Metasurface and dodging device

Abstract

The invention discloses a metasurface and a dodging device. The metasurface is obtained through the following steps that the repetition period of the metasurface and the energy proportion of the corresponding diffraction order under the repetition period are determined; determining the phase distribution of the metasurface, and mapping each phase value in the phase distribution into the transverse size of the corresponding unit structure; building a physical model of the metasurface based on the repetition period of the metasurface, the energy ratio of the corresponding diffraction order and the transverse size of each unit structure; and performing diffraction verification on the physical model to obtain the actual diffraction efficiency of each diffraction order, and performing convolution operation on the energy distribution corresponding to the actual diffraction efficiency of each diffraction order and the far-field light field of the light source array at the target surface to obtain an output light field meeting the distribution requirement of the target light field at the target surface. By means of the method, the efficient and accurate light uniformizing effect can be achieved, and the requirements of related application fields are met.

Description

Technical Field

[0001] This application generally relates to the field of optical device technology. More specifically, this application relates to a metasurface. Furthermore, this application also relates to a light homogenizing device. Background Technology

[0002] Beam homogenization devices are widely used in time-of-flight (ToF) ranging, facial recognition, automotive radar, head-up displays, and other fields. In existing technologies, beam homogenization devices often employ microlens arrays to achieve uniform light field distribution, with their microstructure units typically arranged in periodic or random arrays. Meanwhile, metasurfaces, as a rapidly developing emerging optical element in recent years, consist of two-dimensionally arranged subwavelength structures and possess the ability to freely control the amplitude, phase, and polarization of electromagnetic waves in multiple dimensions, providing a new direction for the design of beam homogenization devices.

[0003] However, existing technologies still have many problems in practical applications. On the one hand, when the target field of view is greater than 120°, the light homogenizing device using a microlens array faces two key problems. First, the aspect ratio of a single microlens will exceed 1 and the maximum tilt angle of the surface will be greater than 65°. Due to the limited detection capabilities of current market-available inspection equipment, the surface shape cannot be effectively iterated during the manufacturing process. Second, when the microlens structure surface is used as the light emission surface, due to the large maximum tilt angle of the surface shape, some of the light incident on the structure surface will be greater than the total internal reflection angle, causing the light to be reflected multiple times inside the light homogenizing device and unable to exit from the preset angle. This results in a decrease in the efficiency of the light homogenizing device and uncontrolled beam quality. On the other hand, the design method of diffractive homogenizing devices generally adopts the iterative Fourier algorithm. The phase distribution obtained by this algorithm has many jumps, which will lead to many speckles in the projected light field. At the same time, for vertical cavity surface-emitting laser (VCSEL) light sources, if the target light field is directly used as the target field for the iterative Fourier algorithm, the size of the homogenizing device obtained by the final optimization is often large, usually reaching the millimeter level, which cannot be verified by vector simulation, and may lead to a large deviation between the design results and the actual situation.

[0004] In view of this, this application provides a design scheme for a light homogenizing device to achieve efficient and accurate light homogenization effect and meet the needs of related application fields. Summary of the Invention

[0005] In order to at least solve one or more of the technical problems mentioned above, this application proposes a design scheme for a light-shielding device in the following aspects.

[0006] In a first aspect, this application provides a metasurface, which is obtained through the following operations: determining the repetition period of the metasurface and the energy proportion of the corresponding diffraction order under the repetition period according to the specifications of the light source array and the distribution requirements of the target light field on the target surface; determining the phase distribution of the metasurface based on the distribution requirements of the target light field, and mapping each phase value in the phase distribution to the lateral dimension of the corresponding unit structure; building a physical model of the metasurface based on the repetition period of the metasurface, the energy proportion of the corresponding diffraction order, and the lateral dimension of each unit structure; performing diffraction verification on the physical model to obtain the actual diffraction efficiency of each diffraction order, and performing convolution operation between the energy distribution corresponding to the actual diffraction efficiency of each diffraction order and the far-field light field of the light source array at the target surface to obtain an output light field at the target surface that meets the distribution requirements of the target light field.

[0007] In some implementations, the specifications include the center wavelength, divergence angle, and size of the emitting region; the distribution requirements include the shape of the light field, energy distribution, maximum size, and distance between the target surface and the metasurface; the energy distribution is either a uniform distribution or a distribution with a specific energy ratio.

[0008] In some implementations, determining the repetition period of the metasurface includes: determining the maximum diffraction angle of the target light field at the target surface based on the distribution requirements of the target light field; determining the theoretical minimum value of the repetition period based on the maximum diffraction angle, the center wavelength and diffraction order of the light source array, and the grating equation; determining the range of values ​​for the repetition period based on the theoretical minimum value and the maximum lateral dimension of each unit structure; selecting a value from the range as the final repetition period, and verifying through projection simulation that the diffraction order corresponding to the final repetition period covers the maximum size of the target light field.

