Fabry-Perot cavity-based metasurface light field three-dimensional regulation and control device, light field regulation and control method and optical device

Abstract

The invention discloses a metasurface device combined with an F-P (Fabry-Perot) cavity, the metasurface device structurally comprises an upper reflecting layer, a metasurface layer and a lower reflecting layer, the upper high reflecting layer and the lower high reflecting layer form a micro-nano F-P cavity, and the metasurface layer in the middle is formed by an anisotropic medium nano column array. Based on the wavelength selection principle of the F-P cavity, narrow-band filtering can be realized; based on a geometric phase principle, phase regulation and amplitude regulation can be realized by arranging medium nano-columns with specific shapes, sizes and azimuth angles. The geometric phase metasurface is embedded into the micro-nano F-P cavity, and the wavelength, the phase and the amplitude of a light field can be modulated independently at the same time. The invention has the advantages of flexible design, compact structure, strong regulation and control capability, high regulation and control degree of freedom and the like, and has very high application prospects in various practical applications such as light field regulation and control, color printing and holographic display, information storage, optical anti-counterfeiting and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano optical metasurfaces, and particularly relates to a metasurface optical field three-dimensional regulation device based on a Fabry-Perot (F-P) cavity, an optical field regulation method, and an optical device. By embedding a geometric phase metasurface into a micro-nano F-P cavity, the device realizes three-dimensional joint regulation of the wavelength, phase, and amplitude of the optical field, and can be widely applied to fields such as optical field regulation, color holographic display, optical anti-counterfeiting, and information storage. Background Art

[0002] Optical field regulation is a process of arbitrarily modulating basic parameters of light such as wavelength, phase, amplitude, polarization, etc., and plays an important role in various applied optical fields. With the development of information technology, the demand for multi-dimensional free regulation of the optical field is increasing. However, traditional optical field regulation devices have limited modulation capabilities and single modulation dimensions.

[0003] A metasurface is a new type of material composed of sub-wavelength structures. This material can realize spatial control of electromagnetic waves by using the strong interaction between sub-wavelength structures and electromagnetic waves, and flexibly manipulate basic characteristics of light, such as amplitude, phase, polarization, and spectral response.

[0004] In recent years, researchers have tried to combine metasurfaces with optical resonators to enhance the regulation ability. The Fabry-Perot (F-P) cavity has become an important candidate due to its narrowband filtering characteristics and high field enhancement effect. However, in the prior art, the combination of the F-P cavity and the metasurface mostly focuses on single functions (such as wavelength selection or phase modulation), and fails to achieve independent joint regulation of wavelength, phase, and amplitude. In addition, the coupling between the cavity structure and the metasurface in traditional designs often leads to limited regulation degrees of freedom or introduces complex multi-layer structures, sacrificing the compactness of the device. Summary of the Invention

[0005] Aiming at problems such as limited regulation dimensions, high crosstalk, and low integration degree in the above-mentioned prior art, the present invention provides a metasurface optical field three-dimensional regulation device based on a Fabry-Perot cavity, an optical field regulation method, and an optical device, aiming to solve the limitation that current metasurface devices can only regulate the complex amplitude of the optical field or the wavelength of the optical field alone. The metasurface device provided by the present invention can realize three-dimensional joint regulation of wavelength, phase, and amplitude without sacrificing the integration degree, enhances the regulation ability of the metasurface, and can be applied to fields such as optical field regulation, color holography and display.

[0006] The technical solution of the present invention is as follows:

[0007] A metasurface optical field three-dimensional regulation device based on a Fabry-Perot cavity, characterized by comprising:

[0008] An upper reflective layer and a lower reflective layer, and the upper reflective layer and the lower reflective layer form a micro-nano F-P cavity;

[0009] A metasurface layer, located between the upper reflective layer and the lower reflective layer, is composed of an anisotropic dielectric nanocolumn array arranged in a sub-wavelength period; wherein,

[0010] The metasurface layer independently regulates the wavelength, phase, and amplitude of the light field by adjusting the major axis, minor axis dimensions, and azimuth angle of the dielectric nanocolumns;

[0011] The resonance wavelength of the micro-nano F-P cavity is jointly determined by the equivalent refractive index of the dielectric nanocolumns and the height of the F-P cavity, and the phase modulation of the metasurface layer satisfies the relational expression where θ is the azimuth angle of the dielectric nanocolumns.

