An adjustable metasurface system

Abstract

The present invention provides an adjustable metasurface system, comprising: a wavefront modulator, an optical focusing device and a metasurface structure. The metasurface structure includes a plurality of nanostructures made of phase change materials, and the phase states of the phase change materials include a crystalline state and an amorphous state. The wavefront modulator performs wavefront modulation on the incident control light and emits the wavefront-modulated control light to the optical focusing device. The optical focusing device is configured to focus the wavefront-modulated control light to form a plurality of light foci. The metasurface structure is located at the focal plane formed by the plurality of light foci and is configured to perform phase modulation on the incident working light, and the optical path of the working light does not overlap with that of the wavefront modulator and the optical focusing device. Through the adjustable metasurface system provided by the embodiments of the present invention, independent optical control of the nanostructures can be achieved without being affected by wiring. Moreover, light foci on the order of a hundred nanometers can be formed, which can be applicable to smaller pixels or a larger number of pixels, and can be applied to a wider range of scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of optical elements, and more particularly, to an adjustable metasurface system. Background Art

[0002] The optical performance of a metasurface is mainly determined by two factors: ① the geometric shape and size of the structural unit; ② the dielectric constant of the material. After a metasurface device is fabricated, it is difficult to change the geometric shape and size of its structure. Therefore, the optical performance of the device can be adjusted or reconstructed by changing the dielectric constant of the material.

[0003] Phase change materials can be converted between the crystalline state and the amorphous state, and different states of phase change materials can achieve different modulation effects, which can greatly change the dielectric constant. For example, when a beam of light is incident on a phase change material, when the phase change material is in the amorphous state, the outgoing left-handed light deflects to the right; when the phase change material is in the crystalline state, the outgoing light deflects to the left, achieving binary modulation. In addition, some solutions utilize the characteristic that the phase change material can be partially crystallized, so that the process from the amorphous state to the crystalline state is a gradual change process, thereby realizing continuous regulation of the reflection phase.

[0004] Currently, the state conversion of phase change materials is mainly achieved by an electric control method. For example, electrodes can be respectively arranged on the upper and lower sides of the phase change material, and the phase change material is heated by electric control to achieve the effect of an adjustable metasurface. However, all electric controls need to solve the wiring problem. When there are many pixels (such as more than one million), the wiring needs to be pulled very far, resulting in the pixel count not being able to be too high; on the other hand, due to the limitations of the electronic wiring process, it is extremely challenging to make a single electron reach the scale of one hundred nanometers, thus limiting the pixel count and pixel size of the adjustable phase change metasurface. Summary of the Invention

[0005] To solve the above problems, an object of the embodiments of the present invention is to provide an adjustable metasurface system.

[0006] The embodiments of the present invention provide an adjustable metasurface system, including: a wavefront modulator, an optical focusing device, and a metasurface structure. The metasurface structure includes a plurality of nanostructures made of a phase change material, and the phase states of the phase change material include a crystalline state and an amorphous state;

[0007] The wavefront modulator is located on a side of the optical focusing device away from the metasurface structure, and is configured to perform wavefront modulation on the incident control light and emit the wavefront-modulated control light to the optical focusing device;

[0008] The optical focusing device is configured to focus the wavefront-modulated control light to form a plurality of light foci;

[0009] The metasurface structure is located at the focal plane formed by a plurality of the light foci, and at least a part of the nanostructures corresponds to the positions of the light foci; the metasurface structure is used for phase modulation of the incident working light, and the optical path of the working light does not overlap with that of the wavefront modulator and the optical focusing device.

[0010] In a possible implementation, the metasurface structure further includes a transparent substrate; a plurality of the nanostructures are located on one side of the transparent substrate;

[0011] One end of the nanostructure close to the transparent substrate corresponds to the position of the light focus.

[0012] In a possible implementation, the metasurface structure further includes a metal reflection layer;

[0013] The metal reflection layer is located between the nanostructure and the transparent substrate, and the side of the metal reflection layer close to the nanostructure is the reflective side.

[0014] In a possible implementation, the wavefront modulator and the optical focusing device are located on the side of the metal reflection layer away from the nanostructure.

