Nonlinear beam shaping method based on stacked Moire metasurface

Abstract

The invention relates to the technical field of metasurfaces, and particularly discloses a stacked Moire metasurface-based nonlinear beam shaping method, which comprises the following steps of: acquiring a frequency doubling wavelength of fundamental frequency light and a target emission angle of a nonlinear beam; calculating to obtain a Moire lattice quasi-period of the stacked Moire metasurface; the corresponding relation between the lattice period and the distortion angle of the stacked Moire metasurface is obtained through calculation; obtaining the stacked Moire metasurface with the corresponding relation; the fundamental frequency light irradiates the surface of the stacked Moire metasurface to form a nonlinear light beam, and the value of the emission angle of the nonlinear light beam is the target emission angle. According to the method, the corresponding relation between the lattice periods and the distortion angles of the stacked Moire metasurface is calculated according to the target emission angle of the nonlinear light beam, the stacked Moire metasurface with different lattice periods and distortion angles is manufactured, rich momentum components are formed through combination of reciprocal lattice vectors of a plurality of basic metasurfaces, and the deformation of the momentum components is reduced. Therefore, the nonlinear light beam is accurately modulated.

Description

Technical Field

[0001] The present invention relates to the field of metasurface technology, and in particular to a nonlinear beam shaping method based on stacked moiré metasurfaces. Background Art

[0002] Momentum transfer plays an important role in controlling the interaction of photons with matter. This effect is prominently observed in diffraction from periodic structures such as gratings, where the momentum associated with the reciprocal lattice vector is transferred to the photon, changing the direction of light propagation. The concept of momentum transfer is crucial for designing optical components to control and manipulate light, aiding applications such as beam steering, beam splitting, information processing, and multi-channel communications. It is fundamental to the advancement of optical technology and has a wide impact on different fields of science and engineering.

[0003] To improve the flexibility of light manipulation, it is necessary to establish flexibly designed reciprocal spaces that can generate customizable momentum component spectra. The moiré effect, which arises from the superposition of two or more periodic lattices with twist angles or mismatched lattice constants, emerges as a general strategy to generate a variety of lattices with variable symmetry and period. This variability is achieved by directly manipulating the twist angle or lattice constant mismatch. With its inherent ability, the moiré effect provides a promising route to create new Brillouin bands, forming a rich momentum space.

[0004] The field of metasurfaces is well known for its flexibility in manipulating light, providing a fascinating framework for designing real and reciprocal lattices. The fusion of the metasurface concept with moiré photonics has already achieved many substantial advances in the linear domain. However, these studies have not yet been extended to the nonlinear domain.

[0005] In addition, compared with the unique engineering method of twisted double-layer two-dimensional materials, the fabrication of photonic moiré metasurfaces requires complex technology. Generally speaking, photonic moiré structures are mainly divided into two strategies. On the one hand, optical moiré metasurfaces can write two sets of lattices into the same layer to form a single-layer moiré superlattice, and this manufacturing process is relatively simple. On the other hand, by controlling the twist angle and interlayer distance, the twisted double-layer moiré metasurface provides greater freedom in light manipulation, has higher mechanical strength, and shows excellent application potential in tunable systems, but the processing is more difficult. The difficulty of etching typical nonlinear crystals (such as lithium niobate) further limits the expansion of moiré metasurfaces into nonlinear fields. Summary of the invention

[0006] The present invention aims to solve the problem of lack of research on nonlinear optical modulation using stacked moiré metasurfaces. To this end, the present invention provides a nonlinear beam shaping method based on stacked moiré metasurfaces, which calculates the correspondence between the lattice period and the twist angle of the stacked moiré metasurface according to the target emission angle of the nonlinear beam, and manufactures stacked moiré metasurfaces with different lattice periods and twist angles. By combining the reciprocal lattice vectors of multiple basic metasurfaces of the stacked moiré metasurface, a rich momentum component is formed, thereby accurately modulating the nonlinear beam.

