Diffractive optical element and terminal device

Abstract

A diffractive optical element and a terminal device are disclosed. The diffractive optical element is applicable to AR devices and head-up display (HUD) devices in the augmented reality (AR) field, VR devices in the virtual reality (VR) field, or filters, optical splitters, and spectrum detection devices. The diffractive optical element includes a grating element periodically distributed in a first dimension. The grating element includes N optical waveguides. The N optical waveguides include M optical waveguides periodically varying in a second dimension. At least two of the M optical waveguides periodically varying in the second dimension have different structures. The included angle between the second dimension and the first dimension is greater than 0 degrees and less than 180 degrees. N is an integer greater than 1. M is an integer greater than 1 and equal to or less than N. By using the M optical waveguides periodically varying in the second dimension, a specific band of light at a specific angle can be selected to achieve both a narrowband response and tuning for reflection at unusual angles.

Description

[Technical field]

[0001] [Technical field] The present application relates to the field of diffractive optical element technology, and in particular to diffractive optical elements and terminal devices. [Background technology]

[0002] Augmented reality (AR) technology integrates the real world and the virtual world. This technology allows sensory (e.g., visual, auditory, and tactile) experiences that do not exist in the real world and are generated by a computer to be simulated and superimposed on a real-world scenario, so that the sensory experience is perceived by the user. In this way, a sensory experience that exceeds the real world is achieved and the real-world scenario is enhanced. AR technology can be applied to a wide range of scenarios and has been successfully applied in the military, industrial production, medical, and education fields. In recent years, as 5G high-speed mobile communication technology becomes increasingly popular, the application scenarios of AR technology for consumer terminals continue to expand, and the prospects for large-scale application are increasingly expected.

[0003] Among several types of sensory experiences simulated by AR technology, visual experience is one of the most important types. Therefore, synthesizing light containing virtual information with light containing external environment information is one of the core problems of AR technology. How to implement a small and lightweight AR system that can efficiently combine virtual optical images with real optical images is one of the hot topics of current research. AR systems are usually divided into two parts: an optical projection system and an optical combiner. The optical combiner needs to transmit the real ambient light and also reflect the projection light of the projection system to the human eye. The optical combiner is the core optical component for virtual-real image fusion and is also one of the important optical components that determine the user experience of the AR system. Currently, the optical combiners in existing AR systems are usually semi-reflective semi-transparent mirrors, polarizing beam splitters, waveguide lenses, etc. These types of optical combiners cannot realize both narrow-band response and adjustment for reflection at unusual angles. Therefore, when the volume of an AR system is compact, the AR system cannot meet the requirements for high transmittance of ambient light and high reflectance of projected light.

[0004] In conclusion, providing an optical element that can provide both a narrowband response and adjustment for reflections at unusual angles is a technical problem that currently needs to be solved urgently. Summary of the Invention

[0005] The present application provides a diffractive optical element and a terminal device such that the diffractive optical element can achieve both a narrowband response and tuning for reflections at unusual angles.

[0006] According to a first aspect, the present application provides a diffractive optical element. The diffractive optical element includes a grating component periodically distributed in a first dimension. The grating component includes N optical waveguides. The N optical waveguides include M optical waveguides periodically varying in a second dimension. At least two of the M optical waveguides periodically varying in the second dimension have different structures. An included angle between the second dimension and the first dimension is greater than 0 degrees and less than 180 degrees. N is an integer greater than 1. M is an integer greater than 1 and less than or equal to N.

[0007] By using M optical waveguides that vary periodically in the second dimension, a specific band of light can be selected based on the diffractive optical element, i.e., a narrow-band response is realized. A lattice structure is formed using lattice elements that are periodically distributed in the first dimension to realize the function of tuning the reflection at an abnormal angle. Furthermore, the diffraction efficiency of the diffractive optical element for the reflection at an abnormal angle can be increased in a specific band. The diffractive optical element can realize both a narrow-band response and tuning for the reflection at an abnormal angle. Therefore, when the diffractive optical element is applied to an AR or VR device, the optical combiner can realize efficient diffractive imaging in a compact volume in the projection light band and high transmittance of ambient light in another band.

[0008] In a possible implementation, at least two of the M optical waveguides that are periodically varied in the second dimension have different structures. For example, at least two of the M optical waveguides that are periodically varied in the second dimension may have different periodic variation schemes. In another example, at least two of the M optical waveguides that are periodically varied in the second dimension have different waveguide periods. In yet another example, at least two of the M optical waveguides that are periodically varied in the second dimension have different shapes.

[0009] In a possible implementation, M optical waveguides that are periodically varied in the second dimension have different structures that correspond to different resonant wavelengths of the guided mode resonance, allowing M different resonant wavelengths to be selected, i.e., narrowband responses in M ​​different bands can be achieved.

[0010] In a possible implementation, the M optical waveguides that are periodically varied in the second dimension are configured to reflect a particular band of light. The M optical waveguides that are periodically varied in the second dimension may also be understood to be reflective optical waveguides in a narrow band of wavelengths.

[0011] In a possible implementation, at least one of the M optical waveguides that are periodically varied in the second dimension has at least two different waveguide periods.

[0012] Further, optionally, the optical waveguide having at least two different waveguide periods includes a top of the optical waveguide having at least two different waveguide periods. Alternatively, any one of two sidewalls of the optical waveguide has at least two different waveguide periods. Alternatively, each sidewall of the optical waveguide has at least one waveguide period, and the two sidewalls have different waveguide periods.

[0013] In a possible implementation, the periodic variation scheme of the optical waveguide includes any one of the following:

[0014] Method 1: The optical waveguide has periodic protrusions or periodic recesses.

[0015] In Scheme 1, the periodic change scheme of the optical waveguide is that the optical waveguide has periodic protrusions or periodic recesses, and the protrusions or recesses are located on the top or at least one sidewall of the optical waveguide.

[0016] In the first scheme, diffractive optical elements are applicable to scenarios where the response band (also called filtering band) is narrow. For example, diffractive optical elements are applicable to broadband light emitted from a light source, but the narrow band requires a high-resolution optical imaging system.

[0017] Method 2: The optical waveguide has periodic gaps.

[0018] In scheme 2, the periodic variation scheme of the optical waveguide is that the optical waveguide has periodic gaps, and the length of the gaps in the second dimension satisfies that the incident light can be coupled between two adjacent parts of the optical waveguide to form a guided mode, so that the guided mode resonance can be realized, thereby realizing high diffraction efficiency and selecting a narrow band.

[0019] Further, optionally, the length of the gap in the second dimension is less than or equal to the central wavelength of the operating band.

[0020] In a possible implementation, the included angle between the gap direction and the first dimension is less than 90 degrees.

[0021] In the second method, the diffractive optical element is applicable to scenarios where the requirements for narrow-band filtering are not high, such as imaging systems where the light source is a narrow-band laser light source. In addition, the requirements for process accuracy are low, so the diffractive optical element can be easily fabricated.

[0022] Method 3: The optical waveguide includes periodically distributed small holes, which are hollow or filled with a material whose refractive index is different from that of the material of the optical waveguide.

[0023] In scheme 3, diffractive optical elements are applicable to scenarios that require narrow filtering bands, for example, broadband light emitted from a light source, but narrow bands require high resolution optical imaging systems.

[0024] Manner 4: The periodically distributed diffractive structures are in contact with the optical waveguide, or the distance between the periodically distributed diffractive structures and the optical waveguide does not exceed a preset distance, respectively.

[0025] In Scheme 4, the periodic change scheme of the optical waveguide is that the periodically distributed diffractive structures are in contact with the optical waveguide, or the distance between the periodically distributed diffractive structures and the optical waveguide does not exceed a preset distance, respectively, and the diffractive structures are in contact with the top or at least one sidewall of the optical waveguide, or the diffractive structures are in a position that is less than or equal to a preset distance from one sidewall of the optical waveguide, respectively.

[0026] In a possible implementation, a preset distance between the diffractive structure and the light guide satisfies that a light field formed in the light guide spatially overlaps with the diffractive structure.

[0027] Further, optionally, the preset distance between the diffractive structure and the optical waveguide is less than or equal to a central wavelength of the operating band.

[0028] In method 4, the diffractive optical element is applicable to scenarios where the narrow band (or called filtering band) that requires response is narrow. For example, the diffractive optical element is applicable to broadband light emitted from a light source, but the narrow band requires a high-resolution optical imaging system. Alternatively, the diffractive optical element is applicable to scenarios where the requirements for the narrowband filtering function are not high, for example, imaging systems where the light source is a narrowband light source. In addition, the diffractive optical element can be easily fabricated, since the requirements imposed on the process accuracy are low.

[0029] Method 5: The refractive index of the optical waveguide changes periodically.

[0030] In scheme 5, the diffractive optical element is applicable to scenarios where the narrow band (or called filtering band) that requires response is narrow. For example, the diffractive optical element is applicable to broadband light emitted from a light source, but the narrow band requires a high-resolution optical imaging system. Alternatively, the diffractive optical element is applicable to scenarios where the requirements for the narrow-band filtering function are not high, for example, imaging systems where the light source is a narrow-band light source. In addition, the refractive index of the optical waveguide can be changed periodically by doping, and the requirements imposed on the process accuracy are low, so that the diffractive optical element can be easily fabricated.

[0031] In a possible implementation, the grating period in the first dimension is 2 microns or less, allowing a wide range of incident angles to be reflected into a particular direction in space.

[0032] In a possible implementation, each of the N optical waveguides has a thickness of 300 nanometers or less, which facilitates fabrication of the optical waveguides and the miniaturization of the diffractive optical element.