[0009] In some implementations, determining the energy percentage of the corresponding diffraction order includes: determining the diffraction angle corresponding to each diffraction order based on the repetition period and the center wavelength of the light source array, combined with the grating equation; and determining the energy percentage corresponding to each diffraction order based on the diffraction angle corresponding to each diffraction order, combined with the energy compensation rule.

[0010] In some implementations, when the energy distribution of the target light field is uniform, the energy compensation rule is expressed as the following formula:

[0011] in, The diffraction angle corresponding to the diffraction order. This represents the relative energy percentage of the diffraction orders. It is the adjustment coefficient, and The value range is [1, 2].

[0012] In some embodiments, the transmittance function of the metasurface is expressed by the following formula:

[0013] in, Let P and Q be the number of periods of the metasurface in the x and y directions, respectively, and M and N be the sampling resolution of the metasurface in the x and y directions, respectively. and These are the sampling unit sizes in the x and y directions, respectively; It is the transmittance function within a single repetition cycle.

[0014] In some implementations, the transmittance function within a single repetition cycle Expressed using the following formula:

[0015] in, Let be the complex amplitude transmittance sampling function of the metasurface. Let be the amplitude modulation function of the (n,m)th sampling cell of the metasurface. Let be the phase modulation amount of the (n,m)th sampling unit of the metasurface. It is a rectangular window function for a single unit structure of a metasurface, used to characterize the spatial extent of a single unit structure.

[0016] In some embodiments, the light field of the light source array at the metasurface is represented by the following formula:

[0017] in, and Let be a rectangular function, representing the range of the light-emitting region of the light source array on the metasurface. Let be the waist radius of the light source array at the metasurface. It is a Gaussian function, which characterizes the attenuation characteristics of the light field intensity of the light source along the x and y directions; This represents the initial phase term of the light field from the light source. This is the initial phase.

[0018] In some embodiments, the output light field after the light field of the light source is modulated by the metasurface is expressed by the following formula: ;as well as For the output light field Performing a Fourier transform yields:

[0019] in, , , and They are , , and Fourier transform; The convolution operation describes the superposition of the periodic structural response of the metasurface and the light field of the source in the frequency domain, ultimately yielding the frequency domain distribution of the output light field.

[0020] In a second aspect, this application provides a light homogenizing device, comprising: a light source array configured to provide incident light for a target light field; a metasurface obtained by the operations described in any of the first aspects and implementations thereof, configured to perform phase and amplitude modulation on the emitted light from the light source array to split the light according to a specific diffraction order and regulate the energy distribution; and a substrate configured to support the metasurface.

[0021] Through the above-described design scheme of the homogenizing device, this embodiment of the application determines the repetition period of the metasurface and the energy proportion of the corresponding diffraction order under the repetition period based on the specifications of the light source array and the distribution requirements of the target light field on the target surface, so that the diffraction order matches the target light field. At the same time, combined with the divergence angle of the array light source itself, the discrete diffraction orders can be fused together to finally achieve the homogenizing effect. Relying on the characteristics of periodic design, a periodic metasurface structure can be obtained, avoiding the problem of excessive size caused by non-periodic structures. At the same time, the physical model of the constructed metasurface is verified and simulated by using vector design software to determine the energy proportion of each diffraction order and the overall efficiency, which can ensure the consistency between the design results and the actual situation. In addition, the periodic design is adapted to the planar structure characteristics of the metasurface, and the surface processing does not require complex curved surface forming process, making the operation easier to implement. It can also ensure that the incident light rays are emitted at a preset angle, avoiding energy loss due to total internal reflection and maintaining the homogenizing efficiency and beam quality stability. These design advantages work together to enable this method to further meet the application requirements of efficient and accurate homogenization in fields such as ToF ranging, face recognition, automotive radar, and head-up display. Attached Figure Description

[0022] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein: Figure 1 An exemplary flowchart illustrating the operation process for obtaining a metasurface according to an embodiment of this application is shown; Figure 2 A geometrical schematic diagram of the unit structure according to an embodiment of this application is shown; Figure 3 A schematic diagram of the phase response curve of an embodiment of this application is shown; Figure 4 An exemplary structural diagram of a light-diffusing device constructed using a microlens array is shown; Figure 5 An exemplary structural diagram of a light-uniforming device constructed using a metasurface, according to an embodiment of this application, is shown. Figure 6 This paper shows a schematic diagram of the light-emitting point distribution of the VCSEL light source according to an embodiment of this application; Figure 7 This paper shows a schematic diagram of the light intensity distribution of the VCSEL light source at z=1m according to an embodiment of this application. Figure 8 A schematic diagram of the distribution of the target light field on the target surface according to an embodiment of this application is shown; Figure 9 A schematic diagram of the light spot projection effect at z=1m for a certain tilt level is shown; Figure 10 This paper shows a schematic diagram of the distribution of the target light field at z=1m in an embodiment of this application. Figure 11 This paper illustrates a schematic diagram of the convolution results between each diffraction order and the light spot projected from the light source in an embodiment of this application. Figure 12 A schematic diagram of the phase distribution within a single repetition period according to an embodiment of this application is shown; Figure 13 A schematic diagram of the unit structure distribution of the metasurface according to an embodiment of this application is shown; Figure 14 A schematic diagram of the homogenization effect corresponding to the actual diffraction efficiency of an embodiment of this application is shown. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

