 625 nm. Also, other values ​​may be used for other wavelengths as long as the grating spacing d is larger than the wavelength of the light specifically diffracted.

[0158] Fig.13 Shown based on Fig.12 The performance of the diffraction grating with a certain geometry.

[0159] from Fig.13 It can be seen that the maximum diffraction efficiency is 55%, which can be considered low. 2 Value (2.3 to 2.5) of the material, the efficiency will increase significantly. 2 = 2.105 The value used is based on available silicon nitride electron beam lithography compatible materials.

[0160] When considering a combination placed on a surface with a refractive index n 2 , Width W 2 and a total height H between two similar blocks with a refractive index n 3 , Width W i and a symmetric superelement of a block of height H, such as Fig.12 As shown, nanofluidic analysis towards higher levels of energy transfer can be performed.

[0161] Assume that n 1 is the refractive index of the main dielectric, and n 1 <n 2 <n 3 .

[0162] Fig.14A and 14B A cross-sectional view of a dual-material meta-element is shown, wherein the dual-material meta-element includes a material having a refractive index n 2 The two blocks ME22 and ME21 and have a refractive index n 3 The block insert B3, for a superelement with the following parameters, the three blocks ME22, ME21 and B3 have equal heights ( Fig.14A ) and in the xy plane ( Fig.14A The power density distribution of the right side is: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H =305nm, H 2 =300nm. λ = 625nm, for Fig.14A ,θ i= 0° (vertical incidence), for Fig. 14B ,θ i =30°.

[0163] As a result, at normal incidence ( Fig.14A ), respectively, by having a refractive index n 2 The dielectric ME21 has a refractive index n 1 The outer edge of the main dielectric on the other hand has a refractive index n 2 The dielectric ME22 has a refractive index n 1 Two NJ beams are generated at the outer edges of the main dielectric. The two NJ beams are at angles θ B1 Propagation. In a 2 The block ME22 (or the corresponding block ME21) and the block ME22 having a refractive index n 3 Two NJs are generated at the edges of blocks B3. The two NJs are at angles θ B2 Spread (see Fig.14A ).

[0164] exist Fig.14A With a refractive index n 2 The two hot spots of power distribution within similar blocks (ME21, ME22) correspond to the intersection of two NJs with different radiation angles. The propagation of the jet beam diffracted by the outer wedge into the central part of the meta-element (insert B3) leads to the generation of new hot spots outside the structure along the symmetry axis of the meta-element.

[0165] It should be noted that the schematic distribution of NJs shown does not take into account refraction phenomena that cause the intersection points of the NJs to be offset along the symmetry axis. For each metaelement, the presence of such NJ hot spots explains the high intensity of the 0th diffraction order at normal incidence (see Fig.13 ).

[0166] Fig.15 (a) shows Fig.12 The Hy component field distribution of the superelement in the xy plane is shown, Fig.15 (b) shows Fig.12 The power density distribution of the superelement in the xy plane is shown, where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H =305nm, H 2 =300nm. Fig.12 The geometry shown is related to the refractive index n 3When placed together with a dielectric material substrate, for three different incident angles, λ = 625nm.

[0167] By varying the incident angle of the electromagnetic wave from 0 to +30 degrees, the wave diffracted by the inner wedge (the wedge of the insert) is transmitted into the substrate (see Fig.15 (a)) and input to the 2nd diffraction order. Fig.15 The power distribution shown in (b) shows the dense lobes within the substrate produced by the interference of the diffracted waves. For negative angles of incidence, there is an enhancement of the ±2nd diffraction orders. As in the case of the metaelement with insert ( Figure 6 ), the total internal reflection phenomenon plays a key role by changing the propagation direction of the diffracted wave and causing power redistribution among the corresponding diffraction orders.

[0168] 5.2.3 Twin structure

[0169] Fig.16 The basic pattern of another embodiment according to the present principles is shown. In this embodiment, the basic pattern of the structure is based on depositing and electron beam irradiating a refractive index of n 3 The refractive index of the glass substrate ME3 is n 2 According to the present embodiment, this results in a single high refractive index material having a refractive index n 2 Two blocks ME21 and ME22 of a single material having the same size are placed on top of the substrate ME3 and separated by a determined distance W 1 The space separating the two blocks ME21 and ME22 is naturally filled with a main dielectric (with a refractive index n 1 ).

