Three-dimensional optical focus regulation and control device, optical system and augmented reality display equipment

Abstract

The invention discloses a three-dimensional optical focus regulation and control device, and relates to the technical field of micro-nano optics. The three cascaded metasurfaces are arranged to be capable of relatively rotating and moving, and the three metasurfaces have the synergistically designed phase distribution functions, so that decoupling control of axial focus change and transverse focus offset is realized. Specifically, a complementary rotation pair is formed by a second metasurface and a third metasurface, and the relative rotation of the second metasurface and the third metasurface is used for adjusting an axial focus and inhibiting aberration (such as coma and astigmatism) introduced by a lateral offset term at the same time; the relative rotation of the first metasurface and the second metasurface mainly regulates and controls an angular phase item to realize the lateral offset of a focus; due to the fact that the phase function is designed to be separable in angular modulation and radial modulation, controlled focuses can transversely move and axially move through different rotation pairs, and independence of the two control modes, namely decoupling regulation and control, is achieved.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optics technology, and in particular to a three-dimensional optical focus control device and its application in optical systems and augmented reality display devices. Background Technology

[0002] Dynamic control of optical focus in three-dimensional space is a core requirement of many modern optical systems, such as in microscopy, laser processing, optical capture, and especially augmented reality (AR) near-eye displays. In AR displays, the human eye's convergence and focus need to be matched; otherwise, visual fatigue and discomfort will occur, a phenomenon known as Vergence-Accommodation Conflict (VAC). One key to solving the VAC problem is the ability to dynamically adjust the focus to generate virtual images of different depths.

[0003] Traditional optical zoom and focus scanning largely rely on mechanical actuation, such as changing the focus by moving lens groups or using galvanometers for lateral scanning. Traditional methods suffer from large size, slow response speed, high power consumption, and difficulty in stable operation in miniaturized systems. Mechanically-free solutions, such as liquid crystal lenses or electrowetting lenses, while reducing size, often face challenges such as small aperture, narrow operating wavelength, polarization sensitivity, and large aberrations. Diffractive optical elements incorporating metasurfaces can precisely control the amplitude, phase, and polarization of light waves through subwavelength arrays. However, single metasurfaces typically have fixed functions, making dynamic focus control difficult. In recent years, methods have emerged that use the relative rotation of multiple metasurfaces to introduce dynamic phase modulation for focus control, such as based on the Moiré effect.

[0004] However, existing solutions have made progress in achieving a single function (such as axial zoom only or lateral deflection only), and it is difficult to achieve independent and continuous control of axial focus and lateral position in a single optical device at the same time, nor can it achieve decoupled control of axial focus change and lateral focus shift. Summary of the Invention

[0005] The main objective of this invention is to propose a three-dimensional optical focus control device, which aims to solve the technical problems of existing three-dimensional optical control devices being unable to simultaneously achieve independent and continuous control of the axial focus and lateral position, as well as the lack of decoupled control of axial focus change and lateral focus offset.

[0006] To achieve the above objectives, this invention proposes a three-dimensional optical focus control device, comprising a first metasurface element, a second metasurface element, and a third metasurface element arranged in cascades and rotatable relative to each other. The phase distribution functions of the first, second, and third metasurface elements are configured in polar coordinates as follows: the phase distribution function of the first metasurface element includes an angular modulation term; the phase distribution function of the second metasurface element includes radial and angular modulation terms; and the phase distribution function of the third metasurface element includes terms complementary to the radial and angular modulation terms of the second metasurface element. When the second and third metasurface elements rotate relative to each other, the three-dimensional optical focus control device generates an axial focus change. When the first and second metasurface elements rotate relative to each other, the three-dimensional optical focus control device generates a lateral focus shift. The lateral focus shift and the axial focus change are decoupled through the phase distribution functions.

[0007] Preferably, the phase distribution function is as follows: The phase distribution function of the first metasurface element is: ; The phase distribution function of the second metasurface element is: ; The phase distribution function of the third metasurface element is: .

[0008] Preferably, the first metasurface element, the second metasurface element, and the third metasurface element are all composed of a subwavelength nanostructure array, and the nanostructure is a polarization-independent structure.

[0009] Preferably, the nanostructure is made of a high-refractive-index dielectric material, including titanium dioxide, gallium nitride, or silicon nitride.