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

[0025] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the 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 understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0026] As used in this specification and claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [described condition or event] is detected," or "in response to detection of [described condition or event]."

[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 one of ordinary skill in the art to which this application pertains.

[0028] The specific embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0029] Figure 1 An exemplary flowchart of the operation process 100 for obtaining a metasurface according to this application is shown. It will be understood that the operation process 100 can be performed by any suitable device with data processing capabilities, such as including but not limited to terminal devices and servers.

[0030] like Figure 1 As shown, in step S101, the repetition period of the metasurface and the energy percentage of the corresponding diffraction order under the repetition period can be determined according to the specifications of the light source array and the distribution requirements of the target light field on the target surface.

[0031] The light source array can be a vertical-cavity surface-emitting laser (VCSEL) source, comprising multiple sub-sources (also referred to as multiple emission points) to provide incident light for generating the target light field. The emitted light from a VCSEL source is divergent, with a divergence angle typically in the range of 20–30°, and possesses random polarization characteristics, allowing it to adapt to most applications without additional polarization control components. Furthermore, in applications such as Time-of-Flight (ToF) ranging, facial recognition, automotive radar, and head-up displays, where near-infrared light signals are often relied upon to reduce ambient light interference, the preferred operating wavelength for the VCSEL source is 850 nm or 940 nm. Additionally, the specifications of the light source array may include, but are not limited to, the center wavelength, divergence angle, and emission region size; these parameters directly affect the diffraction order and energy distribution design of the metasurface.

[0032] The target surface is directly related to the application scenario. For example, in Time-of-Flight (ToF) ranging, the target surface corresponds to the surface of the object being measured; in face recognition, the target surface corresponds to the plane where the face is located; and in automotive radar, the target surface corresponds to the reference plane of the detection area. The design of the metasurface aims to form a light field on the target surface that meets the specific requirements, which is the core focus of design method 100.

[0033] The distribution requirements of the target light field can include, but are not limited to, the shape of the light field, energy distribution, maximum size, and the distance between the target surface and the metasurface. The shape of the light field can be any shape such as rectangle, square, triangle, circle, trapezoid, etc., to adapt to the light spot coverage requirements of different scenarios. The energy distribution can be uniform or a specific energy ratio distribution. Uniform distribution meets the general light uniformity requirements, while a specific energy ratio distribution is suitable for customized energy distribution scenarios (such as high energy in key areas). The maximum size and the distance between the target surface are directly related to the diffraction coverage of the metasurface to ensure that the light field can completely cover the target surface.

[0034] Metasurfaces consist of multiple unit structures, which can be arranged in a square or hexagonal mesh, with equal spacing between any two adjacent unit structures. This spacing is defined as the arrangement period of the unit structures. In practical applications, the unit structures can be cylindrical (e.g., ...). Figure 2 As shown in the middle left figure), a square column structure (such as...) Figure 2 (As shown in the middle right figure) or other geometric configurations with C4 symmetry. C4 symmetry means that the unit structure completely coincides with the original structure after rotating 90 degrees around its central axis. Because such C4-symmetric structures have a consistent phase modulation response to different polarization directions of incident light (such as horizontal polarization, vertical polarization, and linear polarization at arbitrary angles), metasurfaces using this type of structure can enable homogenizing devices to possess polarization insensitivity characteristics. This ensures that the phase and amplitude modulation of the light field can still be stably achieved when the polarization state of the incident light changes, guaranteeing that the homogenizing effect is not affected by polarization.

[0035] On a metasurface, multiple unit structures can form a combined structure. The metasurface contains multiple such combined structures, and the spacing between any two adjacent combined structures is equal. This spacing is defined as the repetition period of the combined structure, i.e., the metasurface repetition period referred to in this application. To adapt to a wider range of application scenarios such as large field-of-view detection (e.g., automotive radar scenarios with a target field of view greater than 120°) and long-distance optical field manipulation (e.g., target surface distances of several meters to tens of meters in ToF ranging), while taking into account the feasibility of existing micro-nano fabrication processes and the efficiency and accuracy of vector simulation, this application sets the value range of the metasurface repetition period to generally between tens of micrometers and 200 μm. This range can satisfy the full coverage of diffraction orders under large field of view, and can avoid the problem of excessively long simulation time or increased fabrication difficulty caused by excessively large periods.

