Variable-focus sudden automatic focusing light beam generation system based on metasurface

Abstract

The embodiment of the invention provides a variable-focus sudden automatic focusing light beam generation system based on a metasurface, and the system comprises a laser light source which is used for emitting an incident light beam; the metasurface is used for enabling an emergent light beam after phase modulation of an incident light beam to be a sudden automatic focusing light beam, the metasurface comprises a substrate and a nano column arranged on the substrate, and the metasurface is arranged on the elastic substrate; and the voltage source is connected with the elastic substrate and the voltage adjusting device and is used for adjusting voltage applied to the elastic substrate under the control of the voltage adjusting device, so that the elastic substrate deforms and drives the substrate to deform, and the phase distribution of the nanorods is adjusted so as to adjust the focal length of the emergent light beam. According to the system, by combining the nano column for adjusting the phase of the incident light beam with the substrate capable of deforming under the action of voltage, the incident Gaussian light beam is converted into a sudden automatic focusing light beam with sharp focusing and self-healing characteristics; and the focal length can be continuously adjusted.

Description

Technical Field

[0001] The embodiments of this specification relate to the field of optical modulation technology, and in particular to a variable-focus sudden automatic focusing light beam generation system based on a metasurface. Background Art

[0002] The abrupt autofocusing (AAF) beam, which is composed of the Airy beam replicated along the axis, has a sharp focusing characteristic. The cross-sectional intensity of the beam is distributed in a ring before the focal plane. It is quickly focused when it reaches the vicinity of the focal plane, and the beam energy is accurately projected to the desired area. At the same time, because the beam also has the characteristic of self-healing, even if there is an obstacle in the propagation area of ​​the beam and partially blocks the beam, the abrupt autofocusing beam can focus the beam into a point almost unaffected and deliver the energy to the designated location. In view of the above characteristics of the abrupt autofocusing beam, it has broad prospects in applications such as laser processing and laser surgery.

[0003] In the prior art, a lens is added after the light beam is emitted from the phase-encoded metasurface. The lens acts as a Fourier lens to perform Fourier transform on the emitted light beam and then convert it into a sudden autofocusing light beam. This method makes the focal length of the sudden autofocusing light beam a fixed value. If the requirements of different focal lengths for many application scenarios are to be met, it is necessary to design corresponding lenses for each focal length, which increases the number of system components and the design and manufacturing costs. Summary of the invention

[0004] In view of the above-mentioned problems in the prior art, the purpose of the embodiments of this specification is to provide a variable-focus sudden automatic focusing light beam generating system based on a metasurface, so as to realize convenient adjustment of the focal length of the sudden automatic focusing light beam.

[0005] In order to solve the above technical problems, the specific technical solutions of the embodiments of this specification are as follows:

[0006] The embodiment of this specification provides a variable-focus sudden automatic focusing beam generation system based on a metasurface, comprising:

[0007] A laser light source, for emitting an incident light beam;

[0008] A metasurface, used for phase modulating an incident light beam, so that an outgoing light beam after the phase modulation of the incident light beam is a sudden autofocusing light beam, the metasurface comprising a substrate and nanopillars arranged on the substrate, and the metasurface is arranged on an elastic substrate;

[0009] A voltage source is connected to the elastic base and the voltage regulating device, and is used to adjust the voltage applied to the elastic base under the control of the voltage regulating device, so that the elastic base is deformed and drives the substrate to deform, so as to adjust the phase distribution of the nanocolumns and thus adjust the focal length of the outgoing light beam.

[0010] Specifically, a first electrode is disposed between the elastic substrate and the metasurface, and a second electrode is disposed on a side of the elastic substrate away from the metasurface;

[0011] One pole of the voltage source is connected to the first electrode, and the other pole of the voltage source is connected to the second electrode; the elastic substrate is deformed in a direction perpendicular to the axis under the voltage of the voltage source.

[0012] Specifically, the metasurface is arranged on an end surface of the elastic base away from the laser light source, and the nanocolumn is arranged on a side of the substrate away from the elastic base;

[0013] Two adjacent nano-pillars are arranged with an interval therebetween.

