Design method of metasurface element and projection device

Abstract

The invention discloses a design method of a metasurface element and a projection device. The design method comprises the following steps: determining a collimation phase and a diffraction phase of the metasurface element according to an array light source and a projection dot matrix; superposing the collimation phase and the diffraction phase to obtain a composite phase of the metasurface element, and converting the composite phase into a structure size of the metasurface element; and preparing a metasurface element based on the structure size, changing the defocusing amount by adjusting the axial distance between the array light source and the metasurface element, testing the distribution of the projection dot matrix under different defocusing amount conditions, and determining a target defocusing amount which enables the distribution of the projection dot matrix to meet a preset requirement. By means of the design method of the metasurface element, the energy regulation and control limitation of a conventional level replication method can be broken through, and the energy of all the points of the projection dot matrix can be distributed according to the preset proportion.

Description

Technical Field

[0001] The present application generally relates to the field of optical device technology. More specifically, the present application relates to a design method and projection device for a metasurface element. Background Art

[0002] The direct time-of-flight (dToF) projection module is a core component for realizing 3D sensing, spatial ranging and other fields. It measures distance by projecting a laser dot matrix and detecting the flight time of light. Conventional dToF projection modules usually adopt a combined structure of "collimator + diffraction optical element (DOE)", that is, the divergent light of the light source is first collimated by a collimator, and then the dot matrix is ​​replicated and projected by the DOE. With the increasing demand for miniaturization and high performance, metasurfaces, as an emerging optical element composed of a two-dimensional subwavelength structure, can integrate the collimation and dot matrix replication functions into a single structure by virtue of their multi-dimensional control capabilities over the amplitude, phase, and polarization of electromagnetic waves, thereby reducing the size of the device while optimizing performance.

[0003] However, existing technologies have significant limitations in light source selection and array energy control. When using a single point light source, the target field energy is weak, making it difficult to meet the requirements of long-range or high-resolution detection. When using an array light source to boost energy, existing designs rely on conventional level replication methods, which results in consistent energy distribution at each projection point within the same level. This fails to meet the requirement for a specific energy distribution ratio across the target field.

[0004] In view of this, there is an urgent need to provide a design scheme for metasurface elements so as to realize the integration of collimation and dot matrix replication functions to reduce the size of the device, while being able to enhance the target field energy by adapting the array light source, and breaking through the energy control limitations of conventional hierarchical replication methods, so that the energy of each point of the projection dot matrix can be distributed according to a preset ratio, thereby comprehensively improving the performance adaptability of the dToF projection module. Summary of the Invention

[0005] In order to at least solve one or more of the technical problems mentioned above, the present application proposes a design scheme for a metasurface element in the following aspects.

[0006] In a first aspect, the present application provides a method for designing a metasurface element, comprising: determining a collimation phase and a diffraction phase of the metasurface element based on an array light source and a projection dot matrix; superimposing the collimation phase and the diffraction phase to obtain a composite phase of the metasurface element, and converting the composite phase into a structural dimension of the metasurface element; preparing a metasurface element based on the structural dimension, changing the defocus amount by adjusting the axial spacing between the array light source and the metasurface element, testing the distribution of the projection dot matrix under different defocus conditions, and determining a target defocus amount that makes the distribution of the projection dot matrix meet preset requirements.

[0007] In some embodiments, determining the collimation phase of the metasurface element based on the array light source and the projection dot matrix includes: determining the focal length based on the diagonal length of the array light source and the angular width of a single point of the projection dot matrix; and determining the collimation phase of the metasurface element based on the focal length.

[0008] In some embodiments, the focal length f is determined based on the diagonal length of the array light source and the angular width of a single point of the projection array using the following formula:

[0009] Where D is the diagonal length of the array light source, is the angular width of a single point in the projection array.

[0010] In some embodiments, determining the diffraction phase of the metasurface element based on the array light source and the projection point matrix includes: determining the period of the diffraction phase of the metasurface element based on the vertical distance from the metasurface element to the target projection surface and the coordinate position error of the projection point matrix; and generating the diffraction phase of the metasurface element using an iterative Fourier algorithm with the period as a constraint condition.