[0033] In a possible implementation, the material of the N optical waveguides is silicon nitride or titanium dioxide.

[0034] When the material of the optical waveguide is silicon nitride or titanium dioxide, the diffractive optical element can be fabricated by mature semiconductor micro-nano fabrication process. Therefore, it is easy to mass-produce. In addition, the performance of materials such as silicon nitride or titanium dioxide is stable, so that the diffractive optical element can have as stable performance as possible even under different environmental conditions. Furthermore, silicon nitride or titanium dioxide is transparent to visible light, which helps to improve light transmittance.

[0035] In a possible implementation, the acute angle formed between any two adjacent optical waveguides of the N optical waveguides is less than or equal to a preset angle.

[0036] Any two adjacent optical waveguides among the N optical waveguides are arranged in parallel or nearly parallel, so that more optical waveguides can be arranged in the grating element, and the more optical waveguides, the more flexible the adjustment of the light field can be.

[0037] In a possible implementation, the first dimension is perpendicular to the second dimension, for example, the first dimension can be the direction of the grating period and the second dimension can be the extension direction of the optical waveguide.

[0038] To facilitate ease of manufacture of the diffractive optical element and to make the response more uniform, the first dimension is perpendicular to the second dimension.

[0039] According to a second aspect, the present application provides a terminal device. The terminal device includes at least one layer of diffractive optical elements according to the first aspect or any one of the possible implementations of the first aspect, and at least one layer of a substrate. One layer of the diffractive optical elements corresponds to one layer of the substrate. Each layer of the diffractive optical elements is fixed to a corresponding substrate.

[0040] In a possible implementation, parameters of the grating elements in the diffractive optical elements fixed to different regions of the substrate are different, including the grating period and / or the tilt angle.

[0041] In a possible implementation, the terminal device includes an optical projector configured to transmit a light beam carrying image information to the diffractive optical element.

[0042] For the technical effects that can be achieved in any one of the second to fifth aspects, please refer to the description of the beneficial effects in the first aspect, and the details will not be described again in this specification. [Brief description of the drawings]

[0043] [Figure 1] FIG. 2 is a schematic diagram of a diffraction grating diffracting light according to the present application. [Diagram 2]FIG. 1 is a schematic diagram of a possible application scenario according to the present application. [Diagram 3] 1 is a schematic diagram of a structure of a diffractive optical element according to the present application; [Figure 4a] 1 is a schematic diagram of a structure of periodic recesses in an optical waveguide according to the present application; [Figure 4b] FIG. 2 is a schematic diagram of another structure of periodic recesses in an optical waveguide according to the present application; [Diagram 5] FIG. 2 is a schematic diagram of a periodic gap structure of an optical waveguide according to the present application; [Figure 6] 1 is a schematic diagram of a structure of an optical waveguide including periodically distributed small holes according to the present application; [Figure 7a] FIG. 2 is a schematic diagram of the positional relationship between a periodically distributed diffractive structure and an optical waveguide according to the present application. [Figure 7b] 1 is a schematic diagram of a structure of contact between a periodically distributed diffractive structure and an optical waveguide according to the present application; [Figure 7c] 1 is a schematic diagram of another positional relationship between a periodically distributed diffractive structure and an optical waveguide according to the present application. FIG. [Figure 7d] 1 is a schematic diagram of another structure of contact between a periodically distributed diffractive structure and an optical waveguide according to the present application; [Figure 7e] 1 is a schematic diagram of yet another positional relationship between a periodically distributed diffractive structure and an optical waveguide according to the present application. FIG. [Figure 8] 1 is a schematic diagram of a periodically varying refractive index structure of an optical waveguide according to the present application; [Figure 9a] 2 is a schematic diagram of an optical waveguide structure having at least two different waveguide periods in a second dimension according to the present application. FIG. [Figure 9b] 4 is a schematic diagram of another structure of an optical waveguide having two different waveguide periods in the second dimension in accordance with the present application. [Figure 9c] 1 is a schematic diagram of yet another structure of an optical waveguide having at least two different waveguide periods in a second dimension in accordance with the present application. [Figure 9d]1 is a schematic diagram of yet another structure of an optical waveguide having at least two different waveguide periods in a second dimension in accordance with the present application. [Figure 9e] 1 is a schematic diagram of yet another structure of an optical waveguide having at least two different waveguide periods in a second dimension in accordance with the present application. [Figure 9f] FIG. 2 is a schematic diagram of the formation principle of an optical waveguide having two different waveguide periods in the second dimension according to the present application. [Figure 10a] FIG. 2 is a top view of a structure of a diffractive optical element according to the present application. [Figure 10b] FIG. 2 is a side view of a diffractive optical element structure according to the present application. [Figure 10c] FIG. 2 is a top view of another structure of a diffractive optical element according to the present application. [Figure 10d] FIG. 2 is a top view of yet another structure of a diffractive optical element according to the present application. [Figure 10e] FIG. 2 is a top view of yet another structure of a diffractive optical element according to the present application. [Figure 11a] 2 is a schematic diagram of the structure of another diffractive optical element according to the present application. [Figure 11b] FIG. 2 is a side view of a diffractive optical element according to the present application. [Figure 11c] 1 is a schematic diagram of simulated diffraction efficiency distributions of zeroth, first and second order diffracted light at different wavelengths according to the present application. [Figure 11d] 4 is a schematic diagram of yet another structure of a diffractive optical element according to the present application. [Figure 11e] FIG. 13 is another schematic diagram of simulated diffraction efficiency distributions of zeroth, first and second order diffracted light at different wavelengths according to the present application. [Figure 11f] 4 is a schematic diagram of yet another structure of a diffractive optical element according to the present application. [Figure 11g] 13 is yet another schematic diagram of simulated diffraction efficiency distributions of zeroth, first and second order diffracted light at different wavelengths according to the present application. [Figure 12] 1 is a schematic diagram of a structure of a grating element having the same parameters in different regions of a substrate according to the present application. [Figure 13a] 1 is a schematic diagram of a structure of a grating element having different parameters in different regions of a substrate according to the present application. [Figure 13b] 2 is a schematic diagram of focusing formed by a diffractive optical element according to the present application; [Figure 14] FIG. 2 is a schematic diagram of the structure of a diffractive optical element used for spectral sensing according to the present application. [Figure 15] FIG. 2 is a schematic diagram of the structure of a terminal device according to the present application; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings.

[0045] Some terms in this application are explained below. Please note that these explanations are intended to facilitate understanding by those skilled in the art, but do not constitute limitations on the scope of protection claimed in this application.

[0046] 1. Diffraction Grating

[0047] Diffraction gratings are micro-nano-optical elements that exhibit periodic structural or refractive index changes on a near-wavelength scale and can produce periodic spatial modulation of the amplitude and / or phase of incident light.

[0048] Diffraction gratings can be classified as reflective and transmissive. Reflective gratings can reflect incident light at one or more specific angles. This process can be described using the grating's diffraction equation (Equation 1), where different reflection angles correspond to specific diffraction levels. sinθ i -sinθ m = mλ / d Equation 1

[0049] θ i is the angle of incidence, and θ mis the diffraction angle of diffraction order m, λ is the wavelength of the incident light, and d is the grating period (also called the grating constant).

[0050] As shown in Fig. 1, the diffraction angle (θ 0 ) is the angle of incidence of the incident light (θ i ) In other words, the diffraction angle of the zeroth order diffracted light is equal to the incident angle, which belongs to symmetric reflection and is unrelated to the grating period. The diffraction angles of higher orders (±1 order and above) of diffracted light are asymmetric with respect to the incident angle of the incident light, which belongs to reflection at abnormal angles and is related to the grating period. It can also be understood that the diffraction angles of higher order diffracted lights can be adjusted by changing the grating period, but the diffraction angle of the zeroth order diffracted light cannot be adjusted.

[0051] It should be understood that in Equation 1, the incident light is on the same plane. The diffraction angle of the zeroth order diffracted light is the diffraction angle of the diffracted light whose diffraction order is zero. The diffraction angle of the higher order diffracted light is the diffraction angle of the diffracted light whose diffraction order is ±1 or more.

[0052] 2. Guided-mode resonance (GMR)

[0053] Guided mode resonance refers to the phenomenon that by introducing a periodic diffractive element (e.g., a diffraction grating) into a waveguide, when free-space incident light of a specific wavelength satisfies the phase matching condition, a guided mode is excited and the light field leaks into free space. This is due to the coupling between the free-space incident light of a specific wavelength and the leaky mode supported by the diffraction grating. It can be seen that the leaky mode corresponds to the guided mode in the optical waveguide structure.

[0054] A diffraction grating can be viewed as a periodic modulation of an optical waveguide. For a particular incident wavelength, when the diffracted light of the diffraction grating is close in terms of parameters (e.g., wave vector) to the guided mode supported by the optical waveguide (i.e., phase-matched), the guided mode can leak into free space to form a guided mode resonance. The guided mode resonance can achieve high diffraction efficiency and select a narrow band of wavelengths (or is called a narrow band wavelength response).

[0055] 3. Waveguide Mode

[0056] The electromagnetic field types that can propagate in a waveguide are called waveguide modes. There are two eigenmodes in a waveguide: transverse electric (TE) and transverse magnetic (TM) modes, which can be defined in terms of the polarization directions of the electric and magnetic fields of the light, respectively. The electric field is polarized only in the y direction, parallel to the waveguide interface. The electric field is perpendicular to the light transmission direction z, and the magnetic field is horizontal. This is called the transverse electric mode. The magnetic field is polarized only in the y direction, parallel to the waveguide interface. In this case, the magnetic field is perpendicular to the light transmission direction z, and the magnetic field is horizontal. This is called the transverse magnetic mode.