[0007] The present invention provides a nonlinear beam shaping method based on stacked moiré metasurfaces, and the technical solution adopted is as follows: Obtaining the frequency-doubled wavelength of the fundamental frequency light and the target emission angle of the nonlinear light beam; The moiré lattice quasi-period of the stacked moiré metasurface is calculated according to the frequency-doubled wavelength of the fundamental frequency light and the target emission angle of the nonlinear light beam; According to the moiré lattice quasi-period of the stacked moiré metasurface, a corresponding relationship between the lattice period and the distortion angle of the stacked moiré metasurface is calculated; Acquire a stacked moiré metasurface having the corresponding relationship; The fundamental frequency light is irradiated onto the stacked moiré metastructure surface to form the nonlinear light beam, and the emission angle of the nonlinear light beam is the target emission angle, thereby realizing nonlinear beam shaping. The emission angle of the nonlinear light beam is the angle between the beam path of the nonlinear light beam and the normal line of the stacked moiré metastructure surface.

[0008] Furthermore, the moiré lattice quasi-periodicity of the stacked moiré metasurface The calculation formula is: in, is the doubled wavelength of the fundamental frequency light, is the target emission angle of the nonlinear beam.

[0009] Furthermore, according to the moiré lattice quasi-period of the stacked moiré metasurface, the corresponding relationship between the lattice period and the distortion angle of the stacked moiré metasurface is calculated as follows: in, is the quasi-periodicity of the moiré lattice, is the lattice period, is the twist angle.

[0010] Furthermore, the process of obtaining a stacked moiré metasurface having the corresponding relationship is as follows: Selecting one or more sets of values ​​of the lattice period and the twist angle that meet the corresponding relationship; According to the values ​​of the lattice period and the twist angle, a nonlinear film is processed using a focused ion beam to obtain a stacked moiré metasurface.

[0011] Furthermore, the stacked moiré metastructure surface has two layers.

[0012] Furthermore, the processing process of the stacked moiré metasurface is as follows: Fixing the nonlinear film without substrate support on a workbench; According to the value of the lattice period, using a focused ion beam, a periodic array of a basic metasurface A and a basic metasurface B is processed on the nonlinear film; Using a focused ion beam, cutting a portion of the edge of the basic metasurface A; The tip of the nanomanipulator is welded to the edge of the basic metasurface A by platinum deposition. Using a focused ion beam, cutting the remaining connected portion of the edge of the basic metasurface A; Move the nanomanipulator and rotate the workbench by the value of the twist angle so that the basic metasurface A covers the basic metasurface B; Welding the basic metasurface A and the basic metasurface B by platinum deposition; The needle tip is cut off by using a focused ion beam, and the edge of the basic metasurface B is cut to obtain the stacked moiré metasurface.

[0013] Furthermore, the nonlinear film is a metal film or a dielectric film.

[0014] Furthermore, the dielectric film is made of lithium niobate, lithium tantalate, zinc oxide, gallium arsenide, gallium phosphide, boron nitride, niobium oxide dihalide or transition metal disulfide.

[0015] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: 1. The present invention uses nonlinear materials to prepare stacked moiré metasurfaces, and controls the emission angle of nonlinear beams by adjusting the lattice period and twist angle of the stacked moiré metasurfaces, thereby precisely modulating the nonlinear beams. The present invention designs a stacked moiré metasurface, which is composed of two or more layers of nonlinear periodic metasurfaces stacked at different angles. When excited by a fundamental frequency beam, nonlinear polarization dipoles are generated inside the moiré metasurface through the second-order magnetic susceptibility. These dipoles oscillate at twice the frequency of the fundamental frequency field, acting as a secondary source for radiating second harmonics (SHG) to the far field. The array on the moiré metasurface forms a nonlinear photonic lattice with alternating distribution of zero and non-zero. In addition, in addition to the intrinsic lattice momentum of each basic metasurface, moiré lattice momentum is also generated due to the interlayer coupling between the stacked layers, which is transferred to the SHG photons and modulates the propagation direction of the SHG wave. The spatial variation of moiré SHG diffraction corresponds to different emission directions of SHG. Therefore, the emission angle of SHG can be controlled by adjusting the lattice period and twist angle of the stacked moiré metasurface, that is, directional emission of SHG can be achieved.

[0016] 2. The present invention uses focused ion beam and platinum deposition technology to achieve precise moiré metasurface processing, and uses a matching nanomanipulator to release the metasurface from the original film and transfer it to another location, and controls the rotation angle of the workbench to stack two moiré metasurfaces at a specific angle. The processing method of the stacked moiré metasurface of the present invention can achieve arbitrary twisting angle stacking of multiple layers of basic metasurfaces, and is a high-quality, highly repeatable processing method. The processed stacked moiré metasurface has higher mechanical strength and greater manipulation freedom, and shows excellent application potential in tunable systems.