[0011] In some embodiments, the period of the diffraction phase of the metasurface element is determined based on the vertical distance from the metasurface element to the target projection surface and the coordinate position error of the projection point array, using the following formula:

[0012] Where P is the period, is the working wavelength, z is the vertical distance from the metasurface element to the target projection surface, is the coordinate position error of the projected point array, , is the coordinate angle error of the projected point array.

[0013] In some embodiments, the axial spacing between the array light source and the metasurface element is adjusted by moving the array light source toward the metasurface element so that the axial spacing between the array light source and the metasurface element is is not equal to the focal length f and is smaller than the focal length f.

[0014] In some embodiments, when adjusting the axial spacing between the array light source and the metasurface element, the beam waist parameter of the projection point array is determined using the following formula: When the array light source is not defocused, the beam waist radius after being collimated by the metasurface element is satisfy:

[0015] in, is the working wavelength, is the focal length, is the beam waist radius of the array light source, and the beam waist is located at the image focus of the metasurface element.

[0016] In some embodiments, the method further comprises: When the array light source is defocused, the beam waist radius after being collimated by the metasurface element is satisfy:

[0017] Waist position satisfy:

[0018] in, is the Rayleigh distance of the array light source, and the array light source is processed as a Gaussian light source.

[0019] In some embodiments, the distribution of the projection point array includes spatial distribution and energy distribution; the spatial distribution is uniform distribution in angle space, uniform distribution in K space, or distribution with staggered positions between each row; the energy distribution is uniform distribution or distribution that meets a preset energy ratio.

[0020] In a second aspect, the present application provides a projection device, comprising: an array light source configured to provide light energy for generating a projection dot matrix; a metasurface element, the metasurface element being obtained by the design method of the metasurface element described in the first aspect and multiple embodiments, and being configured to collimate the output light of the array light source and replicate the projection dot matrix; and a substrate configured to carry the metasurface element.

[0021] Through the design scheme of the metasurface element provided above, the embodiment of the present application realizes the integration of collimation and lattice replication functions by superimposing the collimation phase and the diffraction phase, without the need for an additional collimating lens, reducing the system complexity and reducing the device volume; at the same time, by adopting a defocus design, the axial spacing between the array light source and the metasurface element is adjusted so that each sub-light source is fused into a single point that meets the requirements after passing through the metasurface structure, effectively avoiding the problem of consistent energy of the replicated light sources within the same level in conventional lattice replication, adapting the array light source to enhance the target field energy, and enabling the energy of each point of the projection lattice to be distributed according to a preset ratio, thereby comprehensively improving the performance adaptability of the dToF projection module. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of the exemplary embodiments of the present application will become readily understood by reading the detailed description below with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present application are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein: Figure 1 An exemplary flow chart of a design method of a metasurface element of the present application is shown; Figure 2 A schematic diagram showing that the projection point array is uniformly distributed in the angular space; Figure 3 A schematic diagram showing a projected dot matrix with staggered distribution between each row is shown; Figure 4 A schematic diagram showing the geometric structure of a unit structure of a metasurface element of the present application is shown; Figure 5 A schematic diagram showing the transmittance and phase response curve of the present application is shown; Figure 6 shows an exemplary structural schematic diagram of a conventional projection device; Figure 7 shows an exemplary structural diagram of the projection device provided by the present application; Figure 8 A schematic diagram of the light-emitting point distribution of a VCSEL light source is shown; Figure 9 shows a schematic diagram of the collimation phase implemented in this application; Figure 10 shows a schematic diagram of the diffraction phase implemented in this application; Figure 11 A schematic diagram showing the unit structure distribution of the metasurface element according to an embodiment of the present application is shown; Figure 12 The figure shows the distribution diagram of the projected dot matrix when the VCSEL light source is located at the object focus of the collimated phase according to the embodiment of the present application; Figure 13 Shown Figure 12 An enlarged schematic diagram of the distribution of the projected dot matrix; Figure 14 The figure shows the distribution of the projected dot matrix when the VCSEL light source is out of focus according to an embodiment of the present application. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0024] It should be understood that the terms "include" and "comprising" used in the description and claims of this application indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0025] It should also be understood that the terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. As used in this specification and claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should also be further understood that the term "and / or" as used in this specification and claims refers to any and all possible combinations of one or more of the associated listed items, including and including these combinations.