[0014] Furthermore, the heights of the nano-pillars are the same, and the diameters of the nano-pillars that are spaced at different distances from the center of the end surface of the substrate are different.

[0015] Preferably, the nanorods are cylindrical.

[0016] Specifically, the phase required for the metasurface to generate the sudden autofocusing beam with adjustable focal length is:

[0017]

[0018] in, is a phase distribution obtained by Fourier transforming the complex light field of the sudden autofocusing light beam; is the focusing phase;

[0019]

[0020]

[0021] Among them, β and γ are adjustable parameters related to the spatial phase distribution; r is the distance between any point on the end surface of the substrate and the center of the end surface, λ is the wavelength of the incident light beam, and f is the focal length.

[0022] Furthermore, the complex light field of the sudden automatic focusing light beam is:

[0023] E0=Ai[(r0-r) / w]exp[a(r0-r) / w];

[0024] Among them, Ai is the Airy function, r is the distance between any point on the end surface of the elastic substrate and the center of the end surface circle, r0 is the radius of the main ring of the intensity distribution of the sudden autofocusing beam in the initial plane, w is the proportional factor, and a is the exponential decay factor.

[0025] Furthermore, after the substrate is deformed, the metasurface phase distribution required to generate a sudden auto-focusing beam with adjustable focal length is:

[0026]

[0027] Where s is the stretch coefficient of the elastic substrate under the action of voltage.

[0028] Furthermore, the relationship between the phases of the nanorod and the sudden autofocusing beam is:

[0029]

[0030] Where λ is the wavelength of the incident beam, n eff is the effective refractive index related to the diameter of the nanorod, and H is the height of the nanorod.

[0031] Preferably, the elastic base and the base plate are both made of electroactive polymer material.

[0032] By adopting the above technical scheme, the variable-focus sudden automatic focusing beam generating system based on metasurface provided in the embodiment of this specification realizes the transformation of the incident Gaussian beam into a sudden automatic focusing beam with sharp focusing and self-healing characteristics by combining a nanocolumn for realizing phase adjustment of the incident beam with a substrate capable of generating deformation, and driving the substrate to generate a continuous tensile deformation through the continuous change of the voltage applied to the elastic substrate; and realizes continuous adjustment of the focal length, thus having a wide range of applications.

[0033] In order to make the above and other purposes, features and advantages of the embodiments of this specification more obvious and easy to understand, the following specifically cites preferred embodiments and describes them in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of this specification or the technical solutions in 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 only some embodiments of this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 A schematic diagram of the structure of a variable-focus sudden automatic focusing light beam generation system based on a metasurface provided in an embodiment of this specification is shown;

[0036] Figure 2(a) shows the intensity distribution of the suddenly autofocused beam in the initial plane after it emerges from the metasurface;

[0037] Figure 2(b) shows the intensity distribution of the sudden autofocus beam in the focal plane;

[0038] FIG3( a ) shows a light propagation diagram when an obstacle appears on the propagation axis of the sudden autofocus beam;

[0039] FIG3( b ) shows a light propagation diagram when an obstacle appears at an offset propagation axis of the sudden autofocus beam;

[0040] Figure 4 A schematic diagram of the structure of a metasurface cross section in an embodiment of this specification is shown;

[0041] Figure 5 A schematic diagram of the structure of a metasurface in an embodiment of this specification is shown;

[0042] Figure 6 A schematic diagram of the structure of another metasurface in an embodiment of this specification is shown;

[0043] Figure 7 A schematic diagram of the structure of the nanocolumn in the embodiment of this specification is shown;

[0044] Figure 8 A schematic diagram of the phase distribution of the metasurface in the embodiment of this specification is shown;

[0045] Fig. 9 A schematic diagram showing the relationship between the diameter of the nanocolumn and the phase and transmittance provided by the nanocolumn;

[0046] FIG10( a ) shows a schematic diagram of the focal length (phase) of the metasurface before voltage is applied;

[0047] FIG10( b ) shows a schematic diagram of the focal length (phase) of the metasurface after voltage is applied.