[0017] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a flow chart provided by the present invention.

[0020] Figure 2 It is a diagram of the manufacturing process of the stacked moiré metasurface provided by the present invention.

[0021] Figure 3It is the shaping light pattern of the nonlinear light beam provided by the present invention.

[0022] Figure 4 This is a SEM image of the stacked moiré metastructure surface provided by the present invention.

[0023] Figure 5 It is a schematic diagram of the moiré lattice of the stacked moiré metasurface provided by the present invention.

[0024] Figure 6 This is the SHG spot distribution diagram provided by the present invention.

[0025] Figure 7 It is a schematic diagram of the SHG spot provided by the present invention changing with the twist angle.

[0026] Figure 8 It is a curve diagram of twist angle-emission angle provided by the present invention.

[0027] Fig. 9 It is a curve diagram of lattice period-emission angle provided by the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0029] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0030] Moiré metasurfaces, which are composed of multiple layers of periodic lattices with twisted or mismatched lattice constants, have attracted considerable attention in the field of electronics, especially in the context of twisted bilayer two-dimensional (2D) materials. The study of the properties of 2D materials has gradually expanded to the field of photonics and has gradually developed into moiré metasurfaces with more large tuning freedom. Superposition of two or more periodic structures to form moiré patterns is becoming a promising platform for confining and manipulating light. Compared with the unique engineering methods of 2D materials, the fabrication of photonic moiré metasurfaces requires complex techniques. In general, photonic moiré structures are mainly divided into two strategies. On the one hand, optical moiré metasurfaces can write two sets of lattices into the same layer to form a single-layer moiré superlattice, and this fabrication process is relatively simple. On the other hand, by controlling the twist angle and interlayer distance, twisted bilayer moiré metasurfaces provide greater freedom for light manipulation, have higher mechanical strength, and show excellent application potential in tunable systems. In recent years, although many significant advances have been made in the linear field of moiré superlattices, nonlinear moiré metasurfaces remain an unexplored experimental frontier. Manipulation of light propagation through moiré metasurfaces at the nanoscale provides a new platform for nonlinear optical modulation.

[0031] Combine the following Figures 1 to 9 The present invention is further described in detail, and a nonlinear beam shaping method based on stacked moiré metasurfaces is described in the present invention:

[0032] In this embodiment, Figure 1 As shown, a nonlinear beam shaping method based on a stacked moiré metasurface is provided, comprising the following steps: Step 1: Obtain the doubled wavelength of the fundamental light and the target emission angle of the nonlinear light beam.

[0033] Step 2: Calculate the moiré lattice quasi-period of the stacked moiré metasurface according to the frequency-doubled wavelength of the fundamental frequency light and the target emission angle of the nonlinear light beam.

[0034] The moiré lattice quasi-periodicity of the stacked moiré metasurface The calculation formula is: in, is the doubled wavelength of the fundamental frequency light, is the target emission angle of the nonlinear beam.

[0035] Step 3: According to the moiré lattice quasi-period of the stacked moiré metasurface, the corresponding relationship between the lattice period and the distortion angle of the stacked moiré metasurface is calculated, and the calculation formula is: in, is the quasi-periodicity of the moiré lattice, is the lattice period, is the twist angle.

[0036] Step 4: Obtaining a stacked moiré metasurface having the corresponding relationship, the specific process is as follows: One or more groups of values ​​of the lattice period and the twist angle that meet the corresponding relationship are selected; the experimenter selects the values ​​of the lattice period and the twist angle that are conducive to equipment processing based on personal experience.

[0037] According to the values ​​of the lattice period and the twist angle, a nonlinear film is processed by a focused ion beam to obtain a stacked moiré metasurface. According to each set of the values ​​of the lattice period and the twist angle, a stacked moiré metasurface is processed.

[0038] The nonlinear film is a metal film, such as gold, or a dielectric film, such as lithium niobate (LiNbO3), lithium tantalate (LiTaO3), zinc oxide (ZnO), gallium arsenide (GaAs), gallium phosphide (GaP), boron nitride (BN), niobium oxide dihalide (NbOX2), transition metal disulfide (MX2), etc.

[0039] Taking the processing of two layers of stacked moiré metastructure surfaces as an example, the processing method of the stacked moiré metastructure surface adopted in the present method is described, and the specific process is as follows: Step 4.1: Fix the nonlinear film without substrate support on the workbench.