[0026] As used in this specification and claims, the term “if” can be interpreted as “when” or “upon” or “in response to determining” or “in response to detecting,” depending on the context. Similarly, the phrase “if it is determined” or “if [described condition or event] is detected” can be interpreted as meaning “upon determination” or “in response to determining” or “upon detection of [described condition or event]” or “in response to detecting [described condition or event],” depending on the context.

[0027] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0028] The specific implementation of the present application will be described in detail below with reference to the accompanying drawings.

[0029] Figure 1 FIG1 shows an exemplary flow chart of a design method 100 of a metasurface element of the present application. It is understood that the method 100 can be executed by any appropriate device with data processing capabilities, such as but not limited to a terminal device and a server.

[0030] like Figure 1 As shown, at step S101, the collimation phase and diffraction phase of the metasurface element can be determined according to the array light source and the projection point matrix.

[0031] The array light source can be a vertical cavity surface emitting laser (VCSEL) light source, which includes multiple sub-light sources (also called multiple light-emitting points) to provide light energy for generating a projection dot matrix. The output light of the VCSEL light source is generally divergent light with a divergence angle of approximately 20 to 30 degrees, and the light source has a random polarization characteristic. In addition, in dToF applications, since it is mainly in the near-infrared band, the operating wavelength of the VCSEL light source is preferably 850nm or 940nm.

[0032] The projection dot matrix is ​​a structured light distribution formed in the target field after the output light of the array light source is regulated by the metasurface element. Generally, the distribution of the projection dot matrix can include spatial distribution and energy distribution. The spatial distribution can be a uniform distribution in the angular space (such as Figure 2 As shown), uniform distribution in K space or staggered distribution between each row (as shown Figure 3 As shown); the energy distribution can be uniform or meet a preset energy ratio distribution.

[0033] The metasurface element includes multiple unit structures, and the unit structure can be a cylindrical structure (such as Figure 4 As shown in the middle left picture), square column structure (such as Figure 4 The C4 symmetry refers to the fact that a unit structure completely overlaps with the original structure after being rotated 90 degrees about its central axis. Because such C4-symmetric structures exhibit consistent phase control responses to incident light of different polarization directions (such as horizontal polarization, vertical polarization, and linear polarization at any angle), metasurface elements employing such structures can make projection devices polarization-insensitive. This ensures that even when the polarization state of the incident light changes, the light field can still be stably collimated and the lattice replication can be controlled, ensuring that the distribution accuracy and energy characteristics of the projection lattice are not affected by polarization.

[0034] In the embodiments of the present application, the phase of the metasurface element satisfies: (1) Among them, mod is the remainder function, is the collimation phase, which is used to collimate the divergent light of the VCSEL light source. is the diffraction phase, used for lattice replication, It is the superposition of the collimation phase and the diffraction phase, which realizes the functions of collimation and lattice replication.

[0035] Based on this, in step S102, the collimated phase and the diffraction phase can be superimposed to obtain the composite phase of the metasurface element, and then the composite phase is converted into the structural size of the metasurface element.

[0036] In the embodiments of this application, a metasurface element modulates its phase response by varying the lateral dimensions (e.g., radius) of its unit structures, with the phase response covering a range of 2π. Consequently, the correspondence between the lateral dimensions (e.g., radius) and phase of a unit structure can be exploited to convert the composite phase into the structural dimensions of the metasurface element. Specifically, each composite phase in the composite phase is converted into the lateral dimensions (e.g., radius) of each unit structure, enabling the metasurface element to precisely control the phase of the light field.