[0036] Specifically, the repetition period of the metasurface can be determined by the following steps: First, based on the distribution requirements of the target light field, determine the maximum diffraction angle of the target light field at the target surface. This angle directly determines the diffraction coverage of the metasurface, ensuring that the light field can cover the entire target surface. Second, based on the maximum diffraction angle, the center wavelength of the light source array, and the diffraction order, determine the theoretical minimum value of the repetition period in conjunction with the grating equation. Then, based on the theoretical minimum value and the maximum lateral dimension of each unit structure, determine the range of values ​​for the repetition period to avoid overlap of unit structures during the arrangement process. Finally, select a value from the range as the final repetition period, and verify through projection simulation that the diffraction order corresponding to the final repetition period covers the maximum size of the target light field, ensuring that no area of ​​the light field is missed.

[0037] Furthermore, the corresponding diffraction order refers to the diffraction order that matches the target light field distribution requirements, i.e., the diffracted light of each order that can work together to form the target light field, such as ±1st order, ±2nd order, etc., specifically determined based on the target field of view and center wavelength, rather than all possible diffraction orders generated by the metasurface. Further, the energy proportion of the corresponding diffraction order can be determined by performing the following operations: first, based on the repetition period and the center wavelength of the light source array, and combined with the grating equation, determine the diffraction angle corresponding to each diffraction order; then, based on the diffraction angle corresponding to each diffraction order, and combined with the energy compensation rule, determine the energy proportion corresponding to each diffraction order, ensuring that the light field energy distribution of the target surface meets the preset requirements.

[0038] To compensate for the decrease in illuminance caused by the increased projected area in large-angle diffraction orders, the energy of each diffraction order corresponding to the metasurface needs to be compensated. Furthermore, the energy compensation rule varies depending on the energy distribution of the target light field. In one example, when the energy distribution of the target light field is uniform, the energy compensation rule is expressed as the following formula: (1) in, The diffraction angle corresponding to the diffraction order. This represents the relative energy percentage of the diffraction orders. It is the adjustment coefficient, and The value range is [1, 2]. By adjusting... It can accurately match the illumination compensation needs of different angles.

[0039] In another example, when the energy distribution of the target light field is a specific energy ratio distribution, the energy compensation rule needs to be determined according to the preset diffraction angle-energy ratio mapping relationship: First, clarify the energy ratio requirements of different regions of the target light field (e.g., 40% energy ratio in the central region and 60% energy ratio in the edge region). Then, according to the diffraction angles corresponding to different regions of the target surface, allocate the energy ratio of each diffraction order through a custom compensation formula or lookup table method, so that the energy of each diffraction order, after convolution operation, forms a preset specific energy ratio distribution on the target surface. For example, for the key detection area of ​​automotive radar, the energy ratio of the corresponding diffraction order in that area can be increased to enhance the detection sensitivity.

[0040] In practical applications, in addition to determining the repetition period of the metasurface and the energy percentage of the corresponding diffraction order under that repetition period, it is also possible to further determine the arrangement period, height and radius scanning range of the unit structure, as well as the number of periods and sampling resolution of the metasurface in the x and y directions.

[0041] Specifically, the arrangement period, height, and radius scanning range of the unit structure can be determined based on the geometric configuration of the unit structure (such as cylindrical or square prism), the phase control range, and the processing accuracy requirements. At the same time, based on the maximum size of the target light field, the metasurface repetition period, and the sampling accuracy requirements, the number of periods and sampling resolution of the metasurface in the x and y directions can be determined to ensure that the metasurface structure can accurately characterize the detailed features of the target light field.

[0042] Next, in step S102, based on the distribution requirements of the target light field, the phase distribution of the metasurface can be determined by an iterative Fourier transform algorithm. This algorithm optimizes the frequency domain and spatial domain light fields through multiple iterations, gradually reducing the deviation between the calculated light field and the target light field, ensuring that the phase distribution can accurately invert the target light field. Then, according to the lateral dimension-phase response relationship of the metasurface unit structure, each phase value in the phase distribution is mapped to the lateral dimension of the corresponding unit structure, realizing the direct conversion from phase requirements to structural parameters, and providing a structural basis for the physical realization of the metasurface.

[0043] In this application, the metasurface modulates its phase response by changing the lateral dimensions (such as the radius) of its unit structures, and the range of this phase response must cover 2π. Therefore, by utilizing the correspondence between the lateral dimensions (such as the radius) of the unit structures and the phase, the phase distribution of the metasurface can be converted into the structural dimensions of the metasurface, that is, each phase value in the phase distribution is mapped to the corresponding lateral dimension (such as the radius) of the unit structure, thereby enabling the metasurface to precisely achieve phase modulation of the light field of the light source.