[0040] Step 4.2: According to the value of the lattice period, a periodic array of basic metasurface A and basic metasurface B is processed on the nonlinear film using a focused ion beam, such as Figure 2 (a) and Figure 2 (e) shown.

[0041] Step 4.3: Using a focused ion beam, cut a portion of the edge of the basic metasurface A.

[0042] Step 4.4: Use platinum deposition to weld the tip of the nanomanipulator to the edge of the basic metasurface A, as shown in Figure 2 (b) and Figure 2 (f) shown.

[0043] Step 4.5: Using a focused ion beam, cut the remaining connected portion of the edge of the basic metasurface A; at this time, the basic metasurface A is completely cut off from the film.

[0044] Step 4.6: Move the nanomanipulator as Figure 2 (c) and Figure 2As shown in (g), the working table is rotated at the value of the twist angle so that the basic metasurface A covers the basic metasurface B; when the working table rotates, the nonlinear film is driven to rotate together.

[0045] Step 4.7: Welding the basic metasurface A and the basic metasurface B by platinum deposition; welding the basic metasurface A and the basic metasurface B at their edges.

[0046] Step 4.8: Using a focused ion beam, cut off the needle tip and cut the edge of the basic metasurface B to obtain the stacked moiré metasurface. At this time, the basic metasurface B is completely cut off from the film, such as Figure 2 (d) and Figure 2 (h) shown.

[0047] When the present invention uses a stacked moiré metasurface processing method to process more than two layers of stacked moiré metasurfaces, more groups of periodic arrays of basic metasurfaces are processed in step 4.2, and steps 4.3 to 4.7 are repeated to increase the number of stacked layers. The present invention uses a focused ion beam to achieve precise metasurface processing, and uses a matching nanomanipulator to release the metasurface from the original film and transfer it to other locations, and controls the rotation angle of the workbench to stack the two metasurfaces at a specific angle. The stacked moiré metasurface processing method used in the present invention can achieve arbitrary twisting angle stacking of multiple layers of basic metasurfaces, and is a high-quality, highly repeatable processing method. The processed stacked moiré metasurface has higher mechanical strength and greater manipulation freedom, and shows excellent application potential in tunable systems.

[0048] Step 5: The fundamental frequency light is irradiated onto the stacked moiré metastructure surface to form the nonlinear light beam, and the emission angle of the nonlinear light beam is the target emission angle, thereby realizing nonlinear beam shaping. The emission angle of the nonlinear light beam is the angle between the beam path of the nonlinear light beam and the normal line of the stacked moiré metastructure surface.

[0049] The shaping effect of the stacked moiré metasurface of the present invention on nonlinear light beams is verified by experiments below. 1. Nonlinear beam shaping optical path

[0050] like Figure 3As shown in the figure, the shaping optical path includes a tunable titanium sapphire femtosecond laser (Maitai, Spectra-Physics, 80MHz, 230fs), a Glan-Taylor prism (GTP), a half-wave plate (HWP), a 10x objective lens (Obj110x, NA=0.25), a stacked moiré metastructure surface, a 100x objective lens (Obj2 100x, NA=0.90), a short-pass filter (BG40 colored glass) and a translucent plastic screen (Plastic screen) arranged in sequence. A camera (CCD) is arranged behind the plastic screen. The pump laser beam is focused onto the stacked moiré metastructure surface through the 10x objective lens to form a focused spot with a diameter of about 10µm. The SHG wave transmitted from the other side of the stacked moiré metastructure surface is collected by the 100x objective lens and the short-pass filter filters out the fundamental frequency light, forming an SHG pattern on the translucent plastic screen, which is captured by the camera.

[0051] In the experiment, the pump wavelength was selected at 950nm, and the corresponding SHG wavelength was 475nm, which is smaller than the lattice period (600nm) of the moiré metasurface, which is conducive to the effective diffraction of SHG light. Since the interaction length of the light beam in the moiré metasurface studied is short, the diffraction of SHG belongs to the Raman-Nath mechanism. In this case, the lattice momentum transfer along the transverse direction is dominant, thereby adjusting the propagation direction of the SHG wave. 2. Stacked moiré metasurfaces

[0052] There are two factors related to the stacked moiré metasurface that affect the SHG wave emission angle, namely the lattice period of the moiré metasurface and the twist angle between the moiré metasurface layers. In order to facilitate the experiment, three stacked moiré metasurfaces were fabricated in this experiment. The nonlinear film was a lithium niobate film (LN film) with a thickness of 210nm. The area of ​​the moiré metasurface was 25×25µm. 2 The diameter of the periodic array of pores is 225nm, the lattice period is 600nm, and the twisting angles are 15°, 30°, and 45°, respectively.

