Diffractive optical device and terminal device

Abstract

A diffractive optical device and a terminal device, the diffractive optical device can be applied to the field of augmented reality (AR), such as AR devices, head-up display (HUD) devices, etc.; or applied to the field of virtual reality (VR), such as VR devices; or applied to filters, light splitters, spectral detection devices, etc. The diffractive optical device comprises a grating assembly exhibiting a periodic distribution in a first dimension, the grating assembly comprising N optical waveguides, the N optical waveguides comprising M optical waveguides exhibiting a periodic variation in a second dimension, at least two of the M optical waveguides exhibiting a different structure in the second dimension; an 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 not greater than N. Through the M optical waveguides exhibiting a periodic variation in the second dimension, light of a specific waveband at a specific angle can be selected, that is, both narrowband response and abnormal angle regulation can be achieved.

Description

Technical Field

[0001] This application relates to the field of diffractive optical device technology, and in particular to a diffractive optical device and terminal equipment. Background Technology

[0002] Augmented reality (AR) technology is a technology that merges the real world with the virtual world. It can simulate sensory experiences (such as sight, hearing, and touch) that do not exist in the real world through computer generation and superimpose them onto real-world scenes, allowing users to perceive them and achieving a sensory experience that transcends reality, thus enhancing the real-world scene. AR technology has a wide range of applications and has already been successfully applied in military, industrial production, medical, and educational fields. In recent years, with the gradual popularization of 5G high-speed mobile communication technology, the application scenarios of AR technology for consumer terminals have been continuously expanded, and the prospect of large-scale application is becoming increasingly clear.

[0003] Among the various sensory experiences simulated by AR technology, vision is the most important. Therefore, achieving the combination of light containing virtual information and light containing information about the external environment is one of the core issues of AR technology. How to realize a compact, lightweight AR system that can efficiently combine virtual and real optical images is currently a hot research topic. AR systems can generally be divided into two main parts: an optical projection system and an optical overlay unit. The optical overlay unit, which needs to transmit both ambient light and reflect the projected light from the projection system to the human eye, is the core optical component responsible for fusing virtual and real images and is also one of the key optical components determining the user experience of the AR system. Currently, the optical overlay units in existing AR systems are generally semi-reflective mirrors, polarizing beam splitters, waveguides, etc. These types of optical overlay units cannot simultaneously achieve narrowband response and control of abnormal angle reflections. Therefore, AR systems struggle to meet the requirements of high transmittance of ambient light and high reflectivity of projected light within a compact size.

[0004] In summary, providing an optical device that can achieve both narrowband response and the ability to control abnormal angle reflections is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This application provides a diffractive optical device and a terminal device, which enables the diffractive optical device to achieve both narrowband response and the ability to control abnormal angle reflection.

[0006] In a first aspect, this application provides a diffractive optical device, which includes a grating assembly that exhibits a periodic distribution in a first dimension. The grating assembly includes N optical waveguides, among which M optical waveguides exhibit periodic variations in a second dimension. At least two of the M optical waveguides exhibiting periodic variations in the second dimension have different structures. The 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 not greater than N.

[0007] Based on the aforementioned diffractive optical device, specific wavelengths of light can be selected using M periodically varying optical waveguides in the second dimension, thus achieving a narrowband response. A grating structure is formed by periodically distributed grating components in the first dimension, enabling the control of anomalous angle reflections. Furthermore, the diffraction efficiency of the diffractive optical device at anomalous reflection angles can be enhanced within a specific wavelength band. Since this diffractive optical device can achieve both narrowband response and control of anomalous angle reflections, when applied to AR or VR devices, it can achieve efficient diffraction imaging of the projected light band within a compact volume, while simultaneously achieving high transmittance for ambient light in other bands.

[0008] In one possible implementation, at least two of the M optical waveguides exhibiting periodic changes in the second dimension have different structures. For example, the periodic changes of at least two of the M optical waveguides exhibiting periodic changes in the second dimension may differ in the manner in which they change; or the waveguide periods of at least two of the M optical waveguides exhibiting periodic changes in the second dimension may differ; or the shapes of at least two of the M optical waveguides exhibiting periodic changes in the second dimension may differ.

[0009] In one possible implementation, the guided mode resonates at different wavelengths in M ​​optical waveguides with periodic variations in the second dimension. This allows for the selection of M different resonant wavelengths, thus enabling narrowband responses in M ​​different bands.

[0010] In one possible implementation, M optical waveguides exhibiting periodic variations in the second dimension are used to reflect light of a specific wavelength band. This can also be understood as the M optical waveguides exhibiting periodic variations in the second dimension being narrowband wavelength reflective optical waveguides.

[0011] In one possible implementation, at least one of the M optical waveguides exhibiting periodic changes in the second dimension exhibits at least two different waveguide periods.

[0012] Further, optionally, the optical waveguide exhibits at least two different waveguide periods, including the top of the optical waveguide exhibiting at least two different waveguide periods; or, either of the two sidewalls of the optical waveguide exhibiting at least two different waveguide periods; or, each sidewall of the optical waveguide exhibiting at least one waveguide period, and the two sidewalls exhibiting different waveguide periods.

[0013] In one possible implementation, the periodic variation of the optical waveguide can be achieved in any of the following ways.

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

[0015] Based on this method, the periodic variation of the optical waveguide is that the optical waveguide presents periodic protrusions or recesses, with the protrusions or recesses located at the top of the optical waveguide or at least one sidewall.

[0016] Using this method, diffractive optics can be applied to scenarios where a narrow band (or filtered band) of response is required. For example, it can be used in high-resolution optical imaging systems where the light source emits wide-band light but a narrow band is needed.

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

[0018] Based on this second method, the periodic variation of the optical waveguide is achieved by the waveguide exhibiting periodic gaps. The length of these gaps in the second dimension is sufficient to allow incident light to couple between adjacent sections of the waveguide, forming waveguide modes. This enables guided-mode resonance, resulting in high diffraction efficiency and the selection of narrowband wavelengths.

[0019] Furthermore, optionally, the length of the gap in the second dimension is not greater than the center wavelength of the working band.

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

[0021] Using the second method described above, diffractive optical devices are suitable for applications where narrowband filtering requirements are not high, such as imaging systems using narrowband laser sources. Furthermore, they have lower requirements for manufacturing precision, thus facilitating the fabrication of diffractive optical devices.

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

[0023] Using the method described above (method 3), this diffractive optical device can be applied to scenarios requiring a relatively narrow filtering band. For example, it can be used in high-resolution optical imaging systems where the light source emits wide-band light but a narrow-band band is required.

[0024] Method 4: The periodically distributed diffraction structure is in contact with the optical waveguide, or the distance between the periodically distributed diffraction structure and the optical waveguide does not exceed a preset distance.

[0025] Based on this method four, the periodic changes of the optical waveguide are as follows: the periodically distributed diffraction structure is in contact with the optical waveguide or the distance between the diffraction structure and the optical waveguide does not exceed a preset distance, and the diffraction structure is in contact with the top of the optical waveguide or at least one sidewall; or, the diffraction structure is located at a position no more than a preset distance from one sidewall of the optical waveguide.

[0026] In one possible implementation, the preset distance between the diffraction structure and the optical waveguide satisfies the requirement that the optical field formed in the optical waveguide and the diffraction structure overlap spatially.

[0027] Furthermore, optionally, the preset distance between the diffraction structure and the optical waveguide is not greater than the center wavelength of the operating band.

[0028] Using the method described above (method four), this diffractive optical device can be applied to scenarios where a narrow band (or filtering band) of response is required. For example, it can be used in high-resolution optical imaging systems where the light source emits wide-band light but a narrow band is needed. Alternatively, it can be used in scenarios where the requirements for narrow-band filtering are not high, such as imaging systems where the light source itself is narrow-band. Furthermore, it has lower requirements for process precision, thus facilitating the fabrication of diffractive optical devices.

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

[0030] Using the method described above (method five), this diffractive optical device can be applied to scenarios where a narrow band (or filtering band) of response is required. For example, it can be used in high-resolution optical imaging systems where the light source emits wide-band light but requires a narrow band. Alternatively, it can be used in scenarios where the requirements for narrow-band filtering are not high, such as imaging systems where the light source itself is narrow-band. Furthermore, the periodic variation of the refractive index of the optical waveguide can be achieved through doping, requiring lower process precision and thus facilitating the fabrication of diffractive optical devices.

[0031] In one possible implementation, the grating period in the first dimension is no greater than 2 micrometers. This allows for reflection of incident angles over a relatively large range into a specific direction in space.

[0032] In one possible implementation, the thickness of each of the N optical waveguides is no greater than 300 nanometers. This facilitates the fabrication of the optical waveguides and also contributes to the miniaturization of the diffractive optical device.

[0033] In one possible implementation, the N optical waveguides are made of silicon nitride or titanium dioxide.

[0034] When the waveguide material is silicon nitride or titanium dioxide, diffractive optical devices can be fabricated using mature semiconductor micro / nano fabrication processes, making mass production relatively easy. Furthermore, materials such as silicon nitride and titanium dioxide offer stable performance, allowing the diffractive optical device to maintain consistent performance under varying environmental conditions. Additionally, silicon nitride or titanium dioxide is transparent to visible light, which helps improve light transmittance.

[0035] In one possible implementation, the acute angle formed between any two adjacent optical waveguides in the N optical waveguides is no greater than a preset angle.

[0036] By setting any two adjacent optical waveguides in N optical waveguides to be parallel or approximately parallel, more optical waveguides can be set in the grating assembly. More optical waveguides provide more freedom in controlling the optical field.