[0057] 4. Phase Delay

[0058] Because the speed of a light wave is slowed down when it passes through a material with a particular refractive index, a phase delay effect is caused, which is called phase retardation.

[0059] 5. Wavefront

[0060] A wavefront is a plane that exists when a wave propagates through a medium and is formed by the material points that begin to displace at a specific moment. A wavefront is a wave plane (or wave array plane), perpendicular to the direction of wave propagation. It can also be understood as the surface formed by the points in front of the displacement at a specific moment.

[0061] 6. Evanescent waves

[0062] Evanescent waves are also called evanescent waves or evanescent waves. When total internal reflection occurs for light, the light wave is not completely reflected by the first medium at the interface, but enters the second medium at a depth of about one wavelength, travels along the interface for a distance on the wavelength scale, and then returns to the first medium and is emitted in the direction of the reflected light. This wave along the surface of the second medium is called an evanescent wave.

[0063] 7. Resonance wavelength

[0064] When the wavelength of the incident light satisfies the phase matching condition, the guided mode resonance phenomenon is induced and the wavelength becomes the resonant wavelength.

[0065] Some terms in this application are explained above, and application scenarios in this application are explained below. Please note that these explanations are intended to facilitate the understanding of those skilled in the art, but do not constitute limitations on the scope of protection claimed in this application.

[0066] In this application, the diffractive optical element is applicable to an imaging system. The imaging system is applicable to the AR field, for example, AR glasses, AR helmets, and head-up display (HUD) devices. Alternatively, the imaging system is applicable to the virtual reality (VR) field, for example, VR glasses or VR helmets. In the AR or VR field, in order to meet both compact volume, high reflectance of projected light, and high transmittance of ambient light, it is necessary to realize a response (e.g., reflection) to light of a specific band (or called a specific wavelength range), and it is necessary to adjust the reflection at an abnormal angle.

[0067] FIG. 2 shows a possible application scenario according to the present application. AR glasses are used as an example in this application scenario. The AR glasses may include a light combiner and an optical projection system. The optical projection system is configured to transmit a specific band of light. The specific band of light carries image information. The light combiner is configured to reflect the specific band of light to the human eye for imaging at a specific angle. Ambient light may also be propagated to the human eye through the light combiner for imaging to realize the visual effect of fusion of real world images and virtual world images in the AR glasses. It should be understood that in this scenario, a diffractive optical element may be used as the light combiner.

[0068] Based on possible application scenarios, it can be seen that the light combiner needs to be able to respond to a specific band of light and adjust the specific band of light to be emitted in a specific direction into space. However, the light combiner in the prior art is usually a semi-transparent semi-reflective mirror or a polarizing beam splitter. Neither type of light combiner can realize both the response to a specific band of light and the adjustment of the direction in which the specific band of light is emitted into space. In addition, in order to propagate the light of the image generated by the optical projection system to the human eye, the optical projection system needs to be combined with other optical elements. This is not conducive to the miniaturization of the AR glasses. In addition, the existing semi-transparent semi-reflective mirror or polarizing beam splitter cannot meet the requirements for high transmittance of ambient light and high reflectance of the optical projector.

[0069] It should be noted that the scenarios are merely examples, and the diffractive optical element provided in this application can be further applied to multiple scenarios where tuning for narrowband wavelength response and / or reflection at unusual angles is required. For example, in a spectral detection scenario, the presence or change in concentration of a substance to be detected changes the refractive index outside the diffractive optical element, causing a change in the wavelength of the reflected light. Thus, by detecting the change in the reflected light spectrum, information about the substance to be detected can be obtained. Another example is the space optical communication scenario.

[0070] In light of this, the present application provides a diffractive optical element that can accommodate specific bands of light and can tailor its reflection at unusual angles.

[0071] The diffractive optical element provided in the present application will be specifically described below with reference to FIGS.

[0072] According to the above, the present application provides a diffractive optical element. The diffractive optical element may include grating elements periodically distributed in a first dimension. The grating elements include N optical waveguides. The N optical waveguides include M optical waveguides periodically varying in a second dimension. At least two of the M optical waveguides periodically varying in the second dimension have different structures. The included angle between the second dimension and the first dimension is greater than 0 degrees and less than 180 degrees. N is an integer greater than 1. M is an integer greater than 1 and equal to or less than N.

[0073] FIG. 3 is a schematic diagram of the structure of a diffractive optical element according to the present application. In this example, the first dimension is in the direction of the x-axis, and the second dimension is in the direction of the y-axis. The grating elements are periodically distributed in the first dimension. In this example, there are two grating elements in the first dimension. The grating elements may also be understood to be periodically arranged in the first dimension. In other words, the grating elements are the smallest repeatable units in the first dimension, and the period size in the first dimension may be called the grating period and is denoted as Tx. The grating elements include three optical waveguides. The three optical waveguides include two optical waveguides that vary periodically in the second dimension. The two optical waveguides have different structures. The period in the second dimension may be called the waveguide period. The waveguide period of one optical waveguide is T y1 and the waveguide period of the other optical waveguide is T y2 In this example, T y1 is T y2It should be understood that in this example, the periodic variation manner in the second dimension and the structure of the two optical waveguides having different structures in the second dimension are merely examples and may be other manners. For details, please refer to the related description below. For details, the present specification will not be described again.

[0074] By using M optical waveguides that vary periodically in the second dimension, a specific band of light can be selected based on the diffractive optical element, i.e., a narrow band response is realized. A grating structure is formed using grating elements that are periodically distributed in the first dimension to realize the function of adjusting the reflection at an abnormal angle. In other words, the reflection at an abnormal angle can be realized by using the high order diffraction of the grating structure. Furthermore, by using the diffractive optical element shown in FIG. 3, the diffraction efficiency of the reflection at an abnormal angle of the diffractive optical element can be increased in a specific band.

[0075] It should be noted that the optical waveguide is periodically changed in the second dimension (i.e., in the extending direction of the optical waveguide). This periodic change can excite a guided mode in the optical waveguide when a free-space light of a certain wavelength is incident, and can perform phase matching with the diffracted light of the free-space light to form a leaky-wave mode that can be efficiently reflected back to free space. In this case, the reflection efficiency is greatly improved (i.e., the guided-mode resonance phenomenon). For other light of wavelengths that do not satisfy the phase matching condition, the reflection efficiency is very low. Specifically, after the incident light of a certain band interacts with the optical waveguide that is periodically changed in the second dimension, the diffracted light can be reflected at a certain angle. In other words, the principle of guided-mode resonance is used for the optical waveguide that is periodically changed in the second dimension. After the incident light of a certain band interacts with the optical waveguide that is periodically changed in the second dimension, the diffracted light is reflected at a certain angle (called the extraordinary angle). In addition, the incident light of another wavelength does not have a similar response. Therefore, a narrow-band response can be realized. In other words, narrow band selection can be realized. In addition, due to the difference in the waveguide size or resonant wavelength, different optical waveguides in the grating element have different phase delays with respect to the incident light, so that a reflected light wavefront distribution at a specific angle can be formed.

[0076] A certain band of light may be called a narrow band, and the narrow band range may be, for example, less than 30 nanometers (nm), or less than 50 nm. Furthermore, the incident light may be an optical band, for example, a visible light band, an infrared band, or an ultraviolet band, or may be terahertz, microwave, radio, etc. Referring to Equation 1, when the incident angle and the diffraction order are fixed, the longer the wavelength of the incident light, the larger the size of the diffractive optical element (e.g., the grating period of the grating element, the length of the optical waveguide, the width of the optical waveguide, and the thickness of the optical waveguide), and the larger the size, the lower the requirements for manufacturing precision. For example, when the incident light is a visible light band light, the grating period may be 2 microns (μm) or less.

[0077] In a possible implementation, the M optical waveguides that are periodically changed in the second dimension are configured to reflect a specific band of light. The M optical waveguides that are periodically changed in the second dimension may also be understood to be specific band (narrow band) reflective optical waveguides. The specific band may be, for example, 525 nm ± 5 nm. In addition, optionally, optical waveguides other than the M optical waveguides among the N optical waveguides may also perform phase adjustment on the incident light. In other words, the N optical waveguides can cause different phase delays on the incident light to achieve the function of phase adjustment, thereby improving the efficiency of a certain order of diffracted light and decreasing the efficiency of another order of diffracted light.

[0078] In a possible implementation, the first dimension is perpendicular to the second dimension. The first dimension can be the direction of the grating period, and the second dimension can be the extension direction of the optical waveguide. For example, the first dimension is in the direction of the x-axis, and the second dimension is in the direction of the y-axis. See FIG. 3. This makes the diffractive optical element easier to manufacture and more uniform in response. It should be understood that the first dimension can be approximately perpendicular to the second dimension.

[0079] In a possible implementation, the material of the light guide can be a material that is transparent to visible light or not transparent to visible light and can diffract light at a large incident angle, such as silicon nitride, titanium oxide, silicon, silicon oxide, polymer, or metal. This is not limited in this application. It should be noted that when the incident light is in the visible light band, the material of the light guide is usually a transparent material, such as silicon nitride or titanium oxide. This improves the transmittance of light. In addition, if the material of the light guide is silicon nitride or titanium oxide, the diffractive optical element can be fabricated with a mature semiconductor micro-nano fabrication process. Therefore, it is easy to mass-produce. In addition, the performance of materials such as silicon nitride or titanium oxide is stable, and the diffractive optical element can have as stable performance as possible even in different environmental conditions.