[0053] The stacked moiré metastructure surface was processed by focused ion beam and platinum deposition. The focused ion beam used gallium cations, 30kV, 24pA. The SEM image of the stacked moiré metastructure surface is shown in Figure 2. Figure 4 shown. Figure 4 (a) is a representative cross-sectional SEM image of the moiré metasurface, showing a periodic structure with a moiré lattice quasi-period of 600 nm and a pore diameter of 225 nm. Figure 4 (a) It is confirmed that the pores of the fabricated metasurface are uniform in size and have steep sidewalls. The suspended structure enhances the refractive index contrast between the film and the substrate environment, which can effectively promote the light field confinement in the vertical direction, which is the key to achieving high-quality optical performance. Figure 4 (b) Top-down SEM image of the moiré metasurface, showing the twist angle A double-layer stacked moiré metasurface with an angle of 30°.

[0054] The moiré lattices formed by stacking moiré metasurfaces with twist angles of 15°, 30°, and 45° are shown in Figure 2. Figure 5 shown. Figure 5 The three groups of pictures in the figure have a distortion angle of 15°, 30° and 45° from left to right. Figure 5 (a)- Figure 5 (c) is a schematic diagram of a stacked moiré metasurface formed by the same square lattice; Figure 5 (d)- Figure 5 (f) is the theoretical calculation result of the moiré lattice pattern of the stacked moiré metasurface; Figure 5 (g) - Figure 5 (i) The experimental observation of the moiré lattice pattern of stacked moiré metasurfaces captured by light microscopy. The stacking process of the moiré metasurface introduces new quasi-periodic features, especially the enlarged moiré lattice generated by the 15° and 30° distortions. Figure 5 (d) and Figure 5 The black dashed squares in (e) highlight this feature. The present invention incorporates incommensurate twist angles, which results in non-periodic moiré patterns. The quasi-periodicity of the moiré lattice can be determined by the formula Furthermore, the 45° twist forms a moiré lattice that is consistent with the Ammann-Beenker puzzle and exhibits a remarkable 8-fold rotational symmetry. Figure 5 (g) - Figure 5 (i) The actual pattern photographed under a light microscope is shown, which is very close to the theoretical pattern, visually confirming the stacked moiré metasurface constructed by the present invention. 3. Stacked moiré metasurfaces to shape nonlinear beams

[0055] The SHG spot distribution captured by the camera is as follows: Figure 6 shown. Figure 6 (a) shows the SHG spot measured from a single-layer moiré metasurface, and the dashed circle indicates the aperture of the 100x objective lens. Figure 6 (b) shows the reciprocal lattice corresponding to the single-layer moiré metasurface. The momentum transfer of the SHG spot produces the first-order diffraction spot on the periphery. Figure 6 Marked with blue circles in (a). Figure 6 (c)- Figure 6 (n) Shows the SHG spots and reciprocal lattices of stacked moiré metasurfaces with twist angles of 15°, 30°, and 45°, respectively. Figure 6 (c) Figure 6 (g) and Figure 6 (k) are the measured SHG spots. Figure 6 (d) Figure 6 (h) and Figure 6 (l) The reciprocal lattice of the undistorted moiré metasurface in blue and the distorted moiré metasurface in red, respectively. Figure 6 (e) Figure 6 (i) Figure 6 (m), Figure 6 (f) Figure 6 (j) and Figure 6 (n) respectively describe the reciprocal lattice vectors, which are composed of the reciprocal lattice vectors of the moiré metasurface. According to different vector combination configurations, these vectors are divided into four groups, including , , and ,exist Figure 6 In the figure, dark green, light green, dark yellow and light yellow are used respectively.