[0037] It is understood that when converting the composite phase into the structural dimensions of a metasurface element using the correspondence between the radius and phase of the unit structure, it is also necessary to consider whether the light transmittance corresponding to the lateral dimension (e.g., radius) meets a preset condition. Typically, this preset condition is a transmittance greater than 80% and less than or equal to 100%.

[0038] Based on this, the transmittance and phase response curves can be obtained by scanning using a strict coupling algorithm, such as Figure 5 As shown. Figure 5 In the figure, the horizontal axis represents radius, the left vertical axis represents transmittance, and the right vertical axis represents phase. The upper and lower curves represent the transmittance curve and the phase response curve, respectively. As can be seen from the figure, the phase axis ranges from 0 to 8, meaning that the phase response range covers 2π. Furthermore, the transmittance curve is always greater than 80% and less than or equal to 100%, meeting the preset conditions.

[0039] In step S103, a metasurface element can be prepared based on the structural dimensions determined in step S102, and then the defocus amount can be changed by adjusting the axial spacing between the array light source and the metasurface element. The distribution of the projected dot matrix under different defocus conditions can be tested to determine the target defocus amount that makes the distribution of the projected dot matrix meet the preset requirements.

[0040] In the embodiments of the present application, in order to achieve the fusion of the light emitted by each sub-light source in the array light source into a single point that meets the preset requirements in the target field after being regulated by the metasurface element, a targeted defocus design is required. The defocus design can break the fixed order constraint of the light field diffraction in conventional order replication, avoid the problem of energy distribution consistency caused by the diffraction spots corresponding to each sub-light source being focused on the same focal plane, and ensure that the light field after phase regulation by the metasurface element is accurately fused into a specific point of the projection dot matrix on the target projection surface, thereby solving the technical limitation of the traditional method of replicating the consistent energy of the light source within the same order, and providing a basis for the proportional distribution of energy at each point in the projection dot matrix. Furthermore, in order to shorten the overall device length of the dToF projection module to adapt to the needs of miniaturized applications, the present application adopts a defocus adjustment method of moving the array light source toward the direction of the metasurface element. Specifically, when adjusting the axial distance between the array light source and the metasurface element in step S103, by controlling the array light source to move toward the metasurface element, that is, controlling the array light source to approach the metasurface element, the actual axial distance between the two is adjusted. is not equal to the focal length f of the metasurface element when it is working, and satisfies This design actively reduces the axial distance between the light source and the metasurface element, effectively compressing the axial space occupied by the device while achieving the defocusing function, taking into account the dual requirements of light field fusion effect and structural compactness. When the array light source is not out of focus (i.e. the array light source is located at the object focal plane, ), the beam waist radius after collimation by the metasurface element satisfy: (2) in, is the working wavelength, is the focal length of the metasurface element when it is working, is the beam waist radius of the array light source, which is located at the image-side focus of the metasurface element.

[0041] In the case of defocused array light source, the axial distance between the array light source and the metasurface element is shortened by moving the array light source closer to the metasurface element. , at this time the beam waist radius after collimation by the metasurface element is satisfy: (3) in, is the Rayleigh distance of the array light source. This formula (3) clearly reflects the relationship between the beam waist radius and the axial spacing, focal length and Rayleigh distance in the defocused state. By adjusting the axial spacing The beam waist radius can be flexibly adjusted to provide a quantitative basis for the control of the optoelectronic capabilities of the target field.

[0042] At the same time, the beam waist position after being regulated by the metasurface element changes dynamically with the defocus state. Here, the array light source is treated as a Gaussian light source, and the beam waist position after the metasurface element satisfy: (4) The formula (4) clearly describes the relationship between the beam waist position and the axial spacing, focal length and Rayleigh distance. When , formula (4) returns to the non-defocused beam waist at the image side focus ( ), which verifies the consistency of the formula.

[0043] Through the application of the above-mentioned defocus design and quantization formula, this application not only realizes the precise fusion of the sub-light source light field, but also effectively compresses the device length by shortening the axial spacing between the array light source and the metasurface element, taking into account the dual technical goals of light field control accuracy and structural compactness.