[0048] Description of the accompanying symbols:

[0049] 10. Laser light source;

[0050] 11. Incident beam;

[0051] 12. Outgoing beam;

[0052] 20. Metasurface;

[0053] 21. Substrate;

[0054] 22. Nanopillars;

[0055] 30. Voltage source;

[0056] 31. a first electrode;

[0057] 32. a second electrode;

[0058] 40. Elastic base;

[0059] 50. Obstacles;

[0060] 60. Focal plane. DETAILED DESCRIPTION

[0061] The following will be combined with the drawings in the embodiments of this specification to clearly and completely describe the technical solutions in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this specification.

[0062] It should be noted that the terms "first", "second", etc. in this specification and claims and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of this specification described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, device, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0063] In the prior art, a lens is applied to the outgoing light beam after phase modulation by a metasurface to convert the outgoing light beam into a sudden autofocusing light beam. However, this method makes the focal length of the sudden autofocusing light beam a fixed value, which makes it difficult to achieve the focal length of the sudden autofocusing light beam. In order to solve the above problem, the embodiment of this specification provides a variable focus sudden autofocusing light beam generation system based on a metasurface. Specifically, Figure 1 As shown, the system may include:

[0064] A laser light source 10, for emitting an incident light beam 11;

[0065] A metasurface 20, used for phase modulating an incident light beam 11, so that an outgoing light beam 12 after the phase modulation of the incident light beam 11 is a sudden autofocusing light beam, the metasurface 20 comprises a substrate 21 and a plurality of nanorods 22 arranged on the substrate 21, and the metasurface 20 is arranged on an elastic substrate 40;

[0066] The voltage source 30 is connected to the elastic base 40 and a voltage regulating device (not shown in the figure), and is used to adjust the voltage applied to the elastic base 40 under the control of the voltage regulating device, so that the elastic base 40 is deformed and drives the substrate 21 to deform, so as to adjust the phase distribution of the nanorods 22 and thus adjust the focal length of the outgoing light beam 12.

[0067] The embodiment of this specification provides a variable-focus sudden automatic focusing beam generation system based on a metasurface, wherein the incident beam is a Gaussian beam;

[0068] Metasurface refers to a planar device composed of sub-wavelength structural units formed on a two-dimensional plane to achieve specific functions.

[0069] After the incident light beam is phase modulated by the metasurface, the output light beam is a sudden autofocusing light beam, which is formed by a symmetrical combination of Airy beams around the propagation axis (i.e., the normal direction passing through the center of the metasurface). This light beam has a sharp focusing characteristic: on the initial plane where it leaves the metasurface, the light intensity distribution presents a circular ring distribution as shown in Figure 2(a); in the process of propagating along the propagation axis, the light ring gradually shrinks and suddenly focuses at the focal plane, forming a Bessel function-like light intensity distribution, as shown in Figure 2(b). The sudden autofocusing light beam can bypass the obstacle 50 that appears on the propagation axis during propagation, and focus on the focal plane 60 behind the obstacle without being affected, as shown in Figure 3(a). At the same time, this light beam also has the characteristic of self-healing. After the output light is partially blocked by the obstacle 50 that is offset from its propagation axis, the light beam can still be focused at the focal plane 60 and produce a focused light spot with a Bessel function distribution, as shown in Figure 3(b).

[0070] The embodiments of the present specification provide a variable-focus sudden automatic focusing light beam generating system based on a metasurface, wherein nanocolumns are used to perform phase modulation on an outgoing light beam, and an elastic substrate is used to generate tensile deformation under the action of a voltage; thus, when the elastic substrate generates tensile deformation, the substrate of the metasurface will be driven to generate tensile deformation synchronously, and the phase distribution of the nanocolumns of the metasurface will also be adjusted synchronously, thereby realizing the adjustment of the focal length of the sudden automatic focusing light beam.