[0015] In a possible implementation, the metasurface structure further includes a plurality of photothermal conversion structures;

[0016] A plurality of photothermal conversion structures are located on the side of the transparent substrate close to the nanostructure, and the photothermal conversion structures correspond to the nanostructures one by one;

[0017] The photothermal conversion structure is used for converting the light energy of the incident control light into heat energy.

[0018] In a possible implementation, the metasurface structure further includes a dielectric matching layer;

[0019] The dielectric matching layer is located between the nanostructure and the transparent substrate and abuts against the nanostructure.

[0020] In a possible implementation, the metasurface structure further includes a filling material that is transparent in the working band;

[0021] The filling material is filled between the nanostructures, and the difference between the refractive index of the filling material and the refractive index of the nanostructure is not less than 0.5.

[0022] In a possible implementation, the numerical aperture of the optical focusing device is greater than a preset threshold;

[0023] When the numerical aperture of the optical focusing device is the preset threshold, the size of the light focus formed by the optical focusing device on the metasurface structure is not greater than the period of the nanostructure.

[0024] In a possible implementation, the preset threshold is greater than or equal to 0.6.

[0025] In a possible implementation, the wavefront aberration of the optical focusing device is less than 0.3λ, where λ represents the wavelength of the control light.

[0026] In a possible implementation, the optical focusing device includes: a combined lens;

[0027] The combined lens is composed of multiple lenses; or, composed of at least one lens and at least one metalens; or, composed of multiple metalenses.

[0028] In a possible implementation, the optical focusing device is an on-axis multi-focus focusing device or an off-axis multi-focus focusing device.

[0029] In a possible implementation, the wavelength of the control light is different from that of the working light; and / or, the control light is parallel light.

[0030] In a possible implementation, the phase change material includes at least one of germanium antimony telluride, germanium telluride, antimony telluride, and silver antimony telluride.

[0031] In a possible implementation, the wavefront modulator is located at the entrance pupil position of the optical focusing device.

[0032] In the solution provided by the embodiments of the present invention, by using a wavefront modulator and an optical focusing device, multiple controllable light foci can be generated at the position where the metasurface structure is located. The light foci correspond to the positions of the nanostructures made of a phase change material, so that independent optical control of the nanostructures can be realized, and the phase change state of the nanostructures can be independently changed in an optical control manner, thereby enabling pixel-level phase change control. This tunable metasurface system controls the phase change state of the metasurface structure in an optical control manner, does not require an electrically controlled wiring, and is not restricted by the wiring process; moreover, the wavefront modulator and the optical focusing device can form light foci on the order of hundreds of nanometers, which can be applied to smaller pixels or a larger number of pixels. The number of pixels and the pixel size of the metasurface structure can be designed based on actual requirements, and it can be applied to a wider range of scenarios.

[0033] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specific embodiments are given, and detailed descriptions are made in conjunction with the accompanying drawings as follows. Description of the Drawings

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0035] Figure 1 Fig. 4 shows a schematic structural diagram of an adjustable metasurface system provided by an embodiment of the present invention;

[0036] Figure 2 Fig. 8 shows another schematic structural diagram of an adjustable metasurface system provided by an embodiment of the present invention;

[0037] Figure 3A Fig. 12 shows a first schematic structural diagram of an optical focusing device in an adjustable metasurface system provided by an embodiment of the present invention;

[0038] Figure 3B Fig. 16 shows a first schematic structural diagram of an optical focusing device in an adjustable metasurface system provided by an embodiment of the present invention;

[0039] Figure 3C Fig. 20 shows a first schematic structural diagram of an optical focusing device in an adjustable metasurface system provided by an embodiment of the present invention;

[0040] Figure 4 Fig. 24 shows yet another schematic structural diagram of an adjustable metasurface system provided by an embodiment of the present invention;

[0041] Figure 5A Fig. 28 shows a first schematic structural diagram of a transmissive metasurface structure provided by an embodiment of the present invention;

[0042] Figure 5B Fig. 32 shows a second schematic structural diagram of a transmissive metasurface structure provided by an embodiment of the present invention;

[0043] Figure 6A Fig. 36 shows a third schematic structural diagram of a transmissive metasurface structure provided by an embodiment of the present invention;

[0044] Figure 6B Fig. 40 shows a fourth schematic structural diagram of a transmissive metasurface structure provided by an embodiment of the present invention;