[0037] In one possible implementation, the first dimension is perpendicular to the second dimension. For example, the first dimension could be the direction of the grating period, and the second dimension could be the direction along the optical waveguide.

[0038] The first dimension being perpendicular to the second dimension facilitates the fabrication of diffractive optical devices and results in a more uniform response.

[0039] Secondly, this application provides a terminal device, which includes at least one diffractive optical device of the first aspect or any one of the first aspects, and at least one substrate, wherein each diffractive optical device is fixed on the corresponding substrate.

[0040] In one possible implementation, the parameters of the grating components in the diffractive optical device, which are fixed in different regions of the substrate, are different, including the grating period and / or tilt angle.

[0041] In one possible implementation, the terminal device includes an optical projector used to emit a beam of light carrying image information toward a diffractive optical device.

[0042] The technical effects that can be achieved by any of the second to fifth aspects mentioned above can be referred to the description of the beneficial effects in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0043] Figure 1 A schematic diagram of the diffracted light of a diffraction grating provided in this application;

[0044] Figure 2 A schematic diagram illustrating a possible application scenario provided in this application;

[0045] Figure 3This is a schematic diagram of the structure of a diffractive optical device provided in this application;

[0046] Figure 4a A schematic diagram of a periodic recessed portion in an optical waveguide provided in this application;

[0047] Figure 4b A schematic diagram of another optical waveguide with periodic recesses provided in this application;

[0048] Figure 5 A schematic diagram of an optical waveguide exhibiting periodic gaps, provided for this application;

[0049] Figure 6 A schematic diagram of an optical waveguide provided in this application, comprising periodically distributed small holes;

[0050] Figure 7a A schematic diagram showing the positional relationship between a periodically distributed diffraction structure and an optical waveguide provided in this application;

[0051] Figure 7b A schematic diagram of a periodically distributed diffraction structure in contact with the optical waveguide provided in this application;

[0052] Figure 7c A schematic diagram showing the positional relationship between another periodically distributed diffraction structure and the optical waveguide provided in this application;

[0053] Figure 7d A schematic diagram of another periodically distributed diffraction structure provided in this application in contact with the optical waveguide;

[0054] Figure 7e A schematic diagram showing the positional relationship between another periodically distributed diffraction structure and the optical waveguide provided in this application;

[0055] Figure 8 A schematic diagram of a waveguide with a periodic change in refractive index provided in this application;

[0056] Figure 9a A schematic diagram of an optical waveguide structure that presents at least two different waveguide periods in the second dimension, provided for this application;

[0057] Figure 9b Another schematic diagram of an optical waveguide structure that presents two different waveguide periods in the second dimension, provided for this application;

[0058] Figure 9c Another schematic diagram of an optical waveguide structure that presents at least two different waveguide periods in the second dimension, provided for this application;

[0059] Figure 9dAnother schematic diagram of an optical waveguide structure that presents at least two different waveguide periods in the second dimension, provided for this application;

[0060] Figure 9e Another schematic diagram of an optical waveguide structure that presents at least two different waveguide periods in the second dimension, provided for this application;

[0061] Figure 9f A schematic diagram illustrating the formation principle of an optical waveguide exhibiting two different waveguide periods in the second dimension, provided for this application;

[0062] Figure 10a A top view of the structure of a diffractive optical device provided in this application;

[0063] Figure 10b A side view of the structure of a diffractive optical device provided in this application;

[0064] Figure 10c Top view of the structure of another diffractive optical device provided in this application;

[0065] Figure 10d Top view of the structure of another diffractive optical device provided in this application;

[0066] Figure 10e Top view of the structure of another diffractive optical device provided in this application;

[0067] Figure 11a A schematic diagram of another diffractive optical device provided in this application;

[0068] Figure 11b A side view of a diffractive optical device provided in this application;

[0069] Figure 11c A schematic diagram showing the diffraction efficiency distribution of 0th, 1st, and 2nd order diffracted light at different wavelengths, provided for this application;

[0070] Figure 11d A schematic diagram of another diffractive optical device provided in this application;

[0071] Figure 11e A schematic diagram showing the diffraction efficiency distribution of 0th, 1st, and 2nd order diffracted light at different wavelengths, provided for this application;

[0072] Figure 11f A schematic diagram of the structure of yet another diffractive optical device provided in this application;

[0073] Figure 11g Another schematic diagram of the diffraction efficiency distribution of 0th, 1st and 2nd order diffracted light at different wavelengths, provided for this application;

[0074] Figure 12 A schematic diagram of a substrate with identical parameters in different regions provided in this application;

[0075] Figure 13a A schematic diagram showing the different parameters of a grating assembly in different regions of a substrate provided in this application;

[0076] Figure 13b A schematic diagram illustrating the focusing effect of a diffractive optical device provided in this application;

[0077] Figure 14 A schematic diagram of the structure of a diffractive optical device for spectral detection provided in this application;

[0078] Figure 15 This is a schematic diagram of the structure of a terminal device provided in this application. Detailed Implementation

[0079] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0080] The following provides explanations for some of the terms used in this application. It should be noted that these explanations are for the convenience of those skilled in the art and do not constitute a limitation on the scope of protection claimed in this application.

[0081] I. Diffraction Grating

[0082] A diffraction grating is a micro- or nano-optical device that exhibits periodic structural or refractive index variations at near-wavelength scales, enabling periodic spatial modulation of the amplitude and / or phase of incident light.

[0083] Diffraction gratings can be divided into reflection diffraction gratings and transmission diffraction gratings. Reflection diffraction gratings can reflect incident light at one or more specific angles. This process can be described by the diffraction equation of the grating (Formula 1), and different reflection angles correspond to specific diffraction orders.

[0084] sin θ i -sin θ m =mλ / d Formula 1

[0085] Where, θ i Let θ be the angle of incidence. m λ is the diffraction angle with diffraction order m, λ is the wavelength of the incident light, and d is the grating period (or grating constant).

[0086] like Figure 1 As shown, the diffraction angle (θ0) of the zeroth-order diffracted light of the diffraction grating is different from the incident angle (θ) of the incident light. iThe diffraction angle of the zeroth-order diffracted light is symmetrical about the normal to the grating surface, meaning the diffraction angle is equal to the incident angle, which is symmetrical reflection and independent of the grating period. However, the diffraction angles of higher-order (±1st order and above) diffracted light are asymmetrical with respect to the incident angle, constituting anomalous angle reflection, which is related to the grating period. In other words, by changing the grating period, the diffraction angle of higher-order diffracted light can be controlled, but the diffraction angle of the zeroth-order diffracted light cannot be controlled.

[0087] It should be understood that Formula 1 above is for the case where the incident light is coplanar. The diffraction angle of zero-order diffracted light refers to the diffraction angle of diffracted light with a diffraction order of 0, while the diffraction angle of higher-order diffracted light refers to the diffraction angle of diffracted light with a diffraction order of ±1 or higher.

[0088] II. Guided-mode resonance (GMR)

[0089] Guided-mode resonance refers to a phenomenon where introducing periodic diffraction elements (such as diffraction gratings) into a waveguide, when incident free-space light of a specific wavelength satisfies the phase-matching condition, can excite waveguide modes and leak the optical field into free space. This is due to the coupling between the incident free-space light of a specific wavelength and the leaked mode supported by the diffraction grating. Therefore, the leaked mode corresponds to a waveguide mode in the optical waveguide structure.

[0090] A diffraction grating can be viewed as a periodic modulation of an optical waveguide. At a specific incident wavelength, when the diffracted light from the grating is close to the waveguide mode supported by the waveguide in terms of parameters (e.g., phase matching), the waveguide mode can leak into free space, forming guided mode resonance. Guided mode resonance can achieve high diffraction efficiency and select narrowband wavelengths (or narrowband wavelength response).

[0091] III. Waveguide Mode

[0092] The electromagnetic field patterns that can propagate in a waveguide are called waveguide modes. There are two eigenmodes in a waveguide: transverse electric mode (TE) and transverse magnetic mode (TM), which can be defined by the polarization directions of the electric and magnetic fields of light. The electric field is polarized only along the y-direction parallel to the waveguide interface, and is perpendicular to the light propagation direction z; it is transverse and called a transverse electric mode. The magnetic field is polarized only along the y-direction parallel to the waveguide interface, and is perpendicular to the light propagation direction z; it is transverse and called a transverse magnetic mode.

[0093] IV. Phase Delay

[0094] Because light waves slow down when passing through materials with a certain refractive index, this has a phase delay effect, which is called phase delay.

[0095] V. Wavefront

[0096] A wavefront is the surface formed by the particles that have just begun to move as a wave propagates through a medium. It is a wavefront (or wavefront surface) perpendicular to the direction of wave propagation. It can also be understood as the curved surface formed by connecting the points at the very front of the wave at a given moment.

[0097] VI. Fleeting Waves

[0098] Evanescent waves, also known as vanishing waves, occur when light undergoes total internal reflection. Instead of being completely reflected back to the first medium at the interface, the light wave travels to a depth of approximately one wavelength in the second medium, flows along the interface for a distance on the order of the wavelength, and then returns to the first medium, exiting in the same direction as the reflected light. This wave traveling along the surface of the second medium is called a vanishing wave.

[0099] VII. Resonant Wavelength

[0100] When the wavelength of the incident light satisfies the phase matching condition, the guided mode resonance phenomenon is excited, and this wavelength is called the resonant wavelength.