[0071] In the system provided by the embodiment of this specification, when the applied voltage increases continuously, the deformation of the elastic substrate will increase continuously; thus, the deformation of the substrate increases continuously, and the adjustment of the phase of the nanorods on the substrate and the adjustment of the focal length also change continuously. Therefore, a structural design can meet the needs of different focal lengths of sudden automatic focusing beams in many application scenarios.

[0072] like Figure 4As shown, in the embodiment of this specification, a first electrode 31 is disposed between the elastic substrate 40 and the metasurface 20, and a second electrode 32 is disposed on a side of the elastic substrate 40 away from the metasurface 20;

[0073] One pole of the voltage source 30 is connected to the first electrode 31 , and the other pole of the voltage source 30 is connected to the second electrode 32 ; the elastic substrate 40 is deformed in a direction perpendicular to the axis under the voltage of the voltage source 30 .

[0074] Specifically, the positive electrode of the voltage source 30 can be connected to the first electrode 31, and the negative electrode of the voltage source 30 can be connected to the second electrode 32, so as to apply a voltage to the elastic substrate 40, so that the elastic substrate 40 produces a tensile deformation under the action of the voltage, so that the substrate 21 of the metasurface 20 located on the elastic substrate 40 also produces a tensile deformation synchronously, and the phase of the nanorods 22 of the metasurface 20 changes synchronously.

[0075] Since voltage needs to be applied on both sides of the substrate to cause deformation, electrodes need to be provided on both sides of the substrate; and nanopillars cannot be directly manufactured on electrodes. Therefore, the variable focus sudden automatic focusing beam generation system provided in the embodiment of this specification is also provided with an elastic substrate, so that the substrate and nanopillars are provided on the elastic substrate, and electrodes are provided on both sides of the elastic substrate. The deformation of the elastic substrate under the action of voltage synchronously drives the substrate located thereon to deform, thereby realizing the adjustment of the distance between nanopillars, and then realizing the adjustment of the focal length of the outgoing beam.

[0076] It should be noted that the electrode will not block the emission of the incident light beam.

[0077] It should be noted that the thickness of the elastic base and the substrate should be limited. The thickness must ensure that it has a certain bearing capacity for the nanocolumns arranged thereon, while not affecting the transmittance of the incident light beam and the ability of the elastic base and the base to produce tensile deformation in a direction perpendicular to the axis under the action of voltage.

[0078] In a possible embodiment, if Figure 4 and Figure 5 As shown, the metasurface 20 is arranged on the end surface of the elastic base 40 away from the laser light source 10, and the nanorods 22 are arranged on the side of the substrate 21 away from the elastic base 40;

[0079] Two adjacent nanorods 22 are spaced apart from each other.

[0080] In some feasible embodiments, the nanorods 22 are arranged on the substrate 21 in the shape of a plurality of concentric rings, such as Figure 5In some other feasible embodiments, the arrangement of the nanorods 22 on the substrate 21 is as follows: Figure 6 As shown, it is not in the shape of regular concentric circles.

[0081] In the embodiments of the present specification, multiple nanopillars can be prepared on the substrate by etching technology (e.g., direct writing etching, pattern transfer etching, and mixed pattern etching, etc.), which can facilitate the manufacture of the metasurface. The nanopillars are arranged at intervals so that when a voltage is applied to the elastic substrate, the distance between two adjacent nanopillars changes, thereby adjusting the phase distribution of the metasurface.

[0082] In the embodiment of this specification, the heights of the nanorods 22 are the same, and the diameters of the nanorods 22 that are spaced at different distances from the center of the end surface of the substrate 21 are different.

[0083] The height of the nanorods is limited by the processing conditions. For example, in nanorods working in visible light, the height usually does not exceed 2 microns. Nanorods of different diameters provide different phase compensation. Figure 8 The phase distribution shown is to configure the nanopillar that satisfies the phase compensation required at the position at the position, that is, a nanopillar array is composed of nanopillars with different diameters, thereby obtaining a metasurface.

[0084] In the embodiments of this specification, Figures 5 to 7 As shown, the nanorod 22 is cylindrical.