[0045] Figure 7A Fig. 44 shows a fifth schematic structural diagram of a transmissive metasurface structure provided by an embodiment of the present invention;

[0046] Figure 7B Fig. 48 shows a sixth schematic structural diagram of a transmissive metasurface structure provided by an embodiment of the present invention;

[0047] Figure 8A Shows the first schematic structural diagram of the reflective metasurface structure provided by the embodiments of the present invention;

[0048] Figure 8B Shows the second schematic structural diagram of the reflective metasurface structure provided by the embodiments of the present invention;

[0049] Figure 9A Shows the third schematic structural diagram of the reflective metasurface structure provided by the embodiments of the present invention;

[0050] Figure 9B Shows the fourth schematic structural diagram of the reflective metasurface structure provided by the embodiments of the present invention;

[0051] Figure 10A Shows the fifth schematic structural diagram of the reflective metasurface structure provided by the embodiments of the present invention;

[0052] Figure 10B Shows the sixth schematic structural diagram of the reflective metasurface structure provided by the embodiments of the present invention;

[0053] Figure 11 Shows a light focus distribution method and its entrance pupil phase diagram provided by the embodiments of the present invention;

[0054] Figure 12 Shows another light focus distribution method and its entrance pupil phase diagram provided by the embodiments of the present invention.

[0055] Icon:

[0056] 10 - Wavefront modulator, 20 - Optical focusing device, 30 - Metasurface structure, 301 - Nanostructure, 302 - Transparent substrate, 303 - Metal reflection layer, 304 - Photothermal conversion structure, 305 - Dielectric matching layer, 306 - Filling material, 201 - Lens, 202 - Metalens. Detailed implementation manners

[0057] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0058] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0059] In the present invention, unless otherwise clearly specified and defined, terms such as "mounted", "connected", "coupled", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0060] The present invention provides an adjustable metasurface system, which shows the phase adjustability of the metasurface by means of light control. Refer to Figure 1 As shown, the adjustable metasurface system includes: a wavefront modulator 10, an optical focusing device 20, and a metasurface structure 30. The metasurface structure 30 includes a plurality of nanostructures 301 made of a phase change material, and the phase states of the phase change material at least include a crystalline state and an amorphous state.

[0061] Among them, the wavefront modulator is located on the side of the optical focusing device 20 away from the metasurface structure 30, that is, the optical focusing device 20 is located between the wavefront modulator 10 and the metasurface structure 30; for the convenience of controlling the wavefront modulator 10, optionally, the wavefront modulator is located at the entrance pupil position of the optical focusing device 20. The wavefront modulator 10 is used to perform wavefront modulation on the incident control light A and emit the wavefront-modulated control light A to the optical focusing device 20. The optical focusing device 20 is used to focus the wavefront-modulated control light A to form a plurality of focal points. The metasurface structure 30 is located at the focal plane formed by the plurality of focal points, and at least some of the nanostructures 301 correspond to the focal point positions; the metasurface structure 30 is used to perform phase modulation on the incident working light B, and the optical path of the working light B does not overlap with that of the wavefront modulator 10 and the optical focusing device 20. The nanostructure 301 is an all-dielectric structure unit and has a high transmittance in the working band (such as the visible light band). The nanostructures 301 are arranged in a periodic array such as a regular hexagon, a square, a sector, etc. For example, the nanostructures 301 can be located at the center position and / or vertex position of a period.

[0062] In the embodiments of the present invention, a nanostructure 301 is fabricated based on a phase change material. Under an external excitation such as a laser, the phase change material can change the internal lattice of the substance, significantly change the dielectric constant, and cause a change in the state of the phase change material, thereby enabling phase adjustment. In the embodiments of the present invention, the adjustable metasurface system can focus the control light A on the corresponding nanostructure 301, and by controlling the light to excite the nanostructure 301, the phase control of the metasurface structure 30 can be achieved. Among them, in the embodiments of the present invention, the wavefront modulator 10 and the optical focusing device 20 are used to focus the control light A on the nanostructure 301.