[0101] The preceding text has introduced some of the terms used in this application. The following section describes the application scenarios involved in this application. It should be noted that these explanations are for the convenience of those skilled in the art and do not constitute a limitation on the scope of protection claimed in this application.

[0102] In this application, the diffractive optical device can be applied to an imaging system that can be used in the AR field, such as AR glasses, AR helmets, and head-up display (HUD) devices. Alternatively, the imaging system can also be used in the virtual reality (VR) field, such as VR glasses or VR helmets. In the AR or VR fields, in order to simultaneously meet the requirements of compact size, high reflectivity of the projected light, and high transmittance of the ambient light, it is necessary to achieve a response (e.g., reflection) to light of a specific wavelength band (or a specific wavelength range), and it is also necessary to control abnormal angle reflections.

[0103] like Figure 2The diagram illustrates a possible application scenario provided by this application. This application scenario uses AR glasses as an example. AR glasses may include an optical overlay device and an optical projection system. The optical projection system emits light of a specific wavelength, which carries image information. The optical overlay device reflects this specific wavelength of light to the human eye at a specific angle to form an image. Ambient light can also be transmitted through this optical overlay device to the human eye to form an image, thereby achieving a visual effect of merging real and virtual world images in the AR glasses. It should be understood that diffractive optics can serve as the optical overlay device in this scenario.

[0104] Based on the aforementioned potential application scenarios, it can be seen that optical superimposed devices need to be able to respond to light of a specific wavelength band and also control the direction of that light band in space. However, existing optical superimposed devices are usually semi-transparent mirrors or polarizing beam splitters. Neither of these types of optical superimposed devices can simultaneously meet the requirements of responding to light of a specific wavelength band and controlling the direction of that light band in space. Furthermore, they need to be combined with other optical components to transmit the light from the image generated by the optical projection system to the human eye. This is not conducive to the miniaturization of AR glasses. Moreover, existing semi-transparent mirrors or polarizing beam splitters are difficult to achieve both high transmittance to ambient light and high reflectivity to optical projectors.

[0105] It should be noted that the above scenarios are merely examples. The diffractive optical devices provided in this application can also be applied to various scenarios requiring narrowband wavelength response and / or anomalous angle reflection modulation. For example, in spectral detection scenarios, the presence or concentration change of the detected substance causes a change in the refractive index outside the diffractive optical device, altering the wavelength of the reflected light. Therefore, information about the detected substance can be obtained by detecting the change in the reflected spectrum. Another example is space optical communication scenarios.

[0106] In view of this, this application provides a diffractive optical device that can respond to light in a specific wavelength band and can control abnormal angle reflections.

[0107] The following is in conjunction with the appendix Figure 3 To be continued Figure 14 This application provides a detailed description of the diffractive optical device proposed in this application.

[0108] Based on the above, this application provides a diffractive optical device, which may include a grating component that exhibits a periodic distribution in a first dimension. The grating component includes N optical waveguides, among which M optical waveguides exhibit periodic changes in a second dimension. At least two of the M optical waveguides exhibiting periodic changes in the second dimension have different structures. The 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 not greater than N.

[0109] like Figure 3 The diagram shown is a structural schematic of a diffractive optical device provided in this application. This example uses the x-axis as the first dimension and the y-axis as the second dimension. The grating components exhibit a periodic distribution in the first dimension; in this example, two grating components are included in the first dimension. This can also be understood as the grating components being periodically arranged in the first dimension, meaning the grating component is the smallest repeatable unit in the first dimension. The period in the first dimension can be called the grating period, denoted by Tx. The grating component includes three optical waveguides, two of which exhibit periodic changes in the second dimension. These two waveguides have different structures, and the period in the second dimension can be called the waveguide period. The waveguide period of one of the waveguides can be represented by Tx. y1 This indicates that the waveguide period of another optical waveguide can be represented by T. y2 In this example, T y1 With T y2 Different. It should be understood that the periodic changes in the second dimension and the structures of the two optical waveguides with different structures in the second dimension in this example are merely examples. There could be other ways, which can be described in the relevant descriptions below and will not be repeated here.

[0110] Based on the aforementioned diffractive optical devices, by using M optical waveguides exhibiting periodic variations in the second dimension, light of a specific wavelength band can be selected, thus achieving a narrowband response. By forming a grating structure with grating components exhibiting periodic distribution in the first dimension, the function of controlling anomalous angle reflection can be realized; that is, anomalous angle reflection can be achieved using the advanced diffraction of the grating structure. Furthermore, through the aforementioned… Figure 3 The diffractive optical device shown can also enhance the diffraction efficiency of the diffractive optical device at abnormal reflection angles within a specific wavelength band.

[0111] It should be noted that the optical waveguide exhibits a periodic variation in the second dimension (i.e., the direction of its extension). This periodic variation allows the waveguide modes within the waveguide to be excited and phase-matched with the diffracted light when free-space light of a specific wavelength is incident, forming a leakage wave mode that can be efficiently reflected into free space. At this point, the reflection efficiency is greatly enhanced (i.e., guided-mode resonance). For other wavelengths of light that do not meet the phase-matching condition, the reflection efficiency is extremely low. In other words, the interaction between incident light of a specific wavelength and the periodically varied optical waveguide in the second dimension causes the diffracted light to be reflected at a specific angle. In other words, the periodically varied optical waveguide in the second dimension utilizes the guided-mode resonance principle; the interaction between incident light of a specific wavelength and this periodically varied waveguide causes the diffracted light to be reflected at a specific angle (called the anomalous angle), and other wavelengths of incident light do not have a similar response. Therefore, it exhibits a narrowband response, enabling narrowband selection. In addition, due to differences in waveguide size or resonant wavelength, different optical waveguides within the grating assembly have different phase delays for incident light, thereby forming a wavefront distribution of reflected light at a specific angle.

[0112] The aforementioned specific wavelength band can be referred to as a narrowband band, and the narrowband range can be, for example, less than 30 nanometers (nm) or less than 50 nm. Furthermore, the incident light can be an optical band, such as the visible light band, infrared band, ultraviolet band, etc.; or it can be terahertz, microwave, radio, etc. Combining with Equation 1 above, given a fixed incident angle and diffraction order, the longer the wavelength of the incident light, the larger the size of the diffractive optical device (e.g., the grating period of the grating assembly, the length of the optical waveguide, the width of the optical waveguide, and the thickness of the optical waveguide, etc.). The larger the size, the lower the precision requirement for fabrication. For example, when the incident light is in the visible light band, the grating period can be no greater than 2 micrometers (µm).

[0113] In one possible implementation, M optical waveguides exhibiting periodic variations in the second dimension are used to reflect light in a specific wavelength band. This can also be understood as M optical waveguides exhibiting periodic variations in the second dimension being reflective waveguides for a specific wavelength band (narrowband). The specific wavelength band could be, for example, 525nm ± 5nm. Further, optionally, the optical waveguides other than the M waveguides among the N waveguides can also perform phase modulation on the incident light. That is, these N optical waveguides can induce different phase delays in the incident light, achieving phase modulation, thereby improving the efficiency of a certain order of diffraction and reducing the efficiency of other orders of diffraction.

[0114] In one possible implementation, the first dimension is perpendicular to the second dimension, where the first dimension can be the direction of the grating period, and the second dimension can be the direction extending along the optical waveguide. For example, the first dimension is the x-axis direction, and the second dimension is the y-axis direction, as described above. Figure 3 This facilitates the fabrication of diffractive optical devices and results in a more uniform response. It should be understood that the first and second dimensions can also be approximately perpendicular.

[0115] In one possible implementation, the optical waveguide material can be either transparent to visible light or opaque to visible light, and capable of diffracting light at large incident angles. Examples include silicon nitride, titanium oxide, silicon, polymers, or metals, etc., and this application does not limit this choice. It should be noted that when the incident light is in the visible light band, the optical waveguide material is typically a transparent material, such as silicon nitride or titanium oxide, which helps to improve light transmittance. Furthermore, when the optical waveguide material is silicon nitride or titanium oxide, diffractive optical devices can be fabricated using mature semiconductor micro / nano fabrication processes, making mass production easier. Moreover, materials such as silicon nitride or titanium oxide have stable properties, allowing the diffractive optical device to maintain stable performance under different environmental conditions.

[0116] Furthermore, optionally, the cross-sectional profile of the optical waveguide can be rectangular (e.g., ...). Figure 10b It can be a trapezoid, or any other regular or irregular shape.

[0117] In the second dimension, the widths of the N optical waveguides included in the grating assembly can be the same or different; similarly, the thicknesses of the N optical waveguides can be the same or different. Further, optionally, the thickness of the optical waveguide is no greater than 1 μm. Further, optionally, the thickness of the optical waveguide is no greater than 300 nanometers (nm).

[0118] In one possible implementation, the acute angle formed between any two adjacent optical waveguides among the N optical waveguides is no greater than a preset angle. This preset angle can be, for example, 0 degrees, meaning the N optical waveguides are parallel to each other; or, for example, a preset angle greater than 0 degrees and no greater than 10 degrees, meaning the N optical waveguides are approximately parallel to each other. In other words, the preset angle can be any angle no greater than 10 degrees, such as 0 degrees, 0.5 degrees, 1 degree, 1.2 degrees, 3 degrees, 10 degrees, etc. It can also be understood as any two adjacent optical waveguides among the N optical waveguides being parallel or approximately parallel to each other. This allows for the placement of more optical waveguides within the grating assembly, providing greater freedom in controlling the optical field.