[0010] Preferably, the overall optical thickness of the device is less than 2 mm.

[0011] Preferably, the three metasurface elements are integrated on different layers of the same substrate, or are disposed on different independent substrates.

[0012] An optical system comprising the aforementioned three-dimensional optical focus control device.

[0013] Preferably, the optical system is one of a near-eye display system, a microscopic imaging system, an optical capture system, a laser processing system, or a three-dimensional projection system.

[0014] An augmented reality display device includes the aforementioned three-dimensional optical focus control device; it also includes an image source; wherein the three-dimensional optical focus control device is configured to receive light from the image source and perform wavefront modulation on the light to generate a virtual image whose position can be dynamically adjusted in three-dimensional space, thereby alleviating convergence-focusing conflict.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves decoupled control of axial focus change and lateral focus shift by configuring three cascaded metasurfaces capable of relative rotational motion, and by having a cooperatively designed phase distribution function for the three metasurfaces. Specifically, the second and third metasurfaces form a complementary rotation pair, and their relative rotation is used to adjust the axial focus while simultaneously suppressing aberrations (such as coma and astigmatism) introduced by the lateral shift term. The relative rotation of the first and second metasurfaces mainly modulates the angular phase term, achieving lateral focus shift. Since the phase function is designed so that angular modulation and radial modulation are separable, the lateral and axial focus movements controlled by different rotation pairs achieve independence between the two control modes, i.e., decoupled control.

[0016] Based on decoupled control, this invention enables continuous and dynamic positioning of the focal point in three-dimensional space within a compact optical device, breaking through the volume and speed limitations of traditional optical focal point control.

[0017] When applied to augmented reality display devices, the 3D optical focus control device can dynamically adjust the depth and lateral position of the virtual image to produce a virtual image whose position can be dynamically adjusted in 3D space, effectively alleviating convergence-focus conflict (VAC) and expanding the eye-tracking range (Eyebox), significantly improving the user experience. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0019] Figure 1 This is a schematic diagram of the structure of a three-dimensional optical focus control device provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the phase distribution function of three metasurfaces provided in an embodiment of the present invention; Figure 3 This is a theoretical and experimental curve of the axial focal length of the device as a function of rotation angle provided in an embodiment of the present invention, as well as a schematic diagram of the light field intensity distribution under different focal lengths; Figure 4 This is an experimental verification diagram of the lateral focus shift of the device provided in an embodiment of the present invention at a fixed focal length.

[0020] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0022] Implementation 1 This embodiment provides a three-dimensional optical focus control device.

[0023] In this embodiment, as Figure 1 and Figure 2 As shown, the three-dimensional optical focus control device includes a first metasurface element (metasurface 1), a second metasurface element (metasurface 2), and a third metasurface element (metasurface 3) arranged in sequence and rotatable relative to each other. The phase distribution functions of the first, second, and third metasurface elements are configured in polar coordinates as follows: the phase distribution function of the first metasurface element includes an angular modulation term; the phase distribution function of the second metasurface element includes a radial modulation term and an angular modulation term; and the phase distribution function of the third metasurface element includes a term complementary to the radial and angular modulation terms of the second metasurface element. When the second and third metasurface elements rotate relative to each other, the three-dimensional optical focus control device generates an axial focus change; when the first and second metasurface elements rotate relative to each other, the three-dimensional optical focus control device generates a lateral focus shift. The lateral focus shift and the axial focus change are decoupled through the phase distribution function.

[0024] Specifically, this invention configures three cascaded metasurfaces to rotate relative to each other, with the three metasurfaces having a cooperatively designed phase distribution function. The second and third metasurface elements form a complementary rotation pair (containing equal-amplitude, opposite parabolic and linear prism terms). The phase distribution function of the second metasurface element includes radial and angular modulation terms, while the phase distribution function of the third metasurface element includes terms complementary to the radial and angular modulation terms of the second metasurface element. Their relative rotation is used to adjust the axial focus and simultaneously suppress aberrations (such as coma and astigmatism) introduced by the lateral shift term. The phase distribution function of the first metasurface element includes an angular modulation term, allowing the relative rotation of the first and second metasurfaces to modulate the angular phase term, achieving lateral shift of the focus. Because the phase function is designed so that angular and radial modulation are separable, the lateral and axial movement of the focus controlled by different rotation pairs achieves independence of the two control modes, i.e., decoupled control.