[0012] Furthermore, the amplitude modulation of the metasurface layer is related to the cross-polarization efficiency of the dielectric nanocolumns and is achieved by changing the shape of the dielectric nanocolumns.

[0013] Furthermore, the remaining part of the micro-nano F-P cavity formed by the upper and lower reflective layers is filled with a low refractive index material (or air), and the greater the refractive index difference between the filling material and the metasurface material, the better. The refractive index difference between the two materials determines the regulation range of the resonance wavelength of the device.

[0014] The metasurface layer is based on the geometric phase principle. The periodic size of the metasurface is at the sub-wavelength level and is composed of anisotropic dielectric nanocolumns, with the functions of phase modulation and amplitude modulation. Designing a dielectric nanocolumn array with a specific shape, size, and azimuth angle can independently modulate the phase and amplitude of the light field. According to the geometric phase principle, when the incident right (left) circularly polarized light passes through the anisotropic dielectric nanocolumns, it will become left (right) circularly polarized light and carry a phase, and this phase has a two-fold relationship with the azimuth angle of the nanocolumns. Assuming the azimuth angle of the nanocolumns is θ, the transmission coefficient of the left-handed light generated by the right-handed light incident on the metasurface can be expressed as:

[0015]

[0016] where t xx , t yy , respectively represent the transmission amplitude and phase in the x polarization direction and the y polarization direction, and the phase factor carried in t +- is the geometric phase, and the magnitude of the geometric phase only depends on the azimuth angle of the nanocolumns. The geometric phase and the azimuth angle θ satisfy t +- The coefficient in front determines the cross-polarization efficiency, that is, the transmission amplitude, and can be adjusted by changing the shape of the dielectric nanocolumnsxx ,t yy , Specifically, amplitude modulation is achieved by changing the lengths of the major and minor axes of the nano-columns. The greater the difference between the major and minor axes of the dielectric nano-columns, the greater the transmission amplitude. Based on this design method, amplitude modulation and phase modulation can be achieved, and the amplitude modulation and phase modulation are independent of each other.

[0017] The upper and lower reflective layers are broadband high-reflection layers, which are composed of metal thin films or dielectric / semiconductor distributed Bragg reflection layers. The two broadband high-reflection layers form a micro-nano F-P cavity, which can accurately filter out the light of the designed wavelength from broadband light waves. Light reflects back and forth between the upper and lower high-reflection surfaces. At a specific wavelength, the light waves reflected multiple times will form a peak signal, while other wavelengths will cancel each other out, and a narrowband high-Q resonance peak will appear in the transmission spectrum. The resonance condition is:

[0018] λ = 2n eff l cavity cosβ / m (2)

[0019] where λ is the resonance wavelength, n eff is the equivalent refractive index of the F-P cavity, l cavity is the height of the F-P cavity, β is the incident angle, m is the order, m = 1, 2, 3..., and from formula (2), it can be seen that by changing the height and refractive index of the F-P cavity, the resonance wavelength will change accordingly. In the present invention, the equivalent refractive index n eff of the F-P cavity is changed to regulate the resonance wavelength. By changing the size of the dielectric nano-columns embedded in the F-P cavity, the equivalent refractive index n eff of the F-P cavity can be changed, eff thus realizing wavelength regulation. The wavelength adjustment range Δλ = 2Δn cavity l eff / m, where Δn

[0020] is determined by the refractive index difference between the metasurface material and the rest of the materials in the F-P cavity. The greater the refractive index difference between the two materials, the larger the adjustable wavelength range. Embedding the geometric phase metasurface into the F-P cavity can achieve three-dimensional joint regulation of the wavelength, amplitude, and phase of the light field. For the structural design scheme of the metasurface device described in this invention: Select appropriate materials as the upper and lower reflective layers according to the designed working band of the device to form the F-P cavity, and optimize the height of the F-P cavity and the size of the nano-columns so that a narrowband resonance peak appears in the designed working band. Then, adjusting the size of the nano-columns can control the resonance wavelength, and adjusting the azimuth angle and shape of the nano-columns can control the phase and amplitude. According to the required functions of the metasurface device, calculate the phase and amplitude distributions, and then arrange the nano-columns with corresponding sizes, azimuth angles, and shapes, and it is possible to shape the wavefront with arbitrary functions while regulating the spectral response of the device.