[0119] Furthermore, optionally, the M optical waveguides exhibiting periodic changes in the second dimension have different resonant wavelengths corresponding to their different guided modes. That is, the M optical waveguides with different structures correspond to M resonant wavelengths. This allows for the selection of M wavebands. For example, it can be applied to scenarios requiring multi-wavelength selection, such as color displays.

[0120] The following is about Figure 3 The diffractive optical device shown is described in two dimensions to provide an exemplary implementation scheme.

[0121] I. Structure in the Second Dimension

[0122] In one possible implementation, M of the N optical waveguides in the grating assembly exhibit periodic variations in the second dimension. At least two of the M waveguides exhibiting periodic variations in the second dimension have different structures.

[0123] The following examples illustrate three possible implementations of optical waveguides with different structures.

[0124] Implementation method one: at least two of the M optical waveguides exhibiting periodic changes in the second dimension have different patterns of periodicity. Implementation method two: at least two of the M optical waveguides exhibiting periodic changes in the second dimension have different period sizes. Implementation method three: at least two of the M optical waveguides exhibiting periodic changes in the second dimension have different shapes. It should be understood that different structures of at least two optical waveguides can also be a combination of the above three implementation methods. For ease of explanation, two of the M waveguides are used as an example. For example, the two optical waveguides have different period sizes and different patterns of periodicity; or, for example, the two optical waveguides have different period sizes and different shapes; or, for example, the two optical waveguides have different patterns of periodicity and different shapes; or, for example, the two optical waveguides have different period sizes, different patterns of periodicity, and different shapes.

[0125] In one possible implementation, the period (e.g., T) of each of the M optical waveguides that exhibit periodic variation in the second dimension is... y The period T of the optical waveguide in the second dimension is less than the center wavelength of the operating band. For example, the period T of the optical waveguide in the second dimension is... y The range is 0.2–0.4 μm.

[0126] The following examples illustrate five possible ways of periodic change.

[0127] Method 1: The optical waveguide exhibits periodic protrusions or recesses.

[0128] In one possible implementation, in the second dimension, periodic recesses or protrusions are present on the top or sidewalls of the optical waveguide. For example... Figure 4a The diagram shown is a schematic representation of a periodically recessed portion in an optical waveguide provided in this application. This recess is located on one sidewall of the optical waveguide, and due to the periodic variation of the waveguide, the width of the waveguide varies periodically along its extension direction (i.e., in the second dimension). It should be understood that... Figure 4a This example uses the recessed portion located on the left side wall of the optical waveguide as an example; the recessed portion can also be located on the right side wall of the optical waveguide.

[0129] like Figure 4b The diagram shows another optical waveguide with periodic recesses provided in this application. These recesses are located on both sidewalls of the optical waveguide, and due to the periodic variation of the waveguide, its width varies periodically along the waveguide's extension direction (i.e., in the second dimension). It should be understood that... Figure 4b The example given is that the recesses on the two sidewalls are symmetrical about the centerline of the optical waveguide. These two recesses can also be asymmetrical about the centerline of the optical waveguide. For example, they can have the same period on both sides but different degrees of recess; or they can have the same period and the same degree of recess but have displacement along the second dimension, that is, the recesses on the two sidewalls are not strictly aligned (see 9c below).

[0130] It should be noted that when the top of the optical waveguide has periodic recesses or protrusions, the thickness of the optical waveguide changes periodically along the direction of its extension.

[0131] It should also be noted that the periodic changes in an optical waveguide can be abrupt, as described above. Figure 4a or Figure 4b The shape shown is a right-angled sawtooth; or the periodic variation of the optical waveguide can be gradual, such as triangular sawtooth, undulating, semi-circular protrusion, or semi-circular concavity. It should be understood that any shape that can be achieved through micro-nano fabrication processes is acceptable.

[0132] Based on the first method described above, this diffractive optical device can be applied to scenarios where a narrow band (or filter band) is required for the response. For example, it can be applied to high-resolution optical imaging systems where the light source emits wide-band light but a narrow band is needed.

[0133] Method 2: The optical waveguide exhibits periodic gaps.

[0134] In one possible implementation, the optical waveguide exhibits periodic gaps in the second dimension. This can also be understood as the optical waveguide being periodically truncated in the second dimension, with the gap between two adjacent truncated sections called a gap. The direction of the gap can be understood as the direction of the truncation. Figure 5 The diagram shown is a schematic representation of a periodic gap in an optical waveguide provided in this application. The length of the gap in the second dimension should be controlled within a certain range; for example, the length of the gap in the second dimension should satisfy the requirement that incident light can pass through adjacent portions of the optical waveguide (e.g.,...). Figure 5 The waveguide modes are formed by coupling between A and B in the waveguide. In this way, guided mode resonance can be achieved, thereby achieving high diffraction efficiency and selecting narrowband bands.

[0135] For example, the length of the gap in the second dimension is no greater than the center wavelength of the operating band. Furthermore, the length of the gap in the second dimension is less than half the center wavelength of the operating band, thereby allowing the optical fields between adjacent portions within the waveguide to couple and form waveguide modes.

[0136] Further, optionally, the angle between the direction of the optical waveguide gap and the first dimension is less than 90 degrees. For example, the angle between the direction of the optical waveguide gap and the first dimension is 0 degrees (see...). Figure 5 For example, the angle between the direction of the optical waveguide gap and the first dimension is 45 degrees; for example, the angle between the direction of the optical waveguide gap and the first dimension is any angle between (0° and 45°); for example, the angle between the direction of the optical waveguide gap and the first dimension is any angle between (45° and 90°). It should be understood that when the angle between the direction of the optical waveguide gap and the first dimension is any angle between (0° and 90°), the direction of the optical waveguide gap is tilted.

[0137] Based on the second method described above, this diffractive optical device is suitable for applications where narrowband filtering requirements are not high, such as imaging systems where the light source itself is narrowband. Furthermore, it has lower requirements for manufacturing precision, thus facilitating the fabrication of the diffractive optical device.

[0138] Method 3: The optical waveguide includes periodically distributed small holes, which are either hollow or filled with a material having a different refractive index than the material of the optical waveguide.

[0139] In one possible implementation, the optical waveguide exhibits a periodically distributed array of small apertures in the second dimension. For example... Figure 6 The diagram shown is a schematic representation of an optical waveguide provided in this application, comprising periodically distributed small holes. These holes can be hollow, meaning the optical waveguide is hollowed out at corresponding locations; or they can be filled with a material whose refractive index differs from that of the optical waveguide material. For example, silicon oxide.

[0140] It should be noted that the shape of the aperture includes, but is not limited to, circles, squares, triangles, etc., any shape that can be achieved through micro-nano fabrication processes.

[0141] Based on method three above, this diffractive optical device can be applied to scenarios requiring a relatively narrow filtering band. For example, it can be used in high-resolution optical imaging systems where the light source emits wide-band light but a narrow-band band is required.

[0142] Method 4: The periodically distributed diffraction structure (or micro / nano structure) is in contact with the optical waveguide or the distance between the diffraction structure and the optical waveguide does not exceed a preset distance.

[0143] In one possible implementation, in the second dimension, the periodically distributed diffraction structure is in contact with the optical waveguide, or the distance between the periodically distributed diffraction structure and the optical waveguide does not exceed a preset distance. In other words, the periodically distributed diffraction structure is disposed in the vicinity of the optical waveguide or on the optical waveguide. This can also be understood as the periodically distributed diffraction structure being disposed on the optical waveguide, or at a distance equal to a preset distance from the optical waveguide, or at a distance less than a preset distance from the optical waveguide, and the diffraction structure exhibiting a periodic distribution in the second dimension. The diffraction structure can be periodically disposed on the top, one sidewall, or both sidewalls of the optical waveguide; or the diffraction structure can be periodically disposed near the top, one sidewall, or both sidewalls of the optical waveguide, and the distance between it and one sidewall of the optical waveguide does not exceed a preset distance.

[0144] Further, optionally, the preset distance between the diffraction structure and the optical waveguide must satisfy the requirement that the optical field formed in the optical waveguide and the diffraction structure spatially overlap. That is, the diffraction structure can interact with the optical field of the waveguide mode in the optical waveguide. For example, the preset distance between the diffraction structure and the optical waveguide is no greater than the center wavelength of the operating band (e.g., 525 nm). Further, the preset distance between the diffraction structure and the optical waveguide can be less than one-quarter of the center wavelength of the operating band. It should be understood that when light propagates within the preset distance range outside the optical waveguide, the light can be called an evanescent wave.

[0145] In one possible implementation, the shape of the diffraction structure can be circular, square, rectangular, triangular, etc. Any shape that can be realized by semiconductor micro-nano processes is acceptable, and this application does not limit it.

[0146] In one possible implementation, the material of the diffraction structure can be, for example, silicon nitride, titanium oxide, silicon, silicon oxide, polymer, metal, etc.

[0147] In one possible implementation, the maximum size of the diffraction structure is no greater than the width of the optical waveguide. For example, the diffraction structure is circular, and its diameter is no greater than the width of the optical waveguide; or, in the positive direction, its side length is no greater than the width of the optical waveguide; or, in the longitudinal direction, its short side is no greater than the width of the optical waveguide.

[0148] like Figure 7a The diagram shown is a schematic representation of a periodically distributed diffraction structure adjacent to the optical waveguide provided in this application. In this example, the diffraction structure is located near one sidewall of the optical waveguide, and its shape is square.