[0044] Understandably, when converting the phase distribution into the structural dimensions of a metasurface 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 dimensions (such as the radius) meets the preset requirements. Typically, this preset requirement is a transmittance greater than 80% and less than or equal to 100%.

[0045] Based on this, the phase response curve can be obtained by scanning using a strictly coupled algorithm, such as... Figure 3 As shown. In Figure 3 In the graph, the horizontal axis represents the radius, the left vertical axis represents transmittance, and the right vertical axis represents the phase. The upper and lower curves in the graph are the transmittance curve and the phase response curve, respectively. As can be seen from the graph, the phase vertical axis ranges from 0 to 8, meaning the phase response can cover a range of 2π. Simultaneously, the transmittance value is always greater than 80% and less than or equal to 100%, thus meeting the preset requirements.

[0046] In step S103, a physical model of the metasurface can be built based on the repeating period of the metasurface, the energy proportion of the corresponding diffraction orders, and the lateral dimensions of each unit structure. This physical model needs to completely reproduce the periodic arrangement of the metasurface, the geometric parameters (such as radius and height) of the unit structures, and the energy distribution constraints to ensure that the model can truly reflect the physical properties and optical response of the metasurface, providing a reliable simulation object for subsequent diffraction verification and performance evaluation.

[0047] In step S104, electromagnetic simulation, such as the finite-time difference method (FDTD), can be used to perform diffraction verification on the physical model to obtain the actual diffraction efficiency of each diffraction order. Then, the energy distribution corresponding to the actual diffraction efficiency of each diffraction order is convolved with the far-field light field of the light source array at the target surface. By superimposing the light field contributions of each diffraction order through convolution, the output light field at the target surface that meets the distribution requirements of the target light field is finally obtained, thus completing the closed-loop verification of the metasurface design.

[0048] In this application, the transmittance function of the metasurface can be expressed by the following formula: (2) in, Let P and Q be the number of periods of the metasurface in the x and y directions, respectively, and M and N be the sampling resolution of the metasurface in the x and y directions, respectively. and These are the sampling unit sizes in the x and y directions, respectively; The transmittance function within a single repetition cycle describes the amplitude and phase modulation characteristics of a single composite structure for incident light.

[0049] Transmittance function within a single repetition cycle This can be expressed using the following formula: (3) in, Let be the complex amplitude transmittance sampling function of the metasurface. Let be the amplitude modulation function of the (n,m)th sampling cell of the metasurface. Let be the phase modulation amount of the (n,m)th sampling unit of the metasurface. It is a rectangular window function for a single unit structure of a metasurface, used to define the spatial extent of a single unit structure and ensure that there is no overlap between unit structures.

[0050] Furthermore, the light field of the light source array at the metasurface can be expressed by the following formula: (4) in, and Let be a rectangular function, representing the range of the light-emitting region of the light source array on the metasurface. Let be the waist radius of the light source array at the metasurface. It is a Gaussian function, which characterizes the attenuation characteristics of the light field intensity of the light source along the x and y directions; This represents the initial phase term of the light field from the light source. The initial phase is usually set based on the characteristics of the light source itself.

[0051] Based on this, the output light field of the light source after being modulated by the metasurface can be expressed by the following formula: (5) Formula (5) directly reflects the combined modulation effect of the metasurface transmittance function on the amplitude and phase of the light field of the source, generating a preliminary modulated light field; at the same time, it affects the output light field. Performing a Fourier transform yields: (6) in, , , and They are , , and Fourier transform; This represents the convolution operation, which describes the superposition of the periodic structural response of the metasurface and the light field of the source in the frequency domain, ultimately yielding the frequency domain distribution of the output light field. This facilitates intuitive analysis of the frequency domain characteristics and energy proportions of each diffraction order.

[0052] The above combination Figures 1 to 3 This application describes the process of obtaining a metasurface. In this process, based on the specifications of the light source array and the distribution requirements of the target light field on the target surface, the repetition period of the metasurface and the energy proportion of the corresponding diffraction orders within that repetition period are determined, ensuring that the diffraction orders match the target light field. Simultaneously, by combining the divergence angle of the array light source itself, the discrete diffraction orders can be fused together, ultimately achieving a uniform light effect. The repetition period of the metasurface ranges from tens of micrometers to 200 micrometers. Leveraging the characteristics of small-period design, a periodic metasurface structure can be obtained, avoiding the excessively large size problem caused by aperiodic structures. The vector design software performs diffraction verification and simulation on the constructed metasurface physical model, determining the energy proportion of each diffraction order and the overall efficiency, ensuring the consistency between the design results and the actual situation. In addition, the periodic design adapts to the planar structural characteristics of the metasurface, eliminating the need for complex curved surface forming processes in surface machining, making the operation easier to implement, and ensuring that the incident light rays exit at a preset angle, avoiding energy loss due to total internal reflection, and maintaining stable beam homogenization efficiency and beam quality. These design advantages work together to enable this method to further meet the application requirements of efficient and accurate beam homogenization in fields such as ToF ranging, face recognition, automotive radar, and head-up displays.