[0044] In the aforementioned step S101, the following operations can be further performed to determine the collimation phase of the metasurface element based on the array light source and the projection dot matrix: the focal length is determined based on the diagonal length of the array light source and the angular width of a single point of the projection dot matrix; and the collimation phase of the metasurface element is determined based on the focal length.

[0045] Specifically, the focal length f is determined based on the diagonal length of the array light source and the angular width of a single point of the projection array, and the following formula can be used: (5) Where D is the diagonal length of the array light source, It is the angular width of a single point in the projected array, usually 1° or 2°.

[0046] Next, the collimation phase can be determined using the following formula: : (6) in, is the operating wavelength of the metasurface element, r is the distance between the unit structure and the center of the metasurface element, is a constant, and f is the focal length of the metasurface element when it is working.

[0047] Alternatively, in another optional embodiment of the present application, the following formula can also be used to determine the collimation phase:

[0048] (7) Among them, the projection matrix includes A dot matrix, is the operating wavelength of the metasurface element, is the phase coefficient, r is the distance between the unit structure and the center of the metasurface element, is a constant.

[0049] The above-mentioned method of directly calculating the collimation phase using formula (6) or (7) is particularly suitable for scenarios with clear theoretical models and well-defined design parameters. In another optional embodiment of the present application, the collimation phase can also be optimized and calculated using optical design software. This method is based on an iterative algorithm, using the target field characteristics (such as collimation and energy distribution) as constraints, and continuously adjusting the phase parameters to obtain the optimal solution.

[0050] In contrast, using optical design software to optimize the collimation phase can more fully consider non-ideal factors in practical applications (such as the divergence angle of the light source, manufacturing errors, etc.), thereby obtaining better collimation performance and light field control effects, and is therefore the preferred embodiment of this application.

[0051] In an embodiment of the present application, the aforementioned diffraction phase has a periodic characteristic in spatial distribution. Therefore, in the aforementioned step S101, the following operations can be further performed to determine the diffraction phase of the metasurface element based on the array light source and the projection lattice: the period of the diffraction phase of the metasurface element is determined based on the vertical distance between the metasurface element and the target projection surface and the coordinate position error of the projection lattice; and the diffraction phase of the metasurface element is generated using an iterative Fourier algorithm, such as the GS algorithm, with the period as a constraint. This ensures the accuracy of the diffraction phase and ensures that the diffraction phase replicates the lattice of the light source.

[0052] Specifically, the period of the diffraction phase of the metasurface element is determined based on the vertical distance from the metasurface element to the target projection surface and the coordinate position error of the projection point array. The following formula can be used: (8) Where P is the period, is the working wavelength, z is the vertical distance from the metasurface element to the target projection surface, is the coordinate position error of the projected point array, , is the coordinate angle error of the projected point array.

[0053] From the perspective of diffraction optics, the period of the diffraction phase directly affects the spatial distribution characteristics of the diffracted light field: if the period P is too small, the interference superposition effect between the diffraction orders will be enhanced, which will easily cause the projection point to produce an offset error beyond the allowable range on the target projection surface; and when When the period parameters are properly designed, the coordinate deviation caused by the diffraction effect can be controlled within Within, thereby ensuring that the spatial distribution of the projection point array is consistent with the theoretical preset, and improving the ranging accuracy and three-dimensional imaging stability of the dToF projection module.

[0054] The iterative Fourier algorithm (IFTA) is an iterative optimization method based on Fourier transform. It gradually approaches the phase distribution that meets the target light field requirements by alternately applying intensity constraints between the object plane and the diffraction plane and repeatedly performing Fourier transform and inverse transform. In the design of projection lattice, this algorithm breaks through the limitation of conventional order replication methods that rely on the inherent energy distribution law of diffraction orders. In traditional order replication, the energy of replicated light sources within the same order usually tends to be consistent and difficult to flexibly control. However, IFTA can accurately control the energy weight of each projection point by independently modulating the diffraction order of each sub-light source during the iterative process. For example, it can set the amplitude distribution of different sub-light sources on the object plane or specify the energy ratio of each projection point on the diffraction plane, so that the energy of each point in the projection lattice can be distributed according to the preset ratio to meet the diverse light field control needs.