[0056] like Figure 6 (a) and Figure 6 As shown in (b), due to the conservation of momentum of the light spot, a vertically incident light beam will produce an SHG light spot with zero transverse momentum, resulting in a prominent central light spot. Four obvious peripheral light spots (marked by four blue circles) can also be seen in the far field, indicating that the transverse momentum is not zero. The existence of these peripheral light spots indicates that the momentum is transferred from the reciprocal lattice to the SHG light spot. The reciprocal lattice of the moiré metasurface appears as a square matrix, which is ,in, and is an integer, and is a unit vector in reciprocal space. SHG wave and zero reciprocal lattice vector The interaction between the reciprocal lattice vectors produces the central spot in the experiment. The central spot is called the zeroth-order SHG diffraction. and The momentum transfer results in four peripheral light spots, i.e., first-order diffraction.

[0057] When two moiré metasurfaces are stacked together, interlayer coupling introduces a superposition of the reciprocal lattices from a single moiré metasurface. The reciprocal lattice of the twisted layer is expressed as ,in, and is an integer, and is the unit vector in the reciprocal space of the distorted element surface, , Therefore, the reciprocal vector of the stacked moiré metasurface, that is, the sum of the reciprocal vectors of each layer, can be expressed as .

[0058] like Figure 6 As shown in (c), in addition to the fourth-order diffraction spot in the center, we also obtained two different groups of first-order peripheral spots, distinguished by blue and red circles. These two groups of spots correspond to two layers of moiré metasurfaces, and the two groups show a relative angular offset of 15°. Figure 6 (d) shows the basic reciprocal lattices of the two-layer moiré metasurface, represented by red and blue dots respectively. The single-layer moiré metasurface only has zero-order and first-order diffraction, while the interlayer-distorted double-layer moiré metasurface shows additional SHG spots. These spots are composed of the reciprocal lattice vectors of the two basic lattices. Figure 6 As shown in (e), the vector (blue horizontal arrow) and (red arrow) produces a vector (Dark green short arrows). The momentum transfer of these vectors forms the SHG spot tightly surrounding the zeroth-order spot, as shown in Figure 6 As shown in the dark green circles in (c), this group of spots is classified as . Similarly, vector (blue vertical arrow) and Generate a vector (light green arrow), this group of spots is classified as Since this group of light spots is close to the edge of the objective lens aperture, two light spots are missing in the experiment, such as Figure 6 As shown in the dashed circle in (c), these spots are formed by the combination of two reciprocal lattice unit vectors, which is called second-order diffraction. In addition, Figure 6 (f) shows that the vector and Further combining to produce a vector (dark yellow arrow), which forms a set of third-order SHG diffraction spots, marked as ,exist Figure 6 Marked by dark yellow circles in (c), these diffraction spots confirm the existence of abundant high-order diffraction in the non-periodic stacked moiré metasurface.

[0059] Figure 6 (g) - Figure 6 (n) shows the SHG spots of stacked moiré metasurfaces with twist angles of 30° and 45°, including diffraction components from the zeroth to the third order. It is intuitively shown that the twist angle has a significant effect on the position and symmetry of the SHG spots. In addition, the stacked moiré metasurface with a twist angle of 45° shows two different sets of third-order diffraction spots. Figure 6 In (k), dark yellow ( ) and light yellow ( ) circles to distinguish.

[0060] To intuitively illustrate the complex regulation of the twist angle on SHG emission, Figure 7 Describes the trajectory of the SHG spot as the twist angle changes. Figure 7 As shown in (a), as the twist angle increases, The SHG spot migrates outward from the origin of the reciprocal space to the four corners along the quarter arc. Figure 7 As shown in (b), The SHG spots also move along a quarter arc, but their trajectories are similar to The trajectories of show mirror symmetry on the diagonal of the reciprocal grid. As the twist angle increases, these spots move from the four corners to the center, which is a unique dynamic feature of SHG emission. Figure 7 As shown in (c), with the change of the torsion angle, The SHG spot moves along a unique path similar to a quatrefoil. These intricate trajectories prove that the twist angle directly affects the spatial distribution of the SHG spot. Changing the twist angle between the layers of the stacked moiré metasurface can shape the SHG.

[0061] like Figure 8 As shown, the twist angle has an influence on the emission angle of SHG. The effect of emission angle is the angle between the SHG beam path and the normal line of the stacked moiré metasurface. The emission direction of SHG can be controlled by changing the twist angle between the layers of the stacked moiré metasurface.