[0170] For this geometry, no glass etching is required and no multiple electron beam lithography is required, which is advantageous for microfabrication. In the example given here, the structure is also very shallow, with a height H of 200 nm. 2 , much smaller than Figure 6 The structure in the embodiment shown in FIG. 1 has a height of 700 nm.

[0171] Fig.17 Shows Fig.16 The performance of the twin structure is Fig.17 We can see that from 3 to 30 and -30 to -3 degrees η max =75%, Γ=64%.

[0172] The performance is very good as a maximum diffraction efficiency of 75% and a diffraction uniformity of 64% are achieved. These values ​​are excellent and when compared to Figure 6 and 12 represents a real improvement when compared to the structure of

[0173] To compare with the above results, Fig.18 shows a glass substrate with a refractive index of n3 deposited on a glass substrate with a refractive index of n 2 of single material. Fig.19 The very poor second order diffraction efficiency in this case is shown.

[0174] Fig. 20 (a) shows Fig.16 a cross-sectional view of a single-material metaelement of the illustrated embodiment, Fig. 20 The structure of (a) has a refractive index of n 2 The two blocks ME21 and ME22 of the single material are filled with a refractive index n 1 The main dielectric distance W 1 separate. Fig. 20 (b) shows a cross-sectional view of a single-material metaelement consisting of a single block (B1). Fig. 20 (a) and 20(b), the parameters are as follows: n 1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =130nm, H = 200nm, θ i =0°.

[0175] Fig.21 (a) and (b) show the Fig. 20 (a) Same view as (b), but with the incident angle θ i =30°.

[0176] Fig.22A It is shown that for three different incident angles, Fig. 20 The Hy component field distribution (a) and power density distribution (b) of a single NJ element B1 in the xy plane of the right part, Fig. 22B Shown for Fig. 20 The Hy component field distribution (c) and power density distribution (d) of the dual-structure super-elements ME21 and ME22 in the xy plane of the left part of FIG. In both cases, the parameters are as follows: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H 2 =200nm,λ=625nm.

[0177] The phenomenon of total internal reflection helps to change the response of the system in the case of a single material element. Fig. 20 (a) and 21(a), W 1is the distance between elements, n 1 is the refractive index of the main dielectric, n 1 <n 2 <n 3 .

[0178] exist Fig. 20 In the single NJ element system shown in (b) and 21(b), there are two NJs associated with the two outer edges (left and right edges) of block B1 (see Fig. 20 (b), the dashed line corresponds to the B1 of the NJ beam).

[0179] exist Fig. 20 There are two additional edges in the dual-block system or dual structure shown in (a), for θ i = 0 degrees, resulting in an offset angle θ B1 The radiation of four NJs (two NJs in each block for the left and right edges) (see Fig. 20 The dashed lines in (a), indicated by the IJW, correspond to the NJ beams generated by the inner edges in the twin system ( Fig. 20 (a)). By varying the distance between the inner edges, the conditions for constructive and destructive interference of the corresponding waves diffracted by the right or left edge of the block and propagating in the same direction are satisfied. For the parameters of the above system, the diffracted waves propagating in the same direction will interfere destructively or constructively. Thus, the distribution of the corresponding angles can be strengthened or suppressed (see Fig. 22B (c)).

[0180] For vertical incidence, the radiation angle of all NJs is the same θ B1 Compared to the power distribution of the single-material system and the two-material system, it appears that in the case of the twinned structure, the presence of two additional inner edges leads to a reduction in the strength of the central NJ (which is oriented along the symmetry axis of the super-element, resulting from the intersection of the NJs generated by the outer edges of one or more blocks) and to the beginning of two additional NJs with higher strength resulting from the intersection of the NJs generated by the outer and inner edges of the blocks.