[0025] Based on decoupled control, this invention enables continuous and dynamic positioning of the focal point in three-dimensional space within a compact optical device, breaking through the volume and speed limitations of traditional optical focal point control.

[0026] In this embodiment, the phase distribution function of the first metasurface element can be expressed as: Formula (1); The phase distribution function of the second metasurface element can be expressed as: Formula (2); The phase distribution function of the third metasurface element can be expressed as: Formula (3); In formulas (1)~(3): These are polar radial and angular coordinates, respectively; It is a constant.

[0027] In this embodiment, the structure of the three cascaded metasurface elements and their respective phase functions are designed in a coordinated manner: the second and third metasurface elements form a complementary pair (containing parabolic terms and linear prism terms of equal amplitude and opposite direction), and the equivalent focal length formed during relative rotation is continuously adjustable. Simultaneously, the tilting of the principal ray and astigmatism introduced by the lateral offset term are suppressed, ensuring image quality stability during axial zoom; the angular coupling term of the first metasurface element... Then with the second piece A separable angular-radial coupling pair is formed, which makes the lateral focus offset and axial focus adjustment approximately orthogonal and do not interfere with each other under small-angle rotation, thereby achieving continuous and controllable three-dimensional (axial focus and lateral position offset) decoupling.

[0028] Assumption , , Rotated clockwise relative to the reference angle (initial angle) , , The final transmission equation is: Formula (4); The phase distribution of the first metasurface element, the second metasurface element, and the third metasurface element can be adjusted by adjusting parameters a, c, etc. to achieve different minimum focal lengths and lateral offset ranges.

[0029] In this embodiment, as Figure 1 As shown, the overall diameter of the device can be 1 mm and the spacing can be 300 μm, which facilitates miniaturization and integration.

[0030] In this embodiment, the first metasurface element, the second metasurface element, and the third metasurface element are respectively mounted on three rotating platforms to achieve rotation control, and the step angle of the rotating platforms is controlled by the processing of the optical system in which they are located.

[0031] In this embodiment, as Figure 3As shown in Table 1, by adjusting the relative rotation angles between the first, second, and third metasurface elements, the focal length can be continuously adjusted from a few millimeters to tens of millimeters, and the focal position can be flexibly shifted in the lateral plane. The dynamic eye-tracking range can be expanded according to specific design parameters to meet the observation needs of different users.

[0032] In this embodiment, the nominal operating wavelength is 532 nm (achromatic processing is not performed here). By adjusting the relative rotation angle between each metasurface element, the equivalent focal length along the optical axis can be continuously adjusted from a few millimeters to tens of millimeters, and the focal position can be flexibly shifted in the lateral plane; the dynamic eye-tracking range can be expanded according to the design parameters to meet the observation needs of different users.

[0033] Meanwhile, to verify the focal length tuning capability along the optical axis (z-axis), the first and second metasurface elements can be fixed, while only the third metasurface element is rotated relative to its initial angle within the range of 0–360°, and 12 sets of scanning light field data can be acquired in 30° increments. For example... Figure 3 As shown in Figure a, the red dots represent experimental results, the green curve represents theoretical predictions, and the blue dots represent the working efficiency of the three-dimensional optical focus control device. The working efficiency of the three-dimensional optical focus control device is defined as the ratio of incident light power to total incident light power within the focal region. The focal region is defined by the isointense line where the intensity decreases to half its maximum value at the center. The average efficiency of the three-dimensional optical focus control device is 14.2%. For ease of demonstration, four representative rotation angles of 60°, 120°, 180°, and 240° (labeled I, II, III, and IV, respectively) are selected, and their corresponding three-dimensional scanning light fields are shown below. Figure 3 As shown in b, it can be observed that when the equivalent focal length is shorter, the focus is sharper, the depth of field is reduced, and the energy is more concentrated; when the equivalent focal length increases, the focus becomes softer, the depth of field is increased, and the energy distribution is more diffused. That is, a longer equivalent focal length corresponds to a smaller numerical aperture (NA), which corresponds to a larger NA at a shorter focal length. Specifically, the working efficiency of the three-dimensional optical focus control device and the specific experimental data on the variation of axial focal length with rotation angle are shown in Table 1.

[0034] Table 1. Working efficiency and axial focal length variation with rotation angle of the three-dimensional optical focus control device.