[0055] In summary, the design method of the metasurface element provided in the present application realizes the integration of collimation and dot matrix replication functions by superimposing the collimation phase and the diffraction phase, without the need for an additional collimating lens, reducing the system complexity and reducing the device volume; at the same time, by adopting a defocus design, the axial spacing between the array light source and the metasurface element is adjusted so that each sub-light source is fused into a single point that meets the requirements after passing through the metasurface structure, effectively avoiding the problem of consistent energy of the replicated light sources within the same level in conventional dot matrix replication, adapting the array light source to enhance the target field energy, and enabling the energy of each point of the projection dot matrix to be distributed according to a preset ratio, thereby comprehensively improving the performance adaptability of the dToF projection module.

[0056] As an example, Figure 6 The schematic diagram shows an exemplary structure of a conventional projection device, which is arranged in sequence along the optical axis with a diffractive optical element (DOE), a second lens (Lens2), a first lens (Lens1), and a vertical cavity surface emitting laser (VCSEL light source). The DOE is used to diffract and split the light field to form a target dot matrix; Lens1 and Lens2, as traditional optical lenses, respectively perform optical modulation functions such as collimation and focusing. Conventional projection devices rely on a discrete component combination architecture of "DOE + multiple lenses" to achieve light field projection through the optical collaboration of these components. As a result, they have the technical characteristics of a large number of components, high assembly complexity, and large axial dimensions.

[0057] Figure 7 FIG. 1 shows an exemplary structural diagram of the projection device 700 provided in this application. Figure 7As shown, the projection device 700 includes an array light source 701, a metasurface element 702, and a substrate 703. The array light source 701 is configured to provide light energy for generating a projection dot matrix, the metasurface element 702 is configured to collimate the output light of the array light source 701 and replicate the projection dot matrix, and the substrate 703 is configured to support the metasurface element 702. In an embodiment of the present application, the array light source 701 can be a vertical cavity surface emitting laser (VCSEL light source), which includes multiple sub-light sources. The output light of the array light source 701 is generally divergent light with a divergence angle of approximately 20 to 30 degrees, and the light source has a random polarization characteristic.

[0058] The substrate 703 is preferably a glass substrate, a common type of which is Schott D263T. When the substrate is D263T, the unit structure material of the metasurface element 702 is amorphous silicon (aSi). At an operating wavelength of 940nm, the refractive index of the D263T substrate is 1.5137, and the refractive index of the aSi unit material is 3.6.

[0059] The metasurface element 702 is obtained by the above-mentioned metasurface element design method, that is, the metasurface element in the projection device of the present application is the same as the metasurface element in the above-mentioned method. Regarding the structure and parameter limitations of the metasurface element, please refer to the description in the above-mentioned method, which will not be repeated here.

[0060] Based on the phase control properties of subwavelength micro-nanostructures, metasurface element 702 integrates the optical functions of traditional DOEs and multiple lenses (such as collimation, diffraction beam splitting, and wavefront shaping). This allows for integrated control of the light field emitted by an array light source to form a target dot matrix. Compared to conventional projection devices, the projection device provided in this application replaces the traditional multi-element combination with a single element, achieving a minimalist design. This device offers significant advantages such as a reduced number of components, a short axial length, and a high level of integration, making it more suitable for applications such as dToF (direct time of flight) that require stringent device miniaturization.

[0061] The following further describes examples of design methods for projection devices and metasurface elements applicable to the above-mentioned embodiments with reference to the accompanying drawings. It should be noted that the following embodiments are applicable to all embodiments of the present application. Figures 1 to 7 The described features may similarly apply to the embodiments described below.

[0062] In this embodiment, the unit structure of the metasurface element adopts the above-mentioned Figure 4The cylindrical structure shown in the center left image operates at a wavelength of 940nm and is polarization-insensitive. The substrate beneath the unit cell is D263T, and the unit cell is made of sSi. At a wavelength of 940nm, the refractive index of the D263T substrate is 1.5137, while the refractive index of the aSi unit cell is 3.6.