[0149] like Figure 7b The diagram shown is a schematic representation of a periodically distributed diffraction structure in contact with the optical waveguide, as provided in this application. In this example, the diffraction structure is located on one sidewall of the optical waveguide, i.e., the diffraction structure is in contact with the optical waveguide, and the shape of the diffraction structure is square, as an example.

[0150] like Figure 7c The diagram shows another periodically distributed diffraction structure provided in this application, adjacent to the optical waveguide. In this example, the diffraction structure is located near two sidewalls of the optical waveguide, and its shape is square. It should be noted that the diffraction structures located near the sides of the optical waveguide can be symmetrical about the centerline of the waveguide.

[0151] like Figure 7d The diagram shows another example of a periodically distributed diffraction structure provided in this application in contact with the optical waveguide. In this example, the diffraction structure contacts two sidewalls of the optical waveguide, and the shape of the diffraction structure is square. It should be noted that the diffraction structure in contact with the two sides of the optical waveguide can be symmetrical about the centerline of the optical waveguide.

[0152] It should be noted that the diffraction structures located near the two sides of the optical waveguide can be asymmetrical about the centerline of the waveguide. For example, the waveguide periods of the two sidewall diffraction structures may be the same, but their distances from the optical waveguide may differ, such as the left diffraction structure being closer to the optical waveguide than the right diffraction structure, or vice versa. Alternatively, the waveguide periods of the two sidewall diffraction structures may be the same, but there may be a displacement along the second dimension, meaning that the diffraction structures near the two sidewalls are not strictly aligned (see [reference needed]). Figure 7e ).

[0153] Based on method four above, this diffractive optical device can be applied to scenarios where a narrow band (or filtering band) of response is required. For example, it can be used in high-resolution optical imaging systems where the light source emits wide-band light but requires a narrow band. Alternatively, it can be used in scenarios where the requirements for narrow-band filtering are not high, such as imaging systems where the light source itself is narrow-band. Furthermore, it has lower requirements for process precision, thus facilitating the fabrication of diffractive optical devices.

[0154] Method 5: The refractive index of the optical waveguide exhibits periodic changes.

[0155] In one possible implementation, the refractive index of the optical waveguide exhibits a periodic variation in the second dimension; see [link to relevant documentation]. Figure 8 The optical waveguide is made of at least two materials with different refractive indices, n1 and n2, which alternate and change periodically.

[0156] Furthermore, optionally, the periodic variation of the refractive index of the optical waveguide can be formed by doping the optical waveguide, or by inserting materials with different refractive indices into the optical waveguide.

[0157] Based on method five above, this diffractive optical device can be applied to scenarios where a narrow band (or filtering band) of response is required. For example, it can be used in high-resolution optical imaging systems where the light source emits wide-band light but requires a narrow band. Alternatively, it can be used in scenarios where the narrow-band filtering function is not critical, such as imaging systems where the light source itself is narrow-band. Furthermore, the periodic variation of the refractive index of the optical waveguide can be achieved through doping, requiring lower process precision and thus facilitating the fabrication of diffractive optical devices.

[0158] In one possible implementation, at least one of the M optical waveguides exhibiting periodicity in the second dimension displays at least two different waveguide periods. For ease of explanation, the following example uses an optical waveguide exhibiting periodicity in the second dimension, and which displays two different waveguide periods.

[0159] It should be noted that the above methods one through five are based on the example of an optical waveguide exhibiting one waveguide period. Methods based on the periodic changes of the optical waveguide located at the top or sidewall can be described in two scenarios as follows.

[0160] In scenario 1, the periodic variation of the optical waveguide is located at the top of the optical waveguide.

[0161] Based on scenario 1, at least one of the M optical waveguides exhibiting periodic changes in the second dimension has at least two different waveguide periods at its top.

[0162] Based on the periodic changes described in Method 1 above, please refer to... Figure 9a This is a cross-sectional schematic diagram of an optical waveguide exhibiting at least two different waveguide periods in the second dimension, as provided in this application. The recessed portion of the optical waveguide is located at the top of the waveguide, and the waveguide exhibits two different waveguide periods in the second dimension, namely T... y11 and T y12 Thus, narrowband responses to two wavelengths can be achieved simultaneously on the same optical waveguide. It should be understood that... Figure 9a This is a side view of an optical waveguide. Exemplarily, the bottom end of the optical waveguide is disposed on a substrate.

[0163] When the periodic variation of the optical waveguide is in the manner described in Method 2, Method 3, Method 4, or Method 5, at least one of the M optical waveguides exhibiting periodic variation in the second dimension can also be designed to exhibit at least two different periods. This simply involves replacing the method of periodic variation in the second dimension. Further details will not be repeated here; please refer to [link to relevant documentation]. Figure 9a In this way.

[0164] Scenario 2: The periodic variation of the optical waveguide is located on the sidewall of the optical waveguide.

[0165] Based on scenario 2, we can further elaborate on the following four scenarios.

[0166] Case 2.1 presents two different waveguide periods on each side of the optical waveguide.

[0167] The optical waveguide, based on the periodic variation of method one described above, exhibits two different waveguide periods on each side. Please refer to... Figure 9b This is a schematic diagram of an optical waveguide structure that exhibits two different waveguide periods in the second dimension, as provided in this application. The recessed portion of the optical waveguide is located on two sidewalls and is symmetrical about the centerline of the waveguide. Each sidewall of the optical waveguide exhibits two different waveguide periods in the second dimension, namely T... y11 and T y12 In this way, the function of selecting two wavelengths can be realized simultaneously on the same optical waveguide.

[0168] It can also be understood as, Figure 9b Through Figure 9f The optical waveguide 1 and optical waveguide 2 are superimposed in the image, and optical waveguide 1 exhibits a period (T) in the second dimension. y11 That is, every T of optical waveguide 1 y11 A concave point appears at the distance; waveguide 2 also exhibits a period (T) in the second dimension. y12 That is, the width of optical waveguide 2 is every T y12 A concave point appears at the distance. The superposition of optical waveguide 1 and optical waveguide 2 results in... Figure 9bThe optical waveguide shown is located at intervals of T. y11 A concave point appears at a distance of T, and at the same time, every T y12 A concave point appears at the distance.

[0169] When the optical waveguides are varied according to methods two, three, four, and five mentioned above, at least one of the M optical waveguides exhibiting periodic variations in the second dimension can also be designed to exhibit at least two different waveguide periods. This simply involves replacing the periodic variation pattern in the second dimension. Further details will not be repeated here; please refer to [link to relevant documentation]. Figure 9b .

[0170] In scenario 2.2, a waveguide period is present on each side of the optical waveguide, and the two waveguide periods on the two sides are of different sizes.

[0171] The optical waveguide exhibits a waveguide period on each side, based on the periodic variation described in method five above, with these two periods differing in size. This can also be understood as the diffraction structure being asymmetrical about the centerline of the optical waveguide. Please refer to [link to relevant documentation]. Figure 9c This is a schematic diagram of an optical waveguide structure that exhibits at least two different waveguide periods in the second dimension, as provided in this application. The diffraction structure is located on the two sidewalls of the optical waveguide, with each sidewall corresponding to one waveguide period. The waveguide period of the left sidewall is T. y11 The waveguide period on the right side wall is T. y12 In this way, the function of narrowband response to two wavelengths can be realized simultaneously on the same optical waveguide.

[0172] It should be understood that the waveguide period of the two sidewalls of an optical waveguide can be greater on the left than on the right (i.e., T). y11 >T y12 Alternatively, the waveguide period on the right can be greater than the waveguide period on the left (T). y12 >T y11 ).

[0173] When the periodic variation of the optical waveguide is in the manner described in Methods 1, 2, 3, and 4 above, at least one of the M optical waveguides exhibiting periodic variation in the second dimension can also be designed to exhibit at least two different waveguide periods, similar to Case 2.2. This simply involves replacing the method of periodic variation in the second dimension. Further details will not be repeated here; please refer to [link to relevant documentation]. Figure 9c .

[0174] Case 2.3: Two waveguide periods are presented on one side of the optical waveguide, and these two waveguide periods are different; one waveguide period is presented on the other side, which can be the same as or different from either of the two waveguide periods on the opposite side.

[0175] Based on the periodic variation of Method 1 described above, two different waveguide periods are present on one side of the optical waveguide, while only one waveguide period is present on the other side. Please refer to [link / reference]. Figure 9d This is a schematic diagram of another optical waveguide structure that exhibits at least two different waveguide periods in the second dimension, as provided in this application. The recessed portion of this optical waveguide is located on two sidewalls, which are asymmetrical about the centerline of the waveguide. The recessed portion on one side of the optical waveguide exhibits two different waveguide periods in the second dimension, namely T... y11 and T y12 On the other side, a waveguide with a period of T is presented. y13 T y13 Can be with T y11 and T y12 It can be the same as any of them, or it can be the same as T. y11 and T y12 They are all different. Thus, at least two wavelengths can be selected simultaneously on the same optical waveguide. If T y13 With T y11 and T y12 If any one of them is the same, then filtering of two wavelengths can be achieved; if T y13 With T y11 and T y12 If they are all different, then filtering of three wavelengths can be achieved, that is, selecting three wavelengths.

[0176] Furthermore, optionally, T y11 :T y12 =2:3.

[0177] When the periodic variation of the optical waveguide is in the manner described in methods two, three, four, and five above, at least one of the M optical waveguides exhibiting periodic variation in the second dimension can also be designed to exhibit at least two different waveguide periods, similar to scenario 2.3. This is achieved by simply replacing the periodic variation method in the second dimension. For details, please refer to [link to relevant documentation]. Figure 9d .