[0021] The present invention also provides a light field control method, which uses the above-mentioned metasurface light field three-dimensional control device based on the Fabry-Perot cavity, and is characterized in that it includes the following steps:

[0022] ① According to the target resonance wavelength λ, the equivalent refractive index n of the FP cavity is changed by adjusting the major and minor axis dimensions of the dielectric nanocolumns. eff , and combined with the height l of the FP cavity cavity , so that λ=2n eff l cavity cosβ / m, where β is the angle of incidence, m is the order, m = 1, 2, 3, ...;

[0023] ② By rotating the azimuth angle θ of the dielectric nanorod, a phase distribution of 0-2π is loaded according to the geometric phase principle to satisfy

[0024] ③ By adjusting the difference between the long axis and the short axis of the dielectric nanorod, Δ(lw), the cross-polarization efficiency is controlled to achieve independent modulation of the transmission amplitude;

[0025] The independent control of wavelength, phase and amplitude is combined to generate a light field with a specific spectral response and wavefront distribution.

[0026] Furthermore, when the metasurface device is used for multi-wavelength holographic display, it is divided into multiple independent control areas, each area corresponds to a nanocolumn array with a different resonance wavelength, and the azimuth angle and major axis / minor axis difference of the nanocolumns in each area are arranged according to the phase and amplitude distribution of the hologram, thereby realizing multi-channel color holographic synthesis.

[0027] Third, the present invention also provides an optical device, comprising the above-mentioned metasurface light field three-dimensional control device based on Fabry-Perot cavity, wherein the device is any one of the following:

[0028] Color printing devices that generate micro-nanostructure color pixels through multi-wavelength nanopillar arrays;

[0029] Color holographic display system, which uses multi-wavelength nanorod arrays and their phase and amplitude control to achieve color holographic projection;

[0030] Optical anti-counterfeiting labels use three-dimensional joint control characteristics to generate non-replicable optical features;

[0031] High-density information storage device that achieves multi-dimensional optical information storage through wavelength-phase-amplitude encoding.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The three-dimensional joint control of the wavelength, phase, and amplitude of the optical field is realized using a single metasurface without sacrificing integration. While independently controlling the spectral response, an arbitrary functional wavefront can be shaped. Compared with some traditional technologies, the modulation of the spectral response and complex amplitude of this device is independent, with the advantages of high degrees of freedom and strong control ability. Brief Description of the Drawings

[0034] Figure 1 Schematic structural diagram of the three-dimensional optical field control device of the metasurface based on the F-P cavity of the present invention

[0035] Figure 2 Schematic diagram of the unit structure parameters of the embodiment of the present invention

[0036] Figure 3 Transmittance curve of the right-handed circularly polarized light orthogonal polarization conversion by the metasurface in the embodiment of the present invention

[0037] Figure 4 Modulation relationship between the azimuth angle θ of the metasurface nanorods and the phase and amplitude in the embodiment of the present invention

[0038] Figure 5 Amplitude curve of the metasurface nanorods with different major and minor axis structure parameters in the embodiment of the present invention

[0039] Figure 6 Modulation relationship between the difference between the major and minor axes of the structure parameters of the metasurface nanorods and the amplitude in the embodiment of the present invention Detailed Description of the Invention

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will elaborate on each embodiment of the present invention in conjunction with the drawings. However, those of ordinary skill in the art can understand that in each embodiment of the present invention, many technical details are provided for the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation to the specific implementation of the present invention. The various embodiments can be combined and cross-referenced with each other on the premise of no contradiction.

[0041] Figure 1 Schematic structural diagram of the three-dimensional optical field control device of the metasurface based on the F-P cavity of the present invention. As shown in the figure, from top to bottom, it sequentially includes: an upper reflective layer, a metasurface layer, and a lower reflective layer. Among them, the upper reflective layer and the lower reflective layer form a micro-nano F-P cavity, and the middle metasurface layer is composed of an anisotropic dielectric nanorod array.