[0080] Furthermore, optionally, the cross-sectional profile of the optical waveguide may be rectangular (as shown in FIG. 10b), trapezoidal, or any other regular or irregular shape.

[0081] In the second dimension, the widths of the N optical waveguides included in the grating element may be the same or different. In another example, the thicknesses of the N optical waveguides may be the same or different. Further, optionally, the thickness of the optical waveguide is 1 μm or less. Further, optionally, the thickness of the optical waveguide is 300 nanometers (nm) or less.

[0082] In a possible implementation, the acute angle formed between any two adjacent light guides among the N light guides is equal to or less than a preset angle. The preset angle may be, for example, 0 degrees, i.e., the N light guides are parallel to each other. As another example, the preset angle may be greater than 0 degrees and equal to or less than 10 degrees, i.e., the N light guides are approximately parallel to each other. In other words, the preset angle may be any angle equal to or less than 10 degrees, for example, 0 degrees, 0.5 degrees, 1 degree, 1.2 degrees, 3 degrees, or 10 degrees. It may also be understood that any two adjacent light guides among the N light guides are parallel or approximately parallel to each other. In this way, more light guides can be arranged in the grating component, and more light guides can provide more flexibility in adjusting the light field.

[0083] Further, optionally, among the M optical waveguides periodically varying in the second dimension, the optical waveguides having different structures correspond to different resonant wavelengths of the guided mode resonance. In other words, the M optical waveguides having different structures correspond to M resonant wavelengths. In this way, M bands can be selected. For example, this is applicable to scenarios where multiple wavelength selection is required, such as color display.

[0084] In the following, the structure of the diffractive optical element shown in FIG. 3 in two dimensions will be described separately to provide an example of a specific implementation solution.

[0085] 1. Structure in the second dimension

[0086] In a possible implementation, M of the N optical waveguides included in the grating element are periodically varied in the second dimension, and at least two of the M optical waveguides that are periodically varied in the second dimension have different structures.

[0087] In the following, three possible implementations of optical waveguides with different structures are given as examples.

[0088] In implementation 1, at least two of the M optical waveguides that are periodically varied in the second dimension have different periodic variation schemes. In implementation 2, at least two of the M optical waveguides that are periodically varied in the second dimension have different periods. In implementation 3, at least two of the M optical waveguides that are periodically varied in the second dimension have different shapes. It should be understood that at least two optical waveguides having different structures can be a combination of the three implementations mentioned above. To facilitate the explanation of the solution, two of the M optical waveguides are used as an example for explanation. For example, the two optical waveguides have different periods and different periodic variation schemes. In another example, the two optical waveguides have different periods and different shapes. In yet another example, the two optical waveguides have different periodic variation schemes and different shapes. In yet another example, the two optical waveguides have different periods, different periodic variation schemes, and different shapes.

[0089] In a possible implementation, the period of each of the M optical waveguides that are periodically varied in the second dimension (e.g., T y ) is less than the central wavelength of the operating band. For example, the period T of the optical waveguide in the second dimension y ranges from 0.2 μm to 0.4 μm.

[0090] In the following, five possible periodic variation schemes are given as examples.

[0091] Method 1: The optical waveguide has periodic protrusions or periodic recesses.

[0092] In a possible implementation, in the second dimension, the top or sidewall of the light guide has periodic recesses or periodic protrusions. Figure 4a is a schematic diagram of the structure of periodic recesses of the light guide according to the present application. The recesses are located on the sidewalls of the light guide. In this periodic variation scheme of the light guide, the width of the light guide changes periodically in the extension direction (i.e., the second dimension) of the light guide. In Figure 4a, an example is used in which the recesses are located on the left sidewall of the light guide, but it should be understood that the recesses may also be on the right sidewall of the light guide.

[0093] FIG. 4b is a schematic diagram of another structure of periodic recesses of a light guide according to the present application. The recesses are located on two side walls of the light guide. In this periodic variation of the light guide, the width of the light guide varies periodically in the extension direction (i.e., the second dimension) of the light guide. It should be understood that FIG. 4b uses an example in which the recesses located on the two side walls are symmetrical with respect to the center line of the light guide. The center lines of the two recesses of the light guide may be asymmetric. For example, the two recesses may have the same period and different concaveness. Alternatively, the two recesses may have the same period and concaveness, but with a displacement in the second dimension. In other words, the recesses on the two side walls are not strictly aligned (see FIG. 9c below).

[0094] It should be noted that when the top of the optical waveguide has periodic recesses or periodic protrusions, the thickness of the optical waveguide changes periodically in the extending direction of the optical waveguide.

[0095] It is further noted that the optical waveguide may be periodically varied in an abrupt manner, such as, for example, the rectangular sawtooth shape shown in Figure 4a or Figure 4b. Alternatively, the optical waveguide may be periodically varied in a gradually varying manner, such as, for example, triangular sawtooth, serpentine concave-convex, semicircular convex, semicircular concave, etc. It is understood that any shape that can be implemented using micro-nano fabrication processes may be used.

[0096] In the first scheme, diffractive optical elements are applicable to scenarios where the narrow band (also called filtering band) of the response is narrow. For example, diffractive optical elements are applicable to broadband light emitted from a light source, but the narrow band requires a high-resolution optical imaging system.

[0097] Method 2: The optical waveguide has periodic gaps.

[0098] In a possible implementation, in the second dimension, the optical waveguide has periodic gaps. In the second dimension, the optical waveguide can also be understood to be periodically cut to form gaps between two adjacent cut surfaces. The direction of the gaps can be understood as the cutting direction. FIG. 5 is a schematic diagram of the structure of periodic gaps of the optical waveguide according to the present application. The length of the gap of the optical waveguide in the second dimension should be controlled within a certain range. For example, the length of the gap in the second dimension satisfies that the incident light can be coupled between two adjacent parts of the optical waveguide (e.g., A and B in FIG. 5) to form a guided mode. This can realize the guided mode resonance, thereby realizing high diffraction efficiency and selecting a narrow band.

[0099] For example, the length of the gap in the second dimension is less than or equal to the central wavelength of the operating band. Furthermore, the length of the gap in the second dimension is less than half the central wavelength of the operating band, so that the light fields between two adjacent portions of the waveguide can be coupled to form a waveguide mode.

[0100] Further, optionally, the included angle between the direction of the gap of the light guide and the first dimension is less than 90 degrees. For example, the included angle between the direction of the gap of the light guide and the first dimension is 0 degrees (see FIG. 5). In another example, the included angle between the direction of the gap of the light guide and the first dimension is 45 degrees. In yet another example, the included angle between the direction of the gap of the light guide and the first dimension is any angle between (0, 45°). In yet another example, the included angle between the direction of the gap of the light guide and the first dimension is any angle between (45, 90°). It should be understood that when the included angle between the direction of the gap of the light guide and the first dimension is any angle between (0, 90°), the direction of the gap of the light guide is tilted.

[0101] In the second method, the diffractive optical element is applicable to scenarios where the requirements for narrow-band filtering are not high, such as imaging systems where the light source is a narrow-band light source. In addition, the requirements for process accuracy are low, so the diffractive optical element can be easily fabricated.

[0102] Method 3: The optical waveguide includes periodically distributed small holes, which are hollow or filled with a material whose refractive index is different from that of the material of the optical waveguide.

[0103] In a possible implementation, in the second dimension, the light guide has periodically distributed small holes. Figure 6 is a schematic diagram of a structure of a light guide including periodically distributed small holes according to the present application. The small holes can be hollow, i.e. the light guide is hollowed out at the corresponding positions. Alternatively, the small holes can be filled with a material whose refractive index is different from that of the material of the light guide, for example, silicon oxide.

[0104] It should be noted that the shape of the pores may be any shape that can be achieved using micro-nano fabrication processes, including but not limited to circular, square, triangular, etc.

[0105] In scheme 3, diffractive optical elements are applicable to scenarios that require narrow filtering bands, for example, broadband light emitted from a light source, but narrow bands require high resolution optical imaging systems.

[0106] Method 4: The periodically distributed diffractive structure (or called micro-nano structure) is in contact with the optical waveguide, or the distance between the periodically distributed diffractive structure and the optical waveguide does not exceed a predetermined distance, respectively.

[0107] In a possible implementation, in the second dimension, the periodically distributed diffractive structure is in contact with the light guide, or the distance between the periodically distributed diffractive structure and the light guide does not exceed a preset distance, respectively. In other words, the periodically distributed diffractive structure is disposed at a position adjacent to the light guide or on the light guide. The periodically distributed diffractive structure is disposed on the light guide at a position where the distance from the light guide is equal to a preset distance, or where the distance from the light guide is less than a preset distance, and the diffractive structure can also be understood to be periodically distributed in the second dimension. The diffractive structure can be periodically disposed on the top, one sidewall, or two sidewalls of the light guide. Alternatively, the diffractive structure may be periodically disposed near the top, one sidewall, or two sidewalls of the light guide, and the distance between the diffractive structure and one sidewall of the light guide does not exceed a preset distance.

[0108] Furthermore, optionally, the preset distance between the diffractive structure and the light guide must satisfy that the light field formed in the light guide spatially overlaps with the diffractive structure. In other words, the diffractive structure may interact with the light field in the light guide in a guided mode. For example, the preset distance between the diffractive structure and the light guide is equal to or less than the central wavelength of the operating band (e.g., 525 nm). Furthermore, the preset distance between the diffractive structure and the light guide may be less than a quarter of the central wavelength of the operating band. It should be understood that when light propagates within a preset distance range outside the light guide, the light may be called an evanescent wave.