[0063] Specifically, the wavefront modulator 10 (also known as a wavefront regulator) can change the phase of light (e.g., by means of the birefringence effect, etc.), thereby being able to change and control the wavefront of light. As Figure 1 shown, the control light A enters the wavefront modulator 10, and the wavefront modulator 10 can modulate the wavefront of the control light A and send the control light A with the modulated wavefront to the optical focusing device 20. Optionally, the control light A can be parallel light; as Figure 1 shown, the wavefront modulator can modulate the wavefront of the parallel light into a converging wavefront. The wavefront modulator 10 can be transmissive (as Figure 1 shown), or reflective, and this embodiment does not make any limitations in this regard. For example, the wavefront modulator 10 can be a liquid crystal spatial light modulator (LCSLM), a digital micromirror device (DMD), or a spatial light modulator composed of an adjustable metasurface, etc.

[0064] The optical focusing device 20 can focus the control light A with the modulated wavefront and can form multiple light foci. Specifically, the wavefront modulator is located at the entrance pupil position of the optical focusing device 20, and the optical focusing device 20 can generate multiple light foci with a spacing of nanometers or micrometers. For example, the spacing between the light foci is at the order of hundreds of nanometers, so that different light foci can correspond to different nanostructures 301, thereby being able to focus the control light A on different nanostructures 301, realizing the independent control of different nanostructures 301, and enabling the metasurface structure 30 to achieve pixel-level phase change. Among them, the phase relationship between the adjustable focal position and the entrance pupil position is shown by the following formula:

[0065]

[0066] where x and z represent the coordinate axes on the entrance pupil plane of the optical focusing device 20, and their maximum and minimum values are determined by the entrance pupil aperture of the optical focusing device 20, k is the wave number, a i and b i are the coordinates of the i-th focal point on the focal plane in the focal plane, respectively.

[0067] In the embodiments of the present invention, by controlling the modulation effect of the wavefront modulator 10, multiple optical foci can be generated at different positions. The multiple optical foci are located on the same plane, which is called the focal plane, and the metasurface structure 30 is located on this focal plane, so that the nanostructures 301 can be located at the optical foci. For example, there is a one-to-one correspondence between the generated optical foci and the nanostructures 301 in the metasurface structure 30; moreover, through the wavefront modulator 10, it can be controlled at which nanostructures 301 the optical foci are formed, so that optical control can be achieved for each nanostructure 301, and the phase of the nanostructure 301 can be adjusted.

[0068] Among them, the phase change material has different modulation effects in different phase states, and the phase state specifically includes the crystalline state, amorphous state, etc. For example, the phase change material for fabricating the nanostructures 301 can be germanium antimony telluride (Ge X Sb Y Te Z ), germanium telluride (Ge X Te Y ), antimony telluride (Sb X Te Y ), silver antimony telluride (Ag X Sb Y Te Z ), etc. For example, the phase change material is GST (Ge2Sb2Te5). Generally, GST is in the amorphous state; after applying laser excitation to GST, GST is heated, and the amorphous GST will phase change to the crystalline state, realizing a rapid conversion from the amorphous state to the crystalline state. Moreover, when the crystalline GST is heated by the laser above the melting point and then rapidly cooled, it can be converted back to the amorphous state again, and the entire cooling process can be completed rapidly within 10 ns, so that a rapid conversion from the crystalline state to the amorphous state can also be achieved. In the embodiments of the present invention, if the nanostructures 301 are fabricated with GST, the temperature of the nanostructures 301 can be changed by controlling the focused light beam A, so that a rapid conversion between the crystalline state and the amorphous state can be realized.

[0069] In the embodiments of the present invention, the control light beam A is used to provide excitation to the nanostructures 301, while the metasurface structure 30 is used to modulate the phase of other light beams. In this embodiment, the light beam that the metasurface structure 30 needs to modulate the phase is called the working light beam, and is denoted by B. To avoid the wavefront modulator 10 and the optical focusing device 20 affecting the working light beam B, in the embodiments of the present invention, the wavefront modulator 10 and the optical focusing device 20 are arranged at other positions except the optical path of the working light beam B, that is, the optical path of the working light beam B does not overlap with the wavefront modulator 10 and the optical focusing device 20.