[0063] Furthermore, the period of the unit structure is selected to be 400nm, the cylinder height is 550nm, and the radius scanning range is 40~150nm. The phase response of the unit structure within this parameter range is scanned using the strict coupled wave algorithm, and the corresponding relationship between the radius and phase of the unit structure is obtained, that is, the phase response curve is as mentioned above. Figure 5 As shown. Figure 5 It can be seen that the obtained phase response curve can cover the phase difference range of 0 to 2π, meeting the phase control requirements of metasurface elements.

[0064] The array light source used in this embodiment is a VCSEL light source. Figure 8 As shown, the VCSEL light source has a total of 12 light-emitting points, and the overall size of the light source is 85×82um 2 The projection matrix is ​​as mentioned above. Figure 3 The staggered dot matrix shown has a horizontal field of view of 100° and a vertical field of view of 80°. The angular width of a single point of the projected dot matrix is ​​2°, and the coordinate angle error is less than ±1°.

[0065] Next, the design method of the metasurface element in this embodiment is described: (1) Using the above formula (5), that is, , the minimum focal length f is calculated to be about 3.4mm. Then the collimation phase is obtained by optimizing the calculation using optical design software. ,like Figure 9 shown.

[0066] (2) Determine the diffraction phase based on the coordinate distribution of the projected point array The corresponding minimum period P is 53.8 μm. Furthermore, the period P can be set to 55 μm, and the maximum angle error is calculated to be 0.79°, which meets the coordinate angle error requirement of the projection dot matrix (less than ±1°).

[0067] (3) Determine the diffraction phase After the corresponding minimum period P, the diffraction phase is obtained using the iterative Fourier algorithm. ,like Figure 10 shown.

[0068] (4) Collimation phase and diffraction phase Composite phase , and combined with the corresponding relationship between the unit structure radius and phase of the metasurface element (as mentioned above Figure 5 As shown in ), the unit structure distribution diagram of the metasurface element is finally generated (as shown in Figure 11 As shown, due to the large size of the structure, only a partial area is shown in the figure. As can be seen from Figure 11, the projections of each unit structure on the substrate are all circular, that is, the cross-sectional shape of each unit structure parallel to the substrate is circular, and at least some of the unit structures have different radii.

[0069] (5) When the VCSEL light source is located at the object focus of the collimated phase, the projection effect is simulated to obtain the distribution diagram of the projection dot matrix as shown in the figure. Figure 12 and Figure 13 As shown, Figure 13 is the distribution diagram of the projected dot matrix after magnification. Figure 12 and Figure 13 It can be seen that due to the lack of defocus design, different light-emitting points in the VCSEL light source appear separated in the target field after being controlled by the metasurface element, and cannot form a single fusion point that meets the requirements. Therefore, a defocus design needs to be introduced.

[0070] When defocusing, the VCSEL light source is moved toward the metasurface element to achieve defocusing. After adjustment, the axial distance between the VCSEL light source and the metasurface element is reduced to 3.2 mm (less than the focal length of the collimated phase, 3.4 mm). At this time, according to the above formula (3), the waist radius of the Gaussian beam collimated by the metasurface element increases after defocusing, so that the originally separated light points are merged into a single point that meets the requirements in the target field, as shown in Figure 3. Figure 14 At the same time, the overall axial length of the device is shortened by 0.2mm compared to the non-defocused solution, taking into account both the light field fusion effect and the compact structure.

[0071] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects: (1) Based on the phase control characteristics of subwavelength micro-nanostructures, metasurface elements can simultaneously realize the collimated wavefront modulation and diffraction beam splitting functions of the incident light, without the need for additional collimating lenses, and directly control the VCSEL output light to the target projection dot matrix. This integrated design significantly reduces the number of components and assembly difficulty of the system, while effectively reducing the axial volume of the device, providing a structural foundation for the miniaturization of dToF projection modules.