[0109] In possible implementations, the shape of the diffractive structure can be circular, square, rectangular, triangular, etc. Any shape that can be realized using semiconductor micro-nano processes can be used, which is not limited in this application.

[0110] In possible implementations, the material of the diffractive structure can be, for example, silicon nitride, titanium oxide, silicon, silicon oxide, a polymer, or a metal.

[0111] In a possible implementation, the maximum size of the diffractive structure is equal to or less than the width of the light guide. For example, the diffractive structure is circular and the diameter of the diffractive structure is equal to or less than the width of the light guide. In another example, the diffractive structure is square and the side length of the diffractive structure is equal to or less than the width of the light guide. In yet another example, the diffractive structure is rectangular and the short side of the diffractive structure is equal to or less than the width of the light guide.

[0112] 7a is a schematic diagram of a periodically distributed diffractive structure adjacent to a light guide according to the present application. In this example, the diffractive structure is located adjacent to the sidewall of the light guide, and the diffractive structure is square in shape.

[0113] 7b is a schematic diagram of the structure of contact between the periodically distributed diffractive structure and the light guide according to the present application. In this example, the diffractive structure is located on the side wall of the light guide. In other words, the diffractive structure is in contact with the light guide, and the diffractive structure is in the shape of a square.

[0114] 7c is a schematic diagram of another structure in which a periodically distributed diffractive structure is adjacent to a light guide according to the present application. In this example, the diffractive structure is located near two side walls of the light guide, and the diffractive structure is a square shape. It should be noted that the diffractive structure located near two sides of the light guide can be symmetrical with respect to the center line of the light guide.

[0115] Fig. 7d is a schematic diagram of another structure of contact between a periodically distributed diffractive structure and a light guide according to the present application. In this example, the diffractive structure contacts two side walls of the light guide, and the diffractive structure is in the shape of a square. It should be noted that the diffractive structure contacting the two sides of the light guide can be symmetrical with respect to the center line of the light guide.

[0116] It should be noted that the diffraction structures near the two sides of the light guide may be asymmetric with respect to the center line of the light guide. For example, the diffraction structures near the two side walls have the same waveguide period but are at different distances from the light guide. For example, the diffraction structure on the left side is closer to the light guide than the diffraction structure on the right side. Alternatively, the diffraction structure on the right side is closer to the light guide than the diffraction structure on the left side. Alternatively, the diffraction structures near the two side walls may have the same waveguide period but there is a displacement in the second dimension. In other words, the diffraction structures near the two side walls are not strictly aligned (see FIG. 7e).

[0117] In method 4, the diffractive optical element is applicable to scenarios where the narrow band (or called filtering band) that requires response is narrow. For example, the diffractive optical element is applicable to broadband light emitted from a light source, but the narrow band requires a high-resolution optical imaging system. Alternatively, the diffractive optical element is applicable to scenarios where the requirements for the narrowband filtering function are not high, for example, imaging systems where the light source is a narrowband light source. In addition, the diffractive optical element can be easily fabricated, since the requirements imposed on the process accuracy are low.

[0118] Method 5: The refractive index of the optical waveguide changes periodically.

[0119] In a possible implementation, the refractive index of the optical waveguide varies periodically in the second dimension, see Fig. 8. The optical waveguide is composed of at least two materials with different refractive indices, the refractive indices n1, n2 of the two materials being staggered and varying periodically.

[0120] Furthermore, optionally, the refractive index of the optical waveguide may be periodically varied by doping the waveguide or may be formed by inserting a material within the optical waveguide that has a refractive index different from that of the optical waveguide.

[0121] In scheme 5, the diffractive optical element is applicable to scenarios where the narrow band (or called filtering band) that requires response is narrow. For example, the diffractive optical element is applicable to broadband light emitted from a light source, but the narrow band requires a high-resolution optical imaging system. Alternatively, the diffractive optical element is applicable to scenarios where the requirements for the narrow-band filtering function are not high, for example, imaging systems where the light source is a narrow-band light source. In addition, the refractive index of the optical waveguide can be changed periodically by doping, and the requirements imposed on the process accuracy are low, so that the diffractive optical element can be easily fabricated.

[0122] In a possible implementation, at least one of the M optical waveguides that are periodically varied in the second dimension has at least two different waveguide periods. To facilitate the description of the solution, the following describes an example in which the optical waveguide is periodically varied in the second dimension and the optical waveguide has two different waveguide periods.

[0123] Please note that in the above method 1 to method 5, an example in which one optical waveguide has one waveguide period is used for explanation. The periodic change of the optical waveguide is located at the top or sidewall, and can be described in the following two cases:

[0124] Case 1: The periodic variation of the optical waveguide is located at the top of the optical waveguide.

[0125] In Case 1, the apex of at least one of the M optical waveguides that are periodically varied in the second dimension has at least two different waveguide periods.

[0126] In the aforementioned periodic variation method 1, FIG. 9a is a schematic diagram of a cross section of an optical waveguide having at least two different waveguide periods in the second dimension according to the present application. The recess of the optical waveguide is located at the top of the optical waveguide. The optical waveguide has two different waveguide periods in the second dimension, T y11 and T y12 This allows for narrowband response to two wavelengths on the same optical waveguide. It should be understood that FIG. 9a is a side view of the optical waveguide. For example, the bottom of the optical waveguide is placed on a substrate.

[0127] When the periodic variation manner of the optical waveguide is the above-mentioned manner 2, manner 3, manner 4 or manner 5, at least one of the M optical waveguides that are periodically varied in the second dimension can be designed to have at least two different periods. In other words, the periodic variation manner in the second dimension can be replaced. Details are not described again in this specification. For details, please refer to the scheme in Figure 9a.

[0128] Case 2: The periodic variation of the optical waveguide is located on the sidewall of the optical waveguide.

[0129] In case 2, the following four cases can be detailed:

[0130] Case 2.1: The optical waveguide has two different waveguide periods on each side.

[0131] In the aforementioned periodic variation scheme 1, the optical waveguide has two different waveguide periods on each side. Figure 9b is a schematic diagram of another structure of an optical waveguide having two different waveguide periods in the second dimension according to the present application. The recesses of the optical waveguide are located on the two side walls of the optical waveguide and are symmetrical with respect to the center line of the optical waveguide. Each side wall of the optical waveguide has two different waveguide periods in the second dimension, T y11 and T y12 This makes it possible to realize a function for selecting two wavelengths on the same optical waveguide.

[0132] It can also be seen that Fig. 9b is obtained by superposing optical waveguide 1 on optical waveguide 2 in Fig. 9f. Optical waveguide 1 has a period (T y11 ), that is, T y11 In addition, the optical waveguide 2 has a period (T y12 ), that is, T on the width of the optical waveguide 2. y12 After the optical waveguide 1 and the optical waveguide 2 are superimposed, the optical waveguide shown in FIG. 9b is formed. In other words, the concave points are formed at intervals of T y11 The concave points appear at intervals of T y12 appears at intervals of

[0133] When the change manner of the optical waveguide is the above-mentioned manner 2, manner 3, manner 4, and manner 5, at least one of the M optical waveguides that are periodically changed in the second dimension can be designed to have at least two different waveguide periods. In other words, the periodic change manner in the second dimension can be replaced. Details are not described again in this specification. For details, please refer to FIG. 9b.

[0134] Case 2.2: The optical waveguide has one waveguide period on each of the two sides, and the two waveguide periods on the two sides are different.

[0135] In the aforementioned periodic variation scheme 5, the optical waveguide has one waveguide period on each of the two sides, and the two waveguide periods on the two sides are different. It can also be seen that the diffractive structure is asymmetric with respect to the center line of the optical waveguide. Figure 9c is a schematic diagram of yet another structure of an optical waveguide having at least two different waveguide periods in the second dimension according to the present application. The diffractive structure is located on two side walls of the optical waveguide. One side wall corresponds to one waveguide period. The left side wall has a waveguide period of T y11 and the period of the waveguide on the right side wall is T y12 This makes it possible to realize narrowband response functions for two wavelengths on the same optical functional waveguide.

[0136] The waveguide periods of the two side walls of the optical waveguide are such that the left side waveguide period is larger than the right side waveguide period (i.e., T y11 >T y12 ) or the period of the right-hand waveguide is greater than the period of the left-hand waveguide (T y12 >T y11 ) may be satisfied.

[0137] When the periodic variation manner of the optical waveguide is the above-mentioned manner 1, manner 2, manner 3, and manner 4, at least one of the M optical waveguides that are periodically varied in the second dimension can be designed to have at least two different waveguide periods similar to those in case 2.2. In other words, the periodic variation manner in the second dimension can be replaced. Details are not described again in this specification. For details, please refer to FIG. 9c.

[0138] Case 2.3: The optical waveguide has two waveguide periods on one side, and the two waveguide periods are different. The optical waveguide has one waveguide period on the other side, and the waveguide period may be the same as or different from either one of the two waveguide periods on the other side.

[0139] In the aforementioned periodic variation method 1, the optical waveguide has two waveguide periods on one side, and the two waveguide periods are different. The optical waveguide has one waveguide period on the other side. Figure 9d is a schematic diagram of yet another structure of an optical waveguide having at least two different waveguide periods in the second dimension according to the present application. The recesses of the optical waveguide are located on two side walls of the optical waveguide, and the two side walls are asymmetric with respect to the center line of the optical waveguide. The recesses on one side of the optical waveguide have two different waveguide periods in the second dimension, respectively T y11 and T y12 The recess on the other side has a waveguide period T y13 T y13 is T y11 and T y12 or T y11 and T y12This allows the selection of at least two wavelengths on the same optical waveguide. y13 but, y11 and T y12 If the two wavelengths are the same, then the two wavelengths can be filtered. y13 but y11 and T y12 If different from , then three wavelengths can be filtered, i.e., three wavelengths are selected.