[0042] In this embodiment, the upper reflective layer is an Ag thin film with a thickness of d, which has a high reflectivity (>95%) in the visible light band (400 - 700 nm), and can effectively limit the multiple reflections of the light field in the F-P cavity. The metasurface layer is composed of an array of dielectric nanocolumns in the shape of different ellipsoids. The material of the dielectric nanocolumns is silicon, and the rest of the F-P cavity is filled with air. The period of the dielectric nanocolumns is p, the height is h, the major axis length is l, the minor axis length is w, and the azimuth angle is θ. There is a silica spacer layer with a thickness of g between the dielectric nanocolumns and the Ag thin film to reduce plasma coupling and maintain the cavity mode purity. The lower reflective layer is symmetric to the upper reflective layer and is also an Ag thin film with the same thickness of d, and together with the upper reflective layer, it forms a micro-nano F-P cavity.

[0043] Figure 2 It is a schematic diagram of the unit structure parameters of the embodiment of the present invention. Using the CST STUDIO SUITE electromagnetic simulation tool, optimize each structure parameter to form a narrowband transmission peak in the visible light band. At the same time, by optimizing the major axis length l and the minor axis length w of the nanocolumns, the transmission peak can be designed to be located at the desired wavelength, such as Figure 3 It is the transmittance curve of the orthogonal polarization conversion of the metasurface to right-handed circularly polarized light in the embodiment of the present invention. By only adjusting the l and w parameters, the resonance wavelengths are respectively achieved at 450 nm, 532 nm, and 650 nm, corresponding to blue light, green light, and red light respectively. The specific parameters are shown in Table 1.

[0044] Table 1 Specific parameters of the unit structure of the embodiment of the present invention

[0045]

[0046] By changing the azimuth angle of the nanocolumns, arbitrary phase modulation can be achieved. Taking the blue light nanocolumn as an example, Figure 4 It is the modulation relationship of the azimuth angle θ of the nanocolumn to the phase and amplitude. The phase As the azimuth angle changes from 0 - 180°, the phase completely covers 0 - 2π, and the change in the azimuth angle of the nanocolumn has no effect on the wavelength and amplitude. The phase modulation is independent of the amplitude modulation and wavelength modulation.

[0047] By adjusting the l and w parameters of the nanocolumns, the amplitude can be modulated. To ensure the independence of the amplitude modulation and wavelength modulation, the equivalent refractive index n of the micro-nano F-P cavity eff needs to remain unchanged. Empirically, when the product of l and w is a constant value, the resonance wavelength remains unchanged. On this premise, by changing the difference between l and w to modulate the amplitude, the smaller the difference between l and w, the smaller the amplitude. Taking the blue light nanocolumn with a resonance wavelength of 450 nm as an example, Figure 5Amplitude curves of nanocolumns with different major and minor axis structure parameters. As can be seen from the figure, by selecting appropriate major axis l and minor axis w of the nanocolumns, while fixing the resonance wavelength at 450 nm, amplitude modulation of different magnitudes can be achieved. Figure 6 The modulation relationship between the difference l - w of the major and minor axes of the nanocolumns and the amplitude is shown. The amplitude increases as the difference between l and w increases. The amplitude modulation and wavelength modulation are also independent of each other.

[0048] According to the designed device functions, calculate the required wavelength, phase, and amplitude distributions. Combining with the optimized nanocolumn structure parameters, arranging the corresponding nanocolumns at each pixel position can obtain the target spectral response and wavefront functions.

[0049] In this embodiment, three-dimensional joint control of the wavelength, phase, and amplitude of the light field is achieved without sacrificing the integration level. While independently controlling the spectral information, arbitrary functional wavefronts can be shaped. The present invention has the advantages of flexible design, compact structure, strong control ability, and high control freedom.

[0050] The above embodiments of the present invention do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A three-dimensional control device of a metasurface light field based on a Fabry-Perot cavity, characterized in that: include: An upper reflection layer and a lower reflection layer, wherein the upper reflection layer and the lower reflection layer constitute a micro-nano FP cavity; The super surface layer is located between the upper reflection layer and the lower reflection layer, and is composed of an anisotropic dielectric nanocolumn array arranged in a sub-wavelength periodic manner; wherein, The super surface layer independently regulates the wavelength, phase and amplitude of the light field by adjusting the major axis, minor axis size and azimuth angle of the dielectric nanocolumns; The resonance wavelength of the micro-nano FP cavity is determined by the equivalent refractive index of the dielectric nanocolumn and the FP cavity height, and the phase φ modulation of the metasurface layer satisfies the relationship φ=2θ, where θ is the azimuth angle of the dielectric nanocolumn.