[0070] In the embodiments of the present invention, a phase change material having a crystalline state and an amorphous state is used to fabricate the nanostructure 301, so that phase modulation can be achieved without changing the transmission and reflection characteristics of the metasurface structure 30, that is, the metasurface structure 30 is always a reflective metasurface or a transmissive metasurface, to facilitate setting the positions of the wavefront modulator 10 and the optical focusing device 20 and avoid overlapping with the optical path of the working light B. When the metasurface structure 30 is a reflective metasurface, the nanostructure 301 and the wavefront modulator 10 can be arranged on both sides of the reflective metasurface structure 30 to achieve coaxiality. For example, the metasurface structure 30 includes a metal reflective layer and a plurality of nanostructures, the wavefront modulator 10 and the optical focusing device 20 are arranged on one side of the metal reflective layer, and the plurality of nanostructures are arranged on the other side of the metal reflective layer, and the other side of the metal reflective layer is the reflective side, and the working light B can enter the metasurface structure 30 from the other side of the metal reflective layer.

[0071] For example, referring to Figure 1 As shown, if the metasurface structure 30 is a reflective metasurface, it can reflect the incident working light B1, and its reflected light is B2; the wavefront modulator 10 and the optical focusing device 20 can be arranged on the other side of the metasurface structure 30, and the wavefront modulator 10, the optical focusing device 20, and the metasurface structure 30 can be coaxial, and the optical focusing device 20 is an on-axis multi-focus focusing device. Or, referring to Figure 2 As shown, if the metasurface structure 30 is a transmissive metasurface (such as a metalens), the metasurface structure 30 can perform phase modulation on the incident working light B1 and transmit the modulated working light B2; the wavefront modulator 10 and the optical focusing device 20 can be arranged on any side of the metasurface structure 30, as long as it is ensured that there is no overlap with the working light; in this case, the optical focusing device 20 and the metasurface structure 30 are not coaxial, and the optical focusing device 20 needs to be able to generate off-axis multi-foci, and it is an off-axis multi-focus focusing device. Optionally, the wavelength of the control light is different from that of the working light to avoid the control light affecting the working light as much as possible.

[0072] An adjustable metasurface system provided by an embodiment of the present invention can generate multiple controllable light foci at the position where the metasurface structure 30 is located by using a wavefront modulator 10 and an optical focusing device 20. The light foci correspond to the positions of nanostructures 301 made of phase change materials, so that independent optical control of the nanostructures 301 can be realized, and the phase change state of the nanostructures 301 can be independently changed in an optical control manner, thereby controlling pixel-level phase change. The adjustable metasurface system controls the phase change state of the metasurface structure 30 in an optical control manner, without the need for wiring and is not restricted by wiring processes. Moreover, the wavefront modulator 10 and the optical focusing device 20 can form light foci on the order of hundreds of nanometers, which can be applied to smaller pixels or a larger number of pixels. The number of pixels and the pixel size of the metasurface structure 30 can be designed based on actual requirements, and it can be applied to a wider range of scenarios, such as all-solid-state lidar, etc.

[0073] Optionally, the numerical aperture of the optical focusing device 20 is greater than a preset threshold. When the numerical aperture of the optical focusing device 20 is the preset threshold, the size of the light foci formed by the optical focusing device 20 on the metasurface structure 30 is not greater than the period of the nanostructures 301. For example, the preset threshold is greater than or equal to 0.6. Additionally optionally, the wavefront aberration of the optical focusing device 20 is less than 0.3λ, where λ represents the wavelength of the control light ray A.

[0074] In an embodiment of the present invention, the optical focusing device 20 is an optical system with a large numerical aperture and / or a small wave aberration, so as to be able to generate light foci with a spacing of hundreds of nanometers. The large numerical aperture and the small wave aberration ensure that the light foci are smaller and the energy is concentrated, which is more conducive to pixel-level precise regulation.

[0075] Optionally, the optical focusing device 20 includes: a combined lens; as shown in Figures 3A - 3C The combined lens is composed of multiple lenses 201; or, it is composed of at least one lens 201 and at least one metalens 202; or, it is composed of multiple metalenses 202. Among them, the lens 201 is a traditional refractive lens. For example, as shown in Figure 4 The optical focusing device 20 can be a microscope objective; the microscope objective has good aberration correction, meets the system requirements, and can form the required light foci.

[0076] Based on any of the above embodiments, in addition to including the nanostructures 301 made of phase change materials, the metasurface structure 30, as shown in Figure 5A also includes a transparent substrate 302; a plurality of nanostructures 301 are located on one side of the transparent substrate 302; and the end of the nanostructures 301 close to the transparent substrate 302 corresponds to the position of the light foci.