[0053] Next, combine Figure 4 and Figure 5 This application provides a detailed description of the light-diffusing device. Figure 4 A light-diffusing device 400 constructed using a microlens array is shown. Figure 5 This illustrates the light homogenizing device 500 constructed using a metasurface, as provided in this application.

[0054] like Figure 4 As shown, the light homogenizing device 400 includes a light source array 401 for providing incident light, a microlens array 402 for modulating the phase and amplitude of the outgoing light from the light source array 401, and a substrate 403 for supporting the microlens array 402.

[0055] Depend on Figure 4As can be seen, the microlens array 402 has a curved structure, and its surface processing requires a complex curved surface forming process. Therefore, in practical applications, when the target field of view is greater than 120°, the homogenizing device 400 faces two key problems: First, the aspect ratio of a single microlens will exceed 1, and the maximum tilt angle of the surface will be greater than 65°. Due to the limited detection capabilities of currently available inspection equipment, the surface shape cannot be effectively iterated during the manufacturing process. Second, when the microlens structure surface is used as the light emission surface, due to the large maximum tilt angle of the surface, some of the light incident on the structure surface will be greater than the total internal reflection angle, causing the light to be reflected multiple times inside the homogenizing device and unable to exit from the preset angle. This results in a decrease in the efficiency of the homogenizing device and difficulty in effectively controlling the beam quality.

[0056] The homogenizing device 500 comprises a light source array 501, a metasurface 502, and a substrate 503. The light source array 501 is configured to provide incident light for the target light field. The metasurface 502 is configured to modulate the phase and amplitude of the outgoing light from the light source array 501, thereby achieving beam splitting according to a specific diffraction order and controlling the energy distribution. The substrate 503 supports the metasurface 502. It can be understood that the metasurface 502 is formed by combining the above-described components... Figures 1 to 3 The metasurface was designed using the method described above, and will not be elaborated further here.

[0057] Depend on Figure 5 As can be seen, metasurfaces possess planar structural characteristics, eliminating the need for complex curved surface forming processes in their fabrication, making operation easier. Furthermore, they ensure that incident light rays exit at a predetermined angle, avoiding energy loss due to total internal reflection and maintaining stable beam homogenization efficiency and quality. Simultaneously, utilizing the aforementioned... Figures 1 to 3 The metasurface 502 designed using the described metasurface design method has a diffraction order that matches the target light field. Combined with the divergence angle of the array light source, it can fuse discrete diffraction orders together, ultimately achieving a uniform light effect. The repetition period of the metasurface ranges from tens of micrometers to 200 micrometers. Leveraging the characteristics of small-period design, a periodic metasurface structure can be obtained, avoiding the excessive size problem caused by aperiodic structures. Furthermore, the physical model of the constructed metasurface is verified and simulated using vector design software to determine the energy proportion of each diffraction order and the overall efficiency, ensuring consistency between the design results and actual conditions. These design advantages work together to enable the uniform light device 500 to further meet the application requirements of efficient and precise uniform light in fields such as ToF ranging, facial recognition, automotive radar, and head-up displays.

[0058] The following description, with reference to the accompanying drawings, further illustrates examples of the light-diffusing device applicable to the above embodiments and the operation process for obtaining metasurfaces. It should be noted that the following embodiments are applicable to all embodiments of this application. Therefore, the foregoing description, in conjunction with... Figures 1 to 5The described features can be similarly applied to the following embodiments.

[0059] In this embodiment, the metasurface unit structure adopts the method described above. Figure 2 The cylindrical structure shown in the middle left figure operates at a wavelength of 940 nm and exhibits polarization insensitivity. The substrate beneath the unit structure is D263T, and the unit structure itself is made of sSi. At a wavelength of 940 nm, the refractive index of the D263T substrate is 1.5137, while the refractive index of the aSi unit material is 3.6.

[0060] Furthermore, the period of the unit cell structure was selected to be 400 nm, the cylinder height to be 550 nm, and the radius scan range to be 40–150 nm. The phase response of the unit cell structure within this parameter range was scanned using a rigorous coupled-wave algorithm, and the resulting relationship between the radius and phase of the unit cell structure (i.e., the phase response curve) is as described above. Figure 3 As shown. By Figure 3 It can be seen that the obtained phase response curve can cover the phase difference range of 0 to 2π, which meets the phase control requirements of metasurface.