[0178] Case 2.4: Two waveguide periods are present on one side of the optical waveguide, and these two waveguide periods are different; two waveguide periods are also present on the other side, and at least one of these two waveguide periods is different from either of the two waveguide periods on the opposite side.

[0179] The optical waveguide, based on the periodic variation of Method 1 described above, exhibits two different waveguide periods on one side; and also two waveguide periods on the other side, at least one of these two waveguide periods being different from either of the two waveguide periods on the opposite side. Please refer to [link / reference]. Figure 9eThis is a schematic diagram of another optical waveguide structure that exhibits at least two different waveguide periods in the second dimension, as provided in this application. The recessed portion of this optical waveguide is located on two sidewalls, which are asymmetrical about the centerline of the waveguide. The recessed portion on one side of the optical waveguide exhibits two different waveguide periods in the second dimension, namely T... y11 and T y12 On the other side, there are also two waveguide periods, namely T. y13 and T y14 T y13 and T y14 At least one of them is related to T y11 and T y12 None of them are the same. In this way, the function of selecting at least three wavelengths can be realized simultaneously on the same optical waveguide.

[0180] Furthermore, optionally, T y11 :T y12 =2:3, T y13 :T y14 =2:3.

[0181] When the periodic variation of the optical waveguide follows the methods described in Methods 2, 3, 4, and 5 above, at least one of the M optical waveguides exhibiting periodic variation in the second dimension can also be designed to exhibit at least two different waveguide periods, similar to Case 2.4. This simply involves replacing the method of periodic variation in the second dimension. Further details will not be repeated here; please refer to [link to relevant documentation]. Figure 9e .

[0182] It should be noted that the above Figures 9b to 9e This is a top view; the bottom of the optical waveguide is located on the substrate. Figures 9b to 9e The dashed box represents the base.

[0183] II. Structure in the First Dimension

[0184] In one possible implementation, the width of each optical waveguide within the grating assembly in the first dimension is less than half the grating period, thus allowing the grating assembly to include at least two optical waveguides. Exemplarily, the grating period ranges from not less than 100 nm to not more than 2 μm.

[0185] In the following description, we will take the example of a grating assembly that includes three optical waveguides, two of which have different structures that exhibit periodic changes in the second dimension.

[0186] like Figure 10a The image shown is a top view of a diffractive optical device provided in this application. The viewing direction is perpendicular to the surface of the diffractive optical device (i.e., Figure 10a The z-axis direction in the first dimension. Figure 10a The grating components are periodically distributed along the x-axis (in the x-axis direction). Each grating component includes three (N=3) optical waveguides, which are parallel to each other. Two of these (M=2) optical waveguides are in the second dimension (in the x-axis direction). Figure 10a The y-axis direction in the optical waveguide exhibits a periodic variation (the periodic variation follows the method described above), and these two optical waveguides have different waveguide periods, namely T. y1 and T y2 In the two optical waveguides that exhibit periodic changes in the second dimension, each waveguide is symmetrical about its centerline.

[0187] Figure 10b An example is shown Figure 10a The diagram shows a side view of the diffractive optical device at the cut-off point, with the viewing angle of the side view parallel to the surface of the diffractive optical device.

[0188] like Figure 10c The diagram shown is a structural schematic of another diffractive optical device provided in this application. This diffractive optical device may include components in a first dimension (…). Figure 10c A grating assembly is periodically distributed along the x-axis (in the x-axis direction). The grating assembly includes three (N=3) optical waveguides, which are parallel to each other. Two of these (M=2) waveguides are located in the second dimension (in the x-axis direction). Figure 10c The y-axis direction in the optical waveguide exhibits periodic changes (the periodic changes are in the manner described in Method 5 above), and these two optical waveguides have different waveguide periods.

[0189] like Figure 10d The diagram shown is a structural schematic of another diffractive optical device provided in this application. This diffractive optical device may include components in a first dimension (…). Figure 10d A grating assembly is periodically distributed along the x-axis (in the x-axis direction). The grating assembly includes three (N=3) optical waveguides, which are parallel to each other. Two of these (M=2) waveguides are located in the second dimension (in the x-axis direction). Figure 10c The y-axis direction in the optical waveguide exhibits a periodic change. One optical waveguide exhibits a periodic change in the manner described in Method 1 above, and the optical waveguide exhibits a waveguide period, that is, the waveguide periods of the two sidewalls of the optical waveguide are the same. The other optical waveguide exhibits a periodic change in the manner described in Method 1 above, and the waveguide periods on both sides of the optical waveguide are based on the above-described Case 2.1.

[0190] like Figure 10e The diagram shown is a structural schematic of another diffractive optical device provided in this application. This diffractive optical device may include components in a first dimension (…). Figure 10e A grating assembly is periodically distributed along the x-axis (in the x-axis direction). The grating assembly includes three (N=3) optical waveguides, which are parallel to each other. Two of these (M=2) waveguides are located in the second dimension (in the x-axis direction). Figure 10e The optical waveguide exhibits a periodic change along the y-axis direction. One optical waveguide exhibits a periodic change in the manner described in Method 5 above, and it also exhibits a waveguide period. The other optical waveguide exhibits a periodic change in the manner described in Method 1 above, and it also exhibits a waveguide period. The waveguide periods of the two optical waveguides are different.

[0191] It should be noted that, in the above embodiments, unless otherwise specified or there is a logical conflict, the terms and / or descriptions between different embodiments are consistent and can be referenced by each other. The technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationship, which will not be listed one by one here.

[0192] Based on the above, the diffraction angle, response band, and diffraction efficiency of diffractive optical devices can be controlled. The following is a detailed description of different scenarios. In one possible implementation, the structural and material parameters of the diffractive optical device can be set according to the required diffraction angle and wavelength, enabling the device to perform specific functions.

[0193] Scenario 1: Adjust the diffraction angle.

[0194] In one possible implementation, the diffraction angle of the diffraction optics response can be controlled by designing the grating period of the grating assembly and / or the tilt angle of the grating assembly.

[0195] Combining Formula 1 above, the grating period can be designed based on the incident angle and wavelength of the incident light. Figures 10a to 10e The Tx and tilt angle are used to obtain the desired diffraction angle at a specific diffraction order. The specific principle can be found in Formula 1 above, and will not be repeated here.

[0196] For example, for coplanar incident light, refer to Formula 1 above, where the wavelength of the incident light is 525nm (visible light), the incident angle is 60°, the distribution of the grating period is between 0.3um and 1.5um, and the distribution range of the diffraction angle of the first-order diffracted light is -30° to 30°.

[0197] Based on this scenario, it is possible to control the abnormal angle reflection of the diffractive optical device.

[0198] Scenario 2: Adjusting the response band.

[0199] In one possible implementation, the resonant wavelength of the guided mode resonance can be controlled by designing parameters within the grating assembly, for example, by designing the waveguide period of at least one of the M optical waveguides that exhibit periodic changes in the second dimension, thereby achieving the optical response of the diffractive optical device to a specific band, i.e., controlling the band in which the narrowband response is located.

[0200] In combination with the above Figure 10a , Figure 10c Figure 10e It can be achieved by designing T y1 and / or T y2 This controls the resonant wavelength of the guided mode resonance, thereby modulating the narrowband response band of the diffractive optics. Combined with the above... Figure 10d It can be achieved by designing T y11 and / or T y12 and / or T y13 This controls the resonant wavelength of the guided mode resonance, thus modulating the narrowband response band of the diffractive optics. It should be understood that the resonant wavelength is related to the waveguide period T. y1 and / or waveguide T y2 related.

[0201] Scenario 3: Adjusting diffraction efficiency.

[0202] In one possible implementation, parameters within the grating assembly can be designed, such as the width and / or thickness of each of the N optical waveguides, and / or the position (which can be determined by designing the distance between the optical waveguides), and / or the periodic variation of at least one of the M optical waveguides exhibiting periodic variations in the second dimension. This allows the different optical waveguides to cause different phase delays in the incident light due to differences in size or resonant wavelength, forming a wavefront distribution of reflected light at a specific angle. Consequently, the diffraction energy is concentrated more at a certain diffraction order (such as the first-order diffracted light of 12b and 12c simulated in the figure below), thereby increasing the diffraction efficiency at a specific diffraction angle.

[0203] Based on the above, the following section provides a detailed explanation of the diffractive optical device provided in this application, which can achieve the functions of controlling narrowband response and abnormal angle reflection, combined with simulation results.

[0204] This simulation verification is based on an incident light wavelength of 525 nm, with the incident light making a 60-degree angle with the normal direction of the grating surface (i.e., an incident angle of 60°). According to the grating equation (see Formula 1 above), for incident light with a wavelength of 525 nm, the grating period Tx is 606 nm, and the angles corresponding to the first three diffraction orders of the diffracted light can be determined to be 60 degrees (0th order), 0 degrees (1st order), and -60 degrees (2nd order).

[0205] Figure 11aThis is a schematic diagram of a diffractive optical device used in the simulation. In the simulation, the waveguide material is silicon nitride, the substrate material is silicon oxide, and air is positioned above the grating assembly. The grating period Tx is 606 nm, and the waveguide thickness is set to 200 nm. Each grating assembly includes two waveguides that exhibit periodic changes in the second dimension. These two waveguides have the same period of 356 nm in the second dimension; however, their shapes differ in the second dimension. That is, the structural difference between the two waveguides lies in the difference in the specific shape of their periodic changes in the second dimension, including the different lengths of the recesses. Based on the above... Figure 11a The diffractive optical device shown Figure 11b A side view of the aforementioned diffractive optical device is shown as an example.