[0181] For oblique incidence, we obtain B1 The first pair of NJ and has a radiation angle θ″ B1 The second pair of NJ. For θ′ B1 and θ″ B1 The equation for this is used previously in the dual material solution with insert ( Fig.10 ) and will not be repeated here.

[0182] For certain angles of incidence, the combination of constructive and destructive phenomena of each pair and the total internal reflection of the wave again results in a redistribution of the intensity between the corresponding diffraction orders of the periodic array of metaelements. Fig.17 and 19 As shown in the comparison, the ±1st order diffraction is suppressed and the intensity of the ±2nd order diffraction is increased.

[0183] The ±2nd diffraction orders of the twin element topology can be further enhanced by considering some parameter restrictions. In order to obtain the maximum intensity of the 2nd diffraction order, at negative angles of incidence, the following parameters are considered:

[0184] 1. Select To change the direction of NJ generated by the left vertical edge of the block;

[0185] 2. Select To avoid the reflection of NJ generated by the right vertical edge of the block;

[0186] 3. The width of the corresponding block and the distance between blocks depend on the period of the diffraction grating: and Ideally, to provide constructive interference between NJs generated by the left or right edge of a block, it is preferred to have or However, in optimizing these parameters, it must be considered that good diffraction uniformity of the system is desired over a wide range of incident angles. Therefore, it is not possible to provide constructive interference for all incident angles within the market.

[0187] 4. Note that within each block, the NJs generated by the opposite edges intersect at point A (see Fig.21 ). The distance between the top of each block and this intersection can be determined as In order to obtain the maximum NJ input to the corresponding diffraction order, the angle of deviation of the focus A from the vertical axis is should approximate the angle of the corresponding diffraction order distribution. Furthermore, the focus A should be chosen to be close to the boundary between the block and the substrate (H 2 →H A ).

[0188] At normal incidence, employing twin elements with the above parameters provides an enhanced +2 diffraction order.

[0189] Considering that Fig.16 The diffraction grating shown, which exhibits a periodic array of twinned metaelements placed on a substrate with a lower refractive index, has the angular NJ deviation affected by the refraction of waves diffracted by the edges of the metaelements at the boundary between the substrate and the elements. Fig.23 The power density distribution in the xy plane of a twin structure superelement with the following parameters is shown:1 =1.0,n 2 =2.105,W 1 =260nm, W 2 =130nm, H 2 =200nm, λ=625nm; and for the left column n 3 =2.105, for the right column n 3 =1.52.

[0190] 5.2.4 U-shaped structure

[0191] Fig.24 Another embodiment of a basis pattern of a diffraction grating of an optical device according to the present principles is shown. According to this embodiment, the basis pattern comprises a refractive index n 2 The single material block ME2 is U-shaped and located at a refractive index of n 3 on top of the substrate ME3. Fig.24 The values ​​presented above are examples only. More precisely, the U-shaped form is often referred to as forming Fig.24 The form of the letter U. Fig.24 It can be seen that block ME2 has two 2 , Width W 2 The refractive index is n 2 The petals or blocks are made of a single material, and the two petals or blocks are separated by a height H 1 , Width W 1 The refractive index is n 2 Separate strips made of the same single material.

[0192] From a geometric point of view, the high refractive index n 2 A single material is deposited and electron beam irradiated on a glass substrate ME3. No glass etching is required, and no multiple electron beam lithography is required, and these two facts are advantageous for micro-fabrication.

[0193] and Figure 6 The structure is also very shallow, with a height of 200 nm, compared to the disclosed embodiment with a height of 700 nm.

[0194] like Fig.25 As shown, the performance is very good since a maximum diffraction efficiency of 65% is obtained, which is slightly lower than the efficiency obtained with the twin structure. However, the diffraction uniformity has a value of Γ = 87%, which is excellent. These properties are excellent and when compared with Figure 6 and 12 shows real improvement when compared to the structure of

[0195] Fig.26 Shows Fig.24The Hy component distribution (top) and power density distribution (bottom) of the U-shaped superelement in the xy plane are shown, where the parameters are: n 1 =1.0,n 2 =2.105,n 3 =1.52,W 1 =260nm, W 2 =130nm, H 2 =200nm, H 1 =50nm,λ=625nm.