[0140] Additionally, optionally, T y11 :T y12 =2:3.

[0141] When the periodic variation scheme of the optical waveguide is the above-mentioned scheme 2, scheme 3, scheme 4, and scheme 5, at least one of the M optical waveguides that are periodically varied in the second dimension can be designed to have at least two different waveguide periods similar to those in case 2.3. In other words, the periodic variation scheme in the second dimension can be replaced. For details, please refer to Fig. 9d.

[0142] Case 2.4: An optical waveguide has two waveguide periods on one side, where the two waveguide periods are different, and also has two waveguide periods on the other side, where at least one of the two waveguide periods is different from either of the two waveguide periods on the opposite side.

[0143] In the above periodic variation method 1, the optical waveguide has two waveguide periods on one side of the optical waveguide, and the two waveguide periods are different. The optical waveguide also has two waveguide periods on the other side, and at least one of the two waveguide periods is different from either of the two waveguide periods on the opposite side. Figure 9e is a schematic diagram of yet another structure of an optical waveguide having at least two different waveguide periods in a second dimension according to the present application. The recesses of the optical waveguide are located on two side walls of the optical waveguide, and the two side surfaces are asymmetric with respect to the center line of the optical waveguide. The recesses on one side of the optical waveguide have two different waveguide periods in the second dimension, respectively T y11 and Ty12 The recess on the other side also has two waveguide periods, T y13 and T y14 T y13 and T y14 At least one of the y11 and T y12 This makes it possible to realize the function of selecting at least three wavelengths on the same optical waveguide.

[0144] Additionally, optionally, T y11 :T y12 =2:3 and T y13 :T y14 =2:3.

[0145] When the periodic variation manner of the optical waveguide is the above-mentioned manner 2, manner 3, manner 4, and manner 5, at least one of the M optical waveguides that are periodically varied in the second dimension can be designed to have at least two different waveguide periods similar to those in case 2.4. In other words, the periodic variation manner in the second dimension can be replaced. Details are not described again in this specification. For details, please refer to Figure 9e.

[0146] Note that Figures 9b to 9e are top views, the bottom of the optical waveguide rests on the substrate, and the dashed boxes in Figures 9b to 9e indicate the substrate.

[0147] 2. Structure in the first dimension

[0148] In a possible implementation, the width of each optical waveguide in the grating element in the first dimension is less than half the grating period, so that the grating element includes at least two optical waveguides. For example, the grating period ranges from 100 nm to 2 μm.

[0149] In the following, an example is described in which the grating element includes three optical waveguides, two of which are periodically varied in the second dimension and have different structures.

[0150] FIG. 10a is a top view of a diffractive optical element according to the present application. The viewing direction is perpendicular to the surface of the diffractive optical element (i.e., along the z-axis in FIG. 10a). The diffractive optical element may include grating elements that are periodically distributed in a first dimension (i.e., along the x-axis in FIG. 10a). Each grating element includes three (i.e., N=3) optical waveguides, which are parallel to each other. Two (i.e., M=2) optical waveguides are periodically varied in a second dimension (i.e., along the y-axis in FIG. 10a) (in the periodic variation scheme, which is scheme 1 above), and the two optical waveguides have different waveguide periods, T y1 and T y2 Each of the two optical waveguides that are periodically varied in the second dimension is symmetrical about a centerline of the optical waveguide.

[0151] Figure 10b shows an example of a side view of the diffractive optical element at the cutting position shown in Figure 10a, the observation direction of the side view being parallel to the surface of the diffractive optical element.

[0152] Fig. 10c is a schematic diagram of another structure of a diffractive optical element according to the present application. The diffractive optical element may include grating elements that are periodically distributed in a first dimension (the direction of the x-axis in Fig. 10c). The grating elements include three (i.e., N=3) optical waveguides, where the three optical waveguides are parallel to each other. Two (i.e., M=2) optical waveguides are periodically varied in a second dimension (the direction of the y-axis in Fig. 10c) (in a periodic variation scheme, which is scheme 5 above), where the two optical waveguides have different waveguide periods.

[0153] Fig. 10d is a schematic diagram of yet another structure of a diffractive optical element according to the present application. The diffractive optical element may include grating elements that are periodically distributed in a first dimension (the direction of the x-axis in Fig. 10d). The grating elements include three (i.e., N=3) optical waveguides, and the three optical waveguides are parallel to each other. Two (i.e., M=2) optical waveguides are periodically changed in a second dimension (the direction of the y-axis in Fig. 10c). The periodic change method of one optical waveguide is the above-mentioned method 1, and the optical waveguide has one waveguide period. In other words, the two side walls of the optical waveguide have the same waveguide period. The periodic change method of the other optical waveguide is the above-mentioned method 1, and the waveguide periods on the two sides of the optical waveguide are based on the above-mentioned case 2.1.

[0154] FIG. 10e is a schematic diagram of yet another structure of a diffractive optical element according to the present application. The diffractive optical element may include grating elements that are periodically distributed in a first dimension (the direction of the x-axis in FIG. 10e). The grating elements include three (i.e., N=3) optical waveguides, which are parallel to each other. Two (i.e., M=2) optical waveguides are periodically changed in a second dimension (the direction of the y-axis in FIG. 10e). The periodic change method of one optical waveguide is the above-mentioned method 5, and the optical waveguide has one waveguide period. The periodic change method of the other optical waveguide is the above-mentioned method 1, and this optical waveguide also has one waveguide period, and the waveguide periods of the two optical waveguides are different.

[0155] It should be noted that in the above embodiments, unless otherwise stated or there is no logical contradiction, the terms and / or descriptions in different embodiments are consistent and may be mutually referenced, and the technical features in different embodiments may be combined based on their internal logical relationships to form a new embodiment. This specification does not list examples one by one.

[0156] Based on the above, the diffraction angle, response band and diffraction efficiency of the diffractive optical element can be adjusted. Detailed explanations are provided for each case below. In possible implementations, the structure parameters and material parameters of the diffractive optical element can be set based on the diffraction angle and wavelength requirements of light so that the diffractive optical element achieves a specific function.

[0157] Case 1: Adjust the diffraction angle.

[0158] In a possible implementation, the grating period of the grating elements and / or the tilt angle of the grating elements can be designed to tune the diffraction angle responded to by the diffractive optical element.

[0159] Referring to the above formula 1, the grating period (Tx in Fig. 10a to Fig. 10e) and the tilt angle can be designed based on the incident angle and wavelength of the incident light to obtain the required diffraction angle at a specific diffraction order. For the specific principle, please refer to the above formula 1. The details will not be described again in this specification.

[0160] For example, for coplanar incident light, see Equation 1 above. The wavelength of the incident light is 525 nm (visible light), the incident angle is 60°, the grating period is distributed between 0.3 μm and 1.5 μm, and the diffraction angle distribution range of the first-order diffracted light is -30° to 30°.

[0161] In case 1, an adjustment can be made for reflections at unusual angles of the diffractive optical element.

[0162] Case 2: Adjust the response band.

[0163] In a possible implementation, parameters within the grating components can be engineered, for example, the waveguide period of at least one of the M optical waveguides that are periodically varied in the second dimension can be engineered to control the resonant wavelength of the guided mode resonance, thereby achieving an optical response of the diffractive optical element to a specific band, i.e., controlling the band in which the narrowband response is located.

[0164] Referring to Figures 10a, 10c, and 10e, T y1 and / or T y2 can be designed to control the resonant wavelength of the guided mode resonance and tune the bandwidth of the narrowband response of the diffractive optical element. y11 , T y12 and / or T y13 can be designed to control the resonant wavelength of the guided mode resonance and tune the bandwidth of the narrowband response of the diffractive optical element. The resonant wavelength is determined by the waveguide period T y1 and / or T y2 It should be understood that this is related to.

[0165] Case 3: Adjust the diffraction efficiency.

[0166] In a possible implementation, the parameters in the grating element, such as the width, thickness, and position of each of the N optical waveguides can be designed (the distance between the optical waveguides can be designed), and / or the periodic variation scheme of at least one of the M optical waveguides that varies periodically in the second dimension can be designed, so that different optical waveguides cause different phase delays of the incident light due to differences in size or resonant wavelength, forming a wavefront distribution of the reflected light at a certain angle. Thus, more diffracted energy is concentrated in a certain diffraction order (e.g., the first order diffracted light in Figures 11b and 11c simulated in the following figures), enhancing the diffraction efficiency at a certain diffraction angle.

[0167] Based on the above, the following describes in detail the diffractive optical element provided in the present application, which can tailor narrowband response and reflection at extraordinary angles, with reference to simulation results.

[0168] This simulation verification is performed using an example where the wavelength of the incident light is 525 nm, and the direction of the normal of the incident light forms an angle of 60 degrees with the grating surface (i.e., the incident angle is 60°). According to the diffraction grating formula (see Equation 1 above), for the incident light having a wavelength of 525 nm, the grating period Tx can be determined to be 606 nm, and the angles corresponding to the first three diffraction orders of the diffracted light are 60 degrees (0th order), 0 degrees (1st order), and -60 degrees (2nd order), respectively.