[0206] Based on the above Figure 11a The structure of the diffractive optical device shown is as follows: Figure 11c The diagram shown illustrates the simulated diffraction efficiency distributions of 0th, 1st, and 2nd order diffracted light at different wavelengths, as provided in this application. The simulation uses rigorous coupled-wave analysis (RCWA) to calculate the diffraction efficiency distributions of 0th, 1st, and 2nd order diffracted light at different wavelengths. Figure 11c The results show that the efficiency of the first-order diffracted light is significantly improved near the wavelength of 525 nm, while the efficiency is lower in other wavelength bands, exhibiting a narrowband response. Simultaneously, the efficiency of the first-order diffracted light near the wavelength of 525 nm is also higher than that of the 0th and 2nd orders, indicating that most of the reflected energy of light incident at a 60-degree angle is reflected at a 0-degree angle, exhibiting an anomalous angle reflection. Therefore, the simulation results demonstrate that the aforementioned diffractive optical device can achieve anomalous angle reflection functionality within a narrowband band.

[0207] Figure 11d This is a schematic diagram of another diffractive optical device used in the simulation. In the simulation, the waveguide material is silicon nitride, the substrate material is silicon oxide, and air is positioned above the grating assembly. The grating period Tx is 606 nm, and the waveguide thickness is set to 200 nm. Each grating assembly includes two waveguides that exhibit periodic variations in the second dimension, and both waveguides have identical structures.

[0208] Based on the above Figure 11d The structure of the diffractive optical device shown is as follows: Figure 11e The diagram shown illustrates the simulated diffraction efficiency distribution of 0th, 1st, and 2nd order diffracted light at different wavelengths, as provided in this application. The simulation also uses RCWA to calculate the diffraction efficiency distribution of 0th, 1st, and 2nd order diffracted light at different wavelengths. Figure 11e The results show that the 0th order diffracted light exhibits a significant efficiency improvement near the wavelength of 475nm, while the efficiency is lower in other wavelength bands, showing a narrow band response. At the same time, the efficiency of the 0th order diffracted light near the wavelength of 475nm is also higher than that of the 1st and 2nd order diffracted light, indicating that most of the reflected energy of the light incident at an angle of 60 degrees is reflected at an angle of 60 degrees, showing weak anomalous angle reflection.

[0209] Figure 11f This is a schematic diagram of another diffractive optical device used for simulation. In the simulation, the waveguide material is silicon nitride, the substrate material is silicon oxide, and air is positioned above the grating assembly. The grating period Tx is 606 nm, and the waveguide thickness is set to 200 nm. Each grating assembly includes two waveguides, one of which has a periodic variation in the second dimension.

[0210] Based on the above Figure 11f The structure of the diffractive optical device shown is as follows: Figure 11g The diagram shown illustrates another simulated diffraction efficiency distribution of 0th, 1st, and 2nd order diffracted light at different wavelengths, provided in this application. This simulation also uses RCWA to calculate the diffraction efficiency distribution of 0th, 1st, and 2nd order diffracted light at different wavelengths. Figure 11g The results show that the 0th order diffracted light exhibits a significant efficiency improvement near the wavelength of 485nm, while the efficiency is lower in other wavelength bands, showing a narrow band response. At the same time, the efficiency of the 0th order diffracted light near the wavelength of 525nm is also higher than that of the 1st and 2nd order diffracted light, indicating that most of the reflected energy of the light incident at a 60-degree angle is reflected at a 60-degree angle, and it basically cannot exhibit abnormal angle reflection.

[0211] Through the above Figure 11c , Figure 11e and Figure 11gIt can be seen that when only one of the two waveguides in the grating assembly exhibits a periodic change in the second dimension, the diffraction efficiency of the 0th-order diffracted light is significantly improved. This indicates that most of the energy of light incident at a 60-degree angle is reflected at the same angle, making it difficult to achieve the function of anomalous angle reflection. When two of the two waveguides in the grating assembly exhibit a periodic change in the second dimension, and these two waveguides have identical structures, both the diffraction efficiency of the 0th-order and 2nd-order diffracted light are relatively high. This indicates that most of the reflected energy of light incident at a 60-degree angle is reflected at the same angle, with some reflected at -60 degrees, which can exhibit some anomalous angle reflection, but it is difficult to achieve a narrowband response. When two of the two optical waveguides in the grating assembly exhibit periodic variations in the second dimension, and these two waveguides have different structures, the diffraction efficiency of the first-order diffracted light is significantly improved, while the efficiency is lower in other wavelength bands, exhibiting a narrowband response. Furthermore, the efficiency of the first-order diffracted light near a wavelength of 525 nm is higher than that of the 0th and 2nd orders, indicating that most of the reflected energy of light incident at a 60-degree angle is reflected at a 0-degree angle, exhibiting an anomalous angle reflection. In other words, by having at least two of the M optical waveguides exhibiting periodic variations in the second dimension have different structures, both anomalous angle reflection and narrowband response can be achieved.

[0212] In this application, the diffractive optical device may also include a substrate. The substrate is described exemplarily below.

[0213] In one possible implementation, the grating assembly can be disposed on a substrate. The substrate material includes, but is not limited to, silicon oxide, silicon nitride, titanium oxide, silicon, polymers, or metals.

[0214] Furthermore, optionally, the substrate can be single-layered or multi-layered. For example, the side of the substrate closest to the grating assembly may also contain a planar optical waveguide structure or multiple layers of materials with varying refractive indices. When the substrate is multi-layered, a Bragg reflector can be formed, thereby reflecting incident light in a specific wavelength band.

[0215] The parameters of the grating components, based on different regions of the substrate, can be categorized into two types. These parameters include the grating period, tilt angle, and structural parameters within the grating component.

[0216] In scenario A, the parameters of the grating components in different regions of the substrate are the same.

[0217] like Figure 12The diagram shown is a structural schematic of a grating assembly with identical parameters in different regions of a substrate provided in this application. The parameter design of the grating assembly in different regions of the substrate is uniform, therefore the optical response (e.g., the selected narrowband band or anomalous angle) of the entire grating assembly is consistent.

[0218] In scenario B, the parameters of the grating components differ in different regions of the substrate.

[0219] In one possible implementation, the parameters of the grating assembly in the diffractive optical device are different for different regions of the substrate. For example... Figure 13a The diagram shown illustrates a structure with different parameters for a grating assembly in different regions of a substrate provided in this application. This allows for focusing on a narrowband response. Furthermore, it can be applied to AR glasses, AR headsets, VR glasses, or VR headsets, etc.

[0220] By setting grating components with different parameters in different regions of the substrate, incident light incident from the same direction can achieve different diffraction angle responses at different regions of the substrate, or achieve narrowband anomalous angle reflections of different wavelengths. This allows for focusing, collimation, or imaging of light in a specific narrowband wavelength range. For example, incident light incident from the same direction (such as incident light with a specific wavelength range) can all be reflected towards a single spatial location to form focused light. (See reference...) Figure 13b It should be understood that only light of that specific wavelength band is collimated to a certain spatial location, while incident light of other wavelengths has no response. This can also be understood as the diffractive optical device having a filtering function. Grating components in different regions of the substrate can achieve a response to light of different wavelengths. Figure 13b Different line types indicate different wavebands.

[0221] It should be noted that this diffractive optical device can diffract incident light with arbitrary wavefront spatial distribution within a specific wavelength band to form reflected light with arbitrary wavefront spatial distribution, and is not limited to the focusing or collimation examples mentioned above. That is to say, the incident light can be parallel or non-parallel, and the diffracted light can be focused to a point or reflected to different positions.

[0222] Based on scenario B above, this diffractive optical device can be applied to the above... Figure 2 The imaging optical system shown serves as an optical superimposed device for the imaging optical system. This diffractive optical device allows incident light of a specific wavelength emitted from the optical projection system to be reflected at different diffraction angles in different regions, projecting the light of that specific wavelength into the human eye for imaging. At the same time, ambient light of other wavelengths can also be transmitted through the diffractive optical device into the human eye for imaging.

[0223] Optical superimpossibilities based on this diffractive optical device can simultaneously achieve high transmittance for ambient light and high reflectance for projection, which is beneficial for improving the visual effect of blending real and virtual world images in AR display systems. It should be understood that the substrate in the diffractive optical device used in AR display systems is transparent.

[0224] It should be noted that this diffractive optical device can also be used in optical systems for virtual reality (VR), where the substrate is opaque or has reflective properties. For example, metals or Bragg mirrors can be used in the substrate to enhance the reflection efficiency of the diffractive optical device.

[0225] For example, the diffractive optical device described above may be an optical element (e.g., a filter or beam splitter) with a response in a specific wavelength band, or it may be an imaging device (e.g., an optical superimposition device).

[0226] Based on the diffractive optical device in any of the above embodiments, such as Figure 14 The image shows a diffractive optical device for spectral detection provided in this application. The response band or diffraction angle of this diffractive optical device is affected by the detected substance. The working principle of the diffractive optical device for spectral detection is as follows: the presence, composition, concentration, or refractive index of the detected substance affects the effective refractive index of the optical waveguide within the grating assembly, causing a change in the resonant wavelength of the guided mode resonance; or it changes the phase delay of the incident light caused by altering the optical waveguide within the grating assembly, thus changing the diffraction angle.