[0196] With a higher refractive index n 2 The U-shaped superelement helps to reduce the intensity of the central NJ at normal incidence and increase the intensity of the lobes. For the U-shaped topology, the intensity of the ±2 diffraction orders at small incident angles can be increased, and the diffraction uniformity can be improved, such as Fig.25 Performance shown.

[0197] The height (H1) of the center block is obtained by considering that for some specific angles of incidence, the NJ generated by the left edge of the left block (in the case of negative angles of incidence) or by the right edge of the right block (in the case of normal angles of incidence) is not reflected by the opposite edge and does not change the propagation direction. For the rest of the angles of incidence, possible choices are

[0198] For θ′ B1 The equations for have been discussed previously in the dual material scheme with inserts (Fig. ?) and will not be repeated here.

[0199] The width W of the center band separating the two petals of the U 1 It should also satisfy the requirement that W in the twin structure 1 and W 2 Defined relationship.

[0200] 5.2.5 Spacing tolerance

[0201] The values ​​provided for the U-shaped structure should be chosen to be tolerance robust and in order to check the accuracy required for manufacturing, the performance of different spacing sizes is measured with Fig. 27 The original spacing is d=823nm.

[0202] Fig. 27 The tolerances for the pitch dimensions of d=818 nm and d=832 nm are shown. Fig. 27 The top of the graph shows the performance of d = 818 nm. It has η max =65%, Γ=81.8%. Fig. 27 The bottom of the graph shows the performance for a spacing of d = 832 nm. It has η max =78.5%, Γ=76.2%.

[0203] Fig. 27 It is shown that for d=823±5 nm, the diffraction orders ±2 still have high diffraction efficiency and uniformity.

[0204] 5.4 Nanojet-enhanced single-mode high-order diffraction

[0205] The above principles (with ultra-wavelength grating spacing and second order diffraction) can also be extended to inner couplers, which only shift the image to a single side of the waveguide, instead of shifting positive angles to one direction and negative angles to the other.

[0206] To do this, the geometry needs to break the symmetry so that one diffraction order is enhanced. Fig.28 The geometry and pitch dimensions of alternative embodiments of the base pattern of the diffraction grating are shown. Fig.28 As can be seen in the figure, the pitch of the grating is even larger than the pitch of the grating disclosed above (988nm in this case), it is almost a micron-sized spacing with an aspect ratio close to 1.

[0207] According to this embodiment, the base pattern is similar to Figure 6 The geometry shown in , but with the height on the right lower than the height on the left to break the symmetry.

[0208] Fig.29 The performance of this geometry is shown. The horizontal axis spans ±12 degrees. The curve represents the +2 diffraction order efficiency as a function of the angle of incidence. This structure achieves a maximum efficiency of 84% and a uniformity of 54% for input angles spanning ±12 degrees.

[0209] 5.5 Diffraction gratings using structures with modified base angles

[0210] Fig.33 A single-material meta-element with non-vertical edges (n 2 =n 3 ) of a cross-sectional view ( Fig.33 a, Fig.33 b) and a single-material metaelement with a top surface that is not parallel to the xz plane (n 2 =n 3 ) of a cross-sectional view ( Fig.33 c).

[0211] Here we consider structures with vertical edges and / or top surfaces that are not parallel to the xz plane. To demonstrate the effect of the base angle of the components of the diffraction grating elements, we consider Fig.24 The bottom angle of the top surface of the U-shaped block is shown as α 1 and α 2The base angles correspond to the angles between the top surface of the U-shape and the side faces of one of the blocks of the U-shape, respectively.

[0212] Here we consider a single-material metaelement, the refractive index n of the U-shaped structure 2 and the refractive index n of the substrate 3 equal.

[0213] Fig.33 shows the general topological structure of a single-material element. From these structures, it can be seen that the base angle α j ≠90°, where j is 1 or 2. The NJ beam radiation angle can be determined using the following approximate consensus: where j is 1 or 2, n 1 is the refractive index of the bulk dielectric, and n 2 is the refractive index of the microlens material.