[0169] FIG. 11a is a schematic diagram of the structure of the diffractive optical element on which the simulation is based. In this simulation, the material of the optical waveguide is silicon nitride, the material of the substrate is silicon oxide, and air is above the grating elements. The grating period Tx is set to 606 nm, and the thickness of the optical waveguide is set to 200 nm. Each grating element includes two optical waveguides. The two optical waveguides vary periodically in the second dimension. The waveguide periods of the two optical waveguides in the second dimension are equal and are 356 nm. However, the two optical waveguides have different shapes in the second dimension. In other words, the different structures of the two optical waveguides are reflected in that the two optical waveguides that vary periodically in the second dimension have different specific shapes, including different recess lengths. Based on the diffractive optical element shown in FIG. 11a, FIG. 11b shows a side view of an example of a diffractive optical element.

[0170] Based on the structure of the diffractive optical element shown in FIG. 11a, FIG. 11c is a schematic diagram of the simulated diffraction efficiency distribution of the zeroth, first and second order diffracted light at different wavelengths according to the present application. In this simulation, rigorous coupled wave analysis (RCWA) is used to calculate the diffraction efficiency distribution of the zeroth, first and second order diffracted light at different wavelengths. As can be seen from the result of FIG. 11c, the first order diffracted light has a significantly improved efficiency around the wavelength of 525 nm, and has a lower efficiency and narrowband response in another band. In addition, the first order diffracted light has a higher diffraction efficiency around the wavelength of 525 nm compared with the zeroth and second order diffracted lights. This indicates that in this case, most of the reflection energy of the light incident at an angle of 60 degrees is reflected at an angle of 0 degrees and reflected at an abnormal angle. Therefore, the simulation result can show that the diffractive optical element can realize the function of reflection at an abnormal angle in a narrow band.

[0171] Figure 11d is a schematic diagram of yet another structure of the diffractive optical element on which the simulation is based. In this simulation, the material of the optical waveguide is silicon nitride, the material of the substrate is silicon oxide, and there is air above the grating elements. The grating period Tx is 606 nm, and the thickness of the optical waveguide is set to 200 nm. Each grating element contains two optical waveguides. The two optical waveguides are periodically varied in the second dimension, and the structures of the two optical waveguides are completely identical.

[0172] Based on the structure of the diffractive optical element shown in FIG. 11d, FIG. 11e is another schematic diagram of the simulated diffraction efficiency distribution of the zeroth, first and second order diffracted light at different wavelengths according to the present application. In this simulation, RCWA is also used to calculate the diffraction efficiency distribution of the zeroth, first and second order diffracted light at different wavelengths. As can be seen from the result in FIG. 11e, the zeroth order diffracted light has a significantly improved efficiency around the wavelength of 475 nm, and has a lower efficiency and narrowband response in other bands. In addition, the zeroth order diffracted light has a higher diffraction efficiency around the wavelength of 475 nm compared with the first and second order diffracted lights. This indicates that in this case, most of the reflected energy of the light incident at an angle of 60 degrees is reflected at an angle of 60 degrees, and is weakly reflected at abnormal angles.

[0173] Figure 11f is a schematic diagram of yet another structure of the diffractive optical element on which the simulation is based. In this simulation, the material of the optical waveguide is silicon nitride, the material of the substrate is silicon oxide, and there is air above the grating elements. The grating period Tx is set to 606 nm and the thickness of the optical waveguide is set to 200 nm. Each grating element contains two optical waveguides, one of which is periodically varied in the second dimension.

[0174] Based on the structure of the diffractive optical element shown in FIG. 11f, FIG. 11g is yet another schematic diagram of the simulated diffraction efficiency distribution of the zeroth, first and second order diffracted light at different wavelengths according to the present application. In this simulation, RCWA is also used to calculate the diffraction efficiency distribution of the zeroth, first and second order diffracted light at different wavelengths. As can be seen from the result in FIG. 11g, the zeroth order diffracted light has a significantly improved efficiency around the wavelength of 485 nm, and has a lower efficiency and narrowband response in other bands. In addition, the zeroth order diffracted light has a higher diffraction efficiency around the wavelength of 525 nm compared with the first and second order diffracted lights. This indicates that in this case, most of the reflected energy of the light incident at an angle of 60 degrees is reflected at an angle of 60 degrees, and basically cannot be reflected at an abnormal angle.

[0175] As can be seen from Figure 11c, Figure 11e, and Figure 11g, when only one of the two optical waveguides included in the grating component is periodically changed in the second dimension, the diffraction efficiency of the zeroth-order diffracted light is greatly improved. This shows that most of the energy of the light incident at an angle of 60 degrees is reflected at an angle of 60 degrees. In this case, it is difficult to realize the function of reflection at abnormal angles. When two of the two optical waveguides included in the grating component are periodically changed in the second dimension, and the structures of the two optical waveguides are completely the same, the diffraction efficiency of the zeroth-order diffracted light and the diffraction efficiency of the second-order diffracted light are both high. This shows that in this case, most of the reflection energy of the light incident at an angle of 60 degrees is reflected at an angle of 60 degrees, and some reflection energy is reflected at an angle of -60 degrees, which can be reflected at certain abnormal angles, but it is difficult to realize a narrow-band response. In the two optical waveguides included in the grating element, when the two optical waveguides are periodically changed in the second dimension and the two optical waveguides periodically changed in the second dimension have different structures, the first-order diffracted light has a significantly improved diffraction efficiency and a lower efficiency and narrow-band response in another band. In addition, the first-order diffracted light has a higher diffraction efficiency around the wavelength of 525 nm than the zeroth-order diffracted light and the second-order diffracted light. This indicates that in this case, most of the reflected energy of the light incident at an angle of 60 degrees is reflected at an angle of 0 degrees and reflected at an abnormal angle. In other words, at least two of the M optical waveguides periodically changed in the second dimension have different structures, so that both the function of reflection at an abnormal angle and narrow-band response can be realized.

[0176] In the present application, the diffractive optical element may further include a substrate, an example of which is described below.

[0177] In possible implementations, the grating elements may be disposed on a substrate, the materials of which include, but are not limited to, silicon oxide, silicon nitride, titanium oxide, silicon, polymers, metals, and the like.

[0178] Furthermore, optionally, the substrate may be single layer or multi-layered. For example, on the side of the substrate closer to the grating element, there is a layer of planar optical waveguide structure or multiple layers of materials with variable refractive index. If the substrate is multi-layered, a Bragg reflector may be formed, which reflects a specific band of incident light.

[0179] The parameters of the grating components set based on different regions of the substrate can be classified into the following two cases: The parameters of the grating components include grating period, tilt angle, structural parameters within the grating components, etc.

[0180] Case A: The parameters of the grating components in different regions of the substrate are the same.

[0181] 12 is a schematic diagram of the structure of a grating element having the same parameters in different regions of a substrate according to the present application. The parameters of the grating elements in different regions of a substrate are designed in a unified manner. Therefore, the optical response (e.g., selected narrow band or extraordinary angle) presented by the entire grating element is consistent.

[0182] Case B: The parameters of the grating components in different regions of the substrate are different.

[0183] In a possible implementation, the parameters of the grating elements in the diffractive optical element fixed to different regions of the substrate are different. Fig. 13a is a schematic diagram of the structure of the grating elements with different parameters in different regions of the substrate according to the present application. This can achieve focusing to a narrow band of response. Furthermore, this can be applied to AR glasses, AR helmets, VR glasses, VR helmets, etc.

[0184] By setting the grating elements with different parameters in different regions of the substrate, the grating elements in different regions of the substrate respond to the incident light emitted in the same direction at different diffraction angles, or perform narrow-band reflection at unusual angles in different bands, thereby achieving focusing, collimation, imaging, etc. for a specific narrow-band light. For example, the incident light emitted in the same direction (e.g., incident light in a specific band) can be reflected toward a spatial position to form a focused light. See FIG. 13b. It should be understood that only the light in a specific band is collimated to a specific spatial position, and there is no response to the incident light of another wavelength. It can also be understood that the diffractive optical element has a filtering function. The grating elements in different regions of the substrate can respond to light in different bands. In FIG. 13b, different line types indicate different bands.

[0185] It should be noted that the diffractive optical element can diffract incident light with any wavefront spatial distribution in a certain band to form reflected light with any wavefront spatial distribution. This is not limited to focusing or collimation in the above examples. In other words, the incident light may or may not be emitted parallel. The diffracted light may be focused to a point or reflected to different positions.

[0186] Based on case B, the diffractive optical element is applicable to the imaging optical system shown in Fig. 2 and is used as a light combiner of the imaging optical system. The diffractive optical element can reflect the incident light of a specific band sent from the optical projection system at different diffraction angles in different regions and emit the light of a specific band to the human eye for imaging. In addition, the ambient light of another band can also be transmitted to the human eye for imaging through the diffractive optical element.

[0187] The optical combiner based on the diffractive optical element can realize high transmittance of ambient light and high reflectance of the projection, which helps to improve the visual effect of the fusion of real-world images and virtual-world images in the augmented reality display system. It should be noted that the substrate of the diffractive optical element applied in the AR display system is transparent.

[0188] It should be noted that diffractive optical elements can also be used in virtual reality (VR) optical systems. In this case, the substrate is opaque or has a reflective function. For example, metals, Bragg reflectors, etc. can be used in the substrate to increase the reflective efficiency of the diffractive optical element.

[0189] For example, a diffractive optical element may be an optical element that has a response in a particular band (eg, a filter or optical splitter) or may be an imaging device (eg, an optical combiner).

[0190] Based on the diffractive optical element in any one of the above-mentioned embodiments, FIG. 14 shows a diffractive optical element used for spectrum detection according to the present application. The response band or diffraction angle of the diffractive optical element is affected by the detected substance. The working principle of the diffractive optical element used for spectrum detection is as follows: The presence or absence, composition, concentration or refractive index of the detected substance affects the effective refractive index of the optical waveguide in the grating component, and the resonant wavelength of the guided mode resonance changes. Alternatively, the phase delay of the incident light caused by the optical waveguide in the grating component changes, and the diffraction angle changes.