[0077] In the embodiments of the present invention, the transparent substrate 302 is transparent and can at least transmit the control light A, so that the control light A can form a light focus at one end of the nanostructure 301 close to the transparent substrate 302, thereby heating the nanostructure 301 by using the photothermal conversion effect, and further changing the phase change state of the nanostructure 301. Among them, if the metasurface structure 30 is a transmissive metasurface, the transparent substrate 302 is also transparent in the working band. For example, it can transmit the working light B.

[0078] Optionally, as shown in Figure 5B the metasurface structure 30 further includes a filling material 306. The filling material 306 is transparent in the working band; the filling material 306 is filled between the nanostructures 301, and the difference between the refractive index of the filling material 306 and the refractive index of the nanostructure 301 is not less than 0.5. In the embodiments of the present invention, the filling material 306 filled around the nanostructure 301 can play the role of including the nanostructure 301, and the difference between the refractive index of the filling material 306 and the refractive index of the nanostructure 301 is greater than or equal to 0.5 to avoid the filling material 306 affecting the light modulation effect. Among them, the working band refers to the band where the working light B is located, that is, the filling material 306 can at least transmit the working light B.

[0079] Optionally, as shown in Figure 6A the metasurface structure 30 further includes a plurality of photothermal conversion structures 304; the plurality of photothermal conversion structures 304 are located on the side of the transparent substrate 302 close to the nanostructure 301, and the positions of the photothermal conversion structures 304 correspond to those of the nanostructure 301 one by one; the photothermal conversion structure 304 is used to convert the light energy of the control light A into heat energy.

[0080] In the embodiments of the present invention, the photothermal conversion structure 304 corresponding in position is arranged on one side of the nanostructure 301, so that the light focus can be focused on the photothermal conversion structure 304. The photothermal conversion structure 304 can quickly convert light energy into heat energy, thereby improving the phase change speed and efficiency. For example, the photothermal conversion structure 304 can be made of a photothermal sensitive material.

[0081] In addition, optionally, similar to the above Figure 5B shown structure, the metasurface structure 30 can also include a filling material 306. Specifically, as shown in Figure 6B the filling material 306 has the same function as the filling material 306 in the Figure 5B shown embodiment, and will not be elaborated here.

[0082] Optionally, as shown in Figure 7AAs shown, the metasurface structure 30 further includes a dielectric matching layer 305; the dielectric matching layer 305 is located between the nanostructure 301 and the transparent substrate 302 and abuts against the nanostructure 301.

[0083] In an embodiment of the present invention, the difference between the refractive index of the dielectric matching layer 305 and the refractive index of the nanostructure 301 (or the equivalent refractive index of the nanostructure 301) is less than or equal to a preset threshold. For example, the preset threshold is 1 or 0.5, etc., so that the refractive index of the nanostructure 301 matches the refractive index of the dielectric matching layer 305, thereby improving the transmittance of the nanostructure 301. For example, the thickness of the dielectric matching layer 305 can be 30 nm to 1000 nm. Among them, the dielectric matching layer 305 is transparent in the working wavelength band, for example, it can transmit the working light B, etc. For example, the material of the dielectric matching layer 305 can be quartz glass. In addition, optionally, similar to the Figure 5B structure shown above, the metasurface structure 30 may also include a filling material 306, for details, please refer to Figure 7B shown.

[0084] Optionally, referring to Figure 8A shown, the metasurface structure 30 further includes a metal reflection layer 303; the metal reflection layer 303 is located between the nanostructure 301 and the transparent substrate 302, and the side of the metal reflection layer 303 close to the nanostructure 301 is the light-reflecting side.

[0085] In an embodiment of the present invention, the metasurface structure 30 can be a reflective metasurface, which includes a metal reflection layer 303, and the nanostructure 301 is located on the light-reflecting side of the metal reflection layer 303, so that the metasurface structure 30 can perform phase modulation by reflecting incident light. For example, the metal reflection layer 303 can be made of gold, silver, copper, aluminum or their alloys, and its thickness can be 100 nm to 100 μm. In addition, optionally, the metasurface structure 30 may also include a filling material 306, for details, please refer to Figure 8B shown.