[0085] The cylindrical nanorods are insensitive to polarization and can produce the same phase response under incident light of any polarization or unpolarized light source. In some other feasible embodiments, the nanorods can have other shapes, such as prisms, but their shapes must meet the 2π phase coverage range for phase modulation, and the arrangement on the two-dimensional plane can meet the initial phase required for sudden automatic focusing of the light beam.

[0086] In some preferred embodiments, the substrate is square (eg Figure 6 As shown in FIG. 1 , a circular area on the substrate is processed by etching to form a nanocolumn array, and the portion of the substrate outside the circular area is a blank area without nanocolumns. Under the action of voltage, uniform tensile deformation is generated in four directions, so that the distance between two adjacent concentric circles in the array composed of nanocolumns located thereon changes the same, so that after the focal length changes, the focus is still located in the normal direction passing through the center of the metasurface.

[0087] It should be noted that the various drawings in this specification are only used to show the positional connection relationship between the various components in the system, and the sizes of the various components are only used as examples. In fact, the size of the nanocolumns is much smaller than that of the elastic substrate. The elastic substrate undergoes lateral tensile deformation under the action of voltage, while the lateral stretching of the nanocolumns located thereon is extremely small and negligible, so it is manifested as a change in the distance between any two adjacent nanocolumns.

[0088] In the embodiment of this specification, the required phase of the sudden autofocusing light beam with adjustable focal length generated by the metasurface is:

[0089]

[0090] in, generating a desired phase of the abruptly autofocused beam with adjustable focal length for the metasurface, is the phase obtained by Fourier transform of the complex light field of the sudden autofocusing beam, is the focusing phase.

[0091] By combining the initial phase of the sudden autofocus beam with the focusing phase, a phase of the sudden autofocus beam with adjustable focal length is generated.

[0092] Specifically:

[0093]

[0094]

[0095]

[0096] Among them, β and γ are adjustable parameters related to the spatial phase distribution; r is the distance between any point on the end surface of the elastic substrate and the center of the end surface circle, λ is the wavelength of the incident light beam, and f is the focal length. The focal length f is a parameter set artificially according to the actual application needs of the metasurface, and is the initial focal length of the elastic substrate when no voltage is applied.

[0097] The relationship between the phases of the nanorod and the sudden autofocus beam is:

[0098]

[0099] Where λ is the wavelength of the incident light beam, n eff is the effective refractive index related to the diameter of the nanorod, and H is the height of the nanorod. The larger the diameter of the nanorod, the smaller the effective refractive index n eff The larger it gets, the higher the refractive index of the material used for the nanorods is.

[0100] Fig. 9FIG. 4 shows a schematic diagram of the relationship between the diameter of a nanorod (made of gallium nitride material) and the phase and transmittance provided by the nanorod, as shown in FIG. Fig. 9 As shown, when the diameter of the nanorod increases, the phase compensation it provides increases, while the transmittance does not change significantly.

[0101] In the embodiment of this specification, the complex light field of the sudden automatic focusing light beam is:

[0102] E0=Ai[(r0-r) / w]exp[a(r0-r) / w];

[0103] Among them, Ai is the Airy function, r is the distance between any point on the end surface of the elastic substrate and the center of the end surface, r0 is the radius of the main ring of the intensity distribution of the sudden autofocusing beam in the initial plane, w is the proportional factor, exp is the exponential function with the natural constant e as the base, and a is the exponential decay factor.

[0104] A complex light field refers to a light field with a certain spatial distribution in a cross section perpendicular to the direction of light propagation.

[0105] In the embodiments of this specification, the field distribution of a sudden autofocusing light beam in space is first constructed; then, based on the field distribution, the phase distribution required to generate the light beam distribution is obtained through Fourier transform; finally, the surface structure of the metasurface is designed based on the phase distribution, that is, each position corresponds to a nanopillar.