[0227] Therefore, by detecting changes in the reflection angle or spectral changes of the reflected light, one can determine the presence, composition, concentration, or refractive index of the substance being tested.

[0228] It should be understood that pre-calibration can be performed before spectral detection to determine the relationship between the presence of the detected substance and the range of the response band and the diffraction angle; the concentration of the detected substance and the range of the response band and the diffraction angle; the composition of the detected substance and the range of the response band and the diffraction angle; the concentration of the detected substance and the range of the response band and the diffraction angle; and the refractive index of the detected substance and the range of the response band and the diffraction angle, etc.

[0229] Based on the above, the diffractive optical devices can be applied to terminal devices. The terminal device may include K layers of diffractive optical devices in any of the above embodiments and K layers of substrate. The K layers of diffractive optical devices correspond one-to-one with the K layers of substrate. Each layer of diffractive optical devices in the K layers of diffractive optical devices is fixed on the corresponding substrate, and K is a positive integer.

[0230] In one possible implementation, the grating components in different layers of the K layer may respond to the same or different narrowband bands.

[0231] like Figure 15 The diagram shown is a structural schematic of a terminal device provided in this application. The terminal device is exemplified by comprising three layers of diffractive optical components and a three-layer substrate. In this example, the grating components in each of the three layers respond to different narrowband wavelengths, represented by different types of lines. It should be understood that the grating components in the same layer can respond to the same wavelength (e.g., ...). Figure 15 Alternatively, they can be different (see above). Figure 13b ).

[0232] For example, one of these three layers can respond to red-band light, another to green-band light, and the remaining layer to blue-band light. This enables color display. For instance, when the terminal device is an AR or VR device, one of the three layers can respond to red-band light from the color beam of the optical projector and reflect the red-band light in a specific direction in space (e.g., the direction of the area where the human eye is located); another layer can respond to green-band light from the color beam of the optical projector and also reflect the green-band light in that specific direction in space (e.g., the direction of the area where the human eye is located); and the remaining layer can respond to blue-band light from the color beam of the optical projector and also reflect the blue-band light in that specific direction in space (e.g., the direction of the area where the human eye is located). Thus, the image projected onto the human eye by the AR or VR device is a color image; moreover, applying this diffractive optics to the AR or VR device contributes to its miniaturization.

[0233] It should be noted that the incident light can be either parallel or non-parallel. The outgoing light can also be parallel, indicating that the diffractive optical device can collimate multiple incident lights; the outgoing light can also be non-parallel.

[0234] In the various embodiments of this application, unless otherwise specified or in case of logical conflict, the terminology and / or descriptions of different embodiments are consistent and can be referenced by each other. The technical features of different embodiments can be combined to form new embodiments according to their inherent logical relationship.

[0235] In this application, "perpendicular" does not refer to absolute perpendicularity; a certain degree of engineering error is permissible. For example, the aforementioned "the first dimension is perpendicular to the second dimension." "At least one" refers to one or more, while "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple. In the textual description of this application, the character " / " generally indicates an "or" relationship between the preceding and following related objects. In the formulas of this application, the character " / " indicates a "division" relationship between the preceding and following related objects. Additionally, in this application, the term "exemplary" is used to indicate that it is an example, illustration, or description. Any embodiment or design described as "exemplary" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Alternatively, it can be understood that the use of the term "exemplary" is intended to present concepts in a specific manner and does not constitute a limitation on this application. The symbol "(a, b)" represents an open interval, ranging from greater than a to less than b; "[a, b]" represents a closed interval, ranging from greater than or equal to a to less than or equal to b; "(a, b]" represents a half-open interval, ranging from greater than a to less than or equal to b; "(a, b]" represents a half-open interval, ranging from greater than a to less than or equal to b. For example, (0, 90°) represents greater than 0 degrees and less than 90 degrees.

[0236] It is understood that the various numerical designations used in this application are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application. The order of the process numbers described above does not imply the order of execution; the execution order of each process should be determined by its function and inherent logic. Terms such as "first," "second," and similar expressions are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as including a series of steps or units. A method, system, product, or device is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0237] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely illustrative examples of the solutions defined by the appended claims and are to be considered as covering any and all modifications, variations, combinations, or equivalents within the scope of this application.

[0238] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of the invention. Therefore, if these modifications and variations of the embodiments of this application fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.

Claims

1. A diffractive optical device, characterized in that, include: A grating assembly exhibiting a periodic distribution in a first dimension includes N optical waveguides distributed along the first dimension, of which M optical waveguides exhibiting periodic variations in a second dimension, and at least two of the M optical waveguides exhibiting periodic variations in the second dimension have different structures. Wherein, the 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 not greater than N; Among the M optical waveguides that exhibit periodic changes in the second dimension, at least two waveguides have different structures, including any one of the following: Among the M optical waveguides that exhibit periodic changes in the second dimension, at least two optical waveguides exhibit periodic changes in different ways; Among the M optical waveguides that exhibit periodic changes in the second dimension, at least two optical waveguides have different waveguide periods; Among the M optical waveguides that exhibit periodic changes in the second dimension, at least two waveguides have different shapes.

2. The diffractive optical device as described in claim 1, characterized in that, Among the M optical waveguides that exhibit periodic changes in the second dimension, at least one optical waveguide exhibits at least two different waveguide periods.

3. The diffractive optical device as described in claim 2, characterized in that, The optical waveguide exhibits at least two distinct waveguide periods, including any one of the following: The top of the optical waveguide exhibits at least two different waveguide periods; Either of the two sidewalls of the optical waveguide exhibits at least two different waveguide periods; Each sidewall of the optical waveguide exhibits at least one waveguide period, and the waveguide periods of the two sidewalls are different.

4. The diffractive optical device according to any one of claims 1 to 3, characterized in that, The periodic variation of the optical waveguide includes any of the following: The optical waveguide exhibits periodic protrusions or recesses; The optical waveguide exhibits periodic gaps; The optical waveguide includes periodically distributed small holes, which are either hollow or filled with a material with a different refractive index than the material of the optical waveguide. The periodically distributed diffraction structure is in contact with the optical waveguide; The distance between the periodically distributed diffraction structure and the optical waveguide does not exceed a preset distance; The refractive index of the optical waveguide exhibits periodic changes.

5. The diffractive optical device as described in claim 4, characterized in that, The optical waveguide is periodically varied in that it exhibits periodic protrusions or recesses, with the protrusions or recesses located at the top or at least one sidewall of the optical waveguide.

6. The diffractive optical device as described in claim 4, characterized in that, The optical waveguide is periodically varied in that it exhibits periodic gaps, the length of which in the second dimension satisfies the condition that incident light can couple between adjacent portions of the optical waveguide to form a waveguide mode.

7. The diffractive optical device as described in claim 6, characterized in that, The length of the gap in the second dimension is not greater than the center wavelength of the working band.

8. The diffractive optical device as described in claim 4, characterized in that, The angle between the direction of the gap and the first dimension is less than 90 degrees.

9. The diffractive optical device as described in claim 4, characterized in that, The periodic variation of the optical waveguide is as follows: the periodically distributed diffraction structure is in contact with the optical waveguide or the distance between the diffraction structure and the optical waveguide does not exceed a preset distance, and the diffraction structure is in contact with the top or at least one sidewall of the optical waveguide; or, the diffraction structure is located at a position no more than the preset distance from one sidewall of the optical waveguide.

10. The diffractive optical device as described in claim 9, characterized in that, The preset distance between the diffraction structure and the optical waveguide satisfies the condition that the light field formed in the optical waveguide overlaps with the diffraction structure in space.

11. The diffractive optical device as claimed in claim 10, characterized in that, The preset distance between the diffraction structure and the optical waveguide is no greater than the center wavelength of the operating band.

12. The diffractive optical device according to any one of claims 1 to 3, 5 to 11, characterized in that, Among the M optical waveguides that exhibit periodic changes in the second dimension, the waveguides with different structures have different resonant wavelengths for their guided modes.

13. The diffractive optical device according to any one of claims 1 to 3, 5 to 11, characterized in that, The M optical waveguides, which exhibit periodic variations in the second dimension, are used to reflect light in specific wavelength bands.

14. The diffractive optical device according to any one of claims 1 to 3, 5 to 11, characterized in that, The grating period in the first dimension is no greater than 2 micrometers.

15. The diffractive optical device according to any one of claims 1 to 3, 5 to 11, characterized in that, The thickness of each optical waveguide is no greater than 300 nanometers.

16. The diffractive optical device according to any one of claims 1 to 3, 5 to 11, characterized in that, The optical waveguide is made of silicon nitride or titanium dioxide.

17. The diffractive optical device according to any one of claims 1 to 3, 5 to 11, characterized in that, The acute angle formed between any two adjacent optical waveguides in the N optical waveguides shall not be greater than a preset angle.

18. The diffractive optical device according to any one of claims 1 to 3, 5 to 11, characterized in that, The first dimension is perpendicular to the second dimension.

19. A terminal device, characterized in that, It includes at least one diffractive optical device as described in any one of claims 1 to 18, and at least one substrate, wherein one diffractive optical device corresponds to one substrate; Each layer of diffractive optical devices is fixed on its corresponding substrate.

20. The terminal device as described in claim 19, characterized in that, The parameters of the grating components in the diffractive optical device fixed in different regions of the substrate are different, and the parameters of the grating components include the grating period and / or tilt angle.

21. The terminal device as described in claim 19 or 20, characterized in that, The terminal device includes an optical projector, which is used to emit a light beam carrying image information to the diffractive optical device.

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