[0086] For example, when the metasurface structure 30 is a reflective metasurface, as Figure 4 shown, the nanostructure 301, the wavefront modulator 10, and the optical focusing device 20 can be located on both sides of the metal reflection layer 303, that is, the wavefront modulator 10 and the optical focusing device 20 are located on the side of the metal reflection layer 303 away from the nanostructure 301, so that the optical focusing device 20 and the metasurface structure 30 can be coaxial to conveniently form a light focus.

[0087] Optionally, referring to Figure 9AAs shown, the metasurface structure 30 further includes a plurality of photothermal conversion structures 304; the plurality of photothermal conversion structures 304 are located on the side of the transparent substrate 302 close to the nanostructure 301, and the positions of the photothermal conversion structures 304 correspond one-to-one to the positions of the nanostructures 301; the photothermal conversion structure 304 is used to convert the light energy of the control light A into heat energy.

[0088] In an embodiment of the present invention, photothermal conversion structures 304 corresponding in position are arranged on one side of the nanostructure 301, so that the light focus can be focused at the photothermal conversion structure 304, and the photothermal conversion structure 304 can quickly convert light energy into heat energy, thereby improving the phase change speed and efficiency. For example, the photothermal conversion structure 304 is arranged between the transparent substrate 302 and the metal reflection layer 303, so that the tunable metasurface system is a coaxial system, and the control light A can be simply and conveniently irradiated to the photothermal conversion structure 304 and form a light focus. In addition, optionally, the metasurface structure 30 may also include a filling material 306, specifically, refer to Figure 9B as shown.

[0089] Optionally, refer to Figure 10A as shown, the metasurface structure 30 further includes a dielectric matching layer 305; the dielectric matching layer 305 is located between the nanostructure 301 and the transparent substrate 302 and abuts against the nanostructure 301. As Figure 10A shown, the dielectric matching layer 305 may be located between the nanostructure 301 and the metal reflection layer 303.

[0090] In an embodiment of the present invention, the difference between the refractive index of the dielectric matching layer 305 and the refractive index of the nanostructure 301 (or the equivalent refractive index of the nanostructure 301) is less than or equal to a preset threshold. For example, the preset threshold is 1 or 0.5, etc., so that the refractive index of the nanostructure 301 matches the refractive index of the dielectric matching layer 305, thereby improving the transmittance of the nanostructure 301. For example, the thickness of the dielectric matching layer 305 may be 30 nm to 1000 nm. Among them, the dielectric matching layer 305 is transparent in the working band, for example, can transmit the working light B, etc. For example, the material of the dielectric matching layer 305 may be quartz glass. In addition, optionally, the metasurface structure 30 may also include a filling material 306, specifically, refer to Figure 10B as shown.

[0091] The working process of the tunable metasurface system is introduced in detail through an embodiment below.

[0092] In an implementation of the present invention, the nanostructures 301 in the metasurface structure 30 are arranged in a square period and arranged in a 5×5 manner, and each nanostructure 301 corresponds to a pixel. Figure 11The left-middle figure shows the arrangement of the nanostructures 301. The period of the nanostructures 301 is 1000 nm (i.e., Figure 11 the side length of the positive direction in the left-middle figure is 1000 nm), and the height of the nanostructures 301 is 1500 nm. The optical focusing device 20 uses a microscope objective lens with an entrance pupil diameter of 5 mm, i.e., 5000 μm.

[0093] By controlling the modulation effect of the wavefront modulator 10, 5 optical foci are formed on the surface of the metasurface structure 30. The distribution of the optical foci can be seen as shown by the dots in the Figure 11 left-middle figure. At this time, the corresponding entrance pupil phase diagram can be seen in the Figure 11 right-middle figure shown.

[0094] Moreover, by controlling the modulation effect of the wavefront modulator 10, 8 optical foci are formed on the surface of the metasurface structure 30. The distribution of the optical foci can be seen as shown by the dots in the Figure 12 left-middle figure. At this time, the corresponding entrance pupil phase diagram can be seen in the Figure 12 right-middle figure shown.

[0095] As mentioned above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of technical solutions of changes or substitutions, which should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claimed rights.