2. The Fabry-Perot cavity-based metasurface light field three-dimensional control device according to claim 1, characterized in that: The upper reflection layer and the lower reflection layer are broadband high reflection layers, which are composed of metal films or dielectric / semiconductor distributed Bragg reflection layers, and their reflectivity in the target band is greater than 95%.

3. The Fabry-Perot cavity-based metasurface light field three-dimensional control device according to claim 1, characterized in that: The material of the dielectric nanocolumn is one of silicon, silicon nitride or titanium dioxide, with a period of 100-300nm and a height of 50-150nm; the difference between the long axis and the short axis of the dielectric nanocolumn is 10-50nm, and the transmission amplitude increases as the difference increases.

4. The Fabry-Perot cavity-based metasurface light field three-dimensional control device according to claim 1, characterized in that: The filling material of the micro-nano FP cavity is air or a low refractive index medium, the refractive index of which is less than 1.5, and the difference between the refractive index of the air and the medium nano-column material is greater than 1.

5.

5. The Fabry-Perot cavity-based metasurface light field three-dimensional control device according to claim 4, characterized in that: The control range of the resonance wavelength λ satisfies the following conditions: λ=2n eff l cavity cosβ / m Among them, n eff is the equivalent refractive index of the FP cavity, l cavity is the height of the FP cavity, β is the incident angle, and m is the order m=1,2,3...

6. The Fabry-Perot cavity-based metasurface light field three-dimensional control device according to claim 1, characterized in that: The azimuth angle of the dielectric nanocolumn covers 0° to 180°, the phase modulation range covers 0 to 2π, and there is no coupling between the phase modulation and the resonance wavelength and amplitude regulation; when the resonance wavelengths of the dielectric nanocolumns are the same, the product of the long axis and the short axis of the dielectric nanocolumn remains constant to ensure the equivalent refractive index n eff unchanged, thus achieving independent regulation of amplitude and wavelength.

7. A method for controlling light field, using the metasurface light field three-dimensional control device based on Fabry-Perot cavity according to any one of claims 1 to 6, characterized in that: The following steps are involved: ① According to the target resonance wavelength λ, the equivalent refractive index n of the FP cavity is changed by adjusting the major and minor axis dimensions of the dielectric nanocolumns. eff , and combined with the height l of the FP cavity cavity , so that λ=2n eff l cavity cosβ / m, where β is the angle of incidence, m is the order, m = 1, 2, 3, ...; ② By rotating the azimuth angle θ of the dielectric nanorod, a phase distribution of 0-2π is loaded according to the geometric phase principle to satisfy φ=2θ; ③ By adjusting the difference between the long axis and the short axis of the dielectric nanocolumn Δl-w, the cross-polarization efficiency is controlled to achieve independent modulation of the transmission amplitude; The independent control of wavelength, phase and amplitude is combined to generate a light field with a specific spectral response and wavefront distribution.

8. The light field control method according to claim 7, characterized in that: When the metasurface device is used for multi-wavelength holographic display, it is divided into multiple independent control areas, each area corresponds to a nanocolumn array with a different resonance wavelength, and the azimuth angle and major axis / minor axis difference of the nanocolumns in each area are arranged according to the phase and amplitude distribution of the hologram, thereby realizing multi-channel color holographic synthesis.

9. An optical device, comprising the Fabry-Perot cavity-based metasurface light field three-dimensional control device according to any one of claims 1 to 6, characterized in that: The device is any of the following: Color printing devices that generate micro-nanostructure color pixels through multi-wavelength nanopillar arrays; Color holographic display system, which uses multi-wavelength nanorod arrays and their phase and amplitude control to achieve color holographic projection; Optical anti-counterfeiting labels use three-dimensional joint control characteristics to generate non-replicable optical features; High-density information storage device that achieves multi-dimensional optical information storage through wavelength-phase-amplitude encoding.

Images