[0072] (2) This application breaks the fixed energy distribution constraint of the diffraction order through the phase control and defocus design of the metasurface element, so that the energy of the single point after fusion in the target field can be flexibly adjusted according to demand, solving the problem of consistent energy of the replicated light source within the same order in conventional dot matrix replication.

[0073] (3) By adopting a defocusing method of moving the array light source toward the metasurface element, the light-emitting points of the array light source can be fused together during projection to form a single point that meets the requirements. At the same time, the shortening of the distance between the array light source and the metasurface element directly compresses the axial space occupied by the device and reduces the overall length of the device.

[0074] Although multiple embodiments of the present application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Those skilled in the art can conceive of many changes, modifications, and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein can be adopted. The accompanying claims are intended to define the scope of protection of the present application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A method for designing a metasurface element, characterized in that: include: Determining the collimation phase and diffraction phase of the metasurface element according to the array light source and the projection point matrix; Superimposing the collimated phase and the diffraction phase to obtain a composite phase of the metasurface element, and converting the composite phase into a structural size of the metasurface element; A metasurface element is prepared based on the structural dimensions, and the defocus amount is changed by adjusting the axial spacing between the array light source and the metasurface element. The distribution of the projected point array under different defocus conditions is tested to determine the target defocus amount that makes the distribution of the projected point array meet the preset requirements.

2. The design method according to claim 1, characterized in that: Determining the collimation phase of the metasurface element according to the array light source and the projection dot matrix includes: The focal length is determined based on the diagonal length of the array light source and the angular width of a single point of the projection array; Based on the focal length, a collimation phase of the metasurface element is determined.

3. The design method according to claim 2, characterized in that: The focal length f is determined based on the diagonal length of the array light source and the angular width of a single point of the projection array using the following formula: Where D is the diagonal length of the array light source, is the angular width of a single point in the projection array.

4. The design method according to claim 1, characterized in that: Determining the diffraction phase of the metasurface element according to the array light source and the projection dot matrix includes: Determining a period of the diffraction phase of the metasurface element according to a vertical distance from the metasurface element to a target projection surface and a coordinate position error of the projection point array; Taking the period as a constraint, an iterative Fourier algorithm is used to generate the diffraction phase of the metasurface element.

5. The design method according to claim 4, characterized in that: The period of the diffraction phase of the metasurface element is determined according to the vertical distance from the metasurface element to the target projection surface and the coordinate position error of the projection point array, using the following formula: Where P is the period, is the working wavelength, z is the vertical distance from the metasurface element to the target projection surface, is the coordinate position error of the projected point array, , is the coordinate angle error of the projected point array.

6. The design method according to claim 2, characterized in that: Adjusting the axial distance between the array light source and the metasurface element is achieved by moving the array light source toward the metasurface element so that the axial distance between the array light source and the metasurface element is is not equal to the focal length f and is smaller than the focal length f.

7. The design method according to claim 6, characterized in that: When adjusting the axial spacing between the array light source and the metasurface element, the beam waist parameter of the projection point array is determined using the following formula: When the array light source is not defocused, the beam waist radius after being collimated by the metasurface element is satisfy: in, is the working wavelength, is the focal length, is the beam waist radius of the array light source, and the beam waist is located at the image focus of the metasurface element.

8. The design method according to claim 7, characterized in that: Also includes: When the array light source is defocused, the beam waist radius after being collimated by the metasurface element is satisfy: Waist position satisfy: in, is the Rayleigh distance of the array light source, and the array light source is processed as a Gaussian light source.

9. The design method according to any one of claims 1 to 8, characterized in that: The distribution of the projection point array includes spatial distribution and energy distribution; the spatial distribution is uniform distribution in angle space, uniform distribution in K space, or distribution with staggered positions between each row; the energy distribution is uniform distribution or distribution that meets a preset energy ratio.

10. A projection device, characterized in that: include: an array light source configured to provide light energy for generating a projection dot array; A metasurface element, obtained by the metasurface element design method according to any one of claims 1 to 9, configured to collimate the outgoing light of the array light source and replicate the projected dot matrix; A substrate is configured to carry the metasurface element.

Images