[0214] It should also be mentioned that the angle of the NJ distribution is modified due to internal reflections at the non-vertical edges of the element.

[0215] Fig.33 The structure presented in (c) is optimized to provide the best performance for blue wavelengths at λ = 460 nm. The system is illuminated by a linearly polarized plane wave H = {0; 0; 1} (TM). For n 2 = 1.9, the grating pitch size d = 487.4nm, and the modified U-shaped structure uses Fig.24 The same reference used in the reference, with W 1 =60nm; H 1 =220nm; W 2 =180nm; H 2 =360nm and n 3 =1.9.

[0216] To change the angle of the scattered jet wave, the base angle of the top of the U-shaped unit cell was changed by adding a symmetrical pyramid with a height ΔH = 360 nm (see Fig.34 (a)). Fig.34 (b) shows the diffraction performance of the grating with the above parameters. There is absolutely no crosstalk between the +2 and -2 orders of each design. The 0, +1 and -1 orders are not coupled into the waveguide, they are transmitted through and do not degrade the virtual image contrast.

[0217] This modification of the U-shaped topology is to have a lower refractive index material (n 3 =n 2 ) provides a very high second-order diffraction efficiency. Unfortunately, the diffraction uniformity of the system is not very high, and the system is very sensitive to the angle of incidence.

[0218] 5.6 Diffraction Gratings for AR / VR Glasses

[0219] Fig.32 An exemplary diffraction grating according to an embodiment of the present disclosure is shown. According to this embodiment, the base pattern of the diffraction grating has Fig.24 The U-shape shown.

[0220] According to an embodiment of the present disclosure, a diffraction grating with a base pattern according to any of the embodiments disclosed herein can be dedicated to diffracting only a given wavelength. For example, when used in an optical waveguide, one diffraction grating per RGB color can be used. This embodiment allows minimization of chromatic aberrations, and a grating dedicated to a narrow band has much better performance in terms of FoV.

[0221] According to another embodiment of the present disclosure, the diffraction grating is configured to diffract light of a group of wavelengths including more than one wavelength. In this case, the NJ structure basis pattern of the diffraction grating is configured so that the grating pitch is higher than the highest wavelength in the group of wavelengths. For example, in And M=2, where n is the refractive index of the substrate.

[0222] According to an embodiment of the present disclosure, a diffraction grating with a base pattern according to any of the embodiments disclosed herein may be used in an optical waveguide, for example, a waveguide in AR / VR glasses.

[0223] According to this embodiment, the diffraction grating may be configured to incouple light entering the optical waveguide or extract light from the optical waveguide depending on the formation position of the diffraction grating on the waveguide.

[0224] According to another embodiment of the present disclosure, a light guide may include two diffraction gratings according to any of the embodiments disclosed herein: one diffraction grating is configured for in-coupling light into the light guide, and the other diffraction grating is configured for extracting light from the light guide.

[0225] Each diffraction grating has a grating pitch that is higher than a wavelength of light it is configured to incouple or outcouple, and both diffraction gratings are configured to diffract the light with diffraction orders having an absolute value equal to or greater than two.

[0226] According to an embodiment of the present disclosure, a glasses apparatus is disclosed, which includes the optical device according to any one of the embodiments disclosed above.

[0227] Fig.30 A schematic perspective view of an eyeglass device according to an embodiment of the present disclosure is shown, and Fig.31 Shows Fig.30 Schematic front view of the eyeglass device shown in .

[0228] According to an embodiment of the present disclosure, the eyeglass device includes:

[0229] - a light display engine (not shown) configured to emit an image to be displayed, said light engine display being placed, for example, on a branch of said eyeglass device,

[0230] - an optical device group (OPTICS) configured for coupling incident light from the light display engine to the light guide (WG).

[0231] According to an embodiment, a light waveguide (WG) is configured to guide incident light toward an eye of a user to make an image visible to the user.