[0191] Therefore, by detecting changes in the reflection angle of the reflected light or changes in the spectrum of the reflected light, information such as the presence or absence, composition, concentration, and refractive index of the target substance can be determined.

[0192] Relationship between the presence or absence of a detected substance and the range of the response band and the diffraction angle , coveredIt should be understood that calibration may be performed prior to spectral detection so that the relationship between the composition of the detection substance and the range of the response band and diffraction angle, the relationship between the concentration of the detected substance and the range of the response band and diffraction angle, the relationship between the refractive index of the detected substance and the range of the response band and diffraction angle, etc. can be determined separately.

[0193] Based on the above, the diffractive optical element is applicable to a terminal device. The terminal device may include K layers of diffractive optical elements and K layers of substrates in any one of the above-mentioned embodiments. The K layers of the diffractive optical elements have a one-to-one correspondence with the K layers of the substrates. Each of the K layers of the diffractive optical elements is fixed on a corresponding substrate, and K is a positive integer.

[0194] In possible implementations, grating elements in different ones of the K layers may be responsive to the same narrow band or to different narrow bands.

[0195] FIG. 15 is a schematic diagram of the structure of a terminal device according to the present application. For example, the terminal device includes three layers of diffractive optical elements and three layers of a substrate. In this example, the grating elements in each of the three layers respond to different narrow bands, and different line types indicate different response bands. It should be understood that the grating elements in the same layer may respond to the same band (as shown in FIG. 15) or to different bands (see FIG. 13b).

[0196] For example, one of the three layers may respond to light in the red band, another layer may respond to light in the green band, and the remaining layer may respond to light in the blue band. In this way, a color display may be realized. For example, when the terminal device is an AR device or a VR device, one of the three layers may respond to light in the red band in a colored light beam from an optical projector and reflect the light in the red band in a specific direction in space (e.g., toward the area where the human eye is located). Another layer may respond to light in the green band in a colored light beam from an optical projector and also reflect the light in the green band in a specific direction in space (e.g., toward the area where the human eye is located). The remaining layer may respond to light in the blue band in a colored light beam from an optical projector and also reflect the light in the blue band in a specific direction in space (e.g., toward the area where the human eye is located). In this way, the image projected to the human eye by the AR device or VR device becomes a color image. In addition, by applying a diffractive optical element to the AR device or VR device, the AR device or VR device can be made smaller.

[0197] It should be noted that the incident light may be collimated or non-collimated. The exiting light may also be collimated, which indicates that the diffractive optical element may collimate multiple beams of incident light. The exiting light may also be non-collimated.

[0198] In various embodiments of the present application, unless otherwise stated or there is no logical contradiction, the terms and / or descriptions in different embodiments are consistent and may be cross-referenced, and the technical features in different embodiments may be combined based on their internal logical relationships to form a new embodiment.

[0199] In this application, "perpendicularity" may not mean absolute perpendicularity and some engineering error may be allowed. For example, as mentioned above, "the first dimension is perpendicular to the second dimension." "At least one" means one or more, and "multiple" means more than one. "And / or" describes an association relationship between related objects and indicates that three relationships may exist. For example, A and / or B may represent the cases where only A is present, where both A and B are present, or where only B is present, and A and B may be singular or plural. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of singular items or multiple items. For example, at least one of a, b, or c may refer to a, b, c, a and b, a and c, b and c, or a, b, and c, where a, b, and c may be singular or plural. In the textual description of this application, the character " / " typically indicates an "or" relationship between related objects. In formulas of this application, the character " / " indicates a "divide" relationship between related objects. In addition, the word "example" in this application is used to represent giving an example, illustration, or explanation. Any embodiment or design manner described in this application as an "example" should not be described as being preferred or having more advantages over another embodiment or design manner. Alternatively, it can be understood that the term "example" is used to present a concept in a particular manner and does not constitute a limitation on this application. The symbol "(a,b)" represents an open interval with a range greater than a and less than b, "[a,b]" represents a closed interval with a range greater than a and less than b, "(a,b]" represents a half-open half-closed interval with a range greater than a and less than b, and "(a,b)" represents a half-open half-closed interval with a range greater than a and less than b. [ a,b ) " is a End b less than A semi-automatic closed half Open Represents an interval. For example, (0,90°) represents greater than 0 degrees and less than 90 degrees.

[0200] It can be understood that various numbers in the embodiments of the present application are merely used for distinction to facilitate description, and are not used to limit the scope of the embodiments of the present application. The sequence numbers of the above processes do not mean the execution sequence, and the execution sequence of the processes should be determined based on the functions and internal logic of the processes. The terms "first", "second", and other similar expressions are intended to distinguish similar objects, but do not necessarily indicate a particular order or sequence. In addition, the terms "include", "have", and any variations thereof are intended to cover non-exclusive inclusion, for example, to include a series of steps or units. A method, system, product, or device is not necessarily limited to the literally recited steps or units, and may include other steps or units that are not literally recited or that are inherent to such a process, method, product, or device.

[0201] Although the present application has been described with reference to specific features and embodiments thereof, the present application Example It is apparent that various modifications and combinations may be made thereto without departing from the scope thereof. Correspondingly, the specification and the accompanying drawings are merely examples for illustrating the solutions defined by the appended claims, and any or all of the modifications, variations, combinations or equivalents are to be considered as encompassing the scope of this application.

[0202] It is obvious that those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of the present invention. This application is intended to cover these modifications and variations, provided that they fall within the scope of protection defined by the following claims and their equivalent technologies.

Claims

1. A diffractive optical element, Periodically distributed lattice elements in the first dimension the grating elements having a grating period of the diffractive optical element, each grating element including N optical waveguides, M optical waveguides of the N optical waveguides each being periodically varied in a second dimension, at least two of the M optical waveguides that are periodically varied in the second dimension having different structures; the included angle between the second dimension and the first dimension is greater than 0 degrees and less than 180 degrees, N is an integer greater than 1, and M is an integer greater than 1 and less than or equal to N; Diffractive optical element.

2. the at least two of the M optical waveguides that are periodically varied in the second dimension have different periodic variations; the at least two of the M optical waveguides that are periodically varied in the second dimension have different waveguide periods; or the at least two of the M optical waveguides that are periodically varied in the second dimension have different shapes.

2. The diffractive optical element according to claim 1.

3. 3. A diffractive optical element according to claim 1 or 2, wherein at least one of the M optical waveguides that are periodically varied in the second dimension has at least two different waveguide periods.

4. The optical waveguide has at least two different waveguide periods. the apex of the optical waveguide having at least two different waveguide periods; Any one of the two side walls of the optical waveguide has at least two different waveguide periods; or each sidewall of the optical waveguide has at least one waveguide period, and two sidewalls have different waveguide periods; The diffractive optical element according to claim 2 ,

5. The periodic change method of the optical waveguide is as follows: the optical waveguide has periodic convex portions or periodic concave portions; the optical waveguide having periodic gaps; the optical waveguide comprises periodically distributed small holes, the small holes being hollow or filled with a material whose refractive index differs from that of the material of the optical waveguide; a periodically distributed diffractive structure is in contact with the optical waveguide; The distance between the periodically distributed diffractive structure and the optical waveguide does not exceed a predetermined distance, respectively; or the refractive index of the optical waveguide varies periodically; The diffractive optical element according to claim 2 , comprising any one of:

6. 6. The diffractive optical element according to claim 5, wherein the periodic variation manner of the optical waveguide is such that the optical waveguide has periodic convex portions or periodic concave portions, and the convex portions or the concave portions are located on a top portion or at least one side wall of the optical waveguide.

7. 6. The diffractive optical element of claim 5, wherein the periodic variation of the optical waveguide is such that the optical waveguide has periodic gaps and the length of the gaps in the second dimension is such that incident light can be coupled between two adjacent portions of the optical waveguide to form a guided mode.

8. The diffractive optical element of claim 7 , wherein a length of the gap in the second dimension is less than or equal to a central wavelength of a band of operation.

9. The diffractive optical element of claim 5 , wherein the included angle between the gap direction and the first dimension is less than 90 degrees.

10. 6. The diffractive optical element according to claim 5, wherein the periodic change manner of the optical waveguide is such that the periodically distributed diffractive structure is in contact with the optical waveguide, or the distance between the periodically distributed diffractive structure and the optical waveguide does not exceed the predetermined distance, and the diffractive structure is in contact with a top or at least one sidewall of the optical waveguide, or the diffractive structure is located at a position where the distance from one sidewall of the optical waveguide is equal to or less than the predetermined distance.

11. The diffractive optical element according to claim 10 , wherein the preset distance between the diffractive structure and the optical waveguide satisfies that a light field formed in the optical waveguide spatially overlaps with the diffractive structure.

12. The diffractive optical element according to claim 11 , wherein the preset distance between the diffractive structure and the optical waveguide is equal to or less than a central wavelength of an operating band.

13. A terminal device comprising at least one layer of a diffractive optical element according to any one of claims 1 to 12 and at least one layer of a substrate, wherein one layer of the diffractive optical element corresponds to one layer of the substrate, Each layer of the diffractive optical element is fixed to a corresponding substrate, a terminal device.

14. The terminal device according to claim 13 , wherein parameters of grating elements in the diffractive optical elements fixed to different regions of the substrate are different, the parameters of the grating elements comprising a grating period and / or a tilt angle.

15. 14. The terminal device of claim 13, wherein the terminal device includes an optical projector configured to transmit a light beam carrying image information to the diffractive optical element.

Images