Claims

1. An adjustable metasurface system, characterized in that, Comprising: A wavefront modulator (10), an optical focusing device (20), and a metasurface structure (30). The metasurface structure (30) includes a plurality of nanostructures (301) made of a phase change material, and the phase states of the phase change material include a crystalline state and an amorphous state; The wavefront modulator (10) is located on a side of the optical focusing device (20) away from the metasurface structure (30), and is configured to perform wavefront modulation on incident control light and emit the wavefront-modulated control light to the optical focusing device (20); The optical focusing device (20) is configured to focus the wavefront-modulated control light to form a plurality of light foci; The metasurface structure (30) is located at an optical focal plane formed by the plurality of light foci, and at least a part of the nanostructures (301) corresponds to the positions of the light foci; the metasurface structure (30) is configured to perform phase modulation on incident working light, and the optical path of the working light does not overlap with the wavefront modulator (10) and the optical focusing device (20); Wherein, different light foci formed by the optical focusing device (20) correspond to different nanostructures (301) to achieve independent control of different nanostructures (301).

2. The tunable metasurface system according to claim 1, wherein The metasurface structure (30) further includes a transparent substrate (302); a plurality of the nanostructures (301) are located on one side of the transparent substrate (302); One end of the nanostructure (301) close to the transparent substrate (302) corresponds to the position of the light focus.

3. The tunable metasurface system according to claim 2, characterized in that, The metasurface structure (30) further includes a metal reflection layer (303); The metal reflection layer (303) is located between the nanostructure (301) and the transparent substrate (302), and a side of the metal reflection layer (303) close to the nanostructure (301) is a light-reflecting side.

4. The tunable metasurface system according to claim 3, wherein The wavefront modulator (10) and the optical focusing device (20) are located on a side of the metal reflection layer (303) away from the nanostructure (301).

5. The tunable metasurface system according to any one of claims 2-4, characterized in that, The metasurface structure (30) further includes a plurality of photothermal conversion structures (304); A plurality of the photothermal conversion structures (304) are located on a side of the transparent substrate (302) close to the nanostructure (301), and the photothermal conversion structures (304) correspond to the nanostructures (301) one by one in position; The photothermal conversion structure (304) is configured to convert the light energy of the incident control light into heat energy.

6. The tunable metasurface system according to any one of claims 2-4, characterized in that The metasurface structure (30) further includes a dielectric matching layer (305); The dielectric matching layer (305) is located between the nanostructure (301) and the transparent substrate (302) and abuts against the nanostructure (301).

7. The tunable metasurface system according to any one of claims 2-4, characterized in that The metasurface structure (30) further includes a filling material (306), and the filling material (306) is transparent in the working wavelength band; The filling material (306) fills between the nanostructures (301), and the difference between the refractive index of the filling material (306) and the refractive index of the nanostructures (301) is not less than 0.

5.

8. The tunable metasurface system according to claim 1, wherein The numerical aperture of the optical focusing device (20) is greater than a preset threshold; When the numerical aperture of the optical focusing device (20) is the preset threshold, the size of the light focus formed by the optical focusing device (20) on the metasurface structure (30) is not greater than the period of the nanostructure (301).

9. The tunable metasurface system according to claim 8, wherein The preset threshold is greater than or equal to 0.

6.

10. The tunable metasurface system according to claim 1 or 8, characterized in that, The wavefront aberration of the optical focusing device (20) is less than 0.3λ, where λ represents the wavelength of the control light.

11. The tunable metasurface system according to claim 1, wherein The optical focusing device (20) includes: a combined lens; The combined lens is composed of multiple lenses; alternatively, it is composed of at least one lens and at least one metalens; or it is composed of multiple metalenses.

12. The tunable metasurface system according to claim 1, wherein The optical focusing device (20) is an on-axis multi-focus focusing device or an off-axis multi-focus focusing device.

13. The tunable metasurface system according to claim 1, characterized in that, The wavelength of the control light is different from that of the working light; and / or, the control light is parallel light.

14. The tunable metasurface system according to claim 1, wherein The phase change material includes at least one of germanium antimony telluride, germanium telluride, antimony telluride, and silver antimony telluride.

15. The tunable metasurface system according to claim 1, wherein The wavefront modulator (10) is located at the entrance pupil position of the optical focusing device (20).

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