[0232] according to Fig.30 In the embodiment shown, the optical waveguide (WG), also indicated by "1", includes an input grating ( Fig.30 The input grating may be a diffraction grating according to any one of the above-mentioned embodiments.

[0233] The optical waveguide also includes a vertical pupil expander ( Fig.30 "3" on the top), horizontal pupil dilator ( Fig.30 "4" on the top) and the output grating ( Fig.30 "5" on the output coupler) or output coupler.

[0234] According to an embodiment of the present disclosure, the output grating may be a diffraction grating according to any one of the above-described embodiments.

[0235] like Fig.31 As shown, in order to have a stereoscopic view, images are emitted from two light engines (not shown) respectively placed on two branches of the eyeglass device. The eyeglass device also includes two waveguides (WG) on each side of the device, and two sets of optical devices (OPTICS) for guiding light from the corresponding light engines to the corresponding waveguides.

Claims

1. An optical device, comprising: A diffraction grating, (i) a diffraction grating configured to diffract incident light of a given wavelength on the optical device, the diffraction grating having a grating pitch higher than the given wavelength and configured to diffract the incident light with a diffraction order having an absolute value equal to or greater than 2, and (ii) comprising a substrate including a first dielectric material having a refractive index n3 and at least one second dielectric material having a refractive index n2 on the substrate, wherein n3 <n2; an optical waveguide configured to guide the incident light to be diffracted with a diffraction order having an absolute value equal to or greater than 2; The diffraction grating includes a base pattern, the base pattern including the second dielectric material, the base pattern configured to form a nanojet beam associated with an edge of the base pattern from the incident light; as well as The base pattern comprises a block of the second dielectric material having a refractive index n2 on top of the substrate having a U-shape comprising two lobes having a height H2 and a width W2 separated by a central block having a height H1, wherein H1 is lower than H2, and in θ i is the angle of the incident light relative to the normal to the top surface of the diffraction grating, and n1 is the refractive index of the host dielectric in which the diffraction grating is placed.

2. The optical device according to claim 1, wherein W1 is the width of the central block of the block having a U-shape, and W2 is the width of each of the two lobes, and where W1 and W2 depend on the grating spacing d of the diffraction grating, where and 3. The optical device according to any one of claims 1-2, wherein the diffraction grating is configured to incouple light entering the optical waveguide or to extract light from the optical waveguide.

4. The optical device according to any one of claims 1 to 2, wherein the diffraction grating is configured to incouple light entering the optical waveguide, and wherein the optical waveguide comprises another diffraction grating configured to extract light from the optical waveguide, the other diffraction grating having a grating pitch higher than the wavelength of the light, and the other diffraction grating being configured to diffract the light with a diffraction order having an absolute value equal to or greater than 2.

5. An eyeglass device, comprising an optical device, wherein the optical device comprises: A diffraction grating, (i) a diffraction grating configured to diffract incident light of a given wavelength on the optical device, the diffraction grating having a grating pitch higher than the given wavelength and configured to diffract the incident light with a diffraction order having an absolute value equal to or greater than 2, and (ii) comprising a substrate including a first dielectric material having a refractive index n3 and at least one second dielectric material having a refractive index n2 on the substrate, wherein n3 <n2; an optical waveguide configured to guide the incident light to be diffracted with a diffraction order having an absolute value equal to or greater than 2; The diffraction grating includes a base pattern, the base pattern including the second dielectric material, the base pattern configured to form a nanojet beam associated with an edge of the base pattern from the incident light; as well as The base pattern comprises a block of the second dielectric material having a refractive index n2 on top of the substrate having a U-shape comprising two lobes having a height H2 and a width W2 separated by a central block having a height H1, wherein H1 is lower than H2, and in θ i is the angle of the incident light relative to the normal to the top surface of the diffraction grating, and n1 is the refractive index of the host dielectric in which the diffraction grating is placed.

6. The eyeglass device according to claim 5, further comprising: a light display engine configured to emit an image to be displayed, an optical device configured to couple incident light from the light display engine to the light waveguide, The light guide is configured to direct incident light toward an eye of a user so that the image is visible to the user.

Images