[0062] In this experiment, a number of stacked moiré metasurfaces with different lattice periods were fabricated with a twist angle of 45° and a doubled wavelength of 475nm, and the emission angle of SHG was measured. The results are as follows Fig. 9 As shown. Fig. 9 It can be seen that the emission angle of SHG Changing the lattice period of the stacked moiré metasurface can also shape the SHG. 4. Conclusion

[0063] In summary, this paper explores the potential of moiré metasurfaces in regulating nonlinear optical processes, with a focus on SHG wave shaping. We fabricated stacked moiré metasurfaces with excellent performance, which are characterized by extended non-periodic patterns, resulting in complex diffraction spots, and directional SHG waves controlled by twist angle and lattice period. The present invention demonstrates complex modulation of SHG emission induced by different twist angles and lattice periods. This invention marks a significant progress in exploiting the unique properties of moiré lattices in nonlinear optical and beam shaping applications, and a substantial step forward in exploiting the unique properties of moiré lattices to advance the frontiers of nonlinear optics and spot science.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nonlinear beam shaping method based on stacked moiré metasurfaces. It is characterized in that include: Obtaining the frequency-doubled wavelength of the fundamental frequency light and the target emission angle of the nonlinear light beam; The moiré lattice quasi-period of the stacked moiré metasurface is calculated according to the frequency-doubled wavelength of the fundamental frequency light and the target emission angle of the nonlinear light beam; According to the moiré lattice quasi-period of the stacked moiré metasurface, a corresponding relationship between the lattice period and the distortion angle of the stacked moiré metasurface is calculated; Acquire a stacked moiré metasurface having the corresponding relationship; The fundamental frequency light is irradiated onto the stacked moiré metastructure surface to form the nonlinear light beam, and the emission angle of the nonlinear light beam is the target emission angle, thereby realizing nonlinear beam shaping. The emission angle of the nonlinear light beam is the angle between the beam path of the nonlinear light beam and the normal line of the stacked moiré metastructure surface.

2. A nonlinear beam shaping method based on stacked moiré metasurfaces as claimed in claim 1, It is characterized in that The moiré lattice quasi-periodicity of the stacked moiré metasurface The calculation formula is: in, is the doubled wavelength of the fundamental frequency light, is the target emission angle of the nonlinear beam.

3. The nonlinear beam shaping method based on stacked moiré metasurfaces according to claim 1, It is characterized in that According to the moiré lattice quasi-period of the stacked moiré metasurface, the corresponding relationship between the lattice period and the distortion angle of the stacked moiré metasurface is calculated as follows: in, is the quasi-periodicity of the moiré lattice, is the lattice period, is the twist angle.

4. The nonlinear beam shaping method based on stacked moiré metasurfaces according to claim 3, It is characterized in that The process of obtaining a stacked moiré metasurface having the corresponding relationship is as follows: Selecting one or more sets of values ​​of the lattice period and the twist angle that meet the corresponding relationship; According to the values ​​of the lattice period and the twist angle, a nonlinear film is processed using a focused ion beam to obtain a stacked moiré metasurface.

5. A nonlinear beam shaping method based on stacked moiré metasurfaces as claimed in claim 4, It is characterized in that The stacked moiré metastructure surface has two layers.

6. A nonlinear beam shaping method based on stacked moiré metasurfaces as claimed in claim 5, It is characterized in that The processing process of the stacked moiré metasurface is as follows: Fixing the nonlinear film without substrate support on a workbench; According to the value of the lattice period, using a focused ion beam, a periodic array of a basic metasurface A and a basic metasurface B is processed on the nonlinear film; Using a focused ion beam, cutting a portion of the edge of the basic metasurface A; The tip of the nanomanipulator is welded to the edge of the basic metasurface A by platinum deposition. Using a focused ion beam, cutting the remaining connected portion of the edge of the basic metasurface A; Move the nanomanipulator and rotate the workbench by the value of the twist angle so that the basic metasurface A covers the basic metasurface B; Welding the basic metasurface A and the basic metasurface B by platinum deposition; The needle tip is cut off by using a focused ion beam, and the edge of the basic metasurface B is cut to obtain the stacked moiré metasurface.

7. The nonlinear beam shaping method based on stacked moiré metasurfaces according to claim 6, It is characterized in that The nonlinear film is a metal film or a dielectric film.

8. The nonlinear beam shaping method based on stacked moiré metasurfaces according to claim 7, It is characterized in that The dielectric film is made of lithium niobate, lithium tantalate, zinc oxide, gallium arsenide, gallium phosphide, boron nitride, niobium oxide dihalide or transition metal disulfide.

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