[0061] The light source array used in this embodiment is a VCSEL light source. For example... Figure 6 As shown, the VCSEL light source has 12 emission points, and the overall size of the light source is 85×82um². Its light intensity distribution at the target surface at z=1m is as follows. Figure 7 As shown. The distribution of the target light field on the target surface is as follows. Figure 8 As shown, the target light field has a square shape that is biased into a triangle, a uniform energy distribution, and a diffraction angle exceeding 80° in the positive y-axis direction.

[0062] The following describes the operation process for obtaining the metasurface in this embodiment: (1) Based on the specifications of the light source array and the distribution requirements of the target light field on the target surface, the repetition period of the metasurface and the energy ratio of the corresponding diffraction order under the repetition period are determined. Specifically, in this embodiment, the repetition period is selected as 50 μm.

[0063] Understandably, to avoid optical field cracks after convolution operations on the energy distribution of each diffraction order, the repetition period of the metasurface should not be too small, and its rationality needs to be confirmed through projection simulation. During the projection simulation, the effect of tilted projection needs to be considered: when the projection angle is large, the projected area of ​​the light on the target surface will increase accordingly, leading to a decrease in local energy density. However, the homogenizing device designed using the method of this application will naturally form a relatively smooth transition zone at the projection edge. Figure 9 This diagram illustrates the light spot projection effect at z=1m for a certain tilt level. Figure 9It can be seen that the relatively gentle transition zone naturally formed at the edge of the projection matches the edge requirements of the target light field, which can ensure the continuity and integrity of the overall light field.

[0064] Subsequently, for those located in triangles (such as...) Figure 10 The diffraction orders inside triangle A1B1C1 shown in the figure are used for selection. Figure 10 It can be seen that at this point, each diffraction order is in a lattice state, and the diffraction angles of each diffraction order are different. Convolving these diffraction orders with the corresponding light spots projected by the light source (i.e., the far-field light field of the light source array on the target surface) yields the following result: Figure 11 As shown. To compensate for the decrease in illuminance caused by the increased projected area in large-angle diffraction orders, an adjustment coefficient r of 1.25 was selected in the energy compensation rule. Therefore, the energy at the vertex of the triangle can be seen to be relatively strong.

[0065] (2) After determining the repetition period of the metasurface and the energy proportion of the corresponding diffraction orders under that repetition period, the phase distribution of the metasurface is determined based on the distribution requirements of the target light field. The phase distribution of the metasurface homogenizer within a single repetition period is as follows: Figure 12 As shown, then, using Figure 3 The correspondence between the radius and phase of the unit structure is used to map each phase value in the phase distribution to the lateral dimension of the corresponding unit structure.

[0066] (3) Based on the repetition period of the metasurface, the energy ratio of the corresponding diffraction order, and the lateral dimensions of each unit structure, a physical model of the metasurface is constructed. Figure 13 A schematic diagram of the metasurface's unit cell structure distribution is shown; due to the large size of the structure, only a local area is displayed in the diagram. Figure 13 It can be seen that the projection of each unit structure onto the substrate is circular, that is, the cross-sectional shape of each unit structure along the substrate is circular, and at least some unit structures have different radii.

[0067] (4) The finite-difference time-domain method is used to perform diffraction verification on the physical model to obtain the actual diffraction efficiency of each diffraction order. The energy distribution corresponding to the actual diffraction efficiency of each diffraction order is then convolved with the projected light spot of the light source to obtain the output light field at the target surface that meets the distribution requirements of the target light field, such as... Figure 14 As shown. By Figure 14 It can be seen that the output light field successfully presents an offset triangle that matches the shape of the target light field (as shown in Figure 8), and the energy distribution within the triangle region is uniform. The energy of the large-angle diffraction regions, such as the vertices of the triangle, is also effectively enhanced due to the compensation rule. The overall light field meets the design expectations.

[0068] As can be seen from the above description, the embodiments of this application achieve the following technical effects: (1) Since the metasurface has a planar structure, the problem of the slope being too large to process in the microlens will not occur, which reduces the difficulty of the process and improves the feasibility of processing.

[0069] (2) Because the metasurface has a planar structure, it avoids the situation where some light rays cannot be emitted due to total internal reflection in the microlens homogenizing device, thus reducing energy loss and ensuring homogenizing efficiency and beam quality.

[0070] (3) Since the metasurface has a periodic structure, the relative installation position between the VCSEL light source and the metasurface homogenizing device does not require special high precision, which reduces the assembly difficulty and cost.

[0071] (4) The energy distribution of uniform light can be optimized by controlling the energy distribution of diffraction order. Compared with traditional methods, it is more flexible and convenient and can more accurately match the needs of different target light fields.