[0106] After the elastic substrate is deformed, the metasurface phase distribution required to generate a sudden auto-focusing beam with adjustable focal length is:

[0107]

[0108] Where s is the stretch coefficient of the elastic substrate under the action of voltage. The stretch coefficient is used to quantitatively characterize the change in the tensile deformation of the elastic substrate after the voltage is applied.

[0109] The variable-focus sudden auto-focusing beam generating system based on a metasurface provided in the embodiments of this specification directly arranges the phase of the sudden auto-focusing beam together with the focusing phase of the lens into the metasurface. Through such a configuration, the generation of the sudden auto-focusing beam can be achieved without setting up an additional lens, and the focal length can be controlled.

[0110] In the embodiment of this specification, the elastic base 40 and the base plate 21 are made of electroactive polymer materials, so that they are easy to generate tensile deformation under the action of voltage.

[0111] FIG10(a) and FIG10(b) are schematic diagrams showing the phase modulation of the incident light beam by the nanopillars on the metasurface before and after the voltage is applied. It can be seen from FIG10(a) and FIG10(b) that when the voltage is applied, the substrate undergoes lateral tensile deformation along with the elastic base, so that the distance between two adjacent nanopillars 22 increases accordingly, thereby changing the phase gradient and affecting the profile of the outgoing light wavefront, thereby achieving the adjustment of the focal length of the sudden automatic focusing light beam.

[0112] Furthermore, in the embodiments of the present specification, the lateral tensile deformation of the elastic base and the substrate under voltage control is continuous, and the degree of deformation directly depends on the magnitude of the applied voltage. The greater the voltage, the greater the deformation of the elastic base and the substrate, the greater the spacing between two adjacent nanopillars, and the greater the focal length of the sudden autofocusing beam. That is, the focal length of the sudden autofocusing beam generating system based on the metasurface provided in the embodiments of the present specification is continuously adjustable.

[0113] In addition, the elastic deformation of the elastic base and substrate made of electroactive polymer material under voltage is recoverable. Once the voltage source is turned off to make the applied voltage zero, the deformation of the elastic base and substrate can be restored to the initial state, and the focal length of the sudden automatic focusing light beam can also be restored to the initial focal length.

[0114] Preferably, the nanorods are made of a material with a high refractive index, a low extinction ratio and a high transmittance to ensure the working efficiency of the metasurface.

[0115] If the refractive index is too low, the nanopillars cannot effectively bind light in the material, and cannot effectively achieve the interaction between light and matter. The extinction ratio indicates the ratio of light transmitted when two orthogonally polarized incident lights enter this material. If the extinction ratio is high, it means that only one polarization of light is transmitted through this material. The laser light source used in the embodiments of this specification is usually unpolarized, so it is necessary to use materials with low extinction ratios to improve the working efficiency of the metasurface. However, even if a material with a high refractive index and a low extinction ratio is selected, when light is incident on a unit with specific geometric parameters, it may still be affected by factors such as resonance, causing most of the light to be reflected rather than transmitted. Therefore, to solve this problem, in the embodiments of this specification, a material with a high transmittance is used to make the nanopillars of the metasurface to improve working efficiency.

[0116] The size of the nanopillar varies depending on the wavelength of the incident light beam and the material of the nanopillar. In a feasible embodiment, the operating wavelength is 532nm. At this wavelength, gallium nitride is used as the constituent material of the nanopillar, and the diameter of the nanopillar can range from 95nm to 195nm. The radius of the metasurface is 1mm. When the initial focal length is 10mm, the focal length of the sudden autofocus beam can increase by 0.5mm for every 1kV increase in voltage.

[0117] In summary, the embodiment of this specification provides a variable-focus sudden auto-focusing beam generation system based on a metasurface, which transforms the incident Gaussian beam into a sudden auto-focusing beam with sharp focusing and self-healing characteristics by combining a nanocolumn that realizes phase adjustment of the incident beam with an electroactive polymer substrate that can produce tensile deformation under the action of voltage, and realizes the tensile deformation of the substrate through an elastic substrate, and realizes continuous adjustment of the focal length. It has a wide range of applications, such as laser surgery, laser processing, fluorescence imaging, etc.