[0035] In this embodiment, in order to further verify the adjustability of the focal position in the lateral plane, based on the verification of the variable focal length along the longitudinal (z-axis), the following steps were taken: Figure 3 The equivalent focal length f = 6.8 mm (Plane 1) is marked in section a, and its lateral focus control results are as follows: Figure 4 As shown.

[0036] In this embodiment, the lateral offset angle is defined as: Formula (5); In the formula: s is the focal displacement in the transverse plane; f is the equivalent focal length.

[0037] By synchronously rotating the first metasurface element to achieve different lateral offset angles, and simultaneously adjusting the third metasurface to maintain a constant relative rotation angle between the second and third sheets. Figure 4 As shown, nine positions from 1 to 9 were selected for verification, and the maximum lateral offset angle of the three-dimensional optical focus control device during axial focus adjustment was measured. With a focal angle of 1.6°, it exhibits good decoupling effect between axial focal length and lateral position offset.

[0038] It is worth noting that, in addition to metasurfaces, optical elements that can achieve tunable phase distribution using the above method also include liquid crystal spatial light modulators, diffractive optical elements, or freeform surface optical elements. For example, liquid crystal spatial light modulators can change the phase distribution in real time through electronic control, but they are large in size and limited in response speed and resolution. Diffractive optical elements and freeform surface optical elements also have controllability in some applications, but they usually lack the advantages of metasurfaces, such as thinness and high integration, making it difficult to meet the requirements of modern optical systems for compactness and portability.

[0039] Example 2 Based on Embodiment 1, this embodiment provides an optional solution for the materials and specific structures of the three metasurface elements.

[0040] In this embodiment, the first, second, and third metasurface elements are all composed of subwavelength nanostructure arrays, which possess the ability to phase-modulate the incident light field. The nanostructures are polarization-independent structures, meaning they are insensitive to the polarization of light and require no additional polarization control layer. In optical systems (such as metasurfaces, lenses, and imaging devices), polarization insensitivity means that optical performance does not depend on the polarization state of the input light (linear, circular, elliptical, etc.), and is effective for any polarized light without prior knowledge or control of the input light's polarization.

[0041] In this embodiment, the first metasurface element, the second metasurface element, and the third metasurface element are all cylindrical nanopillar arrays fabricated on a quartz substrate using electron beam lithography and dry etching processes.

[0042] In one specific embodiment, the working wavelength is 532 nm, then the period of the nanopillar can be 300 nm (< working wavelength 532 nm).

[0043] In this embodiment, the polarization-independent structure is specifically a nanopillar with a circular symmetrical cross section. The cylindrical nanopillar produces the same phase delay for x- and y-polarized light at the target wavelength, thereby achieving polarization insensitivity.

[0044] Optionally, the nanostructure is made of a high-refractive-index dielectric material, which may be any one of titanium dioxide, gallium nitride, or silicon nitride.

[0045] In this embodiment, silicon nitride (Si3N4) is specifically used as the nanopillar material, and its refractive index is about 2.0 in the visible light band.

[0046] Example 3 This embodiment provides an optional solution for the integration of metasurface elements, based on any of the above embodiments.

[0047] In this embodiment, the first metasurface element, the second metasurface element, and the third metasurface element are integrated on different layers of the same substrate, or are disposed on different independent substrates respectively.

[0048] In one specific embodiment, the first metasurface element, the second metasurface element, and the third metasurface element are specifically three independent arrays of nanostructures fabricated on glass substrates.

[0049] In this embodiment, the overall optical thickness of the three-dimensional optical focus control device is less than 2 millimeters, which facilitates high integration.

[0050] In one specific embodiment, the first metasurface element, the second metasurface element, and the third metasurface element are each fabricated on a glass substrate with a thickness of 0.5 mm, with a spacing of 100 μm between them, and the total thickness of the device is approximately 1.7 mm.

[0051] In another possible embodiment, a multilayer spin coating, photolithography and etching process is used to sequentially fabricate the nanostructures of the first metasurface element, the second metasurface element and the third metasurface element on both sides of the same fused silica substrate and a silicon dioxide isolation layer in the middle, thereby achieving high integration and the total thickness can be controlled within 500 μm.

[0052] Example 4 This embodiment provides an optical system based on any of the above embodiments.