[0072] It should be understood that the structure or architecture described above is merely exemplary, and the implementation methods and entities of this application are not limited thereto, but can be modified without departing from the spirit of this application. It is understood that the description of the various embodiments in this disclosure emphasizes the differences between the various embodiments, and their similarities or corresponding parts can be referred to mutually. For the purpose of brevity, this disclosure will not elaborate on each one.

[0073] It should be noted that although the operations of the method of this application are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. On the contrary, the steps depicted in the flowchart can be performed in a different order. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0074] While numerous embodiments of this 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. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A metasurface, characterized in that, The metasurface is obtained through the following operations: Based on the specifications of the light source array and the distribution requirements of the target light field on the target surface, the repetition period of the metasurface and the energy proportion of the corresponding diffraction order under that repetition period are determined. Based on the distribution requirements of the target light field, the phase distribution of the metasurface is determined, and each phase value in the phase distribution is mapped to the lateral dimension of the corresponding unit structure. Based on the repetition period of the metasurface, the energy ratio of the corresponding diffraction order, and the lateral dimensions of each unit structure, a physical model of the metasurface is constructed. The physical model is subjected to diffraction verification to obtain the actual diffraction efficiency of each diffraction order. The energy distribution corresponding to the actual diffraction efficiency of each diffraction order is then convolved with the far-field light field of the light source array at the target surface to obtain the output light field at the target surface that meets the distribution requirements of the target light field.

2. The metasurface according to claim 1, characterized in that, The specifications include the center wavelength, divergence angle, and size of the emitting region; the distribution requirements include the shape of the light field, energy distribution, maximum size, and distance between the target surface and the metasurface; the energy distribution is either uniform or a specific energy ratio distribution.

3. The metasurface according to claim 1, characterized in that, Determining the repetition period of a metasurface includes: Based on the distribution requirements of the target light field, determine the maximum diffraction angle of the target light field at the target surface; Based on the maximum diffraction angle and the center wavelength and diffraction order of the light source array, the theoretical minimum value of the repetition period is determined by combining the grating equation. Based on the theoretical minimum value and the maximum lateral dimension of each unit structure, the range of values ​​for the repetition period is determined; A value is selected from the range of values ​​as the final repetition period, and the maximum size of the target light field covered by the diffraction order corresponding to the final repetition period is verified by projection simulation.

4. The metasurface according to claim 1, characterized in that, Determining the energy percentage of the corresponding diffraction order includes: Based on the repetition period and the center wavelength of the light source array, the diffraction angle corresponding to each diffraction order is determined by combining the grating equation. Based on the diffraction angles corresponding to each diffraction order and in conjunction with the energy compensation rule, the energy percentage corresponding to each diffraction order is determined.

5. The metasurface according to claim 4, characterized in that, When the energy distribution of the target light field is uniform, the energy compensation rule is expressed as the following formula: in, The diffraction angle corresponding to the diffraction order. This represents the relative energy percentage of the diffraction orders. It is the adjustment coefficient, and The value range is [1, 2].

6. The metasurface according to claim 1, characterized in that, The transmittance function of the metasurface is expressed by the following formula: in, Let P and Q be the number of periods of the metasurface in the x and y directions, respectively, and M and N be the sampling resolution of the metasurface in the x and y directions, respectively. and These are the sampling unit sizes in the x and y directions, respectively; It is the transmittance function within a single repetition cycle.

7. The metasurface according to claim 6, characterized in that, Transmittance function within a single repetition cycle Expressed using the following formula: in, Let be the complex amplitude transmittance sampling function of the metasurface. Let be the amplitude modulation function of the (n,m)th sampling cell of the metasurface. Let be the phase modulation amount of the (n,m)th sampling unit of the metasurface. It is a rectangular window function for a single unit structure of a metasurface, used to characterize the spatial extent of a single unit structure.

8. The metasurface according to claim 7, characterized in that, The light field of the light source array at the metasurface is expressed by the following formula: in, and Let be a rectangular function, representing the range of the light-emitting region of the light source array on the metasurface. Let be the waist radius of the light source array at the metasurface. It is a Gaussian function, which characterizes the attenuation characteristics of the light field intensity of the light source along the x and y directions; This represents the initial phase term of the light field from the light source. This is the initial phase.

9. The metasurface according to claim 8, characterized in that, The output light field of the light source after being modulated by the metasurface is expressed by the following formula: ; as well as For the output light field Performing a Fourier transform yields: in, , , and They are , , and Fourier transform; This represents the convolution operation, which describes the superposition of the periodic structural response of the metasurface and the light field of the source in the frequency domain, ultimately yielding the frequency domain distribution of the output light field.

10. A light-uniforming device, characterized in that, include: A light source array configured to provide incident light for the target light field; A metasurface, obtained by the operation of any one of claims 1 to 9, is configured to modulate the phase and amplitude of the emitted light from the light source array to split the light according to a specific diffraction order and regulate the energy distribution; A substrate, which is configured to support the metasurface.

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