[0118] The use of the term "comprising" or "including" to describe the combination of elements, ingredients, parts or steps herein also contemplates an embodiment that is basically composed of these elements, ingredients, parts or steps. By using the term "may" here, it is intended to illustrate that any attribute described that "may" include is optional.

[0119] Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other. The above-mentioned embodiment is only for illustrating the technical concept and features of this embodiment. Its purpose is to enable people familiar with this technology to understand the content of the embodiment of this specification and implement it accordingly, and it cannot be used to limit the protection scope of the embodiment of this specification. Any equivalent changes or modifications made according to the spirit of the embodiment of this specification should be covered within the protection scope of the embodiment of this specification.

Claims

1. A variable-focus sudden automatic focusing beam generation system based on metasurface, characterized in that: include: A laser light source (10) for emitting an incident light beam (11); A metasurface (20) is used to phase modulate an incident light beam (11) so that an outgoing light beam (12) after the phase modulation of the incident light beam (11) is a sudden autofocusing light beam, the metasurface (20) comprising a substrate (21) and a plurality of nanorods (22) arranged on the substrate (21), and the metasurface (20) is arranged on an elastic base (40); A voltage source (30) is connected to the elastic base (40) and a voltage regulating device, and is used to adjust the voltage applied to the elastic base (40) under the control of the voltage regulating device, so as to deform the elastic base (40) and drive the substrate (21) to deform, so as to adjust the phase distribution of the nanorods (22) and thus adjust the focal length of the outgoing light beam (12).

2. The system according to claim 1, characterized in that A first electrode (31) is arranged between the elastic substrate (40) and the metasurface (20), and a second electrode (32) is arranged on a side of the elastic substrate (40) away from the metasurface (20); One pole of the voltage source (30) is connected to the first electrode (31), and the other pole of the voltage source (30) is connected to the second electrode (32); the elastic substrate (40) is deformed in a direction perpendicular to the axis under the action of the voltage of the voltage source (30).

3. The system according to claim 2, characterized in that The metasurface (20) is arranged on an end surface of the elastic base (40) away from the laser light source (10), and the nanorods (22) are arranged on a side of the substrate (21) away from the elastic base (40); Two adjacent nanorods (22) are arranged with a gap between them.

4. The system according to claim 3, characterized in that The heights of the nano columns (22) are the same, and the diameters of the nano columns (22) that are spaced at different distances from the center of the end surface of the substrate (21) are different.

5. The system according to claim 4, characterized in that The nanorod (22) is cylindrical.

6. The system according to claim 1, characterized in that The phase required for the metasurface to produce the sudden autofocusing beam with adjustable focal length is: in, is the phase obtained by Fourier transforming the complex light field of the sudden autofocusing light beam; is the focusing phase; Among them, β and γ are adjustable parameters related to the spatial phase distribution; r is the distance between any point on the end surface of the substrate and the center of the end surface, λ is the wavelength of the incident light beam, and f is the focal length.

7. The system according to claim 6, characterized in that The complex light field of the sudden autofocus beam is: E0=Ai[(r0-r) / w]exp[a(r0-r) / w]; Among them, Ai is the Airy function, r is the distance between any point on the end surface of the elastic substrate and the center of the end surface circle, r0 is the radius of the main ring of the intensity distribution of the sudden autofocusing beam in the initial plane, w is the proportional factor, and a is the exponential decay factor.

8. The system according to claim 6, characterized in that After the substrate is deformed, the metasurface phase distribution required to generate a sudden auto-focusing beam with adjustable focal length is: Where s is the stretch coefficient of the elastic substrate under the action of voltage.

9. The system according to claim 6, characterized in that The relationship between the phases of the nanorods and the sudden autofocus beam is: Where λ is the wavelength of the incident light beam, n eff is the effective refractive index related to the diameter of the nanorod, and H is the height of the nanorod.

10. The system according to claim 1, characterized in that The elastic base (40) and the base plate (21) are both made of electroactive polymer materials.

Images