[0053] In this embodiment, the optical system can be any one of a near-eye display system, a microscopic imaging system, an optical capture system, a laser processing system, or a three-dimensional projection system.

[0054] In one specific embodiment, the optical system is a near-eye display system, comprising a miniature OLED display as an image source, additional light-guiding optical elements (such as waveguides), and the aforementioned three-dimensional optical focus control device. In this embodiment, the three-dimensional optical focus control device receives light from the miniature OLED display and dynamically adjusts its relative rotation angle according to the needs of the displayed content, thereby generating virtual images at different depths and lateral positions, providing users with a three-dimensional display effect with accurate depth cues and mitigating VAC (Vibration Ventilation and Air Quality).

[0055] Example 5 This embodiment provides an augmented reality display device based on any of the above embodiments.

[0056] In this embodiment, the augmented reality display device includes an image source and the three-dimensional optical focus control device described in the above embodiments.

[0057] In this embodiment, the three-dimensional optical focus control device is configured to receive light from an image source and perform wavefront modulation on the light to generate a virtual image whose position can be dynamically adjusted in three-dimensional space, thereby alleviating convergence-focusing conflict.

[0058] Specifically, this embodiment uses a miniature laser scanning projector as the image source, which is used in an optical combiner to merge the real-world view with the virtual image. The light rays generated by the image source to create the virtual image are modulated on their wavefront after passing through a three-dimensional optical focus control device, forming a beam of light that appears to originate from a point in three-dimensional space. By rapidly controlling the rotation of the metasurface, this virtual image point can be scanned in the air, thereby drawing a three-dimensional image and allowing the user to see a clear image within a large eye movement range.

[0059] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several equivalent substitutions or obvious modifications can be made without departing from the concept of the present invention, and all such modifications, achieving the same performance or purpose, should be considered within the scope of protection of the present invention.

Claims

1. A three-dimensional optical focus control device, characterized in that, It includes a first metasurface element, a second metasurface element, and a third metasurface element that are cascaded together and can rotate relative to each other; The phase distribution functions of the first metasurface element, the second metasurface element, and the third metasurface element are configured in polar coordinates as follows: The phase distribution function of the first metasurface element includes an angular modulation term. The phase distribution function of the second metasurface element includes radial modulation terms and angular modulation terms. The phase distribution function of the third metasurface element includes terms that are complementary to the radial modulation and angular modulation terms of the second metasurface element; When the second metasurface element and the third metasurface element rotate relative to each other, the three-dimensional optical focus control device generates an axial focus change; when the first metasurface element and the second metasurface element rotate relative to each other, the three-dimensional optical focus control device generates a lateral focus shift. The lateral focus offset and the axial focus change are decoupled through the phase distribution function.

2. The three-dimensional optical focus control device as described in claim 1, characterized in that, The phase distribution function is specifically as follows: The phase distribution function of the first metasurface element is: ; The phase distribution function of the second metasurface element is: ; The phase distribution function of the third metasurface element is: .

3. The three-dimensional optical focus control device as described in claim 1 or 2, characterized in that, The first metasurface element, the second metasurface element, and the third metasurface element are all composed of a subwavelength nanostructure array, and the nanostructure is a polarization-independent structure.

4. The three-dimensional optical focus control device as described in claim 3, characterized in that, The nanostructure is made of a high-refractive-index dielectric material, including titanium dioxide, gallium nitride, or silicon nitride.

5. The three-dimensional optical focus control device as described in claim 1, characterized in that, The overall optical thickness of the device is less than 2 millimeters.

6. The three-dimensional optical focus control device as described in claim 1, characterized in that, The three metasurface elements are integrated on different layers of the same substrate, or are disposed on different independent substrates.

7. An optical system, characterized in that, Includes the three-dimensional optical focus control device as described in any one of claims 1 to 6.

8. The optical system as claimed in claim 7, characterized in that, The optical system is one of a near-eye display system, a microscopic imaging system, an optical capture system, a laser processing system, or a three-dimensional projection system.

9. An augmented reality display device, characterized in that, Includes the three-dimensional optical focus control device as described in any one of claims 1 to 6; It also includes image sources; The three-dimensional optical focus control device is configured to receive light from the image source and perform wavefront modulation on the light to generate a virtual image whose position can be dynamically adjusted in three-dimensional space, thereby alleviating convergence-